Download Operators Manual Day 1 to 4

Day 1:
1. OVERVIEW OF ICT
• 1.1. Definition of ICT
• I.C.T. stands for Information and Communications Technology.
It replaces the term I.T. (Information Technology) because many
machines, including computers, now allow users to
communicate with other people and machines, as well as to
retrieve information
• However, apart from explaining an acronym, there is not a
universally accepted definition of ICT? Why? Because the
concepts, methods and applications involved in ICT are
constantly evolving on an almost daily basis. It’s difficult to
keep up with the changes - they happen so fast.
• A good way to think about ICT is to consider all the uses of
digital technology that already exist to help individuals,
businesses and organizations use information.
• ICT covers any product that will store, retrieve, manipulate, transmit
or receive information electronically in a digital form. For example,
personal computers, digital television, email, robots.
• So ICT is concerned with the storage, retrieval, manipulation,
transmission or receipt of digital data. Importantly, it is also
concerned with the way these different uses can work with each
other.
• ICTs are the key enabler of the knowledge society. Those who have
easy and affordable access to ICTs and Communication networks
can participate fully, while those without have fewer opportunities,
and remain trapped in pre-knowledge economy forms of economic
activity.
• The phenomenon of differential access to ICTs is often labeled the
“digital divide”. This is often assumed to be about the presence of
ICT infrastructure and equipment.
1.2. Role of ICT in National
Development
• Information and communication Technology refers to technologies
and systems supporting the collection processing, dissemination,
access, and prevention of data or information.
• Information Communication Technology is widely recognized as a
potentially powerful tool in the fight against poverty, with a capacity
to provide developing countries unprecedented opportunities to
meet vital developmental goals far more effectively than ever before.
• The possibilities of applying ICT for socioeconomic development
purposes are limitless. The use of information technology can
improve the provision of
• Health care, promote educational achievements, increase
agriculture production, facilitate participatory government and secure
other socioeconomic developments as indicated below:
1.2.1. ICT for Agriculture
• ICT applications can be used to facilitate wide access to
information and intensive sharing of knowledge among
planners, policy makers, practitioners and researchers in
the agriculture sector;
• ICT can assist farmers on such areas as input supply,
extension and use of local knowledge;
• Efficient marketing of agricultural products through
information and telecommunication networks;
• Provision of equitable access to new techniques for
improving agricultural production;
• Reduced food storage losses through more efficient
distribution.
1.2.2. ICT for Health
• The application of innovations such as virtual
medicine and telemedicine make it possible for
patients located in rural areas to have access to
medical experts located thousands of miles
away;
• Enhancement of health administration and
management through medical information
system;
• Establishment of information “health profiles”
and decision support system on regional,
national, rural and district levels.
1.2.3. ICT for Education and Research
• Provide equitable remote access to resources in support of both
distance education and the strengthening of local educational
capacity;
• Connecting schools, universities and research centers to national
and international databases, libraries, research laboratories and
computing facilities;
• Reducing communication and administrative costs by building
communication networks linking all educational establishments;
• Promoting and supporting collaboration among teachers and
researchers;
• Extending the reach of educational facilities in informal learning,
especially to community level.
1.2.4. ICT for Trade and Commerce
• Today’s technological advances have not only opened new
opportunities to advance human development but have also entirely
changed the global economic and business systems. Advances in
ICT have helped accelerate economic globalization that is rapidly
unifying world markets. ICT-based innovations such as e-commerce
have now emerged as a future way of doing business and are
projected to dominate world trade in the future. The opportunities,
which ICT can provide for businesses, include:
• Linking chamber of commerce, trade associations and enterprises to
both national and global trade;
• Reduced commercial transaction costs;
• Online trade related information and import/export opportunities;
• Development and marketing of new products through electronic
networks.
1.2.5. ICT for Good Governance
• ICT is a powerful tool that can be used to facilitate macroeconomic and public sector
management. Efforts to stabilize the macroeconomic environment, and strengthen
the efficiency, accountability, and the transparency of government can benefit a great
deal from the introduction of information technology applications. Information system,
which can help the government design, implementation, and assess policy reforms
are now powerful instruments of public policy. Such information systems could
increase the speed, volume, quality, transparency and accountability of government
transactions; yielding large productivity increases in government services.
• ICT is among the most potent democratization tools that can be used to enhance
participation in the democratic process. ICT can be used to open the government to
the public and can also provide the citizens with the ability to enhance their
interactions with each other and with the government. Citizens can be invited to send
in comments and their views to government officials or parliament. By so doing, their
views can be taken into account before laws are passed and policies made. This can
have the effect of making government more transparent, accessible, and accountable
to its constituents and can reduce public cynicism about the political process.
1.2.6. ICT for Environmental Management
• Increase agricultural productivity by providing farmers with information on
weather forecasts;
• Implementing networks which, as far as possible, provide access to
telecommunications in areas threatened by environmental degradation and
natural disasters;
• Facilitate the use of low cost terrestrial and satellite radio communication
systems in emergency situations where there is no access to adequate
telecommunications;
• Establishing problem monitoring information systems using geographic
information system (GIS) technologies, remote sensing and satellite early
warning systems which provide tools to anticipate such problems in
advance and enable governments and international organizations to be
more proactive and to respond more effectively when the need arises;
• GIS can combine information on soils, hydro-geology and rainfall with socioeconomic data, allowing early warnings.
1.2.7 ICT for Tourism
• Attracting more tourists and other visitors by
offering high-quality information and
telecommunication services in tourist resorts;
• Reducing the costs of international promotions
for attracting tourists;
• Improving the image of the country through online promotional campaigns;
• Provision of tourism related information and
indicators that encourage and facilitate
investment in tourism projects.
• 1.2.8. ICT for Gender
• Improve the rights of women through access to
information and indicators which may be used
for tracking gender issues and elimination of
stereotypes;
• Ensure equitable access of women to
information, technology and technological
education;
• Enhance the role of modern communications
media to promote awareness of equality
between women and men.
1.2.9. ICT for Culture
• Making national museums accessible to all
parts of the regions as well as to the rest of
the world;
• Electronic preservation and documentation
of manuscripts and artifacts;
• Increasing accessibility of rare manuscripts
and artifacts to researchers and the general
public through the development of cultural
CDROM products.
2. ONGOING ICT DEVELOPMENT
PROJECTS IN ETHIOPIA
• In recognition of the critical role of ICT for
sustainable development, democratization and
good governance, the Ethiopian Government
has taken bold and aggressive initiatives on
several fronts in the development of ICT both at
the federal and regional levels. In the context of
the national ICT policy the Government
recognizes the need to implement e-government
and governance structure to bring the
government closer to the people and the
networked globe. The different ICT national
initiatives are outlined as below:
• 2.1 E-Government
• In recognition of the critical role of ICT for democratization and good
governance, the Ethiopian government has taken wide-ranging
measures for its development both at the federal and regional levels.
Within the framework of PSCAP, the government initiated series of
measures to make the civil and public service more efficient and
effective in the delivery of government services, along with
institutional reforms, improvements in working processes and
procedures, and altitudinal changes.
• The program is being carried out within this framework of what has
come to be known as electronic government (E-government).
• The broad objectives of Ethiopian e-government program are:
• Improve administrative efficiency, effectiveness and productivity as
well as information provision and service delivery to the public at the
federal and regional levels of government;
•
•
•
•
•
Reduce administrative, operational and transactional costs of federal and
regional governments, administrative activities, service delivery functions
and operations by reducing operational inefficiencies, redundant spending
and unnecessary excessive paperwork;
Increase the ability of the federal and regional governments to serve
citizens and businesses better by enhancing and improving responsiveness
to citizens and businesses;
Transform government systems into a citizen-centered government as will
facilitate the process of bringing government closer to the people and
making it easy for citizens to obtain services and interact better with
government machinery and agencies at the federal and regional level;
Develop and implement information and communication infrastructure to
support federal and regional level intra and inter-agency electronic service
delivery and information exchange and;
Provide access to information and government services by the public and
enhance good governance and strengthen the democratic process.
• 2.1.1 Woreda-net
• Woreda-net is a terrestrial and satellite-based
network whose primary objective is to provide
ICT services such as video conferencing,
directory services, mail services, voice services,
and Internet connectivity at the federal, regional
and lowest levels of government.
•
• The Woreda net consist a government intranet,
which connects 3 federal offices, 11 regional
offices and 634 Woredas (districts).
• The objectives of Woreda-net include:
• To bridge the technology gap between
urban and rural communities;
• To provide knowledge and information to
citizens;
• To build organizational capacity at all
levels of government;
• To provide the lowest level of government
with accurate and timely information.
• 2.1.2. School-net
• School net arises from the need to integrate ICT
into Ethiopia's school system. It connects about
600 secondary schools of the country through a
wide area network and making Internet and on
line education possible in these schools. The
network will also facilitate the effective
administration and service delivery within the
school system of the country.
• 2. 2 CONTENTS AND APPLICATION
DEVELOPMENT
• In order to obtain maximum benefits from
opportunities provided by ICT, appropriate ICT
content and application need to be developed
and tailored to user needs and local conditions.
The government is committed to the
development of locally relevant ICT content and
application consistent with specific local
situations and that are sure to add value to the
daily lives of communities.
• The components under this initiative include:
• Localize the existing global knowledge and content for
use at the national and local levels
• Develop government portal and messaging solutions and
interoperability between national and local languages in
order for citizens to have unhindered and transparent
access to government services;
• Develop content for preserving the values, wisdom and
acquired knowledge of traditional communities and
cultures;
• Promote initiatives for content and application
development based on local languages, mass
communication and information delivery;
• In this line, the Government is determined to develop
and implement appropriate sector based content and
application in priority areas but spanning over eleven
executing Agencies. These are public administration and
service delivery, agriculture and rural development, trade
and industry, health and education, economic
development, public finance and statistics, archive and
documentation and road transport.
• Five languages will be used during the first phase of
program development and implementation including
Amharigna, Oromifa, Tigrigna, Afarigna and Somaligna.
• The development of government portal
and messaging solutions as well as
interoperability between local languages
will be the components of the current
program.
• Contents and applications to be developed
in priority areas are classified into common
and specific contents and applications.
• 2.3. ICT HUMAN RESOURCE DEVELOPMENT
• The basic objective of the ICT human resource
development project is to facilitate the development of
the required ICT human resource for the nation through
an appropriate mix, quality and quantity. With
developments in ICT
• driven initiatives, the demand for ICT skilled
professionals is expected to rise substantially in the
future. Human resource development is therefore a
challenge that needs to be addresses as matter of
urgency, because there can be no sustainable ICT
development without adequate human resource base.
The planned activities under this project are:
• To develop national ICT human resource development strategy by
identifying the ICT human resource need of the country;
• To improve the overall ICT human resource and skill base within the civil
and public service;
• To train professionals within the civil and public sector to operate and
manage computer systems in government ministries and agencies;
• To increase the supply of adequately trained ICT personnel;
• To develop national curricula for ICT education at all levels in collaboration
with concerned stake holders;
• To designate ICT center of excellence from among ICT training centers and
institutions in the public and private sectors;
• To setup and implement an accreditation system for ICT education; and
training centers and institutions in the public and private sectors;
• Establish ICT career structure for ICT professionals;
• Promote ICT Research and development;
• Promote ICT awareness and Literacy.
2.4 ICT FOR COMMUNITY
• The aim of this initiative is to promote citizens' access to
data/ information by creating conducive environment for
development.
The planned activities under this project include:
• Formulation of ICT for Community Development
Strategy;
• Facilitate the exploitation and application of ICT- based
services within communities;
• Co-ordinate development efforts in local regions for
increased efficiency and effectiveness;
• Promote the development of public information kiosks;
• Conduct study on Local/ Indigenous Knowledge;
2.5 ICT FOR PRIVATE SECTOR DEVELOPMENT
•
•
The Ethiopian Government considers the
private sector as an engine of growth in ICT
development and a strategic partner. Since the
private sector plays a crucial role in
accelerating the process of transforming
Ethiopia into a
knowledge and information economy and
society the Government is committed to
removing obstacles constraining its
development.
This initiative includes:
• Stimulate the private sector as a key driver in the
development of ICT;
• Encourage the private sector to develop a globally
competitive ICT industry and services;
• Establish business incubators to assist entrepreneurs in
ICT and related business to translate ideas into
productive and marketable ventures;
• Promote the development of ICT parks with focus on
local and export markets;
• Promoting and developing electronic commerce,
2.6 REGULATORY FRAMEWORKS AND
STANDARDS
•
The exploitation and application of ICT
requires an appropriate legal and regulatory
environment. In view of dynamic developments
in the global and national ICT environment,
urgent reforms are needed to ensure
equitable, reliable, and affordable access to
ICT. The exploitation and application of ICT
also requires appropriate standards.
The components under this initiative include:
• Establish appropriate legal and regulatory frameworks to facilitate
the development, utilization and application of ICT at all spheres.
• Review and improve upon existing polices, laws and regulations to
facilitate the exploitation of ICT;
• Establish standards and guidelines harmonized at national and
regional levels for the deployment and exploitation of ICT in the
country;
• Establish standards for hardware, software development,
localization, content and document management.
• Introduce character setting and keyboard layout for local language
computerization and adopt UNICODE technology.
2.7 INFORMATON SECURITY
•
•
•
•
The exploitation and application of ICT
requires secure environment.
The objective of this initiative is to ensure that
systems are dependable in the
face of threats that are becoming increasingly
sophisticated worldwide.
Therefore measures should be taken to
develop systems and guidelines aimed at
unconstrained use of ICT in the public and
private sectors.
The components under this initiative include:
• Address national security implications arising
from the widespread application of ICT within the
economy and society,
• Introduce and enforce appropriate legal
measures against misuse of systems and data;
• Protect the existing government networks, data
and information systems against attacks and
unauthorized access, and protect the rights of
citizens;
3. THE WOREDANET ICT
NETWORK
3.1 BACKGROUND:
• WoredaNet is a terrestrial and satellite-based network whose
primary objective is to provide ICT services such as video
conferencing, directory services, mail services, voice services, and
Internet connectivity to the federal-level, regional-level and woredalevel government entities. From conception, the WoredaNet was
established to leverage its infrastructure so as to establish a three
tier structure for the provision of government based quality ICT
service to the pubic sector driven by user requirements. This was to
be achieved by harmonizing efforts undertaken by other government
institutions in terms of ICT capacity building or service delivery by
use of and/or extension of the WoredaNet infrastructure.
3.2 CONCEPTUALIZATION:
• How does The Government Architecture look like? What should be the
pattern of the aggregated network infrastructure?
• The WoredaNet ICT Network is instituted as an infrastructure frame
(Skeleton) that goes in line with the FDRE’s Federal and Regional
government’s hierarchy. The upgrading works of this system are designed
to cover the government’s administrative, legislative and executive organs
hierarchical structure.
• There is one National Data Center, NDC, with high speed Fiber optic
Network connectivity with the Ethiopian Telecom Broad band Metro Network
(BBMN). NDC has redundant and failover systems by design.
• The 3 Federal Data Centers (Ministry of Capacity Building, The Prime
Ministers Office and Ministry of Federal Affairs); Regional Systems except
that of Afar, Benihshangul Gumuz and Gambella are all connected via a
Terrestrial connectivity to the ETC BBMN. The Rest of the Woredas are
connected via satellite VSAT (Very Small Aperture Terminals).
• The following two diagrams shall demonstrate FDRE’s Federal and
Regional government hierarchy.
ETC
7500
IP MPLS
3 Regions, 311 Woredos
IP MPLS
Satellite dish
DMZ
Broad Band
Metro
ID
ID S
S
Mail
Relay
IP MPLS
IP MPLS
Federal & Regions
7206
Content
Engine
IP T
3 Federal Offices &
8 Regions
Satellite dish
Call
Manager
Starbak
server
Web
Server
(AD
Backup)
Video
Confer.
Bridge
Media
Exchang
e
Manager
43 X Auxiliary
Switc
h
IP T
42" Plasma
Display
Printer
Satellite dish
Route
r
MS
Exchange
server
IP T
Mic
42" Plasma
Display
Voice IP
Gateway
Router
Cisco
2600
Intranet
server
(Primary
AD)
Workstation
ETC
PSTN
E1
2x
Cisco
6509
Switc
h
Route
r
Mic
IP T
Workstation
IP T
Printe
r
Switc
h
Route
r
42" Plasma
Display
Mic
Workstation
IP T
3.3 VISION OF THE WOREDANET
PROJECT:
• The vision of the of WoredaNet ICT Network is to establish a multiservice IP-based service by the use of Broadband Terrestrial and
VSAT infrastructure for the delivery of services to government and
civil society. This vision is part of a broader ICT initiative to drive
development through a massive program to rollout, develop, and
utilize ICT for the mass empowerment of Ethiopian society and its
people. The vision can be summarized as follows:
• To bridge the digital divide between urban and rural communities
• To create information affluence by dismantling the information
have’s and have -nots
• To build the organizational capacity on the three levels of
government by use of ICTs
• To impact the drive for ethics and transparency through the
availability on public Information on a timely and visible platform
• To assist in the empowerment of the lowest level of government by
the virtue of accurate, timely, and consistent information
3.4 WOREDANET SERVICES:
•
The WoredaNet is capable of delivering the following core services to all of
the federal regional and Woreda sites that are included within its scope:
Web Service:
• To provide wider access to content available on the Internet for education,
health, agriculture and governance by civil servants. Such service will
contribute in the bridging the digital divide currently experienced between
unequal distribution of Web access between urban and rural and between
densely populated towns and thinly populated remote areas.
Voice over IP ( IP-Telephony) Service:
• To establish a common and singular voice over IP (Internet Protocol)
communication infrastructure between Federal, Regional, and Woreda sites
which can be stated to be non-existent at the present.
• This particular service is expected to contribute largely to the increase of the
tele-density of the country by providing an aggregated telephone access
service especially to remote woredas without having to traverse the
traditional telephone exchanges.
Directory Service:
• To establish a government wide catalogue of digital resources for managing
of government folders, files, users, computers, and enforcing of a coherent
usage policy in the sharing of such resources. The directory service can
greatly impact the alignment of government goals from a top down
approach as well as across lateral approach by the design and
implementation of policy across a network such as WoredaNet.
Messaging:
• The role of structured messaging service is very important; In order to
create a consistent and true collaboration environment, whereby free flow
of mail messages can take place The messaging service shall be secured
and structured electronic messaging service that goes inline with the
government’s hierarchical structure. Contact details of a specific resource at
a woreda, e.g. an email address [email protected] can
be published, and common experiences can be posted and shared among
the three tiers/levels of government.
Video Conferencing:
• To reduce distance, time, and cost and to
substitute the value of face-to-face meeting by
use of IP based Videoconferencing devices as
tools for conducting meetings. The value of such
a tool is not only for holding up a one to one
meetings but also in conducting group meetings
and broadcasting recorded sessions, programs
or television content to the remote woredas.
4. INTRODUCTION TO
COMPUTERS
• 4.1 What are Computers?
• A computer is an electronic machine that
receives data from an input device, carries out
arithmetic and logical processing according to a
previously complied set of instructions, stores
the proceed data, sends the processed data to
an output device.
• Schematically, a computer can be represented
as follows
Input
Device
CPU
Main memory: ROM +RAM
Control
Unit
Out Put
Device
Arithmetic
Unit
External (Secondary) Memory
Diskettes
Hard Disk
• Computers are not very intelligent devices, but they
handle instructions flawlessly and fast. They must follow
explicit directions from both the user and computer
programmer. Computers are really nothing more than a
very powerful calculator with some great accessories.
Applications like word processing and games are just a
very complex math problem.
• One of the great strengths of computer platform, which
has led to its overwhelming success in the marketplace,
is its modularity. Most computers are made up of many
different individual components, which can be mixed and
matched in thousands of different configurations. This
lets you customize the PC you either buy or build to
meet your exact needs.
• 4.2 PC PRIMARY COMPONENTS
• Fundamentally, a computer is a lot like the human body.
The human body contains a brain, organs to help the
body function properly, and skin to protect the internal
organs. And everything works together to create a fully
functional human being. Well, the microcomputer has
analogous components to create a fully functional
machine.
• The aim of this Topic is simply to take a look inside the
computer, identify the main components, give operating
principles, and discover how everything works together.
In this section, you'll be introduced to the following
components:
•
•
•
•
•
•
•
•
Mother boards
Microprocessors
Memory
The bus system
Input devices
Hard disk drives and interfaces
Output device
Power supplies
4.2.1 MOTHERBOARDS
The Components on the Motherboard
In addition to the motherboard, processor, and CMOS, you need to
know the components listed below. These components are usually
found inside the system unit. After they are installed, they are
considered a part of the motherboard's sphere of control.
• BIOS and CMOS
• Bus architectures
• Cache memory
• Microprocessors
• Memory
• Storage devices
• Power supply
• I/O ports
• Part of understanding the operation of the
motherboard is understanding its bus
structure. Most of the motherboard exam
questions are about bus architectures.
This section provides you with a brief
overview of the bus structures on the
motherboard.
• The CPU moves data values and signals around
the computer on a network of fine wires that
interconnect it to all the other components on the
motherboard. This network is called the bus.
• The lines that move data within the computer
form the internal bus.
• The lines that communicate with peripherals and
other devices attached to the motherboard form
the external bus.
• You can find four primary types of bus structures on most
motherboards:
• Address: The components on the motherboard pass
memory addresses to one another over the address bus.
• Control: Used by the CPU to send out signals to
coordinate and manage the activities of the motherboard
components.
• Data: Because the primary job of the computer is to
process data, logically the data must be transferred
between peripherals, memory, and the CPU. Obviously,
the data bus can be a very busy hallway.
• Power: The power bus is the river of life for the
motherboard's components, providing each with the
electrical power it needs to operate.
• The number of wires in a bus controls the number of bits that can be
transferred over the bus. For example, a 32-bit bus must have 32
wires.
• A Personal Computer motherboard is a large printed circuit board
that's home to many of the essential parts of the computer, including
the microprocessor, chipset, cache, memory sockets, expansion
bus, parallel and serial ports, mouse and keyboard connectors, and
IDE, EIDE, or SCSI controllers.
• The motherboard is often referred to as a system board. IBM has
always called its motherboard a system board. Apple Computer calls
its motherboard a logic board, while a few others refer to theirs as a
planar board. These terms are still around today; for the most part,
they are interchangeable.
• The motherboard binds the PC's operational
components together. Even devices (such as
printers, hard drives, and CD-ROMs) are either
connected to or controlled by the devices or
controllers on the motherboard.
• Manufacturers attempt to set their motherboards
apart from the others and increase their value by
incorporating more or fewer controllers,
expansion buses, processor sockets, external
connectors, and memory slots.
• For consumers, a wide range of motherboards
with a deep list of features is available to fit into
an even wider range of PCs. However, if you
don't do your homework before buying a new
motherboard, this wide range of selection can be
bad news, and you can end up wit lower-quality
components than you want.
• A typical Pentium motherboard; most of the
capabilities of a computer are contained
within this component.
• Motherboards and system boards are
manufactured under a number of
competing standards. Each was designed
to solve a particular design, engineering,
or marketing problem. Motherboards come
in every size — from tiny to huge. Some
styles even divide the motherboard into
several interconnecting pieces.
2.2 MICROPROCESSORS
• The microprocessor, or CPU, is a single
computer chip about the size of a matchbook
(see Figure). It’s many legs or pins are inserted
into the motherboard. The CPU is responsible
for storing and retrieving information on disks
and other storage media. It also handles moving
information from one part of the computer to
another. Other chips and circuitry support it, but
the CPU is the most important determinant of
computer speed.
2.2.1 Types of Microprocessors
• With the system case open, you should be able to tell what type of
CPU your system contains by reading the information that's printed
on the top of the chip. You'll probably see a combination of numbers
and letters that includes the numbers 386, 486, or 586, or the words
Pentium or Pentium Pro, Pentium I, Pentium II, Pentium III or
Pentium 4. The higher the microprocessor number, the more quickly
it can process information, and the more megabytes of RAM it can
address.
• The type of CPU that a computer contains determines its processing
power-how fast it can execute various instructions. These days,
most CPUs can execute on the order of millions of instructions per
second. The type of CPU also determines the precise repertoire of
instructions the computer understands and therefore which
programs it can run.
• After you locate the chip designator; look
in the same spot for an indication of the
chip's speed, which is expressed in
megahertz and gigahertz. Basically, the
speed of the chip defines the number of
commands it can perform per second. The
higher the number, the faster the CPU
(and thus, your computer) can perform
2.2.2 How Microprocessors Work
• The CPU is kind of like a traffic cop. Information is constantly flowing
back and forth between the various parts of the PC and the CPU.
The CPU stands in the middle, deciding what goes where. One of
the CPU's jobs, then, is control of information flow. When you type at
the keyboard, the CPU receives every keystroke and redirects it to
the right place. When you print a letter, the CPU takes the
characters from the screen or the disk and sends them streaming
through the cable that connects your PC to your printer.
• Every once in a while, the CPU notices that some of the data flowing
by is actually a command to perform a mathematical calculation. It
stops the traffic for a second and performs the calculation. Then it
returns to its traffic-control duties.
• The CPU gets its orders from the software program that is loaded
into the computer's memory. Some of the information being shuttled
around by the CPU takes the form of program commands.
•
•
•
The CPU directs your keystrokes to the computer's electronic memory, or
RAM. Your PC's RAM constantly cycles through millions of characters that
may need the CPU's attention. In order to process the characters stored in
RAM, the CPU must move data to and from RAM at an incredible pace. The
faster the CPU and the more efficiently it moved data to and from RAM, the
more processing power in the computer.
The CPU isn't the only microprocessor in PCs. Coprocessors on graphics,
3-D accelerator and sound cards juggle display and sound data to relieve
the CPU of part of its burden. And special processors, such as the one
inside your keyboard that handles the signals generated whenever you
press a key, perform specialized tasks designed to get data into or out of
the CPU.
One of the most important changes is in the arithmetic logic unit (ALU). The
ALU handles all the data juggling that involves integers, or whole numbers,
such as 1,23,610, or 234. The Pentium is the first Intel processor to have
two ALUs so that it can crunch two sets of numbers at the same time. Like
the 486, the Pentium has a separate calculation unit that's optimized for
handling floating-point numbers or numbers with decimal fractions, such as
1.2 or 33.8942.
•
•
•
•
2.3 MEMORY
You might assume that when you run a program, the CPU fetches instructions from
the hard disk one at a time and executes them, returning to the disk drive every time
it finishes a single step. If this were actually the way computers worked, they
would be so slow as to be unusable.
Most personal computer CPUs are capable of executing between one million and one
hundred million instructions per second. But because it is mechanical-that is,
composed of moving parts-the disk drive cannot deliver program instructions
anywhere near that fast. Reading an instruction from the disk involves both rotating
the disk so that the proper section is below one of the read/write heads and then
moving the head closer to or farther from the center of the disk until it is positioned
directly above the spot where the instruction is recorded. Even on a hard-disk drive,
this process generally takes between 9 and 25 milliseconds.
Now if the CPU can execute millions of instructions per second and the disk drive can
only deliver, say, one hundred thousand instructions per second, you have the
equivalent of an assembly line in which one person on the line (the CPU) is moving
somewhere between 10 and 100 times faster than the previous one (the disk drive). If
this were really the way your computer worked, the speed of the CPU would be
wasted while it waited for the disk drive to deliver the next instruction.
• For the computer to function efficiently, it therefore needs some
repository of information that is capable of keeping pace with the
CPU. This extra piece is called random access memory, usually
referred to as RAM or simply memory for short.
• Physically, RAM consists of a set of separate integrated circuits
(each of which looks something like a small CPU chip) which are
often mounted on fiber-glass boards called SIMMs (Single Inline
Memory Modules) in practice, however, memory is treated as a
single, contiguous set of storage bins.
• The figure shows two types of SIMMs. One uses a 30-pin
configuration, and the other, larger SIMM uses a 72-pin
configuration. Some newer motherboards accept a 168 pin dual in
line module (DIMM).
•
•
•
•
RAM is a type of short-term memory; when power is turned off, the
information is lost. (This is why you must save your work to a floppy or hard
disk before you turn off your computer.) RAM speed is measured in nanoseconds, with a smaller number indicating faster performance. Most
systems today use RAM speeds between 60-100ns.
Memory chips come in different shapes and sizes. DRAM (dynamic
random-access memory) chips are the most common type of computer
memory, and they need to be energized hundreds of times per second to
hold the information.
Another type of RAM chip, usually found in higher-end systems, is called a
DIMM (Dual Inline Memory Module). DIMMs effectively pack twice as much
memory in one package compared to SIMMs, although DIMMs are slightly
longer than SIMMs.
Like the CPU chip, memory chips store and transmit information
electronically. Sending an instruction from memory to the CPU is therefore a
simple matter of transmitting electrical impulses. There is no waiting for a
disk to spin or a read/write head to move to the proper position.
• Because the CPU can move information in and out of
memory so quickly, it uses memory as a kind of
electronic desktop-the place it stores whatever it is
working on this instant or plans to work with shortly.
When you tell your computer that you want to use a
particular program, for example, the first thing it does is
find the program on your hard disk and copy it into
memory. This process is known as loading a program.
This gets the comparatively slow process of reading
instructions from disk over with at the start. Once the
entire program has been loaded, the CPU can quickly
read instructions from memory as needed.
•
•
•
•
•
Upgrading System Memory
Memory is one of the most important components of your computer. In order to run a
program or make changes to a file, that program or file must first be placed into
memory. Once the file is in memory, the computer can read the data and perform
tasks with it.
When you run many programs at one time (which is easy to do with Windows), you
can quickly use up your computer's available memory. Sometimes running only one
complex program with a large file can use up all your available memory. When
Windows runs out of memory, it starts copying the oldest data out of memory to a
temporary holding area on the hard drive called virtual memory. From there, if the
data is later needed back in memory, Windows copies the data back. As you can
imagine, this whole process of copying data in and out of memory slows down your
computer a considerable amount. The only solution is to run fewer programs at the
same time, to use smaller data files, or to add more memory.
When installing memory, you need to consider many things. For example, memory
comes in several flavours: DIP, SIMM, DIMM and RAMBUS. DIP memory chips are
inserted individually, making them more difficult to install. SIMM and DIMM memory
chips are contained on a small board and inserted into special sockets (slots) on the
motherboard, making them simple to install.
RAM is a crucial system component. If it isn't installed properly or isn't the right type
for your system, your system probably won't boot.
2.7 HARD DISK DRIVES AND
INTERFACES
•
•
•
Now we're getting to the real storage. The hard drive is essentially several
non-removable rigid floppy disks stacked together with a drive built around
them. Because the disks are rigid, the read/write heads can be positioned
much more accurately, allowing more information to be written (higher
density). Another advantage is the disks can spin much faster, thousands of
RPM (Revolutions per Minute). As a result of higher recording density and
faster spinning, hard drives can write and retrieve information much faster
than floppy drives. The most important measure associated with a hard
drive is the capacity, how many megabytes it can store.
So exacting are the tolerances in a hard drive- the gaps between the heads
and the platters aren't big enough to admit a human hair-that it's a wonder
the drive can perform its work at all without constant disasters. Instead, it
keeps on plugging away as the repository of perhaps years of work-with
surprisingly few failures.
The capacity, size, and performance of hard drives have changed
dramatically since the introduction in the early 1980s of the first IBM XT with
a hard drive.
•
•
•
•
Back then, a capacity of 10 mega bytes was considered generous. The hard drive was 3 to 4
inches thick and filled a 5.25-inch drive bay. An access time of 87 milliseconds was warp speed
compared to the access times of floppy drives. A decade later, hard drives that hold 3-4 gigabytes
(3,000-4,000 megabytes), smaller than a 3.5-inch floppy drive, and with access speeds of 8
milliseconds are inexpensive and commonplace. Some hard drives pack scores of megabytes on
removable disks no larger than a matchbox. In the future, the size and prices of drives will
continue to decrease at the same time that their capacities increase.
The price of hard storage is becoming so inexpensive that synchronized groups of hard drives,
called drive arrays, are becoming affordable for small businesses and home offices that want the
benefits of speed and dependability that the arrays provide.
One thing about hard drives will stay the same. Unlike other PC components that obey the
commands of software without complaint, the hard drive chatters and groans as it goes about its
job. Those noises arc reminders that the hard drive is one of the few components of a personal
computer that is mechanical as well as electronic. The drive's mechanical components make it the
slowest component in your PC. But they also mean that the hard drive, in more ways than one, is
where the action is.
The disk uses the same characters whether it records a great novel or this week's grocery list.
Another common element is the scheme that determines how the data on the disk is organized.
The computer's operating system, which on most personal computers is Windows95 or MS DOS,
determines the scheme. Even in Windows 95, the older DOS is still there, hidden beneath
Windows's graphic interface. The operating system controls so many of a PC's operations that
many PC users forget that DOS stands for disk operating system and that, originally, it’s primary
function was to control disk drives.
• Before any information can be stored on a magnetic disk, the disk
must first be formatted. Formatting creates a road map that allows
the drive to store and find data in an orderly manner. The road map
consists of magnetic codes that are embedded in the magnetic film
on the surface of the disk. The codes divide the surfaces of the disk
into sectors (pie slices) and tracks (concentric circles). These
divisions organize the disk so tint data can be recorded in a logical
manner and accessed quickly by the read/write heads that move
back and forth over the disk as it spins. The number of sectors and
tracks that fit on a disk determines the disk capacity.
• After a disk's formatted, writing or reading even the simplest file is a
complicated process. This process involves your software, operating
system, the PC's BIOS (basic input/output system), soft- ware
drivers that tell the operating system how to use add-on hardware
such as a SCSI drive or a tape drive and the mechanism of the disk
drive itself.
• There are 2 interfaces you can go with drives: IDE or SCSI
•
•
•
•
•
•
•
•
IDE
IDE is the most common and least expensive. If you have a 586 system, odds are that you have the controller built
into the motherboard so you won't need to buy a card. IDE, however, is slower and puts a greater load on your
CPU. If you are running multiple drives they are difficult to configure and slower.
EIDE
Extended Integrated Drive Electronics (sometimes called Enhanced IDE)EIDE is defined an improved version of
IDE/AT Attachment, with faster Data rates, 32-bit transactions, and (in some drives) DMA (direct Memory Accessthe device speaks directly to memory bypassing the CPU). EIDE was named by Western Digital around 1994, and
the standard is also referred to as ''Fast ATA-2'', based on its ANSI designation.
The IDE ''bus'' only supports two devices - master and slave per controller. But the advantages are much lower
price and equal or greater speeds than many SCSI drives. Also IDE drives are the de facto standard for PC's.
Everything is compatible with IDE, whereas you can run into some problems configuring SCIS devices with some
games and the like.
SCSI
SCSI is much better, faster, and cooler. You can get some pretty buge sizes without difficulty, it is capable of 7
drives on one card and you can plug multiple cards into your system. If you have a SCSI card you can plug in
SCSI hard drives, SCSI scanners, SCSI brain surgery Kits--anything SCSI. Oh. It's pronounced Skuzzy. A good
SCSI controller will put less of a load on your CPU too. Fast SCSI(SCSI-2) is even faster, and fast-wide SCSI
(sometimes incorrectly called SCSI-3) is faster yet. A note on fast-wide SCSI: you can plug 14 devices into it; the
data path is twice as wide; it won't speed up anything unless you have a bunch of SCSI devices plugged in (i.e. 6
SCSI devices on a fast-wide system will go faster than 6 devices on a regular system, but 1 device will run the
same speed on both--usually!).
Disk terms are either relevant to a hard drive or to a drive interface. For drives, you’ll hear the terms summarized
in the following table.
•
•
•
•
•
2.8 POWER SUPPLYS
The power supply is the black or silver box in the back of the PC with the large yellow label telling
you in five languages not to open the box up and warning you that it is dangerous
The basic function of a power supply is to convert the 220 volt AC 50Hz source from your wall
outlet into something the computer can use, specifically +5 v, -5 v, +12 v, -12v, and sometimes 3.3
v. The reason for all of the different voltages is due to the need of the PC components in the
system. Components, such as disk drive motor and other motors use the +12 v signal and
components like the motherboard and other circuit boards use the +5 v signal from the power
supply. In newer PC's the negative voltages are not used very much. Due to a couple of
standards on the ISA bus, these voltages are required to maintain backward compatibility.
The power supply also has built-in self test that prevent it from running unless the required
voltages are present. The power supply sends to the motherboard a special signal called
Power_Good. If this signal is not present than the computer will not run. If your system has ever
seemed dead when the power switch is on and the fan and hard disks are running, you know the
effects losing the Power_Good signal. This process normally only takes 0.1 to 0.5 seconds after
you turn on the power supply switch.If there is not a Power_Good signal then the timer chip
continuously resets the processor, which prevents the system from running under bad or unstable
power conditions, which could cause data corruption.
On newer systems with ATX or LPX form factor motherboards, they also include a special signal
called PS_ON which can be used to turn the power supply off via software. This is evident when
you shut down the computer in Windows XP and then the system will completely shut down and
not display a message like it's safe to shut down the computer. This is sometimes called a soft-off
feature.
•
•
•
•
•
•
•
2.9 INPUT DEVICES
Input devices are parts of the computer that let you input information and data into
the computer. The keyboard, mouse, and joystick are examples of input devices.
Scanners and cameras are also input devices, but are not used as often. Disk drives
and modems can also be used as input devices.
Disk Drives
Disk drives are a very important part of the computer, but choosing them is relatively
easy. There are several types of disk drives: Hard drives, Floppy disk drives, CD
ROM drives, Tape backups, and Zip drives.
Floppy Disk Drive
Every computer comes with a floppy disk drive. They are the main way of putting
information on to the hard drive. They also allow you to save information on a disk,
which is an easy way to transport files and data between different computers. There
are two different sizes of floppy drives. The 5.25” floppy disk is not used very often
any more. It has been replaced by the 3.5” disk, which is smaller and can hold more
information. A 3.5” high-density disk can hold 1.44 megabytes of data.
The media is contained within a rigid case but is itself flexible. Thus, this is not a hard
drive but a floppy drive. NEVER touch the media or the disk will be ruined. To
view the actual media, slide open the metal door and look through the read/write
window.
•
•
•
•
•
The back of the drive has power and data connections. Some 3.5" floppy drives have nonstandard connectors and must have adapters to connect with the data cable. The power
connector will normally attach only one way. This makes it difficult to plug power in wrong. Pin one
of the data connector is usually at the end of the connector next to the power connector. Wire one
on the ribbon cable is most often marked with a different color, usually red, from the others and
the connector has a small arrow or triangle-marking pin one of the connector. This information
should help if you are installing a used floppy to an existing system or if you have no
documentation.
CD ROM Drive
Most computers now come standard with a CD ROM drive. Most programs and games now come
on CD. Many programs are being put on CD’s because they can hold over 600 megabytes of data
on a single disk. A CD ROM drive reads data from a CD that looks much similar to a music CD,
except it holds data rather than music. Much like music CD’s, CD ROMs cannot be written to, so
you cannot save information to a CD ROM. CD’s make it possible to add sound and video to
games and programs. The CD ROM drive comes in several different speeds. Speeds vary from
double speed to 52X speed.
A double speed CD ROM is the minimum. It is still functional but the video and sound are more
likely to be a bit jumpy. The faster a CD ROM can read a CD the smoother the video and sound
becomes. Faster is better, but for most users an 8X speed will work just fine. CD writers are now
available. CD writers allow you to write information to a CD. You have to buy blank CD’s to write
to. Once written, these CD’s can be read by any CD ROM drive. This may sound like a good
solution to your storage problems, but they can be tricky to use. You may waste a few CD’s while
learning how to use it.
•
•
•
CD-ROM (Compact Disk Read Only Memory) drives are very popular, and for good
reason. The drives have become inexpensive to buy and the disks are cheap to make
(figure under two dollars to press a disk). A software maker can put information onto
software that looks at the disk and verifies that it is being accessed from the CD. This
can be used to prevent software piracy. CD-ROM disks can hold 640 Megabytes of
data, more than any application on the market today is likely to need. You don't need
16 3.5" high-density disks to load up your favorite suite of office apps.
The disks require special care. Like 5.25" floppies the media is exposed. Unlike
floppies, you can clean them. Refer to your CD-ROM drive manual for sections on
cleaning the disks. Soft, lint-free, clean cloths only should be used. While I don't
recommend it for software CD's, I have put my music CD's under the tap and washed
them in dish soap, then dried them using a soft, clean, lint-free towel. While it worked
great, I don't recommend it. It could void a warranty.
The attachments for a CD-ROM drive are nearly identical to those for a 3.5" floppy,
and with the same layout. In addition, a sound cable attaches to the CD and runs to a
sound card. To get the drive to work properly, you may be called on to move a jumper
to master or slave selection as required by your system. Again, refer to your
manufacturer's manual for proper installation and troubleshooting.
•
•
•
•
DVD Drive
The latest in mass storage is the DVD drive. DVD stands for digital video
disk. The DVD technology is still developing. A dual layer, dual sided version
of this disk can hold up to 17 gigabytes. The current version, which is single
layer, single sided holds 4.7 gigabytes. Since this technology is still
relatively new, there are not a lot of products that support it. DVD will soon
replace the CD.
Keyboard
Using the keyboard is the primary way of inputting data into many of your
programs. we are sure you know what a keyboard is so I will not go into
much detail to describe it, but we will tell you of a few different kinds of
keyboards. Keyboards are usually described by the number of keys they
have. This keyboard comes standard on most computers. There are also
ergonomic keyboards. These keyboards look like they are broken in half,
and are supposed to make typing less stressful on your wrists. Some
keyboards come with a built in trackball or finger pad. Picking a keyboard is
just a matter of preference. For most everybody, the standard 101 keyboard
will work just fine.
•
•
•
•
•
•
Mouse
The mouse is a very important input device because it makes getting around in your computer
easier. The mouse controls and arrow which can be moved anywhere on the screen. The mouse
is good for doing tasks such as moving and pointing to objects on the screen. There are several
types of mice, and several input devices similar to mice. Alternatives to the mouse include: the
trackball, touchpad, and touch-screen.
A mouse can have two or three buttons. A two button mouse is usually standard.
Another thing to note about your mouse is how it plugs into the computer. A serial mouse plugs
into a 9 pin serial port in the back of the computer. Most computers now come with an input for a
bus mouse, also referred to as a PS/2 mouse. The PS/2 mouse has a round connector similar to
that of the keyboard. This mouse is a better choice, because more computers are using it now.
The trackball is very similar to the mouse, except the ball is on top instead of underneath. You
move the ball with your thumb or palm. This is sometimes easier for children to use because they
can let go of the ball to click the buttons. This is good because the arrow will not move when you
try to click on something. With the mouse, if you let go of it to click a button, it will usually move.
Choosing between the mouse and the trackball is just a matter of preference.
The touch pad and touch screen are very similar. For both you use your finger to move the cursor
on the screen. With the touch pad you move your finger on a pad. With the touch screen you
move your finger directly on the screen. These may be fun additions to your computer, but I prefer
the mouse or trackball.
• Scanners
• Scanners are useful if you need to copy written page or
pictures directly into your computer. If you are using your
computer for business, a scanner could be more useful.
There are three basic types of scanners: Hand scanners,
Page scanners, and Flatbed scanners. Both types come
in black and white or color, with color being more
expensive. A hand scanner is held in the hand and
dragged across the page being scanned. A page
scanner feeds paper through it similar to a printer, but
instead of printing, it scans in whatever is on the paper. A
flatbed scanner looks and works like a copy machine.
You put the object to be scanned in the scanner, and
then it scans it into the computer.
2.10 OUTPUT DEVICES
MONITORS and VIDEO CARDS
• A video display system has 2 major
components: a display monitor and a
video card.
VIDEO CARDS
• Your system's video card is responsible for what you see on your monitor
screen, the video card is the part of the computer that sends the images to
the monitor. Video cards are also referred to as video accelerators. Video
cards usually contain their own memory chips. This memory helps the
computer to load images faster. A video card should contain at lest 32
megabyte of memory, but 64 megabytes is becoming standard. 128
megabytes is quite a bit more expensive, but is even better.
• Besides video cards, video may be integrated on the motherboard. Having it
included on the motherboard eliminates the possibility of choosing a card to
meet your needs. Many have an option by jumper or BIOS setting to disable
the on-board video when updating and adding a true video acceleration
card. Usually this video does not render high resolution large screen
graphics.
• The video processor, along with the system CPU, manipulates this data to
change the screen image and the RAMDAC reads it and sends it to the
monitor.
• RAMDAC (Random Access Memory Digital-Analog
Converter): The screen image information stored in the
video memory (RAM) is digital, because computers
operate on digital numbers The patterns of ones and
zeros control the colour and intensity of every pixel (dot)
on the screen.
• The monitor, however, doesn't use digital information. it
is analog. In order to display the image on the screen,
the information in video memory must be converted to
analog signals and sent to the monitor. The device that
does this is called the RAMDAC.
• PCI vs AGP Video Cards: There are cards for a PCI slot
as well as AGP (Accelerated Graphics Port). AGP was
designed by Intel in 1997, specifically for the video
subsystem. It is a new technology. It is considered a port
not a bus. The idea behind AGP is to create a faster,
dedicated interface between the video chipset and the
system processor. The interface is only between these
two devices. It makes it easier to implement the port,
makes it easier to increase AGP in speed, and makes it
possible to put enhancements into the design that are
specific to video. AGP motherboards have a single
expansion card slot for the AGP video card, and usually
one less PCI slot, and are otherwise quite similar to PCI
motherboards.
THE MONITOR
• A display monitor is a video output device capable of displaying text and
graphics.
• In a very basic Cathode Ray Tube (CRT) a beam of electrons is focused
and aimed by electromagnets, then the electron beam strikes a
phosphorescent surface at the other end of the tube. Light is given off by
the phosphor at the end of the CRT. The entire tube is kept at as close to
vacuum as possible so that the electron stream is not deflected.
• This basic CRT would be a monochrome(one color) monitor. By raising the
number of electrons that strike the screen, the display is made brighter.
Relate this to a black and white television or an amber or a green screen
computer monitor. On a computer monitor, each individual dot is addressed
individually to make part of a shape or character. This dot is called a pixel.
• Color CRT type monitors have three kinds of phosphors to produce Red,
Green and Blue (RGB) light. All of the colors that humans can see can be
produced by some combination of these colors. The first color monitors
used only two brightnesses of red, green and blue to produce colors. Red
could be off, on or on high. A total of only sixteen colors (to include black)
could be displayed because all colors had to match in intensity.
•
•
•
The VGA monitor can display any color. Any limitation is in the video card
used. While early VGA video cards were limited to sixteen colors displayed,
they improved on EGA video cards both in resolution and in pallet depth.
The sixteen colors were chosen from 256 basic colors.
Since that time, true color VGA adapters have allowed the VGA and Super
VGA monitor to display true color. This is the industry name for 24 bit color.
With eight bits per color per pixel, there are 256 levels of red, green or blue
per dot. 1677216 colors to choose from. It would take a 1295 by 1295 pixel
monitor to display all of the colors possible! The largest industry standard
monitor these days measures 1280 by 1024 pixels.
Common VGA or SVGA monitors may be capable of 640x480, 800x600,
1024x768 and 1280x1024 pixels. This is horizontal dots by vertical dots. At
640 by 480, the number of pixels is (640x480=) 307200. The 1280 by 1024
display shows 1,310,720. At 16 colors, each dot has 4 bits of information. At
true color, each dot holds 24 bits. So a monitor showing 640x480 dots at 16
colors has (640x480x4=) 1,228,800 bits of information, while a true color
1280x1024 video card holds 31,457,280 bits of information! This is why the
newer, better video adapter cards demand so much memory.
• Screen savers came along because of a problem with cathode ray
tubes. Recall from the basic CRT description above, the electrons
hitting the phosphor coating on the front of the CRT. As each
electron strikes, it may knock loose an atom! This is called sputter.
When this happens, the phosphor in that spot being gone, there is
less light given off. A display constantly showing the same image will
concentrate this effect, producing screen burn.
• In an early solution to this problem, computer input inactivity would
shut off the video monitor. Activity would start it right back up.
However, thinking the computer off, it often happened that users
would mess something up. Someone wanting to use the computer
might think that, well, if this switch position is OFF, then that way
must be ON. Screen savers, then, must not completely shut off the
screen, but minimize the portion in use when the computer is not
active. Now any program that starts to change screen characteristics
after a period of inactivity may call itself a screen saver.
• Internal to the monitor is the CRT (Cathode Ray Tube). A CRT is a
display device in computer monitors as well as television sets. A
CRT consists of a glass vacuum tube that contains one electron gun
for a monochrome display, or three RGB (red, green, blue) electron
guns for a color display. Electron beams from these guns sweep
rapidly across the inside of the screen from the upper-left to the
lower right of the screen.
• The inside of the screen is coated with thousands of phosphor dots
that glow when they are struck by this beam. The beams sweep rate
is between 43 and 87 times per second (refresh rate) and is
measured in Hz (hertz).
• Like televisions, screen sizes are measured in diagonal inches, the
distance from one corner to the opposite corner diagonally. Several
sizes of monitors are available. The most common are the 14 or 15
inch monitor. There are also 17 and 21 inch monitors available.
• Sound Cards
• Most computers comes standard with a sound card. A sound card
allows your computer to reproduce music, sounds, and voice. This is
a definite necessity if you are going to play multimedia games. If you
are just using your computer for business, then you may not need a
sound card. The market standard for sound cards is the Sound
Blaster. Be sure to get a computer with a Sound Blaster compatible
sound card. There are also different quality of sound cards. Most
computers now come with 16 bit sound cards. The next step up
would be a 32 bit sound card. Some sound cards have a wave table,
which means that it reproduces actual instruments rather than
synthesized sound. Most sound cards also have an input for a
microphone so that you can record your own voice. My choice would
be the Sound Blaster awe32. This is a good quality sound card and
it should work with almost all of your games.
•
•
Modems
The modem comes standard on most computers. If you want to send faxes
or get on the internet, then this is what you need. The modem allows the
computer to communicate with other computers through the telephone lines.
Most modems come with faxing capabilities. Modems are available in
different speeds. The standard speed is 56.6 Kbps. Kbps stands for kilo
bauds per second, which is just the speed of the modem. The 56.6 modem
is also refered to as V.90. This is the name for the standard on which all
56.6 modems are built. The 56.6 Kbps modem replaced the 33.6 Kbps
modem as the standard. 33.6 and 28.8 modems are still widely used, but if
you spend a lot of time on the Internet, you'll appreciate the speed of the
56.6. The 14.4 modem is now outdated. It's just too slow for most
people. Another choice you have with modems is external or internal. If you
buy a new computer it should come with an internal modem. Internal means
that it goes inside your computer, external means that is plugs into your
computer and sits on the desk. Internal modems are usually less expensive
than external modems. The quality between the two is about the same, so it
is just a matter of preference.
• PRINTERS
• All printers whether dot matrix, ink-jet or
LaserJet accomplish essentially the same task:
They create a pattern of dots on a sheet of
paper. The dots may be sized differently or
composed of different inks that are transferred to
the paper by different means, but all of the
images for text or graphics are made up of dots.
The smaller the dots, the more attractive the
printout.
DOTMATRIX PRINTERS
• The dot-matrix printer- noisy, slow, and crude - is a dying
technology. Laser printers are faster and produce more attractive
documents. Ink-jet printers cost little more than a dot-matrix, but
produce beautiful color and resolution. The only thing a dot matrix
printer has on its cousins is that it can handle multi-layer forms carbons - while the others can’t. That’s because a dot- matrix printer
is, like a typewriter, an impact printer. It prints by pounding ink onto
paper. But carbons being, themselves, a sort of retry technology,
even that advantage is dubious.
• Impact printers with 24 or more pins produce documents that rival
the laser printer, and some dot-matrix printers call interpret
commands from PostScript or another page description language.
But most impact printers are simple things, designed to work with
another ancient technology, bitmapped type controlled by ASCII
codes sent to the printer from a PC.
LASER JET PRINTERS
• Every time you send a page 10 your laser printer, you're selling in motion a
complex, inter locked series of steps as efficiently organized as a factory
and as precisely choreographed as a ballet. At the heart of the printer is the
print engine-the mechanism that transfers a black powder to the page,
which is a device that owes its ancestry to the photocopier. Its operation
includes technologies Gutenberg never imagined, including laser imaging,
precise paper movement, and microprocessor control of all its actions.
• To create the nearly typeset-quality output that is characteristic of a laser
printer, the printer must control five different operations at the same time:
• It must interpret the signals coming from a computer,
• Translate those signals into instructions that control the firing and movement
of a laser beam,
• Control the movement of the paper,
• Sensitize the paper so that it will accept the black toner that makes up the
image, An
• Fuse that image to the paper.
• The result is no-compromise printing. Not
only does the laser printer produce hard
copy faster than most any other type of
printer, but the laser printed pages are
more sharply detailed. With the
introduction of color laser printers, the fivering circus turns into a 20-ring bazaar. For
the foreseeable future, the laser is the
standard for high end, day in, day out
office printing.
• COLOR PRINTING
• There have been two revolutions in computer printing in the last
decade. One was the laser printer, which brings typeset quality
printing of text and graphics to the masses. The second was the
development of inexpensive, fast, high quality color printing.
• The complexity of color printing, of course, means trade-offs. At the
low-price end is the color ink-jet printer. It is in some ways a dotmatrix printer without the impact and with four times the colors. A
color ink jet costs barely more than a black and white ink-jet. The
visual detail approaches that of laser printers, in some printers
surpassing it. But ink-jet technology is relatively slow and you
always have to fuss with cleaning and replacing the ink-filled print
beads. Color ink jets are the ideal printer for the home, where
printing volume is small, a budget maybe nonexistent, and the flash
of color in a school report or a greeting card is worth the extra wait.
•
•
For the office there are different color printing solutions that match the
budget of a small business or home office and solutions that give the most
fussy graphic artists the speed, color-matching, and details they need to
create professional results. The crucial difference among color printers is
how they get ink on the paper. Because it involves four colors of ink to
achieve full color printing, a printer must either make multiple passes over
the same sheet of paper-as happens with laser and thermal wax color
printers- or it must manage to transfer all of the colors more or less
simultaneously, which is what happens with solid-ink printers, whose results
are almost photograph-quality.
A common office color printing device is the color thermal printer The
process provides vivid colors because the inks it uses don't bleed into each
other or soak into specially coated paper. But its four-pass method is slow
and wastes ink. The color laser printer provides the most precise detail but
is slow, complicated, and expensive because it requires four separate print
engines that must each take their turn to apply colored toner to the page.
• Two other color-printing methods provide speed and
photographic dazzle: dye sublimation-also called dye
diffusion thermal transfer (D2T2) - and solid ink. By
controlling not only how many dots of color they put on
the page but the intensity of the dots, they produce
continuous tone printing. The result is virtually
indistinguishable from a color photograph even through
its actual resolution maybe no more than the 300 dots
per inch of the old laser printer. If the results you're trying
to get with color printing are really important, these
technologies arc well worth the cost.
Day 2-3:
5. NETWORKING
5.1 Network Fundamentals
•
Imagine 20 years ago working in an office with little or no computer equipment. It’s hard to
imagine now, isn’t it? One could say that we take for granted a lot of what we have gained in
technology the past few decades. Now, imagine having to send a memo to everyone in the
company. Back then we used interoffice mail; today we use e-mail. This is one form of
communication that only became available due to the introduction and growth of networks.
•
Stand-alone personal computers (See Figure 1.1), first introduced in 1970s, gave users the ability
to create documents, spreadsheets, and other types of data and save them for future use. For a
small business user or home computer enthusiast, this was great. For large companies and
organizations, however, it was not enough. The larger the company, the greater the need to share
information between offices, and sometimes over greater distances. The stand-alone computer
was not enough for the following reasons:
•
Their small hard drive capacities were inefficient.
•
To print, each computer required a printer attached locally.
•
Sharing documents was cumbersome. People grew tired of having to save a diskette, then taking
that diskette to the recipient.
•
There was no e-mail. Instead, there was interoffice mail, which was not reliable and frequently
was not delivered in a timely manner.
•
To address these problems, networks were born. A network links two or more computers together
to communicate and share resources.
What is a Computer Network?
• A computer network is a group of computers and
associated peripheral devices connected by a
communication channel capable of sharing files and
other resources among several users. A network can
range from a small network connecting a small number
of users in an office or department, to a Local Area
Network connecting many users over permanently
installed cables and dial-up lines, to a Metropolitan Area
Network or Wide Area Network connecting users on
several net-works spread over a wide geographic area.
• If the computer shown in Figure 1.1 was to
be connected to other computers, then, it
could share data with the other computers
or send documents to a printer. This
connecting together of computers and
other devices is called a network, and the
concept of connected computers sharing
resources is called networking. (See
Figure 1.2)
• A simple computer network
• Benefits of Computer Networking
• application programs that are installed centrally in one location
(application server). Software (application) that is installed centrally
can be managed and upgraded centrally. Such systems are mostly
common in financial system where the main application is stored
centrally and users in different sections of the finance department
are able to run the system from the network.
• It is effective for several reasons
• Less disk storage space is required because the program is stored
only once on the server, instead of being stored on the hard disks of
multiple stand alone computers
• When a new version of the software is released, it is easier to
update on copy of the program on the server than to update many
copies stored on stand alone computer.
• Purchasing a software license for a network can be less expensive
than purchasing a single-user license for every workstation on the
network
In short sharing programs on a network
• Saves disk space
• Reduces maintenance
• Reduce licensing cost
• Sharing Hardware
• Computer networks enable us to share expensive hardware
resource among several computers. A typical example of shared
resource is printer. For example, a company may prefer to acquire
one expensive printer and connect it to the network to provide high
quality printing to users. This avoids the need to have separate
printer for each computer in the office.
• Central Disk storage – Network system provide the possibility of
using a dedicated file server to store all the company data in one
location. Users will be able to access their data over the network
from their workstations. Using central disk storage system facilitates
data backup operations from a central location guarantying complete
data recovery in case of system failures.
Sharing Information/data
Users in a certain network environment have the liberty of sharing data and information
across the network. Data sharing enables different users to work on a certain file
concurrently. Few examples of data sharing are:
• Database: - databases are often managed centrally and several users can have
access to the database at same time. For example, in a networked banking system,
different bank branches can have access to the central account database. This
enables bank clients to carry their transactions on any branch bank office.
• E-mail: email communication can be achieved over the network enabling networked
users in the company to communicate messages across the network using email.
• Intranet: Intranets are similar to World Wide Web (WWW) where centrally stored
hypertext documents can be accessed using the web. Unlike the WWW, intranets
are available only to user with in the company network system. Intranet is a very
common service in large networked organizations.
• Extranet: Although similar to intranet, extranet provides selected users from outside
the organization to access data from the internal network. Extranets are commonly
used by suppliers to provide data to company clients.
• By making information available for sharing,
networks can reduce the need for paper
communication, increase efficiency, and make
nearly any type of data available simultaneously
to every user who needs it. Managers can use
these utilities to communicate quickly and
effectively with large numbers of people and to
organize and schedule meetings with people
drawn from an entire company or business
enterprise far more easily than was previously
possible.
Centralizing Administration and Support
• Networking computers can simplify support tasks as well. It is far more
efficient for technical personnel to support one version of one operating
system or application and to set up all computers in the same manner than
to support many individual and unique systems and setups
• Even if your computer is physically connected to a network, you cannot
typically use network resources until you log into the network. When you
log in, you formally identify yourself to the network by providing your ID and
password.
• Your user ID and password are the basis for your user account. A user
account provides access to network resources and accumulates information
about your network use by tracking when you log in and log out.
• For such network environment a network administrator/supervisor is
required who is responsible for setting up user accounts and maintains a
network. The network administrator provides each new user with a user ID
and starter password. In this way centralized administration and support
can be achieved.
Types of Network Nodes Relationships
• Fundamentally, at any given moment, the computer is either acting as a
client or as a server. A server is a computer that shares its resources across
the network, and a client is one that access shared resources.
• Another way to understand this relationship is to visualize an information
interchange that can best be described as request- response. That is, a
client requests information, and s server responds to such a request by
providing the requested information (or by denying the request). This
relationship, called the client/server relationship.
• In some networking environments, certain computers take on specialized
roles and function more or less exclusively as servers, while ordinary user’s
machines tend to function more or less exclusively as clients. Such network
environments are called client/server networks.
• Based on how the computers in a network are configured and how they
access information, networks are classified into three types: peer-to-peer
client-server and hybrid.
The difference between peer-to-peer and server-based
networks is important because each type possesses
different capabilities. The type of network you choose
to implement will depend on factors such as the:
• Size of the organization
• Level of security required
• Type of business
• Level of administrative support available
• Amount of network traffic
• Needs of the network users
• Network budget
Peer-to-Peer Networks
• In a peer-to-peer network, there are no
dedicated servers, and there is no hierarchy
among the computers. All the computers are
equal and therefore are known as peers. Each
computer functions as both a client and a server,
and there is no administrator responsible for the
entire network. The user at each computer
determines what data on that computer is
shared on the network. Figure 1.4 shows a peerto-peer network in which each computer
functions as both a client and a server.
Size
• Peer-to-peer networks are also called workgroups. The
term "workgroup" implies a small group of people. There
are typically 10 or fewer computers in a peer-to-peer
network.
Cost
• Peer-to-peer networks are relatively simple. Because
each computer functions as a client and a server, there
is no need for a powerful central server or for the other
components required for a high-capacity network. Peerto-peer networks can be less expensive than serverbased networks.
Operating Systems
•
In a peer-to-peer network, the networking software does not require the same standard of
performance and level of security as the networking software designed for dedicated servers.
Dedicated servers function only as servers and not as clients or workstations. They are discussed
in more detail later in the next section.
•
Peer-to-peer networking is built into many operating systems. In those cases, no additional
software is required to set up a peer-to-peer network.
Implementation
•
In typical networking environments, a peer-to-peer implementation offers the following
advantages:
•
Computers are located at users' desks.
•
Users act as their own administrators and plan their own security.
•
Computers in the network are connected by a simple, easily visible cabling system.
•
Peer-to-peer networks are good choices for environments where:
•
There are 10 users or fewer.
•
Users share resources, such as files and printers, but no specialized servers exist.
•
Security is not an issue.
•
The organization and the network will experience only limited growth within the foreseeable future.
•
Where these factors apply, a peer-to-peer network will probably be a better choice than a serverbased network.
Peer-to-Peer Network Considerations
• Although a peer-to-peer network might meet the needs of small
organizations, it is not appropriate for all environments. The rest of
this section describes some of the considerations a network planner
needs to address before choosing which type of network to
implement.
Administration
• Network administration tasks include:
• Managing users and security.
• Making resources available.
• Maintaining applications and data.
• Installing and upgrading application and operating system software.
• In a typical peer-to-peer network, no system manager oversees
administration for the entire network. Instead, individual users
administer their own computers.
Sharing Resources
• All users can share any of their resources in any manner they
choose. These resources include data in shared directories, printers,
fax cards, and so on.
Server Requirements
• In a peer-to-peer environment, each computer must:
• Use a large percentage of its resources to support the user at the
computer, known as the local user.
• Use additional resources such as hard-disk space and memory, to
support the user's accessing resources on the network, known as
the remote user.
• While a server-based network relieves the local user of these
demands, it requires at least one powerful, dedicated server to meet
the demands of all the clients on the network.
Security
• On a computer network, security (making computers and
data stored on them safe from harm or unauthorized
access) consists of setting a password on a resource,
such as a directory, that is shared on the network. All
peer-to-peer network users set their own security, and
shared resources can exist on any computer rather than
on a centralized server only; consequently, centralized
control is very difficult to maintain. This lack of control
has a big impact on network security because some
users may not implement any security measures at all. If
security is an issue, a server-based network might be a
better choice.
Server-Based Networks
• As a network grows, a peer-to-peer network will
probably no longer be able to meet the
increased demand on shared resources. To
accommodate the increased demand and
provide additional functionality, most networks
have dedicated servers. A dedicated server
functions as a server only, not as a client. The
configuration of these servers is optimized to
process requests from network clients.
Client-server networks (see Figure 1.5) have
become standard models for networking.
• Figure 1.5 Server-based network
• As networks increase in size due to the
number of connected computers and the
physical distance and traffic between
them, more than one server is usually
needed. Distributing the network tasks
among several servers ensures that each
task is performed as efficiently as
possible. Also, with the servers performing
the network tasks, the workload on the
individual computers is reduced.
• Advantages of Server-Based Network
• Although it is more complex to install, configure, and
manage, a server-based network has many advantages
over a simple peer-to-peer network. The following are
some of the advantages:
• Sharing Resources
• A server is designed to provide access to many files and
printers while maintaining performance and security for
the user.
• Server-based data sharing can be centrally administered
and controlled. Because these shared resources are
centrally located, they are easier to find and support than
resources on individual computers.
• Security
• Security is often the primary reason for
choosing a server-based approach to
networking. In a server-based
environment, one administrator who sets
the policy and applies it to every user on
the network can manage security. Figure
1.6 depicts security being centrally
administered.
• Backup
• Backups can be scheduled several times a day or once
a week depending on the importance and value of the
data. Server backups can be scheduled to occur
automatically, according to a predetermined schedule,
even if the servers are located on different parts of the
network.
• Redundancy
• Through the use of backup methods known as
redundancy systems, the data on any server can be
duplicated and kept online. Even if harm comes to the
primary data storage area, a backup copy of the data
can be used to restore the data.
• Number of Users
• A server-based network can support thousands of users. This type
of network would be impossible to manage as a peer-to-peer
network, but current monitoring and network-management utilities
make it possible to operate a server-based network for large
numbers of users.
• Hybrid Networks
• In fact it is not unusual to find networks in which workstations
function as peers on peer-to-peer networks and as client on serverbased networks. Such networks are called hybrid networks
sometimes called combination networks. These networks, partake of
the advantages of both peer-to-peer and server-based network. And
they incur the disadvantages of server based networks in their
entirely and those of peer-to-peer networks only to the degree that
peer-to-peer capabilities are exercised.
• Table 1.1 Comparisons of Network Types
ConsiderationPeer-to-Peer NetworkServerBased NetworkSizeGood for 10 or fewer
computersLimited only by server and network
hardware capacitySecuritySecurity established
by the user of each computerExtensive and
consistent resource and user
securityAdministrationIndividual users
responsible for their own administration; no fulltime administrator necessaryCentrally located
for network control; requires at least one
knowledgeable administrator
5.2 Network Media
•
•
•
•
•
Data signal must enter and leave a computer at a point
to allow networked communication to occur. The data
signal travels through transmission media.
Transmission media is a medium or a material through
which data can be transmitted over the long distances.
The speed or rate at which data is transmitted over a
communication channel is denoted by a parameter
called bandwidth. Transmission media having higher
bandwidths are used now -a -days for better
performance.
Transmission media is categorized as:
Bounded (guided) transmission media
Unbounded (unguided) transmission media
Guided Transmission Media
• Guided transmission media uses a cabling system that
guides the data signals along a specific path. The data
signals are bound by the cabling system. Guided media
is also known as bound media. "Cabling" is meant in a
generic sense, and is not meant to be interpreted as
copper wire cabling only.
• The three major categories of cables or guided
transmission medium that connect most networks are:
• Coaxial cable
• Twisted-pair cable
• Fiber-optic cable
Coaxial Cable
• Coaxial cable consists of a copper wire core surrounded by
insulation, a braided metal shielding, and an outer cover. Figure 2.1
shows the various components that make up a coaxial cable.
• The term shielding refers to the woven or stranded metal mesh (or
other material) that surrounds some types of cabling. Shielding
protects transmitted data by absorbing stray electronic signals,
called noise, so that they do not get onto the cable and distort the
data. Cable that contains one layer of foil insulation and one layer of
braided metal shielding is referred to as dual shielded. For
environments that are subject to higher interference, quad shielding
is available. Quad shielding consists of two layers of foil insulation
and two layers of braided metal shielding.
•
•
•
The core of a coaxial cable carries the electronic signals that make up the
data. This wire core can be either solid or stranded. If the core is solid, it is
usually copper.
Surrounding the core is a dielectric insulating layer that separates it from the
wire mesh. The braided wire mesh acts as a ground and protects the core
from electrical noise and crosstalk. (Crosstalk is signal overflow from an
adjacent wire).
The conducting core and the wire mesh must always be kept separate from
each other. If they touch, the cable will experience a short, and noise or
stray signals on the mesh will flow onto the copper wire. An electrical short
occurs when any two conducting wires or a conducting wire and a ground
come into contact with each other. This contact causes a direct flow of
current (or data) in an unintended path. In the case of household electrical
wiring, a short will cause sparking and the blowing of a fuse or circuit
breaker. With electronic devices that use low voltages, the result is not as
dramatic and is often undetectable. These low-voltage shorts generally
cause the failure of a device; and the short, in turn, destroys the data.
• A non-conducting outer shield—usually
made of rubber, Teflon, or plastic—
surrounds the entire cable.
• Coaxial cable is more resistant to
interference and attenuation than twistedpair cabling. Attenuation is the loss of
signal strength that begins to occur as the
signal travels farther along a copper cable.
(See the following figure).
• The stranded, protective sleeve absorbs
stray electronic signals so that they do not
affect data being sent over the inner
copper cable. For this reason, coaxial
cabling is a good choice for longer
distances and for reliably supporting
higher data rates with less sophisticated
equipment.
Types of Coaxial Cable
• There are two types of coaxial cable:
• Thin (thinnet) cable
• Thick (thicknet) cable
Thinnet Cable Thinnet cable is a flexible coaxial
cable about 0.64 centimeters thick. Because this
type of coaxial cable is flexible and easy to work
with, it can be used in almost any type of
network installation.
• Thinnet coaxial cable can carry a signal for a
distance of up to approximately 185 meters
before the signal starts to suffer from
attenuation.
• Thicknet Cable Thicknet cable is a relatively
rigid coaxial cable about 1.27 centimeters in
diameter. Figure 2.3 shows the difference
between thinnet and thicknet cable. Thicknet
cable's copper core is thicker than a thinnet
cable core.
•
•
•
•
The thicker the copper core, the farther the cable can carry signals. This
means that thicknet can carry signals farther than thinnet cable. Thicknet
cable can carry a signal for 500 meters. Therefore, because of thicknet's
ability to support data transfer over longer distances, it is sometimes used
as a backbone to connect several smaller thinnet-based networks.
Thinnet vs. Thicknet: As a general rule, the thicker the cable, the more
difficult it is to work with. Thin cable is flexible, easy to install, and relatively
inexpensive. Thick cable does not bend easily and is, therefore, harder to
install. This is a consideration when an installation calls for pulling cable
through tight spaces such as conduits and troughs. Thick cable is more
expensive than thin cable, but will carry a signal farther.
Coaxial-Cable Connection Hardware
Both thinnet and thicknet cable use a connection component, known as a
BNC connector, to make the connections between the cable and the
computers. There are several important components in the BNC family,
including the following:
• The BNC cable connector: The following
figure shows a BNC cable connector. The
BNC cable connector is either soldered or
crimped to the end of a cable.
• The BNC T connector: The following
figure shows a BNC T connector. This
connector joins the network interface card
(NIC) in the computer to the network
cable.
•
The BNC barrel connector: The
following figure shows a BNC barrel
connector. This connector is used to join
two lengths of thinnet cable to make one
longer length.
•
The BNC terminator: The following
figure shows a BNC terminator. A BNC
terminator closes each end of the bus
cable to absorb stray signals. Otherwise,
the signal will bounce and all network
activity will stop.
• NOTE: The origin of the acronym "BNC" is
unclear, and there have been many names
ascribed to these letters, from "British Naval
Connector" to "Bayonet Neill-Councelman."
Because there is no consensus on the proper
name and because the technology industry
universally refers to these simply as BNC-type
connectors, in this manual we will refer to this
family of hardware simply as BNC
•
•
•
•
It is less susceptible to interference than
twisted-pair cable.
Transmit data for greater distances than
is possible with less expensive cabling.
Transmit voice, video, and data
Offer a familiar technology with
reasonable data security.
Disadvantages of Coaxial Cable
• There are many types of coaxial cables,
each suited for one, or at most, a small
number of LAN systems.
• Due to its high metallic content, coaxial
cable is usually more expensive than other
cable types.
Twisted-Pair Cable
• Twisted-pair cable consists of two insulated strands of
copper wire twisted around each other.
Types of twisted pair cable
• There are two types of twisted-pair cable:
• Unshielded twisted-pair cables (UTP cables)
• Shielded twisted-pair cables (STP cables)
• A number of twisted-pair wires are often grouped
together and enclosed in a protective sheath to form a
cable. The total number of pairs in a cable varies.
The twisting cancels out electrical noise from adjacent
pairs and from other external sources such as motors,
relays, and transformers.
Unshielded Twisted-Pair (UTP) Cable
• UTP, using the 10BaseT (“10” indicates bandwidth of the
cable in Mbps, “Base” refers the type of transmission i.e.
baseband transmission, and “T” indicates the type of the
cable which is twisted pair) specification, is the most
popular type of twisted-pair cable and is becoming the
most popular LAN cabling. The maximum cable length
segment is 100 meters (after 100 meters, the signal gets
weaker and weaker as the result the receiving computer
will not recognize whether it is noise or not).
• Traditional UTP cable consists of two insulated copper
wires. UTP specifications govern how many twists are
permitted per foot of cable; the number of twists allowed
depends on the purpose to which the cable will be put.
There are 7 standard categories of UTP:
• Category 1 This refers to traditional UTP telephone cable that can
carry voice but not data transmissions.
• Category 2 This category certifies UTP cable for data transmissions
up to 4 megabits per second (Mbps). It consists of four twisted pairs
of copper wire.
• Category 3 This category certifies UTP cable for data transmissions
up to 16 Mbps. It consists of four twisted pairs of copper wire.
• Category 4 This category certifies UTP cable for data transmissions
up to 20 Mbps. It consists of four twisted pairs of copper wire.
• Category 5 This category certifies UTP cable for data transmissions
up to 100 Mbps. It consists of four twisted pairs of copper wire.
• Category 5e Improved version of CAT 5 category. The bandwidth is
1000Mbps
• Category 6 Similar to CAT 5 wire, but contains a physical separator
between the 4 pairs to further reduce electromagnetic interference.
Shielded Twisted-Pair (STP) Cable
• STP cable uses a woven copper-braid jacket
that is more protective and of a higher quality
than the jacket used by UTP. Figure 2.9 shows a
two-twisted-pair STP cable. STP also uses a foil
(very thin sheet of metal) wrap around each of
the wire pairs. This gives STP excellent
shielding to protect the transmitted data from
outside interference, which in turn allows it to
support higher transmission rates over longer
distances than UTP.
• Twisted-Pair Cabling Components
• While we have defined twisted-pair cabling by the number of twists
and its ability to transmit data, additional components are necessary
to complete an installation. As it is with telephone cabling, a twistedpair cable network requires connectors and other hardware to
ensure proper installation.
• Connection hardware Twisted-pair cabling uses RJ-45 telephone
connectors to connect to a computer. These are similar to RJ-11
telephone connectors. An RJ-45 connector is shown in Figure 2.10
Although RJ-11 and RJ-45 connectors look alike at first glance,
there are crucial differences between them.
• The RJ-45 connector is slightly larger and will not fit into the RJ-11
telephone jack. The RJ-45 connector houses eight cable
connections, while the RJ-11 houses only four.
Figure 2.10 RJ-45 connector and jack
• Distribution racks and rack shelves
Distribution racks and rack shelves can create
more room for cables where there isn't much
floor space. Using them is a good way to
organize a network that has a lot of connections.
• Expandable patch panels These come in
various versions that support up to 96 ports and
transmission speeds of up to 100 Mbps.
• Jack couplers These single or double RJ-45
jacks snap into patch panels and wall plates and
support data rates of up to 100 Mbps.
• Wall plates these support two or more
couplers.
Advantages UTP
• It has a large installed base and is a
familiar technology.
• It is relatively inexpensive and easy to
install.
• Most LAN systems are readily capable of
running over UTP.
• It does not require bonding and grounding.
• Easy to install.
Disadvantages of UTP
• High-quality UTP systems require specialized
installation procedures.
• UTP is potentially more sensitive to external
electromagnetic interference, crosstalk, and
attenuation than other media.
• Not recommended for LAN that requires a high
level of security and you must be absolutely sure
of data integrity.
• Not suitable for transmitting data over long
distances at high speeds.
Advantage of STP
• Provides better performance than UTP in
environments with high noise levels—high levels
of unwanted electrical signals.
Disadvantages STP
• It is more labor-intensive than UTP to install.
• Not all LAN systems work readily over STP.
• Susceptible to ground faults through the shield.
Fiber-Optic Cable
• In fiber-optic cable, optical fibers carry digital
data signals in the form of modulated pulses of
light. This is a relatively safe way to send data
because, unlike copper-based cables that carry
data in the form of electronic signals, no
electrical impulses are carried over the fiberoptic cable. This means that fiber optic cable
cannot be tapped, and its data cannot be stolen.
• Fiber-optic cable is good for very high-speed,
high-capacity data transmission because of the
purity of the signal and lack of signal attenuation.
Fiber-Optic Cable Composition
• An optical fiber consists of an extremely thin cylinder of glass, called
the core, surrounded by a concentric layer of glass, known as the
cladding. The fibers are sometimes made of plastic. Plastic is easier
to install, but cannot carry the light pulses for as long a distance as
glass.
• Because each glass strand passes signals in only one direction, a
cable includes two strands in separate jackets. One strand transmits
and one receives. A reinforcing layer of plastic surrounds each glass
strand, and Kevlar fibers provide strength. See Figure 2.12 for an
illustration of fiber-optic cable. The Kevlar fibers in the fiber-optic
connector are placed between the two cables. Just as their
counterparts (twisted-pair and coaxial) are, fiber-optic cables are
encased in a plastic coating for protection.
• Optical fiber strands are thin filaments of glass
consisting of an inner core and an outer
cladding. Both the core and the cladding are
glass, and each has a different refractive index.
Signals are transmitted as light pulses through
the core of the optical fiber. When these light
pulses strike the cladding they are reflected back
into the core because the cladding has a lower
refractive index than the core. This keeps the
transmitted signal within the core as it travels
down the fiber.
• Fiber-optic cable transmissions are not
subject to electrical interference and are
extremely fast, currently transmitting about
100 Mbps with demonstrated rates of up to
1 gigabit per second (Gbps). They can
carry a signal—the light pulse—for many
miles.
Fiber-Optic Cabling
Considerations
Advantages of Fiber-Optic
• Optical signals through glass encounter less loss than
electrical signals through copper. This translates into
lower attenuation and higher bandwidth than copper,
allowing transmission to occur over longer distances
and/or at greater speeds.
• High level of immunity to electromagnetic interference
since signals are sent as light and not as electricity.
Disadvantage of Fiber-Optic
• Due to the required conversions between light and
electricity, more expensive electronics are required than
with copper-based systems.
• Requires specialized installation procedures.
Unguided Transmission Media
• Although the majority of LANs connect devices using a physical
cable, there are instances where it is difficult or impossible to install
cable—such as in historical properties or when there is no right-ofway access between adjacent buildings. In such cases, wireless
transmission can be used to connect network devices. Additionally,
certain users within an organization may be required to be mobile
and still have access to the LAN through the use of a laptop or
hand-held computer, such as nurses on their rounds or warehouse
employees. Wireless systems do not physically connect network
devices since the links between the devices are invisible.
• To conclude, unguided transmission media consists of a means for
the data signals to travel but nothing to guide them along a specific
path. The data signals are not bound to a cabling media and are
therefore often called unbound media.
•
•
•
•
•
•
•
The three most common types of unguided transmission medium are
Infrared
Radio Frequency
Microwave
Infrared links
LAN devices connected to each other using infrared light signals work in the
same manner as remote control unit work with television sets. These
systems consist of a base unit connected to the server and device
connections to the stations. The base unit has two optical nodes—one to
receive signals from the station and one to send signals to the station.
Since the system depends on infrared light to transmit, a requirement is that
the base unit and the station connections are in a direct line-of-sight to each
other. Alternatively, some of these systems use a reflective surface
positioned between the base unit and the station for the purpose of
redirecting the signal.
Radio links
• This second type of unguided (wireless) media uses
radio waves to transmit information between the server
and the stations. Most of these systems use spread
spectrum technology where data is transmitted at low
density over a given frequency range.
• Systems based on radio links also work with two
components—a control module connected to the server
and user modules connected to the stations.
• The control module and the user module do not have to
be in direct line-of sight with each other. The radio
signals are capable of passing through most office
building doors and walls.
Microwave
• A cableless medium that use high
frequency radio signals to send data or
information through the air.
Advantages of Unguided (Wireless) Transmission
• Can be used in situations where it is difficult or
impossible to install cable.
• Portability
• Convenience
Disadvantages Unguided (Wireless) Transmission
• Typically, such systems are not able to meet the
performance demands of large or busy networks.
• Transmission can only occur over limited distances and
at limited bit rates.
Networking Equipments and
Instruments
Network Interface Card
• Network interface card (NICs,) also known as
network adapters provide the interface between
cables, and computers. The cards are installed
in an expansion slot in each computer and
server on the network. After the NIC has been
installed, the network cable is attached to the
card’s port to make the actual physical
connection between the computer and the rest
of the network. (See figure 4.1, which is the
sample NIC).
Role of Network Interface Cards
• The network adapter performs the following
functions:
• Prepare data from the computer for the network
cable.
• Send the data to another computer.
• Control the flow of data between the computer
and the cabling system.
• Receive incoming data from the cable and
translate it into bytes that can be understood by
the computer's central processing unit (CPU).
• To provide to the growing networking needs of an organization, you
need to expand the size or improve the performance of a network.
You cannot make networks larger just by adding new computers and
more cable. Each network topology or architecture has limits. You
can, however, install components to increase the size of the network
within its existing environment.
• Components that enable you to expand the network include:
• Modem
• Repeaters and Hubs
• Bridges
• Switches
• Routers
• Gateways
• You can also expand a network by allowing
users to connect to the network from a remote
location. To establish a remote connection, the
three components required are a remote access
client, a remote access server, and physical
connectivity. Network operating systems enable
remote client computers to connect to remote
access servers by using:
• Public Switched Telephone Network (PSTN)
• Integrated Services Digital Network (ISDN)
• Asymmetric Digital Subscriber Line (ADSL)
Modem
• A modem is a device that makes it possible for computers to
communicate over a telephone line.
• When computers are too far apart to be joined by a standard
computer cable, a modem can enable communication between
them. In a network environment, modems serve as a means of
communication between networks and as a way to connect to the
world beyond the local network.
• Computers cannot simply be connected to each other over a
telephone line, because computers communicate by sending digital
electronic pulses (electronic signals), and a telephone line can send
only analog waves (sound).
• As shown in Figure 4.2, the modem at the sending end converts the
computer's digital signals into analog waves and transmits the
analog waves onto the telephone line. A modem at the receiving end
converts the incoming analog signals back into digital signals for the
receiving computer.
• In other words, sending modem
MOdulates digital signals into analog
signals, and receiving modem
DEModulates analog signals back into
digital signals.
Repeaters and Hubs
• You can use repeaters and hubs to
expand a network by adding two or more
segments of cabling. These commonly
used devices are inexpensive and easy to
set up.
Repeaters
• Repeaters receive signals and retransmit them
at their original strength and definition. This
increases the practical length of a cable. (If a
cable is very long, the signal weakens and
become unrecognizable.) Installing a repeater
between cable segments enables to travel
farther. Figure 4.3 shows how repeaters
regenerate weak signals.
• Repeaters do not translate or filter signals. For a
repeater to work, both segments connected to
the repeater must use the same access method.
For example, a repeater cannot translate an
Ethernet packet into a token ring packet.
• Repeaters do not act as filters to restrict the flow
of problem traffic. Repeaters send every bit of
data from one cable segment to another, even if
the data consists of malformed packets or
packets not destined for a computer on another
segment.
Use a repeater to:
• Connect two segments of similar or dissimilar cabling.
• Regenerate the signal to increase the distance
transmitted.
• Transmit all traffic in both directions.
• Connect two segments in the most cost-effective
manner.
Do not use a repeater when:
• There is heavy network traffic.
• Segments are using different access methods.
• Data filtering is needed.
• As shown in Figure 4.4, repeaters can
move packets from one kind of physical
media to another. They can take an
Ethernet packet coming from a thinnet
coaxial-cable segment and pass it on to a
fiber-optic segment, provided the repeater
is capable of accepting the physical
connections.
Hubs
• Hubs are connectivity devices that connect
computers in a star topology. Hubs contain
multiple ports for connecting to network
components. If you use a hub, a break in the
network does not affect the entire network; only
the segment and the computer attached to that
segment fail. A single data packet sent through a
hub goes to all connected computers. Figure 4.5
shows method of hub communication.
There are two basic types of hubs:
• Passive Hubs. Send the incoming signal directly through
their ports without any signal processing. These hubs
are usually wiring panels.
• Active Hubs. Sometimes called multiport repeaters,
receive incoming signals, process the signals, and
retransmit them at their original strengths and definitions
to the connected computers or components.
• Hybrid Hubs. Advanced hubs that will accommodate
several different types of cables are called hybrid hubs.
The following figure shows a main hub (the hybrid) with
three sub-hubs.
Use a hub to:
• Easily change and expand wiring systems
• Use different ports to accommodate a
Varity of cable types
• Enable central monitoring of network
activity and traffic
Bridges
• A bridge is a device that passes data packets
between multiple network segments that use the
same communications protocol. A bridge passes
one signal at a time. If a packet is destined for a
computer within the sender's own network
segment, the bridge retains the packet within
that segment. If the packet is destined for
another segment, it passes the packet to that
segment. Figure 4.7 shows a bridge connecting
two network segments.
MAC Addresses
• As traffic passes through the bridge, information about the sending
computers' MAC addresses is stored in the bridge's memory. The
bridge uses this information to build a table based on these
addresses. As more data is sent, the bridge develops a bridging
table that identifies each computer and its location on network
segments. When the bridge receives a packet, the source address is
compared to the source address listed in the table. If the source
address is not present in the table, it is added to the table. The
bridge then compares the destination address with the destination
address listed in the table. If a bridge recognizes the location of the
destination address, it forwards the packet to this address. If it does
not recognize the destination address, it forwards the packet to all
segments.
Use a bridge to:
• Expand the length of a segment.
• Provide for an increased number of computers on the
network.
• Reduce traffic bottlenecks resulting from an excessive
number of attached computers.
• Split an overloaded network into two separate networks,
thereby reducing the amount of traffic on each segment
and making each network more efficient.
• Link dissimilar physical cables, such as twisted-pair and
coaxial Ethernet cables.
Switches
• Switches are similar to bridges but offer a more direct network
connection between the source and destination computers. When a
switch receives a data packet, it creates a separate internal
connection, or segment, between any two of its ports and forwards
the data packet to the appropriate port of the destination computer
only, based on information in each packet's header. This insulates
the connection from the other ports and gives the source and
destination computers access to the full bandwidth of a network.
• Unlike a hub, switches are comparable to a telephone system with
private lines. In such a system, if one person calls someone, the
operator or telephone switch connects them on a dedicated line.
This allows more conversations to take place at any one time. The
following figure illustrates a switched network.
Use a switch to:
• Send a packet directly from the source
computer to the destination computer.
• Provide for a greater rate of data
transmission.
Router
• A router is a device that acts like a bridge or
switch but provides more functionality. In moving
data between different network segments,
routers examine a packet header to determine
the best path for the packet to travel. A router
knows the path to all of the segments on the
network by accessing information stored in the
routing table. Figure 4.9 shows a router
connecting two network segments. Routers
enable all users in a network to share a single
connection to the Internet or a WAN.
• Router allows you to segment your
network into what are called subnets. A
subnet is a network connected to another
network via a router. The following figure
shows a network divided into subnets
using routers.
Use a router to:
• Send packets directly to a destination computer on another networks
or segment.
• Routers use a more complete packet address than do bridges, for
example, to determine which router or client should next receive
each packet. Routers ensure that packets travel the most efficient
paths to their destinations. If a link between two routers fails, the
sending router can determine an alternate route to keep traffic
moving.
• Reduce stress on the network.
• Routers read addressed network packets only and pass information
only if the network address is known. Therefore, they do not pass
corrupted data. This ability to control the data passing through the
router reduces the amount of traffic between networks and enables
routers to use these links more efficiently than bridges can.
Gateways
• Gateways enable communication between different
network architectures. A gateway takes the data from
one network and repackages it, so that each network
can understand the other network's data.
• A gateway is like an interpreter. For example, if two
groups of people can physically talk to each other but
speak different languages, they need an interpreter to
communicate. Similarly, two networks can have a
physical connection but need a gateway to translate
network communication.
Use a gateway to link two systems that do
not use the same:
• Architecture.
• Set of communication rules and
regulations.
• Data-formatting structures.
Public Switched Telephone Network
• Public Switched Telephone Network (PSTN)
refers to the international telephone standard
based on using copper wires for transmitting
analog voice data. This standard was designed
to carry only the minimal frequencies necessary
to distinguish human voices. Because PSTN
was not designed for data transmissions, there
are limits to the maximum data transmission rate
of a PSTN connection. In addition, analog
communication is susceptible to line noise that
causes a reduction in the data transmission rate.
Integrated Service Digital Network (ISDN)
• Integrated Services Digital Network (ISDN) is an
international communications standard for sending voice,
video, and data over digital telephone lines and standard
telephone wires. ISDN has the ability to simultaneously
deliver two connections over a single pair of telephone
lines. The two connections may be in any combination of
data, voice, video, or fax. The single line uses an ISDN
subscriber service, which is called Basic Rate Interface
(BRI). BRI has two channels, called B channels, at 64
Kbps each, which carry the data, and one data channel
at 16 Kbps for control information. The two B channels
can be combined to form a single 128 Kbps connection.
Asymmetric Digital Subscriber Line (ADSL)
• Asymmetric digital subscriber line (ADSL)
is a technology that allows more data to be
sent over existing copper telephone lines.
ADSL accomplishes this by using the
portion of a telephone line's bandwidth not
utilized by voice, thereby allowing for
simultaneous voice and data transmission.
• Typical remote access users receive much more
information than they send. The asymmetric
nature of the ADSL connection fits well with most
Internet and remote business use. When
receiving data, ADSL supports data rates from
1.5 to 9 Mbps. When sending data, ADSL
supports data rates from 16 to 640 Kbps.
Although ADSL provides higher data
transmission rates than do PSTN and ISDN
connections, the client computer can receive
data at a faster rate than it can send data.
5.4 Network Topologies
• A network topology is the arrangement of
computers, cables, and other components on a
network. It is a map of the physical network. The
type of topology you use affects the type and
capabilities of the network's hardware, its
management, and possibilities for future
expansion.
• Generally, there are two types of topologies,
which are Physical and Logical topologies.
Logical topology
• Logical topology is the method used to pass the
information between the computers. In other
words, looking at that same room, if you were to
try to see how the network works with all the
computers talking (think of the computers
generating traffic and packets of data going
everywhere on the network) you would be
looking at the logical part of the network. The
way the computers will be talking to each other
and the direction of the traffic is controlled by
various protocols.
Physical topology
• The physical topology of a network refers to the layout of cables,
computers and other peripherals. Try to imagine yourself in a room
with a small network, you can see network cables coming out of
every computer that is part of the network, then those cables plug
into a hub or switch. What you're looking at is the physical topology
of that network.
• The physical topology describes the layout of the network, just like a
map shows the layout of various roads, and the logical topology
describes how the data is sent across the network or how the cars
are able to travel (the direction and speed) at every road on the
map.
• The most common types of standard physical topologies are Bus,
Star, Ring, Mesh and Hybrid.
Bus Topology
• In a bus topology, all of the computers in a network are
attached to a continuous cable, or segment, that
connects them in a straight line (See Figure 3.1). In this
straight-line topology, a packet is transmitted to all
network adapters on that segment.
• An advantages of the bus topology are those use of
cable is economical, media is inexpensive and easy to
work with, system is simple and reliable and is easy to
extend.
• Because of the way electrical signals are transmitted
over this cable, the ends of the cable must be terminated
by hardware devices called terminators, which act as the
boundaries for the signal and define the segment.
• If there is a break anywhere in the cable or if an end is
not terminated, the signal will travel back and forth
across the network and all communication will stop.
• The number of computers attached to a bus also affects
network performance. The more computers there are on
the bus, the greater the backup of computers waiting to
put data on the bus, and consequently, the slower the
network. In addition, because of the way computers
communicate in a bus topology, there may be a lot of
noise. Noise is the traffic generated on the network when
computers attempt to communicate with each other
simultaneously. An increase in the number of computers
results in an increase in noise and a corresponding
decrease in network efficiency.
Star Topology
• In a star topology, cable segments from each
computer on the network are connected to a
central component, or hub (See Figure 3.2). A
hub is a device that connects several computers
together. In a star topology, signals are
transmitted from the computer, through the hub,
to all computers on the network. On a larger
scale, multiple LANs can be connected to each
other in a star topology.
• An advantage of the star topology is that if one
computer on the star topology fails, only the
failed computer is unable to send or receive
data. The remainder of the network functions
normally.
• The disadvantage of using this topology is that
because each computer is connected to a hub, if
the hub fails, the entire network fails. In addition,
noise is created on the network in a star
topology.
Ring Topology
• In a ring topology, computers are connected on a single
circle of cable (See Figure 3.3). Unlike the bus topology,
there are no terminated ends. The signals travel around
the loop in one direction and pass through each
computer, which acts as a repeater to boost the signal
and send it to the next computer. On a larger scale,
multiple LANs can be connected to each other in a ring
topology by using ThickNet coaxial or fiber-optic cable.
• The advantage of a ring topology is that each computer
acts as a repeater, regenerating the signal and sending it
on to the next computer, thereby preserving signal
strength.
• The method of transmitting data around the ring is called token
passing. A token is a special series of bits that contains control
information. Possession of the token allows a network device to
transmit data to the network. Each network has only one token.
• The sending computer removes the token from the ring and sends
the requested data around the ring. Each computer passes along
the data until the packet finds the computer that matches the
address on the data. The receiving computer then returns a
message to the sending computer indicating that the data has been
received. After verification, the sending computer creates a new
token and releases it to the network.
• The advantage of a ring topology is that it can handle high-traffic
environments better than bus networks. In addition, the impact of
noise is reduced in the ring topology.
• The disadvantage of a ring topology is that only one computer at a
time can send data on a single token ring. Also, ring topologies are
usually more expensive than bus technologies.
Mesh Topology
• In a mesh topology, each computer is connected
to every other computer by a separate cable
(See Figure 3.4). This arrangement provides
redundant paths through the network so that if
one cable fails, another carries the traffic and the
network continues to function. On a larger scale,
multiple LANs can be connected to each other in
a mesh topology by using leased telephone
lines, ThickNet coaxial cable, or fiber-optic
cable.
• An advantage of a mesh topology is its
back-up capabilities by providing multiple
paths through the network. Because
redundant paths require more cable than
is needed in other topologies, a mesh
topology can be expensive.
Hybrid Topologies
• In a hybrid topology, two or more topologies are
combined to form a complete network design.
Networks are rarely designed using only one
type of topology. For example, you may want to
combine a star with a bus topology to benefit
from the advantages of each.
• Two types of hybrid topologies are commonly in
use: star-bus topology and star-ring topology.
(See Figure 3.5)
Star-Bus
In a star-bus topology, several star topology
networks are linked to a bus connection. After a
star configuration is full, you can add a second
star and use a bus connection to connect the
two star topologies.
• In a star-bus topology, if a single computer fails,
it will not affect the rest of the network. However,
if the central component, or hub, that attaches all
computers in a star fails, all computers attached
to that component fail and are unable to
communicate.
Star-Ring
• In the star-ring topology, the computers are
connected to a central component as in a star
network. These components, however, are wired
to form a ring network.
• Like the star-bus topology, if a single computer
fails, it will not affect the rest of the network. By
using token passing, each computer in a starring topology has an equal chance of
communicating. This allows for greater network
traffic between segments than in a star-bus
topology.
5.5 Network Hardware and
Architecture
• It is possible to use different network technologies to
communicate between computers within LANs and
WANs. You may use a combination of technologies to
get the best cost-benefit and maximum efficiency from
your network design.
• Different network technologies are available, one of the
ways in which these technologies differ is the set of rules
that each uses to place data onto the network cable and
to remove data from the cable. This is called access
method. When data moves on the network, these
various access methods regulate the flow of network
traffic.
Ethernet
• Ethernet is a popular LAN technology that uses
Carrier Sense Multiple Access with Collision
Detection (CSMA/CD) between clients over a
variety of cable types. Ethernet is passive, which
means it requires no power source of its own,
and thus does not fail unless the cable is
physically cut or improperly terminated. Ethernet
is connected by using a bus topology in which
the cable is terminated at both ends.
Token ring
• Token ring networks are implemented in a ring
topology. The physical topology of a token ring
network is the star topology, in which all
computers on the network are physically
connected to a hub. The physical ring is wired
through a hub called a multistation access unit
(MSAU). The logical topology represents the
token's path between computers, which is
similar to a ring.
Asynchronous Transfer Mode (ATM)
• Asynchronous transfer mode (ATM) is a packetswitching network that sends fixed-length
packets over LANs or WANs, instead of the
variable-length packets used in other
technologies. Fixed-length packets, or cells, are
data packets that contain only basic path
information, allowing switching devices to route
the packet quickly. Communication occurs over
a point-to-point system that provides a
permanent and virtual data path between each
station.
Fiber Distributed Data Interface (FDDI)
• A Fiber Distributed Data Interface (FDDI)
network provides high-speed connections for
various types of networks. FDDI was designed
for use with computers that required speeds
greater than the 10 Mbps available from
Ethernet or the 4 Mbps available from existing
token ring architectures. An FDDI network can
support several low-capacity LANs that require a
high-speed backbone.
• An FDDI network consists of two similar
streams of data flowing in opposite
directions around two rings. One ring is
called the primary ring and the other is
called the secondary ring. If there is a
problem with the primary ring, such as a
ring failure or a cable break, the ring
reconfigures itself by transferring data to
the secondary ring, which continues
transmitting.
Frame relay
• Frame relay is a packet-switching network that sends
variable-length packets over LANs or WANs. Variable
length packets, or frames, are data packets that contain
additional addressing and error handling information
necessary for delivery.
• Communication occurs over a network that provides a
permanent and virtual data path between each station.
This type of network uses wide area digital or fiber-optic
links and gives you quick access to data transfer that
you pay for only as you need it.
• Packet switching is a method used to send data over a
WAN by dividing a large package of data into smaller
pieces (packets). These pieces are sent through a
packet switch, which sends the individual packets across
the WAN using the best route currently available.
Although these packets may travel along different paths,
the receiving computer can reassemble the pieces into
the original data frame.
• However, you could have a permanent virtual circuit
(PVC) established, which would use the same path for
all of the packets. This allows for a faster transmission
than by normal frame relay networks and eliminates the
need for packet disassembly and reassembly.
Network Standards and Protocols
• Network client software operates at many different levels
within the sending and receiving computers. Each of
these levels, or tasks, is governed by one or more
protocols (set of rules). These protocols, or rules of
behavior, are standard specifications for formatting and
moving the data. When the sending and receiving
computers follow the same protocols, communication is
assured.
• With the rapid growth of networking hardware and
software, a need arose for standard protocols that could
allow hardware and software from different vendors to
communicate.
Open Systems Interconnection (OSI) Reference Model
• Most networks are a combination of hardware and
software from a variety of vendors. This ability to
combine the products manufactured by different vendors
is made possible by the existence of industry standards
(International Organization for Standardization) (ISO).
ISO is responsible for standardizing the methods by
which computers communicate worldwide. To do so, ISO
created a model for network communication, called the
Open Systems Interconnection (OSI) reference model,
or the OSI model.
• In 1978, the International Organization for Standardization (ISO)
released a set of specifications that described network architecture
for connecting dissimilar devices. The original document applied to
systems that were open to each other because they could all use
the same protocols (the procedures used to control the orderly
exchange of information between stations on a data communication
network) and standards to exchange information.
• The OSI reference model is the best-known and most widely used
guide for visualizing networking environments. Manufacturers
adhere to the OSI reference model when they design network
products. It provides a description of how network hardware and
software work together in a layered fashion to make
communications possible. The model also helps to troubleshoot
problems by providing a frame of reference that describes how
components are supposed to function.
• The OSI reference model architecture divides
network communication into seven layers. Each
layer covers different network activities,
equipment, or protocols. Table 5.1 represents
the layered architecture of the OSI reference
model. (Layering specifies different functions
and services as data moves from one computer
through the network cabling to another
computer.) The OSI reference model defines
how each layer communicates and works with
the layers immediately above and below it.
• Each layer provides some service or action that prepares
the data for delivery over the network to another
computer. The lowest layers—1 and 2—define the
network's physical media and related tasks, such as
putting data bits onto the network interface cards (NICs)
and cable. The highest layers define how applications
access communication services. The higher the layer,
the more complex its task.
• The layers are separated from each other by boundaries
called interfaces. All requests are passed from one layer,
through the interface, to the next layer. Each layer builds
upon the standards and activities of the layer below it.
Relationships among OSI Reference Model Layers
• Each layer provides services to the next-higher layer and
shields the upper layer from the details of how the
services below it are actually implemented. At the same
time, each layer appears to be in direct communication
with its associated layer on the other computer. This
provides a logical, or virtual, communication between
peer layers, as shown in Figure 5.1. In reality, actual
communication between adjacent layers takes place on
one computer only. At each layer, software implements
network functions according to a set of protocols.
• Before data is passed from one layer to another, it is broken down
into packets, or units of information, which are transmitted as a
whole from one device to another on a network. The network passes
a packet from one software layer to another in the same order as
that of the layers. At each layer, the software adds additional
formatting or addressing to the packet, which is needed for the
packet to be successfully transmitted across the network.
• At the receiving end, the packet passes through the layers in
reverse order. A software utility at each layer reads the information
on the packet, strips it away, and passes the packet up to the next
layer. When the packet is finally passed up to the application layer,
the addressing information has been stripped away and the packet
is in its original form, which is readable by the receiver.
• With the exception of the lowest layer in the OSI networking model,
no layer can pass information directly to its counterpart on another
computer. Instead, information on the sending computer must be
passed down through each successive layer until it reaches the
physical layer. The information then moves across the networking
cable to the receiving computer and up that computer's networking
layers until it arrives at the corresponding layer. For example, when
the network layer sends information from computer A, the
information moves down through the data-link and physical layers
on the sending side, over the cable, and up the physical and datalink layers on the receiving side to its final destination at the network
layer on computer B.
• In a client/server environment, an example of the kind of information
sent from the network layer on computer A to the network layer on
computer B would be a network address, with perhaps some errorchecking information added to the packet.
• Interaction between adjacent layers occurs
through an interface. The interface defines the
services offered by the lower networking layer to
the upper one and further defines how those
services will be accessed. In addition, each layer
on one computer appears to be communicating
directly with the same layer on another
computer.
• The following sections describe the purpose of
each of the seven layers of the OSI reference
model, and identify the services that each
provides to adjacent layers.
Memorizing the OSI Reference Model
• Memorizing the layers of the OSI
reference model and their order is very
important, especially when preparing to
take a computer networking exam. Table
5.2 provides two ways to help you recall
the seven layers of the OSI reference
model.
Network Protocol
• To ensure that computers in a network are able to communicate,
they must share a common language known as a protocol. A
protocol is a set of rules or standards that enables communication
between computers in a network.
• Protocols are rules and procedures for communicating. The term
"protocol" is used in a variety of contexts. For example, diplomats
from one country adhere to rules of protocol designed to help them
interact smoothly with diplomats from other countries. Rules of
protocol apply in the same way in the computer environment. When
several computers are networked, the rules and technical
procedures governing their communication and interaction are
called protocols.
• In general protocols are software and must be
installed on network components that need
them. Computers can communicate with each
other only if they use the same protocol. If the
protocol used by a computer in a network is not
compatible with the protocol used by another
computer, the two computers cannot exchange
information. A variety of protocols are available
for use in specific network environments.
Although each protocol facilitates basic network
communication, each has a different function
and accomplishes different tasks.
Keep the following three points in mind when you think about protocols
in a network environment:
• There are many protocols. While each protocol facilitates basic
communications, each has different purposes and accomplishes
different tasks. Each protocol has its own advantages and
restrictions.
• Some protocols work only at particular OSI layers. The layer at
which a protocol works describes its function. For example, a
protocol that works at the physical layer ensures that the data
packet passes through the network interface card (NIC) and out onto
the network cable.
• Protocols can also work together in a protocol stack, or suite. Just
as a network incorporates functions at every layer of the OSI
reference model, different protocols also work together at different
levels in a single protocol stack. The levels in the protocol stack
"map," (you will study in the next sub section) or correspond, to the
layers of the OSI reference model.
How Protocols Work?
• The entire technical operation by which data is
transmitted over the network has to be broken down into
discrete, systematic steps. At each step, certain actions
take place that cannot take place at any other step. Each
step includes its own rules and procedures, or protocol.
• The protocol steps must be carried out in a consistent
order that is the same on every computer in the network.
In the sending computer, these steps must be executed
from the top down. In the receiving computer, these
steps must be carried out from the bottom up.
The Sending Computer
• Protocols at the sending computer:
• Break the data into smaller sections, called
packets that the protocol can handle.
• Add addressing information to the packets so
that the destination computer on the network can
determine that the data belongs to it.
• Prepare the data for transmission through the
NIC and out onto the network cable.
The Receiving Computer
• Protocols at the receiving computer carry out the same series of
steps in reverse order. They:
• Take the data packets off the cable.
• Bring the data packets into the computer through the NIC.
• Strip the data packets of all the transmitting information that was
added by the sending computer.
• Copy the data from the packets to a buffer for reassembly.
• Pass the reassembled data to the application in a usable form.
• Both sending and receiving computers need to perform each step in
the same way so that the data will have the same structure when it
is received as it did when it was sent.
Protocol stacks
• The OSI model defines distinct layers related to packaging, sending, and
receiving data transmissions in a network. A layered set of related protocols
actually carries out these services. This layered set of protocols running on
a network is called a protocol stack. Together, the protocols in the stack
handle all tasks required in packaging, sending, and receiving
transmissions.
• Several protocol stacks are designated as standard protocol models. Some
of the common protocol stacks are TCP/IP, IPX/SPX, and AppleTalk.
Protocols exist at each layer of these stacks, performing the tasks specified
by that layer. Generally, however, the responsibility for performing specific
communication tasks in the network is assigned to protocols working as one
of three types: application protocols, transport protocols, and network
protocols.
• Application Protocols
• Transport Protocols
• Network Protocols
• Application protocols provide data exchange between
applications in a network. Examples of common
application protocols include File Transfer Protocol (FTP)
and Simple Mail Transfer Protocol (SMTP).
• Transport protocols provide for communication
sessions between computers and ensure that data
moves reliably between computers. A common transport
protocol is Transmission Control Protocol (TCP).
• Network protocols provide what are called link
services. These protocols define the rules for
communicating in a particular network environment. A
common protocol that provides network services is
Internet Protocol (IP).
Types of Protocols
• Two types of protocols are available today: open and
vendor-specific.
Open Protocols
• Open protocols are protocols that are written to publicly
known industry standards. A protocol that adheres to
these industry standards is compatible with other
protocols written to the same standards. Open protocols
are nonproprietary (not privately owned). A common
example of an open protocol is Transmission Control
Protocol/Internet Protocol (TCP/IP), which is used as the
standard for communication over the Internet.
Vendor-Specific Protocols
• Vendor-specific protocols are proprietary
and have been developed by different
vendors for use in specific environments.
For example, Novell provides a set of
protocols, such as Internetwork Packet
Exchange/Sequenced Packet Exchange
(IPX/SPX), developed specifically for its
NetWare architecture.
Common Protocols
• Different protocols are needed for
communication with systems, devices, and
computers in various environments. Some
protocols are routable, and others are not.
Based on which protocols are used by a client
computer, you can determine whether or not that
computer can communicate with other
computers in network.
The common network protocols are:
• Transmission Control Protocol/Internet
Protocol (TCP/IP)
• Internetwork Packet Exchange/Sequenced
Packet Exchange (IPX/SPX)
• NetBIOS Enhanced User Interface
(NetBEUI)
• AppleTalk
Transmission Control Protocol/Internet Protocol (TCP/IP)
• TCP/IP is an industry-standard protocol stack (a layered set of
protocols) that enables communication in different networking
environments. Because of the interoperability of TCP/IP among
different types of computers, most networks support TCP/IP.
• TCP/IP supports routing and enables computers to communicate
across network segments. Because of this feature, TCP/IP is the
standard protocol for communications over the Internet. Its reliable
delivery and global use have made TCP/IP a necessity for
accessing worldwide information networks, such as the Internet.
However, you must configure TCP/IP on all computers with which
you want to use the protocol to communicate.
Internetwork Packet Exchange/Sequenced Packet Exchange
(IPX/SPX)
• Internetwork Packet Exchange/Sequenced Packet Exchange
(IPX/SPX) is a protocol stack developed specifically for NetWare
architecture. The IPX/SPX stack includes IPX and SPX. IPX defines
the addressing schemes used on a NetWare network, and SPX
provides security and reliability to the IPX protocol. IPX is a networklayer protocol that is equivalent to the IP of the TCP/IP protocol
stack. SPX provides reliable service at the transport layer.
• IPX/SPX has the following characteristics:
• It is used on networks with NetWare servers.
• It is routable. IPX/SPX enables computers in a routed networking
environment to exchange information across segments.
NetBIOS Enhanced User Interface (NetBEUI)
• NetBIOS Enhanced User Interface (NetBEUI) was one of
the earliest protocols available for use on networks
composed of personal computers. It was designed
around the Network Basic Input/Output System
(NetBIOS) interface to be a small, efficient protocol for
use in department-sized LANs of 20 to 200 computers,
which would not need to be routed to other subnets.
• At present, NetBEUI is used almost exclusively on small,
non-routed networks consisting of computers running a
variety of operating systems.
The advantages of NetBEUI include:
• Small stack size
• No configuration requirement
• High speed of data transfer on the network
• The major disadvantage of NetBEUI is that
it does not support routing. Because of
this, computers running NetBEUI can
communicate only with other computers in
the same network segment.
AppleTalk
• AppleTalk is Apple Computer's proprietary protocol stack designed
to enable Apple Macintosh computers to share files and printers in a
network environment.
• Some of the characteristics of the AppleTalk protocol are:
• It enables Macintosh clients to access a server running Windows or
UNIX system.
• It is routable. Computers running AppleTalk can communicate
across segments in a routed network environment.
• It enables Macintosh clients to access print services provided by a
server running Windows or UNIX system if Print Server for
Macintosh is installed on the server.
5.8 INTERNET AND E-MAIL
• If you're new to the Internet Technologies or a
little unsure about how to use e-mail, this
training can help you get started. The New
Technologies the lecture explains many Internet
and e-mail concepts and provides step-by-step
instructions on using these new technologies.
• Language of the Internet
• The Net, The Information Superhighway: The
Internet
• The Web, WWW, W3, W3: The World Wide Web
• Web Page: A single Web document. Everything you can
see in your browser window at one time (including what
you can see by scrolling) makes up one Web page.
• Browser, Web Browser: The piece of software that runs
on your computer and allows you to view Web pages.
The most common browsers are Netscape and Internet
Explorer.
• Web Site: A set of Web pages that are logically
connected. They usually have a consistent look and feel,
and are all related to the same theme.
• Home Page: The starting, introductory or welcome page
for a Web site. A person's own home page is a Web
page that describes all about them.
•
•
•
•
•
•
Link, Hot Link, Hyper Link: A part of a Web page that can be clicked to get
somewhere else. Links usually turn up a different colour and/or underlined
in your Web browser.
Broken Link: A link that references a page that no longer exists. If you click
on a broken link you will get some kind of "Page not found - Error 404"
message.
Hypertext: Text that can contain links.
HTML: Stands for Hypertexts Markup Language. This is the language that
all Web pages are written in.
URL: Stands for Uniform Resource Locator. This is the address of a Web
page - for example http://www.Geocities.com/Ggiday is the URL of this
Web page.
Web server, Web Server: A Web server is a computer which holds a
number of Web pages, and 'serves' them out to computers that request
them. There is nothing very special about the actual computer - it's just an
ordinary computer (though usually a fairly powerful one) running special
software.
•
•
•
•
•
•
•
Surf: "Surfing the Web" means casually using the Web - not really having any
direction, just clicking the links that look interesting to find yourself in weird and
interesting places.
Cyber: Virtual - not real but existing only in the context of the Internet.
Cyberspace: A conceptual place that doesn't actually physically exist - but you can
roam around in it, visit places, meet other people there, chat to them, go shopping ...
Cyberspace is a real world metaphor for the Internet.
Newbie: A person who is new to the Internet, or new to a particular aspect of the
Internet such as a service (IRC, Usenet) or a particular group (a specific mailing list
or newsgroup).
Post: When you send a message to a discussion forum, you're posting. This word
can be used as a verb ("I posted a message") or a noun ("that was a nice post").
FAQ: Stands for Frequently Asked Questions. They originate from online discussion
forums where more experienced users got sick of answering the same "newbie"
questions over and over again. So they started writing lists of frequently asked
questions and their answers so newbies could refer to those. The concept has grown,
and now a FAQ is more general - designed as an introduction to a certain topic.
http://www.faqs.org/faqs/faqs/about-faqs
•
•
•
•
•
•
Snail Mail: Traditional mail using paper, pen, envelope and stamp.
Remote: Not on your own computer or on a computer directly connected
with yours, but far away out in the Internet somewhere.
Local: On your own computer, or on a computer connected closely with
yours (a local network).
Download: Download a file means transferring that file from a remote
computer to your own computer. Technically, you are downloading a Web
page (and all the elements, such as pictures contained on it) every time you
view it, but the word is usually persevered to describe saving a file
permanently on your own computer.
Shareware: Software that you can use for free on a trial basis. It can often
be downloaded from the Web.
ISP: Stands for Internet Service Provider. They are companies who provide
you with Internet access (for example Ehio-Net or ETC). Usually you use
your telephone connected to a modem to dial up and connect your
computer to your ISP.
• Interactive: Refers to any program which lets the user make
decisions that affect the way the program operates in some way. It
could be as simple as clicking a hypertext link, or more complicated
like answering a quiz question and getting feedback.
• Bandwidth: It has a technical definition, but it is mostly used to
describe how much data you can fit through a single connection at a
time, and is related to how fast your Internet connection is.
• E-Anything: You can prefix the letter E to any activity to make it
mean doing that activity over the Internet. "E-learning" and "Ecommerce","E-government" are common examples of this. This
practice has evolved from the word "Email" (in which the E stands
for Electronic). "E" seems to have taken over from "Cyber" as the
prefix-du-jour.
5.8. 1 History of the Internet
• The Internet had its origins in the cold war
between Russia and America during the
1960's. Concerned about the survivability
of its communications in the event of a
nuclear strike, the US air force needed to
ensure that it could still communicate with
its forces.
• The RAND corporation proposed a system
with no centralized authority, as any
centralized system would be a target of
any possible attack.
• The proposed system, developed by Paul
Baran, suggested a decentralized system
that would still operate even if parts of it
were destroyed.
• All interconnections in the network could
send and receive messages, forwarding
them onto other interconnection points
(called nodes) until the message reached
its destination.
• Information would be sent in little packets
(groups), each packet would be selfcontained and have its own address
information. Packets would travel from
node to node, each node deciding how to
send the packet to the next available
node. Even if some nodes were destroyed,
an alternative route could still send the
message.
• In this way, the network would withstand a nuclear strike.
After implementing the network, it was known as
ARPANET and used by the US military and US
universities. Gradually, as more and more connections
were made, it has evolved to the Internet.
• It was created nearly thirty years ago as a project for the
U.S. Department of Defense (DOD). Its goal was to
create a method for widely separated computers to
transfer data efficiently even in the event of a nuclear
attack. From a handful of computers and users, today
the Internet has grown to thousands of regional networks
that can connect millions of users. Any single individual,
company, or country does not own this global network.
The History of the Internet in Ethiopia
• The Internet connection become Functional Starting From January
1,1997(1989). The EthioNet is connected to the Global Internet at
Washington DC through a SPRINT link connection with 256 Kbps
bandwidth. The Gateway and the domestic routers at the various
locations are connected to the 7500-gateway router in turn.
• The EthioNet Presently provided the following Internet Services to
its customers.
• Email
• World Wide Web (WWW)
• File Transfer Protocol (FTP)
• Telnet to any Internet Host
• USE NET and So on.
• By setting Up Eight Servers through out the
Country and it's planning to provide Various
Domain names and related Services to its
Customers in the near future.
• At the moment the EthioNet Possess more than
15 thousand Customers and there is a plan to
double the number of customers and the Server
Capacity in the Future.
5.8.2 What is the Internet?
• The Internet is a computer network made up of
thousands of networks worldwide. No one knows exactly
how many computers are connected to the Internet. It is
certain, however, that these number in the millions and
are increasing at a rapid rate.
• No one is in charge of the Internet. There are
organizations, which develop technical aspects of this
network and set standards for creating applications on it,
but no governing body is in control. The Internet
backbone, through which Internet traffic flows, is owned
by private companies.
• All computers on the Internet communicate with one another using
the Transmission Control Protocol/Internet Protocol suite,
abbreviated to TCP/IP. Computers on the Internet use client/server
architecture. This means that the remote server machine provides
files and services to the user's local client machine. Software can be
installed on a client computer to take advantage of the latest access
technology.
• An Internet user has access to a wide variety of services: electronic
mail, file transfer, vast information resources, interest group
membership, interactive collaboration, multimedia displays, real-time
broadcasting, shopping opportunities, breaking news, and much
more.
• The Internet consists primarily of a variety of access protocols. Many
of these protocols feature programs that allow users to search for
and retrieve material made available by the protocol.
• In simple terms, the Internet is many computers linked
together. When we use the Internet we pass data from
computer to computer across a vast network of wires,
fiber optic cables (cables which contain thin glass wires
that transmit data using light pulses) and satellite links
•
The Internet's best-known feature, the World Wide Web,
links together millions of documents called Web Pages.
You view Web pages using a Web browser (a software
program that allows you to find, view and send
information over the Internet), such as Netscape or
Microsoft Internet Explorer and so on.
Advantages of Internet:
•
Send and receive messages all over the world: You can send and
receive electronic mail to or from anyone who also has access to the
Internet, anywhere in the world in just seconds.
•
Participate in discussion groups: Thousands of special interest
communities, or newsgroups, provide access to Internet-based discussions
on topics from astrology to zoology.
•
•
Find and access information: You can access information from Ethiopian
Historical tips to New Zealand weather forecasts and the latest women's
health research from South Africa. Millions of documents are available from
libraries, museums, governments, educational institutions, the media,
private corporations and individuals, not to mention your favorite music
group.
Retrieve files: On the Internet, you can access files that contain software
programs, graphic images, music and other types of information, often for
free.
•
•
•
•
•
Do your banking and shopping: Today many banks have web sites that
enable you to check your accounts, pay bills and even make investments
using the Internet. There are also an ever-increasing number of products
and services available for purchase right over the web.
Accessing the Internet
There are several ways to access the Internet. The two most common
methods are through a modem connection or a network connection.
Modem Connection
A modem is a device that adapts a computer to a telephone line. It converts
the computer's digital pulses into audio frequencies for the telephone
system and converts the audio frequencies back into pulses at the receiving
side (the computer). Most home computers use a modem and a phone line
to dial into an Internet Service Provider's (ISP in our case Tele) computer,
which provides access to the Internet. Internet Service Providers will
typically charge a monthly fee for a certain number of hours of access to the
Internet, or, in some cases, for an unlimited number of hours. The speed of
the Internet connection depends on the speed of your computer's modem.
5.8.3 Dial-up connection
procedure
• To establish a conventional dial-up connection to the Internet, you
will need the following:
• An account with an Internet Access Provider (in Ethiopia, at present,
Ethiopian Telecommunication Corporation (ETC) is the only Internet
Access Provider). The account can be either TCP/IP or Shell.
• A telephone connection.
• A computer with serial port (for External modems) or an expansion
slot (for Internal modems)
• A modem (External/Internal)
• A communication (or terminal emulation) software. SLIP/PPP
(TCP/IP) account holders will require browser software (Internet
Mail, Netscape Messenger, Eudora, etc.) For shell account holders,
the browser software (Lynx) and the e-mail software (Pine) are
available on the Shell account menu.
What is a Modem?
• It is a device used to convert digital (computer) data to analog
(telephone) data and vice versa
• This is modulation and demodulation respectively.
• A modem is required to send digital data over an analogue
connection such as a dial up telephone line. Modems change the
digital data to analogue tones that fit within the frequency range of
the voice channel. A modem can also convert these analogue tones
back to the original digital data.
• Nowadays, it is common for the home user to access the Internet via
a dial up telephone connection using a modem. Typically, these
modems run at 28.8Kbps or 33.3Kbps, although 56.6Kbps modems
are now becoming available.
• Web Browser a browser is a software program
that acts as an interface between the user and
the World Wide Web. The browser sends
requests for information that is available on the
Internet and displays the information for the
user. There are many different types of
browsers. A text-based browser shows a user
text only (Lynx). A graphical browser allows the
user to see more of what the WWW has to offer,
such as graphics, photographs and multimedia.
•
•
•
•
•
•
•
•
•
•
Domain Name A domain name is a way to identify and locate computers
connected to the Internet. A domain name must be unique; no two
organizations on the Internet can have the same domain name.
A domain name always contains two or more components separated by
periods called “dots” .The major categories for the top-level domain names
are:
.com for commercial enterprises
.edu for educational institutions
.net organizations directly involved in Internet operation or for
network
.org miscellaneous organizations that don’t fit any other category,
such as non profit organizations.
.gov for government entities
.mil for military service
.int for organizations established by international treaty
.country codes a two letter abbreviation for particular country
such as “et “ for Ethiopia “ fr” for France” it” for Italy and so on
Dial up Internet Configuration
• You will get a New connection wizard and following the
instruction in the wizard when you click next you will get
options to select and choose the second option which
says connect to the network at my workplace, then click
Next and select dialup connection next it asks for name
of your company and Next step is to put the telephone
number you will use for the dialup connection. Last step
of the wizard is to select option that asks to use the
connection for anyone or for this computer only you can
choose either of the two. After you finish the wizard you
will get the following window.
• In this window in the Dial text box you will
give the number 900. And then click on
Dialing rules to provide the rules of dialing
like Areal Code of your area for example
01 is for Addis Ababa.
• When you get this window click on Edit
after giving the area code and you will get
the following window
• In this window you will provide the country
name and dialing type i.e. pulse.
Step-4
• You will get this window in your network
connection and you can right click on the
name of the connection you created and to
connect or dial you double-click on the
icon and get this window
• After this you can click on the Dial button
and get connected to the internet.
Network Connection
• A network connection means that the computer
is part of a network of computers, printers and
other devices. This network has a direct, highspeed connection to the Internet. Universities,
governments and larger companies usually have
this kind of Internet connection, which provides
fast and reliable access to the Internet, but is
expensive, to set up and maintain.
Web browser
• Web browser is a computer program that allows you to
connect to and browse the Internet.
• To connect to the Internet, you may have to complete a
log on sequence. Logging on means that you have to
enter a user name and a password (a series of letters
and/or numbers that the Internet Service Provider sets
up for you).
• From the Windows Start menu, choose your browser (for
example, Internet Explorer or Netscape Communicator).
• If necessary, enter your user ID and password in your
Internet Service Provider's dialog box.
• Your browser will open with the home page displayed.
5.8.4 What is a website?
•
•
A Web site is a collection of digital documents called Web pages that can be
viewed using a piece of software called a Web browser. Typically the first
page of a Web site is called the home page, from which other pages branch
off. The first page you see when you start your browser is also called your
home page.
When you are viewing a Web page, the page's address appears in the
Address bar in the browser.
Each Web page has a unique address, sometimes known as a URL
(Uniform Resource Locator). You can type the address into the browser's
Address bar to go directly to the page. An address (URL) typically starts
with a protocol name, followed by the location on the Internet where the
Web site can be found, followed by the name of the organization that
maintains the Web site, and ending with a suffix that identifies the kind of
organization it is.
•
•
•
•
•
For example, the address http://www.EICTDA.gov.et/ provides the following
information:
http://
The Protocol http stands for Hypertext Transfer Protocol.
A protocol is a set of rules and standards that enable computers to
exchange information.
www The Server A Server is a computer that provides World Wide Web
services on the Internet. The “www” in the Internet address shows that this
Web site is located on the World Wide Web (www).
EICTDA
The Domain The Domain is usually the name of the
company or organization. This indicates that the Ethiopian ICT Development
Agency (EICTDA)) maintains the Web site.
. Gov.et
The Suffix The letters at the end of the address are used to
indicate what kind of site it is. For example, the .et in this address indicates
that it is a Ethiopian Web site. Generally, governmetal organization, for
commercial site addresses end with .com, and the addresses for many
educational institutions end with .edu.
• If the address links to a specific page within a Web site, additional
information will be included after the suffix. For example, the
address for the press release page on the EICTDA Web site looks
like this:
http://www.EICTDA.gov.et/press_Release.
• As you scroll down a Web page you will often see underlined or
colored words and phrases. These are called text links (or
hyperlinks). Links are text items or images on a Web page that have
addresses coded into them that can bring you to other Web sites
and pages. Clicking the link takes you to the new page. Surfing the
Web is browsing, or exploring, from link to link.
• You can tell whether an item is a link by
moving the mouse cursor over the item. If
the pointer changes to a hand, the item is
a link. After you click a text link to go to
another page, the colour of the link
changes. This allows you to tell the
difference between links you have and
have not viewed. Typically, text links that
you have not viewed yet are blue and
viewed links are purple.
5.8.5 What is a browser?
• Browsers are computer programs that allow us to look at the
Internet. There are many different Browsers. They all do similar
things, such as allow you to follow links, go back to sites you have
visited before, type in URLs and add bookmarks.
• The main differences between the browsers are how the above
things are done and what the Internet looks like on your screen.
• Browsers can be roughly divided into two types:
– Text Browsers and
– Graphical Browsers.
• I'll explain the main differences between the two types of Browsers
below. The best way by far, to see how they are different is to look at
the same Internet site in both a Text and a Graphical Browser and
compare them. This has been set up and you will have the chance
to do this at the end of the course.
Text Browsers
• 'Text browsers' allow only the text (writing) on the pages of the
Internet to be seen, not the graphics (graphs, charts, pictures,
diagrams, maps etc). The site you are viewing is the same one;
the only difference is that graphics can't be seen with a text
browser.
• Text browsers can be run on any computer.
• An example of a text browser is Lynx.
Graphical Browsers
• 'Graphical Browsers' are Internet browsers that allow you to see
everything on the pages of the Internet, which includes text (writing)
and graphics (graphs, charts, pictures, diagrams, maps etc).
• There are many graphical browsers, including Mosaic, the Explorer
and Netscape. They usually can only be used if the computer has
the program 'Windows' on it.
Internet Explorer (IE) seems to be the most
popular graphical browser.
• Remember, the site on the Internet is exactly the
same one, regardless of which browser it is
viewed through. The difference is how it looks on
your screen.
• Notice what the page looks like, then go to the
demonstration computer and see what the site
looks like with a text browser.
• Sometimes you will see a page, which says
something like:
• (A) THIS SITE IS BEST VIEWED THROUGH A GRAPHICAL
BROWSER
• This means the site was made with Graphical browsers in mind.
This is common for sites, which have a lot of graphics, which often
do not look very nice with text browsers.
• Other times you may see something like:
• (B) FOR TEXT BROWSERS, CLICK HERE or
• FOR GRAPHICAL BROWSERS, CLICK HERE
• This means the person who made the site has made two different
sites- one for text browsers and another one for graphical browsers.
This is sometimes done when the people likely to visit this site will
be using both types of browsers and the site designer realizes that a
site with lots of graphics will not look good to text browsers.
• Also, a text browser can be useful if you are
accessing the Internet over a slow or noisy
line. You can get the essential information
without having to wait ages for graphics to
arrive.
• However, the tendency in Web page design is
to use more and more graphics and some pages
have essential information contained in the
graphics that you can't see with a text browser.
5.8.6 The Internet Corporation for Assigned
Names and Numbers (ICANN)
• ICANN exists to provide top-level coordination and
management of key naming, addressing, and protocol
systems for the Internet. These systems -- the Domain
Name System, for example -- require some degree of
centralized technical administration in order to function
properly. At the same time, authority over these critical
systems necessitates not just technical competence, but
also credibility in the global policy arena.
• Internet Corporation for Assigned Names and Numbers
• Non-profit, private sector Corporation
• Formed in October 1998
• Coalition of technical, academic, business, user
communities
• IANA
• The authority originally responsible for the oversight of IP
address allocation, assignment of protocol parameters and
DNS management.
• Now under ICANN, IANA continues to play a limited role –
primarily handling delegations and redelegations to managers.
• ICANN’s Purpose
• Take over functions previously handled by the US govt
• Coordination of the DNS
• To set policy
• In a transparent way
• Collaborative
• Consensus
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Globally representative
Four core functions
Domain Name System (DNS)
Allocation of IP addresses
Management of the root server system
Coordinating protocol number assignment
Previously run by the US government using contractors and
volunteers
At Large membership
Designed for Internet users worldwide, to have a voice in ICANN’s
policymaking structure for DNS & numbering systems;
Membership
open to any individual wishing to join
Online application
Active email address
Physical residence verified by postal mail address
• Using Help
• Both Netscape Communicator and
Microsoft Internet Explorer have a built-in
Help feature that you can use to learn
more about the browser's features and to
view step-by-step instructions for the
functions that can be performed with the
software.
•
•
•
•
To use the browser's Help feature:
Click the Help command on the menu bar.
The Help menu opens. Click Contents and Index.
The Help window opens with the Contents tab on top.
Click a section title or icon (book) to view the topics for
that section.
• Click a topic to view that information in the right pane of
the Help window.
• You can also click the Index tab to search for topics
using an index of Help subjects, or click the Search tab
to use full-text search and look for specific words or
phrases.
• In addition, you can use the other commands on the
browser's Help menu to connect directly to the web sites
operated by the browser's manufacturer. These sites
typically provide access to technical resources, new
product upgrades and additional information.
• Using a browser to navigate
• Moving between different web pages is called
"navigating." There are several ways to go to a different
Web page from the page you are currently viewing.
• Navigating Using Web Addresses (URLs)
• Each Web page has a unique address or Uniform
Resource Locator (URL) that provides your computer
with the information it requires to locate the page on the
World Wide Web. When you open a Web page its
address appears in the Address bar at the top of the
browser.
• To navigate to a web site using its address (URL):
• Click your cursor in the Address field and then type the
URL (address) of the Web page you want to view.
• Press the ENTER key on your keyboard.
•
•
•
•
Navigating Using Links and the Toolbar
Links provide a simple and fast way to navigate or "surf" the Web
To navigate using links:
Click any link on the current page. A link can be a picture, a 3-D
image, or colored text (usually underlined). You can tell whether an
item is a link by moving the mouse cursor over the item. If the
pointer changes to a hand, the item is a link.
• The browser retrieves and displays the Web page for that link.
• To navigate using the Forward and Back buttons:
• The buttons on the browser's Toolbar help you navigate the Web.
• Back Button
• If you want to go back to the last page you viewed, click the Back
button on the toolbar. To go more than one page back, you can click
the small down arrow next to the button and then click a Web page
on the list.
Forward Button.
• Once you have gone backward using the Back button, the Forward
button becomes available. Click the Forward button to go to the next
page in a series of pages you have already visited. To go more than
one page forward, you can click the small down arrow next to the
button and then click a Web page on the list.
• 5.8.7 Searching the Web
• Finding Things on the Web
•
•
•
•
•
•
•
•
•
•
The Web is a very big and much disorganized place. Just about any
information you would ever want to know (and a whole lot more that you
wouldn't) exists on the Web somewhere. But finding it is another story.
The reason for this is that it was never designed as a global information
retrieval system, hence there is no central place monitoring where or how
information is stored. The added complication of hypertext makes it very
easy to lose your focus and get lost.
Ways to find information on the Internet
There are a number of basic ways to access information on the Internet:
Join an e-mail discussion group or Usenet newsgroup
Go directly to a site if you have the address
Browse
Explore a subject directory
Conduct a search using a Web search engine
Explore the information stored in live databases on the Web, known as the
"deep Web"
Search Tools
• Trailblazer Pages (Links Pages)
• These are lists of links to other sites related to a
particular subject. The most useful trailblazer pages
have links divided into categories and descriptions of
why each site is useful.
• Enthusiastic amateurs often construct trailblazer pages.
Some librarians are creating trailblazer pages to help
people find information,
• Trailblazer pages can be very useful in your Web
searching. You will often find links to pages that don't
show up in search engines or directories. However, it
can be frustrating to jump from one trailblazer page to
another without finding any pages with actual content!
Subject Trees (Directories)
• A subject tree is a broad list of categories that
branch off into sub-categories, such as that
found in Yahoo. These are not organized by
librarians so the subject classification doesn't
conform to any established system. They aren't
in any way complete - pages are usually only
added to the directory when the writer of the
page requests is.
Search Engines
• These are computer programs that 'whiz around'
the Internet to find documents that contain key
words which you type in. Search engines have
different ways of searching which means that
they will return different results and may be more
or less successful for different searches.
• There are wonderful search engines like Alta
Vista, Infoseek, Webcrawler, Excite, Hotbot,
Google, Dogpile and Lycos. (All follows
www.name of the engine.com)
Limitations of Search Engines
• The ambiguities of language mean that the list of
retrieved documents may contain a high percentage of
irrelevant material.
• Some search only document titles and others search the
entire document.
• Being electronic, they can't discriminate between
valuable documents and ones of dubious quality.
• With millions of people using the Internet they
sometimes become overloaded.
• Search Strategies
• Directories or Trailblazer pages are usually more
successful when you are searching for a site
with some general information about a topic, for
instance:
• Fairy tales
• Pets
• Insects
• Weather
• Poetry
• Public speaking
• Science fiction
• Search engines are more useful when looking for very
specific or obscure information, for instance:
• The history of the settlement of the Gambella.
• The myth of Internet.
• Pictures of baby chicks.
• The Musicians of Bremen' fairy tale.
• Sometimes you will find the information you want almost
immediately - other times you will be led on a wild goose
chase through page after page of links. Don't give up too
easily though, persistence usually pays off.
• Search Tips
• Understand the search engine you are using. Read the 'search tips'
or 'help' for the search engine - for instance Alta Vista's Help.
• Use a variety of key words, use synonyms.
• Search engines often match the first word first so put the most
important word or the broadest category at the beginning.
• Use quotation marks to search for a phrase. Searching for rock and
roll will return documents with any of the words rock, and or roll.
Searching for "rock and roll" will only return documents with the
whole phrase (read the search engine 'help' to see if it supports
phrases).
• Try different arrangements of key words eg. if you are looking for
indigenous women poets try "women writers" AND indigenous. This
is a combination of a phrase and a single word. Remember though,
that in North America they use native rather than indigenous - think
of how your key words will be written on the document.
• Some search engines are case sensitive. Most search engines will
match both upper and lower case if lower case letter are entered,
but only upper case if upper case letters are entered. For instance
"behafta berhe" will match both "behafta berhe" and "Behafta
Berhe", but "Behfta Berhe" will only match "Behafta Berhe".
• Most search engines will match part or whole of a word - eg. sing
will retrieve singer, single, singe etc.
• Think of common misspellings - take into account American
spellings eg. theater, center.
• Most search engines will search for documents with any of the
words you enter - eg. a search for christmas carols will find
documents with just the word christmas, as well as documents with
just the word carols. Documents with both of the words will appear
earlier on in the results. You can use operators to restrict your
search futher (check the 'help' to find out which operators the search
engine uses).
• Results are returned in order of relevance. If there is nothing useful
in the first few pages, chances are there won't be anything useful in
any of the others. Change your search query or use another search
tool.
• Web Searching Activity
• Practice your search strategies and share your insight with others by
completing this activity.
• Pick one of these to do your search on:
• A general site about conservation for your students to use as a
reference in a piece of their writing.
• A page with information about Website that you can adapt into a
worksheet for your students.
• A site containing facts on endangered species from around Ethiopia
and the world.
• Information on why the Endod tree is dying out.
• A site about Ethiopia or New Zealand flora and fauna.
5.8.8 Why people use the Internet?
• To find general information about a subject
• The Web is like a huge encyclopaedia of information - in some ways
it's even better. The volume of information you'll find on the Web is
amazing. For every topic that you've ever wondered about, there's
bound to be someone who's written a Web page about it. The Web
offers many different perspectives on a single topic.
• In fact you can even find online encyclopaedias. Many of these are
now offering a subscription service, which lets you search through
the complete text of the encyclopaedia. There are also many free
encyclopaedias that may give you a cut-down version of what you
would find in a complete encyclopaedia.
–
–
–
http://www.britannica.com
http://encarta.msn.com
http://www.encyclopedia.com
To access information not easily available
elsewhere
• one of the great things about the Web is that it
puts information into your hands that you might
otherwise have to pay for or find out by less
convenient means.
• http://www.timeanddate.com/worldclock- current
local times for cities all over the world - even
knows about daylight savings.
http://www.xe.net/currency/table.htm - get a
table with exchange rates to and from any other
currency.
To correspond with faraway friends
• Email offers a cheap and easy alternative to traditional
methods of correspondence. It's faster and easier than
writing snail mail and cheaper than using the telephone.
Of course, there are disadvantages too. It's not as
personal as a handwritten letter - and not as reliable
either. If you spell the name of the street wrong in a
conventional address, it's not too difficult for the post
office to work out what you mean. However if you spell
anything wrong in an email address, your mail won't be
delivered (you might get it sent back to you or you might
never realise).
To meet people
• The Web is generally a very friendly place. People love
getting email from strangers, and friendships are quick to
form from casual correspondence. The "impersonal"
aspect of email tends to encourage people to reveal
surprisingly personal things about themselves. When
you know you will never have to meet someone face-toface, you may find it easier to tell them your darkest
secrets. Cyber-friendships have often developed into
real life ones too. Many people have even found love on
the Net, and have gone on to marry their cyber-partner.
To discuss their interests with likeminded people
• Did you think you were alone in your
obsession with a singer, TV programme,
author, and hobby? Well, chances are
there's group of people like you discussing
every little detail of your obsession on the
Internet right now.
To have fun
• There’s no doubt that the Internet is a fun
place to be. There's plenty to keep you
occupied on a rainy day.
•
Here are just a few of the many
frivolous things to do on the Web:
• http://postcards.wired2000.net/
• http://www.ethio.com
To learn
• On-line distance education courses Universities
can give you an opportunity to gain a
qualification over the Internet.
To read the news
•
www.dekialula.com
•
www.ethiopiancommentator.com
•
Www.ethiozena.net
•
www.cnn.com
To find software
• The Internet contains a wealth of useful
downloadable shareware. Some pieces of
shareware are limited versions of the full piece
of software, other are time limited trials (you
should pay once the time limit is up). Other
shareware is free for educational institutes, or for
non-commercial purposes.
•
www.shareware.com
To buy things
• The security of on-line shopping is still questionable, but
as long as you are dealing with a reputable company or
Web Site the risks are minimal.
•
www.amazon.com
• Amazon Books is a huge American book store (they
exist only on the Web and are very reputable). Their
prices are very good - it's can be much cheaper to buy
books from here than from ET book stores, especially if
you buy several at once to keep the shipping cost down.
Why do people put things on the Web?
• To advertise a product
• Most company Web sites start up as a big advertisement for their
products and services. It may be hard to see why anyone would
willingly visit a 10 page ad - but these advertisements are very
useful to anyone genuinely interested in finding out about their
products. Companies may also give away some information for free
as an incentive for people to visit their pages. www.adobe.com - a
good way to find out the facts about the excellent software that
Adobe offers.
• To sell a product
• Internet shopping (e-commerce) is still in its infancy - it takes a very
good marketing strategy to actually make money out of selling items
over the Web, but that doesn't stop lots of people from trying.
• Amazon Books - one of the most successful (perhaps the most
successful) e-businesses.
To make money
• A popular way to make money out of the Web is from advertising
revenue. Popular sites have banners at the top of the page enticing
people to click them and be taken to the advertiser's Web site.
These banners are generally animated and very appealing, with
mysterious messages to make users wonder where they will be
taken. For each person that clicks the ad, the host site gets
commission. Making money this way is only successful if the sit gets
lots of visitors (thousands a day); so the sites must be very useful
and offer something of real value to their visitors.
• The Alta Vista Search Engine is an example of a site that makes
money from banner advertisements.
• www.imdb.com-offers a very useful and fun service - it's financed by
advertising and sponsorship.
To share their knowledge with the world
• Many individuals write Web pages to share
information about their interests or hobbies.
They don't expect to make any money out of it they just feel that the Web has given them so
much information that the least they can do is
put something into it that may be useful for
others. Other rewards come from the prestige of
having their site recognized as something good
and the contact inspired by their pages with
others sharing the same interest.
Evaluating Web Resources
• People often assume that any information they
find on a computer is correct. This is a
dangerous assumption regarding the WWW,
where anyone can publish any information they
like, without editorial intervention. Some
information may be perfectly reliable, but other
information may range from out-of-date,
unreliable and inaccurate to biased, misleading
or deliberately false.
Pointers for conducting research on the Web:
• Be clear on what you want. Keep your purpose clearly in focus.
• Be selective, critical, and use a useful set of evaluation criteria.
• Don't take anything you find as undisputed fact.
• Shop around - find a wide range of sites on your topic, don't stop at
the first useful looking page.
• Use your common sense when judging how much faith you should
put into the information you find.
• The World Wide Web is made up of millions of Web sites covering
almost every subject under the sun. If you want to find specific
information and you don't have a list of Web addresses or "URLs”,
then you need to conduct a Web search.
• You can search for information on the Web
in a variety of ways.
To search using the Search button:
• 1. On the Toolbar, click the Search button.
• 2. The Search window is displayed on the left side of the
window. Type the word or phrase you're looking for into
the text box at the top of the Search window, and then
click Search.
• 3. A list of search results is displayed in the Search
window. Click any link in the list to display that Web page
in the right side of the browser window.
• Note: You can close the Search window by clicking the
Search button on the Toolbar again or by clicking the
Close button at the top of the Search window.
To search using a Search Engine:
• A search engine is a service that indexes and
organizes Web sites. Search engines are set up
by organizations that continually scan the Web.
When new pages are found, they are classified
in databases so you can easily search for
information on any topic of interest. You can use
a search engine by typing in its Web address.
• Although each search engine appears
slightly different, each has a box in which
you can enter a search word or phrase
and a button for you to click to begin your
search. This is called a text box.
• The list below provides the addresses of some popular search
engines that you can try:
• Alta Vista: www.altavista.com
• Excite: www.excite.com
• Hotbot: www.hotbot.com
• Infoseek: www.infoseek.com
• Lycos: www.lycos.com
• Yahoo!: www.yahoo.com
• Yahooligans!: www.yahooligans.com
• Webcrawler: www.webcrawler.com etc
• No search engine keeps track of all the content on the Web, so try
several search engines to see which produce the most useful results
for the type of information you're looking for.
• Boolean Searching on the Internet
• Boolean searching is based on a system of symbolic
logic developed by George Boole, a 19th century English
mathematician. Most keyword searchable computer
databases support Boolean searches. Boolean search
techniques may be used to perform accurate searches
without producing many irrelevant documents. When
you perform a Boolean search, you search the computer
database for the keywords that best describe your topic.
The power of Boolean searching is based on
combinations of keywords with connecting terms called
operators. The three basic operators are the terms
AND, OR, and Not.
• The operator AND narrows a search by
combining terms and retrieves every document
that contains both of the words specified. e.g.
• To locate general information on computer Virus
problem computer virus AND data protection
• When the computer searches its database it
retrieves every record containing both of the
words computer virus and data protection, and
the records from the intersection will be retrieved
as the end result. Practice by searching
information on the relationship between poverty
and crime.
• Several keywords may be used to narrow
searches with the AND operator.
• The OR operator broadens or widens a
search to include documents containing
either keyword. The OR search is
particularly useful when there are several
common synonyms for a concept or
variant spellings of a word.
• Computer virus OR data protection
• The computer searches for all documents containing
computer virus and all documents containing body
building and the union of all documents represented by
both terms will be retrieved. OR searches often produce
large numbers of documents. E.g. car or automobile
• Combining search terms with the NOT operator narrows
a search by excluding unwanted terms. To find
information on gambling but not the lottery use:
• Examples:
• gambling NOT lottery
• cats not dogs
• and so on
• The term is sometimes stretched to include searches using other
operators like “near”. E.g. Fashion NEAR show may produce results
on London Fashion Show, New York, etc. but not designers,
producers, etc.
• Boolean search terms may be combined in various ways to carefully
refine searches.
• Examples:
• Oceans OR lakes AND pollution
• Nurses AND malpractice NOT doctors
• Children NOT infants AND psychology
• Note: By default, Goggle only returns pages that include all of
your search terms. There is no need to include Boolean
operators between terms. If a common word is essential to
getting the results you want, you can include it by putting a "+"
sign in front of it. (Be sure to include a space before the "+"
sign.)
Truncations
• Truncations are character substitutes that could be used to retrieve
variant spellings and allow the searcher to insert a truncation
symbol, usually the $ sign, an * or ?
• Examples:
• The search term teen* will locate the terms teens, teenagers, and
teenaged.
• By placing the $ sign at the end of the root word work like work$,
you will retrieve all words beginning with that root (work, worker,
workforce, workplace, etc.).
• Be careful using truncation! If you want to retrieve items about cats,
don’t truncate the word cat. If you do, you will also retrieve
cataclysm, catacomb, catalepsy, catalog, etc., etc. It’s best to use
the Boolean operator “or” in these instances (cat or cats)
• Some databases and search engines automatically
truncate your search terms to find plurals, -ing, or –ed
endings.
• Wild Cards
• Some databases allow for wild cards to be embedded
within a word to replace a single character. For instance,
you can also use $, *, or ? within a word to replace
characters, such as, comp$tion and find composition,
competition, computation, etc.
• You can also limit the number of characters that the wild
card symbol represents such as theat$2 and find theater
or theatre, but not theaters, theatrical, etc.
Saving, Copying and Downloading Information From
Internet
• Saving and Copying Information
• The Internet is not only to be surfed. We can copy and
save information, text or graphics, which we see on a
web page to a floppy diskette and/or make printouts.
• To copy graphics
• You can copy or save any graphic that you see on a web
page.
• Click on the graphic you want to copy.
• Right mouse clicks and choose Copy from the dropdown menu.
To save graphics
• Click on the graphic you want to save.
• Right mouse click and choose Save Picture As from the drop-down
menu
To copy text.
• Position the mouse pointer at the beginning of the text you want to
copy. The mouse pointer changes from an arrow to an “I” beam.
• Drag to select the text.
• Right mouse click and choose Copy from the drop-down menu:
• The text is copied into the clipboard and can be pasted into a blank
word document.
• Note: If there is a large quantity of text, then choose select All from
the drop-down menu.
To save text
• You can save any document that Internet Explorer can display.
• Choose Save As from the File menu. The Save As dialog box is
displayed. The file name is already placed in the dialog box. You
can change this if you want to:
• There are two ways of saving a file:
• As text enables you to paste the text into Word, Excel, PowerPoint
or Access. You are recommended to use this option.
• As HTML keeps all the HTML source code in the page. This option
is not recommended unless you write web pages.
• Click on the Save button
Saving favorite web pages
• As you navigate from Web site to Web site, it soon becomes
impossible to remember the path you took to get to a specific site or
its exact address or URL . Fortunately, you can use the Favorites
feature of your browser to save a list of your favorite Web sites so
that you can easily revisit them in the future. [Note: In Netscape this
feature is called Bookmarks.]
To add a Web page to your list of favorite pages:
• Go to the page you want to add to your list of favorite pages.
• Click the Favorites command on the menu bar at the top of the
browser.
• On the Favorites menu, click Add to Favorites.
• The Add Favorite dialog box opens. Type a new name for the page
in the Name field if you want to. Click OK to add the page.
To view a favorite Web site:
• On the Toolbar, click the Favorites button.
• The Favorites window appears on the left
side of the screen. Click a folder or page
to display the Web page.
• Note: You can hide the Favorites window
by clicking the Favorites button on the
Toolbar again.
Downloading files
• On the Internet, you can access files that contain software programs,
graphic images, music and other types of information, often for free. You
can download (or save) these files onto your computer using your browser.
When you click on an Internet file or program that can be downloaded, your
browser will give you two options: to open the file or to save it to a disk (for
example, onto your computer's hard drive or to a floppy disk).
You should note that some files can contain viruses. A virus is a software
program that is buried within an existing program or file. When you open
that program or file, the virus copies itself onto your computer. The virus
may be a simple prank that pops up a message on your computer screen
but does no serious damage. However, other viruses are quite destructive
and may destroy programs and data on your computer. Therefore, it is
recommended that you save any file or program you wish to download to
disk. This allows you to check the file with a virus detection program (such
as McAfee Virus Scan or Trend Anti-Virus)before you open it.
• For more information on virus protection, you
can link to one or two popular virus detection
program Wesites:
• McAfee Virus Scan
• http://www.mcafee.com/
Trend Anti-Virus
• http://www.trend.com/
The amount of time it will take to download a file
will depend on the size of the file and the speed
of your Internet connection.
To download a file or program:
• Click on the file or program you wish to download.
• The File Download dialog appears. Click the Save this file to disk
option and click OK.
• The Save As dialog appears. Choose a location on your computer
where you'd like to save the file and then click OK.
• A dialog appears showing you the status of the download. When the
file or program has finished downloading, you should check the file
with a virus scanner before opening or installing it.
• Note: If you're downloading a program file, note any installation
instructions provided. Once you have finished downloading the
program, install it according to the instructions on the original Web
page.
E- mail
• Electronic mail (e-mail) is one of the oldest and most
popular services on the Internet. With e-mail, you can
send messages and documents down the hall, across
town or around the world. You can also receive
information through your personal e-mail mailbox, or
"Inbox."
• To send and receive e-mail you need an e-mail account.
You can get this through an Internet Service Provider
(ISP in our case tele). In most cases, if you have
purchased Internet services from an ISP, your monthly
fee includes e-mail service.
•
•
•
•
You also need a piece of software that will create an Inbox on your
computer for messages that you receive. When you check your e-mail, new
messages are downloaded (through the Internet) from your ISP's computer
into your Inbox. You must be connected to the Internet (or to your
organization's network) to send a message or to check if you have new
mail. Most Web browsers include features that allow you to send and
receive messages, or they enable you to link to another program that
handles e-mail. To send e-mail, you have to know the recipient's e-mail
address. E-mail addresses consist of a user ID followed by a domain name
(usually the name of an organization), just like a Web address. In the
example below, the user ID is Abebe and the domain name is
@EICTDA.gov.et.
[email protected].
In many cases, a user ID will be the first initial of the user's name followed
by seven or more characters of their last name. However, many Internet
Service Providers allow their clients to choose their own user ID, so you will
often see e-mail addresses such as:
[email protected]
12.1 Sending e-mail
• Most Web browsers include features that allow you to send and
receive e-mail messages, or they enable you to link to another
program that handles e-mail.
For example, Microsoft's two main e-mail software packages,
Outlook and Exchange, can be used on their own or with the Web
browser Microsoft Internet Explorer. You must be connected to send
an e-mail message over theInternet.
While most e-mail software packages follow the same basic
structure, specific tools and menus vary. Internet Explorer will be
used as the examples in the e-mail demonstrations and practice
exercises in this training.
• Click on the ‘Compose new message’ button on the toolbar. You will
get an empty mail form, which will have the following parts.
• ‘To’ – Enter the e-mail address of the person(s) to whom
the message is sent.
• ‘Cc’ – The carbon Copy field is for the e-mail address of
the person(s) .any addresses included here will be listed
in all outgoing copies of the message.
• 'BCc': This blind carbon copy field unlike address listed
in the Cc field address listed in the BCc.
• Note: Commas must separate multiple addresses; The
Cc and BCc field may be left blank.
• ‘Subject’ – Enter a brief description as to what the
message is about.
• ‘Body’ – Enter the actual message here.
• Some mail programs have the facility to
send blind copies. If this feature is
available, the other recipients of the mail
will not know that you have sent a blind
copy to another person. Almost all e-mail
programs have the following features:
address book, signature feature, and
attachment facility. Now we will see how
to make use of these features.
To send an e-mail message from within Internet Explorer:
• Click the Mail button on the browser's Toolbar.
• Click New Message/write message/compose.
• The New Message window opens. In the To box, type the
recipient's e-mail address. (The recipient is the person to whom
you're sending the message.) If you wish to send the message to
more than one recipient separate each name with a semicolon. If
you wish, you can enter a name(s) into the Cc(Carbon copy) box to
send copies of the message to additional people. Bcc (Blind carbon
Copy)
• Click the Subject box and then type a short description of what the
message is about.
• Click the message area and then type your message.
• Click the Send icon to send the message to the recipient(s).
12.2 Receiving E-mail
• To receive e-mail you need an e-mail account. You can
get this through an Internet Service Provider or "ISP”. In
most cases, if you have purchased Internet services
from an ISP, your monthly fee includes e-mail service.
• To check if you have received any new e-mail messages,
you must open your mail program and enter your mail
account password. After you enter your password, the
program checks for new messages and then download
these from the ISP's computer to your computer. These
messages will appear in your mail program's Inbox.
• You can use the Mail button in your browser to open
your mail program and check for new mail.
To check for new messages from within
Internet Explorer:
• Click the Mail button on the browser's Toolbar.
• Click Read Mail.
• A mail password dialog appears. Enter your user
ID and password.
• The IEl program opens. New messages will
appear in bold text in the right pane of the
Exchange window. Double-click on a message
to open it.
12.3 Attaching a file to a message
• You can send more than simple text in
your e-mail messages. You can also
attach a variety of computer files –
including word-processor documents,
spreadsheets, graphics, and video clips –
to an e-mail message. E-mail is a useful
way to share files with other people. You
can attach a file located on your hard disk,
on a floppy disk, or on the network to an email message.
To attach a file into an e-mail message:
•
For yahoo
• Create the message into which you want to attach
• click attach file.
• Then click browse to open dialog box. Locate and click the file you
want to attach. The name of the file will appear in the File Name box
of the dialog.
• An Attach file into the e-mail message.
• Click OK/open.
•
For Email.com
• click browse to open dialog box. Locate and click the file you want
to attach. The name of the file will appear in the File Name box of
the dialog.
• Click OK/open
• Click attach
• Many e-mail software packages have an
Address Book feature. The Address Book
allows you to create a list of e-mail
addresses that you can use to quickly and
correctly address the e-mail messages
that you send. You can add and delete
names to your Address Book
12.4 Using the Address Book
To address a message using the Address Book feature:
• Open a New message.
• Click the To: button.
• The Address Book window appears. In the Show
Names From: box, select the Address list where the
name you want to find is located.
• To select a name from the address list, type the name or
the first part of the name in the Type Name Or Select
From List: box. The list scrolls to match the letters you
type.
• To add a selected name to an address box, click either
the To or Cc button.
• Click OK.
Day 4:
6. VIDEO CONFERENCING
6.1 INTRODUCTION
• With the ever-increasing reach of the Internet, corporations are
taking advantage of its flexibility and cost-effectiveness to expand
and enhance their traditional IP-based enterprise networks and
• Applications. This increases demand for greater capacities across
the Internet.
• It has also been discovered that the value of IP-based, real-time
voice and video applications is massive.
• As these applications become more commonplace, network
managers are creating networks that overlay voice and video
applications on top of the traditional enterprise network.
• When real-time, media-rich applications are merged with traditional
enterprise applications and networks, several key issues must be
addressed, including latency, jitter, security, NAT and firewalls.
6.2 VIDEOCONFERENCING
DEFINITION AND OVERVIEW
What is videoconferencing?
• Videoconferencing is defined as: "Conducting a conference between
two or more participants at different sites by using computer
networks to transmit audio and video data. For example, a point-topoint (two-person) video conferencing system works much like a
video telephone. Each participant has a video camera, microphone,
and speakers mounted on his or her computer. As the two
participants speak to one another, their voices are carried over the
network and delivered to the other's speakers, and whatever images
appear in front of the video camera appear in a window on the other
participant's monitor."
• Videoconferencing is an interactive tool that incorporates audio,
video, and computing, and communications technologies to allow
people in different locations to electronically collaborate face-to-face,
in real time, and share all types of information including data,
documents, sound and picture. In essence videoconferencing
removes the barrier of distance that separates us.
• "Multipoint videoconferencing allows three or more participants to sit
in a virtual conference room and communicate as if they were sitting
right next to each other. Until the mid 90s, the hardware costs made
videoconferencing prohibitively expensive for most organizations,
but that situation is changing rapidly. Many analysts believe that
videoconferencing will be one of the fastest-growing segments of the
computer industry in the latter half of the decade."
• Expanding this definition slightly to include not only computer
network-based videoconferences but those that utilize ISDN
telecommunications links as well.
• Also, the multimedia nature of modern videoconferencing
technology provides for more than just audio/video conferencing. It
provides for true multimedia conferencing that includes the sharing
of data between applications as well. Lastly, we would like to
emphasize the interactive nature of videoconferencing.
• Thus we might say: Videoconferencing is
• “Conducting an interactive conference
between two or more participants at
different sites by using computer networks
or ISDN telecommunication links to
transmit audio, video, and data. “
6.3 THE BASICS
•
•
•
•
•
•
•
Videoconferencing can conveniently be broken down into 3 components:
-the conference environment, i.e. the room or studio;
-the conference equipment, which generates sound and vision signals from
the participants and converts these into a format that enables transmission
to a remote site over the network;
-the conference network that links the sites together.
All videoconferences must have these three basic elements - however
simple or complex, the conference can always be divided into environment,
equipment and network. Conferencing is not limited to talking heads (i.e. the
participants).
Still images, e.g. 35mm slides or overhead transparencies, can be
introduced to illustrate a particular point. Moving sequences from a video
cassette may be replayed. An application running on a PC, e.g. PowerPoint
or Word, can also be relayed.
It is even possible for a PC application running at one site to be shared with
another site so that the remote site can annotate and take control of the
software. When PC documents are shared in this way it is termed “data
sharing”.
6.4 Technology:
• Videoconferencing actually encompasses a range of technologies
used in a wide range of situations, often it is not just video and audio
that is transmitted, but also data, allowing collaborative working
though shared applications. Videoconferencing may be:• One-to-one meetings, also known as point-to-point communications,
usually involving full two-way audio and video.
• One-to-many involving full audio and video broadcast from the main
site, where other sites may be able to send audio. For example in a
lecture situation, students could ask questions.
• Many-to-many, known as multi-point communication, provides audio
and video between more than two sites. With most multi-point
systems only one site in a conference can be seen at time, with
switching between sites either controlled manually or voice activated
(i.e., the loudest site is on screen).
6.5 VIDEOCONFERENCING
PROTOCOLS
• In order to ensure that systems are able to work with
each other independent of brand and or system type, a
number of standards have been developed by the
International Telecommunications Unit (ITU). You’ll see
and hear these standards referred to by different
equipment manufacturers when describing their
products.
• The following are ITU Videoconferencing standards.
• The Umbrella Protocol H.323 provides specifications for
voice and video communication over an IP network.
• H.320 provides specifications for voice and video
communication over ISDN lines.
• H.324 provides specifications for voice and video
communication over traditional phone lines.
• COMPARISON OF PROTOCOLS:
• H.323 versus H.320
• As described above, there are a number of
videoconferencing technologies in use. In this
presentation we shall concentrate on two that are in
popular: H.320 and H.323-based videoconferencing
technologies.
• H.320
This is a protocol that defines how real-time multimedia
communications and conferencing are handled over
switched or dedicated ISDN telecommunication links.
• The protocol is an international standard of the International
Telecommunications Union (ITU), and it was adopted in 1990.
Multimedia refers to the fact that the standard covers voice, video,
and data. The standard is an umbrella standard and includes many
other protocols that describe, as an example, how to encode and
decode voice and data, how to setup calls between terminals, and
how to handle data connections.
• The above definition of H.320 is rather complex. Lets see if we can
describe it in simpler terms. Lets assume we have a H.320
compliant terminal that has a microphone, a speaker system, a
display, a camera, an ISDN connection to the public telephone
network, and the necessary electronics to implement the H.320
protocols. Assume another similar terminal exists at a remote site.
• The local user can dial the ISDN telephone number of the remote
terminal, and the H.320 protocols handle the call setup between the
terminals. The local terminals microphone and camera picks up the
audio and video from the local user, decodes and compresses the
audio/video stream, and sends it to the remote site all using the
protocols as defined in the H.320 standard. The digital stream is
transmitted via the ISDN telecommunication lines to the remote site
where it is uncompressed, decoded, and displayed and heard by the
remote user.
• A similar audio/video stream is formed at the remote site and sent to
the local site where the audio and video from the remote site can be
heard and seen by the local user. A fully interactive videoconference
can thus be held between the two sites.
• H.320-based videoconferencing is considered to be "traditional", and
has been around for a number of years. The problem is that H.320
terminals are expensive, and they normally are implemented in
videoconferencing rooms that are, in themselves, very expensive to
construct. Vendors have not made H.320 equipment that is
applicable to desktop videoconferencing. In addition, ISDN
telecommunications lines are expensive to install and incur rather
large operating costs. However, there are a lot of H.320 rooms still in
use, and thus H.320 is still an important part of the
videoconferencing implementations over the world.
• H.323
• With the advent of the Internet, a new low-cost
communication medium became available for
communication between sites both local and remote
users. Perhaps we should qualify this and say that at
least the incremental cost to the end user to use the
Internet is low-cost. There are generally no usage costs
for the Internet, the bandwidth, at least between potential
user sites, is quite high, and the reliability is very good.
This motivated developers to create a videoconferencing
technology that uses the Internet to interconnect sites.
H.323 is the resulting protocol they developed.
• H.323 is an umbrella set of standards defining real-time
multimedia communications and conferencing over
packet switched networks.
Fig1. H.323 standard as defined in the OSI
layer.
• H.323 Version 1 was adopted by the ITU
in 1996 and Version 2 was finalized in
1998. Like H.320, it is a part of a family of
H.32X standards. H.323 borrowed many of
the H.32X standards used by H.320,
especially those for encoding/decoding the
audio/video streams and the data sharing
protocol (T.120), but it defined a new set
for handling communication over the
Internet.
• Like H.320, vendors have produced a wide array of
compatible H.323 compliant products. Unlike H.320, the
H.323 products cover a much wider spectrum of
capabilities.
• Videoconferencing has thus moved into the "do it
yourself" category and no longer requires expensive
videoconferencing rooms. This low entry cost for
equipment, the ease of interconnecting H.323 equipment
over the Internet, and the fact that equipment exists that
allows H.320 and H.323 terminals to interoperate in the
same videoconference has led to a rapid deployment of
H.323 equipment for videoconferencing in the
educational environment.
6.6 Broadband VSAT Network
• ETC’s Broadband VSAT Network
implements a high level of VSAT system
so as to provide broadband services
throughout Ethiopia, where there is no
alternative (terrestrial link). The
introduction of broadband VSAT in
Ethiopia will have a great role and it worth
describing its significance for the nation
with no access to terrestrial link.
1.2. Satellite communication
1.2.1. Satellite coverage
•
As it is clear on the footprint of the satellite used
by the broadband VSAT network, covers almost
all Africa and will have a great importance
regarding delivery of broadband services across
Africa for nations who need this service.
Moreover, it will help deploy faster services
almost immediately even in urban areas with
terrestrial link, since the satellite covers every
part of Ethiopia with a strong beam.
•
•
•
•
•
•
•
•
•
•
•
Satellite facts
Huge Geographical Coverage
No ‘line-of-site’ problems
Extremely reliable (99.9% Up time)
Reliable data broadcast or multicast
Single Vendor
Easy to deploy
Supports multiple applications:
Video
Data
Voice
•
•
•
•
•
•
•
•
•
•
•
•
•
Advantages of Broadband VSAT
Simple
Standard platform at every location
Scaleable
Easy to add further applications on demand almost anytime. It is also easy to manage the
necessity of additional sites.
Rapid Deployment
Services can be initiated anywhere almost immediately. Here comes the advantage of
VSAT for even provision of services in urban areas.
The very nature of VSAT is to provide the application of variable communication services in areas
like:
There is no means of alternative link other than satellite;
The necessity of immediate and fast implementation of communication services.
Generally it is the only means in giving a connection for rural areas in developing
countries, since most of the developing countries infrastructure doesn’t have sufficient
microwave and fiber links so that to provide connection all over the country.
* This is the very reason to bring VSAT technology in our country, Ethiopia.
Broadband VSAT Services
• Broadband VSAT provides an all-in-one or integrated Digital
Data, Video Multicast, Internet, and Video Conference services.
• And these capabilities will make Broadband VSAT great
contributor for our country regarding the development of ICT.
Aiming at reaching every nation in an equitable level as of the
country’s vision. Cumulatively, it will enable to achieve or
contribute for the development of the awareness of IT over the
rural areas and/or woreda’s.
• Broadband Sections:
• ETC’s Broadband VSAT Network has three Network Groups:
• School Net Network Group
• Wereda Net Network Group
• Agri Net Network Group
REMOTE SITE VIEW
• Generally, two types of remotes are available for
School-Net, Receive Only and TX/RX.
• And there is one type of TX/RX for Woreda-Net.
The PES remote equipment consists of the
• Radio Frequency Transceiver (RFT), which is
located outdoors,
• An Interfacility Link (IFL) and
• The Indoor Unit (IDU), which is located indoors
at the point of customer interface.
• Fig. PES Remote Equipment Overview
• Radio Frequency Transceiver (RFT):
The Radio Frequency Transceiver (RFT) is
comprised of:
An antenna, and An
Outdoors Digital Unit (ODU)
Antennas
• The antennas have an offset of 22.3 degrees that helps prevent snow and ice from
collecting on the reflector.
• The antenna’s azimuth/elevation (AZ/EL) pointing assembly is attached to the top of a
vertical pipe or mast. The AZ/EL assembly permits adjustment of the antenna’s beam
angle over 360 degrees in azimuth and 5 to 45 degrees in elevation. The antenna
reflector is directly attached to this structure.
• The feed support arm, which supports the ODU electronics package, is attached to
the AZ/EL assembly to avoid any distortion of the reflector during the periods of high
wind loading.
• The PES remote incorporates a pointing feature that enables the installer to view the
strength of the received signal and the “lock” status of the demodulator at the ODU.
• In order to accommodate for the different frequencies supported, ISBN uses different
kinds of antennas.
• For systems using the C-band frequency, a 1.8 or 2.4 meter conical antenna is used.
• Fig. PES C-band Antenna
Outdoor Unit (ODU)
• The ODU is a compact combination of
• Down Converter (LNB), and
• Power amplifier (SSPA, Solid State Power Amplifier), which is powered from the
indoors-electronic unit.
• ODU has the following features:
• Monitor and control of the ODU is exercised from the IDU.
• Controls the uplink and downlink frequency as well as the uplink power.
• The ODU processor communicates across the interfacility link (IFL) with the indoor
unit IFM
• The PES ODU is mounted on the antenna’s feed support arm and is directly attached
to the antenna feed horn. Aperture blockage is minimized by the offset-fed design of
the antenna.
• A 2.0-watt (at 1 dB Compression) Solid State Power Amplifier (SSPA) is available as
an option. The PES C-band incorporates a 5-watt SSPA.
• Both the receiver and the transmitter are stabilized using a common RF source. This
source is stabilized using a frequency locking technique referenced to the outroute
signal from the hub, eliminating frequency drift.
Interfacility Link
• The Interfacility Link (IFL) connects the ODU
with the IDU using a single coaxial cable. This
cable carries:
• DC power (for the ODU)
• Transmit and Receive IF signals
• Transmitter control signals
• ODU status signals
• Reference frequency signal
• A frequency division multiplexing technique is
used to combine these signals.
Indoor Unit
• The IDU contains the satellite modem and
synthesizers, and a number of interface cards as
required for data and voice, and decoders for TV
broadcast reception. Includes a one-way indoor
unit that supports high-speed TCP/IP
applications that is Internet and e-mail. Each
ODU can only operate when connected to the
proper corresponding PES IDU.
Common Codes Interpretations
Common Codes for DW1000
• Commonly the normal state is either 06 or 07
depending of the configuration, if it is rebooting,
displaying 02, 03 and then coming to 06 or 07
on the LED display.
• If there is no LED display, inform to the technical
operator
• Power indicator-Illuminates when downloading
software; when blinking, DW is not ready to
operate.
Common Codes for PES5000/Okemo
How to Interpret PES 5000/Okemo LED Displays: - The PES
5000/Okemo has two LED displays side by side or layer by layer
respectively. The LED display on the right is referred to as the PC
LED/upper layer. The LED on the left/lower layer is referred to as the
IF LED.
PC LED State/Status Display: -Most of the time, each remote card will
display two LED codes that flash alternately at one second intervals.
These codes indicate the current condition (state/status) of the card.
The state and status can be distinguished by the fact that:
• The state code is a single character.
• The status code is a single character followed a dot.
• This alternating display will be indicated by the state and status
separated by a slash (/): State/Status.
Normal State blank
• Online (blank/blank.): - State blank is the normal
operating state of the remote. In this state, the
downloaded user code is running and performing its
protocol–specific functions with the user equipment.
Minor alarms are posted by all blank states except:
• blank/0. and
• blank/blank. Online the blank LED code state is
entered when all code is in memory; no alarms have
occurred; and outroute and SFH sync are attained. This
is the normal operating state of the remote, during which
it can pass user data.
• and distribution system in the headend (see
figure 1 below) digitally compresses and
distributes eight active video channels. Each
video channel is accompanied by two AES
digital audio channels. A single hot standby
encoder is employed to provide redundancy for
the eight primary encoders in the event of any
anomaly. All content provided to the encoding
system uses an SDI interface for the Video and
AES/EBU interface for the audio.
• Head end
• The eight digitally encoded signals are statistically
multiplexed and the variable bit rate streams are then
sent to a multiplexer to be multiplexed into a single ASI
transport stream. A single backup multiplexer is
provided for redundancy management in the event of
any anomalies in the primary multiplexer. A redundancy
switch is employed to switch to the redundant multiplexer
in the event of an anomaly. The network management
system (NMS) monitors and controls the redundancy
switch. One output of the multiplexer is provided to
support monitoring the performance of the system. The
multiplexed ASI stream is next converted into ATM and
delivered across an ATM network from the headend to
the uplink site.
Satellite Link (Sululta Earth Station)
• The 34Mb carrier that is linked to ITMC is directly connected to
Sululta’s ATM Vision and will be converted to ASI back (as it is
formatted first to carrier level at ITMC). And further multiplexed with
a traffic that is processed by Satellite Gateway. The resulting
multiplexed ASI out will be forwarded to the modem. The IF out from
modem goes to the RF Subsystem in such a way to transmit to
Satellite.
• The diagram shown below can be viewed as follows:
• The ATM signal from the Head end is received at the uplink site and
converted back to ASI (see figure 2). A Multiplexer at the uplink site
multiplexes the ASI signal from the Head end with data stream from
a HNS IP Encapsulator Gateway. The Multiplexed signal is then
modulated by HNS equipment for Satellite distribution.
The System Block Diagram (Sululta Side)
ATM Vision
• The 34Mb link that is from ITMC will go directly to ATM Vision. The
ATM (Asynchronous Transmission Module) situated at Sululta is
different from the EMA side one. The ATM at Sululta side performs
the conversion of the 34Mb carrier to an ASI format, in such a way
that to retrieve the ASI, which carries the combined 8 Channels. And
will be combined with the Satellite Gateway traffic to multiplexer.
Then the multiplexed output will be linked to the Redyn Modulator,
which has ASI interface that modulates it with the desired IF
frequency and transmitted to RFT (Radio Frequency Terminal).
• *Though the ATM at Sululta side performs the inverse process, i.e.,
it converts back the 34M input from EMA to ASI format, same
principle and future underlies with the ATM that discussed at EMA
side.
6.7 Point-to-Point Videoconferencing
• Consider two client terminals that are connected
to the Internet. (See Figure 2) An example of a
client terminal or end point is a VCON end point
Falcon IP or Polycom's Viewstation SP. This
terminals and its associated peripherals allow
the user to make a call to another client, send
the local audio/video stream to the remote client,
and hear/view the received audio/video stream
on a local speaker/monitor that is connected to
it.
• Figure2. Point-to-point VC
• Assume one user (the local user) uses a Falcon IP to call a user at a
remote Falcon IP (client terminal) by entering the IP address of the
remote Falcon IP. The clients setup a call between the stations
following the specifications of the H.323 protocol. Once the call is
setup, the clients exchange audio/video streams over the Internet.
The point-to-point videoconference continues until one of the users
"hangs up" the call.
• One of the problems with this type of video call is that IP numbers
are used for the call. IP numbers are difficult to remember; some
users have dynamically assigned (DHCP) IP numbers that can
change every time they boot their system; there are problems in
using IP addressing when different vendor systems are used.
Although it is occasionally used, the use of IP dialing for creating
videoconferencing sessions is not recommended.
• To alleviate the problem of IP dialing, the H.323
standard defines the use of a gatekeeper. (See
Figure 3) The gatekeeper is a system that
connects to the Internet just like the client
terminals. The IP address of the gatekeeper is
configured into the client terminals and when the
clients "power up", they communicate with the
gatekeeper and transfer certain information to
the gatekeeper that describes the client. This
process is known as registration; the client
registers with the gatekeeper.
Figure 3. Use of gatekeeper
• Two identifiers are assigned to and configured in
each client terminal. One is a H.323 Alias. It is
usually descriptive of the particular client
terminal and usually contains alphanumeric
characters. The other descriptor is the H.323
Extension. It usually consists of several numbers
and can be thought of as being the video
telephone number of the client. While it is
possible to use either the H.323 Alias or the
H.323 extension for dialing, it is difficult to dial
alphanumeric characters on most clients; it is the
H.323 extension that is normally used for dialing.
• When the clients register with the gatekeeper, they pass
their IP numbers, H.323 alias, and H.323 extension to
the gatekeeper where it is stored. This allows a local
user to dial a remote user by entering the remote users
H.323 extension (video telephone number) rather than
an IP address. The local client terminal communicates
the H.323 extension to the gatekeeper. The gatekeeper
then checks to see if the remote client is registered with
the gatekeeper. If it has, the gatekeeper sets up the call
between the two clients; if it is not registered, the call is
rejected. Once the call has been setup, the audio/video
streams flow directly between the clients over the
Internet. The gatekeeper can perform a number of other
management functions as well.
6.8 MULTIPOINT VIDEOCONFERENCING
• To this point we have only considered point-to-point
videoconferences. These are conferences between two
client terminals. The question can then be raised, "what
if we have users at three or more clients that want to
hold a videoconference". To handle this situation, the
H.323 standard introduces the concept of a Multipoint
Control Unit (MCU). The MCU (See Figure 4) is an
endpoint that can be thought of as a "video bridge". The
MCU connects to the Internet as does any other
endpoint and registers with the gatekeeper, as does any
other endpoint.
Fig 4. Multipoint Videoconferences
• MCU, depending on its design capacity, can handle a certain
number of simultaneous videoconferences each with each
videoconference being logically separate from the others and with
each having a specified number of users. System administrators
define "services" on the MCU where each service has certain
characteristics that contrast it from other defined services on the
MCU. As an example, a service of 75 to 700 might be defined that
allows for several simultaneous videoconferences to be created
where each have a maximum size of, say, five sites (clients) and
where all must encode their audio/video streams at 384 Kbps. A
specific videoconference on service 75 is then defined by the
service number and by a conference "password" (e.g. 751234).
Each of the simultaneous videoconferences that are held on service
75 is then defined by the service number (75) and by a different
password.
•
•
•
When users want to join a particular videoconferencing session, they dial
the service number/password combination. The gatekeeper checks to see if
that service has been registered by a MCU. If it has, the gatekeeper
completes the call by connecting the client to the specified videoconference
on the MCU; if the service has not been registered, the call is rejected.
Once the call has been connected, the client's audio/video stream is then
sent over the Internet from the client to the MCU. Similarly, other clients
connect to the session and send their audio/video streams to the MCU. The
MCU selects one of the audio/video streams on the videoconference and
returns that audio/video stream to all of the clients (that is all except the
client whose stream was selected).
There are several methods for selecting an audio/video stream. Audio
switching and chairman control are two alternatives. Typically, the method
that is chosen is audio switching where the MCU selects the stream that
currently has active audio (someone is talking or is talking the loudest). We
frequently refer to this selection process by saying that this particular stream
(client) has "captured" the MCU.
• Lets assume that we have several clients connected to a single
videoconferencing session on a MCU. The assumption is that no
users want to have the MCU send them back video of themselves
and no site wants to receive an audio stream that contains their own
audio. So the MCU sends the selected video stream to all the clients
except the client whose stream was selected; the MCU sends the
video from the last site that was selected to the currently selected
site. All of the audio streams are aggregated together and sent back
to each site except with their audio removed. Thus each site gets a
unique audio stream. Each stream only contains the audio from the
other sites.
• As the user(s) at one site stop talking and the user(s) at another site
start to talk, they capture the MCU. The process is repeated with the
video from the newly selected site now being sent to all the other
sites, and the newly selected site getting the video from the
previously selected site.
6.9 VIDEO STREAMING:
• To participate in a H.323 videoconference, users must
have appropriate videoconferencing client terminals and
have Internet connectivity with sufficient bandwidth to
support the videoconference.
• Some users may not have these capabilities but would
still like to be able to participate even if that meant that
they could only see and hear conference participants but
not be able to interact with them. This can be
accomplished if the videoconference session is
captured, encoded in an appropriate format, and
streamed over the Internet although this capability is not
a part of the H.323 standard.
Figure 5 streaming
•
•
•
•
To accomplish the streaming, a H.323 client must be connected to the
conference session to be streamed. This station will be able to capture and
decode the audio/video that the MCU has currently selected. This decoded
audio/video can then be re-encoded and streamed over the Internet.
There are two popular encoding standards that are currently being used:
Real Video and Microsoft Windows Media.
The encoded audio/video can then be either streamed on the Internet by a
server or archived on a disk file for later viewing or both. The system
consists of a H.323 client, an encoder, a server, and an archive storage
system.
Users can receive the stream using a browser on a computer. They enter
the URL of the server, and the server starts the encoded audio/video stream
over the Internet to the computer. Plug-Ins for the browser exist that are
capable of decoding both Real Video and Windows media streams. The
user can thus see and hear the participants in the streamed
videoconference in near real-time. Alternatively, a user can connect to the
server at a latter date and view the archived version of the videoconference.
6.10 IP MULTICASTING
• IP Multicasting is a new technological
phenomenon that contributes a great deal
of investment benefits in delivering
videoconferencing sessions to multiple
users. It is a way of delivering content to
multiple users by utilizing the bandwidth
only once at a time.
• It provides more bandwidth economy than
unicast content delivery.
• Based on TCP/IP multicast theory, using a
common class D multicast group address, an
initiating multicast system (Chairman) is able to
call multiple endpoints and broadcast audio and
video data to them simultaneously. Unlike
unicast transmission, which would require
central MCU hardware or software, multicast
operates with single streams of video and audio,
reducing the overall bandwidth required for the
conference.
• In a unicast call, between two endpoints on the network,
the amount of bandwidth utilized must be doubled, as
there is video and audio data being transmitted by both
endpoints simultaneously.If this conference is expanded
(through centralized MCU hardware or software), the
bandwidth used on the network increases by a factor of
2 for each endpoint added to the conference.
• With multicast, the video and audio data is a one-way
transmission, and therefore, the overall bandwidth of the
conference never changes, regardless of the number of
endpoints that join.
• Interactive Multicast takes this theory one step further - although
multicast is very useful for one-way communication, by adding small,
direct unicast channels between the receiving stations and the
chairman, it is possible to send requests and messages between
participants. This communication 'back channel' thus provides us
with a control method for switching off the multicast at one station
and switching it on at another, effectively switching the source of
transmission amongst participants as required.
• For instance VCON’s Interactive Multicasting technology is an
exclusive software package available for most VCON LAN endpoints and provides the ability to broadcast audio and video streams
from any Interactive Multicast enabled end-point on the network.
Videoconferencing among
different protocols
• So far we have discussed H.323
videoconferencing capabilities. However,
many sites have videoconferencing rooms
that implement the H.320 standard that
uses telecommunication lines (e.g. dial-up
or dedicated ISDN lines).
6.11 GATEWAYS
• H.323 standard was developed after the
H.320 standard and uses many of the
encoding/decoding protocols originally
developed for H.320. The H.320 systems
can be considered to be legacy systems,
but since many of them still exist, it is
important that we continue to support
H.320.
• In addition to supporting pure H.320 videoconferences using H.320
MCUs, gateways between the two protocols can be provided.
• A gateway provides a path between H.320 and H.323 systems. It
translates H.320 commands and audio/video streams to H.323
audio/video streams and vice versa. Users with H.320 client
terminals dial the gateway over ISDN lines. The H.320 client then
needs to input a service/password combination for the selected
session, and the gateway connects the H.320 terminal to the
selected session. All H.323-based users can see and hear the
H.320-based users as if they were on H.323 terminals, and similarly
the H.320-based users can see and hear the H.323 users as if the
were on H.320-based terminals. Multiple H.320 connections can be
made to the gateway up to the capacity of the gateway.
• One other benefit of the gateway is that it
can accept calls from standard
telephones. (See Figure 7)
• Fig. 8 Use of Gateways in making telephone calls to a
network
• In the above picture A user with a standard telephone
dials the ISDN telephone number and is connected to
the gateway. The telephone user then enters a series of
digits to indicate the service/password combination of
the desired videoconferencing session. The user can
then hear the entire audio from the videoconference and
can also interact with others in the conference. The
gateway is able to simultaneously connect multiple
telephone calls and can even connect to a telephone
bridge that could allow participation by a large number of
audio only users.
BANDWIDTH CONSIDERATIONS
• The H.323 client terminals encode the selected audio (usually from
a microphone) and video (usually from a camera) inputs. The
encoded and video are then compressed into a single audio/video
stream and sent to the remote end point (another client terminal or a
MCU).
• Different rates can be selected for the encoding process. As an
example, an encoding rate of 384 Kbps might be selected. 64 Kbps
is reserved for the audio and 320 Kbps is reserved for the video.
The 384 Kbps stream is compressed (redundancy is removed) and
sent to the remote end point. Similarly a 384 Kbps stream is
received from the remote end point. Thus approximately twice 384
Kbps in bandwidth (less any bandwidth saved because of
compression) is required to support the videoconference for this end
point. If there is a lot of motion in the video, very little compression is
achieved. If there is almost no motion in the video, the savings
approaches about 50%. Since we must design for the worst case,
assume a bandwidth requirement of twice 384 Kbps.
• Faster encoding rates can be selected. Most client
terminals support rates up to 768 Kbps. Some
proprietary implementations can encode at speeds up to
2 Mbps.The higher the encoding rate, the better the
quality of the video. However, higher encoding rates also
mean higher bandwidth requirements, greater impact on
the network, and greater impact on the MCU capacity.
Lower encoding speeds can also be selected down to
about 128 Kbps. This of course means lower video
quality. 384 Kbps is a good compromise between quality
on one hand and resource impact on the other. 384 Kbps
will support 30 frames per second video. Lower encoding
speeds yields lower frame rates and choppy video.
There is a discernable but small improvement in quality
between 384 Kbps and 768 Kbps.
• Physically, the most common scenarios of videoconferencing are:
• Desktop videoconferencing - usually a small camera is located on
top of the PC or workstation monitor. The actual video is usually
displayed in a small window, and shared applications, such as a
shared whiteboard are often used.
• Studio-based systems - a studio is specially equipped for
videoconferencing.
• This will normally include one or more cameras, microphones, one
or more large monitors, and possibly other equipment such as an
overhead camera for document viewing. Usually used for more
formal meetings
In practice a 'studio' may not be a dedicated room, but a standard
meeting room with portable equipment that can be set up when
required.