Download L01

CIT 513: Introduction
to Computer
Communication
Mohammed A. Saleh
http://ifm.ac.tz/staff/msaleh/CIT513.html
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Module Description
 Provides
the student with
of fundamentals of how
communicate.
 Provides
the student
understanding of how
interact with different
systems
knowledge
computers
with an
computers
computers
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Prerequisites
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There is no prerequisites
undertaking this course.
before
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Plagiarism Policy
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Plagiarism is a serious offense
Plagiarism is presenting somebody else's work
as your own. It includes:
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Copying information directly from the Web or books without
referencing the material
Submitting joint coursework as an individual effort copying
another student's coursework
Stealing coursework from another student and submitting it as
your own work.
Suspected plagiarism will be investigated and if
found to have occurred will be dealt with
accordingly.
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Cont …
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All material copied or amended from any source
(e.g. internet, books) must be placed in
quotation marks and in italics, with a full
reference to the source directly underneath the
material
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Cont …
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All material copied or amended from any source
(e.g. internet, books) must be placed in
quotation marks and in italics, with a full
reference to the source directly underneath the
material
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Instructor
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There is only one lecturer responsible for this course,
both lectures and tutorials.
Find out about my contact details from my personal
website http://ifm.ac.tz/staff/msaleh
If you need to see me in my office please book an
appointment
by
writing
me
an
email
[email protected]
My office number is Block D, room 016
All notes will be uploaded on the CIT 513 web page,
http://ifm.ac.tz/staff/msaleh/CIT513.html
A hardcopy will be submitted to the class representative
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Basic Rules
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Try to attend ALL lectures
Sign against your name on the register
Try not to be late, if you have to be late, come in
quietly.
If you miss a class find out what was covered
Material covered in lectures is examinable
The course notes are not meant to be
exhaustive, read the recommended books; Read
critically, point out any errors in the lecture
notes.
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Assessment
This module will be assessed by a
combination
of
tests,
tutorials,
unannounced quizzes and the final exam.
 Both the tests will be written tests and the
extent of coverage will be announced in
due time.
 There will also be unannounced quizzes,
which will contribute to your coursework.

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Cont …
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And finally the Final Exam, which will
cover all contents of the course taught
during the semester.
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Final Mark Calculation
Assessment
Marks (%)
Test I
15
Test II
15
Tutorials
5
Unannounced quizzes
5
Total
40
Final Exam
60
Grand Total
100
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Required Readings
Author
Year
Title
Publisher
Hermachandran
L.
2003
Computer Communications
Network
Charulatha
Tanenbaum A. S.
2005
Computer Networks
Prentice-Hall
Galo M. A.
2002
Computer Communications
and Networking
Technologies
Pacific Grove
Rowe S and
Schuch
2005
Computer Networking
Pearson
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Recommended Readings
Author
Year Title
Publisher
Kurose J. F
2001 Computer Networking a
top down approach
Pearson
Halsall
2005 Computer Networking
and Internet
McGraw-Hill
Madhulika J.
2002 Computer Networks
BPB
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Prescribed Materials

If you have issue with getting hold of the book then it will
made it available in a CD with other additional material at
a little fee, not more than TZS 2000/-
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How to survive this course
Materials sound simple and easy, but they
are not.
 Do not leave everything to the exam
night!.
 Not to copy others work!, try them by
yourself.
 You can read the course by yourself, but
the class makes the life for you easier.

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Introduction
What is a Computer Network?
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A network is nothing more than two or more computers
connected to each other so that they can exchange
information, such as e-mail messages or documents, or share
resources, such as disk storage or printers.
These computers may be interconnected in the same building
or different buildings.
In most cases, this connection is made via electrical cables that
carry the information in the form of electrical signals.
The cables transmitting the information are commonly known as
transmission media.
The transmissions media are classified as wired or wireless
transmission media.
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Cont …
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Examples of wired transmission medias are Unshielded
Twisted Pair (UTP), Coaxial Cable or Fiber Optic Cable
(a) Coaxial
(b) Fiber Optic
(c) UTP
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Cont …
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Wireless transmission medias include radio waves,
infrared and Bluetooth
(a) Bluetooth icon
(b) Radio signals
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Cont …
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When a computer is turned on and can be visible by all
other computers, then that computer is said to be online.
If a computer is not turned on and it is not visible by
other networked computers, it is then said to be offline.
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Why Computer Networks?
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Networks are all about sharing. are about sharing three
things: information, resources, and applications.
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Sharing information: allow users to share information in several
different ways. The most common way of sharing information is
to share individual files. For example, two or more people can
work together on a word-processing document.
Sharing resource: certain computer resources, such as printers
or hard drives, can be set up so that network users can share
them. Sharing these resources can result in significant cost
savings. For example, it is cheaper to buy a single high-speed
printer with advanced features that can be shared by an entire
workgroup than it is to buy separate printers for each user in the
group.
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Cont …
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Sharing applications: several users can work together on a
single business application, For example, an accounting
department may have accounting software that can be used from
several computers at the same time.
Other uses
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High reliability: All data can be
copied on two or three
machines, so if one of them is unavailable then other two copies
could be used.
Communication: A computer network can provide a powerful
communication medium along widely separated employees.
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Networks building blocks
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All networks, large or small, require specialized network
hardware to make them work.
Small networks will have less network hardware than
large networks.
Small or large, all networks are built from the following
basic building blocks:
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Client computers
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computers that end users use to access the resources of the network.
located on users’ desks.
usually run a desktop version of Windows such as Windows Vista, Windows
XP, Ubuntu or Open Suse, along with application soft- ware such as
Microsoft Office.
sometimes referred to as workstations.
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Cont …
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Server computers
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Network interface card (NIC)
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Computers that provide shared resources, such as disk storage and printers,
as well as network services, such as e-mail and Internet access.
run a specialized net- work operating system such as Windows Server 2008
or 2003, Ubuntu Server, Leopard (OS X) Server along with special software
to provide network services.
An interface that’s installed in a computer that enables the computer to
communicate over a network.
Every client and every server computer must have a NIC in order to be a
part of a network.
Cable
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Computers in a network are usually physically connected to each other using
a cable
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Cont …
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Switches
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Wireless networks
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Network cable usually doesn’t connect computers directly to each other
Instead, each computer is connected by cable to a device known as a switch
Each switch contains a certain number of ports, typically 8 or 16
computers to communicate via radio signals
radio transmitters and receivers take the place of cables
main advantage of wireless net- working is its flexibility
main disadvantage of wireless networking is that it is inherently less secure
than a cabled network.
Network software
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As important as network hardware.
Server computers typically use a special network operating system (also
known as a NOS) in order to function efficiently.
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Clients and Servers
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The network computer that contains the hard drives,
printers, and other resources that are shared with other
network computers is called a server
Any computer that’s not a server is called a client.
Differences between the two computers:
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The most powerful and expensive computers in a network are
the servers
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The cheaper and less powerful computers in a network are the
clients
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every user on the network shares the server’s resources.
clients’ resources don’t have to be shared
Most networks have more clients than servers
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A network with ten clients can probably get by with one server.
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Types of Computer Networks
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Networks are classified according to their geographical
coverage and size
Network classifications include:
Personal Area Networks (PANs)
Local Area Networks (LANs)
Metropolitan Area Networks (MANs)
Wide Area Networks (WANs)
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Personal Area Networks (PANs)
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Introduced by the presence of wireless technologies.
It is also referred to as Wireless Personal Area Networks
(WPAN).
WPAN refers to the technologies involved in connecting
devices in very close proximity to exchange data or
resources.
An example of this can be seen through connecting a
mobile device with a mobile device to exchange files
(music, photos or documents)
Connecting a laptop with a PDA.
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Cont …
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Because of the close proximity of WPAN networking,
short-range wireless technologies are typically used.
This includes Bluetooth and Infrared
A laptop sending a file to a Personal Digital Assistant
(PDA).
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Cont …
Mobile devices that can form a PAN
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Local Area Network (LAN)
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A network that is restricted to a single geographical
location.
Encompasses a relatively small area such as an office
building or school
The function of the LAN is to interconnect workstation
computers for the purposes of sharing files and
resources.
It is typically high speed and cheaper to set up than a
WAN
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Cont …
Local Area Network
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Cont …
Major Characteristics of LANs
 Every computer has the potential to communicate with
any other computers of the network
 High degree of interconnection between computers
 Easy physical connection of computers in a network
 Inexpensive medium of data transmission
 High data transmission rate
Advantages
 The reliability of network is high because the failure of
one computer in the network does not effect the
functioning for other computers.
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Cont …
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Addition of new computer to network is easy.
High rate of data transmission is possible.
Peripheral devices like magnetic disk and printer can be
shared by other computers.
Disadvantages
 If the central device fails, the entire network system
breaks down.
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Cont …
Use of LAN
 Followings are the major areas where LAN is normally
used:
1. File transfers and Access
2. Word and text processing
3. Electronic message handling
4. Remote access
5. Digital voice transmission and storage
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Wide Area Network (WAN)
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It is used to describe a computer network spanning a
regional, national or global area.
For example, for a large company the head quarters
might be at Dar Es Salaam and regional branches at
Dodoma, Arusha, Mwanza and Morogoro
They are built so that users from one location can
communicate with users from another location
WANs are slower than LANs
Often require additional and costly hardware
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Routers
Dedicated leased line
Complicated implementation procedures
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Example of WAN
Wide Area Network
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Cont …
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Followings are the major characteristics of WAN.
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Communication Facility: For a big company spanning over
different parts of the country the employees can save long
distance phone calls and it overcomes the time lag in
overseas communications. Computer conferencing is another
use of WAN where users communicate with each other
through their computer system.
Remote Data Entry: Remote data entry is possible in WAN. It
means sitting at any location you can enter data, update data
and query other information of any computer attached to the
WAN but located in other cities. For example, suppose you
are sitting at Dar and want to see some data of a computer
located at Arusha, you can do it through WAN.
2.
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Cont …
3.
Centralised Information: In modern computerised
environment you will find that big organisations go for
centralised data storage. This means if the organisation
is spread over many cities, they keep their important
business data in a single place. As the data are
generated at different sites, WAN permits collection of
this data from different sites and save at a single site.
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Difference between LAN and WAN
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Coverage: LAN is restricted to limited geographical
area of few kilometers. But WAN covers great distance
and operate nationwide or even worldwide.
Connectivity: In LAN, the computer terminals and
peripheral devices are connected with wires and coaxial
cables. In WAN there is no physical connection.
Communication is done through telephone lines and
satellite links.
Cost: Cost of data transmission in LAN is less because
the transmission medium is owned by a single
organisation. In case of WAN the cost of data
transmission is very high because the transmission
medium used are hired, either telephone lines or
satellite links.
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Cont …
4.
5.
Speed: The speed of data transmission is much higher
in LAN than in WAN. The transmission speed in LAN
varies from 0.1 to 100 megabits per second. In case of
WAN the speed ranges from 1800 to 9600 bits per
second (bps).
Transmission Errors: Few data transmission errors
occur in LAN compared to WAN. It is because in LAN
the distance covered is negligible.
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Metropolitan Area Network
(MAN)
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A network that usually spans across the city or a large
campus
Interconnects several local area networks
It uses a high-speed cable for the interconnections
between different LANs
It might be owned or operated by a single organization
Its geographical scope falls between a WAN and a LAN
MANs provides internet connectivity for LANs in the
same metropolitan area
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Cont …
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Network Models
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There are two basic wired network models from which to
choose:
Peer-to-peer network model
Client/ server network model
The model used for a network is determined by several
factors
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how the network will be used
how many users will be on the network
budgetary considerations
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Peer-to-peer Network Model
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This is a decentralized network model offering no
centralized storage of data or centralized control over the
sharing of files or resources.
All systems on a peer-to-peer network can share the
resources on their local computer as well as use
resources of other systems.
Advantage:
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They are cheaper and easier to implement than client/server
networks, making them an ideal solution for environments in
which budgets are a concern
It does not work well with large numbers of computer
systems
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Cont …
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Disadvantages:
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As a peer-to-peer network grows, it becomes increasingly
complicated to navigate and access files and resources
connected to each computer because they are distributed
throughout the network.
The lack of centralized data storage makes it difficult to locate
and back up key files
Typically found in small offices or in residential settings
where only a limited number of computers will be
attached and only a few files and resources shared.
Rule of Thumb: Have no more than 10 computers
connected to a peer-to-peer network.
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Client/ server Network Model
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It is the most widely implemented model and the one you
are most likely to encounter when working in real-world
environments.
Advantages:
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It allows for centralized network management of all network
services
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user management,
security and
backup procedures.
Disadvantages:
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It requires technically skilled personnel to implement and
manage the network
Adds the cost of a dedicated server hardware and software
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Questions