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CHAPTER 1
INTRODUCTION TO
NETWORKING
BASIC CONCEPTS OF
COMPUTER NETWORKS
NETWORK
Computer and devices, connected by some type of
media.
 Two computers to thousands of computers connected
across the world via the Internet.
 Networks may link mainframe computers, desktop
computers, printers, plotters, fax machines, and phone
systems.

NETWORK (CONT.)
Manage and administer resources on multiple
computer from one location.
 Networks allow multiple users to share devices and
resources such as:
- printers
- faxes
- program and files

ADVANTAGES OF NETWORKING
•
•
File Sharing : The major advantage of a
computer network is that is allows file sharing
and remote file access. A person sitting at one
workstation of a network can easily see the files
present on the other workstation.
Resource Sharing : If there are four people in a
family, each having their own computer, they will
require four modems (for the Internet connection)
and four printers, if they want to use the
resources at the same time. A computer network,
on the other hand, provides a cheaper alternative
by the provision of resource sharing.
•
•
Increased Storage Capacity : As there is more
than one computer on a network which can
easily share files, the issue of storage capacity
gets resolved to a great extent. When many
computers are on a network, memory of different
computers can be used in such case. One can also
design a storage server on the network in order
to have a huge storage capacity.
Increased Cost Efficiency : There are many
software's available in the market which are
costly and take time for installation. Computer
networks resolve this issue as the software can
be stored or installed on a system or a server and
can be used by the different workstations.
TYPES OF NETWORK

Peer-to-Peer

Client / Server
PEER-TO-PEER NETWORKS
Peer-to-peer networks :
 Resource sharing, processing, and
communication controls are fully
decentralized often called a workgroup.
 All clients are given equal importance in using
the network resources and users are
individually authenticated by workstations.
 No fixed clients and servers.
 Common with up to 12 computers
 Disadvantage – slow transmission
9
Peer-to-Peer Networks
CLIENT / SERVER NETWORKS
Client/server networks
 It is a network where the servers provide
services to different clients.
 A centralized server provides client
authentication services.
 Servers play a key role in managing several
applications like access to shared files,
printers, and hardware.
CLIENT-SERVER
Usually high-powered servers. The types
of servers are: File server (file server) - save the software and data
Data server (database server)-store only
Print Server (Print Server) - control of one or more printers
Fax Server (Fax Server) - manage the fax transmission
Mail server (Mail server) - manages e-mail
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CLIENT-SERVER
Advantages
Disadvantages
Security and data sources are
controlled by the server
spending more costly for a server
All components (client / network /
server) work simultaneously
need maintenance every time the
rates are determined to ensure
the effectiveness of the system.
Sharing data and software applicatio
ns can be done
Networking does not
work if something went
wrong on the server.
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Client/Server Networks
LANS, MANS AND WANS
There are three main categories of networks:
• Local Area Network (LAN) – is a relatively
small network of computers, printers, and other
devices in single building or floor.
• Metropolitan Area Network (MAN) – is a
high-speed internetwork of LANs across a
metropolitan area.
• Wide Area Network (WAN) – traditionally
connects LANs using the PSTN(Public Switched
Telephone Network) or more commonly the
Internet. To provide connectivity over a large
geographic area.
LOCAL AREA NETWORK (LAN)
LAN characteristics:
 They are used within small areas ( such as in
an office building).
 They offer high-speed communicationtypically 100Mbps or faster.
 They provide access for many devices.
 They use LAN- specific equipment such as hub
and NICs-usually no need router.
METROPOLITAN AREA NETWORK
MAN characteristics:




Sites are dispersed across a city/large
campus and perhaps the surrounding
area as well.
With the advent of MANs, historically
slow connection (56Kbps-1.5Mbps)
have given way to communication at
hundreds of megabits per second and
even gigabit speeds.
They use devices such as routers,
telephone switches, and microwave antennas as part of
their communication infrastructure
A MAN usually interconnects a number of (LANs) using a
high-capacity backbone technology, such as fiber-optical links.
WIDE AREA NETWORK
WAN characteristics :
 They can cover a very large geographic area
even span the world.
 They usually communicate at slow speed
(compared to LANs).
 They use devices such as routers, modems, and
WAN switches, connectivity devices specific to
LANs and used to connect to long-haul
transmission media.
COMMON NETWORK ELEMENT





Client
A computer on the network that requesting resources or services.
Server
A computer on the network that manages
network access and shared resources.
Network Interface Card (NIC)
A device inside a computer that connects
a computer to the network media.
Network Operating System(NOS)
Server that enable a computer to control network access and manage
resources. The most popular NOS are Microsoft Windows Server,
Novell NetWare and UNIX.
Host
A device that provides resource sharing for other computers on the
same network.
COMMON NETWORK ELEMENTS (CONT.)
•
•
•
•
•
Node
A device such as, client, server, or other network equipment that
is identified by a unique network address.
Topology
The physical layout of a computer network. Network topology can
be a ring, bus or star formation, or hybrid combinations.
Backbone
The backbone of a network (Cable) that combines smaller
network into a large network.
Transmission Media
Media that carrying the network signal (cable/channel)
Connectivity Devices
Modems, repeaters, bridges, routers, switch, hub and etc.
•
Segment
It is a physical partitioning of network.
NETWORK TOPOLOGIES

Network topology is the layout pattern of
interconnections of the various elements (cable, nodes,
etc.) of a computer network.





Bus
Ring
Star
Hybrid
Mesh
Group Activities…
Hybrid???
Bus???
Ring???
Star???
Mesh???
BUS
Bayonet Neill–Concelman
(BNC connector)
Connect two or more computer using coaxial cable and
BNC connector.
 Terminator are installed on both ends of the cable.
 Without the terminator, the electrical signal that
represent the data would reached the end of cooper
wire and bounce back, causing errors on the network.
 Advantages : inexpensive to install, can easily add
more workstation.
 Disadvantages : If the cable break down, the network
is down, access time and network performance
degrade as devices are added to the network.

Bus Topology
RING
Computer are connected in a ring (circle).
 It has no beginning or end, so there is no need to
terminate the cable.
 Every device have an equal advantage in accessing
the media.
 Advantages : There are no collisions , no terminators
are needed, easy to locate and correct problems with
devices and cable.
 Disadvantages : requires more cable than a bus
network, a break in the cable brings the entire
network down.

Ring Topology
STAR
All computer are connected to a central point such as
hub or switch
 The most common topology used today
 Data on a star topology passes through the hub or
switch before continuing to its destination.
 Advantages : Cable failure will not disrupt the
network.
 Disadvantages : Single point of failure.

Star Topology
HYBRID
•
•
•
•
Combination of any two or more different topologies.
The most commonly used topologies are Star-Bus or
Star-Ring.
Advantages : If a computer fails, it will not affect the
rest of the network
Disadvantages : If the central component, or hub, that
attaches all computers in a star, fails, no computer
will be able to communicate.
MESH
All computer are connected to every other computer
on the network
 Rarely used on a Local Area Network (LAN)
 The topology of the Internet.
 Advantages : Very redundant. No disruption when
expanded.
 Disadvantages : Expensive. Requires a lot of cable and
network interface cards.

ADVANTAGES & DISADVANTAGES OF
TOPOLOGIES
Topology
Advantages
Disadvantages
Bus
Less cable
Easy to install
Network not working even
with 1 PC failed
Cable faulty, entire system
down
Difficult to troubleshoot
Least fault tolerance
Star
Inexpensive
Easy to troubleshoot
Easy to reconfigure
Low data rate
Moderately difficult to install
Require more cables
Ring
Almost no loss in signal
quality over network
Not that easy to install &
troubleshoot
Failure of single connection
can take down entire network
Mesh
Every PC connected to each
other
Most fault tolerance
Large amount of cables
Very expensive & difficult to
manage
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NETWORKING STANDARDS
ORGANIZATIONS
Organizations that set standards for networking:
 American National Standards Institute (ANSI)
 Electronic Industries Alliance (EIA) and
Telecommunication Industry Association (TIA)
 Institute of Electrical and Electronics Engineers (IEEE)
 International Organization for Standardization (ISO)
 International Telecommunication Union (ITU)
 Internet Society (ISOC)
 Internet Assigned Numbers Authority (IANA) and
Internet Corporation for Assigned Names and Numbers
(ICANN)
ORGANIZATIONS
AND
ASSOCIATIONS
Name
Type
Standards
Established
ITU-T
ITU
Telecommunication
Standardization Sector
(formerly CCITT)
one of the three Sectors
of the International
Telecommunication
Union
Standards covering all
fields of
telecommunications
Became ITU-T in
1992
IEEE
Institute of Electrical
and Electronics
Engineers
A non-profit, technical
professional association
Standards for the
computer and
electronics industry
1884
ISO
International
Organization for
Standardization
A network of the national
standards institutes of
157 countries
Promote the
development of
international standards
agreements
1947
IAB
Internet Architecture
Board
A committee; an advisory
body
Oversees the technical
and engineering
development of the
Internet
1979; first named
ICCB
IEC
International
Electrotechnical
Commission
Global organization
Standards for all
electrical, electronic,
and related technologies
1906
ANSI
American National
Standards Institute
Private, non-profit
organization
Seeks to establish
consensus among groups
1918
TIA/EIA
Telecommunications
Industry Association /
Electronic Industries
Alliance
Trade associations
Standards for voice and
data wiring for LANs
After the
deregulation of the
36
U.S. telephone
industry in 1984
SAFETY STANDARDS
OSHA - Occupational Safety and
Health Act
NEC - National Electrical Code
UL - Underwriters Laboratories
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PRINCIPLES OF NETWORKING
Sender
• The first of these elements is the message source, or sender. It
is the device which sends the data messages.
• Message sources are people, or electronic devices, that need
to communicate a message to other individuals or devices.
Destination
•The second element of communication is the destination, or
receiver, of the message.
•The destination receives the message and interprets it.
Source
•A third element, called a channel, provides the pathway over
which the message can travel from source to destination.
RULES OF COMMUNICATION IN
NETWORKING
 Identification of sender and receiver (establish a link)
 Agreed-upon medium or channel (face-to-face, telephone, letter,
photograph)-issue a command and command qualifier
 Appropriate communication mode (spoken, written, illustrated, interactive or
one-way)-acknowledgement of command
 Common language
 Grammar and sentence structure - dissection message
 Error Control and correction
Error detecting and recovering is one of the main functions of
communication protocol. It ensures that data is transmitted without any
error. It also solves the problem if an error is detected.
 Speed and timing of delivery-termination and transmission
 Ex:RS232 –handshaking concept
Protocols define the details of how the message is
transmitted, and delivered. This includes issues of:
 Message format
 Message size
 Timing
 Encapsulation
 Encoding
 Standard message pattern
MESSAGE ENCODING
•Encoding is the process of converting thoughts into the language,
symbols, or sounds, for transmission. Decoding reverses this process in
order to interpret the thought.
In computer communication
Messages sent across the network are first
converted into bits by the sending host.
Each bit is encoded into a pattern of sounds, light waves, or
electrical impulses depending on the network media over which the
bits are transmitted.
The destination host receives and decodes the signals
in order to interpret the message.
Message formatting


Message formats depend on the type of message and the
channel that is used to deliver the message.
Ex: The process of placing one message format (the letter)
inside another message format (the envelope) is called
encapsulation. De-encapsulation occurs when the process is
reversed by the recipient and the letter is removed from the
envelope.
MESSAGE FORMATTING(CONT.)



Each computer message is encapsulated in a specific
format, called a frame before it is send to network.
A frame acts like an envelope; it provides the address of the
intended destination and the address of the source host.
The format and contents of a frame are determined by the
type of message being sent and the channel over which it is
communicated.
MESSAGE SIZE
When long message is sent from one host to
another over a network, it is necessary to break
the message into smaller pieces.
 Each piece is encapsulated in a separate frame
with the address information, and is sent over
the network.
 At the receiving host, the messages are deencapsulated and put back together to be
processed and interpreted.

MESSAGE TIMING
People use timing to determine when to speak,
how fast or slow to talk, and how long to wait for
a response.
 Rules:
a) Access Method




Access Method determines when someone is able to send a
message.
If two people talk at the same time, a collision of
information occurs.
Hosts on a network need an access method to know when to
begin sending messages and how to respond when errors
occur.
MESSAGE TIMING (CONT.)

b) Flow Control




Timing also effects how much information can be sent
and the speed that it can be delivered.
In network communication, a sending host can transmit
messages at a faster rate than the destination host can
receive and process.
Source and destination hosts use flow control to
negotiate correct timing for successful communication.
c) Response Timeout

Hosts on the network also have rules that specify how
long to wait for responses and what action to take if a
response timeout occurs.
MESSAGE PATTERN

Unicast
A one-to-one message pattern
 Only a single destination for the message.


Multicast
One-to-many pattern
 Multicasting is the delivery of the same message to a
group of host destinations simultaneously.



The most complex type of message because they require a
means of identifying a set of specific devices to receive a
message.
Broadcast
If all hosts on the network need to receive the
message at the same time, a broadcast is used.
 One-to-all message pattern.

MESSAGE PATTERN(CONT.)
Unicast: 1-to-1
Multicast: 1-tomany
Broadcast: 1 to all
48
Networking fundamentals
LETS TRY
NETWORK INTERFACE CARDS
Most NICs are internal
PCMCIA slot
determining the speed and performance of a network
The three most common network interface connections are
Ethernet cards, LocalTalk connectors, and Token Ring cards.
50
provides the physical connection between the network and the
computer workstation.
51
Ethernet card.
From top to
bottom:
RJ-45, AUI
(Attachment Unit
Interface) , and BNC
connectors
LOCALTALK
Ethernet Cards
LocalTalk
Fast data transfer
(10 to 100 Mbps)
Expensive - purchased
separately
Slow data transfer
(23 Mbps)
Built into Macintosh
computers
Requires computer slot
No computer slot
necessary
Available for most
computers
Works only on
Macintosh computers
52
TOKEN RING CARDS
One visible difference is the type of connector on
the back end of the card.
Token Ring cards generally have a nine pin DIN
type connector to attach the card to the network
cable.
53
Token Ring network cards look similar to
Ethernet cards.
HARDWARE
54
WORKSTATIONS
A typical workstation is a computer that is configured with a
network interface card, networking software, and the appropriate
cables.
Workstations do not necessarily need floppy disk drives or hard
drives because files can be saved on the file server.
Almost any computer can serve as a network workstation.
55
All of the computers connected to the file server on a network are
called workstations.
SWITCH
In a star topology, twisted-pair wire is run from each
workstation to a central switch/hub.
Switches are:
• Usually configured with 8, 12, or 24 RJ-45 ports
• Often used in a star or star-wired ring topology
• Sold with specialized software for port management
• Also called hubs
• Usually installed in a standardized metal rack that also may store
net modems, bridges, or routers
56
a central connection point for cables from
workstations, servers, and peripherals
REPEATERS
57
The repeater
electrically
amplifies the signal
it receives and
rebroadcasts it.
Repeaters can be
separate devices or
they can be
incorporated into a
concentrator.
They are used when
the total length of
your network cable
exceeds the
standards set for
the type of cable
being used.
BRIDGES
A bridge monitors the information traffic on both sides of
the network.
The bridge manages the traffic to maintain optimum
performance on both sides of the network.
traffic cop at a busy intersection during rush hour
Bridges can be used to connect different types of cabling, or
physical topologies.
They must, however, be used between networks with the
same protocol.
58
A bridge is a device that allows you to segment a large
network into two smaller, more efficient networks.
ROUTERS
routers know
the addresses
of computers,
bridges, and
other routers
on the
network.
Routers can:
59
super
intelligent
bridge
Routers
select the
best path to
route a
message,
based on
the
destination
address and
origin.
Direct signal
traffic efficiently
Route messages
between any two
protocols
Route messages
between linear bus,
star, and star-wired
ring topologies
Route messages
across fiber optic,
coaxial, and twistedpair cabling
GATEWAYS
associated with both a router, which use headers and forwarding
tables to determine where packets are sent, and a switch, which
provides the actual path for the packet in and out of the gateway.
◘ In homes, the gateway is the ISP that connects the user to the
internet.
60
◘ A node on a network that serves as an entrance to another
network.
◘ In enterprises, the gateway is the computer that routes the
traffic from a workstation to the outside network that is serving
the Web pages.
◘ The gateway node often acts as a proxy server and a firewall