1 Computer Network

Topics Covered
•Communication •Computer Network •Types of Network •Network Hardware •Communication
Channels •Network Architecture •Network Topology •Protocol

Communication
Communication is important for people to share their views and
opinions. It is a process in which two or more people share their
knowledge, information, resources and expertise among themselves.
Communication involves a sender transmitting an idea, information, or
feeling to a receiver. Effective communication occurs only if the receiver
understands the exact information that the sender intends to give.

COMPUTER COMMUNICATION
Computers were stand-alone devices when they were first introduced. With the rapid increase
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in the uses of computers, the manufacturers began to design hardware and software that
would allow the computers to communicate with one another.
Computer communication is described as a process in which one computer transfers data,
instructions, and information to another computer(s). Earlier, only large computers had
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communication capabilities. Today, even the smaller computers and devices can communicate
directly with one another, with hundreds of computers on a company network, or with millions
of other computers around the globe—often via Internet. Some communications involve cables
and wires; others are sent wirelessly through the air. For successful computer communication,
you need the following components:
SENDER: It is a sending device that initiates to send data, instructions or information. It can
be a computer or mobile device.
COMMUNICATION CHANNEL OR TRANSMISSION MEDIA: It is a medium on which the data,
instructions, or information can travel. It can be cables, microwave stations, or satellites. IT PLANET - 8 (GIGABYTE)

RECEIVER: It is a receiving device that accepts the transmission of data, instructions, or

information. It can be a computer or mobile device.
PROTOCOL: It is a set of rules that outlines characteristics of how two devices communicate.
Without protocol, two devices may be connected, but cannot transfer or exchange the data. A
protocol may define data format, coding schemes, and the sequence in which data transfers
among devices. For example, a person who knows only English language cannot communicate
with another who knows only Hindi language. For communication between two persons, the
knowledge of same language is a must.

Protocol
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Communication Channel

Sender Receiver
 Computer Network
A computer network is a collection of computers and
devices connected by communication channels. People
connect computers to a network for a variety of reasons,
including the ability to share hardware, software, data
and information, as well as to facilitate communication. Computer Network
A computer network can be as small as two computers
connected to each other, or it may be spread over
different parts of a city, or covering the whole world.

NEED FOR A NETWORK

You can share resources such as hardware devices, software programs, data and information
with the help of a network. Sharing resources saves time and money.
Data And Information Sharing
In a network environment, any authorized user can use a
computer to access data and information stored on other
computers in the network. A large company, for example
might store a database of customer information on the
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hard disk of the server. Any authorized person can connect
to the network and can access this database. The capability
of providing access, and storage of data and information on
shared storage devices is an important feature of network.
Data and Information Sharing
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Hardware Sharing
In a network environment, each computer on a
network can access and use hardware available on the
network. Suppose, there are a number of personal
HUB
computers on a network and each one needs to use a
laser printer. If the personal computers and the laser
printer are connected in a network, each personal
computer user can access the laser printer over the
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Hardware Sharing network, whenever he or she needs it.

Software Sharing
Network lets people gain access to software
programs stored on a central computer. Using their
own computers, individuals can gain access to and
work with these programs. By sharing a program, a
company can avoid having to install a copy of the disc
PROGRAM
CD-ROM

program on each person's computer separately. Software Sharing

Transfer Funds
6 Network allows users to exchange money from one bank account to another via Electronic Fund
Transfer (EFT). Both business houses and consumers use EFT. Examples include, use of credit and
debit cards, direct deposit of funds into bank, online banking, and online bill payment.
NETWORK USER
When your computer is a part of a network, where two or more computers are connected
using a cable or some other communication channels, you can become a network user and
can share files, folders, and computer hardware such as printers attached from one computer
to other computers. These usual resources are referred to as local resources.

SERVER AND WORKSTATIONS

Powerful computers responsible for distributing files to network users are referred to as
servers. Other less powerful computers connected to a server are called workstations. Each
workstation contributes equally in the network and is often called peer.

Types of Network
There are many types of network: Local Area Network (LAN), Metropolitan Area Network
(MAN), Wide Area Network (WAN) and Personal Area Network (PAN). Each one of these is
discussed below:

LAN (Local Area Network) P

A local area network (LAN) is a network that
connects the computers and the devices in a
limited geographical area, such as home, school
computer laboratory, office building or closely
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positioned group of buildings. These computers
are usually within 100 to 300 meters away from LAN
each other.
If you have a home network with two or more
computers, or if you are at your school where
more than 20 computers are connected to each
other, then you are on a LAN.

Each computer or device on the network is a node. Often, the nodes are connected to the IT PLANET - 8 (GIGABYTE)
LAN via cables. LAN can either work with cables and hubs or wirelessly. A Wireless Local Area
Network is also known as WLAN.

WAN (Wide Area Network)

A wide area network (WAN) spans over a large
geographical area, such as an entire city, region, or
even an entire country or all over the world. Two
or more LANs that are relatively far apart are
typically connected by WAN so that users and
computers in one location can communicate with
users and computers in other locations. The 7
WAN
Internet is the world’s largest WAN.
 MAN (Metropolitan Area Network)
MAN is a network that connects the Local Area Networks in a metropolitan area such as a city
or a town. A MAN typically includes one or more LANs but covers a smaller geographical area
than a WAN. Telephone companies, cable television operators, and other organizations use
MAN network.

MAN

PAN (Personal Area Network)

A personal area network (PAN) is a network that
connects personal devices like laptop, smartphones,
digital cameras, printers, etc. in an individual’s workspace
using wired and wireless technology. A PAN may connect
devices through a router using network cables or by
using Bluetooth or Wi-Fi technology. You can transfer
P PAN
files and songs from laptop to a smartphone using PAN.

Network Hardware
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Network hardware consists of physical devices used on a network. All networks need network
hardware to function.

COMPUTER
The most important job of a network is to link computers together.
When computers are linked, the people using the computers can work
more efficiently. Computers connected to a network do not have to
be the same type. For example, a network could contain desktop
computers, such as IBM-compatible and Macintosh or portable
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computers, such as notebooks and Tablet PCs.

NETWORK INTERFACE CARD (NIC)

An expansion card is used to provide network access to a computer or
other device, such as a printer. Network interface cards mediate
between the computer and the physical media such as cables over
which data travels.
CONNECTOR
A connector is a device that joins two networks together. The most common connectors are:
HUB: A hub offers a central location where all the cables on a network meet. It allows you to
8 connect multiple computers to a single network. It also provides the connection for all the
computers on a network, so that they can exchange data. Many types of network structures are
now using hubs as the primary method of connecting computers.
SWITCH: A switch is a device that provides a central point for cables in
a network. A switch receives data from many directions and then
forwards it to one or more destinations. A switch is considered more
advanced than a hub because switch sends the data to a device that
needs or requests for it. Switches can be used in place of hubs.

ROUTER: A router is a device that connects multiple computers

together and transmits data to its correct destination on a network
through a process known as routing. A router acts as a junction
between two or more networks like LAN and WAN to transfer data
packets among them. For example, it is used to connect your home
network (LAN) with the Internet (WAN).

CABLES
A network cable plugs into the NIC (Network Interface
Card) at the back of each computer on the network.
Information, shared files, and other network data travel
through the network cables. A fiber metal or fiber-optic
cable is used to connect computers and other devices on
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a network. These cables are insulated with special
material such as plastic or rubber.
RESOURCE
Any part of a computer system or a network such as a disk drive, printer, or
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memory that can be allotted to a program or a process, while it is running,
is a resource.

Communication Channels
All networks are linked to each other through communication channels.
These are the medium on which the data, instructions, or information can
travel. When you send data from a computer or mobile device, the signal IT PLANET - 8 (GIGABYTE)
that carries the data may travel over various transmission media. Most
commonly used media are physical and wireless.

PHYSICAL TRANSMISSION MEDIA

Physical transmission media use wire or cable to send communications signals. LANs often use
physical transmission media. There are three main types of physical transmission media. They
are twisted pair cable, coaxial cable and fiber optic cable.

Twisted-Pair Cable
Twisted-pair cable consists of one or more twisted-pair wires bundled
together. Each twisted-pair wire consists of two separate insulated copper 9
wires that are twisted together and is color-coded for identification.
Landline phone networks and LANs often use twisted-pair cable.
Twisted-Pair Cable
 Coaxial Cable
Coaxial cable consists of a single copper wire surrounded by at least
three layers. The first one is an insulating material, the second is a
wire mesh, and the third is a plastic outer coating. On coaxial cables,
data travels through a copper wire. Cable TV network wiring uses
coaxial cable. Coaxial Cable

Fiber-Optic Cable
The core of a fiber-optic cable consists of hundreds of thin
strands of glass or plastic that use light to transmit signals..
Inside the fiber-optic cable, an insulating glass cladding and a
protective coating surrounds each optical fiber. Many big
companies use fiber-optic cables in high-traffic networks.
Fiber-Optic Cable

WIRELESS TRANSMISSION MEDIA

Wireless transmission media send communication signals through the air. Many people use this
media because it is more convenient than installing cables. Types of wireless transmission
media used in communications include infrared, broadcast radio, cellular radio, microwaves,
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and communication satellites.

Infrared (IR)
Infrared (IR) is a wireless transmission medium that sends signals using infrared light waves.
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Infrared systems use the same technology as household remote controls. It is also used with
computers and devices like cordless keyboards and mouses.

Broadcast Radio
Broadcast radio is a wireless transmission
medium that distributes radio signals through the
air over long distances, such as between cities,
regions, and countries, and short distances, such
as within an office or home. Bluetooth and Wi-Fi Downloading
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Files
communication technologies use broadcast radio
signals.

Broadcast Radio
Cellular Radio
Cellular radio is a wireless transmission medium that is used for mobile communications. It is
a form of broadcast radio. Several categories of cellular radio transmissions exist, such as 1G
(first generation of cellular transmissions), 2G, 3G, 4G and 5G.

Wi-Fi
10 Wi-Fi is short for wireless fidelity, which is a popular wireless networking technology
that uses radio waves to provide wireless high-speed network connections.
Microwave Earth-based dish

Microwaves provide a high-speed wireless signal

transmission. It involves sending signals from one
microwave station to another. A microwave station
is an earth-based dish that contains the antenna
and other equipment necessary for microwave
communications. Microwave transmission is used
in wide-open areas, such as deserts or lakes.
Microwave

Satellite Communication Satellite

A communication satellite is a space station that
receives microwave signals from an earth-based
station, amplifies (strengthens) the signals, and
broadcasts the signals back over a wide area to
any number of earth-based stations. Applications
such as television and radio broadcasts, weather
P forecasting, videoconferencing, GPS, and Internet
Communication Satellite connections use communication satellites.

Network Architecture
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The network architecture refers to how computers are organised and how tasks are allocated
among these computers. It is mainly categorized into two major types:

PEER-TO-PEER NETWORK Computer

A network of two or more computers that uses
the same type of programs to communicate and
share data is called a Peer-to-Peer network. Each
Computer
computer or peer is considered equal in terms of IT PLANET - 8 (GIGABYTE)
responsibilities, and each acts as a server to PEER
others in the network. Peer-to-Peer networks TO
PEER
work best in a small environment. These
networks are designed primarily for small to
medium local area networks. One should not use
Printer
peer-to-peer network if more than 10 computers
Computer
are to be connected together.

CLIENT/SERVER NETWORK
A network in which one or more computers are designated as server(s), and the other 11
computers on the network, called clients, can request services from the server, is known as
Client/Server Network.
 Server
A server, sometimes called the host computer, controls access to the hardware and software
on the network and provides a centralized storage area for programs, data, and information.
When a user connects to the server, then applications, files, printers, etc. become available.
Some servers perform a specific task and are called dedicated
servers.
For example, a file server stores and manages files.
A print server manages printers and documents being printed.
A database server stores and provides access to a database.
A network server manages network traffic.
A web server is a computer that delivers requested web pages
to your computer.

Client
A Client is a computer system that relies on a
server for all the resources. For example, a
server might store a network version of word
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processing program. Every client on the
network can access the word processing
program on the server. Client/Server Network
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Network Topology
In networking, the term topology refers to the layout structure of connected computers and
devices on a network. A network topology has two levels, i.e., physical and logical.
The physical level refers to the parts of a network that physically exist, such as computers,
cables and connectors. This level specifies where the computers on a network are located and
how all the parts of the network are connected. Cables are the most popular transmission
media to transfer information on a network.
The logical level refers to the path that the information takes to reach its destination on a
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network. The logical level of a network depends on many factors, such as the applications used
and the volume of information transferred over the network. Computers share information by
exchanging electrical signals. Signals are sent via the transmission medium that connects the
computers.

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PHYSICAL LOGICAL

Bus, Star and Ring are the three main types of network topologies.
BUS TOPOLOGY
In this kind of topology, all the computers and their devices are connected to one single cable
called the Bus. This Bus network is also called linear network. It transmits data, instructions
and information in both directions.

Only one computer can communicate at a time in bus topology. A device, wanting to
communicate with another device on the network, sends a broadcast message onto the wire that
all other devices can see, but only the intended recipient accepts and processes the message.

Sending... Receiving...

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In this topology, computer system can be easily added or removed from the network. The
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failure of single node does not affect the performance of the remaining network.

STAR TOPOLOGY
In this kind of topology, connector called a hub is placed at the centre to which all the other
nodes are connected. All the information that is transferred from one computer to another on
the network, passes via the hub. Star network is one of the most common computer network
topologies, because, it is easy to add or remove nodes. A failure in any star network cable will
only take down network access of one computer and not the entire network. When the hub IT PLANET - 8 (GIGABYTE)
fails, then the network also fails.

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Star Topology
 RING TOPOLOGY
In ring topology, nodes are connected in a circular chain
in which each node is connected to the next one and
the last node is connected to the first one. Every device
has exactly two neighbours for communication purpose.
All messages travel through a ring in the same direction
(either "clockwise" or "counter clockwise"). Ring Topology
In this, if one node fails, the whole network goes off.
Computers are usually located close together. A ring
network is easy to set up because the computers are
attached to a single ring of cable and no central
connector, such as hub, is required. There is no
beginning or end in a ring network.

Protocol
A protocol is a set of rules that outlines characteristics of how two devices communicate over
the network. There are different protocols for different operations on the Internet.
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HTTP (Hypertext Transfer Protocol): This is a set of rules that defines how pages transfer on
the Internet and what actions web servers and browsers should take in response to various
commands. Many web addresses begin with http:// as the protocol.
FTP (File Transfer Protocol): This is a set of rules that allows file uploading to and downloading
from other computers on the Internet. Uploading is the process of transferring files from your
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computer to a server on the Internet. Downloading is the process of transferring files from a
server on the Internet to your computer. Web page developers often use FTP to upload their
webpages to a web server.
TCP/IP (Transmission Control Protocol/Internet Protocol): This is a network protocol that
defines how the information or messages are routed from one end of a network to the other,
ensuring the data arrives correctly. It has been used as network standard for Internet
communications.
POP3 (Post Office Protocol version 3): This is an email protocol that stores email messages on a
mail server and allows the user to view, access and manipulate the message after downloading
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or storing it on their computer. Once the messages are downloaded onto your computer, they
are deleted from the mail server. This means that after the email is downloaded, it can only be
accessed using the same computer. If you try to access your email from a different device, the
messages that have been previously downloaded will not be available to you.
IMAP (Internet Message Access Protocol): This is also an email protocol that stores email
messages on a mail server and allows the user to view, access and manipulate the messages on
the mail server from their computer. When you read an email message using IMAP, you are not
actually downloading or storing it on your computer; instead, you are reading it on the mail
server from your computer. As a result, if you try to access your email from a different device,
the same messages will be available to you.
14 SMTP (Simple Mail Transfer Protocol): This is an email protocol for sending email messages
across the Internet. SMTP was originally developed in the early 1980s and remains one of the
most popular protocols in use worldwide. Most email software programs use SMTP for sending
mails and use either the POP3 or IMAP protocol for receiving mails.