Computer network

Unit – 1
What is computer?
A computer is an electronic device that manipulates information or
data. It has the ability to store, retrieve and process data. we already
know that you can use a computer to type documents, send
email, play games, and browse the Web. We can also use it to edit or
create spreadsheets, presentations, and even videos.
The basic parts without which a computer cannot work are as
follows:
o Processor: It executes instructions from software and hardware.
o Memory: It is the primary memory for data transfer between the
CPU and storage.
o Motherboard: It is the part that connects all other parts or
components of a computer.
o Storage Device: It permanently stores the data, e.g., hard drive.
o Input Device: It allows you to communicate with the computer or
to input data, e.g., a keyboard.
o Output Device: It enables you to see the output, e.g., monitor.

Computers are divided into different types based on different

criteria. Based on the size, a computer can be divided into five
types:

1. Micro Computer
2. Mini Computer
3. Mainframe Computer
4. Super Computer
5. Workstations

The characteristics of the computer system are as follows −

Speed

A computer works with much higher speed and accuracy compared to

humans while performing mathematical calculations. Computers can
process millions (1,000,000) of instructions per second. The time taken
by computers for their operations is microseconds and nanoseconds.

Accuracy

Computers perform calculations with 100% accuracy. Errors may occur

due to data inconsistency or inaccuracy.

Diligence

A computer can perform millions of tasks or calculations with the same

consistency and accuracy. It doesn’t feel any fatigue or lack of
concentration. Its memory also makes it superior to that of human
beings.

Versatility

Versatility refers to the capability of a computer to perform different kinds

of works with same accuracy and efficiency.

Reliability

A computer is reliable as it gives consistent result for similar set of data

i.e., if we give same set of input any number of times, we will get the
same result.

Automation
Computer performs all the tasks automatically i.e. it performs tasks
without manual intervention.

Memory

A computer has built-in memory called primary memory where it stores

data. Secondary storage are removable devices such as CDs, pen
drives, etc., which are also used to store data.

6. Print Page

Charles Babbage is the Father of Computers. Charles Babbage

(1791-1871) was an extraordinarily talented scientist,
mathematician, economist and engineer.

Computer network

A computer network is defined as a system that connects two or

more computing devices for transmitting and sharing information.

Uses of Computer Networks

 Communicating using email, video, instant messaging, etc.
 Sharing devices such as printers, scanners, etc.
 Sharing files.
 Sharing software and operating programs on remote systems.
 Allowing network users to easily access and maintain information.

computer network is a group of computers linked to each other that

enables the computer to communicate with another computer and share
their resources, data, and applications.

A computer network can be categorized by their size. A computer

network is mainly of four types:
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o LAN(Local Area Network)

o PAN(Personal Area Network)
o MAN(Metropolitan Area Network)
o WAN(Wide Area Network)

LAN(Local Area Network)

o Local Area Network is a group of computers connected to each
other in a small area such as building, office.
o LAN is used for connecting two or more personal computers
through a communication medium such as twisted pair, coaxial
cable, etc.
o It is less costly as it is built with inexpensive hardware such as
hubs, network adapters, and ethernet cables.
o The data is transferred at an extremely faster rate in Local Area
Network.
o Local Area Network provides higher security.
PAN(Personal Area Network)
o Personal Area Network is a network arranged within an individual
person, typically within a range of 10 meters.
o Personal Area Network is used for connecting the computer
devices of personal use is known as Personal Area Network.
o Thomas Zimmerman was the first research scientist to bring the
idea of the Personal Area Network.
o Personal Area Network covers an area of 30 feet.
o Personal computer devices that are used to develop the personal
area network are the laptop, mobile phones, media player and play
stations.

There are two types of Personal Area Network:

o Wired Personal Area Network

o Wireless Personal Area Network
Wireless Personal Area Network: Wireless Personal Area Network is
developed by simply using wireless technologies such as WiFi,
Bluetooth. It is a low range network.

Wired Personal Area Network: Wired Personal Area Network is

created by using the USB.

MAN(Metropolitan Area Network)

o A metropolitan area network is a network that covers a larger
geographic area by interconnecting a different LAN to form a larger
network.
o Government agencies use MAN to connect to the citizens and
private industries.
o In MAN, various LANs are connected to each other through a
telephone exchange line.
o The most widely used protocols in MAN are RS-232, Frame Relay,
ATM, ISDN, OC-3, ADSL, etc.
o It has a higher range than Local Area Network(LAN).

Uses Of Metropolitan Area Network:

o MAN is used in communication between the banks in a city.
o It can be used in an Airline Reservation.
o It can be used in a college within a city.
 o It can also be used for communication in the military.

WAN(Wide Area Network)

o A Wide Area Network is a network that extends over a large
geographical area such as states or countries.
o A Wide Area Network is quite bigger network than the LAN.
o A Wide Area Network is not limited to a single location, but it spans
over a large geographical area through a telephone line, fibre optic
cable or satellite links.
o The internet is one of the biggest WAN in the world.
o A Wide Area Network is widely used in the field of Business,
government, and education.

Examples Of Wide Area Network:

o Mobile Broadband: A 4G network is widely used across a region
or country.
o Last mile: A telecom company is used to provide the internet
services to the customers in hundreds of cities by connecting their
home with fiber.
 o Private network: A bank provides a private network that connects
the 44 offices. This network is made by using the telephone leased
line provided by the telecom company.

Advantages Of Wide Area Network:

Following are the advantages of the Wide Area Network:

o Geographical area: A Wide Area Network provides a large

geographical area. Suppose if the branch of our office is in a
different city then we can connect with them through WAN. The
internet provides a leased line through which we can connect with
another branch.
o Centralized data: In case of WAN network, data is centralized.
Therefore, we do not need to buy the emails, files or back up
servers.
o Get updated files: Software companies work on the live server.
Therefore, the programmers get the updated files within seconds.
o Exchange messages: In a WAN network, messages are
transmitted fast. The web application like Facebook, Whatsapp,
Skype allows you to communicate with friends.
o Sharing of software and resources: In WAN network, we can
share the software and other resources like a hard drive, RAM.
o Global business: We can do the business over the internet
globally.
o High bandwidth: If we use the leased lines for our company then
this gives the high bandwidth. The high bandwidth increases the
data transfer rate which in turn increases the productivity of our
company.

Disadvantages of Wide Area Network:

The following are the disadvantages of the Wide Area Network:

o Security issue: A WAN network has more security issues as

compared to LAN and MAN network as all the technologies are
combined together that creates the security problem.
 o Needs Firewall & antivirus software: The data is transferred on
the internet which can be changed or hacked by the hackers, so
the firewall needs to be used. Some people can inject the virus in
our system so antivirus is needed to protect from such a virus.
o High Setup cost: An installation cost of the WAN network is high
as it involves the purchasing of routers, switches.
o Troubleshooting problems: It covers a large area so fixing the
problem is difficult.

Network Topology
Topology defines the structure of the network of how all the components
are interconnected to each other.

Bus Topology

o The bus topology is designed in such a way that all the stations
are connected through a single cable known as a backbone cable.
o Each node is either connected to the backbone cable by drop
cable or directly connected to the backbone cable.
o When a node wants to send a message over the network, it puts a
message over the network. All the stations available in the network
will receive the message whether it has been addressed or not.
o The configuration of a bus topology is quite simpler as compared
to other topologies.
o The backbone cable is considered as a "single lane" through
which the message is broadcast to all the stations.
Advantages of Bus Topology
 If N devices are connected to each other in a bus topology, then the
number of cables required to connect them is 1, known as backbone
cable, and N drop lines are required.
 Coaxial or twisted pair cables are mainly used in bus-based
networks that support up to 10 Mbps.
 The cost of the cable is less compared to other topologies, but it is
used to build small networks.
 Bus topology is familiar technology as installation and
troubleshooting techniques are well known.
Disadvantages of Bus Topology
 A bus topology is quite simpler, but still, it requires a lot of cabling.
 If the common cable fails, then the whole system will crash down.
 If the network traffic is heavy, it increases collisions in the network.
Adding new devices to the network would slow down networks.
 Security is very low.
Ring Topology
o Ring topology is like a bus topology, but with connected ends.
o The node that receives the message from the previous computer
will retransmit to the next node.
o The data flows in one direction, i.e., it is unidirectional.
o The data flows in a single loop continuously known as an endless
loop.
o It has no terminated ends, i.e., each node is connected to other
node and having no termination point.
o The data in a ring topology flow in a clockwise direction.

Advantages of Ring Topology

 The data transmission is high-speed.
 The possibility of collision is minimum in this type of topology.
 Cheap to install and expand.
 It is less costly than a star topology.
Disadvantages of Ring Topology
 The failure of a single node in the network can cause the entire
network to fail.
 Troubleshooting is difficult in this topology.
 The addition of stations in between or the removal of stations can
disturb the whole topology.
 Less secure.

3) Star Topology

 Star topology is an arrangement of the network in which every

node is connected to the central hub, switch or a central computer.
 The central computer is known as a server, and the peripheral
devices attached to the server are known as clients.
 Coaxial cable or RJ-45 cables are used to connect the computers.
 Hubs or Switches are mainly used as connection devices in
a physical star topology.
 Star topology is the most popular topology in network
implementation.

Advantages of Star Topology

 If N devices are connected to each other in a star topology, then the
number of cables required to connect them is N. So, it is easy to set
up.
 Each device requires only 1 port i.e. to connect to the hub, therefore
the total number of ports required is N.
 It is Robust. If one link fails only that link will affect and not other
than that.
 Easy to fault identification and fault isolation.
 Star topology is cost-effective as it uses inexpensive coaxial cable.
Disadvantages of Star Topology
 If the concentrator (hub) on which the whole topology relies fails, the
whole system will crash down.
 The cost of installation is high.
 Performance is based on the single concentrator i.e. hub.

Mesh topology

o Mesh technology is an arrangement of the network in which

computers are interconnected with each other through various
redundant connections.
o There are multiple paths from one computer to another computer.
o It does not contain the switch, hub or any central computer which
acts as a central point of communication.
o The Internet is an example of the mesh topology.
o Mesh topology is mainly used for WAN implementations where
communication failures are a critical concern.
o Mesh topology is mainly used for wireless networks.

o
Advantages of Mesh Topology
 Communication is very fast between the nodes.
 Mesh Topology is robust.
 The fault is diagnosed easily. Data is reliable because data is
transferred among the devices through dedicated channels or links.
 Provides security and privacy.
Disadvantages of Mesh Topology
 Installation and configuration are difficult.
 The cost of cables is high as bulk wiring is required, hence suitable
for less number of devices.
 The cost of maintenance is high.

Data transmission media

Transmission media also known as a communication channel is the
physical path between the sender and receiver through which data bits
are transmitted from the source to the destination.
In simple words, when data is transferred from one device to another, it
is transmitted through a medium or communication channel to reach its
destination. This communication channel is referred as transmission
media.
The transmission media is nothing but the physical medium over which
communication takes place in computer network.

Wired transmission media

It is defined as the physical medium through which the signals are
transmitted. It is also known as Bounded media.

Twisted pair:
Twisted pair is a physical media made up of a pair of cables twisted with
each other. A twisted pair cable is cheap as compared to other
transmission media. Installation of the twisted pair cable is easy, and it is
a lightweight cable. The frequency range for twisted pair cable is from 0
to 3.5 KHz.

A twisted pair consists of two insulated copper wires arranged in a

regular spiral pattern.

The degree of reduction in noise interference is determined by the

number of turns per foot. Increasing the number of turns per foot
decreases noise interference.

Types of Twisted pair:

Unshielded Twisted Pair:

An unshielded twisted pair is widely used in telecommunication.

Advantages Of Unshielded Twisted Pair:

o It is cheap.
o Installation of the unshielded twisted pair is easy.
o It can be used for high-speed LAN.

Disadvantage:

o This cable can only be used for shorter distances because of

attenuation.
Shielded Twisted Pair

A shielded twisted pair is a cable that contains the mesh surrounding the
wire that allows the higher transmission rate.

Characteristics Of Shielded Twisted Pair:

o The cost of the shielded twisted pair cable is not very high and not
very low.
o An installation of STP is easy.
o It has higher capacity as compared to unshielded twisted pair
cable.
o It has a higher attenuation.
o It is shielded that provides the higher data transmission rate.

Disadvantages

o It is more expensive as compared to UTP and coaxial cable.

o It has a higher attenuation rate

Coaxial Cable

o Coaxial cable is very commonly used transmission media, for

example, TV wire is usually a coaxial cable.
o The name of the cable is coaxial as it contains two conductors
parallel to each other.
o It has a higher frequency as compared to twisted pair cable.
o The inner conductor of the coaxial cable is made up of copper, and
the outer conductor is made up of copper mesh. The middle core
is made up of non-conductive cover that separates the inner
conductor from the outer conductor.
o The middle core is responsible for the data transferring whereas
the copper mesh prevents from the EMI(Electromagnetic
interference).
Coaxial cable is of two types:

1. Baseband transmission: It is defined as the process of

transmitting a single signal at high speed.
2. Broadband transmission: It is defined as the process of
transmitting multiple signals simultaneously.

Advantages Of Coaxial cable:

o The data can be transmitted at high speed.

o It has better shielding as compared to twisted pair cable.
o It provides higher bandwidth.

Disadvantages Of Coaxial cable:

o It is more expensive as compared to twisted pair cable.

o If any fault occurs in the cable causes the failure in the entire
network.

Fibre Optic

o Fibre optic cable is a cable that uses electrical signals for

communication.
o Fibre optic is a cable that holds the optical fibres coated in plastic
that are used to send the data by pulses of light.
o The plastic coating protects the optical fibres from heat, cold,
electromagnetic interference from other types of wiring.
o Fibre optics provide faster data transmission than copper wires.

Diagrammatic representation of fibre optic cable:

Basic elements of Fibre optic cable:

o Core: The optical fibre consists of a narrow strand of glass or

plastic known as a core. A core is a light transmission area of the
fibre. The more the area of the core, the more light will be
transmitted into the fibre.
o Cladding: The concentric layer of glass is known as cladding. The
main functionality of the cladding is to provide the lower refractive
index at the core interface as to cause the reflection within the core
so that the light waves are transmitted through the fibre.
o Jacket: The protective coating consisting of plastic is known as a
jacket. The main purpose of a jacket is to preserve the fibre
strength, absorb shock and extra fibre protection.

Following are the advantages of fibre optic cable over copper:

o Greater Bandwidth: The fibre optic cable provides more

bandwidth as compared copper. Therefore, the fibre optic carries
more data as compared to copper cable.
o Faster speed: Fibre optic cable carries the data in the form of
light. This allows the fibre optic cable to carry the signals at a
higher speed.
o Longer distances: The fibre optic cable carries the data at a
longer distance as compared to copper cable.
o Better reliability: The fibre optic cable is more reliable than the
copper cable as it is immune to any temperature changes while it
can cause obstruct in the connectivity of copper cable.
o Thinner and Sturdier: Fibre optic cable is thinner and lighter in
weight so it can withstand more pull pressure than copper cable.
o
 wireless transmission

o An unguided transmission transmits the electromagnetic waves

without using any physical medium. Therefore it is also known
as wireless transmission.
o In unguided media, air is the media through which the
electromagnetic energy can flow easily.

Radio waves

o Radio waves are the electromagnetic waves that are transmitted in

all the directions of free space.
o Radio waves are omnidirectional, i.e., the signals are propagated
in all the directions.
o The range in frequencies of radio waves is from 3Khz to 1 khz.
o In the case of radio waves, the sending and receiving antenna are
not aligned, i.e., the wave sent by the sending antenna can be
received by any receiving antenna.
o An example of the radio wave is FM radio.
Advantages Of Radio transmission:

o Radio transmission is mainly used for wide area networks and

mobile cellular phones.
o Radio waves cover a large area, and they can penetrate the walls.
o Radio transmission provides a higher transmission rate.

Disadvantages

1. Radio wave are not effective in bad weather conditions.

2. They are less secure as they can travel large distance.

Microwave
Microwave are a line of sight transmission,meaning both the antennas
sending and receiving should be properly aligned.

Also, the distance covered by the signal is directly proportional to the

height of antenna. Basically we used microwaves in mobile phones
communication and television distribution.

Advantage
1. microwave is a very fast way of communication that can carry 25000
voice channels at the same time.
2. no need of digging and spreading wire.
Disadvantages
1. Microwave are the first expense, their installation and
maintenance are every expensive.
 2. Microwave are also not very effective in bad weather
condition.

Infrared
Infrared is used for short range communication like TV remotes,mobile
phones, personal computer,etc. In science,the infrared is part of a
spectrum that is not visible to the human eye. The limitation of infrared
rays is that they cannot penetrate any obstacles and can only use for
short range.
Advantages

1. Infrared is one of the secure wireless communication medium as it

is used for short range.

2. As compared to other wireless mediums, infrared is quite

inexpensive and this is some reason it is used in many electronic
devices,

Disadvantages

1. Infrared wave can only be used in short range communication.

They cannot penetrate ant obstacles like walls or any building.