Chapter 2: Networking

Concept of communication:
The exchange of data and information between sender and receiver through any given medium
following a common rule is known as communication. So, telecommunication is the art of
communicating at a distance. Telephone, radio and television are the main and popular media
of tele-communication.

After the invention of microcomputers in 1980's, people started using computers and telephone
(Internet) lines to send and receive data from one place to another. The use of computers to
send and receive data from one location to another is known as data communication.

Basic elements of communication

• Sender (source) which creates the message to be transferred.
• Medium which carry message.
• Receiver (sink) which receives the message
• Data: The information or message to be carried.
• Protocol: Rules to carry the data.

Communication System

Modes of communication:
Based on the flow of direction of communication. Communication has 3 modes.

Simplex: It is unidirectional mode of communication on which sender always sends the data and receiver
receives it. In this mode receiver never sends the data. For example, radio, television

Half duplex: It is the bidirectional mode of communication in which sender can send the data and receives the
data as well and vice versa but only one at a time that means sender is not allowed to receive data while it is
sending data. For eg, walkie talkie

Full duplex: It is the bidirectional mode of communication in which both sender and receiver can send and
receives data simultaneously. For eg, mobile phones, telephone etc.
Figure: Communication Mode

Computer Network:
From the very beginning there is an emerging trend of making communication. People use computer to share
different data and information at different location. Thus, the group of computer Interconnected with each
other through any type of transportation media that may be either wired on wireless in order to share different
hardware software and other resources is known as computer network. The concept of connected computer
sharing resources is called Networking. We use different bounded media like twisted pair cable , coaxial cable
and fiberoptics cable or unbounded media like microwave, radio wave, infrared , satellites to establish
connection between different computers at different location

Advantages of computer network

Hardware sharing: Using computer network expensive hardware devices can be shared among multiple
number of computers. For example, in cyber one printer can be shared among multiple number of computers
which help to save money as well time.

Software sharing: Similarly, software also can be shared among computer n a network which helps to access
application program from any remote location.

Centralized control and management: Network provides the centralized control and management that means
every other computer in a network are centrally connected with server which controls and monitor all the
activities within the network. This helps to ensure security Speedy and fast effective communication: Since all
the computer in a Network are interconnected with each other, one can sends and receives messages within
the computer in just few seconds.

Backup and Recovery: Since all the computer are connected with server, it helps to maintain backup at periodic
interval. that means keeping extra copy so that data and the formation can be recover when lost accidentally
or intentionally.

Flexible Access: In a network a computer can easily access files from other computer he/she has authority or
privilege to access/use.
Work group computing: Network allows different user to work in group that means; different user can work
on o single task by dividing work load.

Disadvantage of computer network

Virus Transfer: Since computer Network allows data and information to be transferred , still there remains the
possibility of virus transfer and other malicious program.

Less reliable: Since computer in a network are inter connected with each other performance of one computer
may affect performance of another computer. That means if one computer start malfunctioning in a network
than it may affect another computers in a network.

Security: Computer network is a group of computer interconnected with each other. That means, one
computer in a network can access data and information from other computer. Since there may be also
possibility of unauthorized access there exist security issue in a network.

Expensive: Creating a network among different computer is itself a complex task or job. We may need different
inter networking devices and others special devices and other to establish a network. Buying all the devices,
cables and equipment may be expensive.

Need Technical Manpower: Since establishing a network is a Technical job we need a technical manpower in
order to establish and trouble shoot a network. Hiring technical manpower may be expensive.

Type of Network:
On the basis of geographical area covered

1. LAN
2. MAN
3. WAN
On the basis of network architecture
1. Peer-to- peer
2. Client server

1) LAN: LAN stands for Local Area Network. It is the type of Network which covers small geographical area
such as room, building, school, university etc. Since it covers small area, are interconnected with guided or
wired media such as twisted pair cable, coaxial cable or fiber optic cable. It is one of the fastest network in term
of transmission speed among all other. Since, they are connected with wires they have higher reliability. Some
of the implementation of LAN can be in computer lab, cyber, network between different department.

Advantages of LAN
• It is cheaper to establish.
• Data transmission is faster than MAN and WAN.
• It has higher security to resources of the network
• It is eager to establish, manage es of the network and operate

Disadvantages of LAN
• It is limited only to a small area.
• It can connect less number of computers comparatively.
• Cannot be used as distributed network.
 2) MAN: MAN stands for Metropolitan Area Network. It covers an entire city, district or village. MAN
connects two or more than two LAN together. Big companies like banks, and many organization have their
branches or sub offices in a city or in neighboring city use MAN to connect with each other. The
communication media in MAN can be guided as well as unguided. This network use bridge, repeater,
router, switch etc. to establish a connection. The data transmission speed of MAN is faster compared to
LAN and slower to thot of LAN. Media like microwave, radio wave, infrared etc. are used to connect devices
in a MAN.

Advantages of MAN
• It covers larger geographical area than LAN.
• It can connect large number of computer than LAN.
• We can use guided as well as unguided type of transmission media.

Disadvantages of MAN
• It is expensive to set up then LAN.
• Transmission speed slower compared to LAN.
• It is complex to establish, manage and provides security.

3) WAN: It stands for Wide Area Network, which can be extended to the whole world. It is also known
as the network of networks. They are used to connect LANs together so that users and computers in one
location can communicate with users and computer in another location. WAN is unlimited. It is the slowest
data communication among all of three as it covers entire country, continents or even a whole world. These
type of network use unguided media such as microwave, radio wave, satellites and even fiberoptics some
times to communicate in larger distance. The best example of WAN is Internet which is a public network
whereas Intranet is a private network earn by an organizations
Advantage of WAN
• It covers larger geographical area than LAN and MAN.
• It can connect large number of computer compared to LAN and MAN.
• Using WAN communication can be done over a large distance.

Disadvantage of WAN
• It is expensive to establish, manage and operate.
• It is the slowest type of network compared to that of LAN and MAN.
• Highly qualified manpower are required to establish and run these type of network.

On the basis of Network architecture.

1) Peer-to-peer: These type of network architecture in which all the computers in a network are connected
with each other having equal access and responsibility are known as peer -to-peer network. In this type of
network architecture there is no presence of main computer that is server which provides services to the
network. All the jobs and task are carried out by themselves without having authority from other computer.
Hence, they are known as peers. Each computer in a network behave itself as a client as well as server. This
type of architecture can be used to small work group where security may not be of greater issue.

Advantages
• It is simple cheap and easier to set up.
• Since there is no dedicated server, user can manage their own server.
• Failure of a computer in a network doesn't effect the other computer in a network.

Disadvantages
• Data security is very poor in this type of architecture.
• Data recovery and backup is difficult.
• It is not appropriate for large scale organization.
• Network administration is difficult it without dedicated Server.
2) Client server: Unlike peer to peer Network, client server architecture has the main computer called server
which control and monitors all the computers or client in a network. The server always provides services to the
client. In this type of architecture client cannot carry out any operation without the authority of server. Server
act as a central computer in a network. Due to presence of server this type of architecture is much more secure.
The data and application program are stored on powerful centrally located server. Each workstation or client
on the network shares the resources of the server computer. The server computer is high capacity, high speed
and large memory capacity. In this architecture user having client computer can access server only when he/she
has right to do so. That means , unauthorized person cannot access the server. On this network the client have
to request the server for the data instead of carrying out by themselves.

Advantages
• Centralized administration is possible through this network.
• High security can be provided by suing appropriate server.
• It is appropriate for large organization.
• Data recovery and backup process is easier.

Disadvantages
• If server fails whole network is affected.
• It is expensive due to use of dedicated server.
• It is complex to establish and manage.
• Experienced administrator is required to operate.

Transmission Media:

Wired / guided / bounded

1. Twisted pair cable
2. Co-axial cable
3. Fiber optic cable
Wireless / unguided / unbounded
1. Microwave
2. Infrared
3. Satellites

Transmission media / communication media:

Transmission media are means through which data travel form source to destination. Transmission media are
from often called communication media or communication channel. As we know the basic component of
communication are sender (source), communication media and receiver (sink / destination) which means
communication media are used to transmit data. In other word, the physical channel or pathway through which
data travel from one place to another or from one computer to another is called transmission media or
communication channel.
Depending upon the cost, requirement and reliability, communication media are classified into:

A) Guided / bounded / wired media

Those type of transmission media in which data are restricted to travel inside a physical wire are known as
guided media. In the type of transmission media data have to travel in a closed path. There are different types
of guided media.

1) Twisted pair cable: As a name suggest in this type of transmission media the pair of cable are twisted around
each other. They are twisted in order to reduce the electro magnetic interference (EMI). This type of cable have
greater transmission and fewer chance of error in transmission. It is the most common type of transmission
media used in telephone system and in most of the LAN. Twisted pair offers some significant benefits. It is
cheaper, lighter, thinner, more flexible and easy to install than coaxial cable or fiber optics. Twisted pair cable
are found in one pair, two pair and four pair. The media connector used for 4 pair cable is RJ45. Similarly RJ11
are used for two pair twisted pair. There are 2 types of twisted pair cable.

i) UTP (Unshielded Twisted Pair) It is the type of twisted pair cable in which inner pair of conducting wire are
not shielded. Since the pair of wire are not shielded they are immune to EMI (Electro Magnetic Interference).
It is cheaper and cannot transfer data for longer distance compared to STP. It is the most common twisted pair
cable. Eg CAT5

ii) STP (Shielded Twisted Pair) It is the rare type of twisted pair of cable in which inner pair of conducting wire
are shielded. In order to reduce EMI. They are expensive and can be used for longer distance of transmission.
Eg, lBM type 1.

Advantages
• It is cheaper than other cables.
• It is light and thin. So, it is flexible for LAN.
• It can travel data in short distance with higher bandwidth.

Disadvantage
• It is only used for short distance transmission.
• It can be affected by electrical and magnetic field.
• It is slower type of transmission media compared to other cables.

2) Co-axial cable: It is one of the most common television broadcasting transmission media that carries data
signal of higher frequency and at higher speed than twisted pair cable. Co-axial cable has large bandwidth and
better reliability which means it can handle large volume of data at high speed. The other advantages includes
that it can carry signal over significant speed. Co-axial cable has inner layer of conducting wire covered with an
insulator which is surrounded by a conducting mesh and finally covered with a jacket. Co-axial cable used BNC
connector.

Advantages:
• It is faster and reliable than twisted pair cable.
• It can transfer data over medium range of distance.

Disadvantages:
• It is not appropriate for relatively larger distance.
• It is expensive than twisted pair cable.
• It is rarely used in computer network.

3) Fiber Optics: A fiber optics cable is made up of glass or plastic material in order to transmit data in the form
of light. This cable are different than other cables as it plays different set of rules that means data are
transferred in the form of photons (light) instead of electricity (electron). Since there is no electricity it is
completely immune to Electromagnetic Interference (EMI). Hence data are transferred in a very high speed
with better reliability & less error. It has enormous bandwidth and can carry signal for long distance. It is also
more source than other cable.

Advantages:
• It has higher bandwidth that means it can handle large volume of data.
• This medium can be used for long distance transmission.
• It is the most secured and error free transmission medium.
Disadvantages:
• It is one of the expensive type of transmission media.
• It is not used for short distance transmission.
• Highly qualified and technical manpower are required to operate on fiberoptics.

B) Unguided media / Unbounded / wireless media

Those types of transmission media in which data doesn't have to travel in a close path. Data are not restricted
to travel inside physical wire instead they travel through air medium which are known as unbounded media.
For eg; microwave, satellite communication, infrared etc.

1) Microwave: It is the type of transmission media which are used for longer distance. This type of wave have
higher frequency than radio wave hence it can handle large amount of a data. Microwave signal cannot pass
obstacles like hills, buildings and others. So, it is necessary that microwave transmission (sender and receiver)
must be in line of sight (LOS). The transmitting station must be in visible contact with receiving station.

2) Satellite: They are the microwave transmission system in space. It is used as amplifier or repeater that is
used to receive information from one location on the earth, repeats the data and send it to one or more
receiving location on the earth. The communication is carried out through uplink and downlink. To make
communication possible in even longer distance multiple satellites are used. Satellites are set in geo-stationary
orbit directly over the equator which notates in synchronization to the earth hence it looks stationary from any
point on the earth.

4) Infrared: It is wireless transmission technology that use red-light (below the visibility of human eye) to
transmit information. Like fiber optics, information infrared use light for communication. They are commonly
used for TV remote. They are used for closed area using line of sight communication. That means it cannot
penetrate the wall or any obstacle. It cannot be used in open area or outside the building because sun ray also
contain infrared in it which may interfere the communication.

Network Topology
The physical layout or a geographical orientation of the computer in a network is known as a network topology.
There are many different way for setting up LAN. Therefore, topology is a physical arrangement in which
computers or devices in a network are interconnected with each other. People may choose different topologies
due to different requirement of the user. This requirements may be high speed of data transfer, data security,
cost etc.
Types of Network Topology:
1) Bus Topology: In this type of topology every computers or devices in a network are directly connected to
a single cable called back-bone or trunk in a linear way. The linear cable is connected with terminator at its end
so that, data will not be able to escape. The position of the server is not fixed in this type of topology. The signal
pass through the bus in both direction and can be received by all other nodes. All the nodes, In this type of
topology has equal access to the bus and there is no discrimination.
Advantages:
1. It is easy setup.
2. It is not expensive as it requires least amount of cable.
3. It is easy to implement and extent.
4. Terminator doesn't allow data to escape
5. Each computer in a network has equal access and priority to communicate on the network.
Disadvantages:
• Since every computer in a network are connected to the bus, if the cable fails to work then whole
network is affected.
• As the number of computer increases, performance decreases.
• It cannot cover large geographical area.

2) Ring topology: Ring topology is a type of network configuration in which each device on the
network is connected to two other devices, forming a “ring.” Data travels around the ring in one
direction only, from device to device, until it reaches its destination.
In a ring topology, each node has two neighbors , with the signals travelling in opposite directions
around the ring. If one node fails, the network can reroute signals around the failed node using the
other nodes as alternate paths. This redundancy can improve reliability and fault tolerance, but it also
adds complexity to the network.

Advantages of Ring Topology:

• One major advantage is that it is very difficult for an outsider to tap into or interfere with a network using
this type of configuration.
• Additionally, if one node on the network goes down, the rest of the nodes can continue to communicate
with each other without issue. This can be a big advantage in mission-critical situations where uptime is
key.
• Finally, ring topologies tend to be very easy to expand and add new nodes to as needed.
Disadvantages of Ring Topology:
• First, if one node fails, the entire network fails.
• Second, adding or removing a node from the network can be difficult.
• Third, ring topologies are not well suited for large networks.
• Finally, they are susceptible to broadcast storms.

3) Star Topology: In this type of network every computer and networking devices are connected with
centrally located device called hub. It is not always necessary to form a star in this type of topology. Here,
client and server both are connected with the hub. So that adding and removing extra computer is fairly easy.
Moreover it provides excellent platform for troubleshooting and reconfiguration. In this type of topology
breakdown in any medium won’t effect the entire network. The commonly used transmission media in this
type of topology is twisted pair cable. It is one of the most popular and practical type of network topology.
Advantages:
• Adding and removing computers and devices is very easy.
• If one computer fails to works its doesn’t affect the entire network.
• It is one of the most reliable and practical network topology.
Disadvantage:
• It depends upon a central device so if it fails to work it affect the whole network.
• It maybe expensive as we require maximum number of cables and devices.

Osi Reference Model(V.V.V.I)

OSI (Open Systems Interconnection) is a reference model for how applications communicate over a network.
This model focuses on providing a visual design of how each communications layer is built on top of the
other, starting with the physical cabling, all the way to the application that's trying to communicate with
other devices on a network.
The OSI model is a concept that describes how data communications should take place. It divides the process
into seven groups, called layers. The OSI model defines a "layered" architecture in the form of a protocol
stack. There are specific, discrete functions that take place each layer of the protocol stack with lower-level
layers providing services to upper layers and vice-versa. When two systems communicate on the network,
information is sent down through the protocol stack of one system, over the cable, and then up through the
protocol stack to the appropriate layer on the other system.
Data flow under the OSI model is organized into the following seven layers: Physical, Data Link, Network,
Transport, Session, Presentation, and Application.
1. Application layer: The Application Layer provides direct access to network services. It acts as the interface
between the user and the network by providing services that directly support user applications network.

2. Presentation layer: The Presentation Layer is responsible for data translation (formatting ,compression,
and encryption (It converts readable contents into an unreadable format for data security). The Presentation
Layer is primarily concerned with translation; interpreting and converting the data from various formats. For
example, EBCDIC characters might be converted into ASCII. Data is compressed for transmission and
uncompressed while is received. An encryption technique is also implemented at this layer.

3.Session layer: The Session Layer is responsible for establishing, maintaining, terminating a connection
called a 'session'. A session is a period in which data can be exchanged between computers. Managing the
session involves synchronization of user tasks and dialogue control (e.g., who transmits and for how long).
Synchronization involves the use of checkpoints in the data stream. In the event of a failure, only the from
the last checkpoint have to be resent. Login name recognition and security function take place at this layer.

4. Transport layer: The Transport Layer is responsible for flow control and ensuring messages are delivered
error-free. On the sending side, messages are packaged to form data packets for efficient transmission at this
layer and assigned a tracking number (packet number) so they can be reassembled in proper order. On the
receiving side, the packets are reassembled, checked for errors, and acknowledged. The transport layer
performs error handling in that it ensures all data is received in the proper sequence and without errors. if
there are errors, the data is retransmitted.

5. Network layer: The Network Layer is primarily concerned with addressing and routing Logical addresses
(e.g., an IP address) are translated into physical addresses (i.e., the Mac address) for transmission at the
network layer. On the receiving side, the translation process is reversed. It is at the network layer where the
route from the source to destination computer is determined. Routes are determined based on packet
addresses and network conditions. Traffic control measures are also implemented at the network layer

6. Data link layer: The Data Link Layer defines how the signal will be placed on or taken off from the NIC
(Network Interface Card). In this layer, the data frame is broken down into individual bits that can be
translated into electronic signals and sent over the network. on the receiving side, the bits are reassembled
into frames for processing by upper layers. Error detection and correction are also performed at this layer. If
an acknowledgment expected and not received, the frame will be resent. Corrupted data is also identified at
the data link layer.

7.Physical layer: The Physical Layer of the OSI model establishes the physical characteristics of the network
(e.g., the type of cable, connectors, length of cable, etc.) It also defines the electrical characteristics of the
signals used to transmit the data. The Physical Layer transmits the binary data (bits) as electrical or optical
signals depending on the medium.

Transmission impairment:
Transmission impairment occurs when the received signal is different from the transmitted signal.
As we know, a signal can be transmitted as Analog signal or it can be transmitted as a digital
signal. As a result, this imperfection causes signal impairment and tends to determine the quality of
signals.
There are various causes of transmission impairments:( explanation book bata herne)
• Jitter
• Attenuation
• Distortion
• Noise
 • Echo
• Crosstalk
• Bandwidth

(Yo chai book bata banaune hai)

Different networking devices:
• Network interface card(NIC)
• MODEM
• HUB
• Switch
• Bridge
• Router
• Repeater
• Bluetooth ,wifi
• Gateway
Basic terms used in computer network:
• IP Address
• Subnet Mask
• Mac address
• Internet, Intranet ,Extranet

Class of IP Address:
1.Class A
2.Class B
3.Class C
4.Class D
5.Class E