Computer Networks
A computer network is a network between computers which connects
multiple computers in a manner to enables meaningful transmission and
exchange of data among them.
Sharing of information (both hardware and software) and processing
load is the main objective of a computer network.
Goals of Computer Network
1. Resource sharing: All programs, data and equipment (printers, hard
disks, plotters) available to anyone on the network without the
regard of physical location of the resource and the user.
2. High reliability: Having alternative sources of supply during
hardware failure can provide high reliability.
3. Performance: It is measured in terms of transit time and respond
time. Performance of a computer network depends on type of
transmission medium, capability of connected network, number of
users, efficiency of software.
4. Scalability: Network must be scalable so that it can be extended by
adding new devices.
5. Security: It means protecting data from unauthorized access.
Network allows security to ensure the right to access the certain
data to the users.
Components of Computer Network
1. Hardware :
i. NIC (Network Interface Card): It is a hardware device
that connects a computer to a network both functionally
and physically. The main purpose of NIC is to format
data, send and receive data at receiver node.

ii. Server: These are the computers that holds data that can
be shared over a computer network. It also runs
operating system.
iii. Client: It is a computer that can receive data from the
other computers in computer network.
iv. Transmission Media: In computer network computers
are connected by transmission medium such as wire,
cables etc.
v. HUB: It is a physical layer networking device that connects all the
computer in a network with each other. It works as a central connection
for all the devices that are connected through a hub. Hub has numerous
ports. Hub cannot filter data so data packets are sent to all the computers
that are connected with hub. Hub isn’t capable of storing MAC
addresses. The speed of hub network is up to 10 Mb per second.
Advantages:
 It can easily connects different media types.
 Anyone can use it as it is very cheap.
 It can extend the distance of the network.
 Doesn’t impact on network performance.
 Good for sharing same data.
Disadvantages:
 A network hub has no intelligence.
 It cannot reduce network traffic as it has no mechanism.
 As it can’t filter data and send them to all the devices that are
connected to it; it has no security.
Applications:
 Small home networks.
 Network monitoring.
 Provide connectivity in organizations.

vi. Switch: A switch is a data link layer device which connects multiple
devices within a network. It can perform error checking before
forwarding data. It can manage physical network as well as software
based virtual devices. It uses MAC addresses to send data packets to
selected destination ports. It uses packet switching technique to receive
and forward data from source to destination ports.
Advantages:
 It is an intelligent network device that can be conceived as a
multiport network bridge.
 It support unicast, multicast and broadcast communication.
 Transmission mode is full duplex.
 Have network software and network management capabilities.
 More secure.
 Increase the bandwidth of the network.
Disadvantages:
 They are more costly.
 Broadcast traffic might be problematic.
 They are defenseless against security assaults like catching
Ethernet outlines.
 Must have physical contact with the object to be actuated.
vii. Router: It is a networking device that forwards data packets between
computer networks. It can be connected to two or more data lines from
different IP networks. When a data packet comes in one of the lines,
router reads the address information from the packet header and
determine the destination. Router uses modem to connect devices and
the internet.
Advantages:
 It can choose bet path across the internetworking.
 It reduces network traffic.

 It provides sophisticated routing and flow control.
Disadvantages:
 They are expensive compare to other network devices like hub,
switches.
 They are slower as they have to analyze data.
 Require amount of initial configurations.
Viii. Bridge: It is a network device that connects multiple LAN together
to form a larger LAN. It uses forwarding database or bridge table.
Advantages:
 For some individual nodes bridge increases network bandwidth.
 It reduce network congestion by dividing LAN into small
segments.
 It has higher levels of protocol transparent.
Disadvantages:
 Bridge cost more than hubs and repeaters.
 It cannot filter the broadcast traffic individually.
 As it view all the MAC addresses, they have downgrade
performance.
ix. Repeater: It is a network device that retransmit the data from the
sender to the receiver side of the network.
Advantages:
 It is less costly than other network device.
 The performances are good.
 It has the facility to extend the length of transmission.
Disadvantages:
 Network traffic.
 Increase the possibilities of packet collision.

 It cannot create separate traffic from one cable to a special.
x. Gateway: It is a networking device that enables two different
networks to communicate with each other that connects two different
networks together enable to communicate with each other.
Advantages:
 Expand the network.
 Connect two different types of network.
 Effectively handles the traffic.
Disadvantages:
 Not an intelligent device.
 It doesn’t filter data.
 Costly.
 Transmission rate is slower.
2. Software:
i. Operating System: It facilitate workstation in Network a network
to share files, database, printers etc.
ii. Protocol Suite: It is a guideline or rule followed by computers
for data communication. Two popular protocol suite are-
 OSI Model
 TCP/IP Model
3. Cables and Connections:
I. Twisted Pair Cable: It is also known as Ethernet cable.
Generally used in LAN computer networks. It is a
combination of two separate insulated copper wires twisted
together and run in parallel.
II. Coaxial Cable: It carries high frequency electrical signals
with low losses. It is used in broadband internet networking
cables, cable television signals etc.

III. Fiber Optic Cable: It is an electrical cable that contain one or
more optic fibers that are used to carry light. It is used for
long distance telecommunication, high speed data
connection etc. Thus it needs high maintenance. It is
expensive.
Distributed System: ARPANET
ARPANET was the first technical foundation for INTERNET. It is the
earliest example of a large scale distributed application. The Advanced
Research Projects Agency Network (ARPANET) was the first wide area
packet switching network with distributed control and one of the first
networks to implement the TCP/IP Protocol Suite.
It was developed under the direction of the U.S. Advanced Research
Projects Agency (ARPA) in 1967. In 1969 it become reality with the
interconnection of four university computers.
The initial purpose was to communicate with and share computer
resources among mainly scientific user at the connected institutions.
The development of TCP/IP protocols in 1970s made it possible to
expand the size of the network. In the 1980s, ARPANET was handed
over to a separate new military network, NSFNET. In 1995, NFSNET
turn the backbone of the INTERNET over to commercial backbone
providers.

Computer Network Theory Part1

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