Computer Network

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Basics of Computer Networks and Communication

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Computer Network

The group of interconnected computers through
transmission media in-order to communicate and share
resources like hardware, data and software is known as
communication media. It is a system for communication
between networks. The computers in the network may
be connected through cables,telephone-lines, beams etc.
Advantage of Computer Network





The computers on the network can share hardware devices like printer, scanner etc.
Data and software can be shared within the computer on the network.
Files can be transferred from one computer to another computer.
Computers in the network can communicate with each other.

Disadvantages of Computer Network




Data and information maybe stolen by computer hackers.
If any computer in the network get affected by the virus, there is high chance of
spreading computer virus.
Computers on the network have to depend on the server.

Types of communication media
There are two main types of communication channels. They are:
1. Guided or Bounded or Wired Communication Media
A transmission media where data signals are transmitted along a specific path through cable is
known as Guided Transmission Media. It transfer data from one place to another with the help of
wire. There are three types of cables used for wired network. They are:


Twisted Pair Cable
The twisted pair cable consists of a pair of
insulated copper wire twisted around each other.
The number of twisted pair may 1, 2, 4 or more.
The twisted pair cable is mostly used for
connecting computers on the network.
The twisted pair cable comes into two
categories:

a.

Unshielded Twisted Pair (UTP):A UTP cable is one of the most popular LAN cables.
This cable consists of 4 twisted pairs of metal wires (means there are 8 wires). Adding
RJ-45 connector at both ends of the cable, it becomes a LAN cable that we generally
use.
b. Shielded twisted Pair (STP):A shielded twisted pair cable (also known as IBM Type
I) is similar to UTP but it has metallic covering placed just underneath the plastic
casing. It is more expensive than UTP cables. STP cable offer the best protection from
interference. It can support data transfer rate from 16 to 500 Mb/s (millions of bit per
second).
 Co-axial cable
Coaxial cable have wide bandwidth and noise
immunity. These are widely used in long
distance telephone lines. It's transmission speed
is much higher than twisted pair cables.


Fiber optic cable
Fiber optic cables are made up of plastic or
glass fibers and gives high quality transmission
of signal at a very high speed. Fiber optic cable
transmission are not affected by electromagnetic
interference.These can be used to communicate
either analog or digital signals. These are most
commonly used for point to point one way
communication.

2. Unbounded or Unguided or Wireless Communication Media
The way to transfer data without the help of wire is called Unguided media.
Types of Unguided Media





Microwave: The way to transfer data straightly
from one point to another point in the way of
light in the universe is called microwave system.
Radio wave: Radio wave transmissions are
used for communication between computers in
inaccessible locations or for short range
communications. The other benefit is the
responsibility of reaching rural and hilly area
which are not covered by land telephone line.





Satellite: Satellite communications are like microwave and has relay stations in the sky.
Transponders on the satellite are used to receive and re-transmit signals sent from earth
stations. A transponder has a very high capacity and can handle more than 400 channels.
A computer network is a logical or physical interconnection between two or more
computers such that they could communicate with each other. The process of transferring
data between computers is known as data communication. The data and information can
be transmitted over significant distances through computer network. The communication
of data and information over significant distances is known as telecommunication.

Data Transmission Modes


There are three modes for transmitting data from one device to another.They are as
follows:




1. Simplex
The transmission of data can take place in only one
direction in a simplex. The simplex device can send
only or receive only. The transmission of data through
radios, televisions etc are examples of simplex.




2. Half Duplex
Data can be transmitted in both directions, but only one
at a time in half duplex. A half duplex device can
alternately send and receive data. The transmission of
data through walkie-talkie is an example of half duplex.




3. Full Duplex
A full duplex device can transmit data in both
directions at a time. It improves the efficiency as it can
transmit data in both directions at a time. The
transmission of data through telephones is an example
of full duplex.

Different hardware and software are required for networking computer. here are some of them.

NETWORK ELEMENTS
NIC (Network Interface Card)
It is a hardware device which contains electronic circuitry needed
to ensure reliable communication between workstation and server.

Hub
A hub is simply a multiport repeater and is the control component of the network transmission
mode.

Router
A router is a network connecting device. Although a router can
transfer data between network that uses the same technology, it
commonly transfers data between network using different
technologies.

Gateway
A gateway is a network connecting device that interconnects
two networks using different technologies.

Repeater
A repeater accepts weak signals, electrically regenerates
them and then sends the message on their way.

Bridge
A bridge is the connection of hardware and software that
connects the network that uses similar communication
system.

Bandwidth
It is the amount of data that can be transmitted through communication channel in a fixed time
period. It is expressed in Hertz.

Server
Server is the main computer that provides services, data and
other resources to other computers.
Workstation
It is the place where the client works. It requests services, data and other resources to other
computers.

Modem (Modulator Demodulator)
It is a device which converts analog data to digital and vice versa.
Protocol
A protocol is a set of rule for communicating across the
internet.
List of protocol
1. HTTP (Hypertext Transfer Protocol)
2. FTP (File Transfer Protocol)
3. SMTP (Simple Mail Transfer Protocol)

Networking Architecture
Network Operating System

A network operating system is a computer operating system that is designed primarily to support
workstations, personal computers and old terminals that are connected on a local area network.
They are the server versions of the Windows, Unix, Linux Solaris etc. The computer in which
NOS is installed act as a server and is ideal for file sharing and other network-related jobs. NOS
are also designed for client computers and provide networking functions, so for some NOS the
distinction with a stand-alone operating system are not obvious. The NOS should provide file and
print sharing, account administration for users, and security functions. NOS is equipped with
security modules for controlling the security of the server or client computer, protocols for data
transfer (for file and printer sharing) and administrative tools for account administrations. The
NOS can be run according to two model of computer architecture.
The networking architecture or network model specifies how computers on the network
interacts and communicate with each other. The network of the personal computers may use
Client-server Network or Peer-to-Peer Network.
Client Server Network

In it, computers are connected to a central
device (server) and communication is done
through it. The server is the main computer
which gives services to the workstation. The
server computer provides resources to the
workstations when the request is made. An
unauthorized person cannot access the
resources of the server.There are different types
of server like print server, file server and
network server, etc.
Advantages of Client-Server Network Model





An authorized person can only access the resources of the network.
It is more secured than peer-to-peer network.
All the workstations can be managed from a single server computer.
The required application can be installed on the server computer instead on individual
workstation.

Disadvantages of Client-Server Network




All the workstation has to depend upon server computer.
It is difficult to set up client-server network.
A trained administrator is required to handle it.

Peer to Peer Network

It is sometimes called work groups. In this network, all the
computers have equal responsibilities. Each computer has
access to at least some of the resources on all the
computer. Each computer in this network has equal right.
It is suitable for only small geographical areas such as small
rooms, building, school, etc.
Advantages of Peer-to-Peer Network



It is easy to set up peer-to peer network than client-server network.
Each computer in the network has equal right and can determine resources to be shared.

Disadvantages of Peer-to-Peer Network




It has low level security than client-server network.
The expansion of network is limited.
The network performances degrades with heavy load.

Computer Network Categories
Computer network is classified into three category. They are as follows:



Local Area Network (LAN)

A local area network (LAN) is small network of
computer. It is a network of computers within small
area like room, building, or colleges. Nowadays instead
of cables, wireless media are used as data transmission
channel. LAN where wireless media are used is known
as Wireless Local Area Network.



Metropolitan Area Network (MAN)

It is larger network than LAN.Metropolitan Area
Network (MAN) is a network of computer within a
city or between neighboring cities. Big companies

like banks, offices etc use MAN. In MAN, cables and unbounded communication media
are used as the transmission channels.



Wide Area Network (WAN)

A wide area network (WAN) is a very large network of
computers. WAN is a network of a computer in a wide
geographical areas such as country, neighboring
countries, continent etc. A WAN can be formed by
joining many LANs and WANs. The Internet and
Intranet are the WANs.

Network Topology and Elements of Network
The arrangement or connection patterns of computers or nodes or devices used in the network is
known as network topology.The network topology describes how the computers and networking
devices are linked with each other.
There are different types of network topology they are as follows:
1. Bus Topology

In this topology, all the computers are connected in a
single cable.The common cable is known as network
bus. The network interface card of each computer is
connected to the network bus through a T-connector.
The terminators are attached at both the end of the
network bus.
Advantages
1. It is inexpensive and easy to install because all the computers in the network are attached to one
single cable.
2. The failure of one computer does not affect the performance of the rest of the networks
3. Computers may be easily added or removed from the network.

Disadvantages
1. If a problem arises at any point of the cable, the entire network goes down.
2. It tends to slow down under a heavy load.
3. In this topology, troubleshooting could be difficult.

2. Star Topology

In this topology, all the computers are connected with
switch/hub.It is the most popular topology used today.
In star topology, twisted pair cable is used foe joining
nodes and hub. Each nodes is connected individually in
the network. When any nodes data or message, they
reach to the destination node through the hub/switch.
Advantages
1.
2.
3.
4.

It is easy to add or remove computers from this topology.
If one link fails in network, the other workstations are not affected.
It is more reliable.
In this topology, very high transmission rates is possible.

Disadvantages
1. It the central switch/hub fails, the whole network goes down.
2. Long cable length is required, since each device is directly connected to the hub/switch.
3. It may be costly to install since long length cable is required.

3. Ring topology

In this topology, all the computers or devices are
connected to each other in a closed loop by single
communication cable. Data transfer takes place in one
direction from one node to another around the ring. It is
also called loop network.
Advantages
1. Each computer does not have to depend on the
central device as each computers controls transmission to and from itself.
2. It has short cable connection which increases network reliability.
3. It supports very high data transmission rate.

Disadvantages
1. It is difficult to change network structure.
2. If a single computer fails, at least a portion of network wont work.

Elements of Network












NIC (Network Interface Card) : It is a hardware device which contains electronic circuitry
needed to ensure reliable communication between workstation and server.
Hub: A hub is simply a multiport repeater and is the control component of the network
transmission mode.
Router: A router is a network connecting device. Although a router can transfer data between
network that uses the same technology, it commonly transfers data between network using
different technologies.
Repeater: A repeater accepts weak signals, electrically regenerates them anhd then sends the
message on their way.
Bridge: A bridge is the connection of hardware and software that connects the network that uses
similar communication system.
Bandwidth: It is the amount of data that can be transmitted through communication channel in a
fixed time period. It is expressed in Hertz.
Server: Server is the main computer that provides services, data and other resources to other
computers.
Workstation: It is the place where the client works. It requests services, data and other resources
to other computers.
Modem (Modulator Demodulator) : It is a device which converts analog data to digital and vice
-versa.
Gateway: A gateway is a network connecting device that interconnects two networks using
different technologies.

Protocol

A protocol is a set of rule for communicating across the internet.
List of protocol
1. HTTP (Hypertext Transfer Protocol)
2. FTP (File Transfer Protocol)
3. SMTP (Simple Mail Transfer Protocol)

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