This PPT explains about computer network in easily understandable way. It deals about terminals, computer, communication processor, communication media, telecommunication software, functions of telecommunication software such as security control, error control, access control etc.,

1. Mrs.K.Sudha Rameshwari
Assistant Professor,
Department of Biochemistry,
V.V.Vanniaperumal College for women,
Virudhunagar,Tamilnadu,
India
Computer Networks

2. Introduction
 People need to exchange data and
information electronically with one another
 A good communication system is a must of
every organization
 Organizations depend on interconnected
networks of computers to service their
information processing needs.
 We live in a networked or connected world

3. What is Network?
A network is a group of two or more
computer systems connected
together, and they can communicate
and share resources (e.g.
information)

4. Overview of networks
 A communications Network is any arrangement
where a sender transmuting message to a
receiver over a channel consisting of some type
of medium.
Network consists of five basic components:
 Terminals
 Tele Communication processors
 Telecommunications channels and media
 Computer
 Telecommunication software

5. Terminal
 A terminal is an electronic communication
hardware device that handles the input and
display of data.
 Terminals include video display terminals and
other user workstations input and out device that
uses a network to transmit or receive data is
terminal end includes micro computers,
telephones, fax machines etc.

6. Telecommunication
processors
 Telecommunication processors which support data
transmission and reception between the terminals
and computers.
 Processors perform a variety of control and support
functions in a telecommunication network.
 The functions of processors include converting data
from digital to analog and back, coding and decoding
of data, and controlling various activities like speed,
accuracy, and efficiency of the communications flow
between the computers and the terminals.
 Examples of telecommunication processors are
modems, multiplexers, and internetworked
processors like switches, routers, and hubs.
 These processors perform a variety of support
functions between the computers and other devices
in a telecommunications network.

7. Telecommunications
channels and media
 The media over which data are
transmitted and received are called
telecommunication channels
 Telecommunication channels use
combinations of media such as copper
wires, coaxial cables , fiber optic
cables, microwave systems and
communication satellite systems to
interconnect the other components of a
network

8. Computer
 Networks interconnect computer of all
sizes and types so that they can carry
out the information processing
assignments.
 For example, a mainframe computer
may serves a host computer for a large
organization's network, assisted by
minicomputers acting as network
servers for smaller networks of end user
microcomputer workstations.

9. Telecommunication software
 It consists of programs that reside in
host computer systems, communication
control computers and end user
computers.
 This controls telecommunication
activities of the computer systems and
manage the function of networks.

10. Components of a communication
network

11. Communication processors
 Communication processors resemble
computer CPUs in that they have similar
circuits have memories and can be
programmed , but their purpose is limited
to enable data communications between
two points.
 Communication processors include the
following: modems, message switchers,
multiplexers, concentrators and
controllers, front end processors

12. Modem
 Modems are the most common type of communication
processors
 Modem stands for Modulator and demodulator
 They convert the digital signals(binary code) from a
computer or transmission terminal at one end of a
communications link into analog signals, which can be
transmitted over ordinary telephone lines.
 Modulation is the conversion of data from binary to
analog
 A Modem at the other end of the communications line
converts the transmitted data back into digital forms at
the receiving terminal.
 The process is known as modulation and
demodulation
 The word modem is a combined abbreviation of those

13.  Modems are necessary because ordinary
telephone lines are primarily designed to handle
continuous analog signals such as the human
voice.
 Since data transmissions from computers are in
digital form , devices are necessary to convert
digital signals into appropriate analog
transmission frequencies and vice versa.

14. Communication media –
Twisted pair wire, Coaxial cable, fiber
optic cables

15. Communication media
• Channels also called
communication lines or links
are the means by which data
is transmitted between the
sending and receiving
devices in a network.
• A channel makes use of a
variety media
• These include twisted pair
wire , coaxial cables and fiber
optic cables all of which
physically link the devices in a
network.
• Also included are microwave
systems, communications
satellite systems and cellular
radio, all of which use
microwave and other radio
waves to transmit and receive
data

16. Communication media-Twisted
pair
 This is the oldest and still most
common transmission line and
consists of copper wires twisted
into pairs.
 These lines are used in
established communications
networks throughout the world for
both voice and data transmission

17. Communication media –Coaxial cable
• Coaxial cable consists of a copper or
aluminum are wrapped with spacers to
insulate and protect it.
• The insulation minimize the interference
and distortion of the signals the cable
carries.
• Groups of coaxial cables may be bundled
together in a big cable for ease of
installation
• These high quality lines can be placed
underground and laid on the floors of
lakes and oceans.
• They allow high speed data transmission

18. Communication media- Fiber
optic cables
 Fiber optics use cables consisting of
one or more hair thin filaments of
glass fiber wrapped in a protective
jacket.
 They can conduct light pulses
generated by lasers at transmission
rates as high as 2 billion bits per
second.
 This is about ten times greater than
coaxial cables and 200times better
than twisted pair wires.
 Fiber optic cables provide substantial
size and weight reduction as well as
increased speed and greater

19. Communication media- Fiber optic cables
• A half - inch diameter fiber optic cable
can carry up to 50,000 channels,
compared to about 5500 channels for a
standard coaxial cable.
• Fiber optic cables are not affected by
and do not generate electromagnetic
radiation; therefore multiple fibers can
be placed in the same cable.
• Fiber optic cables have a minimal need
for repeaters for signal transmissions,
unlike electrical wire media.
• Fiber optics also has a much lowered
error rate than other media.

20. Different types of network cables
Twisted
pair wire
Coaxial cable
Fiber optic wire

21. Communication satellites
 Communications satellites in space orbiting 22000
miles above the earth, are also used as
microwave relay stations, because they rotate at
the precise point and speed above the equator
that makes them appear stationary to microwave
transmitters on the ground.
 Among the dozens of satellites now orbiting the
earth and handling voice, video and media
communications are those launched by
INTELSAT, short for international
telecommunications satellite Consortium.
 INTELSAT began with the early Bird satellite in
1965 and now form a world wide communications
system for over 100 countries. It accounts for most

22. Telecommunication software
Software is a virtual component of all telecommunications
networks.
Communications control software includes programs stored
in the host computer as well as programs in the front –
end computers and other communications processors.
This software controls and supports the communications
occurring in a telecommunications network.
Telecommunications software packages for large computer
networks are frequently called telecommunication
monitors or teleprocessing (TP) monitors.
Local area networks (LANs) rely on software called network
operating systems.
Many communications software packages are also
available for microcomputers.

23. Functions of telecommunication software
 Telecommunication software packages provide a variety
of communications support services.
 The number and type of terminals, computers,
communication processors and communications activities
involved determine the capabilities of the programs
required.
 The telecommunications software provides several major
functions such as:
 Access control
 Transmission control
 Network control
 Error control
 Security control

24. Access Control
 This function establishes the connections
between terminals and computers in a network.
 The software works with a communication
processor (such as a modem) to connect and
disconnect communications links and establish
parameters such as transmission speed, mode
and direction.
 The function may also involve automatic
telephone dialing and redialing, logging on and
off with appropriate account number and security
code and automatic answering of telephone calls
from another computer.

25. Transmission control
 This function allows computers and terminals to
send and receive commands, messages, data
programs.
 Some error checking and correction of data
transmissions may also be provided.
 Data and programs are usually transmitted in the
form of files, so this activity is frequently called file
transfer

26. Network control
 This function manages communications in a
network.
 Software determines transmission priorities, route
message, polls terminals in the network and
forms waiting lines (queues) of transmission
requests.
 It also logs statistics of network activity and
resource usage and detects and corrects errors.

27. Error control
 Error control involves detection and correction of
transmission errors
 Errors are usually caused by distortions in the
communications channel, such as lack of noise and
power surges.
 Communications software and processors control errors
in transmission by several methods including parity
checking.
 Additional control codes are usually added to the
message itself.
 These specify surfing information as the destination of
the data, their priority and the beginning and end of the
message, plus additional error detecting information
 Most error correction methods involve retransmissions.
 A signal is sent back to the computer or terminal to

28. Security control
 Security control protects a communications network from
unauthorized access.
 Access control software and other types of programs
restrict access to data and the computing resources in
the network
 This restriction usually involves control procedures that
limit access to all or part of a network by various
categories of users.
 Automatic disconnection and callback procedures may
also be used.
 Data transmissions can also be protected by coding
techniques called encryption.
 Data is scrambled into a coded form before transmission
and decoded upon arrival

29. Reference
 Information technology-Alex leon and Mathew
leon