Data and communication system

1. CHAPTER 5
DATA COMMUNICATIONS
SYSTEM

2. INTRODUCTION
• Data communication is the movement of data
and information from one point to another
point by means of electrical or electromagnetic
devices, fibre-optic cables or microwave
signals.

3. TELECOMMUNICATIONS SYSTEM
Telecommunications system has five
components. These are
1. Sender: - input devices.
2. Channel & Media:-channel characteristics.
• Transmission Speed.
• Transmission Mode.
• Transmission direction

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.Media
• Bounded.
• Unbounded.
3. Hardware: -
• Host Computer,
• Front end Processor,
• Modem,
• Multiplexer,
• Switch.
• Bridge
• Gateway
• Bus.

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4. Software:-
• Access Control.
• Transmission control.
• Network control & Management.
• Error detection & Correction.
• Network Security.
5. Receiver:-Output Devices.

6. Telecommunications Channels
• A data communications channels is a path through a medium that
data can take from sending stations to receiving stations.
Characteristic of channels are:
 Transmission Speed: -
• It is the capacity of a telecommunication channel depending on the
bandwidth. The greater bandwidth the greater amount of
information transmitted over the channel. There are three types of
bandwidth:-
 Voice-band (300 bps to9600 bps),
 Medium band (9600bps to 256000bps).
 Broadband (256000bps to a very large number.)

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 Transmission Mode:-There are two types of transmission mode
• Synchronous:-In this transmission a group of characters transmit
at a time.
• Asynchronous: - In this transmission one character transmit at a
time.
 Transmission direction:- It is the direction in which data is
transmitted . There are three types of directions:
• Simplex: - In this direction data communication devices that can
either send or receive data, but can not do both.
• Half duplex: - In this case two devices are send or received data,
but not at a time.
• Full duplex: - In this case two devices are send or received data at
a time.

8. Telecommunications Media
• There are two types of media over with data is
transmitted.
• Bounded media-The signals are confined to
the medium. Ex-Twisted pair cable, fibre-optic
cables, coaxial cable.
• Unbounded media-The signal are not
restricted to the medium. Ex-Microwaves.

9. DATA COMMUNICATIONS HARDWARE
• Host Computer:-The host performs the data
processing for the network.
• Front-end processor:-The front-end processor is
a minicomputer that acts as a buffer between the
client device and the host computer.
• Modem:-It stands for modulator-demodulator. It
is used for Digital signals are converted into
analog signals and vice-versa.

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• Multiplexer:-It is a device that permits the
simultaneous sending and receiving of
multiple messages over a signal channel.
• Switch:-It is a device which is determines the
data transmission path.
• Switches can control the transmission path
across national or local networks.

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• Bridge and gateway:-
• • A bridge is a device that separates two or more network
segments with in one logical network (e.g. a single IP-
subnet). A bridge is usually placed between two separate
groups
• of computers that talk with each other, but not that much
with the computers in the other group.
• • A gateway is a node (a router) on a TCP/IP network that
serves as an access point to another network. A default
gateway is the node on the computer network that the
network software uses when an IP address does not match
any other routes in the routing table.
• Bus: - A collection of wires through which data is
transmitted from one part of a computer to another.

12. DATA COMMUNICATIONS SOFTWARE
• Software enables all of the data communication hardware
units to work as one system.
• Various types of computer software are:
• Access control software: This software establishes access
between different devices, terminals and computers in the
network and checks the transmission mode, transmission
speed and transmission direction.
• It has two types:-
• 1.centralised
• 2.decentralised.
• Terminal Control Software: This software controls the
transmission of data over the network.

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• Terminal emulation software: This software enables a
microcomputer to behave like specific terminal when in
interact with a mainframe.
• Network control software: The software coordinates
controls and manages the complete operation of the
network. It establish priority for data waiting to be
transmitted, check for any transmission error, route
message, and maintain statistics system used.
• Error correction and detection software: It ensures that
errors, caused by any other problem, are detected and
connected.
• Security software: The software prevents unauthorized
access to data and monitors the use of the network.

14. COMMUNICATION NETWORKS
• There are five types of communication
networks:
1. Private Branch Exchanges (PBXs)
2. Integrated Services Digital Networks (ISDNs)
3. Local Area Networks (LANs)
4. Wide Area Networks (WANs)
5. Value Added Networks (VANs)

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• PBX (private branch exchange) is a telephone
system within an enterprise that switches calls
between enterprise users on local lines while
allowing all users to share a certain number of
external phone lines.
• Integrated Services Digital Networks (ISDNs):
• The ISDN is a digital communication network that
uses the public telephone network and allows
users to transmit data, voice, text, and video
communication in digital form over telephone
lines.

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Local Area Networks (LANS)
• It is connected devices share the resources of a single
processor or server within a small geographic area (for
example, within an office building).
• Major local area network technologies are: Ethernet,
Token Ring, and FDDI(fiber distributed data interface).
Wide Area Networks (WANS)
• It is a collection of computers and network resources
connected via a network over a large geographic area.

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• There are different types of set up a WAN are:-direct
distance dialing (DDD), Wide area telephone service
lines (WATS), leased lines and satellites.
• Example:-banking networks, airline reservation systems
and railway reservation systems.
• The public data networks that add value to the basic
communication services provided by common carriers
by offering specialized services are termed as value
added networks.
• The specialized services include access to commercial
databases and software, correction of transmission
errors, providing compatibility between incompatible
computers and terminals, Email, and video
conferencing.

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Value Added Networks (VANS)
• The public data networks that add value to
the basic communication services provided by
common carriers by offering specialized
services are termed as value added networks.
• The specialized services include access to
commercial databases and software,
correction of transmission errors, providing
compatibility between incompatible
computers and terminals, Email, and video
conferencing.

19. TOPOLOGY OF COMPUTER NETWORK
• The term topology, or more specifically, network
topology, refers to the arrangement or physical
layout of computers, cables, and other components
on the network.
• In addition to the term "topology," you will find
several other terms that are used to define a
network's design:
Physical layout
Design
Diagram
Map

20. Logical vs. Physical topology
• A network's physical topology is the wire itself. A
network's logical topology is the way it carries
signals on the wire.
Standard Topologies
• All network designs stem from four basic
topologies:
Bus
Star
Ring
Mesh

21. Bus topology
• The bus topology is often referred to as a "linear
bus" because the computers are connected in a
straight line. This is the simplest and most
common method of networking computers. It
consists of a single cable called a trunk (also
called a backbone or segment) that connects all
of the computers in the network in a single line.

22. Star Topology
• In the star topology, cable segments from each
computer are connected to a centralized component
called a hub. The star network offers the advantage
of centralized resources and management. However,
because each computer is connected to a central
point, this topology requires a great deal of cable in
a large network installation. Also, if the central
point fails, the entire network goes down.
• If one computer—or the cable that connects it to
the hub—fails on a star network, only the failed
computer will not be able to send or receive
network data. The rest of the network continues to
function normally.

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24. Ring Topology
• The ring topology connects computers on a
single circle of cable. Unlike the bus topology,
there are no terminated ends. The signals
travel around the loop in one direction and
pass through each computer. Each computer
can act as a repeater to boost (regenerate) the
signal and send it on to the next computer.

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One method of transmitting data around a ring
is called token passing. (A token is a special
series of bits that travels around a token-ring
network.

26. Mesh Topology
• This configuration provides redundant paths
throughout the network so that if one cable
fails, another will take over the traffic. These
networks are expensive to install because they
use a lot of cabling.

27. Topology Advantages and
Disadvantages