Computer Network and Communication Overview

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Computer Network and communication

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Introduction
Information transfer between people situated on different
sites on a real time basis is an age-old requirement.
In the 1960s, it was decided to develop computer network
for the purpose of fast and real time data transfer for
scientific research data, where data was in a very large
quantity.
The first useful network was ARPANET.
Definition of Network
A group of computers and associated peripheral devices
connected by a communication channel, capable of sharing
files and other resources between several users is known
as network.

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Objectives of Networking
Provides us with the facility to share distant resources such
as database, processor or software.
Provides high reliability by having alternate resources for
providing distribution of processing so that load sharing
can be achieved.
Networking Considerations
• Cost
Cost of the network involves installation of hardware
and software facilities.

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The hardware includes the computers, peripherals,
communication medium, etc. and software includes
operating system and network environment. Software
also provides network constructs and rules (protocols).
• Training
• Housekeeping Operations
Housekeeping operations have to be performed for a
network to manage resources properly and with better
efficiency.

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• Routine Daily Tasks
✔ Cleaning up the file server hard disk drive.
✔ Installing software upgrades.
✔ Making back-ups.
✔ Restoring damaged or lost files.
✔ Monitoring Traffic.
✔ Collecting accounting data.
✔ Generating reports for management.
• Routine Weekly Tasks
✔ Monitoring and evaluating network performance.
✔ Managing and documenting the network configuration.
✔ Exploring and appraising new hardware and software
technology.

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• Security
Being a multi-user system, security maintenance is a
necessary task.
Advantages of Network Applications
▪ Networks may prove to be very effective in the area of
electronic-mail.
▪ Remote databases can be accessed very easily and
quickly, e.g. steel inventory in plants and warehouses
of Steel Authority of India Ltd. (SAIL).

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▪ Financial transactions can be done through network.
E.g. Electronic Fund Transfer (EFT) in global banks.
▪ Used very effectively in the areas of device sharing,
e.g. hard disks, printers, scanners, etc.
▪ It can also be of vital help at homes by providing stock
market figures, business data, educational material,
etc.
▪ The users of a network can also read a magazine or
some important news by connecting the home
television to some network.

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▪ Networks provide an effective tool for communicating
through the use of e-mail and other work group
software.
Use of work group software reduces the need for face-
to-face meeting and other time-consuming methods of
distributing information.
▪ Networking can also enhance the effect of
communication, as people tend to put more thought
into written communication than into informal
conversation.

Figure 1-1
WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,
Data Communication System Components

Figure 1-2

Figure 2-11

Figure 2-12
Simplex

Figure 2-13
Half-Duplex

Figure 2-14
Full-Duplex

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Network Topologies
Network topology can be defined as the way of physical interconnection
between computers to form a computer network.
Computers are connected to each other through some interconnection
medium known as communication medium.
Some important Network topologies are:
Star Topology
In star configuration, a central controller provides the hardware/software
resources and interface required for connecting different computers in the
network.
The individual computers are not linked directly to each other and can
communicate only via the central controlling computer.

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Advantages:
1) The failure of a single computer or cable doesn't bring
down the entire network.
2) The centralized networking equipment can reduce
costs in the long run by making network management
much easier.
3) It allows several cable types in same network with a
hub that can accommodate multiple cable types.
Disadvantages:
1) Failure of the central hub causes the whole network
failure.
2) It is slightly more expensive than using bus topology.

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3) There are lot of cables and interfaces, which are
probably never used at the same time.
4) We can’t install new hardware in star topology if the
communication port cannot be installed on central
computer.
Ring Topology
In Ring configuration, the computers are connected
through point-to-point links.
All connected computers exercise control of the network
by following common protocols, known as ring protocols.

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Advantage
1) Cable faults are easily located, making trouble
shooting easier.
2) Ring networks are moderately easy to install. It
needs only two cables to get connected to its
preceding and succeeding neighbor in the ring.
Disadvantages:
1) Expansion to the network can cause network
disruption.
2) A single break in the cable can disrupt the entire
network.

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Bus Topology
A bus topology connects each computer (nodes) to a
single segment trunk (a communication line, typically
coax cable, that is referred to as the 'bus'. The signal
travels from one end of the bus to the other.
This network is also known as broadcast network
because of the fact when a data packet is sent out; it
propagates throughout the medium and is received by all
the stations.

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Advantages:
• Failure of one of the station does not affect others.
• Good compromise over the other two topologies as it
allows relatively high rate of data transmission.
• Well suited for temporary networks that must be set
up in a hurry.
• Easy to implement and extend.
Disadvantage:
• Require a network to detect when two nodes are
transmitting at the same time.

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• Does not cope well with heavy traffic rates.
• Difficult to administer/troubleshoot.
• Limited cable length and number of stations.
• The fault diagnosis and isolation of computer from
broadcast is difficult.
• Entire network shuts down if there is a break in the
main cable.

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Types of Networks
Peer to Peer Network (P2P)
These networks are used for a small range of computers.
In this network, all machines have their own resources
and can also have sharable resources for other machines.
P2P networks are useful for many purposes. Sharing
content files containing audio, video, data or anything in
digital format is very common, and realtime data, such as
telephony traffic, is also passed using P2P technology.

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Local Area Network (LAN)
• LAN is a group of computers and associated peripheral
devices connected by a communication channel,
capable of sharing files and other resources between
several users.
• Typically connects computer in a single building or
campus.
• Medium: optical fibers, coaxial cables, twisted pair,
wireless.
• LAN can operate between 10 mbps to 2 gbps.

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• Due to the shorter area coverage, the LAN offers lower
delays than WAN and MAN; delays on a LAN can be
calculated in milliseconds.
• High speed networks (0.2 to 100 Mb/sec) – adequate
for most distributed systems.
• A low error rate in data transfer.
Advantages:
Provides a cost-effective multi-user computer
environment.
Easy physical connection of devices to the media.

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Network data transmission rates are independent of
the rates used by the attached devices, making it
easier for device of one speed to send information to
device operating at another speed.
It provides data integrity.
Metropolitan Area Network (MAN)
A MAN is optimized for a larger geographical area than
a LAN, ranging from several blocks of buildings to
entire cities (50 kms).
MANs can also depend on communications channels of
moderate-to-high data rates (100 mbps or faster).

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A MAN might be owned and operated by a single
organization, but many individuals and organizations
usually use it.
IEEE 802.6 set of standards is dedicated to MAN.
A MAN is designed with two unidirectional buses; each
bus is independent of the other in the transfer of traffic.
The topology can be designed as an open bus or a
closed bus configuration.
It may also utilize the Cable Television Networks
(CATV) to connect computers together.
A typical standard is DQDB (Distributed Queue Dual
Bus).

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Wide Area Network (WAN)
• A network that connects users across larger distances,
often crossing the geographical boundaries of cities,
states or countries.
• WANs normally use public telephone network and
satellite links for data transmission.
• Data transmission rate are below 1 mbps (mega bits
per second).
• It is normally used by multiple organizations.

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• The transmission time is more for WAN because of
longer distances and different transmission mediums
used.
• Medium: communication circuits connected by routers.
• Not (yet) suitable for distributed computing.
Advantages:
• They tend to enhance reliability.
• They are used for remote data collection.
• They allow work groups to be spread across
geographical boundaries.

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Homogeneous and Heterogeneous Networks
Homogeneous Network
• A network that consists of only one type of workstation,
server, operating system and network interface card is
known as a homogeneous network.
• Uses a standard network interface card that plugs into a
personal computer or server and works with the
network.
• All nodes use the same protocol and the same control
procedures in this type of network.

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Heterogeneous Network
• A network that consists of workstations, servers,
network interface cards, operating systems and
applications from many different vendors, all working
together as a single unit known as Heterogeneous
network.
• These networks may also use different media and
different protocols over different network links.

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Examples of Networks
Ethernet
• Ethernet was developed by Xerox Corporation, Digital
Equipment Corporation and Intel, in collaboration.
• Ethernet is the most widely installed local area network
LAN technology.
• Provide transmission speeds up to 10 Mbps.
• In Ethernet, each station can exchange data with any
other station or group of stations.

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• It uses coaxial cables to connect computers to each
other.
• There is high flexibility (i.e. easy adaptability) when
devices and systems are to be added or removed.
• It was traditionally used in office automation but is
now also used in laboratories, industries, robotic
applications, factory automation, etc.

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Ethernet technology supports three different types of
cables and connections. These are:
Thick Wire Ethernet:
• Each Ethernet cable is about ½ inch in diameter and
maximum 500 meters long.
• A resistant material is added between the wire and
braided metal shield to prevent electrical signal
reflection.
• The cable used for Ethernet is a coaxial cable and called
as ether.

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• A transceiver is the device, which is used to join
computers with Ethernet network. This device is
responsible for communication between computers.

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Thin Wire Ethernet:
• It designed to reduce the cost of Ethernet.
• Thin wire Ethernet covers shorter distance and
supports fewer computer connections in the network in
comparison with thick wire Ethernet.
• A thin wire Ethernet segment uses a length of coaxial
cable, which can be shared by up to 29 devices.
• One end of the cable is attached to a repeater, which
joins the segment to the main campus network; the
other end is fitted with a special terminator.

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Twisted Pair Ethernet:
▪ There are a few standards for Ethernet over twisted
pair or copper-based computer networking physical
connectivity methods. The currently most widely used
of these are 10BASE-T, 100BASE-TX, and
1000BASE-T (Gigabit Ethernet), running at 10 Mbit/s,
100 Mbit/s, and 1000 Mbit/s (1 Gbit/s) respectively.

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• These three standards all use the same connectors.
Higher speed implementations nearly always support
the lower speeds as well, so that in most cases
different generations of equipment can be freely
mixed.
• In this scheme each computer is connected to an
Ethernet hub with the help with the help of a pair of
copper wires, very much similar to telephone wires.
• The advantage of this scheme is that it reduces costs
and prevents crashing of the network when one of the
nodes crashes.

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ISO-OSI reference Model
Open System Interconnection (OSI) is an International
Standardization Organization’s (ISO) standard defining
seven layers of a network and invidual communication
protocols for all the layers (all devices could communicate
with each other freely if they all conform to OSI).
A set of protocols is open if:
• Protocol details are publicly available
• Changes are managed by an organization whose
membership and transactions are open to the public.

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A system that implements open protocols is called an
open system.
International Organization for Standards (ISO)
prescribes a standard to connect open systems
•Open system interconnect (OSI)
The ISO defined network model comprises seven layers:
i. Physical layer
ii. Data link layer
iii. Network layer
iv. Transport layer
v. Session layer
vi. Presentation layer
vii. Application layer

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Each layer’s functioning depends on the layer below it
and each layer provides services to its upper layer.
The layer boundary should be chosen to minimize
information flow across interfaces.
When a message is sent to another computer on the
network, the data starts from the top layer of the
computer and travels down all the layers to the bottom.
Then it jumps across to the other computer through the
physical medium.
When the data geta to another computer, it starts at the
bottom layer and moves up to the top layer.

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Application Layer
Presentation Layer
Session Layer
Transport Layer
Network Layer
Data-link Layer
Physical Layer
ISO OSI Reference Model of Network Layer
User User
Application Layer
Presentation Layer
Session Layer
Transport Layer
Network Layer
Data-link Layer
Physical Layer

Figure 3-14
Summary of Layer Functions

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Seven Layers of ISO-OSI Reference
Model
The Physical layer
• The physical layer is a pure hardware, bottom most
layer which defines all the electrical and physical
specifications for devices.
• In particular, it defines the relationship between a
device and a physical medium. This includes the layout
of pins, voltages, cable specifications, Hubs, repeaters,
network adapters, Host Bus Adapters (HBAs used in
Storage Area Networks) and more.

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At physical layer the electrical function, mechanical
function and procedural interface between two
computers (i.e.source computer and destination
computer) are defined.
The major functions and services performed by the
physical layer are:
• Establishment and termination of a connection to a
communications medium.
• Participation in the process whereby the
communication resources are effectively shared
among multiple users. For example, contention
resolution and flow control.

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The Data link layer
• In data link layer, software and hardware both are
involved.
• Transforms basic physical services to enable the
transmission of units of data called frames. Frames carry
data between two points on the same type of physical
network, and maybe relayed if the network is extended.
• They normally contain low level addressing information
and some error checking. This layer may be involved in
arbitrating access to the physical network. The Data
Link layer detects, and possibly corrects errors in the
physical layer.
• This layer also takes care of flow between the machines.

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The Network layer
• This layer provides the network address to the packets
in the data link layer and provides the facility to send
them to the correct network address.
• Responsible for splitting a large-size data block into a
number of uninformized packets.
• Routes for frames can be based on static cables that
are wired into the network and rarely changes.
• If many packets are present in the subnet, they can
get bottlenecked and can get in each other’s way.This
situation is also controlled by the network layer.

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Network layer takes care of the differences in packet
sizes and different protocols used in both.
The Transport layer
• The transport layer provides transparent transfer of
data between end users, providing reliable data
transfer services to the upper layers.
• The transport layer controls the reliability of a given
link through flow control, segmentation /
desegmentation, and error control.

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• Some protocols are state and connection oriented. This
means that the transport layer can keep track of the
segments and retransmit those that fail.
• This layer ensures that the packets have no error.
• Also all the arriving packets are in the correct order.
• It also supports multiplexing of more than one channel
into a single one, in case creating and maintaining a
network connection is expensive.
The Session layer
• The session layer is level five of the seven level OSI
model.

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• It responds to service requests from the presentation
layer and issues service requests to the transport
layer.
• The session layer provides the mechanism for
opening, closing and managing a session between
end-user application processes, i.e. a semi-permanent
dialogue.
• Communication sessions consist of requests and
responses that occur between applications.
• Session layers are commonly used in application
environments that make use of remote procedure
calls (RPCs).

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• This layer can help in keeping track of the turn by
providing time-sharing.
The Presentation layer
• Presentation layer is the sixth level of the seven
layer OSI model. It responds to service requests from
the application layer and issues service requests to the
session layer.
• The presentation layer is responsible for the delivery
and formatting of information to the application layer
for further processing or display.

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• An example of a presentation service would be the
conversion of an EBCDIC-coded text file to an ASCII-
coded file.
• Encryption is typically done at this level too, though it
can be done at the application, session, transport, or
network layer; each having its own advantages and
disadvantages.
• This layer is concerned with syntax of information
translated such as integers, string, data structure, etc.
The Application layer
▪ The application layer is the seventh level of the
seven-layer OSI model.

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▪ It interfaces directly to and performs common
application services for the application processes; it
also issues requests to the presentation layer (OSI).
▪ This layer enables the user to perform jobs like sending
e-mail, or requesting to transfer a file across the
network.
▪ This layer contains variety of protocols that are
commonly needed, there may be different terminals
having different screen layout, escape sequences for
insert delete and moving text or cursor.
▪ This layer is concerned with the layouts of various
terminals and generates a virtual terminal which is
mapped to other terminals using separate functions.

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TCP/IP for Unix
▪ TCP/IP – Transmission Control Protocol/Internet
Protocol.
▪ It is a set of communication protocols, first developed
by developed by Defence Advanced Research Project
Agency (DARPA), USA for their network known as
ARPANET.
▪ TCP/IP and UNIX, both born in the research
community, have experienced phenomenal growth
and commercial success over the past decade. TCP/IP
is the network protocol family of choice on the
Internet, the largest and fastest growing data
communications network in the world today.

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▪ The set of TCP/IP protocol encompasses media access,
packet transport, session communications, file transfer,
e-mail and terminal emulation.
▪ The Unix operating system is often regarded as the
platform for portable applications and open systems.
Because, just like TCP/IP, Unix runs on many different
types of computers.
Networking Communication Devices
For efficient transmission of data between and within
networks several special devices are used known as
network devices.

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Some of the important networking devices are:
Bridges
A network device that connects two nwtworks following
the same set of protocols is known as a bridge.
It is a network device that extends a LAN by linking two
networks that may or may not use the same media type
and is used to forward packets between connected
networks.
Besides sending network messages to hardware
addresses, the bridge may need to reformat the packets
containing those messages while crossing the networks
with different sizes of data frames.

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Ground Floor
First Floor
Top Floor
LAN 1
LAN 2
LAN 3
Bridge 2
Bridge 1
Bridges are used to connect networks which must be
geographically close because a bridge is unable to use
a modem to dial up connection and interconnect
networks across telephone line.

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Gateways
▪ Gateway is a device that connects multiple networks
using different protocols and routes packets among
them.
▪ It is also a computer that translates information from
one format to another, if required, to facilitate neywork
traffic on the networks supporting different hardware.
▪ It extends connectivity of the network by overcoming
packet format differences between connected networks
including differences in protocols.
▪ Gateways operate at applications, or top level of the
OSI reference model.

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▪ They link dissimilar networks by translating from one
set of protocol to another, thereby overcoming
differences in transmission speeds, signal levels, and
data format.
▪ Like most computers, a gateway has to be configured
with an operating system and network protocols
before being put it to work.
Routers
▪ Routers are just like bridges but used for very large
networks (e.g. WAN).
▪ It knows the addresses of all computers and also
about other bridges and routers on the network.

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▪ It keeps this information as a dynamic or static table
in itself so that it can decide the most efficient path to
send each data frame from one place to another.
▪ If one part of the network is busy, the router may
decide to forward a message by using a less busy
route. Hence, it acts like a traffic controller in the
network.
Modem
In order to make the communication effective, it is
required that whatever is communicated by the source,
should reach the destination in the same order and in
the original state.

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Modem (from modulator-demodulator) is a device that
modulates an analog carrier signal to encode digital
information, and also demodulates such a carrier signal
to decode the transmitted information.
The goal is to produce a signal that can be transmitted
easily and decoded to reproduce the original digital data.
Modems can be used over any means of transmitting
analog signals, from driven diodes to radio.
Types of Modems
Modems can be classified on the basis of transmission
speed, and machine and modem interconnection.

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• On the basis of transmission speed modems can be
classified under the following categories:
• Low speed modems which can operate up to a speed
of 600 bps.
• Medium speed modems which can operate from 1200
to 3000 bps.
• High speed modems which can operate over from 4800
to 19.2 kbps.
• Limited distance modems operate over a short distance
(usually up to 50 miles). Transmission rate may range
from 9600 bps to 19.2 kbps.

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• Wide band Modems which can operate at speeds of
over 19.2 kbps.
Cable modem

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On the basis of machine and modem interconnection,
modems can be classified as :
• Internal Direct Connect Modems : These modems
are installed inside the computers. They can be
installed inside the computer in a slot and receive
power supply from the computer itself.
• External Direct Connect Modems: These devices
are kept external to the computer, i.e. they are not
installed within the computer.
They have separate power supply for them and also a
connecting port which is used to connect it with the
computer.

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Decoders-Encoders
• Generally multimedia products are transmitted in
compressed mode.
• The process of compressing data at the sending end is
known as encoding and the process of decompressing
it at the receiving end is known as decoding.
• An encoder is a device used to change a signal(such
as a bitstream) or data into a code. The code may
serve any of a number of purposes such as
compressing information for transmission or storage,
encrypting or adding redundancies to the input code, or
translating from one code to another. This is usually
done by means of a programmed algorithm, especially

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if any part is digital, while most analog encoding is done
with analog circuitry.
• A decoder is a device which does the reverse of an
encoder, undoing the encoding so that the original
information can be retrieved. The same method used to
encode is usually just reversed in order to decode.
• Their task is asymmetric because encoding is needed
only once where as decoding is required a number of
times; whenever user requires to use the data.
• Most of the systems prefer to have decoding faster and
simpler even at the price of making encoding slow and
complicated.

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Multiplexers
• In electronics, a multiplexer or mux (occasionally
the term muldex is also found, for a combination
multiplexer-demultiplexer) is a device that performs
multiplexing; it selects one of many analog or digital
input signals and outputs that into a single line.
• In electronics, a demultiplexer (or demux) is a device
taking a single input signal and selecting one of many
data-output-lines, which is connected to the single
input. A multiplexer is often used with a
complementary demultiplexer on the receiving end.

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• An electronic multiplexer can be considered as a
multiple-input, single-output switch, and a
demultiplexer as a single-input, multiple-output switch..
• The technique of multiplexing is very cost-effective
because a relatively small iinvestment in multiplexing
equipment can produce some astounding multiples in
the information carrying capacity of a data channel.
Multiplexing is of three types:
1. 1. Space Division Multiplexing (SDM)
2. 2. Frequency Division Multiplexing (FDM)
3. 3. Time Division Multiplexing (TDM)

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• If multiple incoming connections need to be connected
with multiple outgoing connections, then hub is
required.
• In a data communications, a hub is a place of
convergence where data arrives from one or more
directions and is forwarded out in one or more other
directions.
• Hubs are multiport repeaters.
• They operate at the OSI Model – Physical layer.
• Used to provide a Physical Star Topology. At the center
of the star is the Hub, with the network nodes located
on the tips of the star.

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Switches
• Switches are used to performing bridges functions as
well as point-to-point dedicated connections.

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• Switch operates at data-link layer of the OSI Model.
• A directed frame appearing on one part of a switch is
forwarded only to the destination port.
• Fast switching is designed to allow multiple sessions
of 10 mbps. Traffic is rapidly switched between the
input and output ports on the switch to create these
multiple sessions.
• We can establish as many concurrent 10 mbps links
as there are available pairs of communications on the
switch. These switches are operating as store and
forward device.

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Physical Communication Media
A data communication channel is a path through a
medium that takes data to accomplish a
communication task.
These communication channels are known as links.
The communication links are established using various
types of transmissiion media.
Some of the major transmission media used for data
transmisson are:
1. Twisted Pair Cables
2. Co-axial Cables
3. Microwave Links

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4. Radio Waves
5. Fibre Optic Cables
6. Satellite Links
Twisted Pair Cables
• Twisted Pair cables consist of two insulated copper
wires approximately 1 mm thick an inter-twined to
nutralize induced signals.
• It can be used for both analogue and digital
transmission.

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• Because of low cost and adequate performance it is
commonly used in telephone systems.
• Twisted pair technology avoids mixing of signals (cross
talks).

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• Twisted pair cabling comes in two varieties: shielded
and unshielded. Unshielded twisted pair (UTP) is the
most popular and is generally the best option for school
networks.
Co-axial Cables
• The term coaxial comes from the inner conductor and
the outer shield sharing the same geometric axis.
• The core of the co-axial cable consists of a solid copper
wire which is surrounded by an insulating material.
• The insulator is encased by a cylindrical conductor and
the outer conductor is covered in a protective insulating
sheath.

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• It can be used for both analogue and digital
transmission and provides a high performance
communication path for applications requiring bulk
transmission of data at high data transfer rate.

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• Co-axial cables are used in implementing a Local Area
Network (LAN).
• Coaxial cables are often used as a transmission line for
radio frequency signals.
• A coaxial cable provides protection of signals from
external electromagnetic interference, and effectively
guides signals with low emission along the length of
the cable.
Micro Wave System
• These systems use very high frequency radio signals for
transmitting data through space.

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• Data may be transmitted along a ground route by a
repeater station which receives the data, amplifies it
and again re-transmits it.

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• These repeater stations are usually located about 40-
50 kilometers apart.
• The microwave signals mayalso be passed onto a
communication satellite that acts as a reflector
accepting signals from one point on earth and returning
the same to another point on earth.
Radio Wave
• To use radio waves as a communication media,
permission has to be obained from the competent
authority who also allocates the frequency at which
transmission and reception is under done.

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• It is illegal to use a frequency that has not been
allocated.
• The radio wave system works similarly as microwave
systems and is used in comparatively small networks.

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Optical fibre
• An optical fiber (or fibre) is a glass or plastic fiber
that carries light along its length.
• Optical fibers are widely used in fiber-optic
communication, which permits transmission over
longer distances and at higher data rates than other
forms of communications.
• Fibers are used instead of metal wires because signals
travel along them with less loss, and they are immune
to electromagnetic interference.

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• Optical fibre provides high performance capabilities of
wide band width, high noise immunity and long distance
spacing between signal amplifiers.
• The bandwidth of an optical transmission system is
extremely large.

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• This system receives an electric signal and converts the
light pulses to their corresponding electric signals.
Light Transmission through Fiber-Optic Cable Outer Cladding
Light kept inside Fiber by total Internal Reflection
Inner
Core
Fig: Optical Transmission

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An optical transmission system consists of mainly three
components:
Light Source : It emits light pulses whenever
an Electric Pulse is applied,
e.g. Light Emitting Diode
(LED).
Transmission Medium : It is an ultra thin wire of glass
fibre or fused silica.
Light Detector : It generates an electric pulse
when light falls on it, e.g.
photo diode.

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Satellite Link
A satellite link is a communications subsystem that
involves a link between a transmitting Earth station and
a receiving Earth station via a communications satellite.
Satellite Transmission

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Beyond a cerain distance it is not possible to communicate
through ground methods due to two main reasons:
• Fading of signals which cannot be amplified without
noise.
• Geographical reasons.
In such cases, data is beamed to a communication satellite
that acts as a reflector by accepting signals from one point
on earth and returning the same signals to some other
point on earth.
Micro waves and lower-frequency radio waves can be used
to create long distance satellite transmission system.

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Baud and Bandwidth
Baud can be defined as the number of times per second
that the transmission signal changes its value.
An ‘n’ baud line need not necessarily transmit ‘n’
bits/second because of the fact that each signal might
convey several bits.
In case of binary signals 0 and 1, the bit rate and baud
rate would be equal.
In case a signal has 8 different levels (0,1,2,,3,4,5,6,7)
each voltage level can be used to represent 3 bits.

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e.g. :
0 Level (VOLT) can represent 000
1 Level (VOLT) can represent 001
2 Level (VOLT) can represent 010, and
so on.
Bandwidth is the range of frequencies in which the
data can be transmitted on a particular media.
Bandwidth of any transmission media depends upon the
following characteristics of the media.
• Material of the medium (Copper, Silver and Iron)
• Diameter of the conductor
• Resistance of the medium

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Bandwidth can be defined as a difference between
highest frequency and lowest frequency.
Bandwidth = Highest Frequency (FH
) – Lowest
Frequency(FL
)
Characteristics of Communication Channels
Narrow Band
▪ Handles low data volumes.
▪ Data transmission rates (band rate) are from 45 to
300.
▪ Used by low speed devices.

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Voice Band
▪ Handles moderate data volumes.
▪ Data transmission rates (band rate) are from 300 to
9600.
▪ Mainly used for telephone voice communication.
Broad Band
▪ Handles very large volume of data.
▪ Data transmission rates (band rate) are more than 1
million bauds.
▪ Application areas are high-speed data analysis and
satellite communication.

Computer Network and Communication Overview

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