Computer network introduction

 Definition & applications of computer network
 Components of computer network
 Network benefits
 Disadvantages of computer network
 Classification by their geographical area
 Network classificationby their component role
 Typesof servers
 SignalClassification
 SignalParameters
 TransmissionImpairments
 MaximumDataRate
 TypesofCommunication
 TransmissionModes

 Computer: Computer once meant a person who did
computations, but now the term almost universally
refers to automated electronic machinery.
 Network: It is a collection of computers, servers,
mainframes, network devices, peripherals, or other
devices connected to one another to allow the
sharing of data. An excellent example of a network is
the Internet, which connects millions of people all
over the world.

 COMPUTER NETWORK:
 A computer network isdefined asthe interconnection of two
or more computers. It isdone to enable the computersto
communicate and share available resources.
 APPLICATIONS:
i. Sharing of resourcessuchasprinters
ii. Sharing of expensive software's and database
iii. Communication from one computer to another
computer
iv. Exchangeof data and information among usersvia
 network
v. Sharing of information over geographically wide areas.

Thereare5basiccomponentsofComputerNetwork:
 Transmitter
 Reciever
 Channel
 Message
 Protocol

 The network provided to the userscan be
divided into two categories:
i. Sharing
ii. Connectivity

 Typesof resources are:
1. Hardware: A network allows usersto share
many hardware devicessuchasprinters,
modems, fax machines, CD ROM, players,
etc.
2. Software: sharing software resourcesreduces
the costof software installation, savesspaceon
hard disk.

o Increased speed
o Reduced cost
o Improved security
o Centralized software managements
o Electronic mail
o Flexible access

o High costofinstallation
o Requires time for administration
o Failure of server
o Cable faults

 LAN isa network which isdesigned to operate
over a small physical area suchasan office,
factory or a group of buildings.
 LAN’s are easy to design and troubleshoot
 Exchange of information and sharing of resources
becomeseasy becauseof LAN.
 In LAN all machines are connected to a single
cable.
 Different types of topologies suchasstar, tree,
bus, ring, etc Can be used
 It isusually a privately ownednetwork.

 When network spansover a large distance or
when the computers to be connected to each other
are at widely separated locations a local area
network cannot be used.A wide area
network(WAN) isinstalled.
 The communication between different usersof
WAN isestablished usingleased telephone
lines, satellite links and similar channels.
 It ischeaper and more efficient to usethe phone
network for the link.
 Most WAN networks are usedto transfer large
blocksof data between its users.

 A personal area network isa computer network
organized around an individual person.
 It generally consistsof a mobile computer, a cell
phone or personal digital assistant. PAN enables
the communication among these devices.
 It can alsobe usedfor communication among
personal devicesthemselves for connecting to a
digital level network and internet.
 The PANs can be constructedusingwirelessor
cables.

PARAMETERS LAN WAN MAN
Ownership of
network
Private Private or public Private or public
Geographical
area covered
Small Very large Moderate
Design and
maintenance
Easy Not easy Not easy
Communication
medium
Coaxial cable
PSTNor satellite
links
Coaxial cables,
PSTN,optical
fibre, cables,
wireless
Bandwidth Low High moderate
Data
rates(speed)
High Low moderate

LOCALAREANETWORK
PEERTO PEER NETWORK CLIENT SERVERNETWORK

 In peer to peer network each computer isresponsible for
making its own resourcesavailable to other computers on the
network.
 Eachcomputer isresponsible for setting up and maintaining
its own security for these resources.
 Alsoeach computer isresponsible for accessingthe required
network resourcesfrom peer to peer relationships.
 Peer to peer network isuseful for a small networkcontaining
lessthan 10computers on a single LAN .
 In peer to peer network each computer can function asboth
client and server.
 Peer to peer networks do not have a central control system.
There are no serversin peer networks.
 Peer networks are amplified into home group.

 Disadvantages:
 Not very secure
 No central point of
storage or file archiving
 Additional load on
computer because of
resource sharing
 Hard to maintain
version control
Advantages:
 Useless expensive
computer hardware
 Easyto administer
 No NOS required
 More built in redundancy
 Easysetup & low cost

 In client-server network relationships, certain computers act
asserverand other act asclients.A server issimply a
computer, that available the network resourcesand provides
serviceto other computers when they request it. A client is
the computer running a program that requeststhe service
from a server.
 Local area network(LAN) isbased on client server network
relationship.
 A client-server network isone n which all available network
resourcessuchasfiles, directories, applications and shared
devices, are centrally managed and hosted and then are
accessedbyclient.
 Client servenetwork are defined by the presenceof serverson
a network that provide security and administration of the
network.

DISADVANTAGES OF CLIENT-
SERVERNETWORK
Advantages:
 Very secure
 Better performance
 Centralized backup
 very reliable
Disadvantages:
 requires professional
administration
 More hardware-
intensive
 More software
intensive
 Expensivededicated
software

 File server: These servers provide the services for
storing, retrieving and moving the data. A user can
read, write, exchange and manage the files with the
help of file servers.
 Printer server: The printer server is used for controlling and
managing printing on the network. It also offers the fax
service to the network users.
 Application server: The expensive software and additional
computing power can be shared by the computers in a
network with he help of application servers.
 Message server: It is used to co-ordinate the interaction
between users, documents and applications. The data can be
used in the for of audio, video, binary, text or graphics.
 Database server: It is a type of application server. It allows the
uses to access the centralised strong database.

 Signals are classified into the following categories:
 Continuous Time and Discrete Time Signals
 Analog & Digital Signals
 Deterministic and Non-deterministic Signals
 Even and Odd Signals
 Periodic and Aperiodic Signals
 Energy and Power Signals
 Real and Imaginary Signals

In communication system, analog signals travel through
transmission media, which tends to deteriorate the quality of
analog signal. This imperfection causes signal impairment.
This means that received signal is not same as the signal that
was send.

Data rate governs the speed of data transmission. A very
important consideration in data communication is how
fast we can send data, in bits per second, over a channel.
Data rate depends upon 3 factors:
 The bandwidth available
 Number of levels in digital signal
 The quality of the channel – level of noise

For a noiseless channel, the Nyquist bit rate formula
defines the theoretical maximum bit rate
 BitRate = 2 * Bandwidth * log2(L)
In the above equation, bandwidth is the bandwidth of the
channel, L is the number of signal levels used to represent
data, and BitRate is the bit rate in bits per second.
Bandwidth is a fixed quantity, so it cannot be changed.
Hence, the data rate is directly proportional to the number
of signal levels.

In reality, we cannot have a noiseless channel; the channel is always
noisy. Shannon capacity is
used, to determine the theoretical highest data rate for a noisy
channel:
 Capacity = bandwidth * log2(1 + SNR)
In the above equation, bandwidth is the bandwidth of the channel,
SNR is the signal-to-noise ratio, and capacity is the capacity of the
channel in bits per second.
Bandwidth is a fixed quantity, so it cannot be changed. Hence, the
channel capacity is directly proportional to the power of the signal,
as SNR = (Power of signal) / (power of noise).
The signal-to-noise ratio (S/N) is usually expressed in decibels (dB)
given by the formula:
 10 * log10(S/N)

Synchronous Transmission:
In Synchronous Transmission, data is sent in form of blocks or frames. This
transmission is the full duplex type. Between sender and receiver the
synchronization is compulsory. In Synchronous transmission, There is no
gap present between data. It is more efficient and more reliable than
asynchronous transmission to transfer the large amount of data.

 Asynchronous Transmission:
In Asynchronous Transmission, data is sent in form of byte or character. This
transmission is the half duplex type transmission. In this transmission start
bits and stop bits are added with data. It does not require synchronization.

Transmission mode means transferring of data between two devices. It is also
known as communication mode. Buses and networks are designed to allow
communication to occur between individual devices that are interconnected.
 In Simplex mode, the communication is unidirectional, as on a one-way
street. Only one of the two devices on a link can transmit, the other can
only receive.
 In half-duplex mode, each station can both transmit and receive, but not at
the same time. When one device is sending, the other can only receive, and
vice versa.
 In full-duplex mode, both stations can transmit and receive
simultaneously.

Computer network introduction

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