The Evolution of Computer Networks Mohammad Firoz Alam Electronics & Communication Engineering AFSET Al!Falah Al!Falah "niversit# Farida$ad %hau 'ar#ana ()ndia*
[email protected]
throu thr ough gh interrac inte acttiv ive e connected by point-to-
terrmin te inal als s
Abstract- The
concept of network is not new. In simple terms it means an interconnected set of some objects. for decades we are familiar with the radio, television, railway, highway, bank and other types of networks. In recent recent years, years, the network that is making making signific significant ant impact in our day-to-day life is the computer network. By computer network we mean an interconnected interconnected set of autonomous computers. The term autonomous implies that the computers can function independent of others. Keywords- !"#$T, Broadcast network , "oint to point network, %#, &#, '#, Internetworking, !outing and (ongestion (ontrol.
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The histor# of electronic computers is not ver# old+ )t came into e,istence in the earl# -./0s and during the first two decades of its e,istence it remained as a centralized s#stem housed in a single large room+ )n those da#s the computers were large in size and were operated $# trained personnel+ To the users it was a remote and m#sterious o$ect having no di dire rect ct com commu muni nica cati tion on wi with th th thee us user ers+ s+ 1o$s were su$mitted in the form of punched carrds or pa ca pape perr ta tape pe an and d ou outtpu putts we were re collected in the form of computer printouts+ The su$ su$mit mitted ted o$ o$ss wer weree e,ec e,ecute uted d $# the comp co mput uter er on onee af afte terr th thee ot othe herr wh whic ich h is referred to as $atch mode of data processing+ )n th this is sc scen enar ario io th ther eree wa wass lo long ng de dela la# # $etween the su$mission of o$s and receipt of the results+In the 1960s, computer
systems system s we were re sti still ll cen centra traliz lize, e, but users use rs pr provi ovided ded wi with th dir direct ect acc access ess
point low-speed low-speed data links with the computer. In this situation, a large number of users some of them located in remote remo te lo locat catio ions ns co coul uld d si simu mult ltane aneou ousl sl# # access acce ss the cent central ralized ized com comput puter er in tim time! e! division multiple,ed mode+ The users could now no w ge gett im imme medi diat atee in inte tera ract ctiv ivee fe feed ed$ac $ack k fro rom m the co com mpu pute terr an and d co corrrec ectt er errror orss immediatel#+ Following the introduction of on!line terminals and time!sharing operating s#stems remote terminals were used to use the central computer+ II.
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Computer networks have emerged as a result of the convergence of two technologies of this centur# computer and communication as show shown n in Fig+ Fig+- The The cons conse2 e2uen uence ce of this this revolutionar# merger is the emergence of a integrated s#stem that transmit all t#pes of data and information+ There is no funda undam menta entall dif differen erence ce $et $etween ween data data commun communica icatio tions ns and data data proces processin sing g and there are no fundamental differences among data voice and video communications+
Fig+- Evolution of computer networks
3ith the advancement of 45S) technolog# and particularl# after the invention of microprocessors in the earl# -.60s the computers $ecame smaller in size and less e,pensive $ut with significant increase in processing power+ New $reed of low!cost computers known as mini and personal computers were introduced+ )nstead of having a single central computer an organization could now afford to own a num$er of computers located in different departments and sections+Side!$#!side riding on the same 45S) technolog# the communication technolog# also advanced leading to the worldwide deplo#ment of telephone network developed primaril# for voice communication+ An organization having computers located geographicall# dispersed locations wanted to have data communications for diverse applications+ Communication was re2uired among the machines of the same kind for colla$oration for the use of common software or data or for sharing of some costl# resources+ This led to the development of computer networks $# successful integration and cross!fertilization of communications and geographicall# dispersed computing facilities+ 7ne significant development was the A89ANET (Advanced 8esearch 9roects Agenc# Network*+ Starting with four!node e,perimental network in -.:. it has su$se2uentl# grown into a network several thousand computers spanning half of the
glo$e from 'awaii to Sweden+ Most of the present!da# concepts such as packet switching evolved from the A89ANET proect+ The low $andwidth (;<'z on a voice grade line* telephone network was the onl# generall# availa$le communication s#stem availa$le for this t#pe of network+ The $andwidth was clearl# a pro$lem and in the late -.60s and earl# =0s another new communication techni2ue known as 5ocal Area Networks (5ANs* evolved which helped computers to communicate at high speed over a small geographical area+ )n the later #ears use of optical fi$er and satellite communication allowed high!speed data communications over long distances+ . (lassification )f (omputer #etworks Based )n Transmission Technology / >roadcast networks? a single communication channel that is shared $# all the machines on the network+
Fig+ @ E,ample of a $roadcast network $ased on shared $us
0/ 9oint!to!point networks? This network consists of man# connections $etween individual pairs of machines+ To go from the source to destination a message (or packet* ma# have to visit one or more intermediate machines+
Fig+ ; Communication network $ased on point!to!point communication
B. (lassification of computer networks Based on cale Fig+ 5ocal Area Network
/ 5AN 15ocal Area Network /2
)t is privatel# owned communication s#stems that cover a small area sa# a $uilding or a comple, of $uildings+ 5ength is a$out -0 meters to few kilometers and operates at a high speed like -0 M>9S to -000 M>9S+
0/ MAN (Metropolitan Area Network*?
)t is pu$lic or privatel# owned communication s#stem that t#picall# covers a complete cit#+ Speed is a$out -0 M>9S and follows %B%> (%istri$uted Bueue %ou$le >us* standard+ )ts relia$ilit# is moderate+
Fig+ : Metropolitan Area Networks
3/ 3AN (3ide Area Network*?
)t covers a large geographical area+ %ata transfer rate is low (few <>9S to -0 M>9S* and error rate is much higher+
medium+ Some e,amples of $roadcast communication networks are? -* @* ;* *
5ocal Area Network (5AN* 9acket 8adio Network Cellular Telephone Network Satellite Network
These networks can $e characterized $# the following three parameters? Transmission media Topolog# Medium access control (MAC* techni2ues • • •
$. Internetworking 4ig. 5 3ide Area Network
(. Internet
)nternet is a collection of networks or network of networks+ 4arious networks such as 5AN and 3AN connected through suita$le hardware and software to work in a seamless manner+ )t allows various applications such as e!mail file transfer remote log!in 3orld 3ide 3e$ Multimedia etc run across the internet+
To make the computer networks more useful and suita$le for man# emerging applications it is necessar# to connect individual heterogeneous networks $oth 5AN and 3AN distri$uted across the world using suita$le hardware and software in such a wa# that it gives the user the illusion of a single network+ >asic motivations $ehind internetworking are as follows? To provide a link $etween networks+ To provide a route for deliver# of data $etween processes on different networks+ To provide an accounting service that keeps track of the use of various networks and routers and also to maintain status information+ To accommodate a num$er of differences among the networks? o Addressing scheme o Ma,imum packet size o Network!access mechanism o Timeouts Error recover# o Status reporting o 8outing techni2ues o "ser!access control o Connection oriented connectionless services • •
•
•
Figure+ = )nternet D network of networks
*. Broadcast (ommunication #etworks
)n >roadcast networks one transmission media is shared $# all the users and information is $roadcast $# an user into the
4+ !outing and (ongestion (ontrol
3hen a packet travels from a source to a destination it is likel# to pass through several routers and normall# there e,ist multiple paths $etween an# two source! destination pairs+ The routing function of the network la#er decides which path a packet to follow from a source node to a destination node+ For a connectionless (datagram t#pe* service each packet is routed independentl# whereas for a virtual!circuit t#pe of service a route is set up at the $eginning and all packets follow the same path+ The attri$utes which are e,pected from a routing function are? correctness, simplicity, robustness, stability fairness and optimality and the routing algorithms can $e classified $ased on different metrics+ various issues related to routing+Three popular routing algorithms namel# Routing Information Protocol (8)9* Open Shortest Path First (7S9F* and Border Gateway Protocol (>9* )nterior atewa# 8outing 9rotocol ()89* Enhanced )nterior atewa# 8outing 9rotocol (E)89*+ A packet switched network ma# $e considered as a network of 2ueues+ )f the rate at which packets arrive and 2ueue up e,ceeds the rate at which packets are dis$ursed the 2ueue size grows without $ounds leading to long dela# and $uffer overflow+ "ltimatel# it ma# lead to deadlock a catastrophic situation in which the throughput drops to zero as shown in+ The o$ective of the congestion control is to maintain the num$er of packets within the network or a region of network $elow the level at which 2ueuing dela#s $low up+
internet which is essentiall# an insecure pu$lic network+ Cr#ptograph# has $een considered to $e the solution to this pro$lem+ Suita$le encryption / decryption techni2ues can $e used for transfer of data through internet $etween an# two hosts in a secured manner+ 5esson =+- of this module provides an overview of the vast su$ect of Cr#ptograph#+ Then lesion =+@ presents how cr#ptograph# can $e applied in a num$er of wa#s to achieve secured communication through an insecure communication network+ Moreover man# organizations have confidential or proprietar# information such as trade secrets product development plans marketing strategies etc+ which should $e protected from unauthorized access and modification+ Although cr#ptographic techni2ues can $e used to protect data in transit it does not protect data from digital pests and hackers+ To accomplish this it is necessar# to perform user authentication and access control to protect a private network from unauthorized traffic+ This can $e performed with the help of a firewall which acts as an interface $etween a private network and an insecure pu$lic network+
III. )M978 TANT >ENEF)TS 7F C7M9"TE8 NET378
6. #etwork ecurity 3ith the a$ilit# to contact an#$od# from an#where and more and more people oining the internet with diverse applications network securit# has $ecome a ver# important issue+ 9eople are now ver# concerned a$out communication in a secured manner through
8esource sharing 9owerful communication medium 'igher relia$ilit# 'igher fle,i$ilit# 5ower cost )ncremental e,pansion 7.
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Computer network can have a large num$er of computers which can share software data$ase and other resources+ )n the event of failure of one computer its workload can $e taken over $# other computers+ So it provides higher relia$ilit# than centralized computing s#stem+ 8e2uirement of software hardware data$ase etc+ increases graduall#+ )n centralized
computing s#stem if one computer is not a$le to serve the purpose we have to replace it $# new one+ 8eplacement of new computer re2uires lot of investment and effort which can $e avoided in computer network s#stem+ )f there is need for more one can $u# another powerful computer add it to computer network and use it+ The various resources like computers peripherals etc+ can $e added in a scala$le manner+
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;rd Edition Springer G/H
Network Securit# 9rivate Communication in a 9u$lic 3orld Charlie
G:H %ata Communications and Networking >ehrouz A+ Forouzan TM' G6H %ata and Computer Communications 3illiam Stallings 9') G=H Computer Networks Andrew S+ Tanen$aum 9') G.H Networking 9rotocol Configurations C)SC7 s#stems retrieved @00=!-0!-:+ G-0H Cisco Certified Network Associated $# 8ichard %eal Tata
G-H 3ireless Communications 9rinciples and 9ractice Theodore E+ 8appaport @nd Edition 9earson Education G@H
Satellite Communications Timoth# 9ratt Charles >ostian and 1erem# Allnutt @nd Edition 3ile#
G;H )nternetworking with TC9)9 9rinciples 9rotocols and Architecture %ouglas E+ Commer ;rd Edition 9rentice 'all of )ndia GH %ata Compression The Complete 8eference %avid Solomon
Mcgraw!'ill Edition+ (@0-0* G--H Computer Networks ># 4+S+ >agad And )+A+ %hotre @E Technical 9u$lication 9une+