Lecture Notes - Introduction to Computer Network

Description:
Welcome to the comprehensive guide on Computer Network concepts, tailored for final year B.Sc. Computer Science students affiliated with Alagappa University. This document covers fundamental principles and advanced topics in Computer Network. PDF content is prepared from the text book Computer Network by Andrew S. Tenanbaum

Key Topics Covered:

Main Topic : Introduction to Computer Network
Sub-Topic : Uses of Computer Networks , Network Hardware and network software , OSI & TCP/IP Reference models, Example Networks : Internet.

Target Audience:

Final year B.Sc. Computer Science students at Alagappa University seeking a solid foundation in Computer Network principles for academic.
About the Author:
Dr. S. Murugan is Associate Professor at Alagappa Government Arts College, Karaikudi. With 23 years of teaching experience in the field of Computer Science, Dr. S. Murugan has a passion for simplifying complex concepts in database management.

Disclaimer:
This document is intended for educational purposes only. The content presented here reflects the author’s understanding in the field of Computer Network as of 2024.

1. Introduction
Computer Network
Dr. S.Murugan
Associate Professor, Department of Computer Science.
AlagappaGovernment Arts College,
(Affiliated by AlagappaUniversity)
Karaikudi.
Email: [email protected]

2. This slides compiled from
Computer Network by
Andrew S. Tenenbaum 4
th
Ed.

3. Introduction
➢Eachofthepastthreecenturieshasbeendominatedby
asingletechnology
➢The18thcenturywastheeraofthegreatmechanical
systemsaccompanyingtheIndustrialRevolution.
➢The19thcenturywastheageofthesteamengine.
➢Duringthe20thcentury,thekeytechnologywas
informationgathering,processing,anddistribution.

4. Introduction -Computer Nework
▪Acollectionofautonomouscomputers
interconnectedbyasingletechnology.
▪Twocomputersaresaidtobeinterconnectedifthey
areabletoexchangeinformation.
▪Theconnectionneednotbeviaacopperwire;fiber
optics,microwaves,infrared,andcommunication
satellitescanalsobeused.

5. Introduction -Computer Nework

6. Internet and World Wide Web
➢Theinternetisamassivenetworkofnetworks,It
connectsmillionsofcomputerstogetherglobally,
forminganetworkinwhichanycomputercan
communicatewithanyothercomputeraslongasthey
arebothconnectedtotheinternet.Informationthat
travelsovertheinternetdoessoviaavarietyof
languagesknownasprotocols.
➢TheWorldWideWeb,orsimplyweb,isawayof
accessinginformationoverthemediumoftheinternet.

7. Internet and Distributed System
➢TheInternetisnotasinglenetwork,but
anetworkofnetworks
➢Inadistributedsystem,acollectionof
independentcomputersappearstoits
usersasasinglecoherentsystem.
➢Awellknownexampleofadistributed
systemistheWorldWideWeb,inwhich
everythinglookslikeadocument(Web
page).

8. Uses of Computer Network
➢Business Applications
➢Home Applications
➢Mobile Users
➢Social Issues

9. Business Applications
➢Manycompanieshaveasubstantialnumberofcomputers.For
example,acompanymayhaveseparatecomputerstomonitor
production,keeptrackofinventories,anddothepayroll
➢Theclientandservermachinesareconnectedbyanetwork,asillustratedin
Fig.1-1.Thiswholearrangementiscalledtheclient-servermodel.
Fig. 1.1 Client Server Model

10. Business Applications –cont…
➢The detailed client server model illustrated in Fig. 1-2.
➢Thecompanyemployeecansharetheirinformationthroughe-mail.
➢Thecompanyemployeecansharetheirideasthroughvideoconferencing.
➢Manycompaniesaredoingbusinesselectronicallywithothercompanies,
especiallysuppliersandcustomers.
➢DoingbusinesswithconsumersovertheInternet.Manycompanies
providecatalogsoftheirgoodsandservicesonlineandtakeorderson-
line.Itiscallede-commerce(electroniccommerce).

11. Home Applications
➢Initially, for word processing and games.
➢more popular uses of the Internet for home users are as follows:
1.Access to remote information.
-surfing the World Wide Web for information
2. Person-to-person communication. (person-to-person communication )
-to distinguish it from the client-server model In this form,
individuals who form a loose group can communicate with others
in the group, as shown in Fig. 1-3.
3. Interactive entertainment.
It may be possible to select any movie or television program ever
made, in any country, and have it displayed on your screen
instantly.
4. Electronic commerce.
Home shopping is already popular and enables users to inspect
the on-line catalogs of thousands of companies. (Fig 1.4)

12. Home Applications -Cont

13. Home Applications -Cont

14. Mobile Users
➢Mobilecomputers,suchasnotebookcomputersandpersonaldigital
assistants(PDAs),areoneofthefastestgrowingsegmentsofthe
computerindustry.
➢Food,drink,andothervendingmachinesarefoundeverywhere.
However,thefooddoesnotgetintothemachinesbymagic.Periodically,
someonecomesbywithatrucktofillthem.Ifthevendingmachines
issuedawirelessreportonceadayannouncingtheircurrentinventories,
thetruckdriverwouldknowwhichmachinesneededservicingandhow
muchofwhichproducttobring.

15. Social Issues
➢newsgroupspeoplecanexchangemessageswithlike-
mindedindividuals.
➢employeerightsversusemployerrights.Manypeopleread
andwritee-mailatwork
➢Thegovernmentdoesnothaveamonopolyonthreatening
people'sprivacy.Theprivatesectordoesitsbittoo.
(companiestotrackusers'activitiesincyberspace)
➢Computernetworksofferthepotentialforsending
anonymousmessages
➢Alotoftheseproblemscouldbesolvedifthecomputer
industrytookcomputersecurityseriously.

16. Network Hardware
➢Criteria 1: Transmission Technology
-Broadcasting
-Point to point
➢Criteria 2: Scale
-Personal Area Network (PAN)
-Local Area Network
-Metropolitan Area Network
-Wide Area Network
-Internetwork
-Wireless network (System Interconnection, Wireless
LAN, Wireless WANs)

17. Network Hardware Cont…
➢Thenetworkhardwarecanbeclassifiedintotwocriterionone
istransmissiontechnologyandanotheroneisscale.
➢There are two types of transmission technology that are in
widespread use. They are as follows:
1. Broadcast links.
2. Point-to-point links
➢Incomputernetworking,broadcastingreferstotransmittinga
packetthatwillbereceivedbyeverydeviceonthenetwork.
➢Multicastisagroupcommunicationwheredatatransmissionis
addressedtoagroupofdestinationcomputers
simultaneously.Multicastcanbeone-to-manyormany-to-
manydistribution.

18. Network Hardware Cont…
➢point-to-pointnetworksconsistofmanyconnectionsbetween
individualpairsofmachines.
➢Togofromthesourcetothedestination,apacketonthistype
ofnetworkmayhavetofirstvisitoneormoreintermediate
machines.
➢Oftenmultipleroutes,ofdifferentlengths,arepossible,so
findinggoodonesisimportantinpoint-to-pointnetworks.
➢Point-to-pointtransmissionwithonesenderandonereceiveris
sometimescalledunicasting.

19. Network Hardware Cont…

20. ➢The network hardware can be classified by their scale. In Fig. 1-6
we classify multiple processor systems by their physical size.
Network Hardware Cont…

21. Personal Area Network
➢Awirelessnetworkconnectingacomputerwithits
mouse,keyboard,andprinterisapersonalarea
network
Computer Networks, Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education-Prentice Hall, 2011

22. ➢Localareanetworks,generallycalledLANs,areprivately-
ownednetworkswithinasinglebuildingorcampusofuptoa
fewkilometersinsize.
➢Theyarewidelyusedtoconnectpersonalcomputersand
workstationsincompanyofficesandfactoriestoshare
resources(e.g.,printers)andexchangeinformation.
➢LANsaredistinguishedfromotherkindsofnetworksbythree
characteristics:
(1)theirsize(Distance)
(2)theirtransmissiontechnology(broadcastor
pointtopoint),and
(3)theirtopology(BusorRing).
Local Area Networks

23. ➢VarioustopologiesarepossibleforbroadcastLANs.Figure
1-7showstwoofthem.
➢AbustopologyisatopologyforaLocalAreaNetwork(LAN)
inwhichallthenodesareconnectedtoasinglecable.
➢Thecabletowhichthenodesconnectiscalleda"backbone".
Ifthebackboneisbroken,theentiresegmentfails.
Local Area Networks

24. ➢Aringnetworkisanetworktopologyinwhicheachnode
connectstoexactlytwoothernodes,formingasingle
continuouspathwayforsignalsthrougheachnode-aring.
➢Datatravelsfromnodetonode,witheachnodealongtheway
handlingeverypacket.
Local Area Networks

25. ➢Ametropolitanareanetwork,orMAN,coversacity.Thebest-
knownexampleofaMANisthecabletelevisionnetwork
availableinmanycities.
➢Ametropolitanareanetwork(MAN)issimilartoalocalarea
network(LAN)butspansanentirecityorcampus.
➢MANsareformedbyconnectingmultipleLANs.Thus,MANs
arelargerthanLANsbutsmallerthanwidearea
networks(WAN).
➢AmetropolitanareanetworkasshowninFigure1-8.
Metropolitan Area Networks

26. Metropolitan Area Networks

27. ➢Awideareanetwork,orWAN,spansalargegeographical
area,oftenacountryorcontinent.
➢Itcontainsacollectionofmachinesorhosts.
➢Thehostsareconnectedbyacommunicationsubnet.
➢Thesubnetisdefinedasthecollectionofroutersand
communicationlinesthatmovedpacketsfromthesourcehost
tothedestinationhost.
➢Thehostsareownedbythecustomers(e.g.,people'spersonal
computers),whereasthecommunicationsubnetistypically
ownedandoperatedbyatelephonecompanyorInternet
serviceprovider.
Wide Area Networks

28. Wide Area Networks

29. ➢Inmostwideareanetworks,thesubnetconsistsoftwodistinct
components:transmissionlinesandswitchingelementsor
routers.
➢Transmissionlinesmovebitsbetweenmachines.Theycanbe
madeofcopperwire,opticalfiber,orevenradiolinks.
➢Switchingelementsarespecializedcomputersthatconnectthree
ormoretransmissionlines
➢Astore-and-forwardsubnetisamessageswitchingcenterin
whichamessageisacceptedfromtheoriginating
user,i.e.,sender,whenitisoffered,heldinaphysicalstorage,
andforwardedtothedestinationuser,i.e.,receiver
➢Relationbetweenhost,subnetandrouterisshowninFigure1-9.
Wide Area Networks

30. ➢Astreamofpacketsfromsendertoreceiverisrepresentedin
Figure1-10.
➢Inthisfigure,allthepacketsfollowtherouteACE,ratherthan
ABDEorACDE.ACEisthebestroute.
Wide Area Networks

31. ➢Astreamofpacketsfromsendertoreceiverisrepresentedin
Figure1-10.
➢Inthisfigure,allthepacketsfollowtherouteACE,ratherthan
ABDEorACDE.ACEisthebestroute.
Wide Area Networks

32. ➢Awirelessnetworkisacomputernetworkthatuses
wirelessdataconnectionsbetweennetworknodes.
➢wirelessnetworkscanbedividedintothreemaincategories:
1.Systeminterconnection.
2.WirelessLANs.
3.WirelessWANs.
➢Systeminterconnectionisallaboutinterconnectingthe
componentsofacomputerusingshort-rangeradio.
➢Inthesimplestform,systeminterconnectionnetworksusethe
master-slaveparadigmofFig.1-11(a).Thesystemunitis
normallythemaster,talkingtothemouse,keyboard,etc.,as
slaves.
➢AWLAN,orwirelessLAN,isanetworkthatallowsdevicesto
connectandcommunicatewirelessly.Fig.1-11(b).
Wireless Networks

33. Wide Area Networks

34. ➢Thefundamentalideaisthatinthefuturemosthomeswillbeset
upfornetworking.
➢Everydeviceinthehomewillbecapableofcommunicatingwith
everyotherdevice,andallofthemwillbeaccessibleoverthe
Internet.
➢Manydevicesarecapableofbeingnetworked.Someofthemore
obviouscategories(withexamples)areasfollows:
1.Computers(desktopPC,notebookPC,PDA,sharedperipherals).
2.Entertainment(TV,DVD,VCR,camera,stereo,MP3).
3.Telecommunications(telephone,mobiletelephone,intercom)
4.Appliances(microwave,refrigerator,clock,lights)
5.Telemetry(utilitymeter,smoke/burglaralarm)
Home Area Networks

35. ➢Acollectionofinterconnectednetworksiscalledaninternetwork
orinternet.
➢AcommonformofinternetisacollectionofLANsconnectedby
aWAN.
➢Thecombinationofasubnetanditshostsformsanetwork.Inthe
caseofaLAN,thecableandthehostsformthenetwork.
Internetwork

36. ➢Toreducetheirdesigncomplexity,mostnetworksareorganized
asastackoflayersorlevels,eachonebuiltupontheonebelow
it.
➢Thenumberoflayers,thenameofeachlayer,thecontentsof
eachlayer,andthefunctionofeachlayerdifferfromnetworkto
network.
➢Thepurposeofeachlayeristooffercertainservicestothehigher
layers
Network Software -Protocol Hierarchies

37. Network Software -Protocol Hierarchies
➢Afive-layernetworkisillustratedinFig.
➢Theentitiescomprisingthecorresponding
layersondifferentmachinesarecalled
peers.Thepeersmaybeprocesses,
hardwaredevices,orevenhumanbeings.
➢virtualcommunicationisshownbydotted
linesandphysicalcommunicationbysolid
lines.
➢Betweeneachpairofadjacentlayersisan
interface.
➢Asetoflayersandprotocolsiscalleda
networkarchitecture.
➢Alistofprotocolsusedbyacertain
system,oneprotocolperlayer,iscalleda
protocolstack.

38. Network Software –Design Issues
➢Everylayerneedsamechanismforidentifyingsendersand
receivers.Sinceanetworknormallyhasmanycomputers.
➢Therulesfordatatransfer.Insomesystems,dataonlytravelin
onedirection;inothers,datacangobothways.Andalsoit
specifiestheprioritiesofdatatransfereithernormalorurgent
datatransfer.
➢Errorcontrolisanimportantissuebecausephysical
communicationcircuitsarenotperfect.Errorcorrectionand
detectionmechanismtohandleerrorduringtransfer.
➢Notallcommunicationchannelspreservetheorderofmessages
sentonthem.ItispossibletolossofSequencing.

39. Network Software –Design Issues Cont…
➢Anissuethatoccursateverylevelishowtokeepafastsender
fromswampingaslowreceiverwithdata.
➢Theinabilityofallprocessestoacceptarbitrarilylongmessages.
Thispropertyleadstomechanismsfordisassembling,
transmitting,andthenreassemblingmessages.
➢Whentherearemultiplepathsbetweensourceanddestination,a
routemustbechosen.

40. Network Software –Connection Oriented and
Connection less services
➢Connection-orientedserviceismodeledafterthetelephone
system.
➢Thesenderpushesobjects(bits)inatoneend,andthereceiver
takesthemoutattheotherend.
➢Inmostcasestheorderispreservedsothatthebitsarriveinthe
ordertheyweresent.
➢Areliableserviceisimplementedthroughacknowledging
concept.
➢Theacknowledgeconceptintroducesoverheadandtimedelay.It
isnotpossibletolosethedata.
➢TCPistheexampleofconnectionorientedservice.

41. Network Software –Connection Oriented and
Connection less services –Cont…
➢Connectionlessserviceismodeledafterthepostalsystem.
➢Eachmessage(letter)carriesthefulldestinationaddress,and
eachoneisroutedthroughthesystemindependentofallthe
others.
➢Normally,whentwomessagesaresenttothesamedestination,
thefirstonesentwillbethefirstonetoarrive.Sometimesthe
ordermaybevarry.
➢Anonreliableserviceisimplementedwithfasterfiletransfer.
➢Itispossibletolosethedata.
➢TheInternetProtocol(IP)andUserDatagramProtocol(UDP)
areconnectionlessprotocols.

42. Network Software –Connection Oriented and
Connection less services –Cont…

43. Network Software –Connection Oriented and
Connection less services

44. Network Software –Service Primitives
➢Aserviceisformallyspecifiedbyasetofprimitives
(operations)availabletoauserprocesstoaccesstheservice.
➢
➢Asaminimalexampleoftheserviceprimitivesthatmightbe
providedtoimplementareliablebytestreaminaclient-server
environment,listedinFigure1-17.

45. Network Software –Service Primitives Cont…
➢First,theserverexecutesLISTENtoindicatethatitis
preparedtoacceptincomingconnections.
➢Next,theclientprocessexecutesCONNECTtoestablisha
connectionwiththeserver.
➢ThenextstepisfortheservertoexecuteRECEIVEtoprepare
toacceptthefirstrequest.
➢ThentheclientexecutesSENDtotransmititsrequest
followedbytheexecutionofRECEIVEtogetthereply.
➢Ifthedatatransferredsuccessfullythenitcanuse
DISCONNECTtoterminatetheconnection.

46. Network Software –Service Primitives Cont…
➢Figure.1-18brieflysummarizeshowclient-server
communicationmightworkoveraconnection-oriented
network.

47. Network Software –Relationships of Service and
Protocol
➢Servicesandprotocolsaredistinctconcepts,althoughthey
arefrequentlyconfused.
➢Aserviceisasetofprimitives(operations)thatalayer
providestothelayeraboveit.
➢Theservicedefineswhatoperationsthelayerispreparedto
performonbehalfofitsusers.
➢Aservicerelatestoaninterfacebetweentwolayers,withthe
lowerlayerbeingtheserviceproviderandtheupperlayer
beingtheserviceuser.
➢Aprotocolisasetofrulesgoverningtheformatand
meaningofthepackets,ormessagesthatareexchangedby
thepeerentitieswithinalayer.

48. Network Software –Relationships of Service and
Protocol
➢servicesrelatetotheinterfacesbetweenlayers,asillustrated
inFig.1-19.Incontrast,protocolsrelatetothepacketssent
betweenpeerentitiesondifferentmachines.

49. Reference Model
➢OSIReferenceModel
➢TCP/IPReferenceModel
➢DifferencebetweenOSIandTCP/IP

50. OSI Reference Model
➢TheOSImodel(minusthephysicalmedium)isshownin
Fig.1-20.
➢Thismodelisbasedonaproposaldevelopedbythe
InternationalStandardsOrganization(ISO)asafirststep
towardinternationalstandardizationoftheprotocolsusedin
thevariouslayers(DayandZimmermann,1983).
➢Itwasrevisedin1995(Day,1995).Themodeliscalledthe
ISOOSI(OpenSystemsInterconnection)ReferenceModel
becauseitdealswithconnectingopensystems—thatis,
systemsthatareopenforcommunicationwithothersystems.

51. OSI Reference Model –Cont…

52. OSI Reference Model
The OSI model has seven layers. The principles of the seven
layers can be summarized as follows:
➢Layerscreatedfordifferentabstractions
➢Eachlayerperformswell-definedfunction
➢Functionoflayerchosenwithdefinitionofinternational
standardprotocolsinmind
➢Minimizeinformationflowacrosstheinterfacesbetween
boundaries
➢Numberoflayersoptimum

53. OSI Reference Model -The Physical Layer
➢Thephysicallayerisconcernedwithtransmittingrawbits
overacommunicationchannel.
➢Thedesignissueshavetodowithmakingsurethatwhenone
sidesendsa1bit,itisreceivedbytheothersideasa1bit,
notasa0bit.
➢Thedesignissuesherelargelydealwithmechanical,
electrical,andtiminginterfaces,andthephysical
transmissionmedium,whichliesbelowthephysicallayer.

54. OSI Reference Model -The Data Link Layer
➢Themaintaskofthedatalinklayeristotransformtheinput
dataintodataframes(typicallyafewhundredorafew
thousandbytes)andtransmittheframessequentiallytothe
networklayer.
➢Iftheserviceisreliable,thereceiverconfirmscorrect
receiptofeachframebysendingbackanacknowledgement
frame.
➢Thedesignissueshere,howtokeepafasttransmitterfrom
drowningaslowreceiverindata.
➢Broadcastnetworkshaveanadditionalissueinthedatalink
layer:howtocontrolaccesstothesharedchannel.Aspecial
sublayerofthedatalinklayer,themediumaccesscontrol
sublayer,dealswiththisproblem.

55. OSI Reference Model -The Network Layer
➢Thenetworklayercontrolstheoperationofthesubnet.
➢Akeydesignissueisdetermininghowpacketsarerouted
fromsourcetodestination.
➢Whenapackethastotravelfromonenetworktoanotherto
gettoitsdestination,manyproblemscanarise.
• Theaddressingusedbythesecondnetworkmaybe
differentfromthefirstone.
• Thesecondonemaynotacceptthepacketatallbecause
itistoolarge.Theprotocolsmaydiffer,andsoon.
• Itisuptothenetworklayertoovercomeallthese
problemstoallowheterogeneousnetworkstobe
interconnected.

56. OSI Reference Model -The Transport Layer
➢Thebasicfunctionofthetransportlayeristoacceptdata
fromthenetworklayerandsplititupintosmallerunitsif
needbe,passthesetothenetworklayer,andensurethatthe
piecesallarrivecorrectlyattheotherend.
➢Thetransportlayeralsodetermineswhattypeofserviceto
providetothesessionlayer,and,ultimately,totheusersof
thenetwork.
➢Themostpopulartypeoftransportconnectionisanerror-
freepoint-to-pointchannelthatdeliversmessagesorbytesin
theorderinwhichtheyweresent.

57. OSI Reference Model -The Transport Layer
➢Aprogramonthesourcemachinecarriesonaconversation
withasimilarprogramonthedestinationmachine,usingthe
messageheadersandcontrolmessages.
➢Thedifferencebetweenlayers1through3,whichare
chained,andlayers4through7,whichareend-to-end,is
illustratedinFig.1-20.

58. OSI Reference Model -The Session Layer
➢Thesessionlayerallowsusersondifferentmachinesto
establishsessionsbetweenthem.
➢Sessionsoffervariousservices,including
▪Dialogcontrol(keepingtrackofwhoseturnitisto
transmit)
▪Tokenmanagement(preventingtwopartiesfrom
attemptingthesamecriticaloperationatthesametime)
▪Synchronization(checkpointinglongtransmissionsto
allowthemtocontinuefromwheretheywereaftera
crash).

59. OSI Reference Model -The Presentation Layer
➢Thepresentationlayerisconcernedwiththesyntaxand
semanticsoftheinformationtransmitted.
➢Inordertomakeitpossibleforcomputerswithdifferentdata
representationstocommunicate,thedatastructurestobe
exchangedcanbedefinedinanabstractway,alongwitha
standardencodingtobeused''onthewire.''
➢Thepresentationlayermanagestheseabstractdatastructures
andallowshigher-leveldatastructures(e.g.,banking
records),tobedefinedandexchanged.

60. OSI Reference Model -The Application Layer
➢Theapplicationlayercontainsavarietyofprotocolsthatare
commonlyneededbyusers.
➢Onewidely-usedapplicationprotocolisHTTP(HyperText
TransferProtocol),whichisthebasisfortheWorldWide
Web.
➢WhenabrowserwantsaWebpage,itsendsthenameofthe
pageitwantstotheserverusingHTTP.
➢Theserverthensendsthepageback.Otherapplication
protocolsareusedforfiletransfer,electronicmail,and
networknews.

61. TCP/IP Reference Model
➢TheARPANET(AdvancedResearchProjectAgency
NETwork)wasaresearchnetworksponsoredbytheDoD
(U.S.DepartmentofDefense).
➢Iteventuallyconnectedhundredsofuniversitiesand
governmentinstallations,usingleasedtelephonelines.
Whensatelliteandradionetworkswereaddedlater,the
existingprotocolshadtroubleinterworkingwiththem,so
anewreferencearchitecturewasneeded.
➢Thus,theabilitytoconnectmultiplenetworksinaseamless
waywasoneofthemajordesigngoalsfromthevery
beginning.Thisarchitecturelaterbecameknownasthe
TCP/IPReferenceModel.

62. TCP/IP Reference Model
➢TheARPANET(AdvancedResearchProjectAgency
NETwork)wasaresearchnetworksponsoredbytheDoD
(U.S.DepartmentofDefense).
➢Iteventuallyconnectedhundredsofuniversitiesand
governmentinstallations,usingleasedtelephonelines.
Whensatelliteandradionetworkswereaddedlater,the
existingprotocolshadtroubleinterworkingwiththem,so
anewreferencearchitecturewasneeded.
➢Thus,theabilitytoconnectmultiplenetworksinaseamless
waywasoneofthemajordesigngoalsfromthevery
beginning.Thisarchitecturelaterbecameknownasthe
TCP/IPReferenceModel.

63. TCP/IP Reference Model -The Internet Layer
➢Theinternetlayerdefinesanofficialpacketformatand
protocolcalledIP(InternetProtocol).
➢TheTCP/IPinternetlayerissimilarinfunctionalitytothe
OSInetworklayer.Figure1-21showsthiscorrespondence.

64. TCP/IP Reference Model -The Transport Layer
➢ThelayerabovetheinternetlayerintheTCP/IPmodelis
nowusuallycalledthetransportlayer.
➢Itisdesignedtoallowpeerentitiesonthesourceand
destinationhoststocarryonaconversation,justasinthe
OSItransportlayer.
➢Twoend-to-endtransportprotocolshavebeendefinedhere.
➢Thefirstone,TCP(TransmissionControlProtocol),isa
reliableconnection-orientedprotocolthatallowsabyte
streamoriginatingononemachinetobedeliveredwithout
erroronanyothermachineintheinternet.

65. TCP/IP Reference Model -The Transport Layer
➢Thesecondprotocolinthislayer,UDP(UserDatagram
Protocol),isanunreliable,connectionlessprotocolfor
applicationsthatdonotwantTCP'ssequencingorflow
controlandwishtoprovidetheirown.
➢TherelationofIP,TCP,andUDPisshowninFig.1-22.

66. TCP/IP Reference Model -The Application Layer
➢TheTCP/IPmodeldoesnothavesessionorpresentation
layers.Ontopofthetransportlayeristheapplicationlayer.
➢Itcontainsallthehigher-levelprotocols.Theearlyones
includedvirtualterminal(TELNET),filetransfer(FTP),and
electronicmail(SMTP),asshowninFig.1-22.
➢
➢Thevirtualterminalprotocolallowsauserononemachine
tologontoadistantmachineandworkthere.
➢Thefiletransferprotocolprovidesawaytomovedata
efficientlyfromonemachinetoanother.
➢Electronicmailwasoriginallyjustakindoffiletransfer,but
lateraspecializedprotocol(SMTP)wasdevelopedforit.

67. TCP/IP Reference Model
The Host-to-Network Layer
➢Belowtheinternetlayerisagreatvoid.
➢TheTCP/IPreferencemodeldoesnotreallysaymuchabout
whathappenshere,excepttopointoutthatthehosthasto
connecttothenetworkusingsomeprotocolsoitcansendIP
packetstoit.
➢Thisprotocolisnotdefinedandvariesfromhosttohostand
networktonetwork.

68. A Comparison of the OSI and TCP/IP Reference Models
➢TheOSIandTCP/IPreferencemodelshavemuchin
common.
➢Botharebasedontheconceptofastackofindependent
protocols.Also,thefunctionalityofthelayersisroughly
similar.
➢Despitethesefundamentalsimilarities,thetwomodelsalso
havemanydifferences.Threeconceptsarecentraltothe
OSImodel:
1.Services.
2.Interfaces.
3.Protocols.

69. A Comparison of the OSI and TCP/IP Reference Models
➢Eachlayerperformssomeservicesforthelayeraboveit.
Theservicedefinitiontellswhatthelayerdoes,nothow
entitiesaboveitaccessitorhowthelayerworks.Itdefines
thelayer'ssemantics.
➢Alayer'sinterfacetellstheprocessesaboveithowtoaccess
it.Itspecifieswhattheparametersareandwhatresultsto
expect.It,too,saysnothingabouthowthelayerworks
inside.
➢Finally,thepeerprotocolsusedinalayerarethelayer's
ownbusiness.Itcanuseanyprotocolsitwantsto,aslongas
itgetsthejobdone(i.e.,providestheofferedservices).Itcan
alsochangethematwillwithoutaffectingsoftwareinhigher
layers.

70. A Comparison of the OSI and TCP/IP Reference Models
➢Thedifferencebetweenthetwomodelsisthenumberof
layers:
➢TheOSImodelhassevenlayers;and
➢TheTCP/IPhasfourlayers.Bothhave(inter)network,
transport,andapplicationlayers,buttheotherlayersare
different.
➢Anotherdifferenceistypeofcommunication.
➢TheOSImodelperformstheconnectionoriented
communicationinthetransportlayer.
➢TheTCP/IPmodelperformsconnectionless
communicationinthenetworklayer.Thischoiceis
especiallyimportantforsimplerequest-response
protocols.

71. A Comparison of the OSI and TCP/IP Reference Models
OSI Reference Model TCP/IP Reference Model
TheOpenSystemInterconnection
(OSI)modeldefinesanetworking
frameworktoimplementprotocols
insevenlayers.
TransmissionControlProtocol/Internet
Protocol(TCP/IP)isthelanguagea
computerusestoaccesstheinternet.
ItisagrandparentofAllnetwork
models.
Itisanetworkmodelusedincurrent
internetarchitecture.
7LayerArchitecture 4LayerArchitecture
Itsupportsbothconnectionlessand
connection-orientedcommunication
inthenetworklayer,butonly
connectionorientedcommunication
inthetransportlayer.
TheTCP/IPmodelhasonlyonemode
inthenetworklayer(connectionless)
butsupportsbothmodesinthe
transportlayer.

72. Example Networks
➢TheInternet
➢TheARPANET
➢NSFNET
➢InternetUsage
➢ArchitectureoftheInternet
➢Connection-OrientedNetworks
➢X.25,
➢FrameRelay
➢ATM
➢Ethernet
➢WirelessLANs:802.11

73. Example Networks
➢Thesubjectofcomputernetworkingcoversmany
differentkindsofnetworks,largeandsmall,well
knownandlesswellknown.
➢Theyhavedifferentgoals,scales,andtechnologies.

74. The Internet
➢TheInternetisnotanetworkatall,butavastcollectionof
differentnetworksthatusecertaincommonprotocolsand
providecertaincommonservices.

75. The Internet -The ARPANET
➢NuclearWar-
➢Non-Distributed,i.e.switchingtelephonesystemusedfor
communication.
➢Distributedsystemusingdigitalpacketswitchingsystem
proposedbyborens,employeeofRAND.
➢PacketswitchingsubnetestablishedbyrobertbyusingDonald
DaviesandWesleyClarkidea.
➢SoftwareimplementedforSubnethostcommunicationbyusing
BBN(Bolt,BeranekandNewman).
➢Roberthadproblemtowritesoftwareforhosttohost
communication.Tosolvethisproblem,heconductedameeting
withstudentsandnetworkexperts.
➢ExperimentalNetworkestablished.
➢CerfandKahnimplementedaTCP/IPprotocolforconnecting
multiplenetwork.

76. The Internet -The ARPANET
➢Thestorybeginsinthelate1950s.
➢AttheheightoftheColdWar,theDoD(DepartmentofDefence)
wantedacommand-and-controlnetworkthatcouldsurvivea
nuclearwar.
➢Atthattime,allmilitarycommunicationsusedthepublic
telephonenetwork,whichwasconsideredvulnerable(affected).
➢Thestructureoftelephonesystemusedbymilitaryasshownin
Fig.1-25(a).Heretheblackdotsrepresenttelephoneswitching
offices,eachofwhichwasconnectedtothousandsoftelephones.
➢Theseswitchingofficeswere,inturn,connectedtohigher-level
switchingoffices(tolloffices),Note:Thereisnodirect
connectionfromoneswitchingofficetoanotheroneswitching
office.

77. The Internet -The ARPANET

78. The Internet -The ARPANET
➢Around1960,theDoD(DepartmentofDefence)awardeda
contracttotheRANDCorporationtofindasolution.
➢Oneofitsemployees,PaulBaran,cameupwiththehighly
distributedandfault-tolerantdesignofFig.1-25(b).
➢Sincethepathsbetweenanytwoswitchingofficeswerenow
muchlongerthananalogsignalscouldtravelwithoutdistortion.
➢Baranproposedusingdigitalpacket-switchingtechnology
throughoutthesystem.But,itwasunabletoimplementdueto
rejectionofAT&T.

79. The Internet -The ARPANET
➢In1963,ARPA,theAdvancedResearchProjectsAgencyisa
branchofDoDisestablished.
➢Initially,ARPAhadnoscientistsorlaboratories.Itdiditsworkby
issuinggrantsandcontractstouniversitiesandcompanieswhose
ideaslookedpromisingtoit.
➢In1967,ComputerNetworkexpertWesleyClark,suggestedto
buildingapacket-switchedsubnet,givingeachhostitsown
router,asillustratedinFig.1-10.
➢In1967,Robertpublishedaresearchpaperinthetopicof
MultipleComputerNetworksandIntercomputer
Communication.

80. The Internet -The ARPANET
➢Atthesametime,thesimilarsystemisdesignedand
implementedbythedirectionofDonaldDaviesattheNational
PhysicalLaboratory(NPL)inEngland.
➢Itdemonstratedthatpacketswitchingcouldbemadetowork.
Furthermore,itcitedBaran'snowdiscardedearlierwork.
➢Fromtheseideas,RoberttrytobuildARPANETfromtheidea
gatheredfromDonaldDavies.
➢ThesubnetwouldconsistofminicomputerscalledIMPs
(InterfaceMessageProcessors)connectedby56-kbps
transmissionlines.
➢Forhighreliability,eachIMPwouldbeconnectedtoatleasttwo
otherIMPs.

81. The Internet -The ARPANET
➢Thesubnetwastobeadatagramsubnet,soifsomelinesand
IMPsweredestroyed,messagescouldbeautomaticallyrerouted
alongalternativepaths.
➢In1968,ARPAselectedandawardedtoBBN(Bolt,Beranekand
Newman)forbuildingthesubnetandwritethesubnetsoftware.
➢Thesoftwarewassplitintotwoparts:subnetandhost.
➢ThesubnetsoftwareconsistedoftheIMPendofthehost-IMP
connection,theIMP-IMPprotocol,andasourceIMPto
destinationIMPprotocoldesignedtoimprovereliability.
➢TheoriginalARPANETdesignisshowninFig.1-26.

82. The Internet -The ARPANET

83. The Internet -The ARPANET
➢Outsidethesubnet,softwarewasalsoneeded,namely,the
hostendofthehost-IMPconnection,thehost-hostprotocol,
andtheapplicationsoftware.
➢ItsoonbecameclearthatBBNfeltthatwhenithadaccepted
amessageonahost-IMPwireandplaceditonthehost-IMP
wireatthedestination,itsjobwasdone.
➢Roberthadproblemtowritesoftwareforhosttohost
communication.
➢Tosolvethisproblem,heconductedameetingwithstudents
andnetworkexperts.
➢Finally,theexperimentalnetworkwentontheairin
December1969withfournodes:atUCLA(,UCSB,SRI,and
theUniversityofUtah.

84. The Internet -The ARPANET
➢Thesefourwerechosenbecauseallhadalargenumberof
ARPAcontracts,andallhaddifferentandcompletely
incompatiblehostcomputers.
➢Figure1-27showshowrapidlytheARPANETgrewinthe
first3years.

85. The Internet -The ARPANET
➢Thisexperimentalsodemonstratedthattheexisting
ARPANETprotocolswerenotsuitableforrunningover
multiplenetworks.
➢In1974,CerfandKahnimplementedaTCP/IPprotocol.
➢Duringthe1980s,additionalnetworks,especiallyLANs,
wereconnectedtotheARPANET.
➢Asthescaleincreased,findinghostsbecameincreasingly
expensive,soDNS(DomainNameSystem)wascreatedto
organizemachinesintodomainsandmaphostnamesontoIP
addresses.

86. The Internet -NSFNET
➢Bythelate1970s,NSF(theU.S.NationalScience
Foundation)sawtheenormousimpacttheARPANETwas
havingonuniversityresearch,allowingscientistsacrossthe
countrytosharedataandcollaborateonresearchprojects.
➢NSFdecidedtobuildabackbonenetworktoconnectitssix
supercomputercenters,inSanDiego,Boulder,Champaign,
Pittsburgh,Ithaca,andPrinceton.
➢Eachsupercomputerwasgivenalittlebrother,consistingof
anLSI-11microcomputercalledafuzzball.
➢Thefuzzballswereconnectedwith56-kbpsleasedlinesand
formedthesubnet,thesamehardwaretechnologyasthe
ARPANETused.

87. The Internet -NSFNET
➢Thesoftwaretechnologywasdifferenthowever:thefuzzballs
spokeTCP/IPrightfromthestart,makingitthefirstTCP/IP
WAN.
➢NSFNETallowstothousandsofuniversities,researchlabs,
libraries,andmuseumstoaccessanyofthesupercomputers
andtocommunicatewithoneanother.
➢ThissetupiscalledNSFNET.
➢AfterthesuccessofNSFNET,thedatacanbetransferred448
kbpsbyusingfiberopticchannelsand1.5mbpsbyusing
routerin1990anditisupdatedatthespeedof45mbpsby
ANSNET(AdvancedNetworksandServices).

88. The Internet -Internet Usage
➢Thenumberofnetworks,machines,andusersconnectedto
theARPANETgrewrapidlyafterTCP/IPbecametheonly
officialprotocolonJanuary1,1983.
➢WhenNSFNETandtheARPANETwereinterconnected,the
growthbecameexponential.
➢Manyregionalnetworksjoinedup,andconnectionswere
madetonetworksinCanada,Europe,andthePacific.
➢Traditionally(meaning1970toabout1990),theInternetand
itspredecessorshadfourmainapplications:

89. The Internet -Internet Usage
1.E-mail.Theabilitytocompose,send,andreceiveelectronic
mailhasbeenaroundsincetheearlydaysoftheARPANET
andisenormouslypopular.
2.News.Newsgroupsarespecializedforumsinwhichusers
withacommoninterestcanexchangemessages.Thousandsof
newsgroupsexist,devotedtotechnicalandnontechnicaltopics,
includingcomputers,science,etc.
3.Remotelogin.Usingthetelnet,rlogin,orsshprograms,users
anywhereontheInternetcanlogontoanyothermachineon
whichtheyhaveanaccount.
4.Filetransfer.UsingtheFTPprogram,userscancopyfiles
fromonemachineontheInternettoanother.Vastnumbersof
articles,databases,andotherinformationareavailablethisway.

90. The Internet -Internet Usage
➢Inthe1990,theWWW(WorldWideWeb)isinventedby
CERNphysicistTimBerners-Lee.
➢Mosaicbrowser,writtenbyMarcAndreessenattheNational
CenterforSupercomputerApplications.
➢Withthehelpofbrowsertheusercansharetheaudio,video,
imageandtextdata.
➢Duringthe1990swasfueledbycompaniescalledISPs
(InternetServiceProviders).
➢Thesearecompaniesthatofferindividualusersathomethe
abilitytocalluponeoftheirmachinesandconnecttothe
Internet,thusgainingaccesstoe-mail,theWWW,andother
Internetservices.

91. The Internet -Internet Usage
➢Thesecompaniessigneduptensofmillionsofnewusersa
yearduringthelate1990s,completelychangingthecharacter
ofthenetworkfromanacademicandmilitaryplaygroundto
apublicutility,muchlikethetelephonesystem.

92. The Internet -Architecture of the Internet
➢Theclientcallshisorherispoveratelephoneline.
➢Modeminthecomputers,convertsthedigitalsignaltoanalog
signalandpassittothetelephoneline.
➢Theanalogsignalsareremovedfromthetelephonesystem
andinjectedtotheISP’sPOP(PointofPresence)regional
network.
➢Nowthesystemisdigitalandpacketswitched.
➢TheISP'sregionalnetworkconsistsofinterconnectedrouters
inthevariouscitiestheISPserves.

93. The Internet -Architecture of the Internet
➢IfthepacketisdestinedforahostserveddirectlybytheISP,
thepacketisdeliveredtothehost.otherwise,itishanded
overtotheISP'sbackboneoperator.
➢TelephonecompanieslikeAT&TandSprintiscalled
Backboneoperator.
➢Theyoperatelargeinternationalbackbonenetworks,with
thousandsofroutersconnectedbyhigh-bandwidthfiber
optics.NAP(NetworkAccessPoint)isaroomfullofrouters,
atleastoneperbackbone.

94. The Internet -Architecture of the Internet

95. Connection-Oriented Networks: X.25, Frame Relay, and
ATM
➢Theconnection-orientednetworkcomesfromtheworldof
telephonecompanies.Allwordsorpacketsfollowthesame
route.Ifalineorswitchonthepathgoesdown,thecallis
aborted.ThispropertyispreciselywhattheDoDdidnotlike
aboutit.
➢Whydothetelephonecompanieslikeitthen?Therearetwo
reasons:
➢1.Qualityofservice.Withaconnectionorientednetwork,
onceaconnectionhasbeensetup,theconnectionwillget
goodservice.Withaconnectionlessnetwork,iftoomany
packetsarriveatthesamerouteratthesamemoment,the
routerwillchokeandprobablylosepackets.
➢2.Billing.:thetelephonecompanieslikeconnection-oriented
serviceisthattheyareaccustomedtochargingforconnect
time.

96. Connection-Oriented Networks: X.25 and Frame Relay
➢X.25wasastandardsuiteofprotocolsusedforpacket-
switchedcommunicationsoverawideareanetwork—
aWAN.
➢Thefirstexampleofaconnection-orientednetworkisX.25,
whichwasthefirstpublicdatanetwork.
➢TouseX.25,acomputerfirstestablishedaconnectiontothe
remotecomputer,thatis,placedatelephonecall.
➢Thisconnectionwasgivenaconnectionnumbertobeusedin
datatransferpackets(becausemultipleconnectionscouldbe
openatthesametime).
➢Datapacketswereverysimple,consistingofa3-byteheader
andupto128bytesofdata.

97. Connection-Oriented Networks: X.25 and Frame Relay
➢Theheaderconsistedofa12-bitconnectionnumber,apacket
sequencenumber,anacknowledgementnumber,andafew
miscellaneousbits.
➢
➢Inthe1980s,theX.25networkswerelargelyreplacedbya
newkindofnetworkcalledframerelay.
➢Theessenceofframerelayisthatitisaconnection-oriented
networkwithnoerrorcontrolandnoflowcontrol.
➢Becauseitwasconnection-oriented,packetsweredelivered
inorder(iftheyweredeliveredatall).Thepropertiesofin-
orderdelivery,noerrorcontrol,andnoflowcontrolmake
framerelaytoawideareaLAN.

98. Connection-Oriented Networks: Asynchronous Transfer
Mode
➢Thesecondexampleofaconnection-orientednetworkis
ATM(AsynchronousTransferMode).
➢Inthetelephonesystem,mosttransmissionissynchronous
andATMisnot.ATMwasdesignedintheearly1990s.
ATMVirtualCircuits
➢Connectionsareoftencalledvirtualcircuits,inanalogywith
thephysicalcircuitsusedwithinthetelephonesystem.
➢Eachconnection,temporaryorpermanent,hasaunique
connectionidentifier.Avirtualcircuitisillustratedin
Fig.1-30.

99. Connection-Oriented Networks: Asynchronous Transfer
Mode
Figure 1-30. A virtual circuit

100. Connection-Oriented Networks: Asynchronous Transfer
Mode
➢Onceaconnectionhasbeenestablished,eithersidecan
begintransmittingdata.
➢ThebasicideabehindATMistotransmitallinformationin
small,fixed-sizepacketscalledcells.
➢Thecellsare53byteslong,ofwhich5bytesareheaderand
48bytesarepayload,asshowninFig.1-31.

101. 1.5.3 Ethernet
➢Ethernetisthetraditionaltechnologyforconnectingwired
localareanetworks(LANs),enablingdevicesto
communicatewitheachotherviaaprotocol
➢AlohawasthebasisforEthernet,alocalareanetwork
protocol.NormanAbramsonistheinventoroftheAloha
system,.InpureAloha,ausercantransmitatanytimebut
riskscollisionswithotherusers'messages.
➢AsketchofEthernetarchitectureisgiveninFig.1-34.
EthernethadamajorimprovementoverALOHANET:
beforetransmitting,acomputerfirstlistenedtothecableto
seeifsomeoneelsewasalreadytransmitting.

102. 1.5.3 Ethernet
➢Ifso,thecomputerheldbackuntilthecurrenttransmission
finished.Doingsoavoidsinterferingwithexisting
transmissions,givingamuchhigherefficiency.
➢ALOHANET didnotworklikethisbecauseitwas
impossibleforaterminalononeislandtosensethe
transmissionofaterminalonadistantisland.Withasingle
cable,thisproblemdoesnotexist.

103. 1.5.4 Wireless LANs: 802.11
➢Almostassoonasnotebookcomputersappeared,many
peoplehadadreamofwalkingintoanofficeandmagically
havingtheirnotebookcomputerbeconnectedtotheInternet.
ThisworkrapidlyledtowirelessLANsbeingmarketedbya
varietyofcompanies.
➢TheIEEEcommitteethatstandardizedthewiredLANswas
giventhetaskofdrawingupawirelessLANstandard.
➢Thestandarditcameupwithwasnamed802.11.Acommon
slangnameforitisWiFi(WirelessFidelity).
Theproposedstandardhadtoworkintwomodes:
1.Inthepresenceofabasestation.
2.Intheabsenceofabasestation.

104. 1.5.4 Wireless LANs: 802.11
➢Intheformercase,allcommunicationwastogothroughthe
basestation,calledanaccesspointin802.11terminology.
➢Inthelattercase,thecomputerswouldjustsendtoone
anotherdirectly.Thismodeisnowsometimescalledadhoc
networking.
➢ThetwomodesareillustratedinFig.1-35.
➢