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BasicNetworkingConcepts

1.Introduction2.Protocols3.ProtocolLayers4.NetworkInterconnection/Internet


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1.Introduction-Anetworkcanbedefinedasagroupofcomputersandotherdevicesconnectedinsomewayssoastobeabletoexchangedata.-Eachofthedevicesonthenetworkcanbethoughtofasanode;eachnodehasauniqueaddress.-Addressesarenumericquantitiesthatareeasyforcomputerstoworkwith,butnotforhumanstoremember.

Example:204.160.241.98

-Somenetworksalsoprovidenamesthathumanscanmoreeasilyrememberthannumbers.

Example:www.javasoft.com,correspondingtotheabovenumericaddress.

NICaddr1NICaddrNNICaddr2


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Addressing

Internetaddress

Consistsof4bytesseparatedbyperiods

Example:136.102.233.49-TheRfirstbytes(R=1,2,3)correspondtothenetworkaddress;-TheremainingHbytes(H=3,2,1)areusedforthehostmachine.-InterNICRegister:organizationinchargeoftheallocationofthe

addressrangescorrespondingtonetworks.-Criteriaconsidered:

.Geographicalarea(country)

.Organization,enterprise

.Department

.HostDomainNameSystem(DNS)

-Mnemonictextualaddressesareprovidedtofacilitatethemanipulationofinternetaddresses.-DNSserversareresponsiblefortranslatingmnemonictextualInternet

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addressesintohardnumericInternetaddresses.


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Ports

-AnIPaddressidentifiesahostmachineontheInternet.

-AnIPportwillidentifyaspecificapplicationrunningonanInternethostmachine.

-Aportisidentifiedbyanumber,theportnumber.

-Thenumberofportsisnotfunctionallylimited,incontrasttoserialcommunicationswhereonly4portsareallowed.

-Therearesomeportnumberswhicharededicatedforspecificapplications.

ApplicationsPortnumbersHTTP80FTP20and21Gopher70SMTP(e-mail)25POP3(e-mail)110Telnet23Finger79

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DataTransmission

-Inmodernnetworks,dataaretransferredusingpacketswitching.

-Messagesarebrokenintounitscalledpackets,andsentfromonecomputertotheother.

-Atthedestination,dataareextractedfromoneormorepacketsandusedtoreconstructtheoriginalmessage.

-Eachpackethasamaximumsize,andconsistsofaheaderandadataarea.

-Theheadercontainstheaddressesofthesourceanddestinationcomputersandsequencinginformationnecessarytoreassemblethemessageatthedestination.

packet

headerdata

1001.101

00010000111000000110001100


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TypesofNetworks

Therearetwoprinciplekindsofnetworks:WideAreaNetworks(WANs)andLocalAreaNetworks(LANs).

WANs

-Covercities,countries,andcontinents.-Basedonpacketswitchingtechnology-ExamplesofWANtechnology:AsynchronousTransferMode(ATM)

IntegratedServicesDigitalNetwork(ISDN)

LANs

-Coverbuildingsorasetofcloselyrelatedbuildings.-ExamplesofLANtechnology:Ethernet,TokenRing,andFibber

DistributedDataInterconnect(FDDI).EthernetLANs:basedonabustopologyandbroadcastcommunication

TokenringLANs:basedonringtopologyFDDILANs:useopticalfibbersandanimprovedtokenringmechanism

basedontworingsflowinginoppositedirections.

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Sharedbus

(a)EthernetLANDualring

Ring

(b)TokenRingLAN(c)FDDILAN


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NetworkconnectivitytypeSpeedTransmissiontimefor10Mbytes(Telephone)dial-upmodem14.4Kbps90minISDNmodem56/128Kbps45/12minT1connection1.54Mbps50sEthernet10Mbps9sTokenring4/16MbpsFastEthernet100MbpsFDDI100MbpsGigabitEthernet1GbpsATM25Mbps/2.4Gbs


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Interconnection

-NetworksoflowcapacitymaybeconnectedtogetherviaabackbonenetworkwhichisanetworkofhighcapacitysuchasaFDDInetwork,aWANnetworketc.

-LANsandWANscanbeinterconnectedviaT1orT3digitalleasedlines

-Accordingtotheprotocolsinvolved,networksinterconnectionisachievedusingoneorseveralofthefollowingdevices:

.Bridge:acomputerordevicethatlinkstwosimilarLANsbasedonthesameprotocol..Router:acommunicationcomputerthatconnectsdifferenttypesofnetworksusingdifferentprotocols..B-routerorBridge/Router:asingledevicethatcombinesboththefunctionsofbridgeandrouter..Gateway:anetworkdevicethatconnectstwodifferentsystems,usingdirectandsystematictranslationbetweenprotocols.9


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TorontobranchEthernetLANRouterVancouverbranchTokenRingLANGatewayFrameRelayATMT1lineNYheadquatersBridge/RouteTokenRingLANRouterBridgeBridge/RouterEthernetEthernetLANRouterVancouverbranchTokenRingLANGatewayFrameRelayATM

T1lineNYheadquatersBridge/RouteTokenRingLANRouterBridgeBridge/RouterEthernet


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NetworkTopologyDiagram

Thespecificationofthenetworktopologydiagramrequiresthedefinitionofthecharacteristicsandentitiesunderlyingthenetwork:-Geographicallocationsofthedifferentcomponentsorsubnets

involvedinthenetwork.-DescriptionoftheLANtopology-DescriptionoftheWANtopology-Descriptionofthenetworkconnectorssuchasrouters,bridges,

repeaters,andgateways.


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2.Protocols-Definetherulesthatgovernthecommunicationsbetweentwocomputersconnectedtothenetwork.

-Roles:addressingandroutingofmessages,errordetectionandrecovery,sequenceandflowcontrolsetc.

-Aprotocolspecificationconsistsofthesyntax,whichdefinesthekindsandformatsofthemessagesexchanged,andthesemantic,whichspecifiestheactiontakenbyeachentitywhenspecificeventsoccur.

Example:HTTPprotocolforcommunicationbetweenwebbrowsersandservers.

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RequestForComments(RFC):specificationsoftheprotocolsinvolvedinInternetCommunications.-Example:sampleofRFC821describingcommunicationsbetween

SMTPserverandclient.

S:MAILFROM:[email protected]:250OKS:RCPTTO:[email protected]:250OKS:DATAR:354Beginningofmail;endingby.S:BlahblahblahS:etc.S:.R:250OK13


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-ProtocolsaredesignedbasedonalayeredarchitecturesuchastheOSI

referencemodel.-Eachentityatalayerncommunicatesonlywithentitiesatlayern-1.-Thedataexchanged,knownasProtocolDataUnit(PDU),goesback

andforththroughthelayers,eachlayeraddsorremovesitsownheaderandvice-versa.ThereforealayernPDUmaybecomealayern-1data.

nthlayernthlayer(n-1)thlayer(n-1)thlayer

Network14


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3.ProtocolLayersTheOSI(OpenSystemsInterconnection)DataModel

-ISOstandardforcomputernetworksdesignandfunctioning.

-Involvesatleast7layers,eachplayingaspecificrolewhenapplicationsarecommunicatingoverthenet.

-Duringthesendingprocess,eachlayer(fromtoptodown)willaddaspecificheadertotherawdata.

-Atthereception,headersareeliminatedconverselyuntilthedataarrivedtothereceivingapplication.


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OSILayers

Physicallayer(definesthephysicalcharacteristicsofthenetwork)Data-linklayer(providessafecommunicationofdataoverthephysicalnetwork)Networklayer(handlesconnectiontothenetworkbythehigherlayers)Transportlayer(providesend-to-enderrorsdetectionandcorrection)Sessionlayer(managessessionsamongapplications)Presentationlayer(providesstandarddatarepresentationsforapplications)Applicationlayer(applicationsconnectedtothenetwork)


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Physicallayer:ensuresasafeandefficienttravelofdata;consistsofelectroniccircuitsfordatatransmissionetc.

Datalinklayer:inchargeofdataencapsulationundertheformofpacketsandtheirinterpretationatthephysicallayer.

Networklayer:inchargeofpacketstransmissionfromasourceAtoadestinationB.

Transportlayer:inchargeofthedeliveryofpacketsfromasourceAtoadestinationB

Sessionlayer:inchargeofthemanagementofnetworkaccess.Presentationlayer:determinestheformatofthedatatransmittedto

applications,datacompressing/decompressing,encryptingetc.

Applicationlayer:containstheapplicationswhichareusedbytheend-user,suchasJava,Wordetc.17


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TheTCP/IPModel

-Consistsofonly4layers:application,transport,internetandnetwork.

Layers

Applicationlayer(applicationsandprocessesrunningonthenetwork)Transportlayer(providesend-to-enddatadeliveryservices)Internetlayer(makesdatagramsandhandlesdatarouting)Networklayer(providesroutinesallowingaccesstothephysicalnetwork)18


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Networklayer

-Providesthesamefunctionalityasthephysical,thedatalinkandnetworklayersintheOSImodel.

-MappingbetweenIPaddressesandnetworkphysicaladdresses.

-EncapsulationofIPdatagrams,e.gpackets,informatunderstandablebythenetwork.

Internetlayer

-LiesattheheartofTCP/IP.

-BasedontheInternetProtocol(IP),whichprovidestheframefortransmittingdatafromplaceAtoplaceB.

Transportlayer

-Basedontwomainprotocols:TCP(TransmissionControlProtocol)andUDP(UserDatagramprotocol)

Applicationlayer

-CombinesthefunctionsoftheOSIapplication,presentation,andsessionlayers.

-Protocolsinvolvedinthislayer:HTTP,FTP,SMTPetc.

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4.NetworksInterconnection/InternetConceptofNetworkInterconnection

-FirstimplementedintheDefenseAdvancedResearchProjectAgencyNetwork(Arpanet),in1966inUSA.-Consistsofconnectingseveralcomputernetworksbasedondifferentprotocols-Requiresthedefinitionofacommoninterconnectionprotocolontopthelocalprotocols.-TheInternetProtocol(IP)playsthisrole,bydefininguniqueaddressesforanetworkandahostmachine.

SNMP

FTPTelnetSMTP

20TCP/UDPIPEthernetArpanetTokenring


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21P1P2P4P3IP


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InternetProtocol(IP)

Overview

-TheIPprotocolprovidestwomainfunctionality:

.Decompositionoftheinitialinformationflowintopacketsofstandardizedsize,andreassemblingatthedestination..Routingofapacketthroughsuccessivenetworks,fromthesourcemachinetothedestinationidentifiedbyitsIPaddress.-Transmittedpacketsarenotguaranteedtobedelivered(datagramprotocol).-TheIPprotocoldoesnotrequestforconnection(connectionless)beforesendingdataanddoesnotmakeanyerrordetection.

Functions

-Decomposetheinitialdata(tobesent)intodatagrams.

-Eachdatagramwillhaveaheaderincluding,theIPaddressandtheportnumberofthedestination.

-Datagramsarethensenttoselectedgateways,e.gIProuters,connected

atthesametimetothelocalnetworkandtoanIPserviceprovider

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network.


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-Datagramsaretransferredfromgatewaystogatewaysuntiltheyarrivedattheirfinaldestination.

packet1Sender

Receiver

packet2

Routers23


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StructureofanIPpacket

-Thefieldsatthebeginningofthepacket,calledtheframeheader,definetheIPprotocolsfunctionalityandlimitations.

-32bitsareallocatedforencodingsourceanddestinationaddresses(32bitsforeachoftheseaddressfields).

-Theremainderoftheheader(16bits)encodesvariousinformationsuchasthetotalpacketlengthinbytes.

-HenceanIPpacketcanbeamaximumof64Kblong.

01012162024

HeaderChecksumSourceaddressDestinationaddressOptions

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Data


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TransmissionControlProtocol(TCP)

Overview

-TCPprovidesbyusingIPpacketsabasicservicethatdoesguaranteesafedelivery:

.errordetection

.safedatatransmission

.assurancethatdataarereceivedinthecorrectorder-Beforesendingdata,TCPrequiresthatthecomputerscommunicatingestablishaconnection(connection-orientedprotocol).

ClientServerTCPSYNSYN_ACKACKDATADATAACKDATAFINFINACK

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-TCPprovidessupportforsendingandreceivingarbitraryamountsof

dataasonebigstreamofbytedata(IPislimitedto64Kb).-TCPdoessobybreakingupthedatastreamintoseparateIPpackets.-Packetsarenumbered,andreassembledonarrival,usingsequenceand

sequenceacknowledgenumbers.-TCPalsoimprovesthecapabilityofIPbyspecifyingportnumbers.

.Thereare65,536differentTCPports(sockets)throughwhicheveryTCP/IPmachinecantalk.StructureofaTCPpacket

02481220

SourceportDestinationportSequenceNo.SequenceAck.No.Misc.headerData

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UserDatagramProtocol(UDP)

Overview

-DatagramprotocolalsobuiltontopofIP.

-Hasthesamepacket-sizelimit(64Kb)asIP,butallowsforportnumberspecification.

-Providesalso65,536differentports.

-Hence,everymachinehastwosetsof65,536ports:oneforTCPandtheotherforUDP.

-Connectionlessprotocol,withoutanyerrordetectionfacility.

-Providesonlysupportfordatatransmissionfromoneendtotheother,withoutanyfurtherverification.

-ThemaininterestofUDPisthatsinceitdoesnotmakefurtherverification,itisveryfast.

-Usefulforsendingsmallsizedatainarepetitivewaysuchastime

information.

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4.5InternetApplicationProtocolsOntopofTCP/IP,severalserviceshavebeendevelopedinordertohomogenizeapplicationsofsamenature:-FTP(FileTransferProtocol)allowsthetransferofcollectionoffilesbetweentwomachinesconnectedtotheInternet.-Telnet(TerminalProtocol)allowsausertoconnecttoaremotehostinterminalmode.-NNTP(NetworkNewsTransferProtocol)allowstheconstitutionofcommunicationgroups(newsgroups)organizedaroundspecifictopics.-SMTP(SimpleMailTransferProtocol)definesabasicserviceforelectronicmails.-SNMP(SimpleNetworkManagementProtocol)allowsthemanagementofthenetwork.

28FTPTelnetSNMPSMTPTCP/UDPIPEthernetArpanetTokenring


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