第一章计算机网络基本原理与机制-教学课件

1第一章计算机网络基本原理与机制1第一章计算机网络基本原理与机制12<<上一页下一页>>

提纲网络基本概念Internet简介协议分层和OSI参考模型End-to-EndArgumentsInternet设计原则2<<上一页下一页>> 提纲23<<上一页下一页>>

提纲网络基本概念Internet简介协议分层和OSI参考模型End-to-EndArgumentsInternet设计原则3<<上一页下一页>> 提纲34<<上一页下一页>>World’ssmallestwebserver/~shri/iPic.html“Cool”Internetappliances

IPpictureframe / Web-enabledtoaster+weatherforecaster4<<上一页下一页>>World’ssmallest45<<上一页下一页>>What’sanetworknetworkedge:millionsofend-systemdevices:

–pc’sworkstations, servers

–PDA’s,phones,toasters runningnetworkappsnetworkcore:routers,switchesforwardingdata

–packets:packetswitching

–calls:circuitswitchingcommunicationlinks

–fiber,copper,radio,…

router server

localnetcompanynet

workstation mobileregionalnet5<<上一页下一页>>What’sanetworkn56<<上一页下一页>>What’saprotocol?ahumanprotocolandacomputernetworkprotocol:

Hi HiGotthe time?

2:00TCPconnection req.TCPconnectionreply.Get

<file>time6<<上一页下一页>>What’saprotocol67<<上一页下一页>>What’saprotocol?humanprotocols:

“what’sthetime?” “Ihaveaquestion”

Introductionsnetworkprotocols:

machinesrather thanhumans allcommunication activityinInternet governedby protocols…specificmsgssent…specificactionstakenwhenmsgsreceived,orotherevents7<<上一页下一页>>What’saprotocol78<<上一页下一页>>

What’saprotocol?协议的组成：

–语法（syntax)：以二进制形式表示的命令和相应的 结构

–语义（semantics)：命令请求、完成的动作和回送的 响应的具体含义

–定时关系（timing)：有关事件顺序的说明protocolsdefineformat,orderofmsgssentandreceivedamongnetworkentities,andactionstakenonmsgtransmission,receipt8<<上一页下一页>> What’saproto89<<上一页下一页>>

Acloserlookatnetwork structurenetworkedge:

–applicationsand hostsnetworkcore:

–routers

–networkof networksaccessnetworks,physicalmedia:

–communication links9<<上一页下一页>> Acloserlooka910<<上一页下一页>>

Thenetworkedgeendsystems(hosts)

–runapplicationprograms

–e.g.,WWW,email

–at“edgeofnetwork”client/servermodel

–clienthostrequests, receivesservicefrom server

–e.g.,WWWclient (browser)/server;email client/serverpeer-peermodel

–hostinteraction symmetric

–e.g.:BT,Maze,e-Donkey10<<上一页下一页>> Thenetworke1011<<上一页下一页>>

Thenetworkcoremeshofinterconnectedroutersthefundamentalquestion:howisdatatransferredthroughnet?

–circuitswitching:

dedicatedcircuitper call:telephonenet

–packetswitching:

datasentthrunetin discrete“chunks”11<<上一页下一页>> Thenetworkc1112<<上一页下一页>>

BroadcastCommunication Network

ATaxonomyof CommunicationNetworksCommunicationnetworkscanbeclassifiedbasedonthewayinwhichthenodesexchangeinformation:

Communication Network

Switched Communication NetworkCircuit-Switched Communication NetworkPacket-Switched Communication NetworkDatagram NetworkVirtualCircuitNetwork12<<上一页下一页>> Broadcast ATa1213<<上一页下一页>>

Broadcastvs.Switched CommunicationNetworksBroadcastcommunicationnetworks

–Informationtransmittedbyonenodeis receivedbyeveryothernodeinthe network

•E.g.,SatelliteNetwork,CCTV-Net

–Problem:coordinatetheaccessofall nodestothesharedcommunication medium(MultipleAccessProblem)Switchedcommunicationnetworks

–Informationistransmittedtoasub-setof designatednodes

•E.g.,WANs(TelephonyNetwork,Internet)

–Problem:howtoforwardinformationto intendednode(s)

•Donebyspecialnodes(e.g.,routers,switches) runningroutingprotocols13<<上一页下一页>> Broadcastvs1314<<上一页下一页>>

ATaxonomyof CommunicationNetworksCommunicationnetworkscanbeclassifiedbasedonthewayinwhichthenodesexchangeinformation:

Communication Network

Switched Communication NetworkCircuit-Switched Communication Network

BroadcastCommunication NetworkPacket-Switched Communication NetworkDatagram NetworkVirtualCircuitNetwork14<<上一页下一页>> ATaxonomyof 1415<<上一页下一页>>

CircuitSwitchingThreephases1.circuitestablishment2.datatransfer3.circuitterminationIfcircuitnotavailable:“Busysignal”Examples–Telephonenetworks–ISDN(IntegratedServicesDigital Networks)15<<上一页下一页>> CircuitSwitch1516<<上一页下一页>>TiminginCircuitSwitchingCircuit EstablishmentHost1Host2Node1Node2

betweenHost1 andNode1propagationdelay

betweenHost2 andNode1Data Transmission

DATACircuit TerminationprocessingdelayatNode1 propagationdelay16<<上一页下一页>>TiminginCircui1617<<上一页下一页>>CircuitSwitching

Anode(switch)inacircuit switchingnetworkincominglinksoutgoinglinksNode17<<上一页下一页>>CircuitSwitchin1718<<上一页下一页>>

CircuitSwitching:Multiplexing/Demultiplexing

Timedividedinframesandframesdividedin

slots

Relativeslotpositioninsideaframedetermines

whichconversationthedatabelongsto Needssynchronizationbetweensenderand receiver Incaseofnon-permanentconversations

–Needstodynamicbindaslottoa conservation18<<上一页下一页>> CircuitSwit1819<<上一页下一页>>

ATaxonomyof CommunicationNetworksCommunicationnetworkscanbeclassifiedbasedonthewayinwhichthenodesexchangeinformation:

Communication Network

BroadcastCommunication Network

Switched Communication NetworkCircuit-Switched Communication NetworkPacket-Switched Communication NetworkDatagram NetworkVirtualCircuitNetwork19<<上一页下一页>> ATaxonomyof 1920<<上一页下一页>>

PacketSwitchingDataaresentasformattedbit-sequences,so-calledpacketsPacketshavethefollowingstructure:

•HeaderandTrailercarrycontrol information(e.g.,destinationaddress, checksum)Eachpacketispassedthroughthenetworkfromnodetonodealongsomepath(Routing)Ateachnodetheentirepacketisreceived,storedbriefly,andthenforwardedtothenextnode(Store-and-ForwardNetworks)HeaderDataTrailer20<<上一页下一页>> PacketSwitchin2021<<上一页下一页>>PacketSwitching

Anodeinapacketswitching networkincominglinksoutgoinglinksNodeMemory21<<上一页下一页>>PacketSwitching2122<<上一页下一页>>

PacketSwitching:Multiplexing/Demultiplexing

Datacanbetransmittedatany giventime Howtotellthemapart?

–Usemeta-data(header)to describedata22<<上一页下一页>> PacketSwit2223<<上一页下一页>>

BroadcastCommunication Network

ATaxonomyof CommunicationNetworksCommunicationnetworkscanbeclassifiedbasedonthewayinwhichthenodesexchangeinformation:

Communication Network

Switched Communication NetworkCircuit-Switched Communication NetworkPacket-Switched Communication NetworkDatagram NetworkVirtualCircuitNetwork23<<上一页下一页>> Broadcast ATa2324<<上一页下一页>>

DatagramPacket Switching

Eachpacketisindependentlyswitched

–Eachpacketheadercontains destinationaddress

Noresourcesarepre-allocated(reserved)inadvance

Example:IPnetworks24<<上一页下一页>> DatagramPac2425<<上一页下一页>>HostAHostBHostEHostDDatagramPacket Switching

HostCNode1Node3Node4Node6Node2 Node5Node725<<上一页下一页>>HostAHostBHost2526<<上一页下一页>>

Howdolossanddelayoccur?

routerbuffersisfull

packetarrivalratetolinkexceedsoutput linkcapacity

Outputlink(loss)A

B

dropped(loss)ifnofreebuffers26<<上一页下一页>> Howdolossand2627<<上一页下一页>>Foursourcesofpacketdelay1.nodalprocessing

–checkbiterrors

–determineoutput link(?)ABtransmission nodal processing

propagationqueueing2.queueing

–timewaitingatoutput linkfortransmission

–dependsoncongestion levelofrouter27<<上一页下一页>>Foursourcesof2728<<上一页下一页>>Foursourcesofpacketdelay3.Transmissiondelay:

R=linkbandwidth(bps) L=packetlength(bits) timetosendbitsinto link=L/RABtransmission nodal processing

propagationqueueing

4.Propagationdelay:

d=lengthofphysicallink s=propagationspeedin medium(~2x108m/sec) propagationdelay=d/sNote:sandRarevery

differentquantities!28<<上一页下一页>>Foursourcesof2829<<上一页下一页>>

BroadcastCommunication Network

ATaxonomyof CommunicationNetworksCommunicationnetworkscanbeclassifiedbasedonthewayinwhichthenodesexchangeinformation:

Communication Network

Switched Communication NetworkCircuit-Switched Communication NetworkPacket-Switched Communication NetworkDatagram NetworkVirtualCircuitNetwork29<<上一页下一页>> Broadcast ATa2930<<上一页下一页>>

Virtual-CircuitPacket SwitchingHybridofcircuitswitchingandpacketswitching

–Dataistransmittedaspackets

–Allpacketsfromonepacketstreamare sentalongapre-establishedpath

(=virtualcircuit)Guaranteesin-sequencedeliveryofpacketsHowever:PacketsfromdifferentvirtualcircuitsmaybeinterleavedExample:ATMnetworks30<<上一页下一页>> Virtual-Circu3031<<上一页下一页>>

Virtual-CircuitPacket SwitchingCommunicationwithvirtualcircuitstakesplaceinthreephases1.VCestablishment2.datatransfer3.VCdisconnectNote:packetheadersdon’tneedtocontainthefulldestinationaddressofthepacket31<<上一页下一页>> Virtual-Circuit3132<<上一页下一页>>Packet1Packet1Packet2Packet3TimingofVirtual-Circuit PacketSwitchingPacket1Packet2Packet3Host1Host2Node1Node2propagationdelaybetweenHost1andNode1VCestablishment

Packet2 Packet3VCterminationDatatransfer32<<上一页下一页>>Packet1Packet13233<<上一页下一页>>HostAHostBHostENode1Node3Node4Node2 Node5Node6Node7HostDVirtual-CircuitPacket Switching

HostC33<<上一页下一页>>HostAHostBHost3334<<上一页下一页>>

Packet-Switchingvs. Circuit-Switching

Mostimportantadvantageofpacket-switchingovercircuitswitching:abilitytoexploitstatisticalmultiplexing

–Efficientbandwidthusage

•ratiobetweenpeekandaveragerateis 3:1foraudio,and15:1fordatatraffic34<<上一页下一页>> Packet-Swit3435<<上一页下一页>>

Packet-Switchingvs. Circuit-Switching

However,packet-switchingneedstodealwithcongestion

–Morecomplexrouters

–Hardertoprovidegoodnetwork services(e.g.,delayandbandwidth guarantees)

Inpracticetheyarecombined

–IPoverSONET,IPoverFrameRelay35<<上一页下一页>> Packet-Switc3536<<上一页下一页>>

提纲网络基本概念Internet简介协议分层和OSI参考模型End-to-EndArgumentsInternet设计原则基本机制回顾36<<上一页下一页>> 提纲3637<<上一页下一页>>

TheInternetGlobalscale,generalpurpose,heterogeneous-technologies,public,computernetworkInternetProtocol

–Openstandard:InternetEngineeringTask Force(IETF)asstandardbody

–Technicalbasisforothertypesof networks

•Intranet:enterpriseIPnetworkDevelopedbytheresearchcommunity37<<上一页下一页>> TheInternet3738<<上一页下一页>>1961:Kleinrock-queueingtheoryshowseffectivenessofpacket-switching1964:PaulBaran-packet-switchinginmilitarynets1967:ARPAnetconceivedbyAdvancedResearchProjectsAgency–LarryRoberts1969:firstARPAnetnodeoperational1972:

–ARPAnet demonstrated publicly

–NCP(Network ControlProtocol) firsthost-host protocol

–firste-mailprogram

–ARPAnethas15 nodes

InternetHistory1961-1972:Earlypacket-switching principles38<<上一页下一页>>1961:Kleinrock3839<<上一页下一页>>

InternetHistory1972-1980:Internetworking,newandproprietary

1970:ALOHAnetsatellite networkinHawaii

principles:

•nointernalchanges requiredto interconnect

late70’s:proprietarynetworks

architectures:DECnet,SNA,–besteffortservice XNAmodel

late70’s:switchingfixed–statelessrouters lengthpackets(ATM precursor)

1979:ARPAnethas200 nodes39<<上一页下一页>> InternetHisto3940<<上一页下一页>>1982:SMTPe-mailprotocoldefined1983:deploymentofTCP/IP1983:DNSdefinedforname-to-IP-addresstranslation1985:FTPprotocoldefined1988:TCPcongestioncontrolnewnationalnetworks:Csnet,BITnet,NSFnet,Minitel100,000hostsconnectedtoconfederationofnetworks

InternetHistory1980-1990:newprotocols,a proliferationofnetworks40<<上一页下一页>>1982:SMTPe-mai4041<<上一页下一页>>

InternetHistory1990,2000’s:commercialization,the Web,newapps

Early1990’s:ARPAnet decommissioned

1991:NSFliftsrestrictionsonLate1990’s–2000’s:

commercialuseofNSFnetmorekillerapps:instant (decommissioned,1995)messaging,peer2peerfile sharing(e.g.,BT,Napster) networksecurityto forefront est.50millionhost,100 million+users

–1994:Mosaic,laterbackbonelinksrunningat NetscapeGbps

–late1990’s: commercializationofthe Web41<<上一页下一页>> InternetHis4142<<上一页下一页>>TimeLineoftheInternet

•Source:InternetSociety42<<上一页下一页>>TimeLineofthe4243<<上一页下一页>>GrowthoftheInternetNumberofHostsontheInternet:

Aug.1981213 Oct.19841,024 Dec.198728,174 Oct.1990313,000 Oct.19932,056,000 Apr.19955,706,000 Jan.199716,146,000 Jan.199956,218,000 Jan.2001109,374,000 Jan.2003171,638,297 Jan.2006394,991,609 July2007489,774,269 Jan.2009625,226,456 July.2009681,064,561Dataavailableat:/43<<上一页下一页>>GrowthoftheIn4344<<上一页下一页>>GrowthoftheInternet44<<上一页下一页>>GrowthoftheIn4445<<上一页下一页>>WhoisWhointheInternet?InternetSociety(ISOC)

–ISOCisaprofessionalmembership societywithmorethan100organization andover20,000individualmembersin over180countries –Itprovidesleadershipinaddressingissues oftheInternet,andistheorganization homeforthegroupsresponsiblefor Internetinfrastructurestandards, includingIETFandIAB45<<上一页下一页>>WhoisWhointh4546<<上一页下一页>>WhoisWhointheInternet?

InternetEngineeringTaskForce(IETF)

–TheIETFistheprotocolengineering anddevelopmentarmoftheInternet

–Subdividedintomanyworking groups,whichspecifyRequestFor CommentsorRFCs46<<上一页下一页>>WhoisWhointh4647<<上一页下一页>>WhoisWhointheInternet?IRTF(InternetResearchTaskForce)

–TheInternetResearchTaskForceis composedofanumberoffocused,long- termandsmallResearchGroupsInternetArchitectureBoard(IAB)

–TheIABisresponsiblefordefiningthe overallarchitectureoftheInternet, providingguidanceandbroaddirectionto theIETF47<<上一页下一页>>WhoisWhointh4748<<上一页下一页>>WhoisWhointheInternet?

TheInternetEngineeringSteeringGroup(IESG)

–TheIESGisresponsiblefor technicalmanagementofIETF activitiesandtheInternetstandards process

–ComposedoftheAreaDirectorsof theIETFworkinggroups48<<上一页下一页>>WhoisWhointh4849<<上一页下一页>>WhoisWhointheInternet?IETFandIESGChair

–RussHousley,Vigil Security,LLCApplicationsArea(app)

–LisaDusseault,Open SourceApplications Foundation

–AlexeyMelnikov,Isode LimitedInternetArea(int)

–JariArkko,Ericsson

–RalphDroms,CiscoOperationsandManagementArea(ops)

–RonaldBonica,Juniper Networks

–DanRomascanu,AvayaReal-timeApplicationsandInfrastructureArea(rai)

–CullenJennings,Cisco Systems

–RobertSparks,TekelecRoutingArea(rtg)

–RossCallon,JuniperNetworks

–AdrianFarrel,HuaweiSecurityArea(sec)

–PasiEronen,Nokia

–TimPolk,NationalInstituteof StandardsandTechnologyTransportArea(tsv)

–LarsEggert,NokiaResearch Center

–MagnusWesterlund,Ericsson49<<上一页下一页>>WhoisWhointh4950<<上一页下一页>>

InternetStandardization Process

AllstandardsoftheInternetarepublishedasRFC(RequestforComments).ButnotallRFCsareInternetStandards

–available:

Atypical(butnotonly)wayofstandardizationis:

–BOF(Birdsofafeather)

–InternetDrafts

–RFC

–ProposedStandard

–DraftStandard(requires2working implementation)

–InternetStandard(declaredbyIAB)50<<上一页下一页>> InternetSta5051<<上一页下一页>>InternetStandardization Process

–DavidClark,MIT,1992:

Wereject:kings,presidents, andvoting.Webelievein: roughconsensusand runningcode.51<<上一页下一页>>InternetStandar5152<<上一页下一页>>

ServicesProvidedbythe Internet

Sharedaccesstocomputingresources

–Telnet(1970’s)

Sharedaccesstodata/files

–FTP,NFS,AFS(1980’s)

Communicationmediumoverwhichpeopleinteract

–Email(1980’s),on-linechatrooms(1990’s)

–Instantmessaging,IPTelephony(2000’s)52<<上一页下一页>> ServicesProvi5253<<上一页下一页>>ServicesProvidedbythe Internet

Amediumforinformation dissemination

–USENET(1980’s)

–WWW(1990’s)

•Replacingnewspaper,magazine?

–Audio,video(2000’s)

•Replacingradio,CD,TV…53<<上一页下一页>>ServicesProvide5354<<上一页下一页>>

Internetstructure:networkof networksroughlyhierarchicalatcenter:“tier-1”ISPs(e.g.,UUNet,BBN/Genuity,Sprint,AT&T),national/internationalcoverage

–treateachotherasequalsTier-1providersinterconnect(peer)privately

Tier1ISP

NAPTier1ISPTier1ISPTier-1providersalsointerconnectatpublicnetworkaccesspoints(NAPs)54<<上一页下一页>> Internetstruct54………55<<上一页下一页>>Tier-1ISP:e.g.,SprintSprintUSbackbonenetworkChicago Roachdale

StocktonSanJose

NewYork Pennsauken RelayWash.DC

SeattleTacomaDS3(45Mbps)OC3(155Mbps)OC12(622Mbps)OC48(2.5Gbps)…Anaheim Atlanta

to/fromcustomers

OrlandoCheyenne

peering

…

KansasCityPOP:point-of-presence

to/frombackbone………55<<上一页下一页>>Tier-1ISP:e5556<<上一页下一页>>Internetstructure:networkof networks

“Tier-2”ISPs:smaller(oftenregional)ISPs

–Connecttooneormoretier-1ISPs,possiblyother tier-2ISPs

Tier-2ISPTier-2ISP

Tier1ISP

NAPTier1ISPTier1ISPTier-2ISPTier-2ISPTier-2ISPpaystier-1ISPforconnectivitytorestofInternet tier-2ISPiscustomeroftier-1provider

Tier-2ISPs alsopeer privatelywith eachother, interconnect atNAPTier-2ISP56<<上一页下一页>>Internetstructu56ISPlocallocalISPISPTier-2ISPTier-2ISPTier1ISPTier1ISPISPISP57<<上一页下一页>>Internetstructure:networkof networks

“Tier-3”ISPsandlocalISPs

–lasthop(“access”)network(closesttoendsystems)Tier3local ISPISPTier-2ISP local ISPcustomersofTier1ISP

localLocalandtier-3ISPsarehighertierNAPISPsconnectingthemtorestofInternet Tier-2ISPTier-2ISP locallocallocal ISPISPlocallocalISPISPTier-2ISPT57localISP58<<上一页下一页>>

Internetstructure:networkof networksapacketpassesthroughmanynetworks!Tier1ISPTier1ISPTier1ISPNAPTier-2ISP

local ISPTier-2ISPlocal ISPlocal ISPlocal ISPTier3 ISPTier-2ISPTier-2ISP local ISPTier-2ISP local ISPlocal ISPTrya traceroute!localISP58<<上一页下一页>> Interne5859<<上一页下一页>>59<<上一页下一页>>5960<<上一页下一页>>60<<上一页下一页>>6061<<上一页下一页>>61<<上一页下一页>>6162<<上一页下一页>>

AccessNetworksQ:Howtoconnectend systemstoedgerouter?

residentialaccessnets institutionalaccess networks(school, company) mobileaccessnetworksKeepinmind:

bandwidth(bitsper second)ofaccess network? sharedordedicated?62<<上一页下一页>> AccessNetwork6263<<上一页下一页>>

Residentialaccess: pointtopointaccess

Dialupviamodem

–upto56Kbpsdirectaccessto router(oftenless)

ISDN:integratedservicesdigital network

–128kbps+regularphonelineADSL:asymmetricdigitalsubscriberline

–upto1Mbpsupstream(todaytypically<256kbps)

–upto8Mbpsdownstream(todaytypically<5Mbps)

–FDM:50kHz-1MHzfordownstream63<<上一页下一页>> Residentia6364<<上一页下一页>>

Residentialaccess: pointtopointaccessADSL:asymmetricdigitalsubscriberline

–ADSL充分利用了双绞铜线的频谱

•(1)传统话音业务频段，约为4ｋＨｚ带宽

•(2)ADSL上行低速信道，位于话音频谱之上

•(3)ADSL下行高速信道，位于高频部分

–频分多路复用(FDM)或回波抵消(Echo Cancellation)技术

–在回波抵消ADSL系统中，下行信道与上行信道有重 叠

–与频分复用技术相比，回波抵消技术消除了因频率叠 加所带来的干涉(如近端串音)，可使ADSL系统在性 能指标上有较大的提高，复杂度较高64<<上一页下一页>> Residential6465<<上一页下一页>>

Residentialaccess: cablemodemsHFC:hybridfibercoax

–asymmetric:upto10Mbps upstream,30MbpsdownstreamnetworkofcableandfiberattacheshomestoISProuter

–sharedaccesstorouteramong homes

–issues:congestion,dimensioningdeployment:availableviacablecompanies,e.g.,ComCast65<<上一页下一页>> Residentiala6566<<上一页下一页>>

Residentialaccess: cablemodemsDiagram:/cmic/diagram.html66<<上一页下一页>> Residentialacc6667<<上一页下一页>>home

cabledistributionnetwork(simplified)CableNetworkArchitecture: Overview

Typically500to5,000homes

cableheadend67<<上一页下一页>>home cabledistr6768<<上一页下一页>>homecabledistribution networkCableNetworkArchitecture: Overview

server(s) cableheadend68<<上一页下一页>>homecabledistri6869<<上一页下一页>>homeCableNetworkArchitecture: Overview

cableheadend

cabledistributionnetwork(simplified)69<<上一页下一页>>homeCableNetwor6970<<上一页下一页>>homecabledistribution network

ChannelscableheadendVVVVVVN

IDEO1

IDEO2

IDEO3

I D EO4

IDEO5

IDEO6DATA7DATA8TROL 9CableNetworkArchitecture: Overview

FDM:

C O70<<上一页下一页>>homecabledistri7071<<上一页下一页>>

Companyaccess:localareanetworkscompany/univlocalareanetwork(LAN)connectsendsystemtoedgerouterEthernet:

–sharedordedicated link(switched Ethernet)connects endsystemand router

–10Mbps,100Mbps, GigabitEthernetdeployment:institutions,homeLANshappeningnowTo/From ISP71<<上一页下一页>> Companyaccess:7172<<上一页下一页>>Wirelessaccessnetworkssharedwirelessaccessnetworkconnectsendsystemtorouter

–viabasestation“accesspoint”wirelessLANs:

–802.11b:11Mbps

–802.11g:54Mbps

–802.11n:Marvell提供450Mbpswider-areawirelessaccess

–providedbytelecomoperator

–3G~384kbps

–WAP/GPRSinEurope

–GPRS/CDMAinChinamobile hostsrouter basestation72<<上一页下一页>>Wirelessaccess7273<<上一页下一页>>

HomenetworksTypicalhomenetworkcomponents:

ADSLorcablemodem router/firewall/NAT Ethernet wirelessaccesspointwireless access pointwireless laptops

cablemodemto/from cableheadendrouter/firewall Ethernet (switched)73<<上一页下一页>> Homenetworksw7374<<上一页下一页>>

提纲网络基本概念Internet简介协议分层和OSI参考模型End-to-EndArgumentsInternet设计原则74<<上一页下一页>> 提纲7475<<上一页下一页>>

TheBigQuestionManydifferentnetworkstylesandtechnologies

–circuit-switchedvspacket- switched,etc.

–wirelessvswiredvsoptical,etc.Manydifferentapplications

–ftp,email,web,P2P,etc.Howdoweorganizethismess?75<<上一页下一页>> TheBigQuest7576<<上一页下一页>>WhyLayering?Dowere-implementeveryapplicationforeverytechnology?Obviouslynot,buthowdoestheInternetarchitectureavoidthis?TelnetFTPNFSPacketradioCoaxialcableFiberopticApplicationTransmissionMediaHTTP76<<上一页下一页>>WhyLayering?Do76

WhyLayering?Solution:introduceanintermediatelayerthatprovidesauniqueabstractionforvariousnetworktechnologiesTelnetFTPNFSPacketradioCoaxialcableFiberopticApplication

Transmission Media<<上一页 下一页>>

77HTTPIntermediatelayer WhyLayering?TelnetFTPNFSPack7778<<上一页下一页>>

Architecture

Architectureisnottheimplementationitself Architectureishowto“organize”implementations

–whatinterfacesaresupported

–wherefunctionalityis implemented

Architectureisthemodulardesignofthenetwork78<<上一页下一页>> Architecture7879<<上一页下一页>>

SoftwareModularityBreaksystemintomodules:

Well-definedinterfacesgives flexibility

–canchangeimplementationofmodules

–canextendfunctionalityofsystemby addingnewmodules

Interfaceshideinformation

–allowsforflexibility

–butcanhurtperformance79<<上一页下一页>> SoftwareModu7980<<上一页下一页>>

NetworkModularityLikesoftwaremodularity,but withatwist:

Implementationdistributed

acrossroutersandhosts Mustdecideboth:

–howtobreaksystemintomodules

–wheremodulesareimplemented80<<上一页下一页>> NetworkModu8081<<上一页下一页>>

LayeringLayeringisaparticularformofmodularizationThesystemisbrokenintoaverticalhierarchyoflogicallydistinctentities(layers)Theserviceprovidedbyonelayerisbasedsolelyontheserviceprovidedbylayerbelow81<<上一页下一页>> Layering8182<<上一页下一页>>

LayeringAdvantages

–Modularity–protocolseasiertomanage andmaintain

–Abstractfunctionality–lowerlayercan bechangedwithoutaffectingtheupper layer

–Reuse–upperlayercanreusethe functionalityprovidedbylowerlayerDisadvantages

–Informationhiding–inefficient implementations82<<上一页下一页>> Layering8283<<上一页下一页>>

Layering–LayerNsoftwareonthedestination computermustreceiveexactlythe messagesentbylayerNsoftwareon thesendingcomputer–Mathematically,ifthesenderapplies atransformationT,thereceivermust applythei