1第一章計算機網絡基本原理與機制1第一章計算機網絡基本原理與機制12<<上一頁下一頁>>

提綱網絡基本概念Internet簡介協議分層和OSI參考模型End-to-EndArgumentsInternet設計原則2<<上一頁下一頁>> 提綱23<<上一頁下一頁>>

提綱網絡基本概念Internet簡介協議分層和OSI參考模型End-to-EndArgumentsInternet設計原則3<<上一頁下一頁>> 提綱34<<上一頁下一頁>>World’ssmallestwebserver/~shri/iPic.html“Cool”Internetappliances

IPpictureframe / Web-enabledtoaster+weatherforecaster4<<上一頁下一頁>>World’ssmallest45<<上一頁下一頁>>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<<上一頁下一頁>>What’sanetworkn56<<上一頁下一頁>>What’saprotocol?ahumanprotocolandacomputernetworkprotocol:

Hi HiGotthe time?

2:00TCPconnection req.TCPconnectionreply.Get

<file>time6<<上一頁下一頁>>What’saprotocol67<<上一頁下一頁>>What’saprotocol?humanprotocols:

“what’sthetime?” “Ihaveaquestion”

Introductionsnetworkprotocols:

machinesrather thanhumans allcommunication activityinInternet governedby protocols…specificmsgssent…specificactionstakenwhenmsgsreceived,orotherevents7<<上一頁下一頁>>What’saprotocol78<<上一頁下一頁>>

What’saprotocol?協議的組成：

–語法（syntax)：以二進制形式表示的命令和相應的 結構

–語義（semantics)：命令請求、完成的動作和回送的 響應的具體含義

–定時關系（timing)：有關事件順序的說明protocolsdefineformat,orderofmsgssentandreceivedamongnetworkentities,andactionstakenonmsgtransmission,receipt8<<上一頁下一頁>> What’saproto89<<上一頁下一頁>>

Acloserlookatnetwork structurenetworkedge:

–applicationsand hostsnetworkcore:

–routers

–networkof networksaccessnetworks,physicalmedia:

–communication links9<<上一頁下一頁>> Acloserlooka910<<上一頁下一頁>>

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<<上一頁下一頁>> Thenetworke1011<<上一頁下一頁>>

Thenetworkcoremeshofinterconnectedroutersthefundamentalquestion:howisdatatransferredthroughnet?

–circuitswitching:

dedicatedcircuitper call:telephonenet

–packetswitching:

datasentthrunetin discrete“chunks”11<<上一頁下一頁>> Thenetworkc1112<<上一頁下一頁>>

BroadcastCommunication Network

ATaxonomyof CommunicationNetworksCommunicationnetworkscanbeclassifiedbasedonthewayinwhichthenodesexchangeinformation:

Communication Network

Switched Communication NetworkCircuit-Switched Communication NetworkPacket-Switched Communication NetworkDatagram NetworkVirtualCircuitNetwork12<<上一頁下一頁>> Broadcast ATa1213<<上一頁下一頁>>

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<<上一頁下一頁>> Broadcastvs1314<<上一頁下一頁>>

ATaxonomyof CommunicationNetworksCommunicationnetworkscanbeclassifiedbasedonthewayinwhichthenodesexchangeinformation:

Communication Network

Switched Communication NetworkCircuit-Switched Communication Network

BroadcastCommunication NetworkPacket-Switched Communication NetworkDatagram NetworkVirtualCircuitNetwork14<<上一頁下一頁>> ATaxonomyof 1415<<上一頁下一頁>>

CircuitSwitchingThreephases1.circuitestablishment2.datatransfer3.circuitterminationIfcircuitnotavailable:“Busysignal”Examples–Telephonenetworks–ISDN(IntegratedServicesDigital Networks)15<<上一頁下一頁>> CircuitSwitch1516<<上一頁下一頁>>TiminginCircuitSwitchingCircuit EstablishmentHost1Host2Node1Node2

betweenHost1 andNode1propagationdelay

betweenHost2 andNode1Data Transmission

DATACircuit TerminationprocessingdelayatNode1 propagationdelay16<<上一頁下一頁>>TiminginCircui1617<<上一頁下一頁>>CircuitSwitching

Anode(switch)inacircuit switchingnetworkincominglinksoutgoinglinksNode17<<上一頁下一頁>>CircuitSwitchin1718<<上一頁下一頁>>

CircuitSwitching:Multiplexing/Demultiplexing

Timedividedinframesandframesdividedin

slots

Relativeslotpositioninsideaframedetermines

whichconversationthedatabelongsto Needssynchronizationbetweensenderand receiver Incaseofnon-permanentconversations

–Needstodynamicbindaslottoa conservation18<<上一頁下一頁>> CircuitSwit1819<<上一頁下一頁>>

ATaxonomyof CommunicationNetworksCommunicationnetworkscanbeclassifiedbasedonthewayinwhichthenodesexchangeinformation:

Communication Network

BroadcastCommunication Network

Switched Communication NetworkCircuit-Switched Communication NetworkPacket-Switched Communication NetworkDatagram NetworkVirtualCircuitNetwork19<<上一頁下一頁>> ATaxonomyof 1920<<上一頁下一頁>>

PacketSwitchingDataaresentasformattedbit-sequences,so-calledpacketsPacketshavethefollowingstructure:

?HeaderandTrailercarrycontrol information(e.g.,destinationaddress, checksum)Eachpacketispassedthroughthenetworkfromnodetonodealongsomepath(Routing)Ateachnodetheentirepacketisreceived,storedbriefly,andthenforwardedtothenextnode(Store-and-ForwardNetworks)HeaderDataTrailer20<<上一頁下一頁>> PacketSwitchin2021<<上一頁下一頁>>PacketSwitching

Anodeinapacketswitching networkincominglinksoutgoinglinksNodeMemory21<<上一頁下一頁>>PacketSwitching2122<<上一頁下一頁>>

PacketSwitching:Multiplexing/Demultiplexing

Datacanbetransmittedatany giventime Howtotellthemapart?

–Usemeta-data(header)to describedata22<<上一頁下一頁>> PacketSwit2223<<上一頁下一頁>>

BroadcastCommunication Network

ATaxonomyof CommunicationNetworksCommunicationnetworkscanbeclassifiedbasedonthewayinwhichthenodesexchangeinformation:

Communication Network

Switched Communication NetworkCircuit-Switched Communication NetworkPacket-Switched Communication NetworkDatagram NetworkVirtualCircuitNetwork23<<上一頁下一頁>> Broadcast ATa2324<<上一頁下一頁>>

DatagramPacket Switching

Eachpacketisindependentlyswitched

–Eachpacketheadercontains destinationaddress

Noresourcesarepre-allocated(reserved)inadvance

Example:IPnetworks24<<上一頁下一頁>> DatagramPac2425<<上一頁下一頁>>HostAHostBHostEHostDDatagramPacket Switching

HostCNode1Node3Node4Node6Node2 Node5Node725<<上一頁下一頁>>HostAHostBHost2526<<上一頁下一頁>>

Howdolossanddelayoccur?

routerbuffersisfull

packetarrivalratetolinkexceedsoutput linkcapacity

Outputlink(loss)A

B

dropped(loss)ifnofreebuffers26<<上一頁下一頁>> Howdolossand2627<<上一頁下一頁>>Foursourcesofpacketdelay1.nodalprocessing

–checkbiterrors

–determineoutput link(?)ABtransmission nodal processing

propagationqueueing2.queueing

–timewaitingatoutput linkfortransmission

–dependsoncongestion levelofrouter27<<上一頁下一頁>>Foursourcesof2728<<上一頁下一頁>>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<<上一頁下一頁>>Foursourcesof2829<<上一頁下一頁>>

BroadcastCommunication Network

ATaxonomyof CommunicationNetworksCommunicationnetworkscanbeclassifiedbasedonthewayinwhichthenodesexchangeinformation:

Communication Network

Switched Communication NetworkCircuit-Switched Communication NetworkPacket-Switched Communication NetworkDatagram NetworkVirtualCircuitNetwork29<<上一頁下一頁>> Broadcast ATa2930<<上一頁下一頁>>

Virtual-CircuitPacket SwitchingHybridofcircuitswitchingandpacketswitching

–Dataistransmittedaspackets

–Allpacketsfromonepacketstreamare sentalongapre-establishedpath

(=virtualcircuit)Guaranteesin-sequencedeliveryofpacketsHowever:PacketsfromdifferentvirtualcircuitsmaybeinterleavedExample:ATMnetworks30<<上一頁下一頁>> Virtual-Circu3031<<上一頁下一頁>>

Virtual-CircuitPacket SwitchingCommunicationwithvirtualcircuitstakesplaceinthreephases1.VCestablishment2.datatransfer3.VCdisconnectNote:packetheadersdon’tneedtocontainthefulldestinationaddressofthepacket31<<上一頁下一頁>> Virtual-Circuit3132<<上一頁下一頁>>Packet1Packet1Packet2Packet3TimingofVirtual-Circuit PacketSwitchingPacket1Packet2Packet3Host1Host2Node1Node2propagationdelaybetweenHost1andNode1VCestablishment

Packet2 Packet3VCterminationDatatransfer32<<上一頁下一頁>>Packet1Packet13233<<上一頁下一頁>>HostAHostBHostENode1Node3Node4Node2 Node5Node6Node7HostDVirtual-CircuitPacket Switching

HostC33<<上一頁下一頁>>HostAHostBHost3334<<上一頁下一頁>>

Packet-Switchingvs. Circuit-Switching

Mostimportantadvantageofpacket-switchingovercircuitswitching:abilitytoexploitstatisticalmultiplexing

–Efficientbandwidthusage

?ratiobetweenpeekandaveragerateis 3:1foraudio,and15:1fordatatraffic34<<上一頁下一頁>> Packet-Swit3435<<上一頁下一頁>>

Packet-Switchingvs. Circuit-Switching

However,packet-switchingneedstodealwithcongestion

–Morecomplexrouters

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

Inpracticetheyarecombined

–IPoverSONET,IPoverFrameRelay35<<上一頁下一頁>> Packet-Switc3536<<上一頁下一頁>>

提綱網絡基本概念Internet簡介協議分層和OSI參考模型End-to-EndArgumentsInternet設計原則基本機制回顧36<<上一頁下一頁>> 提綱3637<<上一頁下一頁>>

TheInternetGlobalscale,generalpurpose,heterogeneous-technologies,public,computernetworkInternetProtocol

–Openstandard:InternetEngineeringTask Force(IETF)asstandardbody

–Technicalbasisforothertypesof networks

?Intranet:enterpriseIPnetworkDevelopedbytheresearchcommunity37<<上一頁下一頁>> TheInternet3738<<上一頁下一頁>>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<<上一頁下一頁>>1961:Kleinrock3839<<上一頁下一頁>>

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<<上一頁下一頁>> InternetHisto3940<<上一頁下一頁>>1982:SMTPe-mailprotocoldefined1983:deploymentofTCP/IP1983:DNSdefinedforname-to-IP-addresstranslation1985:FTPprotocoldefined1988:TCPcongestioncontrolnewnationalnetworks:Csnet,BITnet,NSFnet,Minitel100,000hostsconnectedtoconfederationofnetworks

InternetHistory1980-1990:newprotocols,a proliferationofnetworks40<<上一頁下一頁>>1982:SMTPe-mai4041<<上一頁下一頁>>

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<<上一頁下一頁>> InternetHis4142<<上一頁下一頁>>TimeLineoftheInternet

?Source:InternetSociety42<<上一頁下一頁>>TimeLineofthe4243<<上一頁下一頁>>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<<上一頁下一頁>>GrowthoftheIn4344<<上一頁下一頁>>GrowthoftheInternet44<<上一頁下一頁>>GrowthoftheIn4445<<上一頁下一頁>>WhoisWhointheInternet?InternetSociety(ISOC)

–ISOCisaprofessionalmembership societywithmorethan100organization andover20,000individualmembersin over180countries –Itprovidesleadershipinaddressingissues oftheInternet,andistheorganization homeforthegroupsresponsiblefor Internetinfrastructurestandards, includingIETFandIAB45<<上一頁下一頁>>WhoisWhointh4546<<上一頁下一頁>>WhoisWhointheInternet?

InternetEngineeringTaskForce(IETF)

–TheIETFistheprotocolengineering anddevelopmentarmoftheInternet

–Subdividedintomanyworking groups,whichspecifyRequestFor CommentsorRFCs46<<上一頁下一頁>>WhoisWhointh4647<<上一頁下一頁>>WhoisWhointheInternet?IRTF(InternetResearchTaskForce)

–TheInternetResearchTaskForceis composedofanumberoffocused,long- termandsmallResearchGroupsInternetArchitectureBoard(IAB)

–TheIABisresponsiblefordefiningthe overallarchitectureoftheInternet, providingguidanceandbroaddirectionto theIETF47<<上一頁下一頁>>WhoisWhointh4748<<上一頁下一頁>>WhoisWhointheInternet?

TheInternetEngineeringSteeringGroup(IESG)

–TheIESGisresponsiblefor technicalmanagementofIETF activitiesandtheInternetstandards process

–ComposedoftheAreaDirectorsof theIETFworkinggroups48<<上一頁下一頁>>WhoisWhointh4849<<上一頁下一頁>>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<<上一頁下一頁>>WhoisWhointh4950<<上一頁下一頁>>

InternetStandardization Process

AllstandardsoftheInternetarepublishedasRFC(RequestforComments).ButnotallRFCsareInternetStandards

–available:

Atypical(butnotonly)wayofstandardizationis:

–BOF(Birdsofafeather)

–InternetDrafts

–RFC

–ProposedStandard

–DraftStandard(requires2working implementation)

–InternetStandard(declaredbyIAB)50<<上一頁下一頁>> InternetSta5051<<上一頁下一頁>>InternetStandardization Process

–DavidClark,MIT,1992:

Wereject:kings,presidents, andvoting.Webelievein: roughconsensusand runningcode.51<<上一頁下一頁>>InternetStandar5152<<上一頁下一頁>>

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<<上一頁下一頁>> ServicesProvi5253<<上一頁下一頁>>ServicesProvidedbythe Internet

Amediumforinformation dissemination

–USENET(1980’s)

–WWW(1990’s)

?Replacingnewspaper,magazine?

–Audio,video(2000’s)

?Replacingradio,CD,TV…53<<上一頁下一頁>>ServicesProvide5354<<上一頁下一頁>>

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<<上一頁下一頁>> Internetstruct54………55<<上一頁下一頁>>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<<上一頁下一頁>>Tier-1ISP:e5556<<上一頁下一頁>>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<<上一頁下一頁>>Internetstructu56ISPlocallocalISPISPTier-2ISPTier-2ISPTier1ISPTier1ISPISPISP57<<上一頁下一頁>>Internetstructure:networkof networks

“Tier-3”ISPsandlocalISPs

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

localLocalandtier-3ISPsarehighertierNAPISPsconnectingthemtorestofInternet Tier-2ISPTier-2ISP locallocallocal ISPISPlocallocalISPISPTier-2ISPT57localISP58<<上一頁下一頁>>

Internetstructure:networkof networksapacketpassesthroughmanynetworks!Tier1ISPTier1ISPTier1ISPNAPTier-2ISP

local ISPTier-2ISPlocal ISPlocal ISPlocal ISPTier3 ISPTier-2ISPTier-2ISP local ISPTier-2ISP local ISPlocal ISPTrya traceroute!localISP58<<上一頁下一頁>> Interne5859<<上一頁下一頁>>59<<上一頁下一頁>>5960<<上一頁下一頁>>60<<上一頁下一頁>>6061<<上一頁下一頁>>61<<上一頁下一頁>>6162<<上一頁下一頁>>

AccessNetworksQ:Howtoconnectend systemstoedgerouter?

residentialaccessnets institutionalaccess networks(school, company) mobileaccessnetworksKeepinmind:

bandwidth(bitsper second)ofaccess network? sharedordedicated?62<<上一頁下一頁>> AccessNetwork6263<<上一頁下一頁>>

Residentialaccess: pointtopointaccess

Dialupviamodem

–upto56Kbpsdirectaccessto router(oftenless)

ISDN:integratedservicesdigital network

–128kbps+regularphonelineADSL:asymmetricdigitalsubscriberline

–upto1Mbpsupstream(todaytypically<256kbps)

–upto8Mbpsdownstream(todaytypically<5Mbps)

–FDM:50kHz-1MHzfordownstream63<<上一頁下一頁>> Residentia6364<<上一頁下一頁>>

Residentialaccess: pointtopointaccessADSL:asymmetricdigitalsubscriberline

–ADSL充分利用了雙絞銅線的頻譜

?(1)傳統話音業務頻段，約為4ｋＨｚ帶寬

?(2)ADSL上行低速信道，位于話音頻譜之上

?(3)ADSL下行高速信道，位于高頻部分

–頻分多路復用(FDM)或回波抵消(Echo Cancellation)技術

–在回波抵消ADSL系統中，下行信道與上行信道有重 疊

–與頻分復用技術相比，回波抵消技術消除了因頻率疊 加所帶來的干涉(如近端串音)，可使ADSL系統在性 能指標上有較大的提高，復雜度較高64<<上一頁下一頁>> Residential6465<<上一頁下一頁>>

Residentialaccess: cablemodemsHFC:hybridfibercoax

–asymmetric:upto10Mbps upstream,30MbpsdownstreamnetworkofcableandfiberattacheshomestoISProuter

–sharedaccesstorouteramong homes

–issues:congestion,dimensioningdeployment:availableviacablecompanies,e.g.,ComCast65<<上一頁下一頁>> Residentiala6566<<上一頁下一頁>>

Residentialaccess: cablemodemsDiagram:/cmic/diagram.html66<<上一頁下一頁>> Residentialacc6667<<上一頁下一頁>>home

cabledistributionnetwork(simplified)CableNetworkArchitecture: Overview

Typically500to5,000homes

cableheadend67<<上一頁下一頁>>home cabledistr6768<<上一頁下一頁>>homecabledistribution networkCableNetworkArchitecture: Overview

server(s) cableheadend68<<上一頁下一頁>>homecabledistri6869<<上一頁下一頁>>homeCableNetworkArchitecture: Overview

cableheadend

cabledistributionnetwork(simplified)69<<上一頁下一頁>>homeCableNetwor6970<<上一頁下一頁>>homecabledistribution network

ChannelscableheadendVVVVVVN

IDEO1

IDEO2

IDEO3

I D EO4

IDEO5

IDEO6DATA7DATA8TROL 9CableNetworkArchitecture: Overview

FDM:

C O70<<上一頁下一頁>>homecabledistri7071<<上一頁下一頁>>

Companyaccess:localareanetworkscompany/univlocalareanetwork(LAN)connectsendsystemtoedgerouterEthernet:

–sharedordedicated link(switched Ethernet)connects endsystemand router

–10Mbps,100Mbps, GigabitEthernetdeployment:institutions,homeLANshappeningnowTo/From ISP71<<上一頁下一頁>> Companyaccess:7172<<上一頁下一頁>>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<<上一頁下一頁>>Wirelessaccess7273<<上一頁下一頁>>

HomenetworksTypicalhomenetworkcomponents:

ADSLorcablemodem router/firewall/NAT Ethernet wirelessaccesspointwireless access pointwireless laptops

cablemodemto/from cableheadendrouter/firewall Ethernet (switched)73<<上一頁下一頁>> Homenetworksw7374<<上一頁下一頁>>

提綱網絡基本概念Internet簡介協議分層和OSI參考模型End-to-EndArgumentsInternet設計原則74<<上一頁下一頁>> 提綱7475<<上一頁下一頁>>

TheBigQuestionManydifferentnetworkstylesandtechnologies

–circuit-switchedvspacket- switched,etc.

–wirelessvswiredvsoptical,etc.Manydifferentapplications

–ftp,email,web,P2P,etc.Howdoweorganizethismess?75<<上一頁下一頁>> TheBigQuest7576<<上一頁下一頁>>WhyLayering?Dowere-implementeveryapplicationforeverytechnology?Obviouslynot,buthowdoestheInternetarchitectureavoidthis?TelnetFTPNFSPacketradioCoaxialcableFiberopticApplicationTransmissionMediaHTTP76<<上一頁下一頁>>WhyLayering?Do76

WhyLayering?Solution:introduceanintermediatelayerthatprovidesauniqueabstractionforvariousnetworktechnologiesTelnetFTPNFSPacketradioCoaxialcableFiberopticApplication

Transmission Media<<上一頁 下一頁>>

77HTTPIntermediatelayer WhyLayering?TelnetFTPNFSPack7778<<上一頁下一頁>>

Architecture

Architectureisnottheimplementationitself Architectureishowto“organize”implementations

–whatinterfacesaresupported

–wherefunctionalityis implemented

Architectureisthemodulardesignofthenetwork78<<上一頁下一頁>> Architecture7879<<上一頁下一頁>>

SoftwareModularityBreaksystemintomodules:

Well-definedinterfacesgives flexibility

–canchangeimplementationofmodules

–canextendfunctionalityofsystemby addingnewmodules

Interfaceshideinformation

–allowsforflexibility

–butcanhurtperformance79<<上一頁下一頁>> SoftwareModu7980<<上一頁下一頁>>

NetworkModularityLikesoftwaremodularity,but withatwist:

Implementationdistributed

acrossroutersandhosts Mustdecideboth:

–howtobreaksystemintomodules

–wheremodulesareimplemented80<<上一頁下一頁>> NetworkModu8081<<上一頁下一頁>>

LayeringLayeringisaparticularformofmodularizationThesystemisbrokenintoaverticalhierarchyoflogicallydistinctentities(layers)Theserviceprovidedbyonelayerisbasedsolelyontheserviceprovidedbylayerbelow81<<上一頁下一頁>> Layering8182<<上一頁下一頁>>

LayeringAdvantages

–Modularity–protocolseasiertomanage andmaintain

–Abstractfunctionality–lowerlayercan bechangedwithoutaffectingtheupper layer

–Reuse–upperlayercanreusethe functionalityprovidedbylowerlayerDisadvantages

–Informationhiding–inefficient implementations82<<上一頁下一頁>> Layering8283<<上一頁下一頁>>

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