第一章计算机网络体系结构与Internet2012.ppt
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1、计算机网络体系结构与Internet史长琼长沙理工大学提纲u网络基本概念uInternet简介u协议分层和OSI参考模型提纲u网络基本概念网络基本概念uInternet简介u协议分层和OSI参考模型Whats a networkunetwork edge:millions of end-system devices:pcs workstations,serversPDAs,phones,toastersrunning network appsunetwork core:routers,switches forwarding datapackets:packet switchingcalls:c
2、ircuit switchingucommunication linksfiber,copper,radio,local netcompanynetregional netrouterworkstationservermobile“Cool”Internet appliancesWorlds smallest web serverhttp:/www-ccs.cs.umass.edu/shri/iPic.htmlIP picture framehttp:/ toaster+weather forecasterWhats a protocol?a human protocol and a comp
3、uter network protocol:HiHiGot thetime?2:00TCP connection req.TCP connectionreply.Get http:/ a protocol?human protocols:u“whats the time?”u“I have a question”uIntroductionsnetwork protocols:umachines rather than humansuall communication activity in Internet governed by protocols specific msgs sent sp
4、ecific actions taken when msgs received,or other eventsWhats a protocol?uprotocols define format,order of msgs sent and received among network entities,and actions taken on msg transmission,receipt A closer look at network structureunetwork edge:applications and hostsunetwork core:routersnetwork of
5、networksuaccess networks,physical media:communication linksThe network edgeuend systems(hosts)run application programse.g.,WWW,emailat“edge of network”uclient/server modelclient host requests,receives service from servere.g.,WWW client(browser)/server;email client/serverupeer-peer modelhost interact
6、ion symmetrice.g.:BT,Maze,e-Donkey The network coreumesh of interconnected routersuthe fundamental question:how is data transferred through net?circuit switching:dedicated circuit per call:telephone netpacket-switching:data sent thru net in discrete“chunks”uCommunication networks can be classified b
7、ased on the way in which the nodes exchange information:A Taxonomy of Communication NetworksCommunication Communication NetworkNetworkSwitchedSwitchedCommunication Communication NetworkNetworkBroadcastBroadcastCommunication Communication NetworkNetworkCircuit-SwitchedCircuit-SwitchedCommunication Co
8、mmunication NetworkNetworkPacket-SwitchedPacket-SwitchedCommunication Communication NetworkNetworkDatagramDatagram Network NetworkVirtual Circuit NetworkVirtual Circuit NetworkuBroadcast communication networksInformation transmitted by any node is received by every other node in the networkE.g.,LANs
9、(Ethernet,Wavelan)Problem:coordinate the access of all nodes to the shared communication medium(Multiple Access Problem)uSwitched communication networksInformation is transmitted to a sub-set of designated nodesE.g.,WANs(Telephony Network,Internet)Problem:how to forward information to intended node(
10、s)Done by special nodes(e.g.,routers,switches)running routing protocols Broadcast vs.Switched Communication Networks uCommunication networks can be classified based on the way in which the nodes exchange information:A Taxonomy of Communication NetworksCircuit-SwitchedCircuit-SwitchedCommunication Co
11、mmunication NetworkNetworkCommunication Communication NetworkNetworkSwitchedSwitchedCommunication Communication NetworkNetworkBroadcastBroadcastCommunication Communication NetworkNetworkPacket-SwitchedPacket-SwitchedCommunication Communication NetworkNetworkDatagramDatagram Network NetworkVirtual Ci
12、rcuit NetworkVirtual Circuit NetworkCircuit SwitchinguThree phases1.circuit establishment2.data transfer3.circuit terminationuIf circuit not available:“Busy signal”uExamplesTelephone networksISDN(Integrated Services Digital Networks)Timing in Circuit SwitchingDATACircuit Establishment Data Transmiss
13、ion Circuit Termination propagation delay between Host 1 and Node 1propagation delay between Host 2 and Node 1processing delay at Node 1Circuit SwitchinguA node(switch)in a circuit switching networkincoming linksoutgoing linksNodeuCommunication networks can be classified based on the way in which th
14、e nodes exchange information:A Taxonomy of Communication NetworksCommunication Communication NetworkNetworkSwitchedSwitchedCommunication Communication NetworkNetworkBroadcastBroadcastCommunication Communication NetworkNetworkCircuit-SwitchedCircuit-SwitchedCommunication Communication NetworkNetworkP
15、acket-SwitchedPacket-SwitchedCommunication Communication NetworkNetworkDatagramDatagram Network NetworkVirtual Circuit NetworkVirtual Circuit NetworkPacket SwitchinguData are sent as formatted bit-sequences,so-called packetsuPackets have the following structure:Header and Trailer carry control infor
16、mation(e.g.,destination address,check sum)uEach packet is passed through the network from node to node along some path(Routing)uAt each node the entire packet is received,stored briefly,and then forwarded to the next node(Store-and-Forward Networks)uTypically no capacity is allocated for packetsPack
17、et SwitchinguA node in a packet switching networkincoming linksoutgoing linksNodeMemoryHow do loss and delay occur?packets queue in router buffers upacket arrival rate to link exceeds output link capacityupackets queue,wait for turnABpacket being transmitted(delay)packets queueing(delay)free(availab
18、le)buffers:arriving packets dropped(loss)if no free buffers提纲u网络基本概念uInternet简介简介u协议分层和OSI参考模型The InternetuGlobal scale,general purpose,heterogeneous-technologies,public,computer networkuInternet ProtocolOpen standard:Internet Engineering Task Force(IETF)as standard body(http:/www.ietf.org)Technical
19、 basis for other types of networksIntranet:enterprise IP networkuDeveloped by the research communityGrowth of the InternetuNumber of Hosts on the Internet:Aug.1981 213Oct.1984 1,024Dec.1987 28,174 Oct.1990 313,000 Oct.1993 2,056,000Apr.1995 5,706,000Jan.1997 16,146,000Jan.1999 56,218,000Jan.2001 109
20、,374,000Jan.2003 171,638,297Jan.2006 394,991,609 Data available at:http:/www.isc.org/Services Provided by the InternetuShared access to computing resourcesTelnet(1970s)uShared access to data/filesFTP,NFS,AFS(1980s)uCommunication medium over which people interactEmail(1980s),on-line chat rooms(1990s)
21、Instant messaging,IP Telephony(2000s)Services Provided by the InternetuA medium for information disseminationUSENET (1980s)WWW(1990s)Replacing newspaper,magazine?Audio,video(2000s)Replacing radio,CD,TVInternet structure:network of networksuroughly hierarchicaluat center:“tier-1”ISPs(e.g.,UUNet,BBN/G
22、enuity,Sprint,AT&T),national/international coveragetreat each other as equalsTier 1 ISPTier 1 ISPTier 1 ISPTier-1 providers interconnect(peer)privatelyNAPTier-1 providers also interconnect at public network access points(NAPs)Tier-1 ISP:e.g.,SprintSprint US backbone networkSeattleAtlantaChicagoRoach
23、daleStocktonSan JoseAnaheimFort WorthOrlandoKansas CityCheyenneNew YorkPennsaukenRelayWash.DCTacomaDS3(45 Mbps)OC3(155 Mbps)OC12(622 Mbps)OC48(2.4 Gbps)to/from customerspeering to/from backbonePOP:point-of-presenceInternet structure:network of networksu“Tier-2”ISPs:smaller(often regional)ISPsConnect
24、 to one or more tier-1 ISPs,possibly other tier-2 ISPsTier 1 ISPTier 1 ISPTier 1 ISPNAPTier-2 ISPTier-2 ISPTier-2 ISPTier-2 ISPTier-2 ISPTier-2 ISP pays tier-1 ISP for connectivity to rest of Internetq tier-2 ISP is customer oftier-1 providerTier-2 ISPs also peer privately with each other,interconne
25、ct at NAPInternet structure:network of networksu“Tier-3”ISPs and local ISPs last hop(“access”)network(closest to end systems)Tier 1 ISPTier 1 ISPTier 1 ISPNAPTier-2 ISPTier-2 ISPTier-2 ISPTier-2 ISPTier-2 ISPlocalISPlocalISPlocalISPlocalISPlocalISPTier 3ISPlocalISPlocalISPlocalISPLocal and tier-3 IS
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