Architecture and Layered Structure of computer Network

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Architecture and Layered Structure of computer Network. Our goal: get context, overview, feel of networking more depth, detail later in course approach: Descriptive use Internet as example. Overview: whats the Internet whats a protocol? network edge network core - PowerPoint PPT Presentation


  • Architecture and Layered Structure of computer Network

  • Part I: IntroductionOur goal: get context, overview, feel of networkingmore depth, detail later in courseapproach:Descriptiveuse Internet as example

    Overview:whats the Internetwhats a protocol?network edgenetwork coreaccess net, physical mediaperformance: loss, delayprotocol layers, service modelshistory

  • Whats the Internet: nuts and bolts viewmillions of connected computing devices: hosts, end-systemspcs workstations, serversPDAs phones, toastersrunning network appscommunication linksfiber, copper, radio, satelliterouters: forward packets (chunks) of data thru network

  • Cool internet appliancesWorlds smallest web server picture frame toaster+weather forecaster

  • Whats the Internet: nuts and bolts viewprotocols: control sending, receiving of msgse.g., TCP, IP, HTTP, FTP, PPPInternet: network of networksloosely hierarchicalpublic Internet versus private intranetInternet standardsRFC: Request for commentsIETF: Internet Engineering Task Forcelocal ISPcompanynetworkregional ISProuterworkstationservermobile

  • Whats the Internet: a service viewcommunication infrastructure enables distributed applications:WWW, email, games, e-commerce, database., voting, file (MP3) sharingcommunication services provided:connectionlessconnection-oriented

  • Whats a protocol?human protocols:whats the time?I have a questionintroductions

    specific msgs sent specific actions taken when msgs received, or other eventsnetwork protocols:machines rather than humansall communication activity in Internet governed by protocolsprotocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt

  • Whats a protocol?a human protocol and a computer network protocol:

    Q: Other human protocol? HiHiTCP connection req.

  • A closer look at network structure:network edge: applications and hostsnetwork core: routersnetwork of networksaccess networks, physical media: communication links

  • The network edge:end systems (hosts):run application programse.g., WWW, emailat edge of networkclient/server modelclient host requests, receives service from servere.g., WWW client (browser)/ server; email client/serverpeer-peer model: host interaction symmetrice.g.: Gnutella, KaZaA

  • Network edge: connection-oriented serviceGoal: data transfer between end sys.handshaking: setup (prepare for) data transfer ahead of timeHello, hello back human protocolset up state in two communicating hostsTCP - Transmission Control Protocol Internets connection-oriented service

    TCP service [RFC 793]reliable, in-order byte-stream data transferloss: acknowledgements and retransmissionsflow control: sender wont overwhelm receivercongestion control: senders slow down sending rate when network congested

  • Network edge: connectionless serviceGoal: data transfer between end systemssame as before!UDP - User Datagram Protocol [RFC 768]: Internets connectionless serviceunreliable data transferno flow controlno congestion controlApps using TCP: HTTP (WWW), FTP (file transfer), Telnet (remote login), SMTP (email)

    Apps using UDP:streaming media, teleconferencing, Internet telephony

  • The Network Coremesh of interconnected routersthe fundamental question: how is data transferred through net?circuit switching: dedicated circuit per call: telephone netpacket-switching: data sent thru net in discrete chunks

  • Network Core: Circuit SwitchingEnd-end resources reserved for calllink bandwidth, switch capacitydedicated resources: no sharingcircuit-like (guaranteed) performancecall setup required

  • Network Core: Circuit Switchingnetwork resources (e.g., bandwidth) divided into piecespieces allocated to callsresource piece idle if not used by owning call (no sharing)dividing link bandwidth into piecesfrequency divisiontime divisiondividing link bandwidth into piecesfrequency divisiontime division

  • Circuit Switching: FDMA and TDMA

  • Network Core: Packet Switchingeach end-end data stream divided into packetsuser A, B packets share network resources each packet uses full link bandwidth resources used as needed,

    resource contention: aggregate resource demand can exceed amount availablecongestion: packets queue, wait for link usestore and forward: packets move one hop at a timetransmit over linkwait turn at next link

  • Network Core: Packet SwitchingABC10 MbsEthernet1.5 Mbs45 Mbsstatistical multiplexingqueue of packetswaiting for outputlink

  • Packet switching versus circuit switching1 Mbit linkeach user: 100Kbps when activeactive 10% of time

    circuit-switching: 10 userspacket switching: with 35 users, probability > 10 active less than .0004

    Packet switching allows more users to use network!N users1 Mbps link

  • Access networks and physical mediaQ: How to connection end systems to edge router?residential access netsCable modeminstitutional access networks (school, company)Local area networksmobile access networksPhysical media coax, fiberRadio

  • Delay in packet-switched networkspackets experience delay on end-to-end pathfour sources of delay at each hopnodal processing: check bit errorsdetermine output linkqueueingtime waiting at output link for transmission depends on congestion level of router

  • Delay in packet-switched networksTransmission delay:R=link bandwidth (bps)L=packet length (bits)time to send bits into link = L/RPropagation delay:d = length of physical links = propagation speed in medium (~2x108 m/sec)propagation delay = d/sNote: s and R are very different quantities!

  • Real Internet delays and routes1 cs-gw ( 1 ms 1 ms 2 ms2 ( 1 ms 1 ms 2 ms3 ( 6 ms 5 ms 5 ms4 ( 16 ms 11 ms 13 ms 5 ( 21 ms 18 ms 18 ms 6 ( 22 ms 18 ms 22 ms7 ( 22 ms 22 ms 22 ms8 ( 104 ms 109 ms 106 ms9 ( 109 ms 102 ms 104 ms10 ( 113 ms 121 ms 114 ms11 ( 112 ms 114 ms 112 ms12 ( 111 ms 114 ms 116 ms13 ( 123 ms 125 ms 124 ms14 ( 126 ms 126 ms 124 ms15 ( 135 ms 128 ms 133 ms16 ( 126 ms 128 ms 126 ms17 * * *18 * * *19 ( 132 ms 128 ms 136 mstraceroute (or tracert): routers, rt delays on source-dest path also: pingplotter, various windows programs

  • Part II: Protocol LayersNetworks are complex! many pieces:hostsrouterslinks of various mediaapplicationsprotocolshardware, softwareQuestion: Is there any hope of organizing structure of network?

    Or at least our discussion of networks?

  • Why layered---Reduce the complexity,increase the flexibility

  • Layer principleLayered by the abstract functionAll the needed function and service should have clear ruleDifferent system should be divided to same layer and with the same function in the same layerThe layer function should be chose by the easy slandering principleWhen using the service from underlayer, the service implementation is sightlessThe layer number should be appropriate

  • Related terms and communication layer architectureSource & DestinationEntity & Peer-peer EntityService & InterfaceProtocol & Protocol Data Unit

  • OSI model---Why ?

  • The function of all the layers

  • Data encapsulation

  • Internet protocol stackapplication: supporting network applicationsftp, smtp, httptransport: host-host data transfertcp, udpnetwork: routing of datagrams from source to destinationip, routing protocolslink: data transfer between neighboring network elementsppp, ethernetphysical: bits on the wire

  • Protocol layering and dataEach layer takes data from aboveadds header information to create new data unitpasses new data unit to layer below


  • TCP/IP ArchitectureethernetdriverIPTCPftp clientFDDIdriverIPTCPftpserverIPethernetdriverFDDIdriverethernetFDDIftp protocolTCP protocolIP protocolIP protocole protocolf protocol

  • The compare between OSI and TCP/IPOSI--theory standard TCP/IPInternet virtual standard

  • The protocols of TCP/IP and their layer

  • Part III Internet History1961: Kleinrock - queueing theory shows effectiveness of packet-switching1964: Baran - packet-switching in military nets1967: ARPAnet conceived by Advanced Research Projects Agency1969: first ARPAnet node operational

    1972: ARPAnet demonstrated publiclyNCP (Network Control Protocol) first host-host protocol first e-mail programARPAnet has 15 nodes1961-1972: Early packet-switching principles

  • Internet History1970: ALOHAnet satellite network in Hawaii1973: Metcalfes PhD thesis proposes Ethernet1974: Cerf and Kahn - architecture for interconnecting networkslate70s: proprietary architectures: DECnet, SNA, XNAlate 70s: switching fixed length packets (ATM precursor)1979: ARPAnet has 200 nodesCerf and Kahns internetworking principles:minimalism, autonomy - no internal changes required to interconnect networksbest effort service modelstateless routersdecentralized