计算机网络英文课件：lecture-05-Layering and service models

1、Computer Networking Lecture 4Layering and service modelsMarch 10, 2017Dr. Qingyao WSome slides are from lectures of Prof. J.F Kurose and K.W. RossProtocol “Layers”Networks are complex! many “pieces”: hosts routers links of various media applications protocols hardware, softwareQuestion: Is there any

2、 hope of organizing structure of network?Or at least our discussion of networks?Organization of air travel a series of stepsticket (purchase)baggage (check)gates (load)runway takeoffairplane routingticket (complain)baggage (claim)gates (unload)runway landingairplane routingairplane routingticket (pu

3、rchase)baggage (check)gates (load)runway (takeoff)airplane routingdepartureairportarrivalairportintermediate air-trafficcontrol centersairplane routingairplane routingticket (complain)baggage (claimgates (unload)runway (land)airplane routingticketbaggagegatetakeoff/landingairplane routingLayering of

4、 airline functionalityLayers: each layer implements a service via its own internal-layer actions relying on services provided by layer belowWhy layering?Dealing with complex systems: explicit structure allows identification, relationship of complex systems pieces layered reference model for discussi

5、on modularization eases maintenance, updating of system change of implementation of layers service transparent to rest of system e.g., change in gate procedure doesnt affect rest of systemInternet protocol stack application: supporting network applications FTP, SMTP, HTTP transport: process-process

6、data transfer TCP, UDP network: routing of datagrams from source to destination IP, routing protocols link: data transfer between neighboring network elements PPP, Ethernet physical: bits “on the wire”applicationtransportnetworklinkphysicalISO/OSI reference model presentation: allow applications to

7、interpret meaning of data, e.g., encryption, compression, machine-specific conventions session: synchronization, checkpointing, recovery of data exchange Internet stack “missing” these layers! these services, if needed, must be implemented in application needed?applicationpresentationsessiontranspor

8、tnetworklinkphysicalReview: protocol layers The Internet model Application layer Transport layer Network layer Link layer Physical layer The OSI model Application layer Presentation layer Session layer Transport layer Network layer Link layer Physical layersourceapplicationtransportnetworklinkphysic

9、alHtHnM报文段segmentHt数据报datagramdestinationapplicationtransportnetworklinkphysicalHtHnHlMHtHnMHtMMnetworklinkphysicallinkphysicalHtHnHlMHtHnMHtHnMHtHnHlMrouterswitchEncapsulation报文messageMHtMHn帧frameIntroduction: SummaryCovered a “ton” of material! Internet overview whats a protocol? network edge, core, access network packet-switching versus circuit-switching Internet structure performance: loss, delay, throughput layering, service modelsYou now have: