分布式系统设计.04new

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1、DistributedSystemsPrinciplesandParadigmsMaartenvanSteenVUAmsterdam,Dept.ComputerScienceRoomR4.20,steen@cs.vu.nlChapter04:CommunicationVersion:November5,2009ContentsChapter01:Introduction02:Architectures03:Processes04:Communication05:Naming06:Synchronization07:Consistency&Replication08:FaultToler

2、ance09:Security10:DistributedObject-BasedSystems11:DistributedFileSystems12:DistributedWeb-BasedSystems13:DistributedCoordination-BasedSystems2/52Communication4.1LayeredProtocolsLayeredProtocolsLow-levellayersTransportlayerApplicationlayerMiddlewarelayer3/52Communication4.1LayeredProtocolsBasicn

3、etworkingmodelApplicationprotocolApplication7PresentationprotocolPresentation6SessionprotocolSession5TransportprotocolTransport4NetworkprotocolNetwork3DatalinkprotocolDatalink2PhysicalprotocolPhysical1NetworkDrawbacksFocusonmessage-passingonlyOftenunneededorunwantedfunctionalityViolatesaccesstra

4、nsparency4/52Communication4.1LayeredProtocolsLow-levellayersRecapPhysicallayer:containsthespecificationandimplementationofbits,andtheirtransmissionbetweensenderandreceiverDatalinklayer:prescribesthetransmissionofaseriesofbitsintoaframetoallowforerrorandflowcontrolNetworklayer:describeshowpacketsin

5、anetworkofcomputersaretoberouted.ObservationFormanydistributedsystems,thelowest-levelinterfaceisthatofthenetworklayer.5/52Communication4.1LayeredProtocolsTransportLayerImportantThetransportlayerprovidestheactualcommunicationfacilitiesformostdistributedsystems.StandardInternetprotocolsTCP:connect

6、ion-oriented,reliable,stream-orientedcommunicationUDP:unreliable(best-effort)datagramcommunicationNoteIPmulticastingisoftenconsideredastandardavailableservice(whichmaybedangeroustoassume).6/52Communication4.1LayeredProtocolsMiddlewareLayerObservationMiddlewareisinventedtoprovidecommonservicesand

7、protocolsthatcanbeusedbymanydifferentapplicationsArichsetofcommunicationprotocols(Un)marshalingofdata,necessaryforintegratedsystemsNamingprotocols,toalloweasysharingofresourcesSecurityprotocolsforsecurecommunicationScalingme