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ID:34750320
大小:2.31 MB
页数:124页
时间:2019-03-10
《分布式系统原理与范例_4_Communication.pdf》由会员上传分享,免费在线阅读,更多相关内容在学术论文-天天文库。
1、DistributedSystemsCommunicationOutlineFundamentalsRemoteProcedureCallMessage-orientedCommunicationStream-orientedCommunicationMulticastCommunicationLayeredProtocolsLayeredProtocolsLow-levellayersTransportlayerApplicationlayerMiddlewarelayerTyp
2、eofCommunicationLayeredProtocolsCommunicationsareoftenhandledbylayeredprotocolsCanyouthinkofrealworldexample?•Consideranairlinecompanyandameal-servicecompany.–Decisionastowhichmealtoorderishandledbymanager.–Decisionastohowtocommunicatetheorderishandled
3、bysecretary.Lowerlayersmighthandlethingslikehowtoturnelectricalvoltagesinto1sand0s.Youdon’twanttobedealingwiththatwhenimplementingtheHTTPprotocol.Agreementsandspecificationsareneededateachlevel.TwogeneraltypesofprotocolsProtocolsareformalsetofrulesth
4、atgoverntheformat,contents,andmeaningofthemessagessendandreceived.Connectionorientedandconnectionlessprotocols.Connectionorienteddoessomeinitialworktosetupa“virtualcircuit”.Connectionlessdoesnot.Examples?•Phoneisconnection-oriented.•Mailisconnectionle
5、ss.Prosandcons?•Connection-orientedareusuallymoreefficient.•Connectionlessareusuallymoreefficientforone-offmessages.BasicNetworkingModelDrawbacks:Focusonmessage-passingonlyOftenunneededorunwantedfunctionalityMessageHeaders/TrailersEachlayerwilltypic
6、allyadditsownheader/trailer.Whatisintheheader/trailer?Low-levelLayersPhysicalLayercontainsthespecificationandimplementationofbits,andtheirtransmissionbetweensenderandreceiverExamples:RS-232-CstandardforserialcommunicationlinesDataLinkLayerPrescribe
7、sthetransmissionofaseriesofbitsintoaframe.Physicallayersareunreliable.Mainjobofthislayeristodetectandcorrecterrors.How?•ChecksumofsomekindNetworklayerDescribeshowpacketsinanetworkofcomputersaretoberouted.Examples:connectionlessIP(InternetProtocol)Ob
8、servation:formanydistributedsystems,thelowestlevelinterfaceisthatofthenetworklayer.TransportLayerImportant:Thetransportlayerprovidestheactualcommunicationfacilitiesformostdistributedsystems.StandardInternetprotocols:TCP
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