分布式系统原理与范例_4_Communication.pdf

《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、DistributedSystemsCommunicationOutlineFundamentalsRemoteProcedureCallMessage-orientedCommunicationStream-orientedCommunicationMulticastCommunicationLayeredProtocolsLayeredProtocolsLow-levellayersTransportlayerApplicationlayerMiddlewarelayerTyp

2、eofCommunicationLayeredProtocolsCommunicationsareoftenhandledbylayeredprotocolsCanyouthinkofrealworldexample?•Consideranairlinecompanyandameal-servicecompany.–Decisionastowhichmealtoorderishandledbymanager.–Decisionastohowtocommunicatetheorderishandled

3、bysecretary.Lowerlayersmighthandlethingslikehowtoturnelectricalvoltagesinto1sand0s.Youdon’twanttobedealingwiththatwhenimplementingtheHTTPprotocol.Agreementsandspecificationsareneededateachlevel.TwogeneraltypesofprotocolsProtocolsareformalsetofrulesth

4、atgoverntheformat,contents,andmeaningofthemessagessendandreceived.Connectionorientedandconnectionlessprotocols.Connectionorienteddoessomeinitialworktosetupa“virtualcircuit”.Connectionlessdoesnot.Examples?•Phoneisconnection-oriented.•Mailisconnectionle

5、ss.Prosandcons?•Connection-orientedareusuallymoreefficient.•Connectionlessareusuallymoreefficientforone-offmessages.BasicNetworkingModelDrawbacks:Focusonmessage-passingonlyOftenunneededorunwantedfunctionalityMessageHeaders/TrailersEachlayerwilltypic

6、allyadditsownheader/trailer.Whatisintheheader/trailer?Low-levelLayersPhysicalLayercontainsthespecificationandimplementationofbits,andtheirtransmissionbetweensenderandreceiverExamples:RS-232-CstandardforserialcommunicationlinesDataLinkLayerPrescribe

7、sthetransmissionofaseriesofbitsintoaframe.Physicallayersareunreliable.Mainjobofthislayeristodetectandcorrecterrors.How?•ChecksumofsomekindNetworklayerDescribeshowpacketsinanetworkofcomputersaretoberouted.Examples:connectionlessIP(InternetProtocol)Ob

8、servation:formanydistributedsystems,thelowestlevelinterfaceisthatofthenetworklayer.TransportLayerImportant:Thetransportlayerprovidestheactualcommunicationfacilitiesformostdistributedsystems.StandardInternetprotocols:TCP