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G.8032EthernetRingProtectionOverviewMarch,2008ITU-TQ9–SG15AgendaITU-TSG15/Q9G.8032RecommendationG.8032ObjectivesandPrinciplesG.8032TermsandConceptsG.8032TimersControllingtheProtectionMechanismPhysicaltopologyhasallnodesconnectedinaring ERPguaranteeslackofloopbyblockingtheRPL(linkbetween6&1infigure) Logicaltopologyhasallnodesconnectedwithoutaloop. EachlinkismonitoredbyitstwoadjacentnodesusingETHCCOAMmessages SignalFailureasdefinedinY.1731,istriggertoringprotection LossofContinuity Serverlayerfailure(e.g.PhyLinkDown)ProtectionSwitchingLinkFailureProtectionSwitchingFailureRecoverySignalingChannelInformationR-APSSpecificInformationItemsUnderStudyBackupG.8032BasicFunctionsERPFunctionalityDecompositionStateMachineStateMachineSwitchingTriggersEthernetRingsandtheRPLRPLOwnerreceivesSFmessageandunblocksitsendofRPLlink[row3] StableState–SFmessagesonthering FurtherSFmessagestriggernofurtheraction[row10]WhennodeCandDexpiretheguardtimer,theymayacceptthenewR-APSmessagesthattheyreceive.[inguardtimer] AtexpirationofWTRtimer,RPLownerblocksitsendoftheRPL,sends,NRRBmessage[row11] EachnodethatreceivestheNR,RBmessageitflushesitsFDB.WhenNodesCandDreceiveNRRBmessage,theyremoveblockontheirblockedports.[row13] StablenormalconditionallnodesinIdlestate