G.8032EthernetRingProtectionOverviewMarch,2008ITU-T

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1、G.8032Ethernet Ring Protection OverviewMarch,2008ITU-T Q9 SG 15AgendaG.8032 Recommendation IntroductionG.8032 Objectives and PrinciplesG.8032 ConceptsG.8032 Protection SwitchingG.8032 R-APS MessagesG.8032 Items Under Study2ITU-T SG15/Q9 G.8032 RecommendationG.8032 Recommendation consented February 2

2、008This Recommendation defines the APS protocol and protection switching mechanisms for ETH layer ring topologies.Included are details pertaining to bridged ring protection characteristics,architectures and the ring APS protocol.G.8032 Proposals G.8032 Proposals and Contributionsand ContributionsG.8

3、032 Converged ProposalsG.8032 Converged ProposalsG.8032 ERP Work G.8032 ERP Work Item Approved in Item Approved in ITU-TITU-TG.8032 Objective,G.8032 Objective,Principles,and Principles,and Requirements SettingRequirements SettingG.8032 Recommendation G.8032 Recommendation ConsentConsent3G.8032 Objec

4、tives and PrinciplesUse of standard 802 MAC and OAM frames around the ring.Uses standard 802.1Q(and amended Q bridges),but with xSTP disabled.Ring nodes supports standard FDB MAC learning,forwarding,flush behaviour and port blocking/unblocking mechanisms.Prevents loops within the ring by blocking on

5、e of the links(either a pre-determined link or a failed link).Monitoring of the ETH layer for discovery and identification of Signal Failure(SF)conditions.Protection and recovery switching within 50 ms for typical rings.Total communication for the protection mechanism should consume a very small per

6、centage of total available bandwidth.4G.8032 Terms and Concepts Ring Protection Link(RPL)Link designated by mechanism that is blocked during Idle state to prevent loop on Bridged ring RPL Owner Node connected to RPL that blocks traffic on RPL during Idle state and unblocks during Protected state Lin

7、k Monitoring Links of ring are monitored using standard ETH CC OAM messages(CFM)Signal Fail(SF)Signal Fail is declared when ETH trail signal fail condition is detected No Request(NR)No Request is declared when there are no outstanding conditions(e.g.,SF,etc.)on the node Ring APS(R-APS)Messages Proto

8、col messages defined in Y.1731 and G.8032 Automatic Protection Switching(APS)Channel-Ring-wide VLAN used exclusively for transmission of OAM messages including R-APS messages5G.8032 Timers G.8032 specifies the use of different timers to avoid race conditions and unnecessary switching operationsWTR(W

9、ait to Restore)Timer Used by the RPL Owner to verify that the ring has stabilized before blocking the RPL after SF RecoveryHold-off Timers Used by underlying ETH layer to filter out intermittent link faultsFaults will only be reported to the ring protection mechanism if this timer expires6Controllin

10、g the Protection Mechanism Protection switching triggered by Detection/clearing of Signal Failure(SF)by ETH CC OAMRemote requests over R-APS channel(Y.1731)Expiration of G.8032 timers R-APS requests control the communication and states of the ring nodesTwo basic R-APS messages specified -R-APS(SF)an

11、d R-APS(NR)RPL Owner may modify the R-APS(NR)indicating the RPL is blocked:R-APS(NR,RB)Ring nodes may be in one of two statesIdle normal operation,no link/node faults detected in ringProtecting Protection switching in effect after identifying a signal fault7A.Physical topology has all nodes connecte

12、d in a ringB.ERP guarantees lack of loop by blocking the RPL(link between 6&1 in figure)C.Logical topology has all nodes connected without a loop.D.Each link is monitored by its two adjacent nodes using ETH CC OAM messagesE.Signal Failure as defined in Y.1731,is trigger to ring protectionLoss of Con

13、tinuityServer layer failure(e.g.Phy Link Down)RPL OwnerRPLETH-CCETH-CCETH-CCETH-CCETH-CCETH-CCETH-CCETH-CCETH-CCETH-CCETH-CCETH-CCPhysicaltopologyLogicaltopology126435RPL126435Ring Idle State8Protection Switching Link FailureA.Link/node failure is detected by the nodes adjacent to the failure.B.The

14、nodes adjacent to the failure,block the failed link and report this failure to the ring using R-APS(SF)messageC.R-APS(SF)message triggersRPL Owner unblocks the RPLAll nodes perform FDB flushingD.Ring is in protection stateE.All nodes remain connected in the logical topology.PhysicaltopologyLogicalto

15、pology126435RPL126435RPL126435126435RPL OwnerRPLR-APS(SF)R-APS(SF)R-APS(SF)R-APS(SF)9Protection Switching Failure RecoveryA.When the failed link recovers,the traffic is kept blocked on the nodes adjacent to the recovered linkB.The nodes adjacent to the recovered link transmit R-APS(NR)message indica

16、ting they have no local request present C.When the RPL Owner receives R-APS(NR)message it Starts WTR timerD.Once WTR timer expires,RPL Owner blocks RPL and transmits R-APS(NR,RB)messageE.Nodes receiving the message perform a FDB Flush and unblock their previously blocked portsF.Ring is now returned

17、to Idle stateRPL OwnerRPLR-APS(NR)R-APS(NR)R-APS(NR)R-APS(NR)R-APS(NR,RB)R-APS(NR,RB)PhysicaltopologyLogicaltopology126435RPL126435126435RPL12643510Signaling Channel Information ERP uses R-APS messages to manage and coordinate the protection switching R-APS defined in Y.1731-OAM common fields are de

18、fined in Y.1731.Version 00000 for this version of RecommendationOpCode defined to be 40 in Y.1731Flags 00000000 should be ignored by ERPDefined by Y.1731Defined by G.8032Non-specified content11R-APS Specific Information Specific information(32octets)defined by G.8032Request/Status(4bits)1011=SF|0000

19、=NR|Other=FutureStatus RB(1bit)Set when RPL is blocked(used by RPL Owner in NR)Status DNF(1bit)Set when FDB Flush is not necessary(Future)NodeID(6octets)MAC address of message source node(Informational)Reserved1(4bits),Status Reserved(6bits),Reserved2(24octets)-Future development12348765432187654321

20、8765432187654321Request/StateReserved1StatusNode ID(6 octets)RBDNFStatusReserved(Node ID)Reserved2(24octets)12Items Under Study G.8032 is currently an initial recommendation that will continue to be enhanced.The following topics are under study for future versions of the recommendation:a)Interconnec

21、ted rings scenarios:shared node,shared linksb)RPL blocked at both ends configuration of the ring where both nodes connected to the RPL control the protection mechanismc)Support for Manual Switch administrative decision to close down a link and force a“recovery”situation are necessary for network mai

22、ntenanced)Support for Signal Degrade scenarios SD situations need special consideration for any protection mechanisme)Non-revertive mode Allows the network to remain in“recovery”configuration either until a new signal failure or administrative switchingf)RPL Displacement Displacement of the role of

23、the RPL to another ring link flexibly in the normal(idle)condition g)In-depth analysis of different optimizations(e.g.,FDB flushing)h)Etc.13 Thank You14Backup15G.8032 Basic FunctionsFailureRobustness:Source Steering Protection 50ms Switch TimesConnectivity:Unicast,MC and BC Data Transfers Multicast

24、FlowUnicastFlow16ERP Functionality Decomposition Inputs Local node requests,ETH signals,R-APS messages,WTR Timer.Filters Local Priority Logic,Validity Check,Guard Timer,Priority Logic guarantee that highest priority message arrives for processing.ERP Processing R-APS Request Processing processes fil

25、tered message according to State Machine with knowledge of current state and RPL-Owner indication Outputs Node functions(FDB Flushing,Block/Unblock port),sending(or stopping)R-APS messages17State MachineThree node states Initialization when first defining the ringA(Idle)the normal state of the ring

26、nodes with RPL blocked and all nodes/ports workingB(Protecting)when protection switching is in effect,RPL unblocked,other(usually fault)link is blocked.Different input messages assigned priority as appears in the State Machine description.Priority mechanism to allow proper reaction to faultsState Ma

27、chine describes the actions to be taken by the node dependent on current state and input message.Only message with highest priority will pass through the filtering.Different actions include transmission of R-APS message,blocking/unblocking a port,flushing the FDB,switching current state of node,and

28、starting/stopping timers.18State MachineFDB flushing will clear all of the learned filtering rules within the node.Current Recommendation includes basic optimization only flushing once on fault discovery and once on recovery.DNF status flag is for future definition19Switching Triggers Detection/Clea

29、ring of SF(Signal Fail):SF:Loss of CCM,SF signal passed up from underlying(sub)layerSwitching is performed when hold-off timer expires after detection of SF.Operators request:Lockout,Forced switch,Manual switch,Clear(for future specification)Remote request:Switching request indicated in received R-A

30、PS information from the other node.Protection switching algorithm is based on priorities assigned to all triggers20Ethernet Rings and the RPLEthernet nodes connected in a ring topology.Each node connected to two neighbors via links(E&W ports)Deterministic network topologyAvoid loops within ring by b

31、locking a designated link(RPL)Node responsible to control the blocking state of RPL is RPL ownerRPL is unblocked during protection state and may revert to blocked during recoveryRPL21E.RPL Owner receives SF message and unblocks its end of RPL link row 3F.Stable State SF messages on the ring G.Furthe

32、r SF messages trigger no further action row10BCDEFGASFNormalProtectionstatefailureR-APS ch blockClient ch blockSFSFAScenario A-Normal to ProtectionA.Normal StateB.Failure Occurs C.Nodes C and D detect local Signal Failure condition and after respecting hold-off time and Block failed port row 1D.Node

33、 C and D periodically send SF message,on both ring ports,while SF condition persists.Each node performs a FDB Flush when receiving the SF messageRPL OwnerBMessage sourceSFSFCDESFSFSFSFSFSFF50 msGRPLFlushFlushFlushFlushFlushFlushFlush22E.When node C and D expire the guard timer,they may accept the ne

34、w R-APS messages that they receive.in guard timerF.At expiration of WTR timer,RPL owner blocks its end of the RPL,sends,NR RB message row 11G.Each node that receives the NR,RB message it flushes its FDB.When Nodes C and D receive NR RB message,they remove block on their blocked ports.row 13H.Stable

35、normal condition all nodes in Idle stateBCDEFGRPLANormalProtectionstaterecoveryfailureScenario B recoveryA.Stable SF condition Nodes C and D continue to send SF message every 5 secs.B.Recovery of Link failureC.Nodes C and D detect clearing of SF condition,start guard timer and initiate periodical tr

36、ansmission of NR message on both ring ports.(Guard timer prevents reception of R-APS messages)row 9D.When the RPL Owner receives NR message,it starts the WTR timer row 14RPL OwnerBCSFSFSFSFSFSFFAENRNRNRNRNR,RPL BlockedNR,RPL BlockedNR,RPL BlockedGNRNR,RPL BlockedNR,RPL BlockedNR,RPL BlockedNRNRDFlushFlushFlushFlushFlushFlushFlush50 msConfirmation timeH23