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MPLS and Ethernet OAM Interworking
draft-ietf-pwe3-mpls-eth-oam-iwk-05

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 7023.
Authors Dinesh Mohan , Dr. Nabil N. Bitar , Philippe Niger , Ray Qiu , Simon DeLord
Last updated 2012-04-16
Replaces draft-mohan-pwe3-mpls-eth-oam-iwk
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draft-ietf-pwe3-mpls-eth-oam-iwk-05
PWE3 Working Group                              Dinesh Mohan (Ed.) 
INTERNET-DRAFT                                     Nortel Networks 
Intended status: Standards Track        
Expires: October 2012                            Nabil Bitar (Ed.) 
                                                           Verizon 
                                                                          
                                                 Ali Sajassi (Ed.) 
                                                             Cisco  
                                                                          
                                                                          

                                                         April 12, 2012 
                                         
                       MPLS and Ethernet OAM Interworking 
                     draft-ietf-pwe3-mpls-eth-oam-iwk-05.txt 

     
     Abstract 

        This document specifies the mapping of defect states between 
        Ethernet Attachment Circuits (ACs) and associated Ethernet 
        Pseudowires (PWs) connected in accordance to the PWE3    
        architecture to realize an end-to-end emulated Ethernet service. 
        It standardizes the behavior of Provider Edges (PEs) with 
        respect to Ethernet PW and AC defects. 

     
     Status of this Memo 
   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

  This Internet-Draft will expire on October 12, 2012. 

       
      
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  Copyright Notice 
  
   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

      
     Table of Contents 

        1. Introduction.............................................. 2 
           1.1. Reference Model and Defect Locations................. 4 
           1.2. Abstract Defect States............................... 5 
        2. Terminology............................................... 7 
        3. PW Status and Defects..................................... 8 
           3.1. Use of Native Service (NS) notification.............. 8 
           3.2. Use of PW Status notification for MPLS PSNs.......... 9 
           3.3. Use of BFD Diagnostic Codes.......................... 9 
        4. Ethernet AC Defect States Entry or Exit Criteria......... 10 
           4.1. AC Receive Defect State Entry or Exit............... 10 
           4.2. AC Transmit Defect State Entry or Exit.............. 11 
        5. Ethernet AC and PW Defect States Interworking............ 12 
           5.1. PW Receive Defect Entry Procedures.................. 12 
           5.2. PW Receive Defect Exit Procedures................... 13 
           5.3. PW Transmit Defect Entry Procedures................. 14 
           5.4. PW Transmit Defect Exit Procedures.................. 15 
           5.5. AC Receive Defect Entry Procedures.................. 15 
           5.6. AC Receive Defect Exit Procedures................... 16 
           5.7. AC Transmit Defect Entry Procedures................. 16 
           5.8. AC Transmit Defect Exit Procedures.................. 17 
        6. Acknowledgments.......................................... 17 
        7. Security Considerations.................................. 17 
        8. IANA Considerations...................................... 17 
        9. References............................................... 17 
           9.1. Normative References................................ 17 
           9.2. Informative References.............................. 18 
        10. Appendix A: Ethernet Native Service Management.......... 18 
         
1. Introduction
      

        This document specifies the mapping of defect states between 

      
      
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        Ethernet Attachment Circuits (ACs) and associated Ethernet 
        Pseudowires (PWs) connected in accordance to the PWE3 
        architecture [RFC3985] to realize an end-to-end emulated 
        Ethernet service. This document augments the mapping of defect 
        states between a PW and associated AC of the end-to-end emulated 
        service in [RFC6310]. It covers the following Ethernet OAM 
        (Opertaions, Administration and  Maintenance) mechanisms and 
        their interworking with PW OAM mechanisms: 
         
        - Ethernet Continuity Check (CC) [802.1ag][Y.1731] 
        - Ethernet Alarm Indication Signaling (AIS) and Remote Defect 
          Indication (RDI) [Y.1731] 
        - Ethernet Link OAM [802.3] 
        - Ethernet Local Management Interface {E-LMI} [MEF16] 
         
        Ethernet Link OAM [802.3] allows some Link defect states to be 
        detected and communicated across an Ethernet Link. When an 
        Ethernet AC is an Ethernet physical port, there may be some 
        application of Ethernet Link OAM [802.3]. Further, E-LMI [MEF16] 
        also allows for some Ethernet Virtual Circuit (EVC) defect 
        states to be communicated across an Ethernet UNI where Ethernet 
        UNI constitutes a single hop Ethernet Link (i.e. without any 
        802.1Q/.1ad compliant bridges in between). There may be some 
        application of E-LMI [MEF16] for failure notification across 
        single hop Ethernet AC in certain deployments that specifically 
        do not support [802.1ag] and/or [Y.1731]. [Y.1731] and [802.1ag] 
        based mechanisms are applicable in all types of Ethernet ACs. 
        Ethernet Link OAM [802.3] and E-LMI [MEF16] are optional and 
        their applicability is called out, where applicable. 
         
        Native Service (NS) OAM may be transported transparently over  
        the corresponding PW as user data. This is referred to as "the  
        single emulated OAM loop" mode per [RFC6310]. For Ethernet, as  
        an example, 802.1ag continuity check messages (CCMs) between two 
        Maintenance End Points (MEPs) can be transported transparently 
        as user data over the corresponding PW. At MEP locations, 
        service failure is detected when CCMs are not received over an 
        interval that is 3.5 times the local CCM transmission interval. 
        This is one of the failure conditions detected via CC. 
         

      
      
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        MEP peers can exist between Customer Equipment (CE) pairs (MEPs 
        of a given Maintenance Entity Group (MEG) reside on the CEs), PE 
        pairs (the MEPs of a given MEG reside on the PEs), or between 
        the CE and PE (the MEPs of a given MEG reside on the PE 
        and CE), as long as the MEG domain nesting rules are maintained. 
        It should be noted that Ethernet allows the definition of up to 
        8 MEG domains, each compromising of MEPs (down MEPs and UP MEPs)  
        and Maintenance Intermediate Points (MIPs). These domains can be 
        nested or touching. MEPs and MIPs generate and process messages  
        in the same domain level. Thus, whenever in this document we
        refer to messages sent by a MEP or a MIP to a peer MEP or MIP,
        these MEPs and MIPs are in the same MEG domain level.  

        When interworking two networking domains, such as native 
        Ethernet and PWs to provide an end-to-end emulated service, 
        there is need to identify the failure domain and location even 
        when a PE supports both the NS OAM mechanisms and the PW OAM 
        mechanisms. In addition, scalability constraints may not allow 
        running proactive monitoring, such as CCMs with transmission 
        enabled, at a PE to detect the failure of an EVC across the PW 
        domain. Thus, network-driven alarms generated upon failure 
        detection in the NS or PW domain and their mappings to the other 
        domain are needed. There are also cases where a PE may not be 
        able to process NS OAM messages received on the PW even when 
        such messages are defined, as in Ethernet case, necessitating 
        the need for fault notification message mapping between the PW 
        domain and the NS domain. 

         
        For Multi-Segment PWs (MS-PWs) [RFC5659], Switching PEs (S-PEs) 
        are not aware of the NS. Thus, failure detection and 
        notification at S-PEs will be based on PW OAM mechanisms. 
        Mapping between PW OAM and NS OAM will be required at the 
        Terminating PEs (T-PEs) to propagate the failure notification 
        to the EVC endpoints. 
         
        Similar to [RFC6310], the intent of this document is to 
        standardize the behavior of PEs with respect to failures on 
        Ethernet ACs and PWs, so that there is no ambiguity about the 
        alarms generated and consequent actions undertaken by PEs in 
        response to specific failure conditions. 
      
        1.1. Reference Model and Defect Locations 
         

        Figure 1 is the same as used in [RFC6310] and is reproduced 
        in this document as a reference to highlight defect locations. 
      
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                  ACs             PSN tunnel               ACs 
                          +----+                  +----+ 
          +----+          | PE1|==================| PE2|          +----+ 
          |    |---(a)---(b)..(c)......PW1..(d)..(e)..(f)---(g)---|    | 
          | CE1|   (N1)   |    |                  |    |    (N2)  |CE2 | 
          |    |----------|............PW2.............|----------|    | 
          +----+          |    |==================|    |          +----+ 
               ^          +----+                  +----+          ^ 
               |      Provider Edge 1         Provider Edge 2     | 
               |                                                  | 
               |<-------------- Emulated Service ---------------->| 
           
          Customer                                              Customer 
          Edge 1                                                Edge 2 
      
                  Figure 1: PWE3 Network Defect Locations 
      
        1.2. Abstract Defect States  

        Abstract Defect States are also introduced in [RFC6310]. This 
        document uses the same conventions, as shown in Figure 2 from 
        [RFC6310]. It may be noted however that CE devices, shown in 
        Figure 2, do not necessarily have to be end customer devices. 
        These are essentially devices in client network segments that 
        are connecting to the Packet Switched Network (PSN) for the  
        emuulated services. 
         
                                      +-----+ 
                 ----AC receive ----->|     |-----PW transmit----> 
               CE1                    | PE1 |                       
               PE2/CE2 
                 <---AC transmit------|     |<----PW receive----- 
                                      +-----+ 
          (arrows indicate direction of user traffic impacted by a 
          defect) 
           
          Figure 2: Transmit and Receive Defect States and Notifications 
      
           
          PE1 may detect a receive defect in a local Ethernet AC via one 
          of the following mechanisms: 
           
      
      
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          - An AIS alarm generated at an upstream node in the client 
          domain (CE1 in Figure 2) and received by a local MEP. 
      
          - Failure of the local link on which the AC is configured. 
          Link failure may be detected via physical failures (e.g., loss  
          of signal (LoS)), via Ethernet Link OAM [802.3] critical link  
          event notifications generated at an upstream node CE1 with 
          "Dying Gasp" or "Critical Event" indication, or via a client
          Signal Fail message [Y.1731]. 
      
          - Failure to receive CCMs on the AC if a local MEP is 
          configured for the AC with CCM transmission enabled. 
           
          - A CCM from CE1 with interface status TLV indicating 
          interface down. Other CCM interface status TLVs will not be 
          used to indicate failure or recovery from failure.  
           
          It should be noted when a MEP at a PE or a CE receives a CCM 
          with the wrong MEG ID, MEP ID, or MEP level, the receving PE 
          or CE SHOULD treat such an event as an AC receive defect. In 
          any case, if such events persist for 3.5 times the MEP local 
          CCM transmission time, loss of continuity will be declared at 
          the receiving end.   
           
          An AC receive defect at PE1 impacts the ability of PE1 to 
          receive user traffic from the Client domain attached to PE1 
          via that AC. 
           
          PE1 may detect a receive defect in the PW via one of the 
          following mechanisms: 
              

          - A Forward Defect notification received from PE2. This defect 
          notification could point to problems associated with PE2's 
          inability to transmit traffic on the PW or PE2's inability to 
          receive traffic on its local AC from CE2. 
           
          - Unavailability of a PSN path in the PW domain to PE2. 
           
          A PW forward defect indication received on PE1 impacts the 
          ability of PE1 to receive traffic on the PW. 

      
      
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          PE1 may be notified of an AC transmit defect via one of the 
          following mechanisms: 
           
          - CCMs with RDI (Remote Defect Indication) bit set. 
          - In case when the AC is associated with a physical port, 
          failure of the local link on which the AC is configured (e.g., 
          LOS or via Ethernet Link OAM [802.3] critical link event 
          notifications generated at an upstream node CE1 with "Link 
          Fault" indication). 
           
          An AC transmit defect impacts the ability of PE1 to send user 
          traffic on the local AC. 
           
          Similarly, PE1 may be notified of a PW transmit defect via 
          Reverse Defect indication from PE2, which could point to 
          problems associated with PE2's inability to receive traffic on 
          the PW or PE2's inability to transmit traffic on its local AC. 
          PW transmit defect impacts PE1 ability to send user traffic 
          toward CE2. 
           
          The procedures outlined in this document define the entry and 
          exit criteria for each of the four defect states with respect 
          to Ethernet ACs and corresponding PWs, and the consequent 
          actions that PE1 must support to properly interwork these 
          defect states and corresponding notification messages between 
          the PW domain and the Native Service (NS) domain. Receive 
          Defect state SHOULD have precedence over Transmit Defect state 
          in terms of handling, when both transmit and receive defect 
          states are identified simultaneously. 
         
1.3. Specification of Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

     2. Terminology 

     This document uses the following terms: 
     AIS       Alarm Indication Signal 
     MD Level  Maintenance Domain (MD) Level which identifies a value 
               in the range of 0-7 associated with Ethernet OAM frame. 
               MD Level identifies the span of the Ethernet OAM frame. 
     MEP       Maintenance End Point is responsible for origination 
               and termination of OAM frames for a given MEG 

      
      
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     MIP       Maintenance Intermediate Point is located between peer 
               MEPs and can process OAM frames but does not initiate 
               or terminate them 
     RDI       Remote Defect Indication 
      
     Further, this document also uses the terminology and conventions 
     used in [RFC6310]. 
         

     3. PW Status and Defects 

        [RFC6310] introduces a range of defects that impact PW 
        status. All these defect conditions are applicable for Ethernet 
        PWs. 
         
        Similarly, there are different mechanisms described in [RFC6310] 
        to detect PW defects, depending on the PSN type (e.g. MPLS PSN, 
        MPLS-IP PSN). Any of these mechanisms can be used when 
        monitoring the state of Ethernet PWs. [RFC6310] also discusses 
        the applicability of these failure detection mechanisms. 
         
     3.1. Use of Native Service (NS) notification  

     When a MEP is defined on the PE and associated with an Ethernet 
     PW,the PE can use native service OAM capabilities for failure 
     notifications. Options include: 
         
        - Sending of AIS frames from the local MEP to the MEP on the 
        remote PE when the MEP needs to convey PE receive defects, and 
        when CCM transmission is disabled. 
        - Suspension of CCM frames transmission from the local MEP to 
        the peer MEP on the remote PE to convey PE receive defects, 
        when CCM transmission is enabled. 
        - setting the RDI bit in transmitted CCM frames, when loss of 
        CCMs from the peer MEP is detected or the PE needs to convey PW 
        reverse defects. 
         
        These NS OAM notifications are inserted into the corresponding 
        PW. 
         
        Similarly, when the defect conditions are cleared, a PE can take 
        one of the following actions, depending on the mechanism that  
      
      
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        was used for failure notification, to clear the defect sate on
        the peer PE: 
         
        - Stopping AIS frame transmission from the local MEP to the MEP 
        on the remote PE to clear PW receive defects. 
        - Resuming CCM frames transmission from the local MEP to the  
        peer MEP on the remote PE to clear PW forward defects  
        notification, when CCM transmission is enabled. 
        - Clearing the RDI bit in transmitted CCM frames, to clear PW 
        transmit defects notification, when CCM transmission is enabled. 
      
         

     3.2. Use of PW Status notification for MPLS PSNs  

        When PWs are established using LDP, LDP status notification 
        signaling MUST be used as the default mechanism to signal AC and 
        PW status and defects [RFC4447]. That is known as the "coupled 
        loop mode". For PWs established over an MPLS or MPLS-IP PSN 
        using other mechanisms (e.g. static configuration), inband 
        signaling using VCCV-BFD [RFC5885] SHOULD be used to convey AC 
        and PW status and defects. 
         
        [RFC6310] identifies the following PW defect status codepoints: 
        - Forward defect: corresponds to a logical OR of local AC 
        (ingress) Receive fault, local PSN-facing PW (egress) transmit 
        fault, and PW not forwarding fault. 
        - Reverse defect: corresponds to a logical OR of local AC 
        (egress) transmit fault and local PW PSN-facing (ingress) 
        receive fault. 
         
        There are also scenarios where a PE carries out PW label 
        withdrawal instead of PW status notification. These include 
        administrative disablement of the PW or loss of Target LDP 
        session with the peer PE. 
      
         

     3.3. Use of BFD Diagnostic Codes 

        When using VCCV, the control channel (CC) type and Connectivity 
        Verification (CV) Type are agreed on between the peer PEs using 

      
      
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        the OAM capability sub-TLV signaled as part of the interface 
        parameter TLV when using FEC 129 and the interface parameter 
        sub-TLV when using FEC 128. 
         
        As defined in [RFC6310], when CV type of 0x04 0r 0x1 is used to 
        indicate that BFD is used for PW fault detection only, PW defect 
        is detected via the BFD session while other defects, such as AC 
        defect or PE internal defects preventing it from forwarding 
        traffic, are communicated via LDP Status notification message in 
        MPLS and MPLS-IP PSNs or other mechanisms in L2TP-IP PSN. 
         
        Similarly, when CV type of 0x08 or 0x20 is used to indicate that 
        BFD is used for both PW fault detection and AC/PW Fault 
        Notification, all defects are signaled via BFD. 
         
     4. Ethernet AC Defect States Entry or Exit Criteria 

     4.1. AC Receive Defect State Entry or Exit  

        PE1 enters the AC Receive Defect state if any of the following 
        conditions is met: 
         
        - It detects or is notified of a physical layer fault on the 
        Ethernet interface. Ethernet link failure can be detected based 
        on loss of signal (LoS) or via Ethernet Link OAM [802.3] 
        critical link event notifications generated at an upstream node 
        CE1 with "Dying Gasp" or "Critical Event" indication. 
         
        - A MEP associated with the local AC receives an Ethernet AIS 
        frame. 
      
        - A MEP associated with the local AC does not receive CCM frames 
        from the peer MEP in the client domain (e.g. CE1) within an 
        interval equal to 3.5 times the CCM transmission period 
        configured for the MEP. This is the case when CCM transmission  
        is enabled. 
      
        - A CCM with interface status TLV indicating interface down. 
        Other CCM interface status TLVs will not be used to indicate 
        failure or recovery from failure.  
         

      
      
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        PE1 exits the AC Receive Defect state if all of the conditions 
        that resulted in entering the defect state are cleared. This 
        includes all of the following conditions: 
         
        - Any physical layer fault on the Ethernet interface, if 
        detected or notified previously is renoved (e.g., loss of signal 
        (LoS) cleared, or Ethernet Link OAM [802.3] critical link event 
        notifications with "Dying Gasp" or "Critical Event" indication 
        cleared at an upstream node CE1). 
         
        - A MEP associated with the local AC does not receive any 
        Ethernet AIS frame within a period indicated by previously 
        received AIS, if AIS resulted in entering the defect 
        state.  
           
        - A MEP associated with the local AC and configured with CCM    
        enabled receives a configured number (e.g., 3 or more) of 
        consecutive CCM frames from the peer MEP on CE1 within an 
        interval equal to a multiple (3.5) of the CCM transmission 
        period configured for the MEP.   
      
        - CCM indicates interface status up.  

      
     4.2. AC Transmit Defect State Entry or Exit  

        PE1 enters the AC Transmit Defect state if any of the following 
        conditions is met: 
         
        - It detects or is notified of a physical layer fault on the 
        Ethernet interface (e.g., via loss of signal (LoS) or Ethernet 
        Link OAM [802.3] critical link event notifications generated at 
        an upstream node CE1 with "Link Fault" indication). 
         
        - A MEP configured with CCM transmission enabled and associated 
        with the local AC receives a CCM frame, with its RDI bit set, 
        from the peer MEP in the client domain (e.g., CE1).  
         
        PE1 exits the AC Transmit Defect state if all of the conditions 
        that resulted in entering the defect state are cleared. This  
        includes all of the following conditions: 

      
      
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        - Any physical layer fault on the Ethernet interface, if 
        detected or notified previously is removed (e.g., LOS cleared,
        Ethernet Link OAM [802.3] critical link event notifications 
        with "Link Fault" indication cleared at an upstream node CE1). 
      
        - A MEP configured with CCM transmission enabled and associated 
        with the local AC does not receive a CCM frame with RDI bit set, 
        having received a previous CCM frame with RDI bit set from the 
        peer MEP in the client domain (e.g. CE1). 
       
     5. Ethernet AC and PW Defect States Interworking  

     5.1. PW Receive Defect Entry Procedures  

        When the PW status on PE1 transitions from working to PW Receive 
        Defect state, PE1's ability to receive user traffic from CE2 is 
        impacted. As a result, PE1 needs to notify CE1 about this 
        problem. 
         
        Upon entry to the PW Receive Defect state, the following must be
        done: 
         
        - If PE1 is configured with a down MEP associated with the local 
        AC and CCM transmission is not enabled, the MEP associated with 
        the AC must transmit AIS frames periodically to the peer MEP in 
        the client domain (e.g., on CE1) based on configured AIS 
        transmission period. 
         
        - If PE1 is configured with a down MEP associated with the local 
        AC and CCM transmission is enabled, and the MEP associated with 
        the AC is configured to support Interface Status TLV in CCM 
        messages, the MEP associated with the AC must transmit CCM 
        frames with Interface Status TLV as being down to the peer MEP 
        in the client domain (e.g., on CE1). 
        
        - If PE1 is configured with a down MEP associated with the local 
        AC and CCM transmission is enabled, and the MEP 
        associated with the AC is configured to not support Interface 
        Status TLV in CCM messages, the MEP associated with the AC must 
        stop transmitting CCM frames to the peer MEP in the client  
      
      
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        domain (e.g., on CE1). 
         
        - If PE1 is configured to run E-LMI [MEF16] with CE1 and if 
        E-LMI is used for failure notification, PE1 must transmit E-LMI 
        asynchronous STATUS message with report type Single EVC 
        Asynchronous Status indicating that PW is Not Active. 
         
        Further, when PE1 enters the Receive Defect state, it must 
        assume that PE2 has no knowledge of the defect and must send 
        reverse defect failure notification to PE2. For MPLS PSN or 
        MPLS-IP PSN, this is done via either a PW Status notification 
        message indicating a reverse defect; or via VCCV-BFD diagnostic 
        code of reverse defect if VCCV CV type of 0x08 had been 
        negotiated. When Native Service OAM mechanism is supported on 
        PE1, it can also use the NS OAM notification as specified in 
        Section 3.1. 
         
        If PW receive defect is entered as a result of a forward defect 
        notification from PE2 or via loss of control adjacency, no 
        additional action is needed since PE2 is expected to be aware of 
        the defect. 
      
     5.2. PW Receive Defect Exit Procedures 

        When the PW status transitions from PW Receive Defect state to 
        working, PE1's ability to receive user traffic from CE2 is 
        restored. As a result, PE1 needs to cease defect notification to 
        CE1 by performing the following: 
         
        - If PE1 is configured with a down MEP associated with the local 
        AC and CCM transmission is not enabled, the MEP associated with 
        the AC must stop transmitting AIS frames towards the peer MEP in 
        the client domain (e.g., on CE1). 
         
        - If PE1 is configured with a down MEP associated with the local 
        AC and CCM transmission is enabled, and the MEP associated with 
        the AC is configured to support Interface Status TLV in CCM 
        messages, the MEP associated with the AC must transmit CCM 
        frames with Interface Status TLV as being Up to the peer MEP in 
        the client domain (e.g., on CE1). 
         
      
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        - If PE1 is configured with a down MEP associated with the local 
        AC and CCM transmission is enabled, and the MEP associated with 
        the AC is configured to not support Interface Status TLV in CCM 
        messages, the MEP associated with the AC must resume 
        transmitting  CCM frames to the peer MEP in the client domain 
        (e.g., on CE1). 
         
        - If PE1 is configured to run E-LMI [MEF16] with CE1 and E-LMI 
        is used for fault notification, PE1 must transmit E-LMI 
        asynchronous STATUS message with report type Single EVC 
        Asynchronous Status indicating that PW is Active. 
         
        Further, if the PW receive defect was explicitly detected by 
        PE1, it must now notify PE2 about clearing of Receive Defect 
        state by clearing reverse defect notification. For PWs over 
        MPLS PSN or MPLS-IP PSN, this is either done via PW Status 
        message indicating working; or via VCCV-BFD diagnostic code if 
        VCCV CV type of 0x08/0x20 had been negotiated. When Native 
        Service OAM mechanism is supported on PE, it can also clear the 
        NS OAM notification specified in Section 3.1. 
         
        If PW receive defect was established via notification from PE2 
        or via loss of control adjacency, no additional action is  
        needed, since PE2 is expected to be aware of the defect 
        clearing. 
         
     5.3. PW Transmit Defect Entry Procedures 

        When the PW status transitions from working to PW Transmit 
        Defect state, PE1's ability to transmit user traffic to CE2 is 
        impacted. As a result, PE1 needs to notify CE1 about this 
        problem which has been detected by PE1. 
      
        Upon entry to the PW Transmit Defect state, the following must 
        be done: 
         
        - If PE1 is configured with a down MEP associated with the local 
        AC and CCM transmission is enabled, the MEP associated with the 
        AC MUST set the RDI bit in transmitted CCM frames or send status 
        TLV with interface down to the peer MEP in the client domain 
        (e.g. on CE1). 
         

      
      
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        - If PE1 is configured to run E-LMI [MEF16] with CE1 and E-LMI  
        is used for fault notification, PE1 must transmit E-LMI  
        asynchronous STATUS message with report type Single EVC  
        Asynchronous Status indicating that PW is Not Active. 
      
     5.4. PW Transmit Defect Exit Procedures 

        When the PW status transitions from PW Transmit Defect state to 
        working, PE1's ability to transmit user traffic to CE2 is 
        restored. As a result, PE1 needs to cease defect notifications 
        to CE1 and perform the following: 
         
        - If PE1 is configured with a down MEP associated with the local 
        AC and CCM transmission is enabled, the MEP associated with the 
        AC must clear the RDI bit in the transmitted CCM frames to the 
        peer MEP (e.g., on CE1). 
         
        - If PE1 is configured to run E-LMI [MEF16] with CE1, PE1 must 
        transmit E-LMI asynchronous STATUS message with report type 
        Single EVC Asynchronous Status indicating that PW is Active. 
      

     5.5. AC Receive Defect Entry Procedures 

        When AC status transitions from working to AC Receive Defect 
        state, PE1's ability to receive user traffic from CE1 is 
        impacted. As a result, PE1 needs to notify PE2 and CE1 about 
        this problem. 
         
        If the AC receive defect is detected by PE1, it must notify PE2 
        in the form of a forward defect notification. 
         
        When NS OAM is not supported on PE1, and for PW over MPLS PSN  
        or MPLS-IP PSN, forward defect notification is done via either 
        PW Status message indicating a forward defect or via VCCV-BFD 
        diagnostic code of forward defect if VCCV CV type of 0x08/0x20 
        had been negotiated. 
         
        When Native Service OAM mechanism is supported on PE1, it can 
        also use the NS OAM notification as specified in Section 3.1. 
         
        In addition to above actions, PE1 must perform the following: 
      
      
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        - If PE1 is configured with a down MEP associated with the local 
        AC and CCM transmission is enabled, the MEP associated with the 
        AC must set the RDI bit in transmitted CCM frames.  
         
         
        5.6. AC Receive Defect Exit Procedures 

        When AC status transitions from AC Receive Defect to working, 
        PE1's ability to receive user traffic from CE1 is restored. As 
        a result, PE1 needs to cease defect notifications to PE2 and CE1 
        and perform the following: 
         
        - When NS OAM is not supported on PE1 and for PW over MPLS PSN  
        or MPLS-IP PSN, forward defect notification is cleared via PW  
        Status message indicating a working state; or via VCCV-BFD 
        diagnostic code if VCCV CV type of 0x08 or 0x20 had been 
        negotiated. 
         
        - When Native Service OAM mechanism is supported on PE1, PE1 
        clears the NS OAM notification as specified in Section 3.1. 
         
        - If PE1 is configured with a down MEP associated with the local 
        AC and CCM transmission is enabled, the MEP associated with the 
        AC must clear the RDI bit in transmitted CCM frames to the 
        peer MEP in the client domain (e.g., on CE1).  
            

     5.7. AC Transmit Defect Entry Procedures 

        When AC status transitions from working to AC Transmit Defect, 
        PE1's ability to transmit user traffic to CE1 is impacted. As a 
        result, PE1 needs to notify PE2 about this problem. 
         
        If the AC transmit defect is detected by PE1, it must notify PE2 
        in the form of a reverse defect notification. 
      
        When NS OAM is not supported on PE1, in PW over MPLS PSN or 
        MPLS-IP PSN, reverse defect notification is either done via PW  
        Status message indicating a reverse defect; or via VCCV-BFD  
        diagnostic code of reverse defect if VCCV CV type of 0x08 or   
        0x20 had been negotiated. 
         
      
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        When Native Service OAM mechanism is supported on PE1, it can 
        also use the NS OAM notification as specified in Section 3.1. 
         
     5.8. AC Transmit Defect Exit Procedures 

        When AC status transitions from AC Transmit defect to working, 
        PE1's ability to transmit user traffic to CE1 is restored. As a 
        result, PE1 must clear reverse defect notification to PE2. 
         
        When NS OAM is not supported on PE1 and for PW over MPLS PSN or 
        MPLS-IP PSN, reverse defect notification is cleared via either a 
        PW Status message indicating a working state or via VCCV-BFD 
        diagnostic code if VCCV CV type of 0x08 had been negotiated. 
         
        When Native Service OAM mechanism is supported on PE1, PE1 can 
        clear NS OAM notification as specified in Section 3.1. 
         
     6. Acknowledgments 

        The authors are thankful to Samer Salam for his valuable 
        comments. 
      
7. Security Considerations 

        This document does not impose any security concerns since it 
        makes use of existing OAM mechanisms and mapping of these 
        messages does not change inherent security features. 
         
8. IANA Considerations 

        This document has no actions for IANA. 
      
     9. References 

     9.1. Normative References 

        [Y.1731] "OAM Functions and mechanisms for Ethernet based 
        networks", ITU-T Y.1731, May 2006 
         
        [802.1ag] "Connectivity Fault Management", IEEE 802.1ag/D8.1, 
        July 2007 
         

      
      
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        [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.

       [RFC4447] "Pseudowire Setup and Maintenance using LDP", RFC4447, 
        April 2006 
         
        [RFC5885] "Bidirectional Forwarding Detection (BFD) for the 
        Pseudowire Virtual Circuit Connectivity Verification (VCCV)",  
        RFC5885, June 2010 
         
        [802.3] "CDMA/CD access method and physical layer 
        specifications", Clause 57 for Operations, Administration and 
        Maintenance, 2005 
         
        [MEF16] "Ethernet Local Management Interface", MEF16, January 
                  2006  

     9.2. Informative References 

        [RFC3985] "Pseudo Wire Emulation Edge-to-Edge (PWE3) 
        Architecture", RFC 3985, April 2005 
         
        [RFC6310] "Pseudo Wire (PW) OAM Message Mapping", draft-ietf- 
        pwe3-oam-msg-map-14.txt, Work in progress, October 2010 
         
        [RFC5659] "An Architecture for Multi-Segment Pseudo Wire 
        Emulation Edge-to-Edge", RFC5659, October 2009 
         
     10. Appendix A: Ethernet Native Service Management 

        
        Ethernet OAM mechanisms are broadly classified into two 
        categories:  Fault Management (FM) and Performance Monitoring 
        (PM). ITU-T Y.1731 provides coverage for both FM and PM while 
        IEEE 802.1ag provides coverage for a sub-set of FM functions. 
      
        Ethernet OAM also introduces the concept of Maintenance Entity 
        (ME) which is used to identify the entity that needs to be   
        managed. An ME is inherently a point-to-point association. 
        However, in case of a multipoint association, Maintenance Entity 
        Group (MEG) consisting of different MEs is used. IEEE 802.1 uses 
        the concept of Maintenance Association (MA) which is used to 
        identify both point-to-point and multipoint associations. Each 
        MA consists of Maintenance End Points (MEPs) which are 
        responsible for originating OAM frames. In between the MEPs,  

      
      
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        there can also be Maintenance Intermediate Points (MIPs) which 
        do not originate OAM frames however do respond to OAM frames 
        from MEPs. 
      
        Ethernet OAM allows for hierarchical maintenance entities to 
        allow for simultaneous end-to-end and segment monitoring. This 
        is achieved by having a provision of up to 8 Maintenance Domain 
        Levels (MD Levels) where each MEP or MIP is associated with a 
        specific MD Level. 
        
       It is important to note that the common set of FM mechanisms 
       between IEEE 802.1ag and ITU-T Y.1731 are completely compatible. 
        
       The common FM mechanisms include: 
        
       1) Continuity Check Messages (CCM) 
       2) Loopback Message (LBM) and Loopback Reply (LBR) 
       3) Linktrace Message (LTM) and Linktrace Reply (LTR) 
      
     CCM messages are used for fault detection including misconnections 
     and mis-configurations. Typically CCM messages are sent as 
     multicast frames or Unicast frames and also allow RDI 
     notifications. LBM/LBR are used to perform fault verification,  
     while also allow for MTU verification and CIR/EIR measurements. 
     LTM/LTR can be used for discovering the path traversed between a 
     MEP and another target MIP/MEP in the same MA. LTM/LTR also allow 
     for fault localization. 
      
     In addition, ITU-T Y.1731 also specifies the following FM 
     functions: 
       4) Alarm Indication Signal (AIS) 
           
     AIS allows for fault notification to downstream and upstream nodes 
        
     Further, ITU-T Y.1731 also specifies the following PM functions: 
      
       5) Loss Measurement Message (LMM) and Reply (LMR) 
       6) Delay Measurement Message (DMR) and Reply (DMR) 
       7) 1-way Delay Message (1DM) 
      
     While LMM/LMR is used to measure Frame Loss Ratio (FLR), DMM/DMR is 
     used to measure single-ended (aka two-way) Frame Delay (FD) and 
     Frame Delay Variation (FDV, also known as Jitter). 1DM can be used 
      
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     for dual-ended (aka one-way) FD and FDV measurements. 
      
     Authors' Addresses: 

        Dinesh Mohan 
        Nortel 
        3500 Carling Ave 
        Ottawa, ON K2H8E9 
        Email: dinmohan@hotmail.com 
         
        Nabil Bitar 
        Verizon 
        60 Sylvan Road 
        Waltham, MA 02145 
        Email: nabil.n.bitar@verizon.com 
         
        Simon Delord 
        Telstra   
        242 Exhibition St   
        Melbourne VIC 3000, Australia   
        E-mail: simon.a.delord@team.telstra.com   
      
        Philippe Niger 
        France Telecom 
        2 av. Pierre Marzin 
         22300 LANNION, France 
         E-mail: philippe.niger@francetelecom.com 
       
        Ali Sajassi 
        Cisco 
        170 West Tasman Drive 
        San Jose, CA  95134, US 
        Email: sajassi@cisco.com 
         
        Ray Qiu 
        330 Central Expressway 
        Santa Clara, CA 95050, US 
        Email: ray@huawei.com 

      
      
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