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Versions: (draft-nadeau-pwe3-oam-msg-map) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 RFC 6310

Network Working Group                                 Mustapha Aissaoui
Internet Draft                                         Peter Busschbach
Expires: May 2009                                        Alcatel-Lucent

                                                              Dave Allan
                                                                  Nortel

                                                          Monique Morrow
                                                            Luca Martini
                                                      Cisco Systems Inc.

                                                           Thomas Nadeau
                                                                      BT

                                                                 Editors


                                                        November 3, 2008

                   Pseudo Wire (PW) OAM Message Mapping
                    draft-ietf-pwe3-oam-msg-map-08.txt


Status of this Memo



   By submitting this Internet-Draft, each author represents that any
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   This Internet-Draft will expire on May 3, 2009.

Abstract



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This document specifies the mapping of defect states between a Pseudo
Wire and the Attachment Circuits (AC) of the end-to-end emulated
service. This document covers the case whereby the ACs and the PWs
are of the same type in accordance to the PWE3 architecture [RFC3985]
such that a homogenous PW service can be constructed.



Conventions used in this document

   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 RFC-2119.

Table of Contents


   1. Acknowledgments................................................3
   2. Contributors...................................................3
   3. Introduction...................................................4
   4. Terminology....................................................4
   5. Reference Model and Defect Locations...........................7
   6. Abstract Defect States.........................................8
   7. OAM Models.....................................................9
   8. PW Defect States and Defect Notifications.....................11
      8.1. PW Defect Notification Mechanisms........................11
         8.1.1. LDP Status TLV......................................12
         8.1.2. L2TP Circuit Status AVP.............................14
         8.1.3. BFD Diagnostic Codes................................16
      8.2. PW Defect State Entry/Exit...............................17
         8.2.1. PW Forward Defect State Entry/Exit Criteria.........17
         8.2.2. PW Reverse Defect State Entry/Exit Criteria.........18
   9. Procedures for ATM PW Service.................................19
      9.1. AC forward defect state entry/exit criteria..............19
      9.2. AC reverse defect state entry/exit criteria..............20
      9.3. Consequent Actions.......................................20
         9.3.1. PW forward defect state entry/exit..................20
         9.3.2. PW reverse defect state entry/exit..................21
         9.3.3. PW defect state in ATM Port Mode PW Service.........21
         9.3.4. AC forward defect state entry/exit..................21
         9.3.5. AC reverse defect state entry/exit..................22
   10. Procedures for Frame Relay PW Service........................23
      10.1. AC forward defect state entry/exit criteria.............23
      10.2. AC reverse defect state entry/exit criteria.............23
      10.3. Consequent Actions......................................23
         10.3.1. PW forward defect state entry/exit.................23
         10.3.2. PW reverse defect state entry/exit.................24


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         10.3.3. PW defect state in the FR Port Mode PW service.....24
         10.3.4. AC forward defect state entry/exit.................25
         10.3.5. AC reverse defect state entry/exit.................25
   11. Procedures for TDM PW Service................................25
   12. Procedures for CEP PW Service................................26
   13. Informative Appendix A: Native Service Management............26
      13.1. Frame Relay Management..................................26
      13.2. ATM Management..........................................27
   14. Informative Appendix B: PW Defects and Detection tools.......28
      14.1. PW Defects..............................................28
         14.1.1. Packet Loss........................................29
      14.2. PW Defect Detection Tools...............................29
   15. Security Considerations......................................30
   16. IANA Considerations..........................................30
   17. References...................................................30
      17.1. Normative References....................................30
      17.2. Informative References..................................31
   18. Editor's Addresses...........................................32
   Full Copyright Statement.........................................33
   Intellectual Property Statement..................................34
   Acknowledgment...................................................34

1. Acknowledgments

   The editors would like to acknowledge the important contributions of
   Hari Rakotoranto, Eric Rosen, Mark Townsley, Michel Khouderchah,
   Bertrand Duvivier, Vanson Lim, Chris Metz, Ben Washam, Tiberiu
   Grigoriu, Neil McGill, and Amir Maleki.

2. Contributors

   Thomas D. Nadeau, tom.nadeau@bt.com

   Monique Morrow, mmorrow@cisco.com

   Peter B. Busschbach, busschbach@alcatel-lucent.com

   Mustapha Aissaoui, mustapha.aissaoui@alcatel-lucent.com

   Matthew Bocci, matthew.bocci@alcatel-lucent.co.uk

   David Watkinson, david.watkinson@alcatel-lucent.com

   Yuichi Ikejiri, y.ikejiri@ntt.com

   Kenji Kumaki, kekumaki@kddi.com



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   Satoru Matsushima, satoru@ft.solteria.net

   David Allan, dallan@nortel.com

   Himanshu Shah, hshah@ciena.com

   Simon Delord, simon.delord@gmail.com

   Vasile Radoaca, vasile.radoaca@alcatel-lucent.com

   Carlos Pignataro, cpignata@cisco.com

   Luca Martini, lmartini@cisco.com

3. Introduction

   This document specifies the mapping of defect states between a Pseudo
   Wire and the Attachment Circuits (AC) of the end-to-end emulated
   service. It covers the case whereby the ACs and the PWs    are of the
   same type in accordance to the PWE3 architecture [RFC3985]    such
   that a homogeneous PW service can be constructed.

   This document is motivated by the requirements put forth in [RFC4377]
   and [RFC3916]. Its objective is to standardize the behavior of PEs
   with respects to failures on PWs and ACs, so that there is no
   ambiguity about the alarms generated and consequent actions
   undertaken by PEs in response to specific failure conditions.

   This document covers PWE over MPLS PSN, PWE over IP PSN and PWE over
   L2TP PSN.

   The Ethernet PW service is covered in a separate document [ETH-OAM-
   IWK].

4. Terminology

         AIS   Alarm Indication Signal

         AC    Attachment circuit

         BDI   Backward Defect Indication

         CC    Continuity Check

         CE    Customer Edge

         CPCS  Common Part Convergence Sub-layer


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         DLC   Data Link Connection

         FDI   Forward Defect Indication

         FRBS  Frame Relay Bearer Service

         IWF   Interworking Function

         LB    Loopback

         NE    Network Element

         NS    Native Service

         OAM   Operations and Maintenance

         PE    Provider Edge

         PW    Pseudowire

         PSN   Packet Switched Network

         RDI   Remote Defect Indication

         SDU   Service Data Unit

         VCC   Virtual Channel Connection

         VPC   Virtual Path Connection

   The rest of this document will follow the following conventions.

   The words "defect" and "fault" are used inter-changeably to mean a
   condition which causes user packets not to be forwarded between the
   CE endpoints of the PW service.

   The words "defect notification" and "defect indication" are used
   inter-changeably to mean an OAM message generated by a PE and sent to
   other nodes in the network to convey the defect state local to this
   PE.

   The PW can ride over three types of Packet Switched Network (PSN). A
   PSN which makes use of LSPs as the tunneling technology to forward
   the PW packets will be referred to as an MPLS PSN. A PSN which makes
   use of MPLS-in-IP tunneling [RFC4023], with an MPLS shim header used
   as PW demultiplexer, will be referred to as an MPLS-IP PSN. A PSN
   which makes use of L2TPv3 [RFC3931] as the tunneling technology with


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   the L2TPv3 Session ID as the PW demultiplexer will be referred to as
   L2TP-IP PSN.

   If LSP-Ping [RFC4379] is run over a PW as described in [RFC4377], it
   will be referred to as VCCV-Ping.

   If BFD is run over a PW as described in [RFC4377], it will be
   referred to as VCCV-BFD [VCCV-BFD].

   In the context of this document a PE forwards packets between an AC
   and a PW. The other PE that terminates the PW is the peer PE or
   remote PE and the attachment circuit associated with the far-end PW
   termination is the remote AC.

   Defects are discussed in the context of defect states, and the
   criteria to enter and exit the defect state. The direction of defects
   is discussed from the perspective of the observing PE.

   A forward defect is one that impacts information transfer to the
   observing PE. It impacts the observing PEs ability to receive
   information.

   A reverse defect is one that uniquely impacts information sent or
   relayed by the observing PE.

   A forward defect generally also impacts information sent or relayed
   by the observing PE. Therefore the forward defect state is considered
   to be a superset of the two defect states. Thus, when a PE enters
   both forward and reverse defect states related to the same PW
   service, the forward defect takes precedence over reverse defect in
   terms of the consequent actions.

   A forward defect indication is sent in the same direction as the user
   traffic impacted by the defect. A reverse defect indication is sent
   in the opposite direction of the traffic impacted by the defect.

   When a PE enters a defect state, it always sends a defect indication
   that corresponds to that defect to notify nodes which are downstream
   of the defect. For example, a local PE sends a forward defect
   indication downstream to the CE when it enters the PW forward defect
   state. However, in some cases the PE enters this defect state without
   receiving a defect indication from the peer PE. In this case, the
   local PE will also send a defect indication to the remote PE to
   synchronize the states. In the example above, the local PE will send
   a reverse defect indication to the remote PE. The exact procedures
   are described later in the document.



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5. Reference Model and Defect Locations

   Figure 1 illustrates the PWE3 network reference model with an
   indication of the possible defect locations. This model will be
   referenced in the remainder of this document for describing the OAM
   procedures.





               ACs             PSN tunnel            ACs
                      +----+                  +----+
      +----+          | PE1|==================| PE2|          +----+
      |    |---(a)---(b)..(c)......PW1..(d)..(c)..(f)---(e)---|    |
      | 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

   In all interworking scenarios described in this document, it is
   assumed the AC and the PW are of the same type at PE1. The procedures
   described in this document apply to PE1. PE2 implements the identical
   functionality for a homogeneous service (although it is not required
   to as long as the notifications across the PWs are consistent).

   The following is a brief description of the defect locations:

       a. Defect in the first L2 network (N1). This covers any defect
          in the N1 which impacts all or a subset of ACs terminating in
          PE1. The defect is conveyed to PE1 and to the remote L2
          network (N2) using the native service specific OAM defect
          indication.
       b. Defect on a PE1 AC interface.
       c. Defect on a PE1 PSN interface.
       d. Defect in the PSN network. This covers any defect in the PSN
          which impacts all or a subset of PWs terminating in a PE. The
          defect is conveyed to the PE using a PSN and/or a PW specific
          OAM defect indication. Note that both data plane defects and
          control plane defects must be taken into consideration. Even
          though control messages may follow a different path than the


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          PW data plane traffic, a control plane failure may affect the
          PW status.
       e. Defect in the second L2 network (N2). This covers any defect
          in N2 which impacts all or a subset of ACs terminating in PE2
          (which is considered a remote AC defect in the context of
          procedures outlined in this draft). The defect is conveyed to
          PE2 and to the remote L2 network (N1) using the native
          service OAM defect indication.
       f. Defect on a PE2 AC interface (which is also considered a
          remote AC defect in the context of this draft).

6. Abstract Defect States

   PE1 must track four defect states that reflect the observed states of
   both directions of the PW service on both the AC and the PW sides.
   Defects may impact one or both directions of the PW service.

   The observed state is a combination of defects directly detected by
   PE1 and defects it has been made aware of via notifications.



                              +-----+
           ----AC forward---->|     |-----PW reverse---->
     CE1                      | PE1 |                       PE2/CE2
           <---AC reverse-----|     |<----PW forward-----
                              +-----+

     (arrows indicate direction of user traffic impacted by a defect)
      Figure 2: Forward and Reverse Defect States and Notifications

   PE1 will directly detect or be notified of AC forward or PW forward
   defects as they occur upstream of PE1 and impact traffic being sent
   to PE1. As a result, PE1 enters the AC forward defect state.

   In Figure 2, PE1 may be notified of a forward defect in the AC by
   receiving a Forward Defect indication, e.g., ATM AIS, from an ATM
   switch in L2 network N1. This defect notification indicates that user
   traffic sent by CE1 may not be received by PE1 due to a defect. PE1
   can also directly detect an AC Forward Defect if it resulted from a
   failure of the receive side in the local port or link over which the
   AC is configured.

   Similarly, PE1 may detect or be notified of a forward defect in the
   PW by receiving a Forward Defect indication from PE2. If PW status is
   used for fault notification, this message will indicate a Local PSN-
   facing PW (egress) Transmit Fault or a Local Attachment Circuit


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   (ingress) Receive Fault at PE2, as described in Section 8.1.1. . This
   defect notification indicates that user traffic sent by CE2 may not
   be received by PE1 due to a defect. As a result, PE1 enters the PW
   forward defect state.

   Note that a Forward Defect notification is sent in the same direction
   as the user traffic impacted by the defect.

   PE1 will only be notified of AC reverse or PW reverse defects as they
   universally will be detected by other devices and only impact traffic
   that has already been relayed by PE1. As a result, PE1 enters the AC
   reverse defect state.

   In Figure 2, PE1 may be notified of a reverse defect in the AC by
   receiving a Reverse Defect indication, e.g., ATM RDI, from CE1. This
   defect impacts the traffic sent by PE1 to CE1 on the AC.

   Similarly, PE1 may be notified of a reverse defect in the PW by
   receiving a Reverse Defect indication from PE2. If PW status is used
   for fault notification, this message will indicate a Local PSN-facing
   PW (ingress) Receive Fault or a Local Attachment Circuit (egress)
   Transmit Fault at PE2, as described in Section 8.1.1. . This defect
   impacts the traffic sent by PE1 to CE2. As a result, PE1 enters the
   PW reverse defect state.

   Note that a Reverse Defect notification is sent in the reverse
   direction to the user traffic impacted by the defect.

   The procedures outlined in this document define the entry and exit
   criteria for each of the four states with respect to the set of PW
   services within the document scope and the consequent actions that
   PE1 must perform.

   When a PE enters both forward and reverse defect states related to
   the same PW service, then the forward defect takes precedence over
   reverse defect in terms of the consequent actions.

7. OAM Models

   A homogeneous PW service forwards packets between an AC and a PW of
   the same type. It thus implements both a Native Service OAM
   mechanism and a PW OAM mechanism. PW OAM defect notification
   messages are described in Section 8.1. . NS OAM messages are
   described in Appendix A.





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   This document defines two different modes for operating OAM on a PW
   service which dictate the mapping between the NS OAM the PW OAM
   defect notification messages.

   The first one operates a single emulated OAM loop end-to-end between
   the endpoints of the PW service. This is referred to as "single
   emulated OAM loop" mode and is illustrated in Figure 3.

       |<----- AC ----->|<----- PW ----->|<----- AC ----->|
       |                |                |                |
                     ___ ===============_
     |CE|---=NS-OAM=>---(---=NS-OAM=>---)---=NS-OAM=>---|CE|
                         ===============     /
                            \               /
                             ---=PW-OAM=>---

                  Figure 3: Single Emulated OAM Loop mode

   This mode implements the following behavior:
        a. A PE node MUST transparently relay NS OAM messages over the
          PW.
        b. A PE node MUST signal local failures affecting the AC using a
          NS defect notification OAM message sent over the PW.
        c. A PE MUST signal local failures affecting the AC using a PW
          defect notification OAM message when the defect interferes
          with NS OAM message generation, e.g., NS processing line card
          removed.
        d. A PE node MUST signal local failures affecting the PW using a
          PW defect notification OAM message.
        e. A PE node MUST insert a NS defect notification OAM message
          into the AC when it detects or is notified of a defect in the
          PW or remote AC. This includes support receiving a PW defect
          notification message and translating it into a NS defect
          notification OAM message over the AC. The latter is required
          for handling defects signaled by a peer PE with PW OAM
          messaging.

   The "single emulated OAM loop" mode is suitable for PW services
   which have a widely deployed NS OAM mechanism that operates within
   the AC. This document specifies the use of this mode for ATM PW, TDM
   PW, and CEP PW services. It is the default mode of operation for an
   ATM PW service and the only mode specified for TDM and CEP PW
   services.

   The second mode operates three OAM loops which join at the AC/PW
   boundary of a PE. This is referred to as "coupled OAM loops" mode
   and is illustrated in Figure 4


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       |<----- AC ----->|<----- PW ----->|<----- AC ----->|
       |                |                |                |
                      __ ===============__
     |CE|---=NS-OAM=>---(---------------)---=NS-OAM=>---|CE|
                    \    ===============       /
                     \                        /
                      \                      /
                       -------=PW-OAM=>------

                     Figure 4: Coupled OAM Loops mode

   This mode implements the following behavior:
        a. A PE node MUST terminate and translate a received NS defect
          notification OAM message to a PW defect notification message.
        b. A PE node MUST signal local failures affecting the AC using
          using a PW defect notification OAM message.
        c. A PE node MUST signal local failures affecting the PW using a
          PW defect notification OAM message.
        d. A PE node MUST insert a NS defect notification OAM message
          into the AC when it detects or is notified of a defect in the
          PW or remote AC. This includes support receiving a PW defect
          notification message and translating it into a NS defect
          notification OAM message over the AC.

   This document specifies the use of the "coupled OAM loops" mode for
   a FR PW service and for ATM PW services of type ATM VCC and AAL5
   SDU. It does not specify the use of this mode for TDM PW, CEP PW,
   and the ATM VPC cell mode PW services. In the latter case, a PE node
   must pass transparently VC-level (F5) ATM OAM cells over the PW
   while terminating and translating VP-level (F4) OAM cells. Thus, it
   cannot operate a pure "coupled OAM loops" mode.

8. PW Defect States and Defect Notifications

8.1. PW Defect Notification Mechanisms

   For a MPLS PSN and a MPLS-IP PSN, a PE node which establishes a PW
   using LDP SHALL use LDP status TLV as the mechanism for AC and PW
   status and defect notification [RFC4447]. Additionally, a PE node MAY
   use VCCV-BFD Connectivity Verification (CV) types for fault detection
   only but SHOULD notify the remote PE using LDP Status TLV. These CV
   types are 0x04 and 0x10 [VCCV-BFD].

   A PE node which establishes a PW using other means than LDP, e.g.,
   static configuration, MAY use VCCV-BFD CV types for AC and PW status
   and defect notification. These CV types are 0x08 and 0x20 [VCCV-BFD].


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   These CV types SHOULD NOT be used when the PW is established with the
   LDP control plane.

   For a L2TP-IP PSN, A PE node SHOULD use the Circuit Status AVP as the
   mechanism for AC and PW status and defect notification. In its most
   basic form, the Circuit Status AVP [RFC3931] in a Set-Link-Info (SLI)
   message can signal active/inactive AC status. The Circuit Status AVP
   is proposed to be extended to convey status and defects in the AC and
   the PSN-facing PW in both ingress and egress directions, i.e., four
   independent status bits without the need to tear down the sessions or
   control connection [L2TP-Status].

   When a PE does not support the Circuit Status AVP, it MAY use the
   StopCCN and the CDN message to bring down L2TP sessions in a similar
   way LDP uses the Label Withdrawal to bring down a PW. A PE node may
   use the StopCCN to shutdown the L2TP control connection, and
   implicitly all L2TP sessions associated with that control connection
   without any explicit session control messages. This is in the case of
   a failure which impacts all L2TP sessions, i.e., all PWs, managed by
   the control connection. It may use the CDN message to disconnect a
   specific L2TP session when a failure affects a specific PW.

   Additionally, a PE node MAY use VCCV-BFD CV types 0x04 and 0x10 for
   fault detection only but SHOULD notify the remote PE using the
   Circuit Status AVP. A PE node which establishes a PW using other
   means than L2TP control plane MAY use VCCV-BFD CV types 0x08 and 0x20
   for AC and PW status and defect notification. These CV types SHOULD
   NOT be used when the PW is established with the L2TP control plane.

8.1.1. LDP Status TLV

   [RFC4446] defines the following PW status code points:

   0x00000000 - Pseudo Wire forwarding (clear all failures)
   0x00000001 - Pseudo Wire Not Forwarding
   0x00000002 - Local Attachment Circuit (ingress) Receive Fault
   0x00000004 - Local Attachment Circuit (egress) Transmit Fault
   0x00000008 - Local PSN-facing PW (ingress) Receive Fault
   0x00000010 - Local PSN-facing PW (egress) Transmit Fault


   [RFC4447] specifies that "Pseudo Wire forwarding" code point is used
   to clear all faults. It also specifies that "Pseudo Wire Not
   Forwarding" code is used to convey any other defect that cannot be
   represented by the other code points. In general, this applies to a
   defect that does not cause the PW to be torn down.



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   The code points used in the LDP status TLV in a PW status
   notification message convey the defect view of the originating PE.

   The originating PE conveys this state in the form of a forward defect
   or a reverse defect indication.

   The forward and reverse defect indication definitions used in this
   document map to the LDP Status TLV codes as follows:

            Forward defect indication - corresponds to the logical OR of

                            Local Attachment Circuit (ingress)

                            Receive Fault, Local PSN-facing

                            PW (egress) Transmit Fault, and PW not

                            Forwarding Fault

            Reverse defect indication - corresponds to the logical OR of

                            Local Attachment Circuit (egress)

                            Transmit Fault and Local PSN-facing

                            PW (ingress) Receive Fault

   A PE SHALL thus use PW status notification messages to report all
   failures affecting the PW service including, but not restricted, to
   the following:

            - Failures detected through defect detection mechanisms in
              the MPLS and MPLS-IP PSN

            - Failures detected through VCCV-Ping or VCCV-BFD CV types
              0x04 and 0x10 for fault detection only

            - Failures within the PE that result in an inability to
              forward traffic between the AC and the PW

            - Failures of the AC or in the L2 network affecting the AC
              as per the rules detailed in Section 7. for the "single
              emulated OAM loop" mode and "coupled OAM loops" mode.

   Note that there are a couple of situations which require PW label
   withdrawal as opposed to a PW status notification by the PE. The
   first one is when the PW is taken administratively down in accordance


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   to [RFC4447]. The second one is when the Target LDP session
   established between the two PEs is lost. In the latter case, the PW
   labels will need to be re-signaled when the Targeted LDP session is
   re-established.

8.1.2. L2TP Circuit Status AVP

   [RFC3931] defines the Circuit Status AVP in the Set-Link-Info (SLI)
   message to exchange initial status and status changes in the circuit
   to which the pseudowire is bound. [L2TP-Status] defines extensions to
   the Circuit Status AVP that are analogous to the PW Status TLV
   defined for LDP.  Consequently, for L2TP-IP, the Circuit Status AVP
   is used in the same fashion as the PW Status described in the
   previous section.

   If the extended Circuit Status bits are not supported, and instead
   only the "A-bit" (Active) is used as described in [RFC3931], a PE MAY
   use CDN messages to clear L2TPv3 sessions in the presence of session-
   level failures detected in the L2TP-IP PSN.

   A PE MUST set the Active bit in the Circuit Status to clear all
   faults, and it MUST clear the Active bit in the Circuit Status to
   convey any defect that cannot be represented explicitly with specific
   Circuit Status flags from [RFC3931] or [L2TP-Status].

   The forward and reverse defect indication definitions used in this
   document map to the L2TP Circuit Status AVP as follows:

           Forward defect indication - corresponds to the logical OR of

                            Local Attachment Circuit (ingress)

                            Receive Fault and Local PSN-facing

                            PW (egress) Transmit Fault

           Reverse defect indication- corresponds to the logical OR of

                            Local Attachment Circuit (egress)

                            Transmit Fault and Local PSN-facing

                            PW (ingress) Receive Fault

   The status notification conveys the defect view of the originating
   LCCE (PE).



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   When the extended Circuit Status definition of [L2TP-Status] is
   supported, a PE SHALL use the Circuit Status to report all failures
   affecting the PW service including, but not restricted, to the
   following:

            - Failures detected through defect detection mechanisms in
              the L2TP-IP PSN.

            - Failures detected through VCCV-Ping or VCCV-BFD CV types
              0x04 and 0x10 for fault detection only

            - Failures within the PE that result in an inability to
              forward traffic between the AC and the PW

            - Failures of the AC or in the L2 network affecting the AC
              as per the rules detailed in Section 7. for the "single
              emulated OAM loop" mode and the "coupled OAM loops" mode.

   When the extended Circuit Status definition of [L2TP-Status] is not
   supported, a PE SHALL use the A-bit in the Circuit Status AVP in SLI
   to report:

            - Failures of the AC or in the L2 network affecting the AC
              as per the rules detailed in Section 7. for the "single
              emulated OAM loop" mode and the "coupled OAM loops" mode.

   When the extended Circuit Status definition of [L2TP-Status] is not
   supported, a PE MAY use the CDN and StopCCN messages in a similar way
   to an MPLS PW label withdrawal to report:

            - Failures detected through defect detection mechanisms in
              the L2TP-IP PSN (using StopCCN)

            - Failures detected through VCCV (pseudowire level) (using
              CDN)

            - Failures within the PE that result in an inability to
              forward traffic between ACs and PW (using CDN)

   For ATM L2TPv3 pseudowires, in addition to the Circuit Status AVP, a
   PE MAY use the ATM Alarm Status AVP [RFC4454] to indicate the reason
   for the ATM circuit status and the specific alarm type, if any.  This
   AVP is sent in the SLI message to indicate additional information
   about the ATM circuit status.

   L2TP control connections use Hello messages as a keepalive facility.
   It is important to note that if a PSN failure is such that the loss


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   of conectivity is detected when it triggers a keepalive timeouts, the
   control connection is cleared.  L2TP Hello messages are sent in-band
   with the dataplane, with respect to the source and destination
   addresses, IP protocol number and UDP port (when UDP is used).

8.1.3. BFD Diagnostic Codes

   [BFD] defines a set of diagnostic codes that partially overlap with
   failures that can be communicated through LDP Status TLV or L2TP
   Circuit Status AVP. This section describes the behavior of the PE
   nodes with respect to using one or both methods for detecting and
   propagating defect state.

   For a MPLS-PSN, the PEs negotiate the use of the VCCV capabilities
   when the label mapping messages are exchanged to establish the two
   directions of the PW. An OAM capability TLV is signaled as part of
   the PW FEC interface parameters TLV. For L2TP-IP PSNs, the PEs
   negotiate the use of VCCV during the pseudowire session
   initialization using the VCCV AVP [RFC5085].

   The CV Type Indicators field in this TLV defines a bitmask used to
   indicate the specific OAM capabilities that the PE can make use of
   over the PW being established.

   A CV type of 0x04 or 0x10 indicates that BFD is used for PW fault
   detection only [VCCV-BFD]. These CV types MAY be used any time the PW
   is established using LDP or L2TP control planes.

   In this mode, only the following diagnostic (Diag) codes specified in
   [BFD] will be used, they are:

      0 - No diagnostic:

      1 - Control detection time expired

      7 - Administratively Down

   A PE MUST use code 0 to indicate to its peer PE that is correctly
   receiving BFD control messages. It MUST use the second code to
   indicate that to its peer it has stopped receiving BFD control
   messages. A PE shall use "Administrative down" to bring down the BFD
   session when the PW is brought down administratively. All other
   defects, such as AC/PW defects and PE internal failures that prevent
   it from forwarding traffic, MUST be communicated through LDP Status
   TLV in the case of MPLS PSN or MPLS-IP PSN, or through the
   appropriate L2TP codes in the Circuit Status AVP in the case of L2TP-
   IP PSN.


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   A CV type of 0x08 or 0x20 in the OAM capabilities TLV indicates that
   BFD is used for both PW fault detection and Fault Notification. In
   addition to the above diagnostic codes, a PE used the following codes
   to signal AC defects and other defects impacting forwarding over the
   PW service:

      6 -- Concatenated Path Down

      8 -- Reverse Concatenated Path Down

      TBD -- PW not forwarding

   A PE MAY use the "PW not forwarding" code to convey any other defect
   that cannot be represented by code points 6 and 8. In general, this
   applies to a defect that does not cause the PW to be torn down. This
   implies the BFD session must not be brought down when this defect
   exists.

   The forward and reverse defect indication definitions used in this
   document map to the BFD codes as follows:

           Forward defect indication - corresponds to the logical OR of

                          Concatenated Path Down and PW not forwarding

           Reverse defect indication- corresponds to Reverse

                           Concatenated Path Down

   These diagnostic codes are used to signal forward and reverse defect
   states respectively when the PEs negotiated the use of BFD as the
   mechanism for AC and PW fault detection and status signaling
   notification. As stated in Section 8.1. , these CV types SHOULD NOT
   be used when the PW is established with the LDP or L2TP control
   plane.

8.2. PW Defect State Entry/Exit

8.2.1. PW Forward Defect State Entry/Exit Criteria

   PE1 will enter the PW forward defect state if one or more of the
   following occurs:

            - It receives a forward defect indication from PE2, which
              indicates PE2 detected or was notified of a PW fault
              downstream of it or that there was a forward defect on
              remote AC.


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            - It detects loss of connectivity on the PSN tunnel
              upstream of PE1 which affects the traffic it receives
              from PE2.

            - It detects a loss of PW connectivity through VCCV-BFD or
              VCCV-PING which affects the traffic it receives from PE2.

   Note that if the PW control session between the PEs fails, the PW is
   torn down and needs to be re-established. This includes failure of
   the T-LDP session, the L2TP session, or the L2TP control connection.
   However, the consequent actions towards the ACs are the same as if
   the PW entered the forward defect state.

   PE1 will exit the PW forward defect state when the following
   conditions are true. Note that this may result in a transition to the
   PW operational state or the PW reverse defect state.

            - All defects it had previously detected have disappeared,
              and

            - PE2 cleared the forward defect indication if applicable.

8.2.2. PW Reverse Defect State Entry/Exit Criteria

   PE1 will enter the PW reverse defect state if the following
   conditions are true:

            - it receives a reverse defect indication from PE2 which
              indicates that PE2 detected or was notified of a PW fault
              upstream of it or that there was a reverse fault on the
              remote AC, and

            - it is not already in the PW forward defect state.

   PE1 will exit the reverse defect state if it receives an OAM message
   from PE2 clearing the reverse defect indication, or it has entered
   the PW forward defect state.

   For a PWE3 over a L2TP-IP PSN using the basic Circuit Status AVP
   [RFC3931], the PW reverse defect state is not valid and a PE can only
   enter the PW forward defect state.








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9. Procedures for ATM PW Service

9.1. AC forward defect state entry/exit criteria

   When operating in the "coupled OAM loops" mode, PE1 enters the AC
   forward defect state if any of the following conditions are met:

               a. It detects or is notified of a physical layer fault on
                 the ATM interface.

               b. It receives a segment or end-to-end F4 AIS OAM flow on
                 a VP AC, or a segment or end-to-end F5 AIS OAM flow on
                 a VC AC, indicating that the ATM VPC or VCC is down in
                 the adjacent L2 ATM network.

               c. It detects loss of connectivity on the ATM VPC/VCC
                 while terminating segment or end-to-end ATM continuity
                 check (ATM CC) cells with the local ATM network and
                 CE.

   When operating in the "coupled OAM loops" mode, PE1 exits the AC
   Forward Defect state when all defects it had previously detected have
   disappeared.

   When operating in the "single emulated OAM loop" mode, PE1 enters the
   AC forward defect state if any of the following conditions are met:

               a. It detects or is notified of a physical layer fault on
                 the ATM interface.

               b. It receives a segment F4 AIS OAM flow on a VP AC, or a
                 segment F5 AIS OAM flow on a VC AC, indicating that
                 the ATM VPC or VCC is down in the adjacent L2 ATM
                 network.

               c. It detects loss of connectivity on the ATM VPC/VCC
                 while terminating segment ATM continuity check (ATM
                 CC) cells with the local ATM network and CE.

   When operating in the "single emulated OAM loop" mode, PE1 exits the
   AC Forward Defect state when all defects it had previously detected
   have disappeared.

   The exact conditions under which a PE enters and exits the AIS state,
   or declares that connectivity is restored via ATM CC are defined in
   Section 9.2 of ITU-T Recommendation I.610 [ITU-T I.610].



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9.2. AC reverse defect state entry/exit criteria

   PE1 enters the AC reverse defect state if any of the following
   conditions are met:

               a. It terminates an F4 RDI OAM flow, in the case of a
                 VPC, or an F5 RDI OAM flow, in the case of a VCC,
                 indicating that the ATM VPC or VCC is down in the
                 adjacent L2 ATM.

   PE1 exits the AC Reverse Defect state if the AC state transitions to
   working or to the AC forward defect state. The exact conditions for
   exiting the RDI state are described in Section 9.2 of ITU-T
   Recommendation I.610 [ITU-T I.610].

   Note that the AC reverse defect state is not valid when operating in
   the "single emulated OAM loop" mode as PE1 transparently forwards the
   received RDI cells as user cells over the ATM PW to the remote CE.

9.3. Consequent Actions

   In the reminder of this section, the text refers to AIS, RDI and CC
   without specifying whether it is an F4 (VP-level) flow or an F5 (VC-
   level) flow, or whether it is an end-to-end or a segment flow.
   Precise ATM OAM procedures for each type of flow are specified in
   Section 9.2 of ITU-T Recommendation I.610 [ITU-T I.610].

9.3.1. PW forward defect state entry/exit

   On entry to the PW forward defect state:

               a. PE1 MUST commence AIS insertion into the corresponding
                 AC.

               b. PE1 MUST terminate any CC cell generation on the
                 corresponding AC.

               c. If the PW failure was detected by PE1 without
                 receiving a forward defect notification from PE2, PE1
                 MUST assume PE2 has no knowledge of the defect and
                 MUST notify PE2 in the form of a reverse defect
                 notification.

   On exit from the PW forward defect state:

               a. PE1 MUST cease AIS insertion into the corresponding
                 AC.


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               b. PE1 MUST resume any CC cell generation on the
                 corresponding AC.

               c. PE1 MUST clear the reverse defect notification to PE2
                 if applicable.

9.3.2. PW reverse defect state entry/exit

   On entry to the PW Reverse Defect State:

               a. PE1 MUST commence RDI insertion into the corresponding
                 AC.

               b. If the PW failure was detected by PE1 without
                 receiving a reverse defect notification from PE2, PE1
                 MUST assume PE2 has no knowledge of the defect and
                 MUST notify PE2 in the form of a forward defect
                 notification.

   On exit from the PW Reverse Defect State:

               a. PE1 MUST cease RDI insertion into the corresponding
                 AC.

               b. PE1 MUST clear the forward defect notification to PE2
                 if applicable.

9.3.3. PW defect state in ATM Port Mode PW Service

   In case of transparent cell transport PW service, i.e., "port mode",
   where the PE does not keep track of the status of individual ATM VPCs
   or VCCs, a PE cannot relay PW defect state over these VCCs and VPCs.
   If ATM CC is run on the VCCs and VPCs end-to-end (CE1 to CE2), or on
   a segment originating and terminating in the ATM network and spanning
   the PSN network, it will timeout and cause the CE or ATM switch to
   enter the ATM AIS state.

9.3.4. AC forward defect state entry/exit

   On entry to the AC forward defect state and when operating in the
   "coupled OAM loops" mode:

               a. PE1 MUST send a forward defect notification to PE2.

               b. PE1 MUST commence insertion of ATM RDI cells into the
                 AC towards CE1.



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   On entry to the AC forward defect state and when operating in the
   "single emulated OAM loop" mode:

               a. PE1 MUST commence insertion of ATM AIS cells into the
                 corresponding PW towards CE2.

               b. If the defect interferes with NS OAM message
                 generation, PE1 must send a forward defect
                 notification to PE2.

               c. PE1 MUST terminate any CC cell generation on the
                 corresponding PW.

   On exit from the AC forward defect state and when operating in the
   "coupled OAM loops" mode:

               a. PE1 MUST clear the forward defect notification to PE2.

               b. PE1 MUST cease insertion of ATM RDI cells into the AC.

   On exit from the AC forward defect state and when operating in the
   "single emulated OAM loop" mode:

               a. PE1 MUST cease insertion of ATM AIS cells into the
                 corresponding PW.

               b. PE1 MUST clear the forward defect notification to PE2
                 if applicable.

               c. PE1 MUST resume any CC cell generation on the
                 corresponding PW if applicable.

9.3.5. AC reverse defect state entry/exit

   On entry to the AC reverse defect state and when operating in the
   "coupled OAM loops" mode:

               a. PE1 MUST send a reverse defect notification to PE2.

   On exit from the AC reverse defect state and when operating in the
   "coupled OAM loops" mode:

               a. PE1 MUST clear the reverse defect notification to PE2.






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10. Procedures for Frame Relay PW Service

10.1. AC forward defect state entry/exit criteria

   PE1 enters the AC Forward Defect state if one or more of the
   following conditions are true:

               a. A PVC is not deleted from the Frame Relay network and
                 the Frame Relay network explicitly indicates in a full
                 status report (and optionally by the asynchronous
                 status message) that this Frame Relay PVC is inactive
                 [ITU-T Q.933]. In this case, this status maps across
                 the PE to the corresponding PW only.

               b. The Link Integrity Verification (LIV) indicates that
                 the link from the PE to the Frame Relay network is
                 down [ITU-T Q.933]. In this case, the link down
                 indication maps across the PE to all corresponding
                 PWs.

               c. A physical layer alarm is detected on the FR
                 interface. In this case, this status maps across the
                 PE to all corresponding PWs.

   PE1 exits the AC Forward Defect state when all defects it had
   previously detected have disappeared.

10.2. AC reverse defect state entry/exit criteria

   The AC reverse defect state is not valid for a FR AC.

10.3. Consequent Actions

10.3.1. PW forward defect state entry/exit

   On entry to the PW forward defect state:

               a. PE1 MUST set the Active bit = 0 for the corresponding
                 FR AC in a full status report, and optionally in an
                 asynchronous status message, as per Q.933 annex A
                 [ITU-T Q.933].

               b. If the PW failure was detected by PE1 without
                 receiving a forward defect notification from PE2, PE1
                 MUST assume PE2 has no knowledge of the defect and
                 MUST notify PE2 in the form of a reverse defect
                 notification.


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   On exit from the PW Forward defect state:

               a. PE1 MUST set the Active bit = 1 for the corresponding
                 FR AC in a full status report, and optionally in an
                 asynchronous status message, as per Q.933 annex A. PE1
                 does not apply this procedure on a transition from the
                 PW forward defect state to the PW reverse defect
                 state.

               b. PE1 MUST clear the reverse defect notification to PE2
                 if applicable.

10.3.2. PW reverse defect state entry/exit

   On entry to the PW reverse defect state:

               a. PE1 MUST set the Active bit = 0 for the corresponding
                 FR AC in a full status report, and optionally in an
                 asynchronous status message, as per Q.933 annex A.

               b. If the PW failure was detected by PE1 without
                 receiving a reverse defect notification from PE2, PE1
                 MUST assume PE2 has no knowledge of the defect and
                 MUST notify PE2 in the form of a forward defect
                 notification.

   On exit from the PW reverse defect state:

               a. PE1 MUST set the Active bit = 1 for the corresponding
                 FR AC in a full status report, and optionally in an
                 asynchronous status message, as per Q.933 annex A. PE1
                 does not apply this procedure on a transition from the
                 PW reverse defect state to the PW forward defect
                 state.

               b. PE1 MUST clear the forward defect notification to PE2
                 if applicable.

10.3.3. PW defect state in the FR Port Mode PW service

   In case of port mode PW service, STATUS ENQUIRY and STATUS messages
   are transported transparently over the PW. A PW Failure will
   therefore result in timeouts of the Q.933 link and PVC management
   protocol at the Frame Relay devices at one or both sites of the
   emulated interface.




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10.3.4. AC forward defect state entry/exit

   On entry to the AC forward defect:

               a. PE1 MUST send a forward defect notification to PE2.

   On exit from the AC forward defect state:

               a. PE1 MUST clear the forward defect notification to PE2.

10.3.5. AC reverse defect state entry/exit

   The AC reverse defect state is not valid for a FR AC.

11. Procedures for TDM PW Service

   From an OAM perspective, the PSN carrying a TDM PW provides the same
   function as that of SONET/SDH or ATM network carrying the same low-
   rate TDM stream. Hence the interworking of defect OAM is similar.

   For structure-agnostic TDM PWs, the TDM stream is to be carried
   transparently across the PSN, and this requires TDM OAM indications
   to be transparently transferred along with the TDM data.

   For structure-aware TDM PWs the TDM structure alignment is terminated
   at ingress to the PSN and regenerated at egress, and hence OAM
   indications may need to be signaled by special means. In both cases
   generation of the appropriate emulated OAM indication may be required
   when the PSN is at fault.

   Since TDM is a real-time signal, defect indications and performance
   measurements may be classified into two classes, urgent and
   deferrable. Urgent messages are those whose contents may not be
   significantly delayed with respect to the TDM data that they
   potentially impact, while deferrable messages may arrive at the far
   end delayed with respect to simultaneously generated TDM data. For
   example, a forward indication signifying that the TDM data is invalid
   (e.g. TDM loss of signal, or MPLS loss of packets) is only of use
   when received before the TDM data is to be played out towards the far
   end TDM system. It is hence classified as an urgent message, and we
   can not delegate its signaling to a separate maintenance or
   management flow.  On the other hand, the forward loss of multi-frame
   synchronization, and most reverse indications do not need to be acted
   upon before a particular TDM frame is played out.

   From the above discussion it is evident that the complete solution to
   OAM for TDM PWs needs to have at least two, and perhaps three


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   components. The required functionality is transparent transfer of
   native TDM OAM and urgent transfer of indications (by flags) along
   with the impacted packets.  Optionally there may be mapping between
   TDM and PSN OAM flows.

   TDM AIS generated in the TDM network due to a fault in that network
   is generally carried unaltered, although the TDM encapsulations allow
   for its suppression for bandwidth conservation purposes. Similarly,
   when the TDM loss of signal is detected at the PE, it will generally
   emulate TDM AIS.

   SAToP and the two structure-aware TDM encapsulations have converged
   on a common set of defect indication flags in the PW control word.

   When the PE detects or is informed of lack of validity of the TDM
   signal, it raises the local ("L") defect flag, uniquely identifying
   the defect as originating in the TDM network. The remote PE must
   ensure that TDM AIS is delivered to the remote TDM network. When the
   defect lies in the MPLS network, the remote PE fails to receive
   packets. The remote PE generates TDM AIS towards its TDM network, and
   in addition raises the remote defect ("R") flag in its PSN-bound
   packets, uniquely identifying the defect as originating in the PSN.

   Finally, defects in the remote TDM network that cause RDI generation
   in that network, may optionally be indicated by proper setting of the
   field of valid packets in the opposite direction.

12. Procedures for CEP PW Service

   Loss of Connectivity and other SONET/SDH protocol failures on the PW
   are translated to alarms on the ACs and vice versa. In essence, all
   defect management procedures are handled entirely in the emulated
   protocol. There is no need for an interaction between PW defect
   management and SONET layer defect management.

13. Informative Appendix A: Native Service Management

13.1. Frame Relay Management

   The management of Frame Relay Bearer Service (FRBS) connections can
   be accomplished through two distinct methodologies:

       a. Based on ITU-T Q.933 Annex A, Link Integrity Verification
          procedure, where STATUS and STATUS ENQUIRY signaling messages
          are sent using DLCI=0 over a given UNI and NNI physical link.
          [ITU-T Q.933]



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       b. Based on FRBS LMI, and similar to ATM ILMI where LMI is
          common in private Frame Relay networks.

   In addition, ITU-T I.620 addresses Frame Relay loopback, but the
   deployment of this standard is relatively limited [ITU-T I.620].

   It is possible to use either, or both, of the above options to
   manage Frame Relay interfaces. This document will refer exclusively
   to Q.933 messages.

   The status of any provisioned Frame Relay PVC may be updated
   through:

        a. STATUS messages in response to STATUS ENQUIRY messages, these
          are mandatory.

        b. Optional unsolicited STATUS updates independent of STATUS
          ENQUIRY (typically under the control of management system,
          these updates can be sent periodically (continuous
          monitoring) or only upon detection of specific defects based
          on configuration.

   In Frame Relay, a DLC is either up or down. There is no distinction
   between different directions. To achieve commonality with other
   technologies, down is represented as a forward defect.

   Frame relay connection management is not implemented over the PW
   using either of the techniques native to FR, therefore PW mechanisms
   are used to synchronize the view each PE has of the remote NS/AC. A
   PE will treat a remote NS/AC failure in the same way it would treat
   a PW or PSN failure; that is using AC facing FR connection
   management to notify the CE that FR is down.


13.2. ATM Management

   ATM management and OAM mechanisms are much more evolved than those
   of Frame Relay.  There are five broad management-related categories,
   including fault management (FT), Performance management (PM),
   configuration management (CM), Accounting management (AC), and
   Security management (SM). ITU-T Recommendation I.610 describes the
   functions for the operation and maintenance of the physical layer
   and the ATM layer, that is, management at the bit and cell levels
   [ITU-T I.610]. Because of its scope, this document will concentrate
   on ATM fault management functions. Fault management functions
   include the following:



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        a. Alarm indication signal (AIS)
        b. Remote Defect indication (RDI).
        c. Continuity Check (CC).
        d. Loopback (LB)

   Some of the basic ATM fault management functions are described as
   follows: Alarm indication signal (AIS) sends a message in the same
   direction as that of the signal, to the effect that an error has
   been detected.

   Remote defect indication (RDI) sends a message to the transmitting
   terminal that an error has been detected. RDI is also referred to as
   the far-end reporting failure. Alarms related to the physical layer
   are indicated using path AIS/RDI. Virtual path AIS/RDI and virtual
   channel AIS/RDI are also generated for the ATM layer.

   OAM cells (F4 and F5 cells) are used to instrument virtual paths and
   virtual channels respectively with regard to their performance and
   availability. OAM cells in the F4 and F5 flows are used for
   monitoring a segment of the network and end-to-end monitoring. OAM
   cells in F4 flows have the same VPI as that of the connection being
   monitored. OAM cells in F5 flows have the same VPI and VCI as that
   of the connection being monitored.  The AIS and RDI messages of the
   F4 and F5 flows are sent to the other network nodes via the VPC or
   the VCC to which the message refers. The type of error and its
   location can be indicated in the OAM cells. Continuity check is
   another fault management function. To check whether a VCC that has
   been idle for a period of time is still functioning, the network
   elements can send continuity-check cells along that VCC.


14. Informative Appendix B: PW Defects and Detection tools

14.1. PW Defects

   Possible defects that impact PWs are the following:

         a. Physical layer defect in the PSN interface

         b. PSN tunnel failure which results in a loss of connectivity
           between ingress and egress PE.

         c. Control session failures between ingress and egress PE

   In case of an MPLS PSN and an MPLS-IP PSN there are additional
   defects:



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         a. PW labeling error, which is due to a defect in the ingress
           PE, or to an over-writing of the PW label value somewhere
           along the LSP path.

         b. LSP tunnel Label swapping errors or LSP tunnel label merging
           errors in the MPLS network. This could result in the
           termination of a PW at the wrong egress PE.

         c. Unintended self-replication; e.g., due to loops or denial-
           of-service attacks.

14.1.1. Packet Loss

   Persistent congestion in the PSN or in a PE could impact the proper
   operation of the emulated service.

   A PE can detect packet loss resulting from congestion through several
   methods. If a PE uses the sequence number field in the PWE3 Control
   Word for a specific Pseudo Wire [RFC3985], it has the ability to
   detect packet loss.  Translation of congestion detection to PW defect
   states is outside the scope of this specification.

   Generally, there are congestion alarms which are raised in the node
   and to the management system when congestion occurs. The decision to
   declare the PW Down and to select another path is usually at the
   discretion of the network operator.

14.2. PW Defect Detection Tools

   To detect the defects listed above, Service Providers have a variety
   of options available.

   Physical Layer defect detection and notification mechanisms such as
   SONET/SDH LOS, LOF,and AIS/FERF.

   PSN Defect Detection Mechanisms:

   For PWE3 over an L2TP-IP PSN, with L2TP as encapsulation protocol,
   the defect detection mechanisms described in [RFC3931] apply. This
   includes for example the keepalive mechanism performed with Hello
   messages for detection of loss of connectivity between a pair of
   LCCEs (i.e., dead PE peer and path detection).  Furthermore, the
   tools Ping and Traceroute, based on ICMP Echo Messages apply [RFC792]
   and can be used to detect defects on the IP PSN.  Additionally, ICMP
   Ping [RFC5085] and BFD [VCCV-BFD] can also be used with VCCV to
   detect defects at the individual pseudowire level.



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   For PWE3 over an MPLS PSN and an MPLS-IP PSN, several tools can be
   used.

         a. LSP-Ping and LSP-Traceroute( [RFC4379]) for LSP tunnel
           connectivity verification.

         b. LSP-Ping with Bi-directional Forwarding Detection ([BFD])
           for LSP tunnel continuity checking.

         c. Furthermore, if RSVP-TE is used to setup the PSN Tunnels
           between ingress and egress PE, the hello protocol can be
           used to detect loss of connectivity [RFC3209], but only at
           the control plane.

   PW specific defect detection mechanisms:

   [RFC4377] describes how LSP-Ping and BFD can be used over individual
   PWs for connectivity verification and continuity checking
   respectively. When used as such, we will refer to them as VCCV-Ping
   and VCCV-BFD respectively.

   Furthermore, the detection of a fault could occur at different points
   in the network and there are several ways the observing PE determines
   a fault exists:

        a. egress or ingress PE detection of failure (e.g. BFD)

        b. ingress PE detection of failure (e.g. LSP-PING)

        c. ingress PE notification of failure (e.g. RSVP Path-err)

15. Security Considerations

   The mapping messages described in this document do not change the
   security functions inherent in the actual messages.

16. IANA Considerations

   There is none at this time.

17. References

17.1. Normative References

  [BFD] Katz, D., Ward, D., "Bidirectional Forwarding Detection",
       Internet Draft <draft-ietf-bfd-base-03.txt>, July 2005



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  [FRF.19] Frame Relay Forum, "Frame Relay Operations, Administration,
       and Maintenance Implementation Agreement", March 2001

  [ICMP] Postel, J. "Internet Control Message Protocol" RFC 792

  [ITU-T I.610] Recommendation I.610 "B-ISDN operation and maintenance
       principles and functions", February 1999

  [ITU-T I.620] Recommendation I.620 "Frame relay operation and
       maintenance principles and functions", October 1996

  [ITU-T Q.933] Recommendation Q.933 "ISDN Digital Subscriber
       Signalling System No. 1 (DSS1) Signalling specifications for
       frame mode switched and permanent virtual connection control and
       status monitoring" February 2003

  [RFC3931] Lau, J., et. al. "Layer Two Tunneling Protocol (Version 3",
       RFC 3931, March 2005

  [RFC4023] Worster. T., et al., "Encapsulating MPLS in IP or Generic
       Routing Encapsulation (GRE)", RFC 4023, March 2005

  [RFC4379] Kompella, K., et. al., "Detecting MPLS Data Plane
       Failures", RFC4379, February 2006

  [RFC4447] Martini, L., Rosen, E., Smith, T., "Pseudowire Setup and
       Maintenance using LDP", RFC4447, April 2006

  [RFC5085] Nadeau, T., et al., "Pseudo Wire Virtual Circuit Connection
       Verification (VCCV)", RFC 5085, December 2007

  [VCCV-BFD] Nadeau, T., Pignataro, C., "Bidirectional Forwarding
       Detection (BFD) for the Pseudowire Virtual Circuit Connectivity
       Verification (VCCV)", draft-ietf-pwe3-vccv-bfd-02, June 2008

17.2. Informative References

  [CONGESTION] Rosen, E., Bryant, S., Davie, B., "PWE3 Congestion
       Control Framework", draft-ietf-pwe3-congestion-frmwk-01.txt, May
       2008

  [ETH-OAM-IWK] Mohan, D., et al., "MPLS and Ethernet OAM
       Interworking", draft-mohan-pwe3-mpls-eth-oam-iwk-01, July 2008

  [L2TP-Status] McGill, N. Pignataro, C., "L2TPv3 Extended Circuit
       Status Values", draft-nmcgill-l2tpext-circuit-status-extensions-
       01 (work in progress), June 2008.


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  [RFC3916] Xiao, X., McPherson, D., Pate, P., "Requirements for
       Pseudo Wire Emulation Edge to-Edge (PWE3)", RFC 3916, September
       2004

  [RFC3985] Bryant, S., Pate, P., "PWE3 Architecture", RFC 3985, March
       2005

  [RFC4377] Nadeau, T. et.al., "OAM Requirements for MPLS Networks",
          RFC4377, February 2006

  [RFC4446] Martini, L., et al., "IANA Allocations for pseudo
          Wire Edge to Edge Emulation (PWE3)", RFC4446,
          April 2006

  [RFC4454]  Singh, S., Townsley, M., and C. Pignataro, "Asynchronous
          Transfer Mode (ATM) over Layer 2 Tunneling Protocol
          Version 3 (L2TPv3)", RFC 4454, May 2006

  [RFC4717] Martini, L., et al., "Encapsulation Methods for Transport
          of ATM Cells/Frame Over IP and MPLS Networks", RFC4717,
          December 2006

  [RFC4842] Malis, A., et. al., "SONET/SDH Circuit Emulation over
       Packet (CEP)", RFC 4842, April 2007


18. Editor's Addresses

   Mustapha Aissaoui
   Alcatel-lucent
   600 March Rd
   Kanata, ON, Canada K2K 2E6
   Email: mustapha.aissaoui@alcatel-lucent.com

   Peter B. Busschbach
   Alcatel-Lucent
   67 Whippany Road
   Whippany, NJ, 07981
   Email: busschbach@alcatel-lucent.com

   David Allan
   Nortel Networks
   3500 Carling Ave.,
   Ottawa, Ontario, CANADA
   Email: dallan@nortel.com



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   Luca Martini
   Cisco Systems, Inc.
   9155 East Nichols Avenue, Suite 400
   Englewood, CO, 80112
   Email: lmartini@cisco.com

   Thomas D. Nadeau
   BT
   BT Centre
   81 Newgate Street
   London  EC1A 7AJ
   United Kingdom
   EMail: tom.nadeau@bt.com


   Monique Morrow
   Cisco Systems, Inc.
   Glatt-com
   CH-8301 Glattzentrum
   Switzerland
   EMail: mmorrow@cisco.com



Full Copyright Statement

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   ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS
   FOR A PARTICULAR PURPOSE.








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