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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: October 2009                                    Alcatel-Lucent

                                                              Dave Allan
                                                                  Nortel

                                                          Monique Morrow
                                                            Luca Martini
                                                      Cisco Systems Inc.

                                                           Thomas Nadeau
                                                                      BT

                                                            Yaakov Stein
                                                 RAD Data Communications

                                                                 Editors


                                                          April 15, 2009

                   Pseudo Wire (PW) OAM Message Mapping
                    draft-ietf-pwe3-oam-msg-map-10.txt


Status of this Memo



   This Internet-Draft is submitted to IETF in full conformance with the
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   This Internet-Draft will expire on October 15, 2009.



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 Copyright and License Notice

   Copyright (c) 2009 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 in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

Abstract

   This document specifies the mapping and notification 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................................................4
   2. Contributors...................................................4
   3. Introduction...................................................5
   4. Terminology....................................................5
   5. Reference Model and Defect Locations...........................7
   6. Abstract Defect States.........................................8
   7. OAM Models....................................................10
   8. PW Defect States and Defect Notifications.....................12
      8.1. PW Defect Notification Mechanisms........................12
         8.1.1. LDP Status TLV......................................13
         8.1.2. L2TP Circuit Status AVP.............................14
         8.1.3. BFD Diagnostic Codes................................16
      8.2. PW Defect State Entry/Exit...............................18
         8.2.1. PW receive defect state entry/exit criteria.........18
         8.2.2. PW transmit defect state entry/exit criteria........19
   9. Procedures for ATM PW Service.................................19


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      9.1. AC receive defect state entry/exit criteria..............19
      9.2. AC transmit defect state entry/exit criteria.............20
      9.3. Consequent Actions.......................................21
         9.3.1. PW receive defect state entry/exit..................21
         9.3.2. PW transmit defect state entry/exit.................22
         9.3.3. PW defect state in ATM Port Mode PW Service.........22
         9.3.4. AC receive defect state entry/exit..................22
         9.3.5. AC transmit defect state entry/exit.................24
   10. Procedures for Frame Relay PW Service........................24
      10.1. AC receive defect state entry/exit criteria.............24
      10.2. AC transmit defect state entry/exit criteria............24
      10.3. Consequent Actions......................................25
         10.3.1. PW receive defect state entry/exit.................25
         10.3.2. PW transmit defect state entry/exit................25
         10.3.3. PW defect state in the FR Port Mode PW service.....26
         10.3.4. AC receive defect state entry/exit.................26
         10.3.5. AC transmit defect state entry/exit................26
   11. Procedures for TDM PW Service................................26
      11.1. AC receive defect state entry/exit criteria.............27
      11.2. AC transmit defect state entry/exit criteria............27
      11.3. Consequent Actions......................................28
         11.3.1. PW receive defect state entry/exit.................28
         11.3.2. PW transmit defect state entry/exit................28
         11.3.3. AC receive defect state entry/exit.................28
   12. Procedures for CEP PW Service................................29
      12.1. Defect states...........................................30
         12.1.1. PW receive defect state entry/exit criteria........30
         12.1.2. PW transmit defect state entry/exit criteria.......30
         12.1.3. AC receive defect state entry/exit criteria........30
         12.1.4. AC transmit defect state entry/exit criteria.......30
      12.2. Consequent actions......................................31
         12.2.1. PW receive defect state entry/exit.................31
         12.2.2. PW transmit defect state entry/exit................31
         12.2.3. AC receive defect state entry/exit.................31
   13. Security Considerations......................................32
   14. IANA Considerations..........................................32
   15. References...................................................32
      15.1. Normative References....................................32
      15.2. Informative References..................................33
   16. Editor's Addresses...........................................34
   Informative Appendix A: Native Service Management................35
      -  Frame Relay Management.....................................35
      -  ATM Management.............................................36
   Informative Appendix B: PW Defects and Detection tools...........37
      -  PW Defects.................................................37
         -  Packet Loss.............................................38
      -  PW Defect Detection Tools..................................38


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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

   Satoru Matsushima, satoru@ft.solteria.net

   David Allan, dallan@nortel.com

   Himanshu Shah, hshah@ciena.com

   Simon Delord, sdelord@uecomm.com.au

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

   Carlos Pignataro, cpignata@cisco.com

   Luca Martini, lmartini@cisco.com

   Yaakov (J) Stein, yaakov_s@rad.com

   Teruyuki Oya, teruyuki.oya@tm.softbank.co.jp






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3. Introduction

   This document specifies the mapping and notification 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 MPLS-IP PSN and PWE
   over L2TP-IP 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

         DLC   Data Link Connection

         FDI   Forward Defect Indication

         FRBS  Frame Relay Bearer Service

         IWF   Interworking Function

         LB    Loopback

         NE    Network Element

         NS    Native Service


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         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
   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.



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

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

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

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


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   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 native service 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 native service 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
          PW data plane traffic, a control plane failure may affect the
          PW status.
       e. Defect in the second native service 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 native service 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.









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                              +-----+
           ----AC receive---->|     |-----PW transmit---->
     CE1                      | PE1 |                       PE2/CE2
           <---AC transmit-----|     |<----PW receive-----
                              +-----+

     (arrows indicate direction of user traffic impacted by a defect)
               Figure 2: Receive and Transmit Defect States

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

   In Figure 2, PE1 may be notified of a receive defect in the AC by
   receiving a Forward Defect indication, e.g., ATM AIS, from an ATM
   switch in 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 receive 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 receive 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
   (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
   receive defect state.

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

   Generally, a PE cannot detect transmit defects directly and will
   therefore need to be notified of AC transmit or PW transmit defects
   by other devices.

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

   Similarly, PE1 may be notified of a transmit 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



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   impacts the traffic sent by PE1 to CE2. As a result, PE1 enters the
   PW transmit defect state.

   Note that a Reverse Defect indication 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 receive and transmit defect states related to
   the same PW service, then the receive defect takes precedence over
   transmit 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.  Native Service (NS) OAM
   messages are described in Appendix A.

   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. We use the words
   upstream and downstream to identify PEs in relation to a specific
   traffic direction.
        a. An upstream PE node MUST transparently relay NS OAM messages
          over the PW.



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        b. An upstream PE node MUST signal local failures affecting the
          AC using a NS defect notification OAM message sent over the
          PW. In the case that it is not possible to generate NS OAM
          messages (e.g. because the defect interferes with NS OAM
          message generation) the PE MUST signal local failures
          affecting the AC using a PW defect notification OAM message.
        c. An upstream PE node MUST signal local failures affecting the
          PW using a PW defect notification OAM message.
        d. A downstream 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 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 all
   ATM cell-mode PW services and the only mode specified for TDM and
   CEP PW services. It is optional for AAL5 PDU transport and AAL5 SDU
   transport modes.

   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.

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

                     Figure 4: Coupled OAM Loops mode

   This mode implements the following behavior. We use the words
   upstream and downstream to identify PEs in relation to a specific
   traffic direction.
        a. An upstream PE node MUST terminate and translate a received
          NS defect notification OAM message to a PW defect
          notification message.




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        b. An upstream PE node MUST signal local failures affecting the
          AC using a PW defect notification OAM message to the remote
          PE.
        c. An upstream PE node MUST signal local failures affecting the
          PW using a PW defect notification OAM message.
        d. A downstream 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 "coupled OAM loops" mode as the default
   mode for a FR PW service and for ATM AAL5 PDU transport and AAL5 SDU
   transport services and as optional for ATM VCC cell mode services.
   It does not specify the use of this mode for TDM PW, CEP PW, and ATM
   VPC cell mode PW services. In the latter last 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].
   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].




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   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.

   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,



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                   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 two 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 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



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   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,

                   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



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

   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




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            - 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 keep-alive facility.
   It is important to note that if a PSN failure is such that the loss
   of connectivity is detected when it triggers a keep-alive timeouts,
   the control connection is cleared.  L2TP Hello messages are sent in-
   band with the data plane, 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



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   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.

   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


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      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 receive 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 receive defect state entry/exit criteria

   PE1 will enter the PW receive 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 receive defect on
              remote AC.

            - 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


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   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 receive defect state.

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

            - All defects it had previously detected have disappeared,
              and

            - PE2 cleared the forward defect indication if applicable.

8.2.2. PW transmit defect state entry/exit criteria

   PE1 will enter the PW transmit 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 transmit fault on the
              remote AC, and

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

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

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



9. Procedures for ATM PW Service

9.1. AC receive defect state entry/exit criteria

   When operating in the "coupled OAM loops" mode, PE1 enters the AC
   receive 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 an end-to-end F4 AIS OAM flow on a VP AC,
                 or an end-to-end F5 AIS OAM flow on a VC AC,


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                 indicating that the ATM VPC or VCC is down in the
                 adjacent L2 ATM network.

               c. It receives a segment F4 AIS OAM flow on a VP AC, or a
                 segment F5 AIS OAM flow on a VC AC,  provided that the
                 operator has provisioned segment OAM and the PE is not
                 a segment end-point

               d. 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
   Receive defect state when all defects it had previously detected have
   disappeared.

   When operating in the "single emulated OAM loop" mode, PE1 enters the
   AC receive 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 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 receive 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].

9.2. AC transmit defect state entry/exit criteria

   When operating in the coupled-loop mode, PE1 enters the AC transmit
   defect state if any of the following conditions are met:

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

               b. It receives a segment F4 RDI OAM flow on a VP AC, or a
                 segment F5 RDI OAM flow on a VC AC,  provided that the


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                 operator has provisioned segment OAM and the PE is not
                 a segment end-point

   PE1 exits the AC transmit defect state if the AC state transitions to
   working or to the AC receive 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 transmit 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 receive defect state entry/exit

   On entry to the PW receive defect state:

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

              b. PE1 MUST cease generation of CC cells on the
                 corresponding AC, if applicable.

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

   On exit from the PW receive defect state:

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

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

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



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9.3.2. PW transmit defect state entry/exit

   On entry to the PW Transmit 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 indication from PE2, PE1
                 MUST assume PE2 has no knowledge of the defect and
                 MUST notify PE2 in the form of a forward defect
                 indication.

   On exit from the PW Transmit Defect State:

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

               b. PE1 MUST clear the forward defect indication 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 receive defect state entry/exit

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

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

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

   When operating in the "single emulated OAM loop" mode, PE1 must be
   able to support two options, subject to the operator's preference.
   The default option is the following:

   On entry to the AC receive defect state:



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               a. PE1 MUST transparently relay ATM AIS cells, or, in the
                 case of a local AC defect, 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 indication
                 to PE2.

               c. PE1 MUST cease the generation of CC cells on the
                 corresponding PW, if applicable.

   In certain operational models, for example in the case that the ATM
   access network is owned by a different provider than the PW, an
   operator may want to distinguish between defects detected in the ATM
   access network and defects detected on the AC directly adjacent to
   the PE. Therefore, the following option must also be supported:

               a. PE1 MUST transparently relay ATM AIS cells over the
                 corresponding PW towards CE2.

               b. Upon detection of a defect on the ATM interface on the
                 PE or in the PE itself, PE1 MUST send a forward defect
                 indication to PE2.

               c. PE1 MUST cease generation of CC cells on the
                 corresponding PW, if applicable.

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

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

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

   On exit from the AC receive 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 indication to PE2 if
                 applicable.

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




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9.3.5. AC transmit defect state entry/exit

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

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

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

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

10. Procedures for Frame Relay PW Service

10.1. AC receive defect state entry/exit criteria

   PE1 enters the AC receive 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 receive defect state when all defects it had
   previously detected have disappeared.

10.2. AC transmit defect state entry/exit criteria

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







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10.3. Consequent Actions

10.3.1. PW receive defect state entry/exit

   On entry to the PW receive 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 indication from PE2, PE1
                 MUST assume PE2 has no knowledge of the defect and
                 MUST notify PE2 in the form of a reverse defect
                 indication.

   On exit from the PW receive 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 receive defect state to the PW transmit defect
                 state.

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

10.3.2. PW transmit defect state entry/exit

   On entry to the PW transmit 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 indication from PE2, PE1
                 MUST assume PE2 has no knowledge of the defect and
                 MUST notify PE2 in the form of a forward defect
                 indication.

   On exit from the PW transmit defect state:

               a. PE1 MUST set the Active bit = 1 for the corresponding
                 FR AC in a full status report, and optionally in an


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                 asynchronous status message, as per Q.933 annex A. PE1
                 does not apply this procedure on a transition from the
                 PW transmit defect state to the PW receive defect
                 state.

               b. PE1 MUST clear the forward defect indication 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.

10.3.4. AC receive defect state entry/exit

   On entry to the AC receive defect state:

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

   On exit from the AC receive defect state:

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

10.3.5. AC transmit defect state entry/exit

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

11. Procedures for TDM PW Service

   The following procedures apply to SAToP ([RFC4553]), CESoPSN
   ([RFC5086]) and TDMoIP ([RFC5087]). These technologies generally
   utilize the single-emulated loop mode (see section 7). Note that
   TDMoIP distinguishes between trail-extended and trail-terminated
   scenarios; the former is essentially the single emulated loop model,
   while the latter differs from the coupled-loop model in that failure
   notifications are not propagated across the PW.

   Since TDM is inherently real-time in nature, many OAM indications
   must be generated or forwarded with essentially no delay. This
   requirement rules out the use of messaging protocols, such as relying
   on the PW status message. Thus, for TDM PWs, alternate mechanism are
   employed.




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   The fact that TDM PW packets are sent at a known constant rate is
   used as an OAM mechanism. Thus, a PE enters the PW receive defect
   state when a preconfigured number of TDM PW packets do not arrive in
   a timely fashion. It exits this state when packets once again arrive
   at the proper rate.

   Native TDM carries OAM indications in overhead fields that travel
   along with the data. TDM PWs emulate this behavior by sending urgent
   OAM messages in the PWE control word.

   The TDM PWE control word contains a set of flags used to indicate PW
   and AC defect conditions. The L bit is an AC forward defect
   indication used by the local PE to signal TDM network defects to the
   remote PE. The M field may be used to modify the meaning of receive
   defects. The R bit is a PW reverse defect indication used by the
   local PE to signal PSN failures to the remote PE. Upon reception of
   packets with the R-bit set, a PE enters the PW transmit defect state.

11.1. AC receive defect state entry/exit criteria

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

               e. It detects a physical layer fault on the TDM interface
                 (Loss of Signal, Loss of Alignment, etc (see G.705)).

               f. It is notified of a previous physical layer fault by
                 detecting of AIS.

   The exact conditions under which a PE enters and exits the AIS state
   are defined in [ITU-T G.775]. Note that Loss of Signal and AIS
   detection can be performed for both structure-agnostic and structure-
   aware TDM PW types. Note that structure-agnostic PEs can not detect
   Loss of Alignment.

11.2. AC transmit defect state entry/exit criteria

   PE1 enters the AC transmit defect state when it detects RDI according
   to the criteria in [ITU-T G.775]. Note that structure-agnostic PEs
   can not detect RDI.









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11.3. Consequent Actions

11.3.1. PW receive defect state entry/exit

   On entry to the PW receive defect state:

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

               b. PE1 MUST set the R bit in all PW packets sent back to
                 PE2.

   On exit from the PW receive defect state:

               c. PE1 MUST cease AIS insertion into the corresponding
                 TDM AC.

               d. PE1 MUST clear the R bit in all PW packets sent back
                 to PE2.

   Note that AIS generation can in general be performed by both
   structure-aware and structure-agnostic PEs.

11.3.2. PW transmit defect state entry/exit

   On entry to the PW Transmit Defect State:

              a. A structure-aware PE1 MUST commence RDI insertion into
                 the corresponding AC.

   On exit from the PW Transmit Defect State:

               b. A structure-aware PE1 MUST cease RDI insertion into
                 the corresponding AC.

   Note that structure-agnostic PEs are not capable of injecting RDI
   into an AC.

11.3.3. AC receive defect state entry/exit

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

               a. PE1 SHOULD overwrite the TDM data with AIS in the PW
                 packets sent towards PE2.

               b. PE1 MUST set the L bit in these packets.


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               c. PE1 MAY omit the payload in order to conserve
                 bandwidth.

               d. A structure-aware PE1 SHOULD send RDI back towards
                 CE1.

               e. A structure-aware PE1 that detects a potentially
                 correctable AC defect MAY use the M field to indicate
                 this.

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

               a. PE1 MUST cease overwriting PW content with AIS and
                 return to forwarding valid TDM data in PW packets sent
                 towards PE2.

               b. PE1 MUST clear the notification bit in PW packets sent
                 towards PE2.

               c. A structure-aware PE1 MUST cease sending RDI towards
                 CE1.





12. Procedures for CEP PW Service

   The following procedures apply to SONET/SDH Circuit Emulation
   ([RFC4842]). They are based on the single-emulated loop mode (see
   section 7).

   Since SONET and SDH are inherently real-time in nature, many OAM
   indications must be generated or forwarded with essentially no delay.
   This requirement rules out the use of messaging protocols, such as
   relying on the PW status message. Thus, for CEP PWs alternate
   mechanism are employed.

   The CEP PWE control word contains a set of flags used to indicate PW
   and AC defect conditions. The L bit is a forward defect indication
   used by the local PE to signal a defect in the attachment circuit to
   the remote PE. The R bit is a PW reverse defect indication used by
   the local PE to signal PSN failures to the remote PE. The combination
   of N and P bit is used by the local PE to signal loss of pointer to
   the remote PE.



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   The fact that CEP PW packets are sent at a known constant rate is
   used as an OAM mechanism. Thus, a PE enters the PW receive defect
   state it loses packet synchronization. It exits this state when it
   regains packet synchronization. See [RFC4842] for further details.

12.1. Defect states

12.1.1. PW receive defect state entry/exit criteria

   In addition to the conditions specified in section 8.2.1. PE1 will
   enter the PW receive defect state if one of the following is true:

      - it receives packets with the L bit set

      - it receives packets with both the N and P bits set

      - it loses packet synchronization

12.1.2. PW transmit defect state entry/exit criteria

   In addition to the conditions specified in section 8.2.2. PE1 will
   enter the PW transmit defect state if it receives packets with the R
   bit set.

12.1.3. AC receive defect state entry/exit criteria

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

               a. It detects a physical layer fault on the TDM interface
                 (Loss of Signal, Loss of Alignment, etc (see
                 [appropriate SONET & SDH reference])).

               b. It is notified of a previous physical layer fault by
                 detecting of AIS.

   The exact conditions under which a PE enters and exits the AIS state
   are defined in[ITU-T G.707] and [ITU-T G.806].

12.1.4. AC transmit defect state entry/exit criteria

   The AC transmit defect state is not valid for CEP PWs. RDI signals
   are forwarded transparently.




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12.2. Consequent actions

12.2.1. PW receive defect state entry/exit

   On entry to the PW receive defect state:

               a. PE1 MUST commence AIS-P/V insertion into the
                 corresponding AC.

               b. PE1 MUST set the R bit in all PW packets sent back to
                 PE2.

   On exit from the PW receive defect state:

               a. PE1 MUST cease AIS-P/V insertion into the
                 corresponding AC.

               b. PE1 MUST clear the R bit in all PW packets sent back
                 to PE2.

   See [RFC4842] for further details.

12.2.2. PW transmit defect state entry/exit

   On entry to the PW Transmit Defect State:

              a. A structure-aware PE1 MUST commence RDI insertion into
                 the corresponding AC.

   On exit from the PW Transmit Defect State:

               a. A structure-aware PE1 MUST cease RDI insertion into
                 the corresponding AC.

12.2.3. AC receive defect state entry/exit

   On entry to the AC receive defect state:

               a. PE1 MUST set the L bit in these packets.

               b. If Dynamic Bandwidth Allocation (DBA) has been
                 enabled, PE1 MAY omit the payload in order to conserve
                 bandwidth.

               c. If Dynamic Bandwidth Allocation (DBA) is not enabled
                 PE1 SHOULD insert AIS-V/P in the SDH/SONET client
                 layer in the PW packets sent towards PE2.


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

               d. PE1 MUST cease overwriting PW content with AIS-P/V and
                 return to forwarding valid data in PW packets sent
                 towards PE2.

               e. PE1 MUST clear the L bit in PW packets sent towards
                 PE2.

   See [RFC4842] for further details.

13. Security Considerations

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

14. IANA Considerations

   There are none at this time.

15. References

15.1. Normative References

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

  [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 G.707] Recommendation G.707 "Network Node Interface For The
       Synchronous Digital Hierarchy", December 2003

  [ITU-T G.775] Recommendation G.775 "Loss of Signal (LOS), Alarm
       Indication Signal(AIS) and Remote Defect Indication (RDI) defect
       detection and clearance criteria for PDH signals", October 1998

  [ITU-T G.806] Recommendation G.806 "Characteristics of transport
       equipment-Description methodology and generic functionality",
       February 2004.

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



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  [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

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

  [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



15.2. 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

  [RFC4553] A.Vainshtein, Y.(J) Stein, "Structure-Agnostic Time
       Division Multiplexing (TDM) over Packet (SAToP)", RFC 4553, June
       2006


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



  [RFC5086] A.Vainshtein et al., "Structure-Aware Time Division
       Multiplexed (TDM) Circuit Emulation Service over Packet Switched
       Network (CESoPSN)", RFC 5086, December 2007

  [RFC5087] Y.(J) Stein et al., "Time Division Multiplexing over IP
       (TDMoIP)", RFC 5087, December 2007

16. 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


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   Whippany, NJ, 07981
   Email: busschbach@alcatel-lucent.com

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

   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

   Yaakov (Jonathan) Stein
   RAD Data Communications
   24 Raoul Wallenberg St., Bldg C
   Tel Aviv  69719
   ISRAEL
   EMail: yaakov_s@rad.com




Informative Appendix A: Native Service Management

- Frame Relay Management

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


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       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]
       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 receive 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.


- 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


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   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:

        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.


Informative Appendix B: PW Defects and Detection tools

- 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.



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         c. Control session failures between ingress and egress PE

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

         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.

- 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.

- 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 keep-alive 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


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   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.

   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 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)














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