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rfc:rfc6310

Internet Engineering Task Force (IETF) M. Aissaoui Request for Comments: 6310 P. Busschbach Category: Standards Track Alcatel-Lucent ISSN: 2070-1721 L. Martini

                                                             M. Morrow
                                                   Cisco Systems, Inc.
                                                             T. Nadeau
                                                       CA Technologies
                                                           Y(J). Stein
                                               RAD Data Communications
                                                             July 2011
 Pseudowire (PW) Operations, Administration, and Maintenance (OAM)
                          Message Mapping

Abstract

 This document specifies the mapping and notification of defect states
 between a pseudowire (PW) and the Attachment Circuits (ACs) of the
 end-to-end emulated service.  It standardizes the behavior of
 Provider Edges (PEs) with respect to PW and AC defects.  It addresses
 ATM, Frame Relay, Time Division Multiplexing (TDM), and Synchronous
 Optical Network / Synchronous Digital Hierarchy (SONET/SDH) PW
 services, carried over MPLS, MPLS/IP, and Layer 2 Tunneling Protocol
 version 3/IP (L2TPv3/IP) Packet Switched Networks (PSNs).

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6310.

Aissaoui, et al. Standards Track [Page 1] RFC 6310 PW OAM Message Mapping July 2011

Copyright Notice

 Copyright (c) 2011 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.
 This document may contain material from IETF Documents or IETF
 Contributions published or made publicly available before November
 10, 2008.  The person(s) controlling the copyright in some of this
 material may not have granted the IETF Trust the right to allow
 modifications of such material outside the IETF Standards Process.
 Without obtaining an adequate license from the person(s) controlling
 the copyright in such materials, this document may not be modified
 outside the IETF Standards Process, and derivative works of it may
 not be created outside the IETF Standards Process, except to format
 it for publication as an RFC or to translate it into languages other
 than English.

Aissaoui, et al. Standards Track [Page 2] RFC 6310 PW OAM Message Mapping July 2011

Table of Contents

 1. Introduction ....................................................4
 2. Abbreviations and Conventions ...................................5
    2.1. Abbreviations ..............................................5
    2.2. Conventions ................................................6
 3. Reference Model and Defect Locations ............................7
 4. Abstract Defect States ..........................................8
 5. OAM Modes .......................................................9
 6. PW Defect States and Defect Notifications ......................11
    6.1. PW Defect Notification Mechanisms .........................11
         6.1.1. LDP Status TLV .....................................13
         6.1.2. L2TP Circuit Status AVP ............................14
         6.1.3. BFD Diagnostic Codes ...............................16
    6.2. PW Defect State Entry/Exit ................................18
         6.2.1. PW Receive Defect State Entry/Exit Criteria ........18
         6.2.2. PW Transmit Defect State Entry/Exit Criteria .......19
 7. Procedures for ATM PW Service ..................................19
    7.1. AC Receive Defect State Entry/Exit Criteria ...............19
    7.2. AC Transmit Defect State Entry/Exit Criteria ..............20
    7.3. Consequent Actions ........................................21
         7.3.1. PW Receive Defect State Entry/Exit .................21
         7.3.2. PW Transmit Defect State Entry/Exit ................21
         7.3.3. PW Defect State in ATM Port Mode PW Service ........22
         7.3.4. AC Receive Defect State Entry/Exit .................22
         7.3.5. AC Transmit Defect State Entry/Exit ................23
 8. Procedures for Frame Relay PW Service ..........................24
    8.1. AC Receive Defect State Entry/Exit Criteria ...............24
    8.2. AC Transmit Defect State Entry/Exit Criteria ..............24
    8.3. Consequent Actions ........................................24
         8.3.1. PW Receive Defect State Entry/Exit .................24
         8.3.2. PW Transmit Defect State Entry/Exit ................25
         8.3.3. PW Defect State in the FR Port Mode PW Service .....25
         8.3.4. AC Receive Defect State Entry/Exit .................25
         8.3.5. AC Transmit Defect State Entry/Exit ................26
 9. Procedures for TDM PW Service ..................................26
    9.1. AC Receive Defect State Entry/Exit Criteria ...............27
    9.2. AC Transmit Defect State Entry/Exit Criteria ..............27
    9.3. Consequent Actions ........................................27
         9.3.1. PW Receive Defect State Entry/Exit .................27
         9.3.2. PW Transmit Defect State Entry/Exit ................27
         9.3.3. AC Receive Defect State Entry/Exit .................28
 10. Procedures for CEP PW Service .................................28
    10.1. Defect States ............................................29
         10.1.1. PW Receive Defect State Entry/Exit ................29
         10.1.2. PW Transmit Defect State Entry/Exit ...............29
         10.1.3. AC Receive Defect State Entry/Exit ................29
         10.1.4. AC Transmit Defect State Entry/Exit ...............30

Aissaoui, et al. Standards Track [Page 3] RFC 6310 PW OAM Message Mapping July 2011

    10.2. Consequent Actions .......................................30
         10.2.1. PW Receive Defect State Entry/Exit ................30
         10.2.2. PW Transmit Defect State Entry/Exit ...............30
         10.2.3. AC Receive Defect State Entry/Exit ................30
 11. Security Considerations .......................................31
 12. Contributors and Acknowledgments ..............................31
 13. References ....................................................32
    13.1. Normative References .....................................32
    13.2. Informative References ...................................34
 Appendix A. Native Service Management (Informative) ...............36
   A.1. Frame Relay Management .....................................36
   A.2. ATM Management .............................................37
 Appendix B. PW Defects and Detection Tools ........................38
   B.1. PW Defects .................................................38
   B.2. Packet Loss ................................................38
   B.3. PW Defect Detection Tools ..................................38
   B.4. PW Specific Defect Detection Mechanisms ....................39

1. Introduction

 This document specifies the mapping and notification of defect states
 between a pseudowire and the Attachment Circuits (AC) of the end-to-
 end emulated service.  It covers the case where the ACs and the PWs
 are of the same type in accordance to the Pseudowire Emulation Edge-
 to-Edge (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 respect to defects 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 addresses PWs over MPLS, MPLS/IP, L2TPv3/IP PSNs, ATM,
 Frame Relay, TDM, and SONET/SDH PW native services.  Due to its
 unique characteristics, the Ethernet PW service is covered in a
 separate document [Eth-OAM-Inter].
 This document provides procedures for PWs set up using Label
 Distribution Protocol (LDP) [RFC4447] or L2TPv3 [RFC3931] control
 protocols.  While we mention fault reporting options for PWs
 established by other means (e.g., by static configuration or via
 BGP), we do not provide detailed procedures for such cases.

Aissaoui, et al. Standards Track [Page 4] RFC 6310 PW OAM Message Mapping July 2011

 This document is scoped only to single segment PWs.  The mechanisms
 described in this document could also be applied to terminating PEs
 (T-PEs) for multi-segment PWs (MS-PWs) ([RFC5254]).  Section 10 of
 [RFC6073] details procedures for generating or relaying PW status by
 a switching PE (S-PE).

2. Abbreviations and Conventions

2.1. Abbreviations

 AAL5  ATM Adaptation Layer 5
 AIS   Alarm Indication Signal
 AC    Attachment Circuit
 ATM   Asynchronous Transfer Mode
 AVP   Attribute Value Pair
 BFD   Bidirectional Forwarding Detection
 CC    Continuity Check
 CDN   Call Disconnect Notify
 CE    Customer Edge
 CV    Connectivity Verification
 DBA   Dynamic Bandwidth Allocation
 DLC   Data Link Connection
 FDI   Forward Defect Indication
 FR    Frame Relay
 FRBS  Frame Relay Bearer Service
 ICMP  Internet Control Message Protocol
 LB    Loopback
 LCCE  L2TP Control Connection Endpoint
 LDP   Label Distribution Protocol
 LSP   Label Switched Path
 L2TP  Layer 2 Tunneling Protocol
 MPLS  Multiprotocol Label Switching
 NE    Network Element
 NS    Native Service
 OAM   Operations, Administration, and Maintenance
 PE    Provider Edge
 PSN   Packet Switched Network
 PW    Pseudowire
 RDI   Reverse Defect Indication
 PDU   Protocol Data Unit
 SDH   Synchronous Digital Hierarchy
 SDU   Service Data Unit
 SONET   Synchronous Optical Network
 TDM   Time Division Multiplexing
 TLV   Type Length Value
 VCC   Virtual Channel Connection
 VCCV  Virtual Connection Connectivity Verification
 VPC   Virtual Path Connection

Aissaoui, et al. Standards Track [Page 5] RFC 6310 PW OAM Message Mapping July 2011

2.2. Conventions

 The words "defect" and "fault" are used interchangeably to mean any
 condition that negatively impacts forwarding of user traffic between
 the CE endpoints of the PW service.
 The words "defect notification" and "defect indication" are used
 interchangeably to mean any 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 be carried over three types of Packet Switched Networks
 (PSNs).  An "MPLS PSN" makes use of MPLS Label Switched Paths
 [RFC3031] as the tunneling technology to forward the PW packets.  An
 "MPLS/IP PSN" makes use of MPLS-in-IP tunneling [RFC4023], with an
 MPLS shim header used as PW demultiplexer.  An "L2TPv3/IP PSN" makes
 use of L2TPv3/IP [RFC3931] as the tunneling technology with the
 L2TPv3/IP Session ID as the PW demultiplexer.
 If LSP-Ping [RFC4379] is run over a PW as described in [RFC5085], it
 will be referred to as "VCCV-Ping".  If BFD is run over a PW as
 described in [RFC5885], it will be referred to as "VCCV-BFD".
 While PWs are inherently bidirectional entities, defects and OAM
 messaging are related to a specific traffic direction.  We use the
 terms "upstream" and "downstream" to identify PEs in relation to the
 traffic direction.  A PE is upstream for the traffic it is forwarding
 and is downstream for the traffic it is receiving.
 We use the terms "local" and "remote" to identify native service
 networks and ACs in relation to a specific PE.  The local AC is
 attached to the PE in question, while the remote AC is attached to
 the PE at the other end of the PW.
 A "transmit defect" is any defect that uniquely impacts traffic sent
 or relayed by the observing PE.  A "receive defect" is any defect
 that impacts information transfer to the observing PE.  Note that a
 receive defect also impacts traffic meant to be relayed, and thus can
 be considered to incorporate two defect states.  Thus, when a PE
 enters both receive and transmit defect states of a PW service, the
 receive defect takes precedence over the transmit defect in terms of
 the consequent actions.
 A "forward defect indication" (FDI) is sent in the same direction as
 the user traffic impacted by the defect.  A "reverse defect
 indication" (RDI) is sent in the direction opposite to that of the
 impacted traffic.

Aissaoui, et al. Standards Track [Page 6] RFC 6310 PW OAM Message Mapping July 2011

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

3. 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)..(e)..(f)---(g)---|    |
      | CE1|   (N1)   |    |                  |    |    (N2)  |CE2 |
      |    |----------|............PW2.............|----------|    |
      +----+          |    |==================|    |          +----+
           ^          +----+                  +----+          ^
           |      Provider Edge 1         Provider Edge 2     |
           |                                                  |
           |<-------------- Emulated Service ---------------->|
     Customer                                                Customer
      Edge 1                                                  Edge 2
                Figure 1: PWE3 Network Defect Locations
 The procedures will be described in this document from the viewpoint
 of PE1, so that N1 is the local native service network and N2 is the
 remote native service network.  PE2 will typically implement the same
 functionality.  Note that PE1 is the upstream PE for traffic
 originating in the local NS network N1, while it is the downstream PE
 for traffic originating in the remote NS network N2.
 The following is a brief description of the defect locations:
 a. Defect in NS network N1.  This covers any defect in network N1
    (including any CE1 defect) that impacts all or some ACs attached
    to PE1, and is thus a local AC defect.  The defect is conveyed to
    PE1 and to NS network N2 using NS specific OAM defect indications.
 b. Defect on a PE1 AC interface (another local AC defect).
 c. Defect on a PE1 PSN interface.
 d. Defect in the PSN network.  This covers any defect in the PSN that
    impacts all or some PWs between PE1 and PE2.  The defect is
    conveyed to the PE using a PSN and/or a PW specific OAM defect

Aissaoui, et al. Standards Track [Page 7] RFC 6310 PW OAM Message Mapping July 2011

    indication.  Note that both data plane defects and control plane
    defects must be taken into consideration.  Although control
    messages may follow a different path than PW data plane traffic, a
    control plane defect may affect the PW status.
 e. Defect on a PE2 PSN interface.
 f. Defect on a PE2 AC interface (a remote AC defect).
 g. Defect in NS network N2 (another remote AC defect).  This covers
    any defect in N2 (including any CE2 defect) that impacts all or a
    subset of ACs attached to PE2.  The defect is conveyed to PE2 and
    to NS network N1 using the NS OAM defect indication.

4. 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 of which it has been made aware via notifications.
                           +-----+
        ----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 CE1 or an
 intervening network.  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 the PW
 status TLV is used for fault notification, this message will indicate
 a Local PSN-facing PW (egress) Transmit Fault or a Local AC (ingress)

Aissaoui, et al. Standards Track [Page 8] RFC 6310 PW OAM Message Mapping July 2011

 Receive Fault at PE2, as described in Section 6.1.1.  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 by itself 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 6.1.1.  This
 defect 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.

5. OAM Modes

 A homogeneous PW service forwards packets between an AC and a PW of
 the same type.  It thus implements both NS OAM and PW OAM mechanisms.
 PW OAM defect notification messages are described in Section 6.1.  NS
 OAM messages are described in Appendix A.
 This document defines two different OAM modes, the distinction being
 the method of mapping between the NS and PW OAM defect notification
 messages.

Aissaoui, et al. Standards Track [Page 9] RFC 6310 PW OAM Message Mapping July 2011

 The first mode, illustrated in Figure 3, is called the "single
 emulated OAM loop" mode.  Here, a single end-to-end NS OAM loop is
 emulated by transparently passing NS OAM messages over the PW.  Note
 that the PW OAM is shown outside the PW in Figure 3, as it is
 transported in LDP messages or in the associated channel, not inside
 the PW itself.
                     +-----+                 +-----+
    +-----+          |     |=================|     |          +-----+
    | CE1 |-=NS-OAM=>| PE1 |----=NS-OAM=>----| PE2 |-=NS-OAM=>| CE2 |
    +-----+          |     |=================|     |          +-----+
                     +-----+                 +-----+
                        \                       /
                         -------=PW-OAM=>-------
                Figure 3: Single Emulated OAM Loop Mode
 The single emulated OAM loop mode implements the following behavior:
 a. The upstream PE (PE1) MUST transparently relay NS OAM messages
    over the PW.
 b. The upstream PE MUST signal local defects affecting the AC using a
    NS defect notification 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 defects affecting the AC using a PW defect
    notification message.
 c. The upstream PE MUST signal local defects affecting the PW using a
    PW defect notification message.
 d. The downstream PE (PE2) MUST insert NS defect notification
    messages into its local AC when it detects or is notified of a
    defect in the PW or remote AC.  This includes translating received
    PW defect notification messages into NS defect notification
    messages for defects signaled by the upstream PE.
 The single emulated OAM loop mode is suitable for PW services that
 have a widely deployed NS OAM mechanism.  This document specifies the
 use of this mode for ATM PW, TDM PW, and Circuit Emulation over
 Packet (CEP) PW services.  It is the default mode of operation for
 all ATM cell mode PW services and the only mode specified for CEP and
 Structure-Agnostic TDM over Packets / Circuit Emulation Service over
 Packet Switched Network (SAToP/CESoPSN) TDM PW services.  It is
 optional for AAL5 PDU transport and AAL5 SDU transport modes.

Aissaoui, et al. Standards Track [Page 10] RFC 6310 PW OAM Message Mapping July 2011

 The second OAM mode operates three OAM loops joined at the AC/PW
 boundaries of the PEs.  This is referred to as the "coupled OAM
 loops" mode and is illustrated in Figure 4.  Note that in contrast to
 Figure 3, NS OAM messages are never carried over the PW.
                     +-----+                 +-----+
    +-----+          |     |=================|     |          +-----+
    | CE1 |-=NS-OAM=>| PE1 |                 | PE2 |-=NS-OAM=>| CE2 |
    +-----+          |     |=================|     |          +-----+
                     +-----+                 +-----+
                        \                       /
                         -------=PW-OAM=>-------
                   Figure 4: Coupled OAM Loops Mode
 The coupled OAM loops mode implements the following behavior:
 a. The upstream PE (PE1) MUST terminate and translate a received NS
    defect notification message into a PW defect notification message.
 b. The upstream PE MUST signal local failures affecting its local AC
    using PW defect notification messages to the downstream PE.
 c. The upstream PE MUST signal local failures affecting the PW using
    PW defect notification messages.
 d. The downstream PE (PE2) MUST insert NS defect notification
    messages into the AC when it detects or is notified of defects in
    the PW or remote AC.  This includes translating received PW defect
    notification messages into NS defect notification messages.
 This document specifies the coupled OAM loops mode as the default
 mode for the Frame Relay, ATM AAL5 PDU transport, and AAL5 SDU
 transport services.  It is an optional mode for ATM VCC cell mode
 services.  This mode is not specified for TDM, CEP, or ATM VPC cell
 mode PW services.  RFC 5087 defines a similar but distinct mode, as
 will be explained in Section 9.  For the ATM VPC cell mode case a
 pure coupled OAM loops mode is not possible as a PE MUST
 transparently pass VC-level (F5) ATM OAM cells over the PW while
 terminating and translating VP-level (F4) OAM cells.

6. PW Defect States and Defect Notifications

6.1. PW Defect Notification Mechanisms

 For MPLS and MPLS/IP PSNs, a PE that establishes a PW using the Label
 Distribution Protocol [RFC5036], and that has negotiated use of the
 LDP status TLV per Section 5.4.3 of [RFC4447], MUST use the PW status

Aissaoui, et al. Standards Track [Page 11] RFC 6310 PW OAM Message Mapping July 2011

 TLV mechanism for AC and PW status and defect notification.
 Additionally, such a PE MAY use VCCV-BFD Connectivity Verification
 (CV) for fault detection only (CV types 0x04 and 0x10 [RFC5885]).
 A PE that establishes an MPLS PW using means other than LDP, e.g., by
 static configuration or by use of BGP, MUST support some alternative
 method of status reporting.  The design of a suitable mechanism to
 carry the aforementioned status TLV in the PW associated channel is
 work in progress [Static-PW-Status].  Additionally, such a PE MAY use
 VCCV-BFD CV for both fault detection and status notification (CV
 types 0x08 and 0x20 [RFC5885]).
 For a L2TPv3/IP PSN, a PE SHOULD use the Circuit Status Attribute
 Value Pair (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 as described in [RFC5641] 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.
 When a PE does not support the Circuit Status AVP, it MAY use the
 Stop-Control-Connection-Notification (StopCCN) and the Call-
 Disconnect-Notify (CDN) messages to tear down L2TP sessions in a
 fashion similar to LDP's use of Label Withdrawal to tear down a PW.
 A PE may use the StopCCN to shut down the L2TP control connection,
 and implicitly all L2TP sessions associated with that control
 connection, without any explicit session control messages.  This is
 useful for the case of a failure which impacts all L2TP sessions (all
 PWs) managed by the control connection.  It MAY use CDN to disconnect
 a specific L2TP session when a failure only affects a specific PW.
 Additionally, a PE 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 that establishes a PW using means other than the
 L2TP control plane, e.g., by static configuration or by use of BGP,
 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 via the L2TP control plane.
 The CV types are defined in Section 6.1.3 of this document.

Aissaoui, et al. Standards Track [Page 12] RFC 6310 PW OAM Message Mapping July 2011

6.1.1. LDP Status TLV

 [RFC4446] defines the following PW status code points:
 0x00000000 -  Pseudowire forwarding (clear all failures)
 0x00000001 -  Pseudowire 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 the "Pseudowire forwarding" code point is
 used to indicate that all faults are to be cleared.  It also
 specifies that the "Pseudowire Not Forwarding" code point means that
 a defect has been detected that is not represented by the defined
 code points.
 The code points used in the LDP status TLV in a PW status
 notification message report defects from the viewpoint 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.
        Reverse defect indication corresponds to the logical OR of:
  • Local Attachment Circuit (egress) Transmit Fault and
  • Local PSN-facing PW (ingress) Receive Fault.

Aissaoui, et al. Standards Track [Page 13] RFC 6310 PW OAM Message Mapping July 2011

 A PE MUST use PW status notification messages to report all defects
 affecting the PW service including, but not restricted to, the
 following:
 o  defects detected through fault detection mechanisms in the MPLS
    and MPLS/IP PSN,
 o  defects detected through VCCV-Ping or VCCV-BFD CV types 0x04 and
    0x10 for fault detection only,
 o  defects within the PE that result in an inability to forward
    traffic between the AC and the PW,
 o  defects of the AC or in the Layer 2 network affecting the AC as
    per the rules detailed in Section 5 for the "single emulated OAM
    loop" mode and "coupled OAM loops" modes.
 Note that there are two situations that require PW label withdrawal
 as opposed to a PW status notification by the PE.  The first one is
 when the PW is taken down administratively in accordance with
 [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.

6.1.2. 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.  [RFC5641] defines extensions to
 the Circuit Status AVP that are analogous to the PW Status TLV
 defined for LDP.  Consequently, for L2TPv3/IP, the Circuit Status AVP
 is used in the same fashion as the PW Status described in the
 previous section.  Extended circuit status for L2TPv3/IP is described
 in [RFC5641].
 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/IP sessions in the presence of
 session-level failures detected in the L2TPv3/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 [RFC5641].

Aissaoui, et al. Standards Track [Page 14] RFC 6310 PW OAM Message Mapping July 2011

 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.
        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 defects from the viewpoint of the
 originating LCCE (PE).
 When the extended Circuit Status definition of [RFC5641] is
 supported, a PE SHALL use the Circuit Status to report all failures
 affecting the PW service including, but not restricted to, the
 following:
 o  defects detected through defect detection mechanisms in the
    L2TPv3/IP PSN,
 o  defects detected through VCCV-Ping or VCCV-BFD CV types 0x04 (BFD
    IP/UDP-encapsulated, for PW Fault Detection only) and 0x10 (BFD
    PW-ACH-encapsulated (without IP/UDP headers), for PW.  Fault
    Detection and AC/PW Fault Status Signaling) for fault detection
    only which are described in Section 6.1.3 of this document,
 o  defects within the PE that result in an inability to forward
    traffic between the AC and the PW,
 o  defects of the AC or in the L2 network affecting the AC as per the
    rules detailed in Section 5 for the "single emulated OAM loop"
    mode and the "coupled OAM loops" modes.
 When the extended Circuit Status definition of [RFC5641] is not
 supported, a PE SHALL use the A bit in the Circuit Status AVP in the
 SLI to report:
 o  defects of the AC or in the L2 network affecting the AC as per the
    rules detailed in Section 5 for the "single emulated OAM loop"
    mode and the "coupled OAM loops" modes.

Aissaoui, et al. Standards Track [Page 15] RFC 6310 PW OAM Message Mapping July 2011

 When the extended Circuit Status definition of [RFC5641] is not
 supported, a PE MAY use the CDN and StopCCN messages in a similar way
 to an MPLS PW label withdrawal to report:
 o  defects detected through defect detection mechanisms in the
    L2TPv3/IP PSN (using StopCCN),
 o  defects detected through VCCV (pseudowire level) (using CDN),
 o  defects within the PE that result in an inability to forward
    traffic between ACs and PW (using CDN).
 For ATM L2TPv3/IP 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 PSN failure is detected by keep-alive
 timeout, the control connection is cleared.  L2TP Hello messages are
 sent in-band so as to follow the data plane with respect to the
 source and destination addresses, IP protocol number, and UDP port
 (when UDP is used).

6.1.3. BFD Diagnostic Codes

 BFD [RFC5880] defines a set of diagnostic codes that partially
 overlap the set of defects that can be communicated through LDP
 Status TLV or L2TP Circuit Status AVP.  This section describes the
 behavior of the PEs with respect to using one or both of these
 methods for detecting and propagating defect state.
 In the case of an MPLS PW established via LDP signaling, the PEs
 negotiate VCCV capabilities during the label mapping messages
 exchange used to establish the two directions of the PW.  This is
 achieved by including a capability TLV in the PW Forward Error
 Correction (FEC) interface parameters TLV.  In the L2TPv3/IP case,
 the PEs negotiate the use of VCCV during the pseudowire session
 initialization using the VCCV AVP [RFC5085].
 The CV Type Indicators field in the OAM capability TLV or VCCV AVP
 defines a bitmask used to indicate the specific OAM capabilities that
 the PE can use over the PW being established.

Aissaoui, et al. Standards Track [Page 16] RFC 6310 PW OAM Message Mapping July 2011

 A CV type of 0x04 or 0x10 [RFC5885] indicates that BFD is used for PW
 fault detection only.  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 [RFC5880] will be
 used:
   0 -  No diagnostic
   1 -  Control detection time expired
   3 -  Neighbor signaled session down
   7 -  Administratively Down
 A PE using VCCV-BFD MUST use diagnostic code 0 to indicate to its
 peer PE that it is correctly receiving BFD control messages.  It MUST
 use diagnostic code 1 to indicate to its peer that it has stopped
 receiving BFD control messages and will thus declare the PW to be
 down in the receive direction.  It MUST use diagnostic code 3 to
 confirm to its peer that the BFD session is going down after
 receiving diagnostic code 1 from this peer.  In this case, it will
 declare the PW to be down in the transmit direction.  A PE MUST use
 diagnostic code 7 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 the LDP Status TLV in the case
 of MPLS or MPLS/IP PSN, or through the appropriate L2TP codes in the
 Circuit Status AVP in the case of L2TPv3/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 uses 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
 As specified in [RFC5085], the PEs negotiate the use of VCCV during
 PW setup.  When a PW transported over an MPLS-PSN is established
 using LDP, the PEs negotiate the use of the VCCV capabilities using
 the optional VCCV Capability Advertisement Sub-TLV parameter in the
 Interface Parameter Sub-TLV field of the LDP PW ID FEC or using an
 Interface Parameters TLV of the LDP Generalized PW ID FEC.  In the
 case of L2TPv3/IP PSNs, the PEs negotiate the use of VCCV during the
 pseudowire session initialization using VCCV AVP.

Aissaoui, et al. Standards Track [Page 17] RFC 6310 PW OAM Message Mapping July 2011

 Note that a defect that causes the generation of the "PW not
 forwarding code" (diagnostic code 6 or 8) does not necessarily result
 in the BFD session going down.  However, if the BFD session times
 out, then diagnostic code 1 MUST be used since it signals a state
 change of the BFD session itself.  In general, when a BFD session
 changes state, the PEs MUST use state change diagnostic codes 0, 1,
 3, and 7 in accordance with [RFC5880], and they MUST override any of
 the AC/PW status diagnostic codes (codes 6 or 8) that may have been
 signaled prior to the BFD session changing state.
 The forward and reverse defect indications used in this document map
 to the following BFD codes:
        Forward defect indication corresponds to the logical OR of:
  • Concatenated Path Down (BFD diagnostic code 06)
  • Pseudowire Not Forwarding (PW status code 0x00000001).
        Reverse defect indication corresponds to:
  • Reverse Concatenated Path Down (BFD diagnostic code 08).
 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 6.1, these CV types SHOULD NOT be
 used when the PW is established with the LDP or L2TP control plane.

6.2. PW Defect State Entry/Exit

6.2.1. PW Receive Defect State Entry/Exit Criteria

 PE1, as downstream PE, will enter the PW receive defect state if one
 or more of the following occurs:
 o  It receives a forward defect indication (FDI) from PE2 indicating
    either a receive defect on the remote AC or that PE2 detected or
    was notified of downstream PW fault.
 o  It detects loss of connectivity on the PSN tunnel upstream of PE1,
    which affects the traffic it receives from PE2.
 o  It detects a loss of PW connectivity through VCCV-BFD or VCCV-
    PING, which affects the traffic it receives from PE2.

Aissaoui, et al. Standards Track [Page 18] RFC 6310 PW OAM Message Mapping July 2011

 Note that if the PW control session (LDP session, the L2TP session,
 or the L2TP control connection) between the PEs fails, the PW is torn
 down and needs to be re-established.  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 met.  Note that this may result in a transition to the
 PW operational state or the PW transmit defect state.
 o  All previously detected defects have disappeared, and
 o  PE2 cleared the FDI, if applicable.

6.2.2. PW Transmit Defect State Entry/Exit Criteria

 PE1, as upstream PE, will enter the PW transmit defect state if the
 following conditions occur:
 o  It receives a Reverse Defect Indication (RDI) from PE2 indicating
    either a transmit fault on the remote AC or that PE2 detected or
    was notified of a upstream PW fault, and
 o  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 RDI, or it has entered the PW receive defect
 state.
 For a PW over L2TPv3/IP 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.

7. Procedures for ATM PW Service

 The following procedures apply to Asynchronous Transfer Mode (ATM)
 pseudowires [RFC4717].  ATM terminology is explained in Appendix A.2
 of this document.

7.1. AC Receive Defect State Entry/Exit Criteria

 When operating in the coupled OAM loops mode, PE1 enters the AC
 receive defect state when any of the following conditions are met:
 a. It detects or is notified of a physical layer fault on the ATM
    interface.

Aissaoui, et al. Standards Track [Page 19] RFC 6310 PW OAM Message Mapping July 2011

 b. It receives an end-to-end Flow 4 OAM (F4) Alarm Indication Signal
    (AIS) OAM flow on a Virtual Path (VP) AC or an end-to-end Flow 5
    (F5) AIS OAM flow on a Virtual Circuit (VC) as per ITU-T
    Recommendation I.610 [I.610], indicating that the ATM VPC or VCC
    is down in the adjacent Layer 2 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 endpoint.
 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 previously detected defects 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 previously detected defects 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 [I.610].

7.2. AC Transmit Defect State Entry/Exit Criteria

 When operating in the coupled OAM loops 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 operator has
    provisioned segment OAM and the PE is not a segment endpoint.

Aissaoui, et al. Standards Track [Page 20] RFC 6310 PW OAM Message Mapping July 2011

 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 [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.

7.3. Consequent Actions

 In the remainder of this section, the text refers to AIS, RDI, and CC
 without specifying whether there 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 [I.610].

7.3.1. 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 defect was detected by PE1 without receiving FDI from
    PE2, PE1 MUST assume PE2 has no knowledge of the defect and MUST
    notify PE2 by sending RDI.
 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 RDI to PE2, if applicable.

7.3.2. 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 RDI from
    PE2, PE1 MUST assume PE2 has no knowledge of the defect and MUST
    notify PE2 by sending FDI.

Aissaoui, et al. Standards Track [Page 21] RFC 6310 PW OAM Message Mapping July 2011

 On exit from the PW Transmit Defect State:
 a. PE1 MUST cease RDI insertion into the corresponding AC.
 b. PE1 MUST clear the FDI to PE2, if applicable.

7.3.3. 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 time out and cause the CE or ATM switch to
 enter the ATM AIS state.

7.3.4. 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 FDI 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:
 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 FDI to PE2.
 c. PE1 MUST cease the generation of CC cells on the corresponding PW,
    if applicable.

Aissaoui, et al. Standards Track [Page 22] RFC 6310 PW OAM Message Mapping July 2011

 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 FDI 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 FDI 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 FDI to PE2, if applicable.
 c. PE1 MUST resume any CC cell generation on the corresponding PW, if
    applicable.

7.3.5. AC Transmit Defect State Entry/Exit

 On entry to the AC transmit defect state and when operating in the
 coupled OAM loops mode:
  • PE1 MUST send RDI to PE2.
 On exit from the AC transmit defect state and when operating in the
 coupled OAM loops mode:
  • PE1 MUST clear the RDI to PE2.

Aissaoui, et al. Standards Track [Page 23] RFC 6310 PW OAM Message Mapping July 2011

8. Procedures for Frame Relay PW Service

 The following procedures apply to Frame Relay (FR) pseudowires
 [RFC4619].  Frame Relay (FR) terminology is explained in Appendix A.1
 of this document.

8.1. AC Receive Defect State Entry/Exit Criteria

 PE1 enters the AC receive defect state if one or more of the
 following conditions are met:
 a. A Permanent Virtual Circuit (PVC) is not deleted from the FR
    network and the FR network explicitly indicates in a full status
    report (and optionally by the asynchronous status message) that
    this PVC is inactive [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 [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 previously detected
 defects have disappeared.

8.2. AC Transmit Defect State Entry/Exit Criteria

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

8.3. Consequent Actions

8.3.1. PW Receive Defect State Entry/Exit

 The A (Active) bit indicates whether the FR PVC is ACTIVE (1) or
 INACTIVE (0) as explained in [RFC4591].
 On entry to the PW receive defect state:
 a. PE1 MUST clear the Active bit 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 FDI from
    PE2, PE1 MUST assume PE2 has no knowledge of the defect and MUST
    notify PE2 by sending RDI.

Aissaoui, et al. Standards Track [Page 24] RFC 6310 PW OAM Message Mapping July 2011

 On exit from the PW receive defect state:
 a. PE1 MUST set the Active bit 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 RDI to PE2, if applicable.

8.3.2. PW Transmit Defect State Entry/Exit

 On entry to the PW transmit defect state:
 a. PE1 MUST clear the Active bit 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 RDI from PE2, PE1
    MUST assume PE2 has no knowledge of the defect and MUST notify PE2
    by sending FDI.
 On exit from the PW transmit defect state:
 a. PE1 MUST set the Active bit 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 transmit defect state to the PW receive
    defect state.
 b. PE1 MUST clear the FDI to PE2, if applicable.

8.3.3. 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.

8.3.4. AC Receive Defect State Entry/Exit

 On entry to the AC receive defect state:
  • PE1 MUST send FDI to PE2.

Aissaoui, et al. Standards Track [Page 25] RFC 6310 PW OAM Message Mapping July 2011

 On exit from the AC receive defect state:
  • PE1 MUST clear the FDI to PE2.

8.3.5. AC Transmit Defect State Entry/Exit

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

9. Procedures for TDM PW Service

 The following procedures apply to SAToP [RFC4553], CESoPSN [RFC5086]
 and TDMoIP [RFC5087].  These technologies utilize the single emulated
 OAM loop mode.  RFC 5087 distinguishes between trail-extended and
 trail-terminated scenarios; the former is essentially the single
 emulated loop model.  The latter applies to cases where the NS
 networks are run by different operators and defect notifications are
 not propagated across the PW.
 Since TDM is inherently real-time in nature, many OAM indications
 must be generated or forwarded with minimal delay.  This requirement
 rules out the use of messaging protocols, such as PW status messages.
 Thus, for TDM PWs, alternate mechanisms are employed.
 The fact that TDM PW packets are sent at a known constant rate can be
 exploited as an OAM mechanism.  Thus, a PE enters the PW receive
 defect state whenever a preconfigured number of TDM PW packets do not
 arrive in a timely fashion.  It exits this state when packets once
 again arrive at their 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 PWE3 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 upstream PE to signal NS network defects to
 the downstream 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 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.
 L bits and R bits are further described in [RFC5087].

Aissaoui, et al. Standards Track [Page 26] RFC 6310 PW OAM Message Mapping July 2011

9.1. 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., as described in [G.775]).
 b. It is notified of a previous physical layer fault by detecting
    AIS.
 The exact conditions under which a PE enters and exits the AIS state
 are defined in [G.775].  Note that Loss of Signal and AIS detection
 can be performed by PEs for both structure-agnostic and structure-
 aware TDM PW types.  Note that PEs implementing structure-agnostic
 PWs cannot detect Loss of Alignment.

9.2. AC Transmit Defect State Entry/Exit Criteria

 PE1 enters the AC transmit defect state when it detects RDI according
 to the criteria in [G.775].  Note that PEs implementing structure-
 agnostic PWs cannot detect RDI.

9.3. Consequent Actions

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 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:
 a. PE1 MUST cease AIS insertion into the corresponding TDM AC.
 b. 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.

9.3.2. PW Transmit Defect State Entry/Exit

 On entry to the PW Transmit Defect State:
  • A structure-aware PE1 MUST commence RDI insertion into the

corresponding AC.

Aissaoui, et al. Standards Track [Page 27] RFC 6310 PW OAM Message Mapping July 2011

 On exit from the PW Transmit Defect State:
  • 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.

9.3.3. 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.
 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 L bit in PW packets sent towards PE2.
 c. A structure-aware PE1 MUST cease sending RDI towards CE1.

10. Procedures for CEP PW Service

 The following procedures apply to SONET/SDH Circuit Emulation
 [RFC4842].  They are based on the single emulated OAM loop mode.
 Since SONET and SDH are inherently real-time in nature, many OAM
 indications must be generated or forwarded with minimal delay.  This
 requirement rules out the use of messaging protocols, such as PW
 status messages.  Thus, for CEP PWs alternate mechanisms are
 employed.

Aissaoui, et al. Standards Track [Page 28] RFC 6310 PW OAM Message Mapping July 2011

 The CEP PWE3 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 upstream PE to signal to the downstream PE a defect in
 its local attachment circuit.  The R bit is a PW reverse defect
 indication used by the PE to signal PSN failures to the remote PE.
 The combination of N and P bits is used by the local PE to signal
 loss of pointer to the remote PE.
 The fact that CEP PW packets are sent at a known constant rate can be
 exploited as an OAM mechanism.  Thus, a PE enters the PW receive
 defect state when it loses packet synchronization.  It exits this
 state when it regains packet synchronization.  See [RFC4842] for
 further details.

10.1. Defect States

10.1.1. PW Receive Defect State Entry/Exit

 In addition to the conditions specified in Section 6.2.1, PE1 will
 enter the PW receive defect state when one of the following becomes
 true:
 o  It receives packets with the L bit set.
 o  It receives packets with both the N and P bits set.
 o  It loses packet synchronization.

10.1.2. PW Transmit Defect State Entry/Exit

 In addition to the conditions specified in Section 6.2.2, PE1 will
 enter the PW transmit defect state if it receives packets with the R
 bit set.

10.1.3. AC Receive Defect State Entry/Exit

 PE1 enters the AC receive defect state when 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.).
 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 [G.707] and [G.783].

Aissaoui, et al. Standards Track [Page 29] RFC 6310 PW OAM Message Mapping July 2011

10.1.4. AC Transmit Defect State Entry/Exit

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

10.2. Consequent Actions

10.2.1. 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.
    See [RFC4842].
 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.

10.2.2. 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.

10.2.3. 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.

Aissaoui, et al. Standards Track [Page 30] RFC 6310 PW OAM Message Mapping July 2011

 On exit from the AC receive defect state:
 a. PE1 MUST cease overwriting PW content with AIS-P/V and return to
    forwarding valid data in PW packets sent towards PE2.
 b. PE1 MUST clear the L bit in PW packets sent towards PE2.
 See [RFC4842] for further details.

11. Security Considerations

 The mapping messages described in this document do not change the
 security functions inherent in the actual messages.  All generic
 security considerations applicable to PW traffic specified in Section
 10 of [RFC3985] are applicable to NS OAM messages transferred inside
 the PW.
 Security considerations in Section 10 of RFC 5085 for VCCV apply to
 the OAM messages thus transferred.  Security considerations
 applicable to the PWE3 control protocol of RFC 4447 Section 8.2 apply
 to OAM indications transferred using the LDP status message.
 Since the mechanisms of this document enable propagation of OAM
 messages and fault conditions between native service networks and
 PSNs, continuity of the end-to-end service depends on a trust
 relationship between the operators of these networks.  Security
 considerations for such scenarios are discussed in Section 7 of
 [RFC5254].

12. Contributors and Acknowledgments

 Mustapha Aissaoui, Peter Busschbach, Luca Martini, Monique Morrow,
 Thomas Nadeau, and Yaakov (J) Stein, were each, in turn, editors of
 one or more revisions of this document.  All of the above were
 contributing authors, as was Dave Allan, david.i.allan@ericsson.com.
 The following contributed significant ideas or text:
    Matthew Bocci, matthew.bocci@alcatel-lucent.co.uk
    Simon Delord, Simon.A.DeLord@team.telstra.com
    Yuichi Ikejiri, y.ikejiri@ntt.com
    Kenji Kumaki, kekumaki@kddi.com
    Satoru Matsushima, satoru.matsushima@tm.softbank.co.jp
    Teruyuki Oya, teruyuki.oya@tm.softbank.co.jp
    Carlos Pignataro, cpignata@cisco.com
    Vasile Radoaca, vasile.radoaca@alcatel-lucent.com
    Himanshu Shah, hshah@ciena.com
    David Watkinson, david.watkinson@alcatel-lucent.com

Aissaoui, et al. Standards Track [Page 31] RFC 6310 PW OAM Message Mapping July 2011

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

13. References

13.1. Normative References

 [RFC2119]           Bradner, S., "Key words for use in RFCs to
                     Indicate Requirement Levels", BCP 14, RFC 2119,
                     March 1997.
 [RFC4379]           Kompella, K. and G. Swallow, "Detecting Multi-
                     Protocol Label Switched (MPLS) Data Plane
                     Failures", RFC 4379, February 2006.
 [RFC4447]           Martini, L., Rosen, E., El-Aawar, N., Smith, T.,
                     and G. Heron, "Pseudowire Setup and Maintenance
                     Using the Label Distribution Protocol (LDP)",
                     RFC 4447, April 2006.
 [RFC4553]           Vainshtein, A. and YJ. Stein, "Structure-Agnostic
                     Time Division Multiplexing (TDM) over Packet
                     (SAToP)", RFC 4553, June 2006.
 [RFC4591]           Townsley, M., Wilkie, G., Booth, S., Bryant, S.,
                     and J. Lau, "Frame Relay over Layer 2 Tunneling
                     Protocol Version 3 (L2TPv3)", RFC 4591,
                     August 2006.
 [RFC4619]           Martini, L., Kawa, C., and A. Malis,
                     "Encapsulation Methods for Transport of Frame
                     Relay over Multiprotocol Label Switching (MPLS)
                     Networks", RFC 4619, September 2006.
 [RFC4717]           Martini, L., Jayakumar, J., Bocci, M., El-Aawar,
                     N., Brayley, J., and G. Koleyni, "Encapsulation
                     Methods for Transport of Asynchronous Transfer
                     Mode (ATM) over MPLS Networks", RFC 4717,
                     December 2006.
 [RFC4842]           Malis, A., Pate, P., Cohen, R., and D. Zelig,
                     "Synchronous Optical Network/Synchronous Digital
                     Hierarchy (SONET/SDH) Circuit Emulation over
                     Packet (CEP)", RFC 4842, April 2007.

Aissaoui, et al. Standards Track [Page 32] RFC 6310 PW OAM Message Mapping July 2011

 [RFC5036]           Andersson, L., Minei, I., and B. Thomas, "LDP
                     Specification", RFC 5036, October 2007.
 [RFC5085]           Nadeau, T. and C. Pignataro, "Pseudowire Virtual
                     Circuit Connectivity Verification (VCCV): A
                     Control Channel for Pseudowires", RFC 5085,
                     December 2007.
 [RFC5641]           McGill, N. and C. Pignataro, "Layer 2 Tunneling
                     Protocol Version 3 (L2TPv3) Extended Circuit
                     Status Values", RFC 5641, August 2009.
 [RFC5880]           Katz, D. and D. Ward, "Bidirectional Forwarding
                     Detection (BFD)", RFC 5880, June 2010.
 [RFC5885]           Nadeau, T. and C. Pignataro, "Bidirectional
                     Forwarding Detection (BFD) for the Pseudowire
                     Virtual Circuit Connectivity Verification
                     (VCCV)", RFC 5885, June 2010.
 [G.707]             "Network node interface for the synchronous
                     digital hierarchy", ITU-T Recommendation G.707,
                     December 2003.
 [G.775]             "Loss of Signal (LOS), Alarm Indication Signal
                     (AIS) and Remote Defect Indication (RDI) defect
                     detection and clearance criteria for PDH
                     signals", ITU-T Recommendation G.775,
                     October 1998.
 [G.783]             "Characteristics of synchronous digital hierarchy
                     (SDH) equipment functional blocks", ITU-
                     T Recommendation G.783, March 2006.
 [I.610]             "B-ISDN operation and maintenance principles and
                     functions", ITU-T Recommendation I.610,
                     February 1999.
 [Q.933]             "ISDN Digital Subscriber Signalling System No. 1
                     (DSS1)  Signalling specifications for frame mode
                     switched and permanent virtual connection control
                     and status monitoring", ITU- T Recommendation
                     Q.993, February 2003.

Aissaoui, et al. Standards Track [Page 33] RFC 6310 PW OAM Message Mapping July 2011

13.2. Informative References

 [RFC0792]           Postel, J., "Internet Control Message Protocol",
                     STD 5, RFC 792, September 1981.
 [RFC3031]           Rosen, E., Viswanathan, A., and R. Callon,
                     "Multiprotocol Label Switching Architecture",
                     RFC 3031, January 2001.
 [RFC3209]           Awduche, D., Berger, L., Gan, D., Li, T.,
                     Srinivasan, V., and G. Swallow, "RSVP-TE:
                     Extensions to RSVP for LSP Tunnels", RFC 3209,
                     December 2001.
 [RFC3916]           Xiao, X., McPherson, D., and P. Pate,
                     "Requirements for Pseudo-Wire Emulation Edge-to-
                     Edge (PWE3)", RFC 3916, September 2004.
 [RFC3931]           Lau, J., Townsley, M., and I. Goyret, "Layer Two
                     Tunneling Protocol - Version 3 (L2TPv3)",
                     RFC 3931, March 2005.
 [RFC3985]           Bryant, S. and P. Pate, "Pseudo Wire Emulation
                     Edge-to-Edge (PWE3) Architecture", RFC 3985,
                     March 2005.
 [RFC4023]           Worster, T., Rekhter, Y., and E. Rosen,
                     "Encapsulating MPLS in IP or Generic Routing
                     Encapsulation (GRE)", RFC 4023, March 2005.
 [RFC4377]           Nadeau, T., Morrow, M., Swallow, G., Allan, D.,
                     and S. Matsushima, "Operations and Management
                     (OAM) Requirements for Multi-Protocol Label
                     Switched (MPLS) Networks", RFC 4377,
                     February 2006.
 [RFC4385]           Bryant, S., Swallow, G., Martini, L., and D.
                     McPherson, "Pseudowire Emulation Edge-to-Edge
                     (PWE3) Control Word for Use over an MPLS PSN",
                     RFC 4385, February 2006.
 [RFC4446]           Martini, L., "IANA Allocations for Pseudowire
                     Edge to Edge Emulation (PWE3)", BCP 116,
                     RFC 4446, April 2006.

Aissaoui, et al. Standards Track [Page 34] RFC 6310 PW OAM Message Mapping July 2011

 [RFC4454]           Singh, S., Townsley, M., and C. Pignataro,
                     "Asynchronous Transfer Mode (ATM) over Layer 2
                     Tunneling Protocol Version 3 (L2TPv3)", RFC 4454,
                     May 2006.
 [RFC5086]           Vainshtein, A., Sasson, I., Metz, E., Frost, T.,
                     and P. Pate, "Structure-Aware Time Division
                     Multiplexed (TDM) Circuit Emulation Service over
                     Packet Switched Network (CESoPSN)", RFC 5086,
                     December 2007.
 [RFC5087]           Stein, Y(J)., Shashoua, R., Insler, R., and M.
                     Anavi, "Time Division Multiplexing over IP
                     (TDMoIP)", RFC 5087, December 2007.
 [RFC5254]           Bitar, N., Bocci, M., and L. Martini,
                     "Requirements for Multi-Segment Pseudowire
                     Emulation Edge-to-Edge (PWE3)", RFC 5254,
                     October 2008.
 [RFC6073]           Martini, L., Metz, C., Nadeau, T., Bocci, M., and
                     M. Aissaoui, "Segmented Pseudowire", RFC 6073,
                     January 2011.
 [Eth-OAM-Inter]     Mohan, D., Bitar, N., DeLord, S., Niger, P.,
                     Sajassi, A., and R. Qiu, "MPLS and Ethernet OAM
                     Interworking", Work in Progress, March 2011.
 [Static-PW-Status]  Martini, L., Swallow, G., Heron, G., and M.
                     Bocci, "Pseudowire Status for Static
                     Pseudowires", Work in Progress, June 2011.
 [I.620]             "Frame relay operation and maintenance principles
                     and functions", ITU-T Recommendation I.620,
                     October 1996.

Aissaoui, et al. Standards Track [Page 35] RFC 6310 PW OAM Message Mapping July 2011

Appendix A. Native Service Management (Informative)

A.1. Frame Relay Management

 The management of Frame Relay Bearer Service (FRBS) connections can
 be accomplished through two distinct methodologies:
 a. Based on [Q.933], Annex A, Link Integrity Verification procedure,
    where STATUS and STATUS ENQUIRY signaling messages are sent using
    DLCI=0 over a given User-Network Interface (UNI) and Network-
    Network Interface (NNI) physical link.
 b. Based on FRBS Local Management Interface (LMI), and similar to ATM
    Integrated LMI (ILMI) where LMI is common in private Frame Relay
    networks.
 In addition, ITU-T I.620 [I.620] addressed Frame Relay loopback.
 This Recommendation was withdrawn in 2004, and its deployment was
 limited.
 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. Frame Relay STATUS messages in response to Frame Relay 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 Data Link Connection (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 Native
 Service/Attachment Circuit (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.

Aissaoui, et al. Standards Track [Page 36] RFC 6310 PW OAM Message Mapping July 2011

A.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).  [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.  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.
 The Remote Defect Indication (RDI) sends a message to the
 transmitting terminal that an error has been detected.  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.

Aissaoui, et al. Standards Track [Page 37] RFC 6310 PW OAM Message Mapping July 2011

Appendix B. PW Defects and Detection Tools

B.1. PW Defects

 Possible defects that impact PWs are the following:
 a. Physical layer defect in the PSN interface.
 b. PSN tunnel failure that 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:
 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.

B.2. 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 pseudowire [RFC3985] and [RFC4385], it has the
 ability to detect packet loss.  Translation of congestion detection
 to PW defect states is beyond the scope of this document.
 There are congestion alarms that 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.

B.3. PW Defect Detection Tools

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

Aissaoui, et al. Standards Track [Page 38] RFC 6310 PW OAM Message Mapping July 2011

 Physical Layer defect detection and notification mechanisms include
 SONET/SDH Loss of Signal (LOS), Loss of Alignment (LOA), and AIS/RDI.
 PSN defect detection mechanisms vary according to the PSN type.
 For PWs over L2TPv3/IP PSNs, with L2TP as encapsulation protocol, the
 defect detection mechanisms described in [RFC3931] apply.  These
 include, 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
 tools Ping and Traceroute, based on ICMP Echo Messages [RFC0792]
 apply and can be used to detect defects on the IP PSN.  Additionally,
 VCCV-Ping [RFC5085] and VCCV-BFD [RFC5885] can also be used to detect
 defects at the individual pseudowire level.
 For PWs over MPLS or MPLS/IP PSNs, 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 [RFC5885] for
    LSP tunnel continuity checking.
 c. Furthermore, if Resource Reservation Protocol - Traffic
    Engineering (RSVP-TE) is used to set up 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.

B.4. 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.
 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).

Aissaoui, et al. Standards Track [Page 39] RFC 6310 PW OAM Message Mapping July 2011

Authors' Addresses

 Mustapha Aissaoui
 Alcatel-Lucent
 600 March Rd
 Kanata, ON  K2K 2E6
 Canada
 EMail: mustapha.aissaoui@alcatel-lucent.com
 Peter Busschbach
 Alcatel-Lucent
 67 Whippany Rd
 Whippany, NJ  07981
 USA
 EMail: busschbach@alcatel-lucent.com
 Luca Martini
 Cisco Systems, Inc.
 9155 East Nichols Avenue, Suite 400
 Englewood, CO  80112
 USA
 EMail: lmartini@cisco.com
 Monique Morrow
 Cisco Systems, Inc.
 Richtistrase 7
 CH-8304 Wallisellen
 Switzerland
 EMail: mmorrow@cisco.com
 Thomas Nadeau
 CA Technologies
 273 Corporate Dr.
 Portsmouth, NH  03801
 USA
 EMail: Thomas.Nadeau@ca.com
 Yaakov (Jonathan) Stein
 RAD Data Communications
 24 Raoul Wallenberg St., Bldg C
 Tel Aviv  69719
 Israel
 EMail: yaakov_s@rad.com

Aissaoui, et al. Standards Track [Page 40]

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