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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

      Pseudo-Wire Edge-to-Edge(PWE3)                      Thomas D. Nadeau
      Internet Draft                                        Monique Morrow
      Expiration Date: March 2006                            Cisco Systems
  
                                                          Peter Busschbach
      Dave Allan                                       Lucent Technologies
      Nortel Networks
                                                         Mustapha Aissaoui
                                                                   Alcatel
  
                                                                   Editors
  
                                                            September 2005
  
  
  
                    Pseudo Wire (PW) OAM Message Mapping
                     draft-ietf-pwe3-oam-msg-map-03.txt
  
  
  
   Status of this Memo
  
     By submitting this Internet-Draft, each author represents that any
     applicable patent or other IPR claims of which he or she is aware
     have been or will be disclosed, and any of which he or she becomes
     aware will be disclosed, in accordance with Section 6 of BCP 79.
     This document may not be modified, and derivative works of it may
     not be created, except to publish it as an RFC and to translate it
     into languages other than English.
  
     Internet-Drafts are working documents of the Internet Engineering
     Task Force (IETF), its areas, and its working groups. Note that
     other groups may also distribute working documents as Internet-
     Drafts.
  
     Internet-Drafts are draft documents valid for a maximum of six
     months and may be updated, replaced, or obsoleted by other
     documents at any time.  It is inappropriate to use Internet-Drafts
     as reference material or to cite them other than as "work in
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     The list of current Internet-Drafts can be accessed at
     http://www.ietf.org/ietf/1id-abstracts.txt.
  
     The list of Internet-Draft Shadow Directories can be accessed at
     http://www.ietf.org/shadow.html.
  
  Abstract
  
     This document specifies the mapping of defect states between a
     Pseudo Wire and the Attachment Circuits (AC) of the end-to-end
     emulated service.  This document covers the case whereby the ACs
  
  
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     and the PWs are of the same type in accordance to the PWE3
     architecture [PWEARCH] such that a homogenous PW service can be
     constructed.
  
  Table of Contents
  
     Status of this Memo.............................................1
     Abstract........................................................1
     Table of Contents...............................................2
     1 Conventions used in this document.............................4
     2 Contributors..................................................4
     3 Scope.........................................................4
     4 Terminology...................................................5
     5 Reference Model and Defect Locations..........................6
     6 Abstract Defect States........................................7
     7 PW Status and Defects.........................................8
      7.1 PW Defects.................................................9
         7.1.1 Packet Loss...........................................9
      7.2 Defect Detection and Notification..........................9
         7.2.1 Defect Detection Tools................................9
         7.2.2 Defect Detection Mechanism Applicability.............10
      7.3 Overview of fault notifications...........................11
         7.3.1 Use of Native Service notifications..................12
         7.3.2 The Use of PW Status for MPLS and MPLS-IP PSNs.......12
         7.3.3 The Use of L2TP STOPCCN and CDN......................13
         7.3.4 The Use of BFD Diagnostic Codes......................14
     8 PW Defect State Entry/Exit...................................16
      8.1 PW Forward Defect Entry/Exit..............................16
      8.2 PW reverse defect state entry/exit........................16
         8.2.1 PW reverse defects that require PE state synchronization
          ...........................................................17
     9 AC Defect States.............................................17
      9.1 FR ACs....................................................17
      9.2 ATM ACs...................................................18
         9.2.1 AC Forward Defect State Entry/Exit...................18
         9.2.2 AC Reverse Defect State Entry/Exit...................18
      9.3 Ethernet AC State.........................................18
     10 PW Forward Defect Entry/Exit procedures.....................19
      10.1 PW Forward Defect Entry Procedures.......................19
         10.1.1 FR AC procedures....................................19
         10.1.2 Ethernet AC Procedures..............................19
         10.1.3 ATM AC procedures...................................19
         10.1.4 Additional procedures for a FR PW, an ATM PW in the
         ææout-of-band ATM OAM over PW methodÆÆ, and an Ethernet PW...19
      10.2 PW Forward Defect Exit Procedures........................20
         10.2.1 FR AC procedures....................................20
         10.2.2 Ethernet AC Procedures..............................20
  
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         10.2.3 ATM AC procedures...................................20
         10.2.4 Additional procedures for a FR PW, an ATM PW in the
         ææout-of-band ATM OAM over PWÆÆ method, and an Ethernet PW...20
      10.3 PW Reverse Defect Entry Procedures.......................20
         10.3.1 FR AC procedures....................................20
         10.3.2 Ethernet AC Procedures..............................21
         10.3.3 ATM AC procedures...................................21
      10.4 PW Reverse Defect Exit Procedures........................21
         10.4.1 FR AC procedures....................................21
         10.4.2 Ethernet AC Procedures..............................21
         10.4.3 ATM AC procedures...................................21
      10.5 Procedures in FR Port Mode...............................21
      10.6 Procedures in ATM Port Mode..............................21
     11 AC Defect Entry/Exit Procedures.............................22
      11.1 AC Forward defect entry:.................................22
         11.1.1 Procedures for a FR PW, an ATM PW in the ææout-of-band
         ATM OAM over PWÆÆ method, or an Ethernet PW.................22
         11.1.2 Procedures for a ATM PW in the ææinband ATM OAM over PWÆÆ
         method.....................................................22
         11.1.3 Additional procedures for ATM ACs...................22
      11.2 AC Reverse defect entry..................................22
         11.2.1 Procedures for a FR PW, an ATM PW in the ææout-of-band
         ATM OAM over PWÆÆ method, or an Ethernet PW.................22
         11.2.2 Procedures for a ATM PW in the ææinband ATM OAM over PWÆÆ
         method.....................................................23
      11.3 AC Forward Defect Exit...................................23
         11.3.1 Procedures for a FR PW, an ATM PW in the ææout-of-band
         ATM OAM over PWÆÆ method, or an Ethernet PW.................23
         11.3.2 Procedures for a ATM PW in the ææinband ATM OAM over PWÆÆ
         method.....................................................23
         11.3.3 Additional procedures for ATM ACs...................24
      11.4 AC Reverse Defect Exit...................................24
         11.4.1 Procedures for a FR PW, an ATM PW in the ææout-of-band
         ATM OAM over PWÆÆ method, or an Ethernet PW.................24
         11.4.2 Procedures for a ATM PW in the ææinband ATM OAM over PWÆÆ
         method.....................................................24
     12 SONET Encapsulation (CEP)...................................24
     13 TDM Encapsulation...........................................24
     14 Appendix A: Native Service Management.......................26
      14.1 Frame Relay Management...................................26
      14.2 ATM Management...........................................26
      14.3 Ethernet Management......................................27
     15 Security Considerations.....................................27
     16 Acknowledgments.............................................28
     17 References..................................................28
     18 Intellectual Property Disclaimer............................29
  
  
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     19 Full Copyright Statement....................................29
     20 Authors' Addresses..........................................30
  
   1 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.
  
   2 Contributors
  
     Thomas D. Nadeau, tnadeau@cisco.com
  
     Monique Morrow, mmorrow@cisco.com
  
     Peter B. Busschbach, busschbach@lucent.com
  
     Mustapha Aissaoui, mustapha.aissaoui@alcatel.com
  
     Matthew Bocci, matthew.bocci@alcatel.co.uk
  
     David Watkinson, david.watkinson@alcatel.com
  
     Yuichi Ikejiri, y.ikejiri@ntt.com
  
     Kenji Kumaki, kekumaki@kddi.com
  
     Satoru Matsushima, satoru@ft.solteria.net
  
     David Allan, dallan@nortelnetworks.com
  
     Himanshu Shah, hshah@ciena.com
  
     Simon Delord, simon.delord@francetelecom.com
  
     Vasile Radoaca, vradoaca@westridgenetworks.com
  
   3 Scope
  
     This document specifies the mapping of defect states between a
     Pseudo Wire and the Attachment Circuits (AC) of the end-to-end
     emulated service.  This document covers the case whereby the ACs
     and the PWs are of the same type in accordance to the PWE3
     architecture [PWEARCH] such that a homogenous PW service can be
     constructed.
  
     Ideally only PW and AC defects need be propagated into the Native
     Service (NS), and NS OAM mechanisms are transported transparently
     over the PW. Some homogenous scenarios use PW specific OAM
     mechanisms to synchronize defect state between PEs due to
     discontinuities in native service OAM between the AC and the PW
     (e.g. FR LMI), or lack of native service OAM (e.g. Ethernet).
  
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     The objective of this document is to standardize the behavior of
     PEs with respects to failures on PWs and ACs, so that there is no
     ambiguity about the alarms generated and consequent actions
     undertaken by PEs in response to specific failure conditions.
  
     This document covers PWE over MPLS PSN, PWE over IP PSN and PWE
     over L2TP PSN.
  
   4 Terminology
  
        AIS   Alarm Indication Signal
        AC    Attachment circuit
        BDI   Backward Defect Indication
        CC    Continuity Check
        CE    Customer Edge
        CPCS  Common Part Convergence Sublayer
        DLC   Data Link Connection
        FDI   Forward Defect Indication
        FRBS  Frame Relay Bearer Service
        IWF   Interworking Function
        LB    Loopback
        NE    Network Element
        NS    Native Service
        OAM   Operations and Maintenance
        PE    Provider Edge
        PW    Pseudowire
        PSN   Packet Switched Network
        RDI   Remote Defect Indication
        SDU   Service Data Unit
        VCC   Virtual Channel Connection
        VPC   Virtual Path Connection
  
     The rest of this document will follow the following convention:
  
     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 [MPLS-in-IP], 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 [L2TPv3] as the
     tunneling technology, will be referred to as L2TP-IP PSN.
  
     If LSP-Ping is run over a PW as described in [VCCV], it will be
     referred to as VCCV-Ping.
  
     If BFD is run over a PW as described in [VCCV], it will be
     referred to as 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 ææpeerÆÆ PE
     and the attachment circuit associated with the far end PW
     termination is the ææremote ACÆÆ.
  
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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 and what the PE may explicitly know about information
     transfer capabilities of the PW service.
  
     A forward defect is one that impacts information transfer to the
     observing PE. It impacts the observing PEÆs ability to receive
     information. A forward defect MAY also imply impact on information
     sent or relayed by the observer (and as it cannot receive is
     therefore unknowable) and so the forward defect state is
     considered to be a superset of the two defect states.
  
     A reverse defect is one that uniquely impacts information sent or
     relayed by observer.
  
     At the present time code points for forward defect and reverse
     defect notifications have not been specified for BFD and LDP PW
     Status signaling. These are referred to as ææforward defectÆÆ and
     ææreverse defectÆÆ indications as placeholders for code point
     assignment. However, a mapping to existing PW status code points
     [PWE3-IANA] may be performed:
  
          Forward defect - corresponds to the logical OR of
                  Local Attachment Circuit (ingress) Receive Fault
                                  AND
                  Local PSN-facing PW (egress) Transmit Fault
  
          Reverse defect - corresponds to the logical OR of
                  Local Attachment Circuit (egress) Transmit Fault
                                  AND
                  Local PSN-facing PW (ingress) Receive Fault
  
   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 ---------------->|
  
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       Customer                                                Customer
        Edge 1                                                  Edge 2
                  Figure 1: PWE3 Network Defect Locations
     In all interworking scenarios described in this document, it is
     assumed that at PE1 the AC and the PW are of the same type. The
     procedures described in this document exclusively apply to PE1.
     PE2 for a homogenous service implements the identical
     functionality (although it is not required to as long as the
     notifications across the PWs are consistent).
  
     The following is a brief description of the defect locations:
  
     (a)  Defect in the first L2 network (N1). This covers any defect
          in the N1 which impacts all or a subset of ACs terminating in
          PE1. The defect is conveyed to PE1 and to the remote L2
          network (N2) using the native service specific OAM defect
          indication.
     (b)  Defect on a PE1 AC interface.
     (c)  Defect on a PE PSN interface.
     (d)  Defect in the PSN network. This covers any defect in the PSN
          which impacts all or a subset of the PSN tunnels and 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
          control plane, i.e., signaling and routing, messages do not
          necessarily follow the path of the user plane messages.
          Defect in the control plane are detected and conveyed
          separately through control plane mechanisms. However, in some
          cases, they have an impact on the status of the PW as
          explained in the next section.
     (e)  Defect in the second L2 network (N2). This covers any defect
          in N2 which impacts all or a subset of ACs terminating in PE2
          (which is considered a ææremote AC defectÆÆ in the context of
          procedures outlined in this draft). The defect is conveyed to
          PE2 and to the remote L2 network (N1) using the native
          service OAM defect indication.
     (f)  Defect on a PE2 AC interface (which is also considered a
          ææremote AC defectÆÆ in the context of this draft).
  
   6 Abstract Defect States
  
     PE1 is obliged to track four abstract defect states that reflect
     the observed state of both directions of the PW service on both
     the AC and the PW sides. Faults may impact only one or both
     directions of the PW.
  
     The observed state is a combination of faults directly detected by
     PE1, or faults it has been made aware of via notifications.
  
                                +-----+
             ----AC forward---->|     |-----PW reverse---->
       CE1                      | PE1 |                       PE2/CE2
  
  
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             <---AC reverse-----|     |<----PW forward-----
                                +-----+
  
      (arrows indicate direction of user traffic impacted by a defect)
      Figure 2: Forward and Reverse Defect States and Notifications
     PE1 will directly detect or be notified of AC forward and PW
     forward defects as they occur upstream of PE1 and impact traffic
     being sent to PE1.
     In Figure 2, PE1 may be notified of a forward defect in the AC by
     receiving a Forward Defect indication, e.g., ATM AIS, from CE1.
     This defect impacts the ability of PE1 to receive user traffic
     from CE1 on the AC. PE1 can also directly detect this defect if it
     resulted from a failure of the receive side in the local port or
     link over which the AC is configured.
     Similarly, PE1 may detect or be notified of a forward defect in
     the PW by receiving a Forward Defect indication from PE2. This
     notification can either be a ææLocal PSN-facing PW (egress)
     Transmit FaultÆÆ or a ææLocal Attachment Circuit (ingress) Receive
     FaultÆÆ. This defect impacts the ability of PE1 to receive user
     traffic from CE2.
     Note that the AC or PW Forward Defect notification is sent in the
     same direction as the user traffic impacted by the defect.
  
     PE1 will only be notified of AC reverse and PW reverse defects as
     they universally will be detected by other devices and only impact
     traffic that has already been relayed by PE1. In Figure 2, PE1 may
     be notified of a reverse defect in the AC by receiving a Reverse
     Defect indication, e.g., ATM RDI, from CE1. This defect impacts
     the ability of PE1 to send user traffic to CE1 on the AC.
     Similarly, PE1 may be notified of a reverse defect in the PW by
     receiving a Reverse Defect indication from PE2. This notification
     can either be a ææLocal PSN-facing PW (ingress) Receive FaultÆÆ or a
     ææLocal Attachment Circuit (egress) Transmit FaultÆÆ. This defect
     impacts the ability of PE1 to send user traffic to CE2.
     Note that the AC or PW Reverse Defect notification is sent in the
     reverse direction to the user traffic impacted by the defect.
  
     The procedures outlined in this document define the entry and exit
     criteria for each of the four states with respect to the set of
     potential ACs and PWs within the document scope and the consequent
     actions that PE1 must perform to properly interwork those
     notifications. The abstract defect states used by PE1 are common
     to all potential interworking combinations of PWs and ACs.
  
     When a PE has multiple sources of notifications from a peer (e.g.
     PSN control plane, LDP control plane, BFD), it is obliged to track
     all sources, but with respect to consequent actions the forward
     state ALWAYS has precedence over the reverse state.
  
   7 PW Status and Defects
  
  
  
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     This section describes possible PW defects, ways to detect them
     and consequent actions.
  
   7.1 PW Defects
  
     Possible defects that impact PWs are the following.
  
     . Physical layer defect in the PSN interface
  
     . PSN tunnel failure which results in a loss of connectivity
     between ingress and egress PE.
  
     . Control session failures between ingress and egress PE
  
     In case of an MPLS PSN and an MPLS-IP PSN there are additional
     defects:
  
     . 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.
  
     . 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.
  
     . Unintended self-replication; e.g., due to loops or denial-of-
     service attacks.
  
   7.1.1 Packet Loss
  
     Persistent congestion in the PSN or in a PE could impact the
     proper operation of the emulated service.
  
     A PE can detect packet loss resulting from congestion through
     several methods. If a PE uses the sequence number field in the
     PWE3 Control Word for a specific Pseudo Wire [PWEARCH], it has the
     ability to detect packet loss. [CONGESTION] discusses other
     possible mechanisms to detect congestion between PWs.
  
     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.
  
   7.2 Defect Detection and Notification
  
   7.2.1 Defect Detection Tools
  
     To detect the defects listed in 7.1, Service Providers have a
     variety of options available:
  
  
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     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 [L2TPv3] apply.
     Furthermore, the tools Ping and Traceroute, based on ICMP Echo
     Messages apply [ICMP].
  
     For PWE3 over an MPLS PSN and an MPLS-IP PSN, several tools can be
     used.
     . LSP-Ping and LSP-Traceroute( [LSPPING]) for LSP tunnel
     connectivity verification.
  
     . LSP-Ping with Bi-directional Forwarding Detection ([BFD]) for
     LSP tunnel continuity checking.
  
     .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 (see [RSVP-TE]), but only at the control
     plane.
  
     PW specific defect detection mechanisms:
  
     [VCCV] 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)
  
   7.2.2 Defect Detection Mechanism Applicability
  
     The discussion below is intended to give some perspective how
     tools mentioned in the previous section can be used to detect
     failures.
  
     Observations:
  
     . Tools like LSP-Ping and BFD can be run periodically or on
     demand. If used for defect detection, as opposed to diagnostic
     usage, they must be run periodically.
  
     . Control protocol failure indications, e.g. detected through L2TP
     Keep-alive messages or the RSVP-TE Hello messages, can be used to
  
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     detect many network failures. However, control protocol failures
     do not necessarily coincide with data plane failures. Therefore, a
     defect detection mechanism in the data plane is required to
     protect against all potential data plane failures. Furthermore,
     fault diagnosis mechanisms for data plane failures are required to
     further analyze detected failures.
  
     . For PWE3 over an MPLS PSN and an MPLS-IP PSN, it is effective to
     run a defect detection mechanism over a PSN Tunnel frequently and
     run one over every individual PW within that PSN Tunnel less
     frequently. However in case the PSN traffic is distributed over
     Equal Cost Multi Paths (ECMP), it may be difficult to guarantee
     that PSN OAM messages follow the same path as a specific PW. A
     Service Provider might therefore decide to focus on defect
     detection over PWs.
  
     . In MPLS networks, execution of LSP Ping would detect MPLS label
     errors, since it requests the receiving node to match the label
     with the original FEC that was used in the LSP set up. BFD can
     also be used since it relies on discriminators. A label error
     would result in a mismatch between the expected discriminator and
     the actual discriminator in the BFD control messages.
  
     . For PWE3 over an MPLS PSN and an MPLS-IP PSN, PEs could detect
     PSN label errors through the execution of LSP-Ping. However, use
     of VCCV is preferred as it is a more accurate detection tool for
     pseudowires.
     Furthermore, it can be run using a BFD mode, i.e., VCCV-BFD, which
     allows it to be used as a light-weight detection mechanism for
     PWs. If, due to a label error in the PSN, a PW would be terminated
     on the wrong egress PE, PEs would detect this through the
     execution of VCCV. LSP ping and/or LSP trace could then be used to
     diagnose the detected failure.
  
     Based on these observations, it is clear that a service provider
     has the disposal of a variety of tools. There are many factors
     that influence which combination of tools best meets its needs.
  
   7.3 Overview of fault notifications
     For a MPLS PSN and a IP PSN using MPLS-in-IP (MPLS-IP PSN), PW
     status signaling messages are used as the default mechanism for AC
     and PW status and defect notification [PWE3-CONTROL].
  
     For a IP PSN using L2TPv3, i.e., a L2TP-IP PSN, StopCCN and CDN
     messages are used for conveying defects in the PSN and PW
     respectively, while the Set-Link-Info (SLI) messages are used to
     convey status and defects in the AC and local L2 network.
  
     Optionally, PEs can negotiate the use of VCCV-BFD for both PW
     fault detection and AC/PW fault notifications as explained in
     Section 7.3.4. What BFD is used for is negotiated:
              i. not used
  
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             ii. used for PW fault detection only(which implies reverse
                 notifications). In this case fault notification is
                 still based on PW status messages.
            iii. used for both PW fault detection and all PW/AC fault
                 notifications. In this case PW status should not be
                 used.
  
     More details are provided in Section 7.3.4.
  
     PE1 will translate the PW defect states to the appropriate failure
     indications on the affected ACs. The exact procedures depend on
     the emulated protocols and will be discussed in the next sections.
  
   7.3.1 Use of Native Service notifications
     In the context of this document, ATM and unstructured SONET/TDM
     PWs are the only examples of a PW that has native service
     notification capability. Frame relay does have the FR OAM
     specification [FRF.19], but this is not commonly deployed. All
     other PWs use PW specific notification mechanisms.
  
     ATM PWs may optionally also use PW specific notification
     mechanisms.
  
     In normal, i.e., defect-free, operation, all the types of ATM OAM
     cells described in Section 14.2 are either terminated at the PE,
     for OAM segments terminating in the AC endpoint, or transparently
     carried over the PSN tunnel [PWE3-ATM]. This is referred to as
     ææinband ATM OAM over PWÆÆ and is the default method.
  
     An optional out-of band method based on relaying the ATM defect
     state over a PW specific defect indication mechanism is provided
     for PEÆs which cannot generate and/or transmit ATM OAM cells over
     the ATM PW. This is referred to as ææOut-of-band ATM OAM over PWÆÆ.
  
   7.3.2 The Use of PW Status for MPLS and MPLS-IP PSNs
     This document specifies the use of PW status signaling as the
     default mechanism for the purpose of conveying the status of a PW
     and ACs between PEs.
  
     For a MPLS PSN and a IP PSN using MPLS-in-IP (MPLS-IP PSN), PW
     status signaling messages are used as the default mechanism for AC
     and PW status and defect indication [PWE3-CONTROL].
  
     [PWE3-IANA] defines the following valid PW status codepoints:
     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
  
  
  
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     [PWE3-CONTROL] specifies that ææPseudo Wire forwardingÆÆ is used to
     clear all faults and that ææPseudo Wire Not ForwardingÆÆ is used to
     convey any other defects that cannot be represented by the other
     codepoints. The remaining codepoints map to the ææforward defectÆÆ
     and ææreverse defectÆÆ defined in this document as follows:
  
          Forward defect - corresponds to the logical OR of
                  Local Attachment Circuit (ingress) Receive Fault
                                  AND
                  Local PSN-facing PW (egress) Transmit Fault
  
          Reverse defect - corresponds to the logical OR of
                  Local Attachment Circuit (egress) Transmit Fault
                                  AND
                  Local PSN-facing PW (ingress) Receive Fault
  
  
     PW status is used to convey the defect view of the PW local to the
     originating PE. This is the local PW state. This state is conveyed
     in the form of a ææforward defectÆÆ or a ææreverse defectÆÆ.
  
     Thus PW status shall be used to report the following failures:
  
     . Failures detected through defect detection mechanisms in the
     MPLS and MPLS-IP PSN
  
     . Failures detected through VCCV-Ping
  
     . Failures within the PE that result in an inability to forward
     traffic between ACs and PW
  
     . State of the AC when the PE does not have native service OAM
     capability or emulation of native service OAM capability is
     prohibitive. This state is conveyed in the form of a ææforward
     defectÆÆ or a ææreverse defectÆÆ.
  
     Note that there are a couple of situations which require PW label
     withdrawal as opposed to a PW status notification by the PE. The
     first one is when the PW is taken administratively down in
     accordance to [PWE3-CONTROL]. The second one is when the Target
     LDP session established between the two PEÆs is lost. In the
     latter case, the PW labels will need to be re-signaled when the
     Targeted LDP session is re-established.
  
   7.3.3 The Use of L2TP STOPCCN and CDN
  
     [L2TPv3] describes the use of STOPCCN and CDN messages to exchange
     alarm information between PEs. A StopCCN message indicates that
     the control connection has been shut down by the remote PE
     [L2TPv3]. This is typically used for defects in the PSN which
     impact both the control connection and the individual data plane
     sessions. On reception of this message, a PE closes the control
  
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     connection and will clear all the sessions managed by this control
     connection. Since each session carries a single PW, the state of
     the corresponding PWs is changed to DOWN. A CDN message indicates
     that the remote peer requests the disconnection of a specific
     session [L2TPv3]. In this case only the state of the corresponding
     PW is changed to DOWN. This is typically used for local defects in
     a PE which impact only a specific session and the corresponding
     PW.
  
     Like PW Status, STOPCCN and CDN messages shall be used to report
     the following failures:
  
     . Failures detected through defect detection mechanisms in the
     L2TP-IP PSN
  
     . Failures detected through VCCV-Ping
  
     . Failures within the PE that result in an inability to forward
     traffic between ACs and PW
  
     In L2TP, the Set-Link-Info (SLI) message is used to convey
     failures on the ACs.
  
   7.3.4 The Use of BFD Diagnostic Codes
  
     [BFD] defines a set of diagnostic codes that partially overlap
     with failures that can be communicated through PW Status messages
     or L2TP STOPCCN and CDN messages. This section describes the
     behavior of the PE nodes with respect to using one or both methods
     for detecting and propagating defect state.
  
     For a MPLS-PSN, the PEÆs negotiate the use of the VCCV
     capabilities when the label mapping messages are exchanged to
     establish the two directions of the PW. A new OAM capability TLV
     is signaled as part of the PW FEC interface parameters TLV.
  
     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. The defined values are:
          0x01  ICMP Ping
          0x02  LSP Ping (VCCV-Ping over a MPLS PSN and MPLS-IP PSN)
          0x04  BFD for PW Fault Detection only
          0x08  BFD for PW Fault Detection and AC/PW Fault Notification
  
     A CV type of 0x04 is part of the VCCV-BFD capability. It indicates
     that BFD is used for PW fault detection only. A BFD message will
     notify the remote PE of the fault and the latter enters into the
     proper PW defect state and triggers the appropriate actions as
     explained in the subsequent sections. All other PW and AC defects
     are indicated using PW status signaling.
  
  
  
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     A CV type of 0x08 is also part of the VCCV-BFD capability. It
     indicates that BFD is used for both PW fault detection and AC/PW
     Fault Notification, even if the fault was not detected via BFD. In
     this case, PW status signaling messages should not be used.
  
     Similarly, [VCCV] describes a L2TPv3 VCCV Capability AVP which
     provides the equivalent means to signal OAM capabilities between
     PEÆs for PWÆs over a L2TP-IP PSN.
  
     [BFD] defined the following diagnostic codes:
  
     Code         Message
     ----   ------------------------------
     0            No Diagnostic
     1            Control Detection Time Expired
     2            Echo Function Failed
     3            Neighbor Signaled Session Down
     4            Forwarding Plane Reset
     5            Path Down (Alarm Suppression)
     6            Concatenated Path Down
     7            Administratively Down
     8            Reverse Concatenated Path Down
     9-31         Reserved for future use
  
     [VCCV] states that, when used over PWs, the asynchronous mode of
     BFD should be used. Of these, 0 is used when the PW is up and 2 is
     not applicable to asynchronous mode. 3 is used as explained below.
     6 and 8 are used to signal AC forward and reverse defect states
     respectively when the PE's negotiated the use of BFD as the
     mechanism for AC and PW fault detection and notification.
  
     The following are the BFD procedures for PW fault detection (valid
     for both CV types 0x04 and 0x08):
  
     When the downstream PE (PE1) does not receive control messages
     from the upstream PE (PE2) during a certain number of transmission
     intervals (a number provisioned by the operator), it declares that
     the PW in its receive direction is down. In other word, PE1 enters
     the ææforward defectÆÆ state for this PW. PE1 sends a message to PE2
     with H=0 (i.e. "I do not hear you") and with diagnostic code 1. In
     turn, PE2 declares the PW is down in its transmit direction and it
     uses diagnostic code 3 in its control messages to PE1. PE2 enters
     the ææreverse defectÆÆ state for this PW.
  
     When a PW is taken administratively down, the PEs will withdraw
     the PW labels or will send L2TP CDN messages with code "Session
     disconnected for administrative reasons". In addition, exchange of
     BFD control messages MUST be suspended. To that end, the PEs MUST
     send control messages with H=0 and diagnostic code 7.
  
  
  
  
  
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   8 PW Defect State Entry/Exit
  
   8.1 PW Forward Defect Entry/Exit
  
     A PE will enter the PW forward defect state if one of the
     following occurs
  
     . It detects loss of connectivity on the PSN tunnel over which the
     PW is riding. This includes label swapping errors and label
     merging errors.
  
     . It receives a message from PE2 indicating PW ææforward defectÆÆ or
     ææPW not forwardingÆÆ, which indicates PE2 detected or was notified
     of a PW fault downstream of it or that there was a remote AC
     fault.
  
     In the case of an L2TP-IP, this is a L2TP StopCCN or CDN message.
  
     . It detects a loss of PW connectivity, including label errors,
     through VCCV-BFD or VCCV-PING in no reply mode.
  
     Note that if the PW control session 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 forward defect state. Precise details of AC defect
     state entry and exit criteria are specified elsewhere (e.g. I.610)
     and such references will supersede the descriptions herein.
  
     PE1 will exit the forward defect state if the notified PW status
     from the PE2 has the ææforward defectÆÆ indication clear, and it has
     established that PW/PSN connectivity is working in the forward
     direction. Note that this may result in a transition to the PW
     working or PW reverse defect states.
  
     For a PWE3 over a L2TP-IP PSN, a PE will exit the PW forward
     defect state when the following conditions are true:
  
     .  All defects it had previously detected have disappeared, and
  
     . A L2TPv3 session is successfully established to carry the PW
     packets.
  
   8.2 PW reverse defect state entry/exit
  
     A PE will enter the PW reverse defect state if one of the
     following occurs
  
     . It receives a message from PE2 indicating PW ææreverse defectÆÆ
     which indicates PE2 detected or was notified of a PW/PSN fault
     upstream of it or that there was a remote AC fault and it is not
     already in the PW forward defect state.
  
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     PE1 will exit the reverse defect state if the notified PW status
     from the PE2 has the ææreverse defectÆÆ indication clear, or it has
     entered the PW forward defect state.
  
     For a PWE3 over a L2TP-IP PSN, the PW reverse defect state is not
     valid and a PE can only enter the PW forward defect state.
  
   8.2.1 PW reverse defects that require PE state synchronization
  
     Some PW mechanisms will result in PW defects being detected by or
     notified to PE1 when PE1 is upstream of the fault but the
     notification did not originate with PE2. The resultant actions are
     identical to that of entering the PW reverse defect state with the
     addition that PE1 needs to synchronize state with PE2 and the PW
     state communicated from PE1 to PE2 needs to indicate state
     accordingly.
  
     When the PSN uses RSVP-TE or proactively uses LSP-PING as a PW
     fault detection mechanism, PE1 must enter to the PW reverse defect
     state.
  
     The exit criteria being when, the RSVP fault state or the LSP-PING
     fault state exit criteria has been met, indicating no PW reverse
     defects.
  
   9 AC Defect States
  
   9.1 FR ACs
     PE1 enters the AC Forward Defect state if any of the following
     conditions are met:
     (i)    A PVC is not ædeletedÆ 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 æinactiveÆ. In this
             case, this status maps across the PE to the corresponding
             PW only.
     (ii)   The LIV indicates that the link from the PE to the Frame
             Relay network is down. In this case, the link down
             indication maps across the PE to all corresponding PWs.
     (iii)  A physical layer alarm is detected on the FR interface. In
             this case, this status maps across the PE to all
             corresponding PWs.
     A PE exits the AC Forward Defect state when all defects it had
     previously detected have disappeared.
  
     The AC reverse defect state is not valid for FR ACs.
  
  
  
  
  
  
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   9.2 ATM ACs
  
   9.2.1 AC Forward Defect State Entry/Exit
  
     PE1 enters the AC forward defect state if any of the following
     conditions are met:
     (i)    It detects or is notified of a physical layer fault on the
             ATM interface and/or it terminates an F4 AIS flow or has
             loss of F4 CC for a VP carrying VCCÆs.
     (ii)   It terminates an F4/F5 AIS OAM flow indicating that the
             ATM VP/VC is down in the adjacent L2 ATM network (e.g., N1
             for PE1). This is applicable to the case of the ææout-of-
             band ATM OAM over PWÆÆ method only.
     (iii)  It detects loss of connectivity on the NS ATM VPC/VCC
             while terminating ATM continuity checking (ATM CC) with
             the local ATM network and CE.
  
     A PE exits the AC Forward Defect state when all defects it had
     previously detected have disappeared. The exact conditions under
     which a PE exits the AIS state, or declares that connectivity is
     restored via ATM CC are defined in I.610 [I.610].
  
   9.2.2 AC Reverse Defect State Entry/Exit
  
     A PE enters the AC reverse defect state if any of the following
     conditions are met:
     (i)    It terminates an F4/F5 RDI OAM flow indicating that the
             ATM VP/VC AC is down in the adjacent L2 ATM network (e.g.,
             N1 for PE1). This is applicable to the case of out-of-band
             ATM OAM over PW only.
  
     A PE exits the AC Reverse Defect state if the AC state transitions
     to working or to the AC forward defect state. The criteria for
     exiting the RDI state are described in I.610.
  
   9.3 Ethernet AC State
  
     PE1 enters the forward defect state if any of the following
     conditions are met:
  
     (i)    A physical layer alarm is detected on the Ethernet
             interface.
  
     A PE exits the Ethernet AC forward defect state when all defects
     it had previously detected have disappeared.
  
  
  
  
  
  
  
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   10 PW Forward Defect Entry/Exit procedures
  
   10.1 PW Forward Defect Entry Procedures
  
   10.1.1 FR AC procedures
     These procedures are applicable only if the transition from the
     working state to the PW Forward defect state. A transition from PW
     reverse defect state to the forward defect state does not require
     any additional notification procedures to the FR AC as it has
     already been told the peer is down.
     (i)    PE1 MUST generate a full status report with the Active bit
             = 0 (and optionally in the asynchronous status message),
             as per Q.933 annex A, into N1 for the corresponding FR
             ACs.
  
   10.1.2 Ethernet AC Procedures
     No procedures are currently defined.
  
   10.1.3 ATM AC procedures
     On entry to the PW Forward Defect State
     (i)    PE1 MUST commence F5 AIS insertion into the corresponding
             AC.
     (ii)   PE1 MUST terminate any F5 CC generation on the
             corresponding AC.
  
   10.1.4 Additional procedures for a FR PW, an ATM PW in the ææout-of-
        band ATM OAM over PW methodÆÆ, and an Ethernet PW
     If the PW failure was explicitly detected by PE1, it MUST assume
     PE2 has no knowledge of the defect and MUST notify PE2 in the form
     of a reverse defect notification:
  
     For PW over MPLS PSN or MPLS-IP PSN
     (i)    A PW Status message indicating a ææreverse defectÆÆ, or
     (ii)   A VCCV-BFD diagnostic code if the optional use of VCCV-BFD
             notification has been negotiated
  
     For PW over L2TP-IP PSN
  
     (i)    An L2TP Set-Link Info (LSI) message with a Circuit Status
             AVP indicating "active" Or,
     (ii)   A VCCV-BFD diagnostic code if the optional use of VCCV-BFD
             notification has been negotiated
  
     Otherwise the entry to the defect state was the result of a
     notification from PE2 (indicating that PE2 already had knowledge
     of the fault) or loss of the control adjacency (similarly visible
     to PE2).
  
  
  
  
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   10.2 PW Forward Defect Exit Procedures
  
   10.2.1 FR AC procedures
     On transition from the PW forward defect state to the reverse
     defect state PE1 takes no action w.r.t. the AC.
  
     On exit from the PW Forward defect state
     (i)    PE1 MUST generate a full status report with the Active bit
             = 1 (and optionally in the asynchronous status message),
             as per Q.933 annex A, into N1 for the corresponding FR
             ACs.
  
   10.2.2 Ethernet AC Procedures
     No procedures are currently defined
  
   10.2.3 ATM AC procedures
     On exit from the PW Forward Defect State
     (i)    PE1 MUST cease F5 AIS insertion into the corresponding AC.
     (ii)   PE1 MUST resume any F5 CC generation on the corresponding
             AC.
  
   10.2.4 Additional procedures for a FR PW, an ATM PW in the ææout-of-
        band ATM OAM over PWÆÆ method, and an Ethernet PW
     If the PW failure was explicitly detected by PE1, it MUST notify
     PE2 in the form of clearing the reverse defect notification:
  
     For PW over MPLS PSN or MPLS-IP PSN
     (i)    A PW Status message with the ææreverse defectÆÆ indication
             clear, and the remaining indicators showing either working
             or a transition to the ææforward defectÆÆ state. Or,
     (ii)   A VCCV-BFD diagnostic code with the same attribute as (i)
             if the optional use of VCCV-BFD notification has been
             negotiated
  
     For PW over L2TP-IP PSN
     (i)    An L2TP Set-Link Info (LSI) message with a Circuit Status
             AVP indicating "active" Or,
     (ii)   A VCCV-BFD diagnostic code with the same attributes as (i)
             if the optional use of VCCV-BFD notification has been
             negotiated
  
  
   10.3 PW Reverse Defect Entry Procedures
  
   10.3.1 FR AC procedures
     On transition from the PW forward defect state to the reverse
     defect state PE1 takes no action w.r.t. the AC.
  
     On entry to the PW reverse defect state
  
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     (i)    PE1 MUST generate a full status report with the Active bit
             = 0 (and optionally in the asynchronous status message),
             as per Q.933 annex A, into N1 for the corresponding FR
             ACs.
  
   10.3.2 Ethernet AC Procedures
     No procedures are currently defined
  
   10.3.3 ATM AC procedures
     On entry to the PW Reverse Defect State
     (i)    PE1 MUST commence F5 RDI insertion into the corresponding
             AC. This applies to the case of an ATM PW in the ææout-of-
             band ATM OAM over PWÆÆ method only.
  
   10.4 PW Reverse Defect Exit Procedures
  
   10.4.1 FR AC procedures
     On transition from the PW reverse defect state to the PW forward
     defect state PE1 takes no action with respect to the AC.
  
     On exit from the PW Reverse defect state
     (i)    PE1 MUST generate a full status report with the Active bit
             = 1 (and optionally in the asynchronous status message),
             as per Q.933 annex A, into N1 for the corresponding FR
             ACs.
  
   10.4.2 Ethernet AC Procedures
     No procedures are currently defined
  
   10.4.3 ATM AC procedures
     On exit from the PW Reverse Defect State
     (i)    PE1 MUST cease F5 RDI insertion into the corresponding AC.
     This applies to the case of an ATM PW in the ææout-of-band ATM OAM
     over PWÆÆ method only.
  
   10.5 Procedures in FR Port Mode
  
     In case of pure port mode, 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.
  
   10.6 Procedures in ATM Port Mode
  
     In case of transparent cell transport, 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
  
  
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     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.
  
   11 AC Defect Entry/Exit Procedures
  
   11.1 AC Forward defect entry:
     On entry to the forward defect state, PE1 may need to perform
     procedures on both the PW and the AC.
  
   11.1.1 Procedures for a FR PW, an ATM PW in the ææout-of-band ATM OAM
        over PWÆÆ method, or an Ethernet PW
     On entry to the AC forward defect state, PE1 notifies PE2 of a
     forward defect:
  
     For PW over MPLS PSN or MPLS-IP PSN
     (i)    A PW Status message indicating ææforward defectÆÆ, or
     (ii)   A VCCV-BFD diagnostic code of ææforward defectÆÆ if the
             optional use of VCCV-BFD notification has been negotiated.
  
     For PW over L2TP-IP PSN
     (i)    An L2TP Set-Link Info (LSI) message with a Circuit Status
             AVP indicating "inactive", or
     (ii)   A VCCV-BFD diagnostic code of ææforward defectÆÆ if the
             optional use of VCCV-BFD notification has been negotiated.
  
  
   11.1.2 Procedures for a ATM PW in the ææinband ATM OAM over PWÆÆ
        method
     On entry to the AC forward defect state, PE1 MUST:
          a. Commence insertion of ATM AIS cells into the corresponding
             PW.
          b. If PE1 is originating F4 or F5 I.610 CC cells, PE1 will
             suspend CC generation for the duration of the defect
             state.
  
   11.1.3 Additional procedures for ATM ACs
     On entry to the AC forward defect state PE1 will commence RDI
     insertion into the AC as per I.610. This procedure is applicable
     to the ææout-of-band ATM OAM over PWÆÆ method only.
  
  11.2 AC Reverse defect entry
  
   11.2.1 Procedures for a FR PW, an ATM PW in the ææout-of-band ATM OAM
        over PWÆÆ method, or an Ethernet PW
     On entry to the AC reverse defect state, PE1 notifies PE2 of a
     reverse defect:
  
     For PW over MPLS PSN or MPLS-IP PSN
     (iii)  A PW Status message indicating ææreverse defectÆÆ,or
  
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     (iv)   A VCCV-BFD diagnostic code of ææreverse defectÆÆ if the
             optional use of VCCV-BFD notification has been negotiated.
  
     For PW over L2TP-IP PSN
     (iii)  An L2TP Set-Link Info (LSI) message with a Circuit Status
             AVP indicating "inactive", or
     (iv)   A VCCV-BFD diagnostic code of ææreverse defectÆÆ if the
             optional use of VCCV-BFD notification has been negotiated.
  
   11.2.2 Procedures for a ATM PW in the ææinband ATM OAM over PWÆÆ
        method
     There are no procedures in this case as the AC reverse defect
     state is not valid for PE1 operating in this method.
  
   11.3 AC Forward Defect Exit
  
   11.3.1 Procedures for a FR PW, an ATM PW in the ææout-of-band ATM OAM
        over PWÆÆ method, or an Ethernet PW
  
     On exit from the AC forward defect state PE1 notifies PE2 that the
     forward defect state has cleared (note that this may be a direct
     state transition to either the working state or the reverse defect
     state):
  
     For PW over MPLS PSN or MPLS-IP PSN
     (i)    A PW Status message with forward defect clear and the
             remaining indicators showing either working or reverse
             defect state, or
     (ii)   A VCCV-BFD diagnostic code with the same attributes as (i)
             if the optional use of VCCV-BFD notification has been
             negotiated.
  
     For PW over L2TP-IP PSN
     (i)    An L2TP Set-Link Info (LSI) message with a Circuit Status
             AVP indicating "active", or
     (ii)   A VCCV-BFD diagnostic code with the same attributes as (i)
             if the optional use of VCCV-BFD notification has been
             negotiated.
  
   11.3.2 Procedures for a ATM PW in the ææinband ATM OAM over PWÆÆ
        method
     On exit from the AC forward defect state, PE1 MUST:
     (i)    Cease insertion of ATM AIS cells into the corresponding
             PW.
     (ii)   If PE1 is originating F4 or F5 I.610 CC cells, PE1 will
             resume CC generation for the duration of the defect state.
  
  
  
  
  
  
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   11.3.3 Additional procedures for ATM ACs
     On exit from the AC forward defect state PE1 will cease RDI
     insertion into the AC as per I.610. This procedure is applicable
     to the ææout-of-band ATM OAM over PWÆÆ method only.
  
   11.4 AC Reverse Defect Exit
  
   11.4.1 Procedures for a FR PW, an ATM PW in the ææout-of-band ATM OAM
        over PWÆÆ method, or an Ethernet PW
     On exit from the AC reverse defect state, PE1 notifies PE2 that
     the reverse defect state has cleared (note that this may be a
     direct state transition to either the working state or the forward
     defect state):
  
     For PW over MPLS PSN or MPLS-IP PSN
     (i)    A PW Status message with the ææreverse defectÆÆ indicator
             cleared and the remaining indicators showing either
             working or a transition to the ææforward defectÆÆ state, or
     (ii)   A VCCV-BFD diagnostic code with the same information as
             (i) if the optional use of VCCV-BFD notification has been
             negotiated.
  
     For PW over L2TP-IP PSN
     (i)    An L2TP Set-Link Info (LSI) message with a Circuit Status
             AVP indicating "active", or
     (ii)   A VCCV-BFD diagnostic code with the same information as
             (i) if the optional use of VCCV-BFD notification has been
             negotiated.
  
   11.4.2 Procedures for a ATM PW in the ææinband ATM OAM over PWÆÆ
        method
     There are no procedures in this case as the AC reverse defect
     state is not valid for PE1 operating in this method.
  
   12 SONET Encapsulation (CEP)
  
     [CEP] discusses how Loss of Connectivity and other SONET/SDH
     protocol failures on the PW are translated to alarms on the ACs
     and vice versa. In essence, all defect management procedures are
     handled entirely in the emulated protocol. There is no need for an
     interaction between PW defect management and SONET layer defect
     management.
  
   13 TDM Encapsulation
  
     From an OAM perspective, the PSN carrying a TDM PW provides the
     same function as that of SONET/SDH or ATM network carrying the
     same low-rate TDM stream. Hence the interworking of defect OAM is
     similar.
  
  
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     For structure-agnostic TDM PWs, the TDM stream is to be carried
     transparently across the PSN, and this requires TDM OAM
     indications to be transparently transferred along with the TDM
     data. For structure-aware TDM PWs the TDM structure alignment is
     terminated at ingress to the PSN and regenerated at egress, and
     hence OAM indications may need to be signaled by special means. In
     both cases generation of the appropriate emulated OAM indication
     may be required when the PSN is at fault.
  
     Since TDM is a real-time signal, defect indications and
     performance measurements may be classified into two classes,
     urgent and deferrable. Urgent messages are those whose contents
     may not be significantly delayed with respect to the TDM data that
     they potentially impact, while deferrable messages may arrive at
     the far end delayed with respect to simultaneously generated TDM
     data. For example, a forward indication signifying that the TDM
     data is invalid (e.g. TDM loss of signal, or MPLS loss of packets)
     is only of use when received before the TDM data is to be played
     out towards the far end TDM system. It is hence classified as an
     urgent message, and we can not delegate its signaling to a
     separate maintenance or management flow. On the other hand, the
     forward loss of multiframe synchronization, and most reverse
     indications do not need to be acted upon before a particular TDM
     frame is played out.
  
     From the above discussion it is evident that the complete solution
     to OAM for TDM PWs needs to have at least two, and perhaps three
     components. The required functionality is transparent transfer of
     native TDM OAM and urgent transfer of indications (by flags) along
     with the impacted packets. Optionally there may be mapping between
     TDM and PSN OAM flows.
  
     TDM AIS generated in the TDM network due to a fault in that
     network is generally carried unaltered, although the TDM
     encapsulations allow for its suppression for bandwidth
     conservation purposes. Similarly, when the TDM loss of signal is
     detected at the PE, it will generally emulate TDM AIS.
  
     SAToP and the two structure-aware TDM encapsulations have
     converged on a common set of defect indication flags in the PW
     control word. When the PE detects or is informed of lack of
     validity of the TDM signal, it raises the local ("L") defect flag,
     uniquely identifying the defect as originating in the TDM network.
     The remote PE must ensure that TDM AIS is delivered to the remote
     TDM network. When the defect lies in the MPLS network, the remote
     PE fails to receive packets. The remote PE generates TDM AIS
     towards its TDM network, and in addition raises the remote defect
     ("R") flag in its PSN-bound packets, uniquely identifying the
     defect as originating in the PSN. Finally, defects in the remote
     TDM network that cause RDI generation in that network, may
     optionally be indicated by proper setting of the field of valid
     packets in the opposite direction.
  
  
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  14 Appendix A: Native Service Management
  
   14.1 Frame Relay Management
  
     The management of Frame Relay Bearer Service (FRBS) connections
     can be accomplished through two distinct methodologies:
  
     1. 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]
  
     2. 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:
  
     . STATUS messages in response to STATUS ENQUIRY messages, these
     are mandatory.
  
     . 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, æædownÆÆ is represented as a forward
     defect.
  
     Frame relay connection management is not implemented over the PW
     using either of the techniques native to FR, therefore PW
     mechanisms are used to synchronize the view each PE has of the
     remote NS/AC. A PE will treat a remote NS/AC failure in the same
     way it would treat a PW or PSN failure, that is using AC facing FR
     connection management to notify the CE that FR is æædownÆÆ.
  
  
   14.2 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
  
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     management (AC), and Security management (SM). ITU-T
     Recommendation I.610 describes the functions for the operation and
     maintenance of the physical layer and the ATM layer, that is,
     management at the bit and cell levels ([ITU-T I.610]). Because of
     its scope, this document will concentrate on ATM fault management
     functions. Fault management functions include the following:
  
     1) Alarm indication signal (AIS)
     2) Remote Defect indication (RDI).
     3) Continuity Check (CC).
     4) Loopback (LB)
  
     Some of the basic ATM fault management functions are described as
     follows: Alarm indication signal (AIS) sends a message in the same
     direction as that of the signal, to the effect that an error has
     been detected.
  
     Remote defect indication (RDI) sends a message to the transmitting
     terminal that an error has been detected. RDI is also referred to
     as the far-end reporting failure. Alarms related to the physical
     layer are indicated using path AIS/RDI. Virtual path AIS/RDI and
     virtual channel AIS/RDI are also generated for the ATM layer.
  
     OAM cells (F4 and F5 cells) are used to instrument virtual paths
     and virtual channels respectively with regard to their performance
     and availability. OAM cells in the F4 and F5 flows are used for
     monitoring a segment of the network and end-to-end monitoring. OAM
     cells in F4 flows have the same VPI as that of the connection
     being monitored. OAM cells in F5 flows have the same VPI and VCI
     as that of the connection being monitored.  The AIS and RDI
     messages of the F4 and F5 flows are sent to the other network
     nodes via the VPC or the VCC to which the message refers. The type
     of error and its location can be indicated in the OAM cells.
     Continuity check is another fault management function. To check
     whether a VCC that has been idle for a period of time is still
     functioning, the network elements can send continuity-check cells
     along that VCC.
  
   14.3 Ethernet Management
  
     At this point in time, inband Ethernet OAM standards are being
     specified in the International Telecommunications Union -                                                             -
     Telecommunications (ITU-T) and the Institute of Electrical and
     Electronics Engineers (IEEE). However, it will take some time
     before they are widely deployed. Therefore, this document
     specifies only the procedures for mapping a defect due to a
     Ethernet physical layer fault. Defects on a remote Ethernet AC or
     defects in a PW cannot be mapped back to the local Ethernet
     network.
  
   15 Security Considerations
  
  
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     The mapping messages described in this document do not change the
     security functions inherent in the actual messages.
  
   16 Acknowledgments
  
     Hari Rakotoranto, Eric Rosen, Mark Townsley, Michel Khouderchah,
     Bertrand Duvivier, Vanson Lim, Chris  Metz, Ben Washam, Tiberiu
     Grigoriu.
  
   17 References
  
     [BFD] Katz, D., Ward, D., "Bidirectional Forwarding Detection",
          Internet Draft <draft-ietf-bfd-base-03.txt>, July 2005
  
     [CEP] Malis, A., et.al., "SONET/SDH Circuit Emulation over Packet
          (CEP)", Internet Draft <draft-ietf-pwe3-sonet-11.txt>, May
          2005
  
     [CONGESTION] Rosen, E., Bryant, S., Davie, B., "PWE3 Congestion
          Control Framework", Internet Draft <draft-rosen-pwe3-
          congestion-02.txt", September 2004
  
     [FRF.19] Frame Relay Forum, ææFrame Relay Operations,
          Administration, and Maintenance Implementation AgreementÆÆ,
          March 2001.
  
     [ICMP] Postel, J. "Internet Control Message Protocol" RFC 792
  
     [ITU-T I.610] Recommendation I.610 "B-ISDN operation and
          maintenance principles and functions", February 1999
  
     [ITU-T I.620] Recommendation I.620 "Frame relay operation and
          maintenance principles and functions", October 1996
  
     [ITU-T Q.933] Recommendation Q.933 " ISDN Digital Subscriber
          Signalling System No. 1 (DSS1) “ Signalling specifications
          for frame mode switched and permanent virtual connection
          control and status monitoring" February 2003
  
     [L2TPv3] Lau, J., et.al. " Layer Two Tunneling Protocol (Version
          3", RFC 3931, March 2005
  
     [LSPPING] Kompella, K., Pan, P., Sheth, N., Cooper, D., Swallow,
          G., Wadhwa, S., Bonica, R., " Detecting MPLS Data Plane
          Failures", Internet Draft < draft-ietf-mpls-lsp-ping-09.txt>,
          May 2005
  
     [MPLS-in-IP] Worster. T., et al., ææEncapsulating MPLS in IP or
          Generic Routing Encapsulation (GRE)ÆÆ, RFC 4023, March 2005.
  
     [OAM REQ] T. Nadeau et.al., "OAM Requirements for MPLS Networks",
          Internet Draft <draft-ietf-mpls-oam-requirements-06>, July
          2005
  
  
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     [PWE3-CONTROL] Martini, L., Rosen, E., Smith, T., "Pseudowire
          Setup and Maintenance using LDP", Internet Draft <draft-ietf-
          pwe3-control-protocol-17.txt>, June 2005
  
     [PWE3-IANA]  Martini, L., et al., ææIANA Allocations for pseudo
          Wire Edge to Edge Emulation (PWE3), Internet Draft <draft-
          ietf-pwe3-iana-allocation-11.txt>, June 2005
  
     [PWEARCH] Bryant, S., Pate, P., "PWE3 Architecture", RFC 3985,
          March 2005
  
     [PWEATM] Martini, L., et al., "Encapsulation Methods for Transport
          of ATM Cells/Frame Over IP and MPLS Networks", Internet Draft
          <draft-ietf-pwe3-atm-encap-09.txt>, June 2005
  
     [PWREQ] Xiao, X., McPherson, D., Pate, P., "Requirements for
          Pseudo Wire Emulation Edge to-Edge (PWE3)", RFC 3916,
          September 2004
  
     [RSVP-TE] Awduche, D., et.al. " RSVP-TE: Extensions to RSVP for
          LSP Tunnels", RFC 3209, December 2001
  
     [VCCV] Nadeau, T., et al."Pseudo Wire Virtual Circuit Connection
          Verification (VCCV)", Internet Draft <draft-ietf-pwe3-vccv-
          05.txt>, August 2005.
  
  
   18 Intellectual Property Disclaimer
  
     The IETF takes no position regarding the validity or scope of any
     intellectual property or other rights that might be claimed to
     pertain to the implementation or use of the technology described
     in this document or the extent to which any license under such
     rights might or might not be available; neither does it represent
     that it has made any effort to identify any such rights.
     Information on the IETF's procedures with respect to rights in
     standards-track and standards-related documentation can be found
     in BCP-11. Copies of claims of rights made available for
     publication and any assurances of licenses to be made available,
     or the result of an attempt made to obtain a general license or
     permission for the use of such proprietary rights by implementers
     or users of this specification can be obtained from the IETF
     Secretariat.
  
     The IETF invites any interested party to bring to its attention
     any copyrights, patents or patent applications, or other
     proprietary rights which may cover technology that may be required
     to practice this standard.  Please address the information to the
     IETF Executive Director.
  
  
   19 Full Copyright Statement
  
  
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     "Copyright (C) The Internet Society (2005). This document is
     subject to the rights, licenses and restrictions contained in BCP
     78, and except as set forth therein, the authors retain all their
     rights."
  
     "This document and the information contained herein are provided
     on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
     REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND
     THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES,
     EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT
     THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR
     ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
     PARTICULAR PURPOSE."
  
   20 Authors' Addresses
  
     Thomas D. Nadeau
     Cisco Systems, Inc.
     300 Beaverbrook Drive
     Boxborough, MA 01824
     Phone: +1-978-936-1470
     Email: tnadeau@cisco.com
  
     Monique Morrow
     Cisco Systems, Inc.
     Glatt-com
     CH-8301 Glattzentrum
     Switzerland
     Email: mmorrow@cisco.com
  
     Peter B. Busschbach
     Lucent Technologies
     67 Whippany Road
     Whippany, NJ, 07981
     Email: busschbach@lucent.com
  
     Mustapha Aissaoui
     Alcatel
     600 March Rd
     Kanata, ON, Canada. K2K 2E6
     Email: mustapha.aissaoui@alcatel.com
  
     Matthew Bocci
     Alcatel
     Voyager Place, Shoppenhangers Rd
     Maidenhead, Berks, UK SL6 2PJ
     Email: matthew.bocci@alcatel.co.uk
  
     David Watkinson
     Alcatel
     600 March Rd
     Kanata, ON, Canada. K2K 2E6
     Email: david.watkinson@alcatel.com
  
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     Yuichi Ikejiri
     NTT Communications Corporation
     1-1-6, Uchisaiwai-cho, Chiyoda-ku
     Tokyo 100-8019, JAPAN
     Email: y.ikejiri@ntt.com
  
     Kenji Kumaki
     KDDI Corporation
     KDDI Bldg. 2-3-2
     Nishishinjuku, Shinjuku-ku
     Tokyo 163-8003,JAPAN
     E-mail : kekumaki@kddi.com
  
     Satoru Matsushima
     Japan Telecom
     JAPAN
     Email: satoru@ft.solteria.net
  
     David Allan
     Nortel Networks
     3500 Carling Ave.,
     Ottawa, Ontario, CANADA
     Email: dallan@nortelnetworks.com
  
     Simon Delord
     France Telecom
     2 av, Pierre Marzin
     22300 LANNION, France
     E-mail: simon.delord@francetelecom.com
  
     Vasile Radoaca
     West Ridge Networks
     Littleton, MA 01460
     Email: vradoaca@westridgenetworks.com
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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