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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: January 2005                          Cisco Systems
  
                                                          Peter Busschbach
                                                       Lucent Technologies
  
                                                         Mustapha Aissaoui
                                                                   Alcatel
  
                                                                   Editors
  
                                                                 July 2004
  
  
  
                    Pseudo Wire (PW) OAM Message Mapping
                     draft-ietf-pwe3-oam-msg-map-00.txt
  
  
  
   Status of this Memo
  
     This document is an Internet-Draft and is in full conformance with
     all provisions of Section 10 of RFC 2026.
  
     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
     progress."
  
     The list of current Internet-Drafts can be accessed at
     http://www.ietf.org/ietf/1id-abstracts.txt.
  
  Abstract
  
     This document enumerates the OAM defect state mapping from pseudo
     wire emulated edge-to-edge services over MPLS and IP transport
     networks to their native attached services.
  
  
  Table of Contents
  
     Status of this Memo.............................................1
     Abstract........................................................1
     Table of Contents...............................................1
     1 Conventions used in this document.............................2
  
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     2 Contributors..................................................3
     3 Scope.........................................................3
     4 Terminology...................................................3
     5 Introduction..................................................4
     6 Reference Model and Defect Locations..........................4
     7 PW Status and Defects.........................................5
      7.1 PW Defects.................................................5
         7.1.1 Packet Loss...........................................6
      7.2 Defect Detection...........................................6
         7.2.1 Defect Detection Tools................................6
         7.2.2 Defect Detection Mechanism Applicability..............7
      7.3 PW Defect Entry and Exit Procedures........................7
         7.3.1 PW Down...............................................8
         7.3.2 PW Up.................................................8
      7.4 Alarm Messages and Consequent Actions......................9
      7.5 The Use of PW Status.......................................9
      7.6 The Use of L2TP SCCN and CDN..............................10
      7.7 The Use of BFD Diagnostic Codes...........................10
     8 Frame Relay Encapsulation....................................11
      8.1 Frame Relay Management....................................11
      8.2 Mapping of Defect States from a PW to a Frame Relay AC....12
         8.2.1 Procedures in FR Port Mode...........................13
      8.3 Frame Relay Network and Attachment Circuit Defects........13
     9 ATM Encapsulation............................................13
      9.1 ATM Management............................................13
      9.2 Mapping ATM and PW Defect States..........................14
      9.3 Mapping of Defect States from a PW to a ATM AC............15
         9.3.1 Inband ATM OAM over PW...............................15
         9.3.2 Out-of-Band ATM OAM over PW..........................15
         9.3.3 Procedures in ATM Port Mode..........................16
      9.4 ATM Network and Attachment Circuit Defects................17
         9.4.1 Inband ATM OAM over PW...............................17
         9.4.2 Out-of-Band ATM OAM over PW..........................17
         9.4.3 Procedures in ATM Port Mode..........................18
     10 SONET Encapsulation (CEP)...................................18
     11 TDM Encapsulation...........................................18
     12 Ethernet Encapsulation......................................19
     13 Security Considerations.....................................20
     14 Acknowledgments.............................................20
     15 References..................................................20
     16 Intellectual Property Disclaimer............................21
     17 Full Copyright Statement....................................21
     18 Authors' Addresses..........................................22
  
   1 Conventions used in this document
  
  
  
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     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
  
  
   3 Scope
  
     This document specifies the mapping of defect states between a
     Pseudo Wire and Attachment Circuits (AC) of the end-to-end
     emulated service.  This document covers the case of PW and ACs of
     the same type in accordance to the PWE3 architecture [PWEARCH].
  
     This document covers both PWE over MPLS PSN and PWE over IP PSN.
  
  
   4 Terminology
  
        AIS   Alarm Indication Signal
        AOM   Administration, Operation and Maintenance
        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
        OAM   Operations and Maintenance
        PE    Provider Edge
        PW    Pseudowire
        PSN   Packet Switched Network
  
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        RDI   Remote Defect Indicator
        SDU   Service Data Unit
        VCC   Virtual Channel Connection
        VPC   Virtual Path Connection
  
     The rest of this document will follow the following convention:
  
     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.
  
   5 Introduction
  
     This document describes how PW defects can be detected; how alarm
     information is exchanged between PEs; and how defects detected in
     pseudo-wires are mapped to OAM messages native to the emulated
     services and vice versa.
  
     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.
  
   6 Reference Model and Defect Locations
  
     Error! Reference source not found.Figure 1 illustrates the PWE3
     network reference model with an indication of the possible defect
     locations. This model will be referenced in the remainder of this
     document for describing the OAM procedures.
  
                 ACs             PSN tunnel               ACs
                        +----+                  +----+
        +----+          | PE1|==================| PE2|          +----+
        |    |---(a)---(b)..(c)......PW1..(d)..(c)..(f)---(e)---|    |
        | CE1|   (N1)   |    |                  |    |    (N2)  |CE2 |
        |    |----------|............PW2.............|----------|    |
        +----+          |    |==================|    |          +----+
             ^          +----+                  +----+          ^
             |      Provider Edge 1         Provider Edge 2     |
             |                                                  |
             |<-------------- Emulated Service ---------------->|
       Customer                                                Customer
        Edge 1                                                  Edge 2
                 Figure 1: PWE3 Network Defect Locations
  
     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
  
  
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          PE1. The defect is conveyed to PE1 and to the remote L2
          network (N2) using a L2 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. The defect is conveyed to PE2 and to the remote L2
          network (N1) using a L2 specific OAM defect indication.
     (f)  Defect on a PE2 AC interface.
  
  
   7 PW Status and Defects
  
     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 a MPLS 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.
  
  
  
  
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   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 re-signal it through
     another path is usually at the discretion of the network operator.
  
   7.2 Defect Detection
  
   7.2.1 Defect Detection Tools
  
     To detect the defects listed in 7.1, Service Providers have a
     variety of options available:
  
     Physical Layer defect detection mechanisms such as SONET/SDH LOS,
     LOF,and AIS/FERF.
  
     PSN Defect Detection Mechanisms:
  
     For PWE3 over an 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, 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.
  
  
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   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
     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, 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, 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 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 PW Defect Entry and Exit Procedures
  
  
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     PWs can fail in a single direction or in both directions. PEs
     SHOULD keep track of the status of each individual direction. In
     other words, a PE SHOULD be able to distinguish between the
     following states: "PW UP", "PW Transmit Direction Down", "PW
     Receive Direction Down", "PW Receive and Transmit Down".
  
     The next two sections discuss under which conditions a PE enters
     and exits these states. To avoid an unnecessarily complicated
     description, only the states "PW UP" and "PW DOWN" are discussed
     without further analysis whether it applies to one or two
     directions of the PW.
  
   7.3.1 PW Down
  
     A PE will consider a PW down if one of the following occurs
  
     . It detects a physical layer alarm on the PSN interface over
     which the PW is riding and cannot re-establish the PW over another
     PSN interface.
  
     . It detects loss of connectivity on the PSN tunnel over which the
     PW is riding and cannot re-establish the PW over another PSN
     tunnel. This includes label swapping errors and label merging
     errors.
  
     . It receives a message from its peer indicating a PW defect,
     which could be one of the following:
  
           o PW Status indicating "PW Receive Fault"; "PW Transmit
             Fault"; or "PW not forwarding"
  
           o An L2TP SCCN or CDN message
  
           o It detects a loss of PW connectivity, including label
     errors, through VCCV.
  
     Note that if the control session between the PEs fails, the PW is
     torn down and needs to be re-established.
  
   7.3.2 PW Up
  
     When a PE determines that all previously existing failures have
     disappeared, it SHOULD send a message to its peer to indicate
     this. E.g. if the original failure was conveyed through a PW
     Status message, the PE should send a PW Status message indicating
     "PW Forwarding (clear all failures)"
  
     When a PE receives a PW Status message indicating "PW Forwarding",
     while it still considers a PW down, and if all previously existing
     failures, if any, have disappeared, it SHOULD respond with a PW
     Status message indicating "PW Forwarding".
  
  
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     For PWE3 over a MPLS PSN, a PE will exit the PW down state when
     the following conditions are true:
  
     .  All defects it had previously detected, as described in Section
     7.3.1, have disappeared, and
  
     . It has received a PW Status message from its peer indicating "PW
     Forwarding"
  
     For a PWE3 over a IP PSN, a PE will exit the PW down state when
     the following conditions are true:
  
     .  All defects it had previously detected, as described in Section
     7.3.1, have disappeared, and
  
     . A L2TPv3 session is successfully established to carry the PW
     packets.
  
     [BFD] and [L2TPv3] define the procedures to exit the PW Down state
     if the original failure notification was done through BFD or L2TP
     messages, respectively.
  
   7.4 Alarm Messages and Consequent Actions
  
     When a PE changes the status of a PW to DOWN, it SHOULD inform its
     peer, by using:
  
     . For PWE3 on MPLS PSN, PW Status messages as defined in
     [CONTROL].
  
     . For PWE3 on IP PSN, L2TPv3 messages Stop Control-Connection
     Notification (SCCN) and Call Disconnect Notify (CDN) as defined in
     [L2TPv3]
  
     Furthermore, in either case, if VCCV-BFD is used, the diagnostic
     code in the VCCV-BFD Control message can be used to exchange alarm
     information.
  
     In general, PW Status messages or L2TP SCCN and CDN should be used
     to communicate failures. VCCV-BFD alarm indications should only be
     used in specific cases, as explained in 4.6.
  
     Both PEs will translate the PW alarms 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.
  
  
   7.5 The Use of PW Status
  
     This document specifies the use of PW status signaling for the
     purpose of conveying the status of a PW and attached ACs between
     PEs.
  
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     At the PW setup, a PE will enter in a negotiation with its remote
     peer of the use of the PW status by inserting the PW Status TLV in
     the label mapping message. If the negotiation process results in
     the usage of the PW status TLV, then the actual PW status is
     determined by the PW status TLV that was sent within the initial
     PW label mapping. Subsequent updates of PW status are conveyed
     through the notification message [CONTROL].
  
     PW Status messages are used to report the following defects:
  
     . Defects detected through defect detection mechanisms in the MPLS
     PSN
  
     . Loss of connectivity detected through VCCV-Ping
  
     . Defects within the PE that result in an inability to forward
     traffic between ACs and PW
  
     If the PW defect is related to one forwarding direction only, the
     PE shall either use "PW Receive Fault" or "PW Transmit Fault". In
     all other cases it shall use "PW Not Forwarding".
  
     Besides reporting PW defects, PW status is used to propagate AC
     defects. When and how to use those messages is dependent on the
     emulated protocol and will be explained in the subsequent
     paragraphs (5.3 and 6.3).
  
   7.6 The Use of L2TP SCCN and CDN
  
     [L2TPv3] describes the use of SCCN and CDN messages to exchange
     alarm information between PEs. Like PW Status, SCCN and CDN
     messages shall be used to report the following failures:
  
     . Failures detected through defect detection mechanisms in the IP
     PSN
  
     . Failures detected through VCCV (except for VCCV-BFD)
  
     . 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.
  
   7.7 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 SCCN and CDN. To avoid ambiguous situations, these
     messages SHOULD be used for all failures that are detected through
     means other than BFD.
  
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     For VCCV-BFD, therefore, only the following diagnostic codes
     apply:
  
     Code   Message
     ----   ------------------------------
     0      No Diagnostic
     1      Control Detection Time Expired
     3      Neighbor Signaled Session Down
     7      Administratively Down
  
     [VCCV] states that, when used over PWs, the asynchronous mode of
     BFD should be used. Diagnostic code 2 (Echo Function Failed) does
     not apply to the asynchronous mode, but to the Demand Mode.
  
     All other BFD diagnostic codes refer to failures that can be
     communicated through PW Status or L2TP SCCN and CDN.
  
     The VCCV-BFD procedures are as follows:
  
     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. 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 PE2.
  
     When a PW is taken administratively down, the PEs will exchange PW
     Status messages with code "Pseudo Wire Not Forwarding" or 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.
  
     Note, according to [BFD], control messages with an incorrect
     discriminator field must be discarded. However, since such an
     occurrence might be caused by swapped or mismerged LSPs, it would
     be better if a new diagnostic code were introduced to discriminate
     between missing control packets and packets with an incorrect
     discriminator. In other words, in most cases one would communicate
     PW failures through PW Status messages except for a well-defined
     set of exceptions where BFD is used. How PW defects that can be
     detected through the use of BFD or through other means, are mapped
     to defect indications on the ACs is described in sections 8 and
     subsequent sections.
  
  
   8 Frame Relay Encapsulation
  
   8.1 Frame Relay Management
  
  
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     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.
  
   8.2 Mapping of Defect States from a PW to a Frame Relay AC
     The following are the OAM procedures for defects in locations (c)
     and (d) in Figure 1.
     In case a PE keeps track of the status of individual Frame Relay
     PVCs (which often, but not necessarily, coincides with the usage
     of 1-1 encapsulation mode), the following procedures apply:
  
     When PE1 determines that one or both directions of a PW is down it
     will indicate this on the corresponding FR ACs by sending Active
     bit = 0 in the full status report (and optionally in the
     asynchronous status message), as per Q.933 annex A. In addition,
     PE1 should send a PW status signaling message, ôPW Not Forwardingö
     to the remote PE to convey the status of the affected PWs. PE2
     should in turn generate a full status report with the Active bit =
     0 (and optionally in the asynchronous status message), as per
     Q.933 annex A, into N2 for the corresponding FR ACs.
  
     When the PE determines that the PW is up, it will indicate this on
     the AC through STATUS messages that indicate that the FR PVCs
     linked to that PW are active.
  
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   8.2.1 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 at the Frame Relay devices at one or both sites
     of the emulated interface.
  
   8.3 Frame Relay Network and Attachment Circuit Defects
  
     The following are the OAM procedures for defects in locations (a)
     and (b) in Figure 1. The handling of a defect in locations (e) and
     (f) is similar to that of locations (a) and (b) respectively.
  
     As explained in [CONTROL], if a PE detects that a Frame Relay PVC
     is "inactive", as defined in [ITU-T Q933] Annex A.5, it will
     convey this information to its peer using a PW status message. The
     remote PE SHOULD generate the corresponding errors and alarms on
     the egress Frame Relay PVC
  
     For PWE3 over MPLS PSN, a PE that detects or is notified of a
     defect in locations (a) or (b) MUST change the local status of the
     corresponding FR ACs to DOWN in PE1 and MUST send a PW Status
     message indicating both "AC Receive Fault" and "AC Transmit
     Fault". On reception of this PW status message, the egress PE 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 N2 for the corresponding FR ACs.
  
     For PWE3 over IP PSN, a PE that detects or is notified of a defect
     in locations (a) or (b) MUST change the local status of the
     corresponding FR ACs to DOWN in PE1 and MUST send an L2TP Set-Link
     Info (LSI) message with a Circuit Status Attribute Value Pair
     (AVP) indicating "inactive". On reception of this LSI message, the
     egress PE 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 N2 for the corresponding FR ACs.
  
  
   9 ATM Encapsulation
  
   9.1 ATM Management
  
     ATM management and OAM mechanisms are much more evolved than those
     of Frame Relay.  There are five broad management-related
     categories, including fault management (FT), Performance
     management (PM), configuration management (CM), Accounting
     management (AC), and Security management (SM). ITU-T
     Recommendation I.610 describes the functions for the operation and
     maintenance of the physical layer and the ATM layer, that is,
     management at the bit and cell levels ([ITU-T I.610]). Because of
  
  
  
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     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 for the control of virtual
     paths and virtual channels with regard to their performance and
     availability. F4 cells are used to monitor a VPC, F5 cells for a
     VCC. 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.
  
   9.2 Mapping ATM and PW Defect States
     In normal, i.e., defect-free, operation, all the types of ATM OAM
     cells described in Section 9.1 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
     ôinband ATM OAM over PWö 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 ôOut-of-band ATM OAM over PWö.
     Note that the out-of-band method assumes that the end-to-end
     circuit consists of three independent segments, <VCC1, ATM PW,
     VCC2>, with defect states relayed across the boundary of these
     segments. An important consequence of this is that when a PE is
     notified of a defect in the remote ATM network, in the remote AC,
     or in the PW, it will always generate a F4/F5 AIS message towards
     the local ATM network and local CE regardless of the stated
  
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     direction of the defect. At the same time, the PE should not relay
     over the PW the defect state of a received F4/F5 RDI from the
     local CE if it is sourcing a F4/F5 AIS on the same AC towards that
     CE. These conditions maintain the independence of the three defect
     loops while relaying the defect states end-to-end. The procedures
     in sections 9.3.2 and 9.4.2 satisfy these two conditions.
  
   9.3 Mapping of Defect States from a PW to a ATM AC
     The following are the OAM procedures for defects in locations (c)
     and (d) in Figure 1.
  
   9.3.1 Inband ATM OAM over PW
  
     When PE1 detects a defect in locations (c) or (d) it MUST change
     the status of the affected PWs to DOWN for the direction of the
     defect. If both directions of the PW are down or if only the
     Receive direction of the PW is down, PE1 MUST generate AIS on the
     affected ACs to convey this status to the ATM network (N1) and CE1
     [PWE3-ATM]. CE1 will reply with a F4/F5 RDI which gets forwarded
     by PE1 over the PW. PE2 will receive the RDI message only if the
     forwards direction of the PW, i.e., PE1-to-PE2, is not affected by
     the defect. In this case, PE2 MUST forward the RDI message to CE2
     through the ATM network (N2).
  
     If only the PW Transmit direction is DOWN at PE1, this is
     generally detected by PE2 through a PSN or a PW continuity
     checking or connectivity verification mechanism as explained in
     Section 7.3.1. PE1 is notified through the return path of that
     specific mechanism. In this case, PE2 will follow the same
     procedures described above for a defect in the PW Receive
     direction.
  
     When the PW status changes back to UP, a PE MUST cease the
     generation of the F4/F5 messages on the AC towards the CE. This
     will result in clearing the AIS or RDI states in the remote PE, in
     CE1, and in CE2.
  
   9.3.2 Out-of-Band ATM OAM over PW
  
     For PWE3 over MPLS PSN, the following operations MUST be performed
     when PE1 detects a defect in locations (c) or (d):
          a. PE1 MUST change the status of the affected PWs to DOWN for
             the direction of the defect.
          b. If both directions of the PW are down, PE1 MUST generate a
             PW status message indicating ôPW not forwardingö.
          c. If only the Receive direction of the PW is down, PE1 MUST
             generate a PW status message indicating ôLocal PSN-facing
             PW (ingress) Receive Faultö.
          d. PE1 MUST generate a F4/F5 AIS on the affected ACs to
             convey this status to the ATM network (N1) and CE1 [PWE3-
             ATM].
  
  
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          e. CE1 replies with a F4/F5 RDI. PE1 MUST terminate the F4/F5
             RDI since it is sourcing a AIS over the same AC towards
             CE1.
          a. On reception of the PW status message, PE2 MUST generate a
             F4/F5 AIS on the related ATM ACs towards CE2.
          f. The termination point of the ATM VCC or VPC in the far-end
             CE, i.e., CE2, generates a F4/F5 RDI in response to the
             received F4/F5 AIS. PE2 MUST terminate the F4/F5 RDI since
             it is sourcing a AIS over the same AC towards CE2.
  
     For PWE3 over IP PSN, the following operations MUST be performed
     when PE1 detects a defect in locations (c) or (d):
          a. PE1 MUST change the status of the affected PWs to DOWN for
             the direction of the defect.
          b. If both directions of the PW are down, or if only the
             Receive direction of the PW is down, PE1 MUST send an
             L2TPv3 SCCN or CDN message.
          c. PE1 MUST generate a F4/F5 AIS on the affected ACs to
             convey this status to the ATM network (N1) and CE1 [PWE3-
             ATM].
          d. CE1 replies with a F4/F5 RDI. PE1 MUST terminate the F4/F5
             RDI since it is sourcing a AIS over the same AC towards
             CE1.
          e. On reception of the SSCN or CDN message, PE2 MUST generate
             a F4/F5 AIS on the related ATM ACs towards CE2.
          f. The termination point of the ATM VCC or VPC in the far-end
             CE, i.e., CE2, generates a F4/F5 RDI in response to the
             received F4/F5 AIS. PE2 MUST terminate the F4/F5 RDI since
             it is sourcing a AIS over the same AC towards CE2.
  
     If only the PW Transmit direction is DOWN at PE1, this is
     generally detected by PE2 through a PSN or a PW continuity
     checking or connectivity verification mechanism as explained in
     Section 7.3.1. PE1 is notified through the return path of that
     specific mechanism. In this case, PE2 will follow the same
     procedures described above for a defect in the PW Receive
     direction.
  
     When the PW status changes back to UP, a PE MUST cease the
     generation of the F4/F5 messages on the AC towards the CE. In
     addition, it MUST generate a PW Status message indicating ôPseudo
     Wire forwarding (clear all failures)ö for PWE3 over a MPLS PSN.
     For PWE3 or an IP PSN, the actions are TBD.
     This will result in clearing the AIS or RDI states in the remote
     PE, in CE1, and in CE2.
  
   9.3.3 Procedures in ATM Port Mode
  
     In case of transparent mapping,(i.e.: "port mode"),
     where the PE does not keep track of the status of individual ATM
     VPCs or VCCs, a PE does not know which VPCs and/or VCCs are
     active. In such a case there is a need for another defect
  
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     indication mechanism on the AC. This is beyond the scope of this
     document.
  
   9.4 ATM Network and Attachment Circuit Defects
  
     The following are the OAM procedures for defects in locations (a)
     and (b) in Figure 1. The handling of a defect in locations (e) and
     (f) is similar to that of locations (a) and (b) respectively.
  
   9.4.1 Inband ATM OAM over PW
  
     PE1 MUST transparently carry the F4/F5 AIS or RDI cells received
     on the corresponding ATM AC (defect a) or the F4/F5 AIS generated
     locally (defect b) over the corresponding ATM PW. The termination
     point of the ATM VCC or VPC in the far-end CE, i.e., CE2,
     generates a F4/F5 RDI in response to a F4/F5 AIS. PE2 MUST forward
     the RDI over the PW and PE1 MUST forward it over the corresponding
     AC. CE1 does not reply to a received F4/F5 RDI message.
  
   9.4.2 Out-of-Band ATM OAM over PW
  
     If PE1 cannot generate and/or transmit ATM OAM cells over the ATM
     PW, it may use the following procedure.
  
     For PWE3 over MPLS PSN, the following operations MUST be performed
     when PE1 receives a F4/F5 AIS or RDI from the ATM network (defect
     a) or when it detects a defect in the Receive or Transmit
     direction of the ATM AC (defect b):
          a. PE1 MUST send a PW Status message indicating "AC Receive
             Fault" for a received F4/F5 AIS.
          b. PE1 MUST send a PW status message indicating "AC Transmit
             Fault" for a received F4/F5 RDI only if it is not sourcing
             a F4/F5 AIS over the same AC towards CE1.
          c. PE1 MUST generate a F4/F5 RDI on the related ACs towards
             CE1 in response to a received F4/F5 AIS only.
          d. On reception of the PW status message,  PE2 MUST generate
             a F4/F5 AIS on the related ATM ACs towards CE2.
          e. The termination point of the ATM VCC or VPC in the far-
             end, i.e., CE2, generates a F4/F5 RDI in response to the
             received F4/F5 AIS. PE2 MUST terminate the F4/F5 RDI since
             it is sourcing a AIS over the same AC towards CE2.
  
     For PEW3 over IP PSN, the following operations MUST be performed
     when PE1 receives a F4/F5 AIS or RDI from the ATM network (defect
     a) or when it detects a defect in the Receive or Transmit
     direction of the ATM AC (defect b):
          b. PE1 MUST send an L2TP Set-Link Info (LSI) message with a
             Circuit Status AVP indicating "inactive". In the case of a
             received F4/F5 RDI, PE1 MUST not generate the LSI message
             if it is sourcing a F4/F5 AIS over the same AC towards
             CE1.
  
  
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          c. PE1 MUST generate a F4/F5 RDI on the related ACs towards
             CE1 in response to a received F4/F5 AIS only.
          d. On reception of the L2TP LSI message, PE2 MUST generate a
             F4/F5 AIS on the related ATM ACs towards CE2.
          e. The termination point of the ATM VCC or VPC in the far-end
             CE, i.e., CE2, generates a F4/F5 RDI in response to the
             received F4/F5 AIS. PE2 MUST terminate the F4/F5 RDI since
             it is sourcing a AIS over the same AC towards CE2.
  
   9.4.3 Procedures in ATM Port Mode
  
     In case of transparent mapping, ,(i.e.: "port mode"), where the PE
     does not know which VCCs and/or VPCs are active, AIS/RDI messages
     are transparently propagated to the remote ATM network without PE
     intervention for defects in the ATM network (location a). For
     defects in the PE ATM AC interface ,location b, the PE MUST send a
     PW-STATUS message to its peer. How the peer propagates that
     message on its AC is beyond the scope of this document.
  
   10 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.
  
   11 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.
  
     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)
  
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     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.
  
   12 Ethernet Encapsulation
  
     At this point in time, Ethernet OAM is not defined. Therefore, the
     procedures for mapping PW failures to Ethernet OAM messages and
     vice versa are currently rudimentary.
  
     When an ingress PE detects that an Ethernet AC is down (because
     the related ethernet physical interface is down), it SHOULD send a
     PW Status message indicating both "AC Receive Fault" and "AC
     Transmit Fault".
  
     If an egress PE determines that all ACs on a specific ethernet
     physical interface are affected (either because of ingress AC
     failures or because of PW failures), it MAY propagate these alarms
     by bringing the entire physical interface down.
  
  
  
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   13 Security Considerations
  
     The mapping messages described in this document do not change the
     security functions inherent in the actual messages.
  
   14 Acknowledgments
  
     Hari Rakotoranto, Eric Rosen, Mark Townsley, Michel Khouderchah,
     Bertrand Duvivier, Vanson Lim and Chris  Metz Cisco Systems
  
   15 References
  
     [BFD] Katz, D., Ward, D., "Bidirectional Forwarding Detection",
          Internet Draft <draft-katz-ward-bfd-02.txt>, May 2004
  
     [CEP] Malis, A., et.al., "SONET/SDH Circuit Emulation over Packet
          (CEP)", Internet Draft <draft-ietf-pwe3-sonet-08.txt>, June
          2004
  
     [CONGESTION] Rosen, E., Bryant, S., Davie, B., "PWE3 Congestion
          Control Framework", Internet Draft <draft-rosen-pwe3-
          congestion-01.txt", March 2004
  
     [CONTROL] Martini, L., Rosen, E., Smith, T., "Pseudowire Setup and
          Maintenance using LDP", Internet Draft <draft-ietf-pwe3-
          control-protocol-08.txt>, July 2004
  
     [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", Internet Draft <draft-ietf-l2tpext-l2tp-base-14.txt>,
          June 2004
  
     [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-06.txt>,
          July 2004
  
     [OAM REQ] T. Nadeau et.al., "OAM Requirements for MPLS Networks",
          Internet Draft <draft-ietf-mpls-oam-requirements-02>, June
          2003
  
  
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     [PWEARCH] Bryant, S., Pate, P., "PWE3 Architecture", Internet
          Draft, < draft-ietf-pwe3-arch-07.txt>, March 2004
  
     [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-06.txt>, July 2004
  
     [PWREQ] Xiao, X., McPherson, D., Pate, P., "Requirements for
          Pseudo Wire Emulation Edge to-Edge (PWE3)", < draft-ietf-
          pwe3-requirements-08.txt>, December 2003
  
     [RSVP-TE] Awduche, D., et.al. " RSVP-TE: Extensions to RSVP for
          LSP Tunnels", RFC 3209
  
     [VCCV] Nadeau, T., et al."Pseudo Wire Virtual Circuit Connection
          Verification (VCCV)", Internet Draft <draft-ietf-pwe3-vccv-
          03.txt>, October 2004.
  
  
   16 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.
  
  
   17 Full Copyright Statement
  
     "Copyright (C) The Internet Society (2004). Except as set forth
     below, authors retain all their rights.
  
     This document and translations of it may be copied and furnished
     to others, and derivative works that comment on or otherwise
     explain it or assist in its implementation may be prepared,
     copied, published and distributed, in whole or in part, without
     restriction of any kind, provided that the above copyright notice
  
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     and this paragraph are included on all such copies and derivative
     works.  However, this document itself may not be modified in any
     way, such as by removing the copyright notice or references to the
     Internet Society or other Internet organizations, except as needed
     for the purpose of developing Internet standards in which case the
     procedures for rights in submissions defined in the IETF Standards
     Process must be followed, or as required to translate it into
     languages other than English.
  
     The limited permissions granted above are perpetual and will not
     be revoked by the Internet Society or its successors or assigns.
  
     This document and the information contained herein is provided on
     an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/S HE
     REPRESENTS (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.
  
  
   18 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
  
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     Email: matthew.bocci@alcatel.co.uk
  
     David Watkinson
     Alcatel
     600 March Rd
     Kanata, ON, Canada. K2K 2E6
     Email: david.watkinson@alcatel.com
  
     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
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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