<pre>Internet Engineering Task Force (IETF)                     D. Mohan, Ed.
Request for Comments: 7023                               Nortel Networks
Category: Standards Track                                  N. Bitar, Ed.
ISSN: 2070-1721                                                  Verizon
                                                         A. Sajassi, Ed.
                                                                   Cisco
                                                               S. Delord
                                                          Alcatel-Lucent
                                                                P. Niger
                                                          France Telecom
                                                                  R. Qiu
                                                                 Juniper
                                                            October 2013


  <span class="h1">MPLS and Ethernet Operations, Administration, and Maintenance (OAM)</span>
                              <span class="h1">Interworking</span>

Abstract

   This document specifies the mapping of defect states between Ethernet
   Attachment Circuits (ACs) and associated Ethernet pseudowires (PWs)
   connected in accordance with the Pseudowire Emulation Edge-to-Edge
   (PWE3) architecture to realize an end-to-end emulated Ethernet
   service.  It standardizes the behavior of Provider Edges (PEs) with
   respect to Ethernet PW and AC defects.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in <a href="./rfc5741#section-2">Section&nbsp;2 of RFC 5741</a>.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   <a href="http://www.rfc-editor.org/info/rfc7023">http://www.rfc-editor.org/info/rfc7023</a>.











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Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a> and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (<a href="http://trustee.ietf.org/license-info">http://trustee.ietf.org/license-info</a>) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.





































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Table of Contents

   <a href="#section-1">1</a>. Introduction ....................................................<a href="#page-4">4</a>
      <a href="#section-1.1">1.1</a>. Specification of Requirements ..............................<a href="#page-4">4</a>
   <a href="#section-2">2</a>. Overview ........................................................<a href="#page-4">4</a>
      <a href="#section-2.1">2.1</a>. Reference Model and Defect Locations .......................<a href="#page-6">6</a>
      <a href="#section-2.2">2.2</a>. Abstract Defect States .....................................<a href="#page-6">6</a>
   <a href="#section-3">3</a>. Abbreviations and Terminology ...................................<a href="#page-7">7</a>
      <a href="#section-3.1">3.1</a>. Abbreviations ..............................................<a href="#page-7">7</a>
      <a href="#section-3.2">3.2</a>. Terminology ................................................<a href="#page-8">8</a>
   <a href="#section-4">4</a>. PW Status and Defects ...........................................<a href="#page-9">9</a>
      <a href="#section-4.1">4.1</a>. Use of Native Service (NS) Notification ....................<a href="#page-9">9</a>
      <a href="#section-4.2">4.2</a>. Use of PW Status Notification for MPLS PSNs ...............<a href="#page-10">10</a>
      <a href="#section-4.3">4.3</a>. Use of BFD Diagnostic Codes ...............................<a href="#page-10">10</a>
      <a href="#section-4.4">4.4</a>. PW Defect States Entry and Exit Criteria ..................<a href="#page-11">11</a>
           <a href="#section-4.4.1">4.4.1</a>. PW Receive Defect State Entry and Exit .............<a href="#page-11">11</a>
           <a href="#section-4.4.2">4.4.2</a>. PW Transmit Defect State Entry and Exit ............<a href="#page-11">11</a>
   <a href="#section-5">5</a>. Ethernet AC Defect States Entry and Exit Criteria ..............<a href="#page-12">12</a>
      <a href="#section-5.1">5.1</a>. AC Receive Defect State Entry and Exit ....................<a href="#page-12">12</a>
      <a href="#section-5.2">5.2</a>. AC Transmit Defect State Entry and Exit ...................<a href="#page-13">13</a>
   <a href="#section-6">6</a>. Ethernet AC and PW Defect States Interworking ..................<a href="#page-14">14</a>
      <a href="#section-6.1">6.1</a>. PW Receive Defect State Entry Procedures ..................<a href="#page-14">14</a>
      <a href="#section-6.2">6.2</a>. PW Receive Defect State Exit Procedures ...................<a href="#page-15">15</a>
      <a href="#section-6.3">6.3</a>. PW Transmit Defect State Entry Procedures .................<a href="#page-16">16</a>
      <a href="#section-6.4">6.4</a>. PW Transmit Defect State Exit Procedures ..................<a href="#page-16">16</a>
      <a href="#section-6.5">6.5</a>. AC Receive Defect State Entry Procedures ..................<a href="#page-16">16</a>
      <a href="#section-6.6">6.6</a>. AC Receive Defect State Exit Procedures ...................<a href="#page-17">17</a>
      <a href="#section-6.7">6.7</a>. AC Transmit Defect State Entry Procedures .................<a href="#page-17">17</a>
      <a href="#section-6.8">6.8</a>. AC Transmit Defect State Exit Procedures ..................<a href="#page-18">18</a>
   <a href="#section-7">7</a>. Security Considerations ........................................<a href="#page-18">18</a>
   <a href="#section-8">8</a>. Acknowledgments ................................................<a href="#page-19">19</a>
   <a href="#section-9">9</a>. References .....................................................<a href="#page-19">19</a>
      <a href="#section-9.1">9.1</a>. Normative References ......................................<a href="#page-19">19</a>
      <a href="#section-9.2">9.2</a>. Informative References ....................................<a href="#page-20">20</a>
   <a href="#appendix-A">Appendix A</a>. Ethernet Native Service Management ....................<a href="#page-21">21</a>
















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<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>.  Introduction</span>

   <a href="./rfc6310">RFC 6310</a> [<a href="./rfc6310" title="&quot;Pseudowire (PW) Operations, Administration, and Maintenance (OAM) Message Mapping&quot;">RFC6310</a>] specifies the mapping and notification of defect
   states between a pseudowire (PW) and the Attachment Circuit (AC) of
   the end-to-end emulated service.  It standardizes the behavior of
   Provider Edges (PEs) with respect to PW and AC defects for a number
   of technologies (e.g., Asynchronous Transfer Mode (ATM) and Frame
   Relay (FR)) emulated over PWs in MPLS and MPLS/IP Packet Switched
   Networks (PSNs).  However, [<a href="./rfc6310" title="&quot;Pseudowire (PW) Operations, Administration, and Maintenance (OAM) Message Mapping&quot;">RFC6310</a>] does not describe this function
   for the Ethernet PW service owing to its unique characteristics.

   This document specifies the mapping of defect states between ACs and
   associated Ethernet PWs connected in accordance with the PWE3
   architecture [<a href="./rfc3985" title="&quot;Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture&quot;">RFC3985</a>] to realize an end-to-end emulated Ethernet
   service.  This document augments the mapping of defect states between
   a PW and associated AC of the end-to-end emulated service in
   [<a href="./rfc6310" title="&quot;Pseudowire (PW) Operations, Administration, and Maintenance (OAM) Message Mapping&quot;">RFC6310</a>].  Similar to [<a href="./rfc6310" title="&quot;Pseudowire (PW) Operations, Administration, and Maintenance (OAM) Message Mapping&quot;">RFC6310</a>], the intent of this document is to
   standardize the behavior of PEs with respect to failures on Ethernet
   ACs and PWs, so that there is no ambiguity about the alarms generated
   and consequent actions undertaken by PEs in response to specific
   failure conditions.

<span class="h3"><a class="selflink" id="section-1.1" href="#section-1.1">1.1</a>.  Specification of Requirements</span>

   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 [<a href="./rfc2119" title="&quot;Key words for use in RFCs to Indicate Requirement Levels&quot;">RFC2119</a>].

<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>.  Overview</span>

   There are a number of Operations, Administration, and Maintenance
   (OAM) technologies defined for Ethernet, providing various
   functionalities.  This document covers the following Ethernet OAM
   mechanisms and their interworking with PW OAM mechanisms:

   -  Ethernet Link OAM [<a href="#ref-802.3" title="&quot;Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications (Clause 57 for Operations, Administration, and Maintenance)&quot;">802.3</a>]
   -  Ethernet Local Management Interface (E-LMI) [<a href="#ref-MEF16" title="&quot;Ethernet Local Management Interface (E-LMI)&quot;">MEF16</a>]
   -  Ethernet Continuity Check (CC) [<a href="#ref-CFM" title="&quot;Connectivity Fault Management clause of IEEE 802.1Q&quot;">CFM</a>] [<a href="#ref-Y.1731" title="&quot;OAM functions and mechanisms for Ethernet based networks&quot;">Y.1731</a>]
   -  Ethernet Alarm Indication Signaling (AIS) and Remote Defect
      Indication (RDI) [<a href="#ref-Y.1731" title="&quot;OAM functions and mechanisms for Ethernet based networks&quot;">Y.1731</a>]

   Ethernet Link OAM [<a href="#ref-802.3" title="&quot;Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications (Clause 57 for Operations, Administration, and Maintenance)&quot;">802.3</a>] allows some link defect states to be
   detected and communicated across an Ethernet link.  When an Ethernet
   AC is an Ethernet physical port, there may be some application of
   Ethernet Link OAM [<a href="#ref-802.3" title="&quot;Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications (Clause 57 for Operations, Administration, and Maintenance)&quot;">802.3</a>].  Further, E-LMI [<a href="#ref-MEF16" title="&quot;Ethernet Local Management Interface (E-LMI)&quot;">MEF16</a>] also allows for
   some Ethernet Virtual Circuit (EVC) defect states to be communicated
   across an Ethernet User Network Interface (UNI) where Ethernet UNI
   constitutes a single-hop Ethernet link (i.e., without any bridges



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   compliant with IEEE 802.1Q/.1ad in between).  There may be some
   application of E-LMI [<a href="#ref-MEF16" title="&quot;Ethernet Local Management Interface (E-LMI)&quot;">MEF16</a>] for failure notification across single-
   hop Ethernet ACs in certain deployments that specifically do not
   support IEEE Connectivity Fault Management [<a href="#ref-CFM" title="&quot;Connectivity Fault Management clause of IEEE 802.1Q&quot;">CFM</a>] and/or ITU-T Y.1731
   [<a href="#ref-Y.1731" title="&quot;OAM functions and mechanisms for Ethernet based networks&quot;">Y.1731</a>], simply referred to as CFM and Y.1731, respectively, in this
   document.  Mechanisms based on Y.1731 and CFM are applicable in all
   types of Ethernet ACs.  Ethernet Link OAM and E-LMI are optional, and
   their applicability is called out, where applicable.

   Native service (NS) OAM may be transported transparently over the
   corresponding PW as user data.  This is referred to as the "single
   emulated OAM loop mode" per [<a href="./rfc6310" title="&quot;Pseudowire (PW) Operations, Administration, and Maintenance (OAM) Message Mapping&quot;">RFC6310</a>].  For Ethernet, as an example,
   CFM continuity check messages (CCMs) between two Maintenance Entity
   Group End Points (MEPs) can be transported transparently as user data
   over the corresponding PW.  At MEP locations, service failure is
   detected when CCMs are not received over an interval that is 3.5
   times the local CCM transmission interval.  This is one of the
   failure conditions detected via continuity check.  MEP peers can
   exist between customer edge (CE) endpoints (MEPs of a given
   Maintenance Entity Group (MEG) reside on the CEs), between PE pairs
   (the MEPs of a given MEG reside on the PEs), or between the CE and PE
   (the MEPs of a given MEG reside on the PE and CE), as long as the MEG
   level nesting rules are maintained.  It should be noted that Ethernet
   allows the definition of up to 8 MEG levels, each comprised of MEPs
   (Down MEPs and Up MEPs) and Maintenance Entity Group Intermediate
   Points (MIPs).  These levels can be nested or touching.  MEPs and
   MIPs generate and process messages in the same MEG level.  Thus, in
   this document, when we refer to messages sent by a MEP or a MIP to a
   peer MEP or MIP, these MEPs and MIPs are in the same MEG level.

   When interworking two networking domains, such as native Ethernet and
   PWs to provide an end-to-end emulated service, there is a need to
   identify the failure domain and location even when a PE supports both
   the NS OAM mechanisms and the PW OAM mechanisms.  In addition,
   scalability constraints may not allow running proactive monitoring,
   such as CCMs with transmission enabled, at a PE to detect the failure
   of an EVC across the PW domain.  Thus, network-driven alarms
   generated upon failure detection in the NS or PW domain and their
   mappings to the other domain are needed.  There are also cases where
   a PE MAY not be able to process NS OAM messages received on the PW
   even when such messages are defined, as in the case of Ethernet,
   necessitating the need for fault notification message mapping between
   the PW domain and the NS domain.








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   For Multi-Segment PWs (MS-PWs) [<a href="./rfc5659" title="&quot;An Architecture for Multi- Segment Pseudowire Emulation Edge-to-Edge&quot;">RFC5659</a>], Switching PEs (S-PEs) are
   not aware of the NS.  Thus, failure detection and notification at
   S-PEs will be based on PW OAM mechanisms.  Mapping between PW OAM and
   NS OAM will be required at the Terminating PEs (T-PEs) to propagate
   the failure notification to the EVC end points.

<span class="h3"><a class="selflink" id="section-2.1" href="#section-2.1">2.1</a>.  Reference Model and Defect Locations</span>

   Figure 1 was used in [<a href="./rfc6310" title="&quot;Pseudowire (PW) Operations, Administration, and Maintenance (OAM) Message Mapping&quot;">RFC6310</a>]; it is reproduced in this document as
   a reference to highlight defect locations.

                 ACs             PSN tunnel               ACs
                        +----+                  +----+
        +----+          | PE1|==================| PE2|          +----+
        |    |---(a)---(b)..(c)......PW1..(d)..(e)..(f)---(g)---|    |
        | CE1|   (N1)   |    |                  |    |    (N2)  |CE2 |
        |    |----------|............PW2.............|----------|    |
        +----+          |    |==================|    |          +----+
             ^          +----+                  +----+          ^
             |      Provider Edge 1         Provider Edge 2     |
             |                                                  |
             |&lt;-------------- Emulated Service ----------------&gt;|

        Customer                                              Customer
        Edge 1                                                Edge 2

                  Figure 1: PWE3 Network Defect Locations

<span class="h3"><a class="selflink" id="section-2.2" href="#section-2.2">2.2</a>.  Abstract Defect States</span>

   Abstract defect states are also introduced in [<a href="./rfc6310" title="&quot;Pseudowire (PW) Operations, Administration, and Maintenance (OAM) Message Mapping&quot;">RFC6310</a>].  As shown in
   Figure 2, this document uses the same conventions as [<a href="./rfc6310" title="&quot;Pseudowire (PW) Operations, Administration, and Maintenance (OAM) Message Mapping&quot;">RFC6310</a>].  It
   may be noted, however, that CE devices, shown in Figure 2, do not
   necessarily have to be end customer devices.  These are essentially
   devices in client network segments that are connecting to the Packet
   Switched Network (PSN) for the emulated services.

                                   +-----+
              ----AC receive -----&gt;|     |-----PW transmit----&gt;
          CE1                      | PE1 |                    PE2/CE2
              &lt;---AC transmit------|     |&lt;----PW receive-----
                                   +-----+
     (arrows indicate direction of user traffic impacted by a defect)

      Figure 2: Transmit and Receive Defect States and Notifications






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   The procedures outlined in this document define the entry and exit
   criteria for each of the four defect states with respect to Ethernet
   ACs and corresponding PWs; this document also defines the consequent
   actions that PE1 MUST support to properly interwork these defect
   states and corresponding notification messages between the PW domain
   and the native service (NS) domain.  Receive defect state SHOULD have
   precedence over transmit defect state in terms of handling, when both
   transmit and receive defect states are identified simultaneously.

   Following is a summary of the defect states from the viewpoint of PE1
   in Figure 2:

   -  A PW receive defect at PE1 impacts PE1's ability to receive
      traffic on the PW.  Entry and exit criteria for the PW receive
      defect state are described in <a href="#section-4.4.1">Section 4.4.1</a>.

   -  A PW transmit defect at PE1 impacts PE1's ability to send user
      traffic toward CE2.  PE1 MAY be notified of a PW transmit defect
      via a Reverse Defect Indication from PE2, which could point to
      problems associated with PE2's inability to receive traffic on the
      PW or PE2's inability to transmit traffic on its local AC.  Entry
      and exit criteria for the PW transmit defect state are described
      in <a href="#section-4.4.2">Section 4.4.2</a>.

   -  An AC receive defect at PE1 impacts PE1's ability to receive user
      traffic from the client domain attached to PE1 via that AC.  Entry
      and exit criteria for the AC receive defect state are described in
      <a href="#section-5.1">Section 5.1</a>.

   -  An AC transmit defect at PE1 impacts PE1's ability to send user
      traffic on the local AC.  Entry and exit criteria for the AC
      transmit defect state are described in <a href="#section-5.2">Section 5.2</a>.



















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<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>.  Abbreviations and Terminology</span>

<span class="h3"><a class="selflink" id="section-3.1" href="#section-3.1">3.1</a>.  Abbreviations</span>

   AC    Attachment Circuit
   AIS   Alarm Indication Signal
   BFD   Bidirectional Forwarding Detection
   CC    Continuity Check
   CCM   Continuity Check Message
   CE    Customer Edge
   CV    Connectivity Verification
   E-LMI Ethernet Local Management Interface
   EVC   Ethernet Virtual Circuit
   LDP   Label Distribution Protocol
   LoS   Loss of Signal
   MA    Maintenance Association
   MD    Maintenance Domain
   ME    Maintenance Entity
   MEG   Maintenance Entity Group
   MEP   MEG End Point
   MIP   MEG Intermediate Point
   MPLS  Multiprotocol Label Switching
   MS-PW Multi-Segment Pseudowire
   NS    Native Service
   OAM   Operations, Administration, and Maintenance
   PE    Provider Edge
   PSN   Packet Switched Network
   PW    Pseudowire
   RDI   Remote Defect Indication when used in the context of CCM
   RDI   Reverse Defect Indication when used to semantically refer to
         defect indication in the reverse direction
   S-PE  Switching Provider Edge
   T-PE  Terminating Provider Edge
   TLV   Type-Length Value
   VCCV  Virtual Circuit Connectivity Verification

<span class="h3"><a class="selflink" id="section-3.2" href="#section-3.2">3.2</a>.  Terminology</span>

   This document uses the following terms with corresponding
   definitions:

   -  MEG Level: identifies a value in the range of 0-7 associated with
      an Ethernet OAM frame.  MEG level identifies the span of the
      Ethernet OAM frame.

   -  MEG End Point (MEP): is responsible for origination and
      termination of OAM frames for a given MEG.




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   -  MEG Intermediate Point (MIP): is located between peer MEPs and can
      process OAM frames but does not initiate them.

   -  MPLS PSN: a PSN that makes use of MPLS Label-Switched Paths
      [<a href="./rfc3031" title="&quot;Multiprotocol Label Switching Architecture&quot;">RFC3031</a>] as the tunneling technology to forward PW packets.

   -  MPLS/IP PSN: a PSN that makes use of MPLS-in-IP tunneling
      [<a href="./rfc4023" title="&quot;Encapsulating MPLS in IP or Generic Routing Encapsulation (GRE)&quot;">RFC4023</a>] to tunnel MPLS-labeled PW packets over IP tunnels.

   Further, this document also uses the terminology and conventions used
   in [<a href="./rfc6310" title="&quot;Pseudowire (PW) Operations, Administration, and Maintenance (OAM) Message Mapping&quot;">RFC6310</a>].

<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>.  PW Status and Defects</span>

   [<a id="ref-RFC6310">RFC6310</a>] introduces a range of defects that impact PW status.  All
   these defect conditions are applicable for Ethernet PWs.

   Similarly, there are different mechanisms described in [<a href="./rfc6310" title="&quot;Pseudowire (PW) Operations, Administration, and Maintenance (OAM) Message Mapping&quot;">RFC6310</a>] to
   detect PW defects, depending on the PSN type (e.g., MPLS PSN or
   MPLS/IP PSN).  Any of these mechanisms can be used when monitoring
   the state of Ethernet PWs.  [<a href="./rfc6310" title="&quot;Pseudowire (PW) Operations, Administration, and Maintenance (OAM) Message Mapping&quot;">RFC6310</a>] also discusses the
   applicability of these failure detection mechanisms.

<span class="h3"><a class="selflink" id="section-4.1" href="#section-4.1">4.1</a>.  Use of Native Service (NS) Notification</span>

   When two PEs terminate an Ethernet PW with associated MEPs, each PE
   can use native service (NS) OAM capabilities for failure
   notifications by transmitting appropriate NS OAM messages over the
   corresponding PW to the remote PE.  Options include:

   -  Sending of AIS frames from the local MEP to the MEP on the remote
      PE when the MEP needs to convey PE receive defects and when CCM
      transmission is disabled.

   -  Suspending transmission of CCM frames from the local MEP to the
      peer MEP on the remote PE to convey PE receive defects when CCM
      transmission is enabled.

   -  Setting the RDI bit in transmitted CCM frames when loss of CCMs
      from the peer MEP is detected or when the PE needs to convey PW
      reverse defects.

   Similarly, when the defect conditions are cleared, a PE can take one
   of the following actions, depending on the mechanism that was used
   for failure notification, to clear the defect state on the peer PE:

   -  Stopping AIS frame transmission from the local MEP to the MEP on
      the remote PE to clear PW receive defects.



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   -  Resuming transmission of CCM frames from the local MEP to the peer
      MEP on the remote PE to clear PW forward defect notification when
      CCM transmission is enabled.

   -  Clearing the RDI bit in transmitted CCM frames to clear PW
      transmit defect notification when CCM transmission is enabled.

<span class="h3"><a class="selflink" id="section-4.2" href="#section-4.2">4.2</a>.  Use of PW Status Notification for MPLS PSNs</span>

   <a href="./rfc4447">RFC 4447</a> [<a href="./rfc4447" title="&quot;Pseudowire Setup and Maintenance Using the Label Distribution Protocol (LDP)&quot;">RFC4447</a>] specifies that for PWs that have been set up using
   the Label Distribution Protocol (LDP), the default mechanism to
   signal status and defects for ACs and PWs is the LDP status
   notification message.  For PWs established over an MPLS or MPLS/IP
   PSN using other mechanisms (e.g., static configuration), in-band
   signaling using VCCV-BFD [<a href="./rfc5885" title="&quot;Bidirectional Forwarding Detection (BFD) for the Pseudowire Virtual Circuit Connectivity Verification (VCCV)&quot;">RFC5885</a>] SHOULD be used to convey AC and PW
   status and defects.  Alternatively, the mechanisms defined in
   [<a href="./rfc6478" title="&quot;Pseudowire Status for Static Pseudowires&quot;">RFC6478</a>] MAY be used.

   [<a id="ref-RFC6310">RFC6310</a>] identifies the following PW defect status code points:

   -  Forward defect: corresponds to a logical OR of Local Attachment
      Circuit (ingress) Receive Fault, Local PSN-facing PW (egress)
      Transmit Fault, and Pseudowire Not Forwarding fault.

   -  Reverse defect: corresponds to a logical OR of Local Attachment
      Circuit (egress) Transmit Fault and Local PSN-facing PW (ingress)
      Receive Fault.

   There are also scenarios where a PE carries out PW label withdrawal
   instead of PW status notification.  These include administrative
   disablement of the PW or loss of the Target LDP session with the peer
   PE.

<span class="h3"><a class="selflink" id="section-4.3" href="#section-4.3">4.3</a>.  Use of BFD Diagnostic Codes</span>

   When using VCCV, the control channel type and Connectivity
   Verification (CV) type are agreed on between the peer PEs using the
   VCCV parameter field signaled as a sub-TLV of the interface
   parameters TLV when using FEC 129 and the interface parameter sub-TLV
   when using FEC 128 [<a href="./rfc5085" title="&quot;Pseudowire Virtual Circuit Connectivity Verification (VCCV): A Control Channel for Pseudowires&quot;">RFC5085</a>].

   As defined in [<a href="./rfc6310" title="&quot;Pseudowire (PW) Operations, Administration, and Maintenance (OAM) Message Mapping&quot;">RFC6310</a>], when a CV type of 0x04 or 0x10 is used to
   indicate that BFD is used for PW fault detection only, PW defect is
   detected via the BFD session while other defects, such as AC defect
   or PE internal defects preventing it from forwarding traffic, are
   communicated via an LDP status notification message in MPLS and
   MPLS/IP PSNs or other mechanisms in L2TP/IP PSNs.




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   Similarly, when a CV type of 0x08 or 0x20 is used to indicate that
   BFD is used for both PW fault detection and AC/PW fault notification,
   all defects are signaled via BFD.

<span class="h3"><a class="selflink" id="section-4.4" href="#section-4.4">4.4</a>.  PW Defect States Entry and Exit Criteria</span>

<span class="h4"><a class="selflink" id="section-4.4.1" href="#section-4.4.1">4.4.1</a>.  PW Receive Defect State Entry and Exit</span>

   As described in <a href="./rfc6310#section-6.2.1">Section&nbsp;6.2.1 of [RFC6310]</a>, PE1 will enter the PW
   receive defect state if one or more of the following occur:

   -  It receives a Forward Defect Indication (FDI) from PE2 either
      indicating a receive defect on the remote AC or indicating that
      PE2 detected or was notified of a downstream PW fault.

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

   -  It detects a loss of PW connectivity through VCCV-BFD, VCCV-Ping,
      or NS OAM mechanisms (i.e., CC) when enabled, which affects the
      traffic it receives from PE2.

   Note that if the PW LDP 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 receive
   defect state.

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

   -  All previously detected defects have disappeared.
   -  PE2 cleared the FDI, if applicable.

<span class="h4"><a class="selflink" id="section-4.4.2" href="#section-4.4.2">4.4.2</a>.  PW Transmit Defect State Entry and Exit</span>

   PE1 will enter the PW transmit defect state if the following
   conditions occur:

   -  It receives a Reverse Defect Indication (RDI) from PE2 either
      indicating a transmit fault on the remote AC or indicating that
      PE2 detected or was notified of an upstream PW fault.

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

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



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<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>.  Ethernet AC Defect States Entry and Exit Criteria</span>

<span class="h3"><a class="selflink" id="section-5.1" href="#section-5.1">5.1</a>.  AC Receive Defect State Entry and Exit</span>

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

   -  It detects or is notified of a physical-layer fault on the
      Ethernet interface.  Ethernet link failure can be detected based
      on loss of signal (LoS) or via Ethernet Link OAM [<a href="#ref-802.3" title="&quot;Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications (Clause 57 for Operations, Administration, and Maintenance)&quot;">802.3</a>] critical
      link event notifications generated at an upstream node CE1 with
      "Dying Gasp" or "Critical Event" indication or via a client Signal
      Fail message [<a href="#ref-Y.1731" title="&quot;OAM functions and mechanisms for Ethernet based networks&quot;">Y.1731</a>].

   -  A MEP associated with the local AC receives an Ethernet AIS frame
      from CE1.

   -  A MEP associated with the local AC does not receive CCM frames
      from the peer MEP in the client domain (e.g., CE1) within an
      interval equal to 3.5 times the CCM transmission period configured
      for the MEP.  This is the case when CCM transmission is enabled.

   -  A CCM has an Interface Status TLV indicating interface down.
      Other CCM Interface Status TLVs will not be used to indicate
      failure or recovery from failure.

   It should be noted that when a MEP at a PE or a CE receives a CCM
   with the wrong MEG ID, MEP ID, or MEP level, the receiving PE or CE
   SHOULD treat such an event as an AC receive defect.  In any case, if
   such events persist for 3.5 times the MEP local CCM transmission
   time, loss of continuity will be declared at the receiving end.

   PE1 exits the AC receive defect state if all of the conditions that
   resulted in entering the defect state are cleared.  This includes all
   of the following conditions:

   -  Any physical-layer fault on the Ethernet interface, if detected or
      where PE1 was notified previously, is removed (e.g., loss of
      signal (LoS) cleared or Ethernet Link OAM [<a href="#ref-802.3" title="&quot;Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications (Clause 57 for Operations, Administration, and Maintenance)&quot;">802.3</a>] critical link
      event notifications with "Dying Gasp" or "Critical Event"
      indications cleared at an upstream node CE1).

   -  A MEP associated with the local AC does not receive any Ethernet
      AIS frame within a period indicated by previously received AIS if
      AIS resulted in entering the defect state.






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   -  A MEP associated with the local AC and configured with CCM enabled
      receives a configured number (e.g., 3 or more) of consecutive CCM
      frames from the peer MEP on CE1 within an interval equal to a
      multiple (3.5) of the CCM transmission period configured for the
      MEP.

   -  CCM indicates interface status up.

<span class="h3"><a class="selflink" id="section-5.2" href="#section-5.2">5.2</a>.  AC Transmit Defect State Entry and Exit</span>

   PE1 enters the AC transmit defect state if any of the following
   conditions is met:

   -  It detects or is notified of a physical-layer fault on the
      Ethernet interface where the AC is configured (e.g., via loss of
      signal (LoS) or Ethernet Link OAM [<a href="#ref-802.3" title="&quot;Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications (Clause 57 for Operations, Administration, and Maintenance)&quot;">802.3</a>] critical link event
      notifications generated at an upstream node CE1 with "Link Fault"
      indication).

   -  A MEP configured with CCM transmission enabled and associated with
      the local AC receives a CCM frame, with its RDI (Remote Defect
      Indication) bit set, from the peer MEP in the client domain (e.g.,
      CE1).

   PE1 exits the AC transmit defect state if all of the conditions that
   resulted in entering the defect state are cleared.  This includes all
   of the following conditions:

   -  Any physical-layer fault on the Ethernet interface, if detected or
      where PE1 was notified previously, is removed (e.g., LoS cleared
      or Ethernet Link OAM [<a href="#ref-802.3" title="&quot;Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications (Clause 57 for Operations, Administration, and Maintenance)&quot;">802.3</a>] critical link event notifications
      with "Link Fault" indication cleared at an upstream node CE1).

   -  A MEP configured with CCM transmission enabled and associated with
      the local AC does not receive a CCM frame with the RDI bit set,
      having received a previous CCM frame with the RDI bit set from the
      peer MEP in the client domain (e.g., CE1).














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<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>.  Ethernet AC and PW Defect States Interworking</span>

<span class="h3"><a class="selflink" id="section-6.1" href="#section-6.1">6.1</a>.  PW Receive Defect State Entry Procedures</span>

   When the PW status on PE1 transitions from working to PW receive
   defect state, PE1's ability to receive user traffic from CE2 is
   impacted.  As a result, PE1 needs to notify CE1 about this problem.

   Upon entry to the PW receive defect state, the following MUST be
   done:

   -  If PE1 is configured with a Down MEP associated with the local AC
      and CCM transmission is not enabled, the MEP associated with the
      AC MUST transmit AIS frames periodically to the peer MEP in the
      client domain (e.g., on CE1) based on the configured AIS
      transmission period.

   -  If PE1 is configured with a Down MEP associated with the local AC,
      CCM transmission is enabled, and the MEP associated with the AC is
      configured to support the Interface Status TLV in CCMs, the MEP
      associated with the AC MUST transmit CCM frames with the Interface
      Status TLV as being Down to the peer MEP in the client domain
      (e.g., on CE1).

   -  If PE1 is configured with a Down MEP associated with the local AC,
      CCM transmission is enabled, and the MEP associated with the AC is
      configured to not support the Interface Status TLV in CCMs, the
      MEP associated with the AC MUST stop transmitting CCM frames to
      the peer MEP in the client domain (e.g., on CE1).

   -  If PE1 is configured to run E-LMI [<a href="#ref-MEF16" title="&quot;Ethernet Local Management Interface (E-LMI)&quot;">MEF16</a>] with CE1 and if E-LMI is
      used for failure notification, PE1 MUST transmit an E-LMI
      asynchronous STATUS message with report type Single EVC
      Asynchronous Status indicating that the PW is Not Active.

   Further, when PE1 enters the receive defect state, it MUST assume
   that PE2 has no knowledge of the defect and MUST send a reverse
   defect failure notification to PE2.  For MPLS PSN or MPLS/IP PSN,
   this is either done via a PW status notification message indicating a
   reverse defect or done via a VCCV-BFD diagnostic code of reverse
   defect if a VCCV CV type of 0x08 or 0x20 had been negotiated.  When a
   native service OAM mechanism is supported on PE1, it can also use the
   NS OAM notification as specified in <a href="#section-4.1">Section 4.1</a>.

   If PW receive defect state is entered as a result of a forward defect
   notification from PE2 or via loss of control adjacency, no additional
   action is needed since PE2 is expected to be aware of the defect.




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<span class="h3"><a class="selflink" id="section-6.2" href="#section-6.2">6.2</a>.  PW Receive Defect State Exit Procedures</span>

   When the PW status transitions from PW receive defect state to
   working, PE1's ability to receive user traffic from CE2 is restored.
   As a result, PE1 needs to cease defect notification to CE1 by
   performing the following:

   -  If PE1 is configured with a Down MEP associated with the local AC
      and CCM transmission is not enabled, the MEP associated with the
      AC MUST stop transmitting AIS frames towards the peer MEP in the
      client domain (e.g., on CE1).

   -  If PE1 is configured with a Down MEP associated with the local AC,
      CCM transmission is enabled, and the MEP associated with the AC is
      configured to support the Interface Status TLV in CCMs, the MEP
      associated with the AC MUST transmit CCM frames with the Interface
      Status TLV as being Up to the peer MEP in the client domain (e.g.,
      on CE1).

   -  If PE1 is configured with a Down MEP associated with the local AC,
      CCM transmission is enabled, and the MEP associated with the AC is
      configured to not support the Interface Status TLV in CCMs, the
      MEP associated with the AC MUST resume transmitting CCM frames to
      the peer MEP in the client domain (e.g., on CE1).

   -  If PE1 is configured to run E-LMI [<a href="#ref-MEF16" title="&quot;Ethernet Local Management Interface (E-LMI)&quot;">MEF16</a>] with CE1 and E-LMI is
      used for fault notification, PE1 MUST transmit an E-LMI
      asynchronous STATUS message with report type Single EVC
      Asynchronous Status indicating that the PW is Active.

   Further, if the PW receive defect was explicitly detected by PE1, it
   MUST now notify PE2 about clearing of receive defect state by
   clearing the reverse defect notification.  For PW over MPLS PSN or
   MPLS/IP PSN, this is either done via a PW status message indicating a
   working state or done via a VCCV-BFD diagnostic code if a VCCV CV
   type of 0x08 or 0x20 had been negotiated.  When a native service OAM
   mechanism is supported on PE, it can also clear the NS OAM
   notification as specified in <a href="#section-4.1">Section 4.1</a>.

   If PW receive defect was established via notification from PE2 or via
   loss of control adjacency, no additional action is needed since PE2
   is expected to be aware of the defect clearing.









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<span class="h3"><a class="selflink" id="section-6.3" href="#section-6.3">6.3</a>.  PW Transmit Defect State Entry Procedures</span>

   When the PW status transitions from working to PW transmit defect
   state, PE1's ability to transmit user traffic to CE2 is impacted.  As
   a result, PE1 needs to notify CE1 about this problem.

   Upon entry to the PW transmit defect state, the following MUST be
   done:

   -  If PE1 is configured with a Down MEP associated with the local AC
      and CCM transmission is enabled, the MEP associated with the AC
      MUST set the RDI bit in transmitted CCM frames or send a status
      TLV with interface down to the peer MEP in the client domain
      (e.g., on CE1).

   -  If PE1 is configured to run E-LMI [<a href="#ref-MEF16" title="&quot;Ethernet Local Management Interface (E-LMI)&quot;">MEF16</a>] with CE1 and E-LMI is
      used for fault notification, PE1 MUST transmit an E-LMI
      asynchronous STATUS message with report type Single EVC
      Asynchronous Status indicating that the PW is Not Active.

   -  If the PW failure was detected by PE1 without receiving a reverse
      defect notification from PE2, PE1 MUST assume PE2 has no knowledge
      of the defect and MUST notify PE2 by sending an FDI.

<span class="h3"><a class="selflink" id="section-6.4" href="#section-6.4">6.4</a>.  PW Transmit Defect State Exit Procedures</span>

   When the PW status transitions from PW transmit defect state to
   working, PE1's ability to transmit user traffic to CE2 is restored.
   As a result, PE1 needs to cease defect notifications to CE1 and
   perform the following:

   -  If PE1 is configured with a Down MEP associated with the local AC
      and CCM transmission is enabled, the MEP associated with the AC
      MUST clear the RDI bit in the transmitted CCM frames to the peer
      MEP or send a status TLV with interface up to the peer MEP in the
      client domain (e.g., on CE1).

   -  If PE1 is configured to run E-LMI [<a href="#ref-MEF16" title="&quot;Ethernet Local Management Interface (E-LMI)&quot;">MEF16</a>] with CE1, PE1 MUST
      transmit an E-LMI asynchronous STATUS message with report type
      Single EVC Asynchronous Status indicating that the PW is Active.

   -  PE1 MUST clear the FDI to PE2, if applicable.

<span class="h3"><a class="selflink" id="section-6.5" href="#section-6.5">6.5</a>.  AC Receive Defect State Entry Procedures</span>

   When AC status transitions from working to AC receive defect state,
   PE1's ability to receive user traffic from CE1 is impacted.  As a
   result, PE1 needs to notify PE2 and CE1 about this problem.



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   If the AC receive defect is detected by PE1, it MUST notify PE2 in
   the form of a forward defect notification.

   When NS OAM is not supported on PE1, in PW over MPLS PSN or MPLS/IP
   PSN, a forward defect notification is either done via a PW status
   message indicating a forward defect or done via a VCCV-BFD diagnostic
   code of forward defect if a VCCV CV type of 0x08 or 0x20 had been
   negotiated.

   When a native service OAM mechanism is supported on PE1, it can also
   use the NS OAM notification as specified in <a href="#section-4.1">Section 4.1</a>.

   In addition to the above actions, PE1 MUST perform the following:

   -  If PE1 is configured with a Down MEP associated with the local AC
      and CCM transmission is enabled, the MEP associated with the AC
      MUST set the RDI bit in transmitted CCM frames.

<span class="h3"><a class="selflink" id="section-6.6" href="#section-6.6">6.6</a>.  AC Receive Defect State Exit Procedures</span>

   When AC status transitions from AC receive defect state to working,
   PE1's ability to receive user traffic from CE1 is restored.  As a
   result, PE1 needs to cease defect notifications to PE2 and CE1 and
   perform the following:

   -  When NS OAM is not supported on PE1, in PW over MPLS PSN or
      MPLS/IP PSN, the forward defect notification is cleared via a PW
      status message indicating a working state or via a VCCV-BFD
      diagnostic code if a VCCV CV type of 0x08 or 0x20 had been
      negotiated.

   -  When a native service OAM mechanism is supported on PE1, PE1
      clears the NS OAM notification as specified in <a href="#section-4.1">Section 4.1</a>.

   -  If PE1 is configured with a Down MEP associated with the local AC
      and CCM transmission is enabled, the MEP associated with the AC
      MUST clear the RDI bit in transmitted CCM frames to the peer MEP
      in the client domain (e.g., on CE1).

<span class="h3"><a class="selflink" id="section-6.7" href="#section-6.7">6.7</a>.  AC Transmit Defect State Entry Procedures</span>

   When AC status transitions from working to AC transmit defect state,
   PE1's ability to transmit user traffic to CE1 is impacted.  As a
   result, PE1 needs to notify PE2 about this problem.

   If the AC transmit defect is detected by PE1, it MUST notify PE2 in
   the form of a reverse defect notification.




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   When NS OAM is not supported on PE1, in PW over MPLS PSN or MPLS/IP
   PSN, a reverse defect notification is either done via a PW status
   message indicating a reverse defect or done via a VCCV-BFD diagnostic
   code of reverse defect if a VCCV CV type of 0x08 or 0x20 had been
   negotiated.

   When a native service OAM mechanism is supported on PE1, it can also
   use the NS OAM notification as specified in <a href="#section-4.1">Section 4.1</a>.

<span class="h3"><a class="selflink" id="section-6.8" href="#section-6.8">6.8</a>.  AC Transmit Defect State Exit Procedures</span>

   When AC status transitions from AC transmit defect state to working,
   PE1's ability to transmit user traffic to CE1 is restored.  As a
   result, PE1 MUST clear the reverse defect notification to PE2.

   When NS OAM is not supported on PE1, in PW over MPLS PSN or MPLS/IP
   PSN, the reverse defect notification is cleared via a PW status
   message indicating a working state or via a VCCV-BFD diagnostic code
   if a VCCV CV type of 0x08 or 0x20 had been negotiated.

   When a native service OAM mechanism is supported on PE1, PE1 can
   clear NS OAM notification as specified in <a href="#section-4.1">Section 4.1</a>.

<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a>.  Security Considerations</span>

   The OAM interworking mechanisms described in this document do not
   change the security functions inherent in the actual messages.  All
   generic security considerations applicable to PW traffic specified in
   <a href="./rfc3985#section-10">Section&nbsp;10 of [RFC3985]</a> are applicable to NS OAM messages transferred
   inside the PW.

   The security considerations in <a href="./rfc5085#section-10">Section&nbsp;10 of [RFC5085]</a> for VCCV apply
   to the OAM messages thus transferred.  Security considerations
   applicable to the PWE3 control protocol as described in <a href="./rfc4447#section-8.2">Section&nbsp;8.2
   of [RFC4447]</a> apply to OAM indications transferred using the LDP
   status message.

   Since the mechanisms of this document enable propagation of OAM
   messages and fault conditions between native service networks and
   PSNs, continuity of the end-to-end service depends on a trust
   relationship between the operators of these networks.  Security
   considerations for such scenarios are discussed in <a href="./rfc5254#section-7">Section&nbsp;7 of
   [RFC5254]</a>.








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<span class="h2"><a class="selflink" id="section-8" href="#section-8">8</a>.  Acknowledgments</span>

   The authors are thankful to Samer Salam, Matthew Bocci, Yaakov Stein,
   David Black, Lizhong Jin, Greg Mirsky, Huub van Helvoort, and Adrian
   Farrel for their valuable input and comments.

<span class="h2"><a class="selflink" id="section-9" href="#section-9">9</a>.  References</span>

<span class="h3"><a class="selflink" id="section-9.1" href="#section-9.1">9.1</a>.  Normative References</span>

   [<a id="ref-802.3">802.3</a>]    IEEE, "Part 3: Carrier Sense Multiple Access with
              Collision Detection (CSMA/CD) Access Method and Physical
              Layer Specifications (Clause 57 for Operations,
              Administration, and Maintenance)", IEEE Std 802.3-2005,
              December 2005.

   [<a id="ref-CFM">CFM</a>]      IEEE, "Connectivity Fault Management clause of IEEE
              802.1Q", IEEE 802.1Q, 2013.

   [<a id="ref-MEF16">MEF16</a>]    Metro Ethernet Forum, "Ethernet Local Management Interface
              (E-LMI)", Technical Specification MEF16, January 2006.

   [<a id="ref-RFC2119">RFC2119</a>]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc2119">RFC 2119</a>, March 1997.

   [<a id="ref-RFC4447">RFC4447</a>]  Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T., and
              G. Heron, "Pseudowire Setup and Maintenance Using the
              Label Distribution Protocol (LDP)", <a href="./rfc4447">RFC 4447</a>, April 2006.

   [<a id="ref-RFC5085">RFC5085</a>]  Nadeau, T., Ed., and C. Pignataro, Ed., "Pseudowire
              Virtual Circuit Connectivity Verification (VCCV): A
              Control Channel for Pseudowires", <a href="./rfc5085">RFC 5085</a>, December 2007.

   [<a id="ref-RFC5885">RFC5885</a>]  Nadeau, T., Ed., and C. Pignataro, Ed., "Bidirectional
              Forwarding Detection (BFD) for the Pseudowire Virtual
              Circuit Connectivity Verification (VCCV)", <a href="./rfc5885">RFC 5885</a>, June
              2010.

   [<a id="ref-RFC6310">RFC6310</a>]  Aissaoui, M., Busschbach, P., Martini, L., Morrow, M.,
              Nadeau, T., and Y(J). Stein, "Pseudowire (PW) Operations,
              Administration, and Maintenance (OAM) Message Mapping",
              <a href="./rfc6310">RFC 6310</a>, July 2011.

   [<a id="ref-RFC6478">RFC6478</a>]  Martini, L., Swallow, G., Heron, G., and M. Bocci,
              "Pseudowire Status for Static Pseudowires", <a href="./rfc6478">RFC 6478</a>, May
              2012.





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   [<a id="ref-Y.1731">Y.1731</a>]   ITU-T, "OAM functions and mechanisms for Ethernet based
              networks", ITU-T Y.1731, July 2011.

<span class="h3"><a class="selflink" id="section-9.2" href="#section-9.2">9.2</a>.  Informative References</span>

   [<a id="ref-RFC3031">RFC3031</a>]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", <a href="./rfc3031">RFC 3031</a>, January 2001.

   [<a id="ref-RFC3985">RFC3985</a>]  Bryant, S., Ed., and P. Pate, Ed., "Pseudo Wire Emulation
              Edge-to-Edge (PWE3) Architecture", <a href="./rfc3985">RFC 3985</a>, March 2005.

   [<a id="ref-RFC4023">RFC4023</a>]  Worster, T., Rekhter, Y., and E. Rosen, Ed.,
              "Encapsulating MPLS in IP or Generic Routing Encapsulation
              (GRE)", <a href="./rfc4023">RFC 4023</a>, March 2005.

   [<a id="ref-RFC5254">RFC5254</a>]  Bitar, N., Ed., Bocci, M., Ed., and L. Martini, Ed.,
              "Requirements for Multi-Segment Pseudowire Emulation Edge-
              to-Edge (PWE3)", <a href="./rfc5254">RFC 5254</a>, October 2008.

   [<a id="ref-RFC5659">RFC5659</a>]  Bocci, M. and S. Bryant, "An Architecture for Multi-
              Segment Pseudowire Emulation Edge-to-Edge", <a href="./rfc5659">RFC 5659</a>,
              October 2009.





























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<span class="h2"><a class="selflink" id="appendix-A" href="#appendix-A">Appendix A</a>.  Ethernet Native Service Management</span>

   This appendix is informative.

   Ethernet OAM mechanisms are broadly classified into two categories:
   Fault Management (FM) and Performance Monitoring (PM).  ITU-T Y.1731
   [<a href="#ref-Y.1731" title="&quot;OAM functions and mechanisms for Ethernet based networks&quot;">Y.1731</a>] provides coverage for both FM and PM while IEEE CFM [<a href="#ref-CFM" title="&quot;Connectivity Fault Management clause of IEEE 802.1Q&quot;">CFM</a>]
   provides coverage for a subset of FM functions.

   Ethernet OAM also introduces the concept of a Maintenance Entity
   (ME), which is used to identify the entity that needs to be managed.
   An ME is inherently a point-to-point association.  However, in the
   case of a multipoint association, a Maintenance Entity Group (MEG)
   consisting of different MEs is used.  IEEE 802.1 uses the concept of
   a Maintenance Association (MA), which is used to identify both point-
   to-point and multipoint associations.  Each MEG/MA consists of MEG
   End Points (MEPs) that are responsible for originating OAM frames.
   In between the MEPs, there can also be MEG Intermediate Points (MIPs)
   that do not originate OAM frames but do respond to OAM frames from
   MEPs.

   Ethernet OAM allows for hierarchical Maintenance Entities to allow
   for simultaneous end-to-end and segment monitoring.  This is achieved
   by having a provision of up to 8 MEG levels (MD levels), where each
   MEP or MIP is associated with a specific MEG level.

   It is important to note that the FM mechanisms common to both IEEE
   CFM [<a href="#ref-CFM" title="&quot;Connectivity Fault Management clause of IEEE 802.1Q&quot;">CFM</a>] and ITU-T Y.1731 [<a href="#ref-Y.1731" title="&quot;OAM functions and mechanisms for Ethernet based networks&quot;">Y.1731</a>] are completely compatible.

   The common FM mechanisms include:

   1) Continuity Check Message (CCM)

   2) Loopback Message (LBM) and Loopback Reply (LBR)

   3) Link Trace Message (LTM) and Link Trace Reply (LTR)

   CCMs are used for fault detection, including misconnections and
   misconfigurations.  Typically, CCMs are sent as multicast frames or
   unicast frames and also allow RDI notifications.  LBM and LBR are
   used to perform fault verification, while also allowing for MTU
   verification and CIR/EIR (Committed Information Rate / Excess
   Information Rate) measurements.  LTM and LTR can be used for
   discovering the path traversed between a MEP and another target
   MIP/MEP in the same MEG.  LTM and LTR also allow for fault
   localization.





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   In addition, ITU-T Y.1731 [<a href="#ref-Y.1731" title="&quot;OAM functions and mechanisms for Ethernet based networks&quot;">Y.1731</a>] also specifies the following FM
   functions:

   4) Alarm Indication Signal (AIS)

   AIS allows for fault notification to downstream and upstream nodes.

   Further, ITU-T Y.1731 [<a href="#ref-Y.1731" title="&quot;OAM functions and mechanisms for Ethernet based networks&quot;">Y.1731</a>] also specifies the following PM
   functions:

   5) Loss Measurement Message (LMM) and Loss Measurement Reply (LMR)

   6) Delay Measurement Message (DMM) and Delay Measurement Reply (DMR)

   7) 1-way Delay Measurement (1DM)

   While LMM and LMR are used to measure Frame Loss Ratio (FLR), DMM and
   DMR are used to measure single-ended (aka two-way) Frame Delay (FD)
   and Frame Delay Variation (FDV, also known as Jitter).  1DM can be
   used for dual-ended (aka one-way) FD and FDV measurements.































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Authors' Addresses

   Dinesh Mohan (editor)
   Nortel Networks
   EMail: dinmohan@hotmail.com


   Nabil Bitar (editor)
   Verizon
   60 Sylvan Road
   Waltham, MA  02145
   United States
   EMail: nabil.n.bitar@verizon.com


   Ali Sajassi (editor)
   Cisco
   170 West Tasman Drive
   San Jose, CA  95134
   United States
   EMail: sajassi@cisco.com


   Simon Delord
   Alcatel-Lucent
   215 Spring Street
   Melbourne
   Australia
   EMail: simon.delord@gmail.com


   Philippe Niger
   France Telecom
   2 av. Pierre Marzin
   22300 Lannion
   France
   EMail: philippe.niger@orange.com


   Ray Qiu
   Juniper
   1194 North Mathilda Avenue
   Sunnyvale, CA  94089
   United States
   EMail: rqiu@juniper.net






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