





Internet Engineering Task Force (IETF)                        T. Mizrahi
Request for Comments: 7276                                       Marvell
Category: Informational                                      N. Sprecher
ISSN: 2070-1721                             Nokia Solutions and Networks
                                                           E. Bellagamba
                                                                Ericsson
                                                           Y. Weingarten
                                                               June 2014


                             An Overview of
        Operations, Administration, and Maintenance (OAM) Tools

Abstract

   Operations, Administration, and Maintenance (OAM) is a general term
   that refers to a toolset for fault detection and isolation, and for
   performance measurement.  Over the years, various OAM tools have been
   defined for various layers in the protocol stack.

   This document summarizes some of the OAM tools defined in the IETF in
   the context of IP unicast, MPLS, MPLS Transport Profile (MPLS-TP),
   pseudowires, and Transparent Interconnection of Lots of Links
   (TRILL).  This document focuses on tools for detecting and isolating
   failures in networks and for performance monitoring.  Control and
   management aspects of OAM are outside the scope of this document.
   Network repair functions such as Fast Reroute (FRR) and protection
   switching, which are often triggered by OAM protocols, are also out
   of the scope of this document.

   The target audience of this document includes network equipment
   vendors, network operators, and standards development organizations.
   This document can be used as an index to some of the main OAM tools
   defined in the IETF.  At the end of the document, a list of the OAM
   toolsets and a list of the OAM functions are presented as a summary.
















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Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   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).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7276.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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





















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Table of Contents

   1. Introduction ....................................................4
      1.1. Background .................................................5
      1.2. Target Audience ............................................6
      1.3. OAM-Related Work in the IETF ...............................6
      1.4. Focusing on the Data Plane .................................7
   2. Terminology .....................................................8
      2.1. Abbreviations ..............................................8
      2.2. Terminology Used in OAM Standards .........................10
           2.2.1. General Terms ......................................10
           2.2.2. Operations, Administration, and Maintenance ........10
           2.2.3. Functions, Tools, and Protocols ....................11
           2.2.4. Data Plane, Control Plane, and Management Plane ....11
           2.2.5. The Players ........................................12
           2.2.6. Proactive and On-Demand Activation .................13
           2.2.7. Connectivity Verification and Continuity Checks ....14
           2.2.8. Connection-Oriented vs. Connectionless
                  Communication ......................................15
           2.2.9. Point-to-Point vs. Point-to-Multipoint Services ....16
           2.2.10. Failures ..........................................16
   3. OAM Functions ..................................................17
   4. OAM Tools in the IETF - A Detailed Description .................18
      4.1. IP Ping ...................................................18
      4.2. IP Traceroute .............................................19
      4.3. Bidirectional Forwarding Detection (BFD) ..................20
           4.3.1. Overview ...........................................20
           4.3.2. Terminology ........................................20
           4.3.3. BFD Control ........................................20
           4.3.4. BFD Echo ...........................................21
      4.4. MPLS OAM ..................................................21
           4.4.1. LSP Ping ...........................................21
           4.4.2. BFD for MPLS .......................................22
           4.4.3. OAM for Virtual Private Networks (VPNs) over MPLS ..23
      4.5. MPLS-TP OAM ...............................................23
           4.5.1. Overview ...........................................23
           4.5.2. Terminology ........................................24
           4.5.3. Generic Associated Channel .........................25
           4.5.4. MPLS-TP OAM Toolset ................................25
                  4.5.4.1. Continuity Check and Connectivity
                           Verification ..............................26
                  4.5.4.2. Route Tracing .............................26
                  4.5.4.3. Lock Instruct .............................27
                  4.5.4.4. Lock Reporting ............................27
                  4.5.4.5. Alarm Reporting ...........................27
                  4.5.4.6. Remote Defect Indication ..................27
                  4.5.4.7. Client Failure Indication .................27




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                  4.5.4.8. Performance Monitoring ....................28
                           4.5.4.8.1. Packet Loss Measurement (LM) ...28
                           4.5.4.8.2. Packet Delay Measurement (DM) ..28
      4.6. Pseudowire OAM ............................................29
           4.6.1. Pseudowire OAM Using Virtual Circuit
                  Connectivity Verification (VCCV) ...................29
           4.6.2. Pseudowire OAM Using G-ACh .........................30
           4.6.3. Attachment Circuit - Pseudowire Mapping ............30
      4.7. OWAMP and TWAMP ...........................................31
           4.7.1. Overview ...........................................31
           4.7.2. Control and Test Protocols .........................32
           4.7.3. OWAMP ..............................................32
           4.7.4. TWAMP ..............................................33
      4.8. TRILL .....................................................33
   5. Summary ........................................................34
      5.1. Summary of OAM Tools ......................................34
      5.2. Summary of OAM Functions ..................................37
      5.3. Guidance to Network Equipment Vendors .....................38
   6. Security Considerations ........................................38
   7. Acknowledgments ................................................39
   8. References .....................................................39
      8.1. Normative References ......................................39
      8.2. Informative References ....................................39
   Appendix A. List of OAM Documents ................................ 46
      A.1. List of IETF OAM Documents ............................... 46
      A.2. List of Selected Non-IETF OAM Documents .................. 50

1.  Introduction

   "OAM" is a general term that refers to a toolset for detecting,
   isolating, and reporting failures, and for monitoring network
   performance.

   There are several different interpretations of the "OAM" acronym.
   This document refers to Operations, Administration, and Maintenance,
   as recommended in Section 3 of [OAM-Def].

   This document summarizes some of the OAM tools defined in the IETF in
   the context of IP unicast, MPLS, MPLS Transport Profile (MPLS-TP),
   pseudowires, and TRILL.

   This document focuses on tools for detecting and isolating failures
   and for performance monitoring.  Hence, this document focuses on the
   tools used for monitoring and measuring the data plane; control and
   management aspects of OAM are outside the scope of this document.
   Network repair functions such as Fast Reroute (FRR) and protection
   switching, which are often triggered by OAM protocols, are also out
   of the scope of this document.



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1.1.  Background

   OAM was originally used in traditional communication technologies
   such as E1 and T1, evolving into Plesiochronous Digital Hierarchy
   (PDH) and then later into Synchronous Optical Network / Synchronous
   Digital Hierarchy (SONET/SDH).  ATM was probably the first technology
   to include inherent OAM support from day one, while in other
   technologies OAM was typically defined in an ad hoc manner after the
   technology was already defined and deployed.  Packet-based networks
   were traditionally considered unreliable and best effort.  As packet-
   based networks evolved, they have become the common transport for
   both data and telephony, replacing traditional transport protocols.
   Consequently, packet-based networks were expected to provide a
   similar "carrier grade" experience, and specifically to support more
   advanced OAM functions, beyond ICMP and router hellos, that were
   traditionally used for fault detection.

   As typical networks have a multi-layer architecture, the set of OAM
   protocols similarly take a multi-layer structure; each layer has its
   own OAM protocols.  Moreover, OAM can be used at different levels of
   hierarchy in the network to form a multi-layer OAM solution, as shown
   in the example in Figure 1.

   Figure 1 illustrates a network in which IP traffic between two
   customer edges is transported over an MPLS provider network.  MPLS
   OAM is used at the provider level for monitoring the connection
   between the two provider edges, while IP OAM is used at the customer
   level for monitoring the end-to-end connection between the two
   customer edges.

           |<-------------- Customer-level OAM -------------->|
                 IP OAM (Ping, Traceroute, OWAMP, TWAMP)

                        |<- Provider-level OAM ->|
                            MPLS OAM (LSP Ping)

     +-----+       +----+                        +----+       +-----+
     |     |       |    |========================|    |       |     |
     |     |-------|    |          MPLS          |    |-------|     |
     |     |  IP   |    |                        |    |  IP   |     |
     +-----+       +----+                        +----+       +-----+
     Customer     Provider                      Provider      Customer
       Edge         Edge                          Edge          Edge

                  Figure 1: Example of Multi-layer OAM






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1.2.  Target Audience

   The target audience of this document includes:

   o  Standards development organizations - Both IETF working groups and
      non-IETF organizations can benefit from this document when
      designing new OAM protocols, or when looking to reuse existing OAM
      tools for new technologies.

   o  Network equipment vendors and network operators can use this
      document as an index to some of the common IETF OAM tools.

   It should be noted that some background in OAM is necessary in order
   to understand and benefit from this document.  Specifically, the
   reader is assumed to be familiar with the term "OAM" [OAM-Def], the
   motivation for using OAM, and the distinction between OAM and network
   management [OAM-Mng].

1.3.  OAM-Related Work in the IETF

   This memo provides an overview of the different sets of OAM tools
   defined by the IETF.  The set of OAM tools described in this memo are
   applicable to IP unicast, MPLS, pseudowires, MPLS Transport Profile
   (MPLS-TP), and TRILL.  While OAM tools that are applicable to other
   technologies exist, they are beyond the scope of this memo.

   This document focuses on IETF documents that have been published as
   RFCs, while other ongoing OAM-related work is outside the scope.

   The IETF has defined OAM protocols and tools in several different
   contexts.  We roughly categorize these efforts into a few sets of
   OAM-related RFCs, listed in Table 1.  Each set defines a logically
   coupled set of RFCs, although the sets are in some cases intertwined
   by common tools and protocols.

   The discussion in this document is ordered according to these sets
   (the acronyms and abbreviations are listed in Section 2.1).














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                        +--------------+------------+
                        | Toolset      | Transport  |
                        |              | Technology |
                        +--------------+------------+
                        |IP Ping       | IPv4/IPv6  |
                        +--------------+------------+
                        |IP Traceroute | IPv4/IPv6  |
                        +--------------+------------+
                        |BFD           | generic    |
                        +--------------+------------+
                        |MPLS OAM      | MPLS       |
                        +--------------+------------+
                        |MPLS-TP OAM   | MPLS-TP    |
                        +--------------+------------+
                        |Pseudowire OAM| Pseudowires|
                        +--------------+------------+
                        |OWAMP and     | IPv4/IPv6  |
                        |TWAMP         |            |
                        +--------------+------------+
                        |TRILL OAM     | TRILL      |
                        +--------------+------------+

                Table 1: OAM Toolset Packages in the IETF Documents

   This document focuses on OAM tools that have been developed in the
   IETF.  A short summary of some of the significant OAM standards that
   have been developed in other standard organizations is presented in
   Appendix A.2.

1.4.  Focusing on the Data Plane

   OAM tools may, and quite often do, work in conjunction with a control
   plane and/or management plane.  OAM provides instrumentation tools
   for measuring and monitoring the data plane.  OAM tools often use
   control-plane functions, e.g., to initialize OAM sessions and to
   exchange various parameters.  The OAM tools communicate with the
   management plane to raise alarms, and often OAM tools may be
   activated by the management plane (as well as by the control plane),
   e.g., to locate and localize problems.

   The considerations of the control-plane maintenance tools and the
   functionality of the management plane are out of scope for this
   document, which concentrates on presenting the data-plane tools that
   are used for OAM.  Network repair functions such as Fast Reroute
   (FRR) and protection switching, which are often triggered by OAM
   protocols, are also out of the scope of this document.





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   Since OAM protocols are used for monitoring the data plane, it is
   imperative for OAM tools to be capable of testing the actual data
   plane with as much accuracy as possible.  Thus, it is important to
   enforce fate-sharing between OAM traffic that monitors the data plane
   and the data-plane traffic it monitors.

2.  Terminology

2.1.  Abbreviations

   ACH      Associated Channel Header

   AIS      Alarm Indication Signal

   ATM      Asynchronous Transfer Mode

   BFD      Bidirectional Forwarding Detection

   CC       Continuity Check

   CC-V     Continuity Check and Connectivity Verification

   CV       Connectivity Verification

   DM       Delay Measurement

   ECMP     Equal-Cost Multipath

   FEC      Forwarding Equivalence Class

   FRR      Fast Reroute

   G-ACh    Generic Associated Channel

   GAL      Generic Associated Channel Label

   ICMP     Internet Control Message Protocol

   L2TP     Layer 2 Tunneling Protocol

   L2VPN    Layer 2 Virtual Private Network

   L3VPN    Layer 3 Virtual Private Network

   LCCE     L2TP Control Connection Endpoint

   LDP      Label Distribution Protocol




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   LER      Label Edge Router

   LM       Loss Measurement

   LSP      Label Switched Path

   LSR      Label Switching Router

   ME       Maintenance Entity

   MEG      Maintenance Entity Group

   MEP      MEG End Point

   MIP      MEG Intermediate Point

   MP       Maintenance Point

   MPLS     Multiprotocol Label Switching

   MPLS-TP  MPLS Transport Profile

   MTU      Maximum Transmission Unit

   OAM      Operations, Administration, and Maintenance

   OWAMP    One-Way Active Measurement Protocol

   PDH      Plesiochronous Digital Hierarchy

   PE       Provider Edge

   PSN      Public Switched Network

   PW       Pseudowire

   PWE3     Pseudowire Emulation Edge-to-Edge

   RBridge  Routing Bridge

   RDI      Remote Defect Indication

   SDH      Synchronous Digital Hierarchy

   SONET    Synchronous Optical Network

   TRILL    Transparent Interconnection of Lots of Links




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   TTL      Time To Live

   TWAMP    Two-Way Active Measurement Protocol

   VCCV     Virtual Circuit Connectivity Verification

   VPN      Virtual Private Network

2.2.  Terminology Used in OAM Standards

2.2.1.  General Terms

   A wide variety of terms is used in various OAM standards.  This
   section presents a comparison of the terms used in various OAM
   standards, without fully quoting the definition of each term.

   An interesting overview of the term "OAM" and its derivatives is
   presented in [OAM-Def].  A thesaurus of terminology for MPLS-TP terms
   is presented in [TP-Term], which provides a good summary of some of
   the OAM-related terminology.

2.2.2.  Operations, Administration, and Maintenance

   The following definition of OAM is quoted from [OAM-Def]:

   The components of the "OAM" acronym (and provisioning) are defined as
   follows:

   o  Operations - Operation activities are undertaken to keep the
      network (and the services that the network provides) up and
      running.  It includes monitoring the network and finding problems.
      Ideally these problems should be found before users are affected.

   o  Administration - Administration activities involve keeping track
      of resources in the network and how they are used.  It includes
      all the bookkeeping that is necessary to track networking
      resources and the network under control.

   o  Maintenance - Maintenance activities are focused on facilitating
      repairs and upgrades -- for example, when equipment must be
      replaced, when a router needs a patch for an operating system
      image, or when a new switch is added to a network.  Maintenance
      also involves corrective and preventive measures to make the
      managed network run more effectively, e.g., adjusting device
      configuration and parameters.






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2.2.3.  Functions, Tools, and Protocols

   OAM Function

      An OAM function is an instrumentation measurement type or
      diagnostic.

      OAM functions are the atomic building blocks of OAM, where each
      function defines an OAM capability.

      Typical examples of OAM functions are presented in Section 3.

   OAM Protocol

      An OAM protocol is a protocol used for implementing one or more
      OAM functions.

      The OWAMP-Test [OWAMP] is an example of an OAM protocol.

   OAM Tool

      An OAM tool is a specific means of applying one or more OAM
      functions.

      In some cases, an OAM protocol *is* an OAM tool, e.g., OWAMP-Test.
      In other cases, an OAM tool uses a set of protocols that are not
      strictly OAM related; for example, Traceroute (Section 4.2) can be
      implemented using UDP and ICMP messages, without using an OAM
      protocol per se.

2.2.4.  Data Plane, Control Plane, and Management Plane

   Data Plane

      The data plane is the set of functions used to transfer data in
      the stratum or layer under consideration [ITU-Terms].

      The data plane is also known as the forwarding plane or the user
      plane.

   Control Plane

      The control plane is the set of protocols and mechanisms that
      enable routers to efficiently learn how to forward packets towards
      their final destination (based on [Comp]).






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   Management Plane

      The term "Management Plane", as described in [Mng], is used to
      describe the exchange of management messages through management
      protocols (often transported by IP and by IP transport protocols)
      between management applications and the managed entities such as
      network nodes.

   Data Plane vs. Control Plane vs. Management Plane

      The distinction between the planes is at times a bit vague.  For
      example, the definition of "Control Plane" above may imply that
      OAM tools such as ping, BFD, and others are in fact in the control
      plane.

      This document focuses on tools used for monitoring the data plane.
      While these tools could arguably be considered to be in the
      control plane, these tools monitor the data plane, and hence it is
      imperative to have fate-sharing between OAM traffic that monitors
      the data plane and the data-plane traffic it monitors.

      Another potentially vague distinction is between the management
      plane and control plane.  The management plane should be seen as
      separate from, but possibly overlapping with, the control plane
      (based on [Mng]).

2.2.5.  The Players

   An OAM tool is used between two (or more) peers.  Various terms are
   used in IETF documents to refer to the players that take part in OAM.
   Table 2 summarizes the terms used in each of the toolsets discussed
   in this document.



















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        +--------------------------+---------------------------+
        | Toolset                  | Terms                     |
        +--------------------------+---------------------------+
        | Ping / Traceroute        |- Host                     |
        | ([ICMPv4], [ICMPv6],     |- Node                     |
        |  [TCPIP-Tools])          |- Interface                |
        |                          |- Gateway                  |
        + ------------------------ + ------------------------- +
        | BFD [BFD]                |- System                   |
        + ------------------------ + ------------------------- +
        | MPLS OAM [MPLS-OAM-FW]   |- LSR                      |
        + ------------------------ + ------------------------- +
        | MPLS-TP OAM [TP-OAM-FW]  |- End Point - MEP          |
        |                          |- Intermediate Point - MIP |
        + ------------------------ + ------------------------- +
        | Pseudowire OAM [VCCV]    |- PE                       |
        |                          |- LCCE                     |
        + ------------------------ + ------------------------- +
        | OWAMP and TWAMP          |- Host                     |
        | ([OWAMP], [TWAMP])       |- End system               |
        + ------------------------ + ------------------------- +
        | TRILL OAM [TRILL-OAM]    |- RBridge                  |
        +--------------------------+---------------------------+

                  Table 2: Maintenance Point Terminology

2.2.6.  Proactive and On-Demand Activation

   The different OAM tools may be used in one of two basic types of
   activation:

   Proactive

      Proactive activation - indicates that the tool is activated on a
      continual basis, where messages are sent periodically, and errors
      are detected when a certain number of expected messages are not
      received.

   On-demand

      On-demand activation - indicates that the tool is activated
      "manually" to detect a specific anomaly.









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2.2.7.  Connectivity Verification and Continuity Checks

   Two distinct classes of failure management functions are used in OAM
   protocols: Connectivity Verification and Continuity Checks.  The
   distinction between these terms is defined in [MPLS-TP-OAM] and is
   used similarly in this document.

   Continuity Check

      Continuity Checks are used to verify that a destination is
      reachable, and are typically sent proactively, though they can be
      invoked on-demand as well.

   Connectivity Verification

      A Connectivity Verification function allows Alice to check whether
      she is connected to Bob or not.  It is noted that while the CV
      function is performed in the data plane, the "expected path" is
      predetermined in either the control plane or the management plane.
      A Connectivity Verification (CV) protocol typically uses a CV
      message, followed by a CV reply that is sent back to the
      originator.  A CV function can be applied proactively or
      on-demand.

      Connectivity Verification tools often perform path verification as
      well, allowing Alice to verify that messages from Bob are received
      through the correct path, thereby verifying not only that the two
      MPs are connected, but also that they are connected through the
      expected path, allowing detection of unexpected topology changes.

      Connectivity Verification functions can also be used for checking
      the MTU of the path between the two peers.

      Connectivity Verification and Continuity Checks are considered
      complementary mechanisms and are often used in conjunction with
      each other.















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2.2.8.  Connection-Oriented vs. Connectionless Communication

   Connection-Oriented

      In connection-oriented technologies, an end-to-end connection is
      established (by a control protocol or provisioned by a management
      system) prior to the transmission of data.

      Typically a connection identifier is used to identify the
      connection.  In connection-oriented technologies, it is often the
      case (although not always) that all packets belonging to a
      specific connection use the same route through the network.

   Connectionless

      In connectionless technologies, data is typically sent between end
      points without prior arrangement.  Packets are routed
      independently based on their destination address, and hence
      different packets may be routed in a different way across the
      network.

   Discussion

      The OAM tools described in this document include tools that
      support connection-oriented technologies, as well as tools for
      connectionless technologies.

      In connection-oriented technologies, OAM is used to monitor a
      *specific* connection; OAM packets are forwarded through the same
      route as the data traffic and receive the same treatment.  In
      connectionless technologies, OAM is used between a source and
      destination pair without defining a specific connection.
      Moreover, in some cases, the route of OAM packets may differ from
      the one of the data traffic.  For example, the connectionless IP
      Ping (Section 4.1) tests the reachability from a source to a given
      destination, while the connection-oriented LSP Ping (Section
      4.4.1) is used for monitoring a specific LSP (connection) and
      provides the capability to monitor all the available paths used by
      an LSP.

      It should be noted that in some cases connectionless protocols are
      monitored by connection-oriented OAM protocols.  For example,
      while IP is a connectionless protocol, it can be monitored by BFD
      (Section 4.3), which is connection oriented.







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2.2.9.  Point-to-Point vs. Point-to-Multipoint Services

   Point-to-point (P2P)

      A P2P service delivers data from a single source to a single
      destination.

   Point-to-multipoint (P2MP)

      A P2MP service delivers data from a single source to a one or more
      destinations (based on [Signal]).

      An MP2MP service is a service that delivers data from more than
      one source to one or more receivers (based on [Signal]).

      Note: the two definitions for P2MP and MP2MP are quoted from
      [Signal].  Although [Signal] describes a specific case of P2MP and
      MP2MP that is MPLS-specific, these two definitions also apply to
      non-MPLS cases.

   Discussion

      The OAM tools described in this document include tools for P2P
      services, as well as tools for P2MP services.

      The distinction between P2P services and P2MP services affects the
      corresponding OAM tools.  A P2P service is typically simpler to
      monitor, as it consists of a single pair of endpoints.  P2MP and
      MP2MP services present several challenges.  For example, in a P2MP
      service, the OAM mechanism not only verifies that each of the
      destinations is reachable from the source but also verifies that
      the P2MP distribution tree is intact and loop-free.

2.2.10.  Failures

   The terms "Failure", "Fault", and "Defect" are used interchangeably
   in the standards, referring to a malfunction that can be detected by
   a Connectivity Verification or a Continuity Check.  In some
   standards, such as 802.1ag [IEEE802.1Q], there is no distinction
   between these terms, while in other standards each of these terms
   refers to a different type of malfunction.










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   The terminology used in IETF MPLS-TP OAM is based on the ITU-T
   terminology, which distinguishes between these three terms in
   [ITU-T-G.806] as follows:

   Fault

   The term "Fault" refers to an inability to perform a required action,
   e.g., an unsuccessful attempt to deliver a packet.

   Defect

   The term "Defect" refers to an interruption in the normal operation,
   such as a consecutive period of time where no packets are delivered
   successfully.

   Failure

   The term "Failure" refers to the termination of the required
   function.  While a Defect typically refers to a limited period of
   time, a failure refers to a long period of time.

3.  OAM Functions

   This subsection provides a brief summary of the common OAM functions
   used in OAM-related standards.  These functions are used as building
   blocks in the OAM standards described in this document.

   o  Connectivity Verification (CV), Path Verification, and Continuity
      Check (CC):
      As defined in Section 2.2.7.

   o  Path Discovery / Fault Localization:
      This function can be used to trace the route to a destination,
      i.e., to identify the nodes along the route to the destination.
      When more than one route is available to a specific destination,
      this function traces one of the available routes.  When a failure
      occurs, this function attempts to detect the location of the
      failure.
      Note that the term "route tracing" (or "Traceroute"), which is
      used in the context of IP and MPLS, is sometimes referred to as
      "path tracing" in the context of other protocols, such as TRILL.










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   o  Performance Monitoring:
      Typically refers to:

      *  Loss Measurement (LM) - monitors the packet loss rate.

      *  Delay Measurement (DM) - monitors the delay and delay variation
         (jitter).

4.  OAM Tools in the IETF - A Detailed Description

   This section presents a detailed description of the sets of OAM-
   related tools in each of the toolsets in Table 1.

4.1.  IP Ping

   Ping is a common network diagnostic application for IP networks that
   use ICMP.  According to [NetTerms], 'Ping' is an abbreviation for
   Packet internet groper, although the term has been so commonly used
   that it stands on its own.  As defined in [NetTerms], it is a program
   used to test reachability of destinations by sending them an ICMP
   Echo request and waiting for a reply.

   The ICMP Echo request/reply exchange in Ping is used as a Continuity
   Check function for the Internet Protocol.  The originator transmits
   an ICMP Echo request packet, and the receiver replies with an Echo
   reply.  ICMP Ping is defined in two variants: [ICMPv4] is used for
   IPv4, and [ICMPv6] is used for IPv6.

   Ping can be invoked to either a unicast destination or a multicast
   destination.  In the latter case, all members of the multicast group
   send an Echo reply back to the originator.

   Ping implementations typically use ICMP messages.  UDP Ping is a
   variant that uses UDP messages instead of ICMP Echo messages.

   Ping is a single-ended Continuity Check, i.e., it allows the
   *initiator* of the Echo request to test the reachability.  If it is
   desirable for both ends to test the reachability, both ends have to
   invoke Ping independently.

   Note that since ICMP filtering is deployed in some routers and
   firewalls, the usefulness of Ping is sometimes limited in the wider
   Internet.  This limitation is equally relevant to Traceroute.








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4.2.  IP Traceroute

   Traceroute ([TCPIP-Tools], [NetTools]) is an application that allows
   users to discover a path between an IP source and an IP destination.

   The most common way to implement Traceroute [TCPIP-Tools] is
   described as follows.  Traceroute sends a sequence of UDP packets to
   UDP port 33434 at the destination.  By default, Traceroute begins by
   sending three packets (the number of packets is configurable in most
   Traceroute implementations), each with an IP Time-To-Live (or Hop
   Limit in IPv6) value of one, to the destination.  These packets
   expire as soon as they reach the first router in the path.
   Consequently, that router sends three ICMP Time Exceeded Messages
   back to the Traceroute application.  Traceroute now sends another
   three UDP packets, each with the TTL value of 2.  These messages
   cause the second router to return ICMP messages.  This process
   continues, with ever-increasing values for the TTL field, until the
   packets actually reach the destination.  Because no application
   listens to port 33434 at the destination, the destination returns
   ICMP Destination Unreachable Messages indicating an unreachable port.
   This event indicates to the Traceroute application that it is
   finished.  The Traceroute program displays the round-trip delay
   associated with each of the attempts.

   While Traceroute is a tool that finds *a* path from A to B, it should
   be noted that traffic from A to B is often forwarded through Equal-
   Cost Multipaths (ECMPs).  Paris Traceroute [PARIS] is an extension to
   Traceroute that attempts to discovers all the available paths from A
   to B by scanning different values of header fields (such as UDP
   ports) in the probe packets.

   It is noted that Traceroute is an application, and not a protocol.
   As such, it has various different implementations.  One of the most
   common ones uses UDP probe packets, as described above.  Other
   implementations exist that use other types of probe messages, such as
   ICMP or TCP.

   Note that IP routing may be asymmetric.  While Traceroute discovers a
   path between a source and destination, it does not reveal the reverse
   path.

   A few ICMP extensions ([ICMP-MP], [ICMP-Int]) have been defined in
   the context of Traceroute.  These documents define several
   extensions, including extensions to the ICMP Destination Unreachable
   message, that can be used by Traceroute applications.






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   Traceroute allows path discovery to *unicast* destination addresses.
   A similar tool [mtrace] was defined for multicast destination
   addresses; it allows tracing the route that a multicast IP packet
   takes from a source to a particular receiver.

4.3.  Bidirectional Forwarding Detection (BFD)

4.3.1.  Overview

   While multiple OAM tools have been defined for various protocols in
   the protocol stack, Bidirectional Forwarding Detection [BFD], defined
   by the IETF BFD working group, is a generic OAM tool that can be
   deployed over various encapsulating protocols, and in various medium
   types.  The IETF has defined variants of the protocol for IP
   ([BFD-IP], [BFD-Multi]), for MPLS LSPs [BFD-LSP], and for pseudowires
   [BFD-VCCV].  The usage of BFD in MPLS-TP is defined in [TP-CC-CV].

   BFD includes two main OAM functions, using two types of BFD packets:
   BFD Control packets and BFD Echo packets.

4.3.2.  Terminology

   BFD operates between *systems*.  The BFD protocol is run between two
   or more systems after establishing a *session*.

4.3.3.  BFD Control

   BFD supports a bidirectional Continuity Check, using BFD Control
   packets that are exchanged within a BFD session.  BFD sessions
   operate in one of two modes:

   o  Asynchronous mode (i.e., proactive): in this mode, BFD Control
      packets are sent periodically.  When the receiver detects that no
      BFD Control packets have been received during a predetermined
      period of time, a failure is reported.

   o  Demand mode: in this mode, BFD Control packets are sent on demand.
      Upon need, a system initiates a series of BFD Control packets to
      check the continuity of the session.  BFD Control packets are sent
      independently in each direction.

   Each of the endpoints (referred to as systems) of the monitored path
   maintains its own session identification, called a Discriminator;
   both Discriminators are included in the BFD Control Packets that are
   exchanged between the endpoints.  At the time of session
   establishment, the Discriminators are exchanged between the two
   endpoints.  In addition, the transmission (and reception) rate is




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   negotiated between the two endpoints, based on information included
   in the control packets.  These transmission rates may be renegotiated
   during the session.

   During normal operation of the session, i.e., when no failures have
   been detected, the BFD session is in the Up state.  If no BFD Control
   packets are received during a period of time called the Detection
   Time, the session is declared to be Down.  The detection time is a
   function of the pre-configured or negotiated transmission rate and a
   parameter called Detect Mult.  Detect Mult determines the number of
   missing BFD Control packets that cause the session to be declared as
   Down.  This parameter is included in the BFD Control packet.

4.3.4.  BFD Echo

   A BFD Echo packet is sent to a peer system and is looped back to the
   originator.  The echo function can be used proactively or on demand.

   The BFD Echo function has been defined in BFD for IPv4 and IPv6
   ([BFD-IP]), but it is not used in BFD for MPLS LSPs or PWs, or in BFD
   for MPLS-TP.

4.4.  MPLS OAM

   The IETF MPLS working group has defined OAM for MPLS LSPs.  The
   requirements and framework of this effort are defined in
   [MPLS-OAM-FW] and [MPLS-OAM], respectively.  The corresponding OAM
   tool defined, in this context, is LSP Ping [LSP-Ping].  OAM for P2MP
   services is defined in [MPLS-P2MP].

   BFD for MPLS [BFD-LSP] is an alternative means for detecting data-
   plane failures, as described below.

4.4.1.  LSP Ping

   LSP Ping is modeled after the Ping/Traceroute paradigm, and thus it
   may be used in one of two modes:

   o  "Ping" mode: In this mode, LSP Ping is used for end-to-end
      Connectivity Verification between two LERs.

   o  "Traceroute" mode: This mode is used for hop-by-hop fault
      isolation.








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   LSP Ping is based on the ICMP Ping operation (of data-plane
   Connectivity Verification) with additional functionality to verify
   data-plane vs. control-plane consistency for a Forwarding Equivalence
   Class (FEC) and also to identify Maximum Transmission Unit (MTU)
   problems.

   The Traceroute functionality may be used to isolate and localize MPLS
   faults, using the Time-To-Live (TTL) indicator to incrementally
   identify the sub-path of the LSP that is successfully traversed
   before the faulty link or node.

   The challenge in MPLS networks is that the traffic of a given LSP may
   be load-balanced across Equal-Cost Multipaths (ECMPs).  LSP Ping
   monitors all the available paths of an LSP by monitoring its
   different FECs.  Note that MPLS-TP does not use ECMP, and thus does
   not require OAM over multiple paths.

   Another challenge is that an MPLS LSP does not necessarily have a
   return path; traffic that is sent back from the egress LSR to the
   ingress LSR is not necessarily sent over an MPLS LSP, but it can be
   sent through a different route, such as an IP route.  Thus,
   responding to an LSP Ping message is not necessarily as trivial as in
   IP Ping, where the responder just swaps the source and destination IP
   addresses.  Note that this challenge is not applicable to MPLS-TP,
   where a return path is always available.

   It should be noted that LSP Ping supports unique identification of
   the LSP within an addressing domain.  The identification is checked
   using the full FEC identification.  LSP Ping is extensible to include
   additional information needed to support new functionality, by use of
   Type-Length-Value (TLV) constructs.  The usage of TLVs is typically
   handled by the control plane, as it is not easy to implement in
   hardware.

   LSP Ping supports both asynchronous and on-demand activation.

4.4.2.  BFD for MPLS

   BFD [BFD-LSP] can be used to detect MPLS LSP data-plane failures.

   A BFD session is established for each MPLS LSP that is being
   monitored.  BFD Control packets must be sent along the same path as
   the monitored LSP.  If the LSP is associated with multiple FECs, a
   BFD session is established for each FEC.







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   While LSP Ping can be used for detecting MPLS data-plane failures and
   for verifying the MPLS LSP data plane against the control plane, BFD
   can only be used for the former.  BFD can be used in conjunction with
   LSP Ping, as is the case in MPLS-TP (see Section 4.5.4).

4.4.3.  OAM for Virtual Private Networks (VPNs) over MPLS

   The IETF has defined two classes of VPNs: Layer 2 VPNs (L2VPNs) and
   Layer 3 VPNs (L3VPNs).  [L2VPN-OAM] provides the requirements and
   framework for OAM in the context of L2VPNs, and specifically it also
   defines the OAM layering of L2VPNs over MPLS.  [L3VPN-OAM] provides a
   framework for the operation and management of L3VPNs.

4.5.  MPLS-TP OAM

4.5.1.  Overview

   The MPLS working group has defined the OAM toolset that fulfills the
   requirements for MPLS-TP OAM.  The full set of requirements for
   MPLS-TP OAM are defined in [MPLS-TP-OAM] and include both general
   requirements for the behavior of the OAM tools and a set of
   operations that should be supported by the OAM toolset.  The set of
   mechanisms required are further elaborated in [TP-OAM-FW], which
   describes the general architecture of the OAM system and also gives
   overviews of the functionality of the OAM toolset.

   Some of the basic requirements for the OAM toolset for MPLS-TP are:

   o  MPLS-TP OAM must be able to support both an IP-based environment
      and a non-IP-based environment.  If the network is IP based, i.e.,
      IP routing and forwarding are available, then the MPLS-TP OAM
      toolset should rely on the IP routing and forwarding capabilities.
      On the other hand, in environments where IP functionality is not
      available, the OAM tools must still be able to operate without
      dependence on IP forwarding and routing.

   o  OAM packets and the user traffic are required to be congruent
      (i.e., OAM packets are transmitted in-band), and there is a need
      to differentiate OAM packets from ordinary user packets in the
      data plane.  Inherent in this requirement is the principle that
      MPLS-TP OAM be independent of any existing control plane, although
      it should not preclude use of the control-plane functionality.
      OAM packets are identified by the Generic Associated Channel Label
      (GAL), which is a reserved MPLS label value (13).







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4.5.2.  Terminology

   Maintenance Entity (ME)

      The MPLS-TP OAM tools are designed to monitor and manage a
      Maintenance Entity (ME).  An ME, as defined in [TP-OAM-FW],
      defines a relationship between two points of a transport path to
      which maintenance and monitoring operations apply.

      The term "Maintenance Entity (ME)" is used in ITU-T
      Recommendations (e.g., [ITU-T-Y1731]), as well as in the MPLS-TP
      terminology ([TP-OAM-FW]).

   Maintenance Entity Group (MEG)

      The collection of one or more MEs that belong to the same
      transport path and that are maintained and monitored as a group
      are known as a Maintenance Entity Group (based on [TP-OAM-FW]).

   Maintenance Point (MP)

      A Maintenance Point (MP) is a functional entity that is defined at
      a node in the network and can initiate and/or react to OAM
      messages.  This document focuses on the data-plane functionality
      of MPs, while MPs interact with the control plane and with the
      management plane as well.

      The term "MP" is used in IEEE 802.1ag and was similarly adopted in
      MPLS-TP ([TP-OAM-FW]).

   MEG End Point (MEP)

      A MEG End Point (MEP) is one of the endpoints of an ME, and can
      initiate OAM messages and respond to them (based on [TP-OAM-FW]).

   MEG Intermediate Point (MIP)

      In between MEPs, there are zero or more intermediate points,
      called MEG Intermediate Points  (based on [TP-OAM-FW]).

      A MEG Intermediate Point (MIP) is an intermediate point that does
      not generally initiate OAM frames (one exception to this is the
      use of AIS notifications) but is able to respond to OAM frames
      that are destined to it.  A MIP in MPLS-TP identifies OAM packets
      destined to it by the expiration of the TTL field in the OAM
      packet.  The term "Maintenance Point" is a general term for MEPs
      and MIPs.




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   Up and Down MEPs

      IEEE 802.1ag [IEEE802.1Q] defines a distinction between Up MEPs
      and Down MEPs.  A MEP monitors traffic in either the direction
      facing the network or the direction facing the bridge.  A Down MEP
      is a MEP that receives OAM packets from and transmits them to the
      direction of the network.  An Up MEP receives OAM packets from and
      transmits them to the direction of the bridging entity.  MPLS-TP
      ([TP-OAM-FW]) uses a similar distinction on the placement of the
      MEP -- at either the ingress, egress, or forwarding function of
      the node (Down / Up MEPs).  This placement is important for
      localization of a failure.

      Note that the terms "Up MEP" and "Down MEP" are entirely unrelated
      to the conventional "Up"/"Down" terminology, where "Down" means
      faulty and "Up" means not faulty.

      The distinction between Up and Down MEPs was defined in
      [TP-OAM-FW], but has not been used in other MPLS-TP RFCs, as of
      the writing of this document.

4.5.3.  Generic Associated Channel

   In order to address the requirement for in-band transmission of
   MPLS-TP OAM traffic, MPLS-TP uses a Generic Associated Channel
   (G-ACh), defined in [G-ACh] for LSP-based OAM traffic.  This
   mechanism is based on the same concepts as the PWE3 ACH [PW-ACH] and
   VCCV [VCCV] mechanisms.  However, to address the needs of LSPs as
   differentiated from PW, the following concepts were defined for
   [G-ACh]:

   o  An Associated Channel Header (ACH), which uses a format similar to
      the PW Control Word [PW-ACH], is a 4-byte header that is prepended
      to OAM packets.

   o  A Generic Associated Channel Label (GAL).  The GAL is a reserved
      MPLS label value (13) that indicates that the packet is an ACH
      packet and the payload follows immediately after the label stack.

   It should be noted that while the G-ACh was defined as part of the
   MPLS-TP definition effort, the G-ACh is a generic tool that can be
   used in MPLS in general, and not only in MPLS-TP.

4.5.4.  MPLS-TP OAM Toolset

   To address the functionality that is required of the OAM toolset, the
   MPLS WG conducted an analysis of the existing IETF and ITU-T OAM
   tools and their ability to fulfill the required functionality.  The



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   conclusions of this analysis are documented in [OAM-Analys].  MPLS-TP
   uses a mixture of OAM tools that are based on previous standards and
   adapted to the requirements of [MPLS-TP-OAM].  Some of the main
   building blocks of this solution are based on:

   o  Bidirectional Forwarding Detection ([BFD], [BFD-LSP]) for
      proactive Continuity Check and Connectivity Verification.

   o  LSP Ping as defined in [LSP-Ping] for on-demand Connectivity
      Verification.

   o  New protocol packets, using G-ACH, to address different
      functionality.

   o  Performance measurement protocols.

   The following subsections describe the OAM tools defined for MPLS-TP
   as described in [TP-OAM-FW].

4.5.4.1.  Continuity Check and Connectivity Verification

   Continuity Checks and Connectivity Verification are presented in
   Section 2.2.7 of this document.  As presented there, these tools may
   be used either proactively or on demand.  When using these tools
   proactively, they are generally used in tandem.

   For MPLS-TP there are two distinct tools: the proactive tool is
   defined in [TP-CC-CV], while the on-demand tool is defined in
   [OnDemand-CV].  In on-demand mode, this function should support
   monitoring between the MEPs and, in addition, between a MEP and MIP.
   [TP-OAM-FW] highlights, when performing Connectivity Verification,
   the need for the CC-V messages to include unique identification of
   the MEG that is being monitored and the MEP that originated the
   message.

   The proactive tool [TP-CC-CV] is based on extensions to BFD (see
   Section 4.3) with the additional limitation that the transmission and
   receiving rates are based on configuration by the operator.  The
   on-demand tool [OnDemand-CV] is an adaptation of LSP Ping (see
   Section 4.4.1) for the required behavior of MPLS-TP.

4.5.4.2.  Route Tracing

   [MPLS-TP-OAM] defines that there is a need for functionality that
   would allow a path endpoint to identify the intermediate and
   endpoints of the path.  This function would be used in on-demand
   mode.  Normally, this path will be used for bidirectional PW, LSP,




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   and Sections; however, unidirectional paths may be supported only if
   a return path exists.  The tool for this is based on the LSP Ping
   (see Section 4.4.1) functionality and is described in [OnDemand-CV].

4.5.4.3.  Lock Instruct

   The Lock Instruct function [Lock-Loop] is used to notify a transport-
   path endpoint of an administrative need to disable the transport
   path.  This functionality will generally be used in conjunction with
   some intrusive OAM function, e.g., performance measurement or
   diagnostic testing, to minimize the side-effect on user data traffic.

4.5.4.4.  Lock Reporting

   Lock Reporting is a function used by an endpoint of a path to report
   to its far-end endpoint that a lock condition has been affected on
   the path.

4.5.4.5.  Alarm Reporting

   Alarm reporting [TP-Fault] provides the means to suppress alarms
   following detection of defect conditions at the server sub-layer.
   Alarm reporting is used by an intermediate point of a path, that
   becomes aware of a fault on the path, to report to the endpoints of
   the path.  [TP-OAM-FW] states that this may occur as a result of a
   defect condition discovered at a server sub-layer.  This generates an
   Alarm Indication Signal (AIS) that continues until the fault is
   cleared.  The consequent action of this function is detailed in
   [TP-OAM-FW].

4.5.4.6.  Remote Defect Indication

   Remote Defect Indication (RDI) is used proactively by a path endpoint
   to report to its peer endpoint that a defect is detected on a
   bidirectional connection between them.  [MPLS-TP-OAM] points out that
   this function may be applied to a unidirectional LSP only if a return
   path exists.  [TP-OAM-FW] points out that this function is associated
   with the proactive CC-V function.

4.5.4.7.  Client Failure Indication

   Client Failure Indication (CFI) is defined in [MPLS-TP-OAM] to allow
   the propagation information from one edge of the network to the
   other.  The information concerns a defect to a client, in the case
   that the client does not support alarm notification.






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4.5.4.8.  Performance Monitoring

   The definition of MPLS performance monitoring was motivated by the
   MPLS-TP requirements [MPLS-TP-OAM] but was defined generically for
   MPLS in [MPLS-LM-DM].  An additional document [TP-LM-DM] defines a
   performance monitoring profile for MPLS-TP.

4.5.4.8.1.  Packet Loss Measurement (LM)

   Packet Loss Measurement is a function used to verify the quality of
   the service.  Packet loss, as defined in [IPPM-1LM] and
   [MPLS-TP-OAM], indicates the ratio of the number of user packets lost
   to the total number of user packets sent during a defined time
   interval.

   There are two possible ways of determining this measurement:

   o  Using OAM packets, it is possible to compute the statistics based
      on a series of OAM packets.  This, however, has the disadvantage
      of being artificial and may not be representative since part of
      the packet loss may be dependent upon packet sizes and upon the
      implementation of the MEPs that take part in the protocol.

   o  Delimiting messages can be sent at the start and end of a
      measurement period during which the source and sink of the path
      count the packets transmitted and received.  After the end
      delimiter, the ratio would be calculated by the path OAM entity.

4.5.4.8.2.  Packet Delay Measurement (DM)

   Packet Delay Measurement is a function that is used to measure one-
   way or two-way delay of a packet transmission between a pair of the
   endpoints of a path (PW, LSP, or Section).  Where:

   o  One-way packet delay, as defined in [IPPM-1DM], is the time
      elapsed from the start of transmission of the first bit of the
      packet by a source node until the reception of the last bit of
      that packet by the destination node.  Note that one-way delay
      measurement requires the clocks of the two endpoints to be
      synchronized.

   o  Two-way packet delay, as defined in [IPPM-2DM], is the time
      elapsed from the start of transmission of the first bit of the
      packet by a source node until the reception of the last bit of the
      looped-back packet by the same source node, when the loopback is
      performed at the packet's destination node.  Note that due to
      possible path asymmetry, the one-way packet delay from one
      endpoint to another is not necessarily equal to half of the



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      two-way packet delay.  As opposed to one-way delay measurement,
      two-way delay measurement does not require the two endpoints to be
      synchronized.

      For each of these two metrics, the DM function allows the MEP to
      measure the delay, as well as the delay variation.  Delay
      measurement is performed by exchanging timestamped OAM packets
      between the participating MEPs.

4.6.  Pseudowire OAM

4.6.1.  Pseudowire OAM Using Virtual Circuit Connectivity Verification
        (VCCV)

   VCCV, as defined in [VCCV], provides a means for end-to-end fault
   detection and diagnostic tools to be used for PWs (regardless of the
   underlying tunneling technology).  The VCCV switching function
   provides a Control Channel associated with each PW.  [VCCV] defines
   three Control Channel (CC) types, i.e., three possible methods for
   transmitting and identifying OAM messages:

   o  Control Channel Type 1: In-band VCCV, as described in [VCCV], is
      also referred to as "PWE3 Control Word with 0001b as first
      nibble".  It uses the PW Associated Channel Header [PW-ACH].

   o  Control Channel Type 2: Out-of-band VCCV, as described in [VCCV],
      is also referred to as "MPLS Router Alert Label".  In this case,
      the Control Channel is created by using the MPLS router alert
      label [MPLS-ENCAPS] immediately above the PW label.

   o  Control Channel Type 3: TTL expiry VCCV, as described in [VCCV],
      is also referred to as "MPLS PW Label with TTL == 1", i.e., the
      Control Channel is identified when the value of the TTL field in
      the PW label is set to 1.

   VCCV currently supports the following OAM tools: ICMP Ping, LSP Ping,
   and BFD.  ICMP and LSP Ping are IP encapsulated before being sent
   over the PW ACH.  BFD for VCCV [BFD-VCCV] supports two modes of
   encapsulation -- either IP/UDP encapsulated (with IP/UDP header) or
   PW-ACH encapsulated (with no IP/UDP header) -- and provides support
   to signal the AC status.  The use of the VCCV Control Channel
   provides the context, based on the MPLS-PW label, required to bind
   and bootstrap the BFD session to a particular pseudowire (FEC),
   eliminating the need to exchange Discriminator values.







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   VCCV consists of two components: (1) the signaled component to
   communicate VCCV capabilities as part of the VC label, and (2) the
   switching component to cause the PW payload to be treated as a
   control packet.

   VCCV is not directly dependent upon the presence of a control plane.
   The VCCV capability advertisement may be performed as part of the PW
   signaling when LDP is used.  In case of manual configuration of the
   PW, it is the responsibility of the operator to set consistent
   options at both ends.  The manual option was created specifically to
   handle MPLS-TP use cases where no control plane was a requirement.
   However, new use cases such as pure mobile backhaul find this
   functionality useful too.

   The PWE3 working group has conducted an implementation survey of VCCV
   [VCCV-SURVEY] that analyzes which VCCV mechanisms are used in
   practice.

4.6.2.  Pseudowire OAM Using G-ACh

   As mentioned above, VCCV enables OAM for PWs by using a Control
   Channel for OAM packets.  When PWs are used in MPLS-TP networks,
   rather than the Control Channels defined in VCCV, the G-ACh can be
   used as an alternative Control Channel.  The usage of the G-ACh for
   PWs is defined in [PW-G-ACh].

4.6.3.  Attachment Circuit - Pseudowire Mapping

   The PWE3 working group has defined a mapping and notification of
   defect states between a pseudowire (PW) and the Attachment Circuits
   (ACs) of the end-to-end emulated service.  This mapping is of key
   importance to the end-to-end functionality.  Specifically, the
   mapping is provided by [PW-MAP], by [L2TP-EC] for L2TPv3 pseudowires,
   and by Section 5.3 of [ATM-L2] for ATM.

   [L2VPN-OAM] provides the requirements and framework for OAM in the
   context of Layer 2 Virtual Private Networks (L2VPNs), and
   specifically it also defines the OAM layering of L2VPNs over
   pseudowires.

   The mapping defined in [Eth-Int] allows an end-to-end emulated
   Ethernet service over pseudowires.









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4.7.  OWAMP and TWAMP

4.7.1.  Overview

   The IPPM working group in the IETF defines common criteria and
   metrics for measuring performance of IP traffic ([IPPM-FW]).  Some of
   the key RFCs published by this working group have defined metrics for
   measuring connectivity [IPPM-Con], delay ([IPPM-1DM], [IPPM-2DM]),
   and packet loss [IPPM-1LM].  It should be noted that the work of the
   IETF in the context of performance metrics is not limited to IP
   networks; [PM-CONS] presents general guidelines for considering new
   performance metrics.

   The IPPM working group has defined not only metrics for performance
   measurement but also protocols that define how the measurement is
   carried out.  The One-Way Active Measurement Protocol [OWAMP] and the
   Two-Way Active Measurement Protocol [TWAMP] each define a method and
   protocol for measuring performance metrics in IP networks.

   OWAMP [OWAMP] enables measurement of one-way characteristics of IP
   networks, such as one-way packet loss and one-way delay.  For its
   proper operation, OWAMP requires accurate time-of-day setting at its
   endpoints.

   TWAMP [TWAMP] is a similar protocol that enables measurement of both
   one-way and two-way (round-trip) characteristics.

   OWAMP and TWAMP are each comprised of two separate protocols:

   o  OWAMP-Control/TWAMP-Control: used to initiate, start, and stop
      test sessions and to fetch their results.  Continuity Check and
      Connectivity Verification are tested and confirmed by establishing
      the OWAMP/TWAMP Control Protocol TCP connection.

   o  OWAMP-Test/TWAMP-Test: used to exchange test packets between two
      measurement nodes.  Enables the loss and delay measurement
      functions, as well as detection of other anomalies, such as packet
      duplication and packet reordering.

   It should be noted that while [OWAMP] and [TWAMP] define tools for
   performance measurement, they do not define the accuracy of these
   tools.  The accuracy depends on scale, implementation, and network
   configurations.

   Alternative protocols for performance monitoring are defined, for
   example, in MPLS-TP OAM ([MPLS-LM-DM], [TP-LM-DM]) and in Ethernet
   OAM [ITU-T-Y1731].




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4.7.2.  Control and Test Protocols

   OWAMP and TWAMP control protocols run over TCP, while the test
   protocols run over UDP.  The purpose of the control protocols is to
   initiate, start, and stop test sessions, and for OWAMP to fetch
   results.  The test protocols introduce test packets (which contain
   sequence numbers and timestamps) along the IP path under test
   according to a schedule, and they record statistics of packet
   arrival.  Multiple sessions may be simultaneously defined, each with
   a session identifier, and defining the number of packets to be sent,
   the amount of padding to be added (and thus the packet size), the
   start time, and the send schedule (which can be either a constant
   time between test packets or exponentially distributed
   pseudorandomly).  Statistics recorded conform to the relevant IPPM
   RFCs.

   From a security perspective, OWAMP and TWAMP test packets are hard to
   detect because they are simply UDP streams between negotiated port
   numbers, with potentially nothing static in the packets.  OWAMP and
   TWAMP also include optional authentication and encryption for both
   control and test packets.

4.7.3.  OWAMP

   OWAMP defines the following logical roles: Session-Sender,
   Session-Receiver, Server, Control-Client, and Fetch-Client.  The
   Session-Sender originates test traffic that is received by the
   Session-Receiver.  The Server configures and manages the session, as
   well as returning the results.  The Control-Client initiates requests
   for test sessions, triggers their start, and may trigger their
   termination.  The Fetch-Client requests the results of a completed
   session.  Multiple roles may be combined in a single host -- for
   example, one host may play the roles of Control-Client, Fetch-Client,
   and Session-Sender, and a second may play the roles of Server and
   Session-Receiver.

   In a typical OWAMP session, the Control-Client establishes a TCP
   connection to port 861 of the Server, which responds with a Server
   greeting message indicating supported security/integrity modes.  The
   Control-Client responds with the chosen communications mode, and the
   Server accepts the mode.  The Control-Client then requests and fully
   describes a test session to which the Server responds with its
   acceptance and supporting information.  More than one test session
   may be requested with additional messages.  The Control-Client then
   starts a test session; the Server acknowledges and then instructs the
   Session-Sender to start the test.  The Session-Sender then sends test
   packets with pseudorandom padding to the Session-Receiver until the
   session is complete or until the Control-Client stops the session.



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   Once finished, the Session-Sender reports to the Server, which
   recovers data from the Session-Receiver.  The Fetch-Client can then
   send a fetch request to the Server, which responds with an
   acknowledgement and, immediately thereafter, the result data.

4.7.4.  TWAMP

   TWAMP defines the following logical roles: Session-Sender,
   Session-Reflector, Server, and Control-Client.  These are similar to
   the OWAMP roles, except that the Session-Reflector does not collect
   any packet information, and there is no need for a Fetch-Client.

   In a typical TWAMP session, the Control-Client establishes a TCP
   connection to port 862 of the Server, and the mode is negotiated as
   in OWAMP.  The Control-Client then requests sessions and starts them.
   The Session-Sender sends test packets with pseudorandom padding to
   the Session-Reflector, which returns them with timestamps inserted.

4.8.  TRILL

   The requirements of OAM in TRILL are defined in [TRILL-OAM].  The
   challenge in TRILL OAM, much like in MPLS networks, is that traffic
   between RBridges RB1 and RB2 may be forwarded through more than one
   path.  Thus, an OAM protocol between RBridges RB1 and RB2 must be
   able to monitor all the available paths between the two RBridges.

   During the writing of this document, the detailed definition of the
   TRILL OAM tools is still work in progress.  This subsection presents
   the main requirements of TRILL OAM.

   The main requirements defined in [TRILL-OAM] are:

   o  Continuity Checking (CC) - the TRILL OAM protocol must support a
      function for CC between any two RBridges RB1 and RB2.

   o  Connectivity Verification (CV) - connectivity between two RBridges
      RB1 and RB2 can be verified on a per-flow basis.

   o  Path Tracing - allows an RBridge to trace all the available paths
      to a peer RBridge.

   o  Performance monitoring - allows an RBridge to monitor the packet
      loss and packet delay to a peer RBridge.








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5.  Summary

   This section summarizes the OAM tools and functions presented in this
   document.  This summary is an index to some of the main OAM tools
   defined in the IETF.  This compact index can be useful to all readers
   from network operators to standards development organizations.  The
   summary includes a short subsection that presents some guidance to
   network equipment vendors.

5.1.  Summary of OAM Tools

   This subsection provides a short summary of each of the OAM toolsets
   described in this document.

   A detailed list of the RFCs related to each toolset is given in
   Appendix A.1.



































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+-----------+------------------------------------------+------------+
| Toolset   | Description                              | Transport  |
|           |                                          | Technology |
+-----------+------------------------------------------+------------+
|IP Ping    | Ping ([IntHost], [NetTerms]) is a simple | IPv4/IPv6  |
|           | application for testing reachability that|            |
|           | uses ICMP Echo messages ([ICMPv4],       |            |
|           | [ICMPv6]).                               |            |
+-----------+------------------------------------------+------------+
|IP         | Traceroute ([TCPIP-Tools], [NetTools]) is| IPv4/IPv6  |
|Traceroute | an application that allows users to trace|            |
|           | the path between an IP source and an IP  |            |
|           | destination, i.e., to identify the nodes |            |
|           | along the path.  If more than one path   |            |
|           | exists between the source and            |            |
|           | destination, Traceroute traces *a* path. |            |
|           | The most common implementation of        |            |
|           | Traceroute uses UDP probe messages,      |            |
|           | although there are other implementations |            |
|           | that use different probes, such as ICMP  |            |
|           | or TCP.  Paris Traceroute [PARIS] is an  |            |
|           | extension that attempts to discover all  |            |
|           | the available paths from A to B by       |            |
|           | scanning different values of header      |            |
|           | fields.                                  |            |
+-----------+------------------------------------------+------------+
|BFD        | Bidirectional Forwarding Detection (BFD) | generic    |
|           | is defined in [BFD] as a framework for a |            |
|           | lightweight generic OAM tool.  The       |            |
|           | intention is to define a base tool       |            |
|           | that can be used with various            |            |
|           | encapsulation types, network             |            |
|           | environments, and various medium         |            |
|           | types.                                   |            |
+-----------+------------------------------------------+------------+
|MPLS OAM   | MPLS LSP Ping, as defined in [MPLS-OAM], | MPLS       |
|           | [MPLS-OAM-FW], and [LSP-Ping], is an OAM |            |
|           | tool for point-to-point and              |            |
|           | point-to-multipoint MPLS LSPs.           |            |
|           | It includes two main functions: Ping and |            |
|           | Traceroute.                              |            |
|           | BFD [BFD-LSP] is an alternative means for|            |
|           | detecting MPLS LSP data-plane failures.  |            |








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+-----------+------------------------------------------+------------+
|MPLS-TP OAM| MPLS-TP OAM is defined in a set of RFCs. | MPLS-TP    |
|           | The OAM requirements for MPLS Transport  |            |
|           | Profile (MPLS-TP) are defined in         |            |
|           | [MPLS-TP-OAM].  Each of the tools in the |            |
|           | OAM toolset is defined in its own RFC, as|            |
|           | specified in Appendix A.1.               |            |
+-----------+------------------------------------------+------------+
|Pseudowire | The PWE3 OAM architecture defines Control| Pseudowire |
|OAM        | Channels that support the use of existing|            |
|           | IETF OAM tools to be used for a pseudo-  |            |
|           | wire (PW).  The Control Channels that are|            |
|           | defined in [VCCV] and [PW-G-ACh] may be  |            |
|           | used in conjunction with ICMP Ping, LSP  |            |
|           | Ping, and BFD to perform CC and CV       |            |
|           | functionality.  In addition, the channels|            |
|           | support use of any of the MPLS-TP-based  |            |
|           | OAM tools for completing their respective|            |
|           | OAM functionality for a PW.              |            |
+-----------+------------------------------------------+------------+
|OWAMP and  | The One-Way Active Measurement Protocol  | IPv4/IPv6  |
|TWAMP      | [OWAMP] and the Two-Way Active Measure-  |            |
|           | ment Protocol [TWAMP] are two protocols  |            |
|           | defined in the IP Performance Metrics    |            |
|           | (IPPM) working group in the IETF.  These |            |
|           | protocols allow various performance      |            |
|           | metrics to be measured, such as packet   |            |
|           | loss, delay, delay variation,            |            |
|           | duplication, and reordering.             |            |
+-----------+------------------------------------------+------------+
|TRILL OAM  | The requirements of OAM in TRILL are     | TRILL      |
|           | defined in [TRILL-OAM].  These           |            |
|           | requirements include Continuity Checking,|            |
|           | Connectivity Verification, path tracing, |            |
|           | and performance monitoring.  During the  |            |
|           | writing of this document, the detailed   |            |
|           | definition of the TRILL OAM tools        |            |
|           | is work in progress.                     |            |
+-----------+------------------------------------------+------------+

             Table 3: Summary of OAM-Related IETF Tools










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5.2.  Summary of OAM Functions

   Table 4 summarizes the OAM functions that are supported in each of
   the toolsets that were analyzed in this section.  The columns of this
   table are the typical OAM functions described in Section 1.3.

+-----------+----------+-------------+----------+----------+-----------+
|           |Continuity|Connectivity |Path      |Perf.     |Other      |
| Toolset   |Check     |Verification |Discovery |Monitoring|Functions  |
|           |          |             |          |          |           |
+-----------+----------+-------------+----------+----------+-----------+
|IP Ping    |Echo      |             |          |          |           |
+-----------+----------+-------------+----------+----------+-----------+
|IP         |          |             |Traceroute|          |           |
|Traceroute |          |             |          |          |           |
+-----------+----------+-------------+----------+----------+-----------+
|BFD        |BFD       |BFD Control  |          |          |RDI using  |
|           |Control/  |             |          |          |BFD Control|
|           |Echo      |             |          |          |           |
+-----------+----------+-------------+----------+----------+-----------+
|MPLS OAM   |          |"Ping" mode  |"Trace-   |          |           |
|(LSP Ping) |          |             |route"    |          |           |
|           |          |             |mode      |          |           |
+-----------+----------+-------------+----------+----------+-----------+
|MPLS-TP    |CC        |CV/proactive |Route     |-LM       |-Diagnostic|
|OAM        |          |or on demand |Tracing   |-DM       | Test      |
|           |          |             |          |          |-Lock      |
|           |          |             |          |          |-Alarm     |
|           |          |             |          |          | Reporting |
|           |          |             |          |          |-Client    |
|           |          |             |          |          | Failure   |
|           |          |             |          |          | Indication|
|           |          |             |          |          |-RDI       |
+-----------+----------+-------------+----------+----------+-----------+
|Pseudowire |BFD       |-BFD         |LSP Ping  |          |           |
|OAM        |          |-ICMP Ping   |          |          |           |
|           |          |-LSP Ping    |          |          |           |
+-----------+----------+-------------+----------+----------+-----------+
|OWAMP and  |     - control          |          |-DM       |           |
|TWAMP      |      protocol          |          |-LM       |           |
+-----------+----------+-------------+----------+----------+-----------+
|TRILL OAM  |CC        |CV           |Path      |-DM       |           |
|           |          |             |tracing   |-LM       |           |
+-----------+----------+-------------+----------+----------+-----------+

       Table 4: Summary of the OAM Functionality in IETF OAM Tools





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5.3.  Guidance to Network Equipment Vendors

   As mentioned in Section 1.4, it is imperative for OAM tools to be
   capable of testing the actual data plane with as much accuracy as
   possible.  While this guideline may appear obvious, it is worthwhile
   to emphasize the key importance of enforcing fate-sharing between OAM
   traffic that monitors the data plane and the data-plane traffic it
   monitors.

6.  Security Considerations

   OAM is tightly coupled with the stability of the network.  A
   successful attack on an OAM protocol can create a false illusion of
   nonexistent failures or prevent the detection of actual ones.  In
   both cases, the attack may result in denial of service.

   Some of the OAM tools presented in this document include security
   mechanisms that provide integrity protection, thereby preventing
   attackers from forging or tampering with OAM packets.  For example,
   [BFD] includes an optional authentication mechanism for BFD Control
   packets, using either SHA1, MD5, or a simple password.  [OWAMP] and
   [TWAMP] have three modes of security: unauthenticated, authenticated,
   and encrypted.  The authentication uses SHA1 as the HMAC algorithm,
   and the encrypted mode uses AES encryption.

   Confidentiality is typically not considered a requirement for OAM
   protocols.  However, the use of encryption (e.g., [OWAMP] and
   [TWAMP]) can make it difficult for attackers to identify OAM packets,
   thus making it more difficult to attack the OAM protocol.

   OAM can also be used as a means for network reconnaissance;
   information about addresses, port numbers, and the network topology
   and performance can be gathered by either passively eavesdropping on
   OAM packets or actively sending OAM packets and gathering information
   from the respective responses.  This information can then be used
   maliciously to attack the network.  Note that some of this
   information, e.g., addresses and port numbers, can be gathered even
   when encryption is used ([OWAMP], [TWAMP]).

   For further details about the security considerations of each OAM
   protocol, the reader is encouraged to review the Security
   Considerations section of each document referenced by this memo.









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7.  Acknowledgments

   The authors gratefully acknowledge Sasha Vainshtein, Carlos
   Pignataro, David Harrington, Dan Romascanu, Ron Bonica, Benoit
   Claise, Stewart Bryant, Tom Nadeau, Elwyn Davies, Al Morton, Sam
   Aldrin, Thomas Narten, and other members of the OPSA WG for their
   helpful comments on the mailing list.

   This document was originally prepared using 2-Word-v2.0.template.dot.

8.  References

8.1.  Normative References

   [OAM-Def]     Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
                 D., and S. Mansfield, "Guidelines for the Use of the
                 "OAM" Acronym in the IETF", BCP 161, RFC 6291, June
                 2011.

8.2.  Informative References

   [ATM-L2]      Singh, S., Townsley, M., and C. Pignataro,
                 "Asynchronous Transfer Mode (ATM) over Layer 2
                 Tunneling Protocol Version 3 (L2TPv3)", RFC 4454, May
                 2006.

   [BFD]         Katz, D. and D. Ward, "Bidirectional Forwarding
                 Detection (BFD)", RFC 5880, June 2010.

   [BFD-Gen]     Katz, D. and D. Ward, "Generic Application of
                 Bidirectional Forwarding Detection (BFD)", RFC 5882,
                 June 2010.

   [BFD-IP]      Katz, D. and D. Ward, "Bidirectional Forwarding
                 Detection (BFD) for IPv4 and IPv6 (Single Hop)", RFC
                 5881, June 2010.

   [BFD-LSP]     Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
                 "Bidirectional Forwarding Detection (BFD) for MPLS
                 Label Switched Paths (LSPs)", RFC 5884, June 2010.

   [BFD-Multi]   Katz, D. and D. Ward, "Bidirectional Forwarding
                 Detection (BFD) for Multihop Paths", RFC 5883, June
                 2010.







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   [BFD-VCCV]    Nadeau, T., Ed., and C. Pignataro, Ed., "Bidirectional
                 Forwarding Detection (BFD) for the Pseudowire Virtual
                 Circuit Connectivity Verification (VCCV)", RFC 5885,
                 June 2010.

   [Comp]        Bonaventure, O., "Computer Networking: Principles,
                 Protocols and Practice", 2008.

   [Dup]         Uijterwaal, H., "A One-Way Packet Duplication Metric",
                 RFC 5560, May 2009.

   [Eth-Int]     Mohan, D., Ed., Bitar, N., Ed., Sajassi, A., Ed.,
                 DeLord, S., Niger, P., and R. Qiu, "MPLS and Ethernet
                 Operations, Administration, and Maintenance (OAM)
                 Interworking", RFC 7023, October 2013.

   [G-ACh]       Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
                 "MPLS Generic Associated Channel", RFC 5586, June 2009.

   [ICMP-Ext]    Bonica, R., Gan, D., Tappan, D., and C. Pignataro,
                 "ICMP Extensions for Multiprotocol Label Switching",
                 RFC 4950, August 2007.

   [ICMP-Int]    Atlas, A., Ed., Bonica, R., Ed., Pignataro, C., Ed.,
                 Shen, N., and JR. Rivers, "Extending ICMP for Interface
                 and Next-Hop Identification", RFC 5837, April 2010.

   [ICMP-MP]     Bonica, R., Gan, D., Tappan, D., and C. Pignataro,
                 "Extended ICMP to Support Multi-Part Messages", RFC
                 4884, April 2007.

   [ICMPv4]      Postel, J., "Internet Control Message Protocol", STD 5,
                 RFC 792, September 1981.

   [ICMPv6]      Conta, A., Deering, S., and M. Gupta, Ed., "Internet
                 Control Message Protocol (ICMPv6) for the Internet
                 Protocol Version 6 (IPv6) Specification", RFC 4443,
                 March 2006.

   [IEEE802.1Q]  IEEE, "IEEE Standard for Local and metropolitan area
                 networks - Media Access Control (MAC) Bridges and
                 Virtual Bridged Local Area Networks", IEEE 802.1Q,
                 October 2012.








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   [IEEE802.3ah] IEEE, "IEEE Standard for Information technology - Local
                 and metropolitan area networks - Carrier sense multiple
                 access with collision detection (CSMA/CD) access method
                 and physical layer specifications", IEEE 802.3ah,
                 clause 57, December 2008.

   [IntHost]     Braden, R., Ed., "Requirements for Internet Hosts -
                 Communication Layers", STD 3, RFC 1122, October 1989.

   [IPPM-1DM]    Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
                 Delay Metric for IPPM", RFC 2679, September 1999.

   [IPPM-1LM]    Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
                 Packet Loss Metric for IPPM", RFC 2680, September 1999.

   [IPPM-2DM]    Almes, G., Kalidindi, S., and M. Zekauskas, "A Round-
                 trip Delay Metric for IPPM", RFC 2681, September 1999.

   [IPPM-Con]    Mahdavi, J. and V. Paxson, "IPPM Metrics for Measuring
                 Connectivity", RFC 2678, September 1999.

   [IPPM-FW]     Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
                 "Framework for IP Performance Metrics", RFC 2330, May
                 1998.

   [ITU-G8113.1] ITU-T, "Operations, Administration and Maintenance
                 mechanism for MPLS-TP in Packet Transport Network
                 (PTN)",  ITU-T Recommendation G.8113.1/Y.1372.1,
                 November 2012.

   [ITU-G8113.2] ITU-T, "Operations, administration and maintenance
                 mechanisms for MPLS-TP networks using the tools defined
                 for MPLS", ITU-T Recommendation G.8113.2/Y.1372.2,
                 November 2012.

   [ITU-T-CT]    Betts, M., "Allocation of a Generic Associated Channel
                 Type for ITU-T MPLS Transport Profile Operation,
                 Maintenance, and Administration (MPLS-TP OAM)", RFC
                 6671, November 2012.

   [ITU-T-G.806] ITU-T, "Characteristics of transport equipment -
                 Description methodology and generic functionality",
                 ITU-T Recommendation G.806, January 2009.

   [ITU-T-Y1711] ITU-T, "Operation & Maintenance mechanism for MPLS
                 networks", ITU-T Recommendation Y.1711, February 2004.





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   [ITU-T-Y1731] ITU-T, "OAM Functions and Mechanisms for Ethernet-based
                 Networks", ITU-T Recommendation G.8013/Y.1731, July
                 2011.

   [ITU-Terms]   ITU-R/ITU-T, "ITU-R/ITU-T Terms and Definitions", 2013,
                 <http://www.itu.int/pub/R-TER-DB>.

   [L2TP-EC]     McGill, N. and C. Pignataro, "Layer 2 Tunneling
                 Protocol Version 3 (L2TPv3) Extended Circuit Status
                 Values", RFC 5641, August 2009.

   [L2VPN-OAM]   Sajassi, A., Ed., and D. Mohan, Ed., "Layer 2 Virtual
                 Private Network (L2VPN) Operations, Administration, and
                 Maintenance (OAM) Requirements and Framework", RFC
                 6136, March 2011.

   [L3VPN-OAM]   El Mghazli, Y., Ed., Nadeau, T., Boucadair, M., Chan,
                 K., and A. Gonguet, "Framework for Layer 3 Virtual
                 Private Networks (L3VPN) Operations and Management",
                 RFC 4176, October 2005.

   [Lock-Loop]   Boutros, S., Ed., Sivabalan, S., Ed., Aggarwal, R.,
                 Ed., Vigoureux, M., Ed., and X. Dai, Ed., "MPLS
                 Transport Profile Lock Instruct and Loopback
                 Functions", RFC 6435, November 2011.

   [LSP-Ping]    Kompella, K. and G. Swallow, "Detecting Multi-Protocol
                 Label Switched (MPLS) Data Plane Failures", RFC 4379,
                 February 2006.

   [Mng]         Farrel, A., "Inclusion of Manageability Sections in
                 Path Computation Element (PCE) Working Group Drafts",
                 RFC 6123, February 2011.

   [MPLS-ENCAPS] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
                 Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
                 Encoding", RFC 3032, January 2001.

   [MPLS-LM-DM]  Frost, D. and S. Bryant, "Packet Loss and Delay
                 Measurement for MPLS Networks", RFC 6374, September
                 2011.

   [MPLS-OAM]    Nadeau, T., Morrow, M., Swallow, G., Allan, D., and S.
                 Matsushima, "Operations and Management (OAM)
                 Requirements for Multi-Protocol Label Switched (MPLS)
                 Networks", RFC 4377, February 2006.





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   [MPLS-OAM-FW] Allan, D., Ed., and T. Nadeau, Ed., "A Framework for
                 Multi-Protocol Label Switching (MPLS) Operations and
                 Management (OAM)", RFC 4378, February 2006.

   [MPLS-P2MP]   Yasukawa, S., Farrel, A., King, D., and T. Nadeau,
                 "Operations and Management (OAM) Requirements for
                 Point-to-Multipoint MPLS Networks", RFC 4687, September
                 2006.

   [MPLS-TP-OAM] Vigoureux, M., Ed., Ward, D., Ed., and M. Betts, Ed.,
                 "Requirements for Operations, Administration, and
                 Maintenance (OAM) in MPLS Transport Networks", RFC
                 5860, May 2010.

   [mtrace]      Fenner, W. and S. Casner, "A "traceroute" facility for
                 IP Multicast", Work in Progress, July 2000.

   [NetTerms]    Jacobsen, O. and D. Lynch, "A Glossary of Networking
                 Terms", RFC 1208, March 1991.

   [NetTools]    Enger, R. and J. Reynolds, "FYI on a Network Management
                 Tool Catalog: Tools for Monitoring and Debugging TCP/IP
                 Internets and Interconnected Devices", FYI 2, RFC 1470,
                 June 1993.

   [OAM-Analys]  Sprecher, N. and L. Fang, "An Overview of the
                 Operations, Administration, and Maintenance (OAM)
                 Toolset for MPLS-Based Transport Networks", RFC 6669,
                 July 2012.

   [OAM-Label]   Ohta, H., "Assignment of the 'OAM Alert Label' for
                 Multiprotocol Label Switching Architecture (MPLS)
                 Operation and Maintenance (OAM) Functions", RFC 3429,
                 November 2002.

   [OAM-Mng]     Ersue, M., Ed., and B. Claise, "An Overview of the IETF
                 Network Management Standards", RFC 6632, June 2012.

   [OnDemand-CV] Gray, E., Bahadur, N., Boutros, S., and R. Aggarwal,
                 "MPLS On-Demand Connectivity Verification and Route
                 Tracing", RFC 6426, November 2011.

   [OWAMP]       Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and
                 M. Zekauskas, "A One-way Active Measurement Protocol
                 (OWAMP)", RFC 4656, September 2006.






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   [PARIS]       Augustin, B., Friedman, T., and R. Teixeira, "Measuring
                 Load-balanced Paths in the Internet", IMC '07
                 Proceedings of the 7th ACM SIGCOMM conference on
                 Internet measurement, 2007.

   [PM-CONS]     Clark, A. and B. Claise, "Guidelines for Considering
                 New Performance Metric Development", BCP 170, RFC 6390,
                 October 2011.

   [PW-ACH]      Bryant, S., Swallow, G., Martini, L., and D. McPherson,
                 "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word
                 for Use over an MPLS PSN", RFC 4385, February 2006.

   [PW-G-ACh]    Li, H., Martini, L., He, J., and F. Huang, "Using the
                 Generic Associated Channel Label for Pseudowire in the
                 MPLS Transport Profile (MPLS-TP)", RFC 6423, November
                 2011.

   [PW-MAP]      Aissaoui, M., Busschbach, P., Martini, L., Morrow, M.,
                 Nadeau, T., and Y(J). Stein, "Pseudowire (PW)
                 Operations, Administration, and Maintenance (OAM)
                 Message Mapping", RFC 6310, July 2011.

   [Reorder]     Morton, A., Ciavattone, L., Ramachandran, G., Shalunov,
                 S., and J. Perser, "Packet Reordering Metrics", RFC
                 4737, November 2006.

   [Signal]      Yasukawa, S., Ed., "Signaling Requirements for Point-
                 to-Multipoint Traffic-Engineered MPLS Label Switched
                 Paths (LSPs)", RFC 4461, April 2006.

   [TCPIP-Tools] Kessler, G. and S. Shepard, "A Primer On Internet and
                 TCP/IP Tools and Utilities", FYI 30, RFC 2151, June
                 1997.

   [TP-CC-CV]    Allan, D., Ed., Swallow Ed., G., and J. Drake Ed.,
                 "Proactive Connectivity Verification, Continuity Check,
                 and Remote Defect Indication for the MPLS Transport
                 Profile", RFC 6428, November 2011.

   [TP-Fault]    Swallow, G., Ed., Fulignoli, A., Ed., Vigoureux, M.,
                 Ed., Boutros, S., and D. Ward, "MPLS Fault Management
                 Operations, Administration, and Maintenance (OAM)", RFC
                 6427, November 2011.

   [TP-LM-DM]    Frost, D., Ed., and S. Bryant, Ed., "A Packet Loss and
                 Delay Measurement Profile for MPLS-Based Transport
                 Networks", RFC 6375, September 2011.



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   [TP-OAM-FW]   Busi, I., Ed., and D. Allan, Ed., "Operations,
                 Administration, and Maintenance Framework for MPLS-
                 Based Transport Networks", RFC 6371, September 2011.

   [TP-Term]     van Helvoort, H., Ed., Andersson, L., Ed., and N.
                 Sprecher, Ed., "A Thesaurus for the Interpretation of
                 Terminology Used in MPLS Transport Profile (MPLS-TP)
                 Internet-Drafts and RFCs in the Context of the ITU-T's
                 Transport Network Recommendations", RFC 7087, December
                 2013.

   [TRILL-OAM]   Senevirathne, T., Bond, D., Aldrin, S., Li, Y., and R.
                 Watve, "Requirements for Operations, Administration,
                 and Maintenance (OAM) in Transparent Interconnection of
                 Lots of Links (TRILL)", RFC 6905, March 2013.

   [TWAMP]       Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and
                 J. Babiarz, "A Two-Way Active Measurement Protocol
                 (TWAMP)", RFC 5357, October 2008.

   [VCCV]        Nadeau, T., Ed., and C. Pignataro, Ed., "Pseudowire
                 Virtual Circuit Connectivity Verification (VCCV): A
                 Control Channel for Pseudowires", RFC 5085, December
                 2007.

   [VCCV-SURVEY] Del Regno, N., Ed., and A. Malis, Ed., "The Pseudowire
                 (PW) and Virtual Circuit Connectivity Verification
                 (VCCV) Implementation Survey Results", RFC 7079,
                 November 2013.






















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Appendix A.  List of OAM Documents

A.1.  List of IETF OAM Documents

   Table 5 summarizes the OAM-related RFCs produced by the IETF.

   It is important to note that the table lists various RFCs that are
   different by nature.  For example, some of these documents define OAM
   tools or OAM protocols (or both), while others define protocols that
   are not strictly OAM related, but are used by OAM tools.  The table
   also includes RFCs that define the requirements or the framework of
   OAM in a specific context (e.g., MPLS-TP).

   The RFCs in the table are categorized in a few sets as defined in
   Section 1.3.

   +-----------+--------------------------------------+----------+
   | Toolset   | Title                                | RFC      |
   +-----------+--------------------------------------+----------+
   |IP Ping    | Requirements for Internet Hosts --   | RFC 1122 |
   |           | Communication Layers [IntHost]       |          |
   |           +--------------------------------------+----------+
   |           | A Glossary of Networking Terms       | RFC 1208 |
   |           | [NetTerms]                           |          |
   |           +--------------------------------------+----------+
   |           | Internet Control Message Protocol    | RFC 792  |
   |           | [ICMPv4]                             |          |
   |           +--------------------------------------+----------+
   |           | Internet Control Message Protocol    | RFC 4443 |
   |           | (ICMPv6) for the Internet Protocol   |          |
   |           | Version 6 (IPv6) Specification       |          |
   |           | [ICMPv6]                             |          |
   +-----------+--------------------------------------+----------+
   |IP         | A Primer On Internet and TCP/IP      | RFC 2151 |
   |Traceroute | Tools and Utilities [TCPIP-Tools]    |          |
   |           +--------------------------------------+----------+
   |           | FYI on a Network Management Tool     | RFC 1470 |
   |           | Catalog: Tools for Monitoring and    |          |
   |           | Debugging TCP/IP Internets and       |          |
   |           | Interconnected Devices [NetTools]    |          |
   |           +--------------------------------------+----------+
   |           | Internet Control Message Protocol    | RFC 792  |
   |           | [ICMPv4]                             |          |
   |           +--------------------------------------+----------+
   |           | Internet Control Message Protocol    | RFC 4443 |
   |           | (ICMPv6) for the Internet Protocol   |          |
   |           | Version 6 (IPv6) Specification       |          |
   |           | [ICMPv6]                             |          |



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   |           +--------------------------------------+----------+
   |           | Extended ICMP to Support Multi-Part  | RFC 4884 |
   |           | Messages [ICMP-MP]                   |          |
   |           +--------------------------------------+----------+
   |           | Extending ICMP for Interface and     | RFC 5837 |
   |           | Next-Hop Identification [ICMP-Int]   |          |
   +-----------+--------------------------------------+----------+
   |BFD        | Bidirectional Forwarding Detection   | RFC 5880 |
   |           | (BFD) [BFD]                          |          |
   |           +--------------------------------------+----------+
   |           | Bidirectional Forwarding Detection   | RFC 5881 |
   |           | (BFD) for IPv4 and IPv6 (Single Hop) |          |
   |           | [BFD-IP]                             |          |
   |           +--------------------------------------+----------+
   |           | Generic Application of Bidirectional | RFC 5882 |
   |           | Forwarding Detection (BFD)[BFD-Gen]  |          |
   |           +--------------------------------------+----------+
   |           | Bidirectional Forwarding Detection   | RFC 5883 |
   |           | (BFD) for Multihop Paths [BFD-Multi] |          |
   |           +--------------------------------------+----------+
   |           | Bidirectional Forwarding Detection   | RFC 5884 |
   |           | (BFD) for MPLS Label Switched Paths  |          |
   |           | (LSPs) [BFD-LSP]                     |          |
   |           +--------------------------------------+----------+
   |           | Bidirectional Forwarding Detection   | RFC 5885 |
   |           | for the Pseudowire Virtual Circuit   |          |
   |           | Connectivity Verification (VCCV)     |          |
   |           | [BFD-VCCV]                           |          |
   +-----------+--------------------------------------+----------+
   |MPLS OAM   | Operations and Management (OAM)      | RFC 4377 |
   |           | Requirements for Multi-Protocol Label|          |
   |           | Switched (MPLS) Networks [MPLS-OAM]  |          |
   |           +--------------------------------------+----------+
   |           | A Framework for Multi-Protocol       | RFC 4378 |
   |           | Label Switching (MPLS) Operations    |          |
   |           | and Management (OAM) [MPLS-OAM-FW]   |          |
   |           +--------------------------------------+----------+
   |           | Detecting Multi-Protocol Label       | RFC 4379 |
   |           | Switched (MPLS) Data Plane Failures  |          |
   |           | [LSP-Ping]                           |          |
   |           +--------------------------------------+----------+
   |           | Operations and Management (OAM)      | RFC 4687 |
   |           | Requirements for Point-to-Multipoint |          |
   |           | MPLS Networks [MPLS-P2MP]            |          |
   |           +--------------------------------------+----------+
   |           | ICMP Extensions for Multiprotocol    | RFC 4950 |
   |           | Label Switching [ICMP-Ext]           |          |




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   |           +--------------------------------------+----------+
   |           | Bidirectional Forwarding Detection   | RFC 5884 |
   |           | for MPLS Label Switched Paths (LSPs) |          |
   |           | [BFD-LSP]                            |          |
   +-----------+--------------------------------------+----------+
   |MPLS-TP    | Requirements for Operations,         | RFC 5860 |
   |OAM        | Administration, and Maintenance (OAM)|          |
   |           | in MPLS Transport Networks           |          |
   |           | [MPLS-TP-OAM]                        |          |
   |           +--------------------------------------+----------+
   |           | MPLS Generic Associated Channel      | RFC 5586 |
   |           | [G-ACh]                              |          |
   |           +--------------------------------------+----------+
   |           | Operations, Administration, and      | RFC 6371 |
   |           | Maintenance Framework for MPLS-Based |          |
   |           | Transport Networks [TP-OAM-FW]       |          |
   |           +--------------------------------------+----------+
   |           | Proactive Connectivity Verification, | RFC 6428 |
   |           | Continuity Check, and Remote Defect  |          |
   |           | Indication for the MPLS Transport    |          |
   |           | Profile [TP-CC-CV]                   |          |
   |           +--------------------------------------+----------+
   |           | MPLS On-Demand Connectivity          | RFC 6426 |
   |           | Verification and Route Tracing       |          |
   |           | [OnDemand-CV]                        |          |
   |           +--------------------------------------+----------+
   |           | MPLS Fault Management Operations,    | RFC 6427 |
   |           | Administration, and Maintenance (OAM)|          |
   |           | [TP-Fault]                           |          |
   |           +--------------------------------------+----------+
   |           | MPLS Transport Profile Lock Instruct | RFC 6435 |
   |           | and Loopback Functions [Lock-Loop]   |          |
   |           +--------------------------------------+----------+
   |           | Packet Loss and Delay Measurement for| RFC 6374 |
   |           | MPLS Networks [MPLS-LM-DM]           |          |
   |           +--------------------------------------+----------+
   |           | A Packet Loss and Delay Measurement  | RFC 6375 |
   |           | Profile for MPLS-Based Transport     |          |
   |           | Networks [TP-LM-DM]                  |          |
   +-----------+--------------------------------------+----------+
   |Pseudowire | Pseudowire Virtual Circuit           | RFC 5085 |
   |OAM        | Connectivity Verification (VCCV):    |          |
   |           | A Control Channel for Pseudowires    |          |
   |           | [VCCV]                               |          |







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   |           +--------------------------------------+----------+
   |           | Bidirectional Forwarding Detection   | RFC 5885 |
   |           | for the Pseudowire Virtual Circuit   |          |
   |           | Connectivity Verification (VCCV)     |          |
   |           | [BFD-VCCV]                           |          |
   |           +--------------------------------------+----------+
   |           | Using the Generic Associated Channel | RFC 6423 |
   |           | Label for Pseudowire in the MPLS     |          |
   |           | Transport Profile (MPLS-TP)          |          |
   |           | [PW-G-ACh]                           |          |
   |           +--------------------------------------+----------+
   |           | Pseudowire (PW) Operations,          | RFC 6310 |
   |           | Administration, and Maintenance (OAM)|          |
   |           | Message Mapping [PW-MAP]             |          |
   |           +--------------------------------------+----------+
   |           | MPLS and Ethernet Operations,        | RFC 7023 |
   |           | Administration, and Maintenance (OAM)|          |
   |           | Interworking [Eth-Int]               |          |
   +-----------+--------------------------------------+----------+
   |OWAMP and  | A One-way Active Measurement Protocol| RFC 4656 |
   |TWAMP      | (OWAMP) [OWAMP]                      |          |
   |           +--------------------------------------+----------+
   |           | A Two-Way Active Measurement Protocol| RFC 5357 |
   |           | (TWAMP) [TWAMP]                      |          |
   |           +--------------------------------------+----------+
   |           | Framework for IP Performance Metrics | RFC 2330 |
   |           | [IPPM-FW]                            |          |
   |           +--------------------------------------+----------+
   |           | IPPM Metrics for Measuring           | RFC 2678 |
   |           | Connectivity [IPPM-Con]              |          |
   |           +--------------------------------------+----------+
   |           | A One-way Delay Metric for IPPM      | RFC 2679 |
   |           | [IPPM-1DM]                           |          |
   |           +--------------------------------------+----------+
   |           | A One-way Packet Loss Metric for IPPM| RFC 2680 |
   |           | [IPPM-1LM]                           |          |
   |           +--------------------------------------+----------+
   |           | A Round-trip Delay Metric for IPPM   | RFC 2681 |
   |           | [IPPM-2DM]                           |          |
   |           +--------------------------------------+----------+
   |           | Packet Reordering Metrics            | RFC 4737 |
   |           | [Reorder]                            |          |
   |           +--------------------------------------+----------+
   |           | A One-Way Packet Duplication Metric  | RFC 5560 |
   |           | [Dup]                                |          |






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   +-----------+--------------------------------------+----------+
   |TRILL OAM  | Requirements for Operations,         | RFC 6905 |
   |           | Administration, and Maintenance (OAM)|          |
   |           | in Transparent Interconnection of    |          |
   |           | Lots of Links (TRILL)                |          |
   +-----------+--------------------------------------+----------+

               Table 5: Summary of IETF OAM-Related RFCs

A.2.  List of Selected Non-IETF OAM Documents

   In addition to the OAM tools defined by the IETF, the IEEE and ITU-T
   have also defined various OAM tools that focus on Ethernet and
   various other transport-network environments.  These various tools,
   defined by the three standard organizations, are often tightly
   coupled and have had a mutual effect on each other.  The ITU-T and
   IETF have both defined OAM tools for MPLS LSPs, [ITU-T-Y1711], and
   [LSP-Ping].  The following OAM standards by the IEEE and ITU-T are to
   some extent linked to the IETF OAM tools listed above and are
   mentioned here only as reference material.

   o  OAM tools for Layer 2 have been defined by the ITU-T in
      [ITU-T-Y1731] and by the IEEE in 802.1ag [IEEE802.1Q].  The IEEE
      802.3 standard defines OAM for one-hop Ethernet links
      [IEEE802.3ah].

   o  The ITU-T has defined OAM for MPLS LSPs in [ITU-T-Y1711] and for
      MPLS-TP OAM in [ITU-G8113.1] and [ITU-G8113.2].

   It should be noted that these non-IETF documents deal in many cases
   with OAM functions below the IP layer (Layer 2, Layer 2.5) and that
   in some cases operators use a multi-layered OAM approach, which is a
   function of the way their networks are designed.


















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   Table 6 summarizes some of the main OAM standards published by
   non-IETF standard organizations.  This document focuses on IETF OAM
   standards, but these non-IETF standards are referenced in this
   document where relevant.

   +-----------+--------------------------------------+---------------+
   |           | Title                                | Document      |
   +-----------+--------------------------------------+---------------+
   |ITU-T      | Operation & Maintenance mechanism    | ITU-T Y.1711  |
   |MPLS OAM   | for MPLS networks [ITU-T-Y1711]      |               |
   |           +--------------------------------------+---------------+
   |           | Assignment of the 'OAM Alert Label'  | RFC 3429      |
   |           | for Multiprotocol Label Switching    |               |
   |           | Architecture (MPLS) Operation and    |               |
   |           | Maintenance (OAM) Functions          |               |
   |           | [OAM-Label]                          |               |
   |           |                                      |               |
   |           |  Note: although this is an IETF      |               |
   |           |  document, it is listed as one of the|               |
   |           |  non-IETF OAM standards, since it    |               |
   |           |  was defined as a complementary part |               |
   |           |  of ITU-T Y.1711.                    |               |
   +-----------+--------------------------------------+---------------+
   |ITU-T      | Operations, administration and       |ITU-T G.8113.2 |
   |MPLS-TP OAM| Maintenance mechanisms for MPLS-TP   |               |
   |           | networks using the tools defined for |               |
   |           | MPLS [ITU-G8113.2]                   |               |
   |           |                                      |               |
   |           |  Note: this document describes the   |               |
   |           |  OAM toolset defined by the IETF for |               |
   |           |  MPLS-TP, whereas ITU-T G.8113.1     |               |
   |           |  describes the OAM toolset defined   |               |
   |           |  by the ITU-T.                       |               |
   |           +--------------------------------------+---------------+
   |           | Operations, Administration and       |ITU-T G.8113.1 |
   |           | Maintenance mechanism for MPLS-TP in |               |
   |           | Packet Transport Network (PTN)       |               |














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   |           +--------------------------------------+---------------+
   |           | Allocation of a Generic Associated   | RFC 6671      |
   |           | Channel Type for ITU-T MPLS Transport|               |
   |           | Profile Operation, Maintenance, and  |               |
   |           | Administration (MPLS-TP OAM)         |               |
   |           | [ITU-T-CT]                           |               |
   |           |                                      |               |
   |           |  Note: although this is an IETF      |               |
   |           |  document, it is listed as one of the|               |
   |           |  non-IETF OAM standards, since it    |               |
   |           |  was defined as a complementary part |               |
   |           |  of ITU-T G.8113.1.                  |               |
   +-----------+--------------------------------------+---------------+
   |ITU-T      | OAM Functions and Mechanisms for     | ITU-T Y.1731  |
   |Ethernet   | Ethernet-based Networks              |               |
   |OAM        | [ITU-T-Y1731]                        |               |
   +-----------+--------------------------------------+---------------+
   |IEEE       | Connectivity Fault Management        | IEEE 802.1ag  |
   |CFM        | [IEEE802.1Q]                         |               |
   |           |                                      |               |
   |           |  Note: CFM was originally published  |               |
   |           |  as IEEE 802.1ag but is now          |               |
   |           |  incorporated in the 802.1Q standard.|               |
   +-----------+--------------------------------------+---------------+
   |IEEE       | Management of Data Driven and Data   | IEEE 802.1ag  |
   |DDCFM      | Dependent Connectivity Faults        |               |
   |           | [IEEE802.1Q]                         |               |
   |           |                                      |               |
   |           |  Note: DDCFM was originally published|               |
   |           |  as IEEE 802.1Qaw but is now         |               |
   |           |  incorporated in the 802.1Q standard.|               |
   +-----------+--------------------------------------+---------------+
   |IEEE       | Media Access Control Parameters,     | IEEE 802.3ah  |
   |802.3      | Physical Layers, and Management      |               |
   |link level | Parameters for Subscriber Access     |               |
   |OAM        | Networks [IEEE802.3ah]               |               |
   |           |                                      |               |
   |           |  Note: link level OAM was originally |               |
   |           |  defined in IEEE 802.3ah and is now  |               |
   |           |  incorporated in the 802.3 standard. |               |
   +-----------+--------------------------------------+---------------+

         Table 6: Non-IETF OAM Standards Mentioned in This Document








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Authors' Addresses

   Tal Mizrahi
   Marvell
   6 Hamada St.
   Yokneam  20692
   Israel

   EMail: talmi@marvell.com


   Nurit Sprecher
   Nokia Solutions and Networks
   3 Hanagar St. Neve Ne'eman B
   Hod Hasharon  45241
   Israel

   EMail: nurit.sprecher@nsn.com


   Elisa Bellagamba
   Ericsson
   6 Farogatan St.
   Stockholm  164 40
   Sweden

   Phone: +46 761440785
   EMail: elisa.bellagamba@ericsson.com


   Yaacov Weingarten
   34 Hagefen St.
   Karnei Shomron  4485500
   Israel

   EMail: wyaacov@gmail.com















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