Operations and Management Area Working Group                  T. Mizrahi
Internet Draft                                                   Marvell
Intended status: Informational                               N. Sprecher
Expires: September 2012 March 2013                               Nokia Siemens Networks
                                                           E. Bellagamba
                                                           Y. Weingarten
                                                Nokia Siemens Networks

                                                      September 12, 2012

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


   Operations, Administration, and Maintenance (OAM) is a general term
   that refers to a toolset that can be used for fault detection and
   isolation, and for performance measurement. OAM mechanisms have been
   defined for various layers in the protocol stack, and are used with a
   variety of protocols.

   This document presents an overview of the OAM mechanisms that have
   been defined and are currently being defined by the IETF.

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Table of Contents

   1. Introduction ................................................. 3
      1.1. Background .............................................. 3
      1.2. The OAM toolsets ........................................ 4
      1.3. IETF OAM Standards ...................................... 5
      1.4. Non-IETF OAM Standards .................................. 8
   2. Basic Terminology ............................................ 9
      2.1. Abbreviations ........................................... 9
      2.2. Terminology used in OAM Standards ...................... 10
         2.2.1. General Terms ..................................... 10
         2.2.2. OAM Maintenance Entities .......................... 11
         2.2.3. OAM Maintenance Points ............................ 11
         2.2.4. Proactive and On-demand activation ................ 12
         2.2.5. Connectivity Verification and Continuity Checks ... 12
         2.2.6. Failures .......................................... 13
   3. OAM Tools ................................................... 13
      3.1. ICMP Ping .............................................. 13
      3.2. Traceroute ............................................. 13
      3.3. Bidirectional Forwarding Detection (BFD) ............... 14
         3.3.1. Overview .......................................... 14
         3.3.2. BFD Control ....................................... 14
         3.3.3. BFD Echo .......................................... 15
      3.4. LSP Ping ............................................... 15
      3.5. PWE3 Virtual Circuit Connectivity Verification (VCCV) .. 16
      3.6. IP Performance Metrics (IPPM) .......................... 17
         3.6.1. Overview .......................................... 17
         3.6.2. Control and Test Protocols ........................ 17
         3.6.3. OWAMP ............................................. 18
         3.6.4. TWAMP ............................................. 18
      3.7. MPLS-TP OAM ............................................ 19
         3.7.1. Overview .......................................... 19
         3.7.2. Generic Associated Channel ........................ 19
         3.7.3. MPLS-TP OAM Toolset ............................... 20
   Continuity Check and Connectivity Verification 20
   Route Tracing ................................ 21
   Lock Instruct ................................ 21
   Lock Reporting ............................... 21
   Alarm Reporting .............................. 21
   Remote Defect Indication ..................... 22
   Client Failure Indication .................... 22
   Packet Loss Measurement ...................... 22
   Packet Delay Measurement ..................... 22
      3.8. Summary of OAM Functions ............................... 23
   4. Security Considerations ..................................... 24
   5. IANA Considerations ......................................... 24
   6. Acknowledgments ............................................. 24
   7. References .................................................. 24
      7.1. Normative References ................................... 24
      7.2. Informative References ................................. 27

1. Introduction

   OAM is a general term that refers to a toolset that can be used for
   detecting, isolating and reporting connection failures or measurement
   of connection performance parameters. The term OAM has been used over
   the years in several different contexts, as discussed in [OAM Def]. [OAM-Def].
   This term as been associated with the 3 logical abstraction layers:
   the forwarding plane, the control plane, and the management plane. In
   the context of this document OAM refers to Operations,
   Administration, and Maintenance. Hence, management aspects are
   outside the scope of this document.

1.1. Background

   The communication of a network may be configured and maintained by
   use of various tools at different layers - these include use of a
   control plane or management plane to configure and maintain the
   connectivity of the network from the outside - looking in - and
   controlling the connections when the need arises. OAM, on the other
   hand, traditionally has been used to maintain the connectivity in-
   band with the actual data traffic, i.e. in the data plane.

   While the OAM tools may, and quite often do, work in conjunction with
   a control-plane or management plane, they are usually defined to be
   independent of the control-plane.  The OAM tools communicate with the
   management plane to raise alarms, and often the on-demand tools may
   be activated by the management, e.g. to locate and localize problems.

   The considerations of the control-plane maintenance tools or the
   functionality of the management-plane are out of scope for this
   document, which will concentrate on presenting the data-plane tools
   that are used for OAM.

1.2. The OAM toolsets

   This memo provides an overview of the different sets of OAM
   mechanisms defined by the IETF. It is intended for those with little
   or no familiarity with the described mechanisms. The set of OAM
   mechanisms described in this memo are applicable to IP unicast, MPLS,
   pseudowires, and MPLS for the transport environment (MPLS-TP). While
   OAM mechanisms 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 mechanisms in several
   different fronts:

   o ICMP Ping:
      ICMP Echo request, also known as Ping, as defined in [ICMPv4], and
      [ICMPv6]. ICMP Ping is a very simple and basic mechanism in
      failure diagnosis. LSP Ping is to some extent based on ICMP Ping.

   o IPPM:
      IP Performance Metrics (IPPM) is a working group in the IETF that
      defined common metrics for performance measurement, as well as a
      protocol for measuring delay and packet loss in IP networks.

   o MPLS:
      MPLS LSP Ping, as defined in [MPLS OAM], [MPLS OAM FW] [MPLS-OAM], [MPLS-OAM-FW] and [LSP [LSP-
      Ping], is an OAM mechanism for point to point MPLS LSPs.

   o MPLS-TP:
      The OAM requirements for MPLS Transport Profile (MPLS-TP) are
      defined in [MPLS-TP OAM], [MPLS-TP-OAM], and the toolset is described in [TP OAM [TP-OAM-

   o BFD:
      Bidirectional Forwarding Detection (BFD) is defined in [BFD] as a
      framework for a lightweight generic OAM mechanism.  The intention
      is to define a base mechanism that can be used with various
      encapsulation types, network environments, and in various medium

   This document summarizes the OAM mechanisms defined by the IETF. We
   first present a comparison of the terminology used in various OAM
   standards, and then summarize the OAM functions that each OAM
   standard provides.

1.3. IETF OAM Standards

   Table 1 summarizes the IETF OAM standards discussed in this document.

   The table includes a "Type" column, specifying the nature of each of
   the listed documents:

   o Tool: documents that define an OAM tool or mechanism.

   o Prof.: documents that define a profile or a variant for an OAM
      tool that is defined in other documents.

   o Inf.: documents that define an infrastructure that is used by OAM

   o Misc.: other OAM related documents, e.g., OAM requirement and
      framework documents.

   |           | Title                                |Type | RFC      |
   |ICMPv4 Ping| Internet Control Message Protocol    |Tool | RFC 792  |
   |           |                                      |     |          |
   |ICMPv6 Ping| Internet Control Message Protocol    |Tool | RFC 4443 |
   |           | (ICMPv6) for the Internet Protocol   |     |          |
   |           | Version 6 (IPv6) Specification       |     |          |
   |Traceroute | A Primer On Internet and TCP/IP      |Tool | RFC 2151 |
   |           | Tools and Utilities                  |     |          |
   |BFD        | Bidirectional Forwarding Detection   |Tool | RFC 5880 |
   |           +--------------------------------------+-----+----------+
   |           | Bidirectional Forwarding Detection   |Prof.| RFC 5881 |
   |           | (BFD) for IPv4 and IPv6 (Single Hop) |     |          |
   |           +--------------------------------------+-----+----------+
   |           | Generic Application of Bidirectional |Misc.| RFC 5882 |
   |           | Forwarding Detection                 |     |          |
   |           +--------------------------------------+-----+----------+
   |           | Bidirectional Forwarding Detection   |Prof.| RFC 5883 |
   |           | (BFD) for Multihop Paths             |     |          |
   |           +--------------------------------------+-----+----------+
   |           | Bidirectional Forwarding Detection   |Prof.| RFC 5884 |
   |           | for MPLS Label Switched Paths (LSPs) |     |          |
   |           +--------------------------------------+-----+----------+
   |           | Bidirectional Forwarding Detection   |Prof.| RFC 5885 |
   |           | for the Pseudowire Virtual Circuit   |     |          |
   |           | Connectivity Verification (VCCV)     |     |          |
   |IETF MPLS  | Operations and Management (OAM)      |Misc.| RFC 4377 |
   |OAM        | Requirements for Multi-Protocol Label|     |          |
   |(LSP Ping) | Switched (MPLS) Networks             |     |          |
   |           +--------------------------------------+-----+----------+
   |           | A Framework for Multi-Protocol       |Misc.| RFC 4378 |
   |           | Label Switching (MPLS) Operations    |     |          |
   |           | and Management (OAM)                 |     |          |
   |           +--------------------------------------+-----+----------+
   |           | Detecting Multi-Protocol Label       |Tool | RFC 4379 |
   |           | Switched (MPLS) Data Plane Failures  |     |          |
   |           +--------------------------------------+-----+----------+
   |           | Operations and Management (OAM)      |Misc.| RFC 4687 |
   |           | Requirements for Point-to-Multipoint |     |          |
   |           | MPLS Networks                        |     |          |
   |           +--------------------------------------+-----+----------+
   |           | ICMP Extensions for Multiprotocol    |Tool | RFC 4950 |
   |           | Label Switching                      |     |          |
   |MPLS-TP    | Requirements for OAM in MPLS-TP      |Misc.| RFC 5860 |
   |OAM        +--------------------------------------+-----+----------+
   |           | MPLS Generic Associated Channel      |Inf. | RFC 5586 |
   |           +--------------------------------------+-----+----------+
   |           | MPLS-TP OAM Framework                |Misc.| RFC 6371 |
   |           +--------------------------------------+-----+----------+
   |           | Proactive Connectivity Verification, |Tool | RFC 6428 |
   |           | Continuity Check, and Remote Defect  |     |          |
   |           | Indication for the MPLS Transport    |     |          |
   |           | Profile                              |     |          |
   |           +--------------------------------------+-----+----------+
   |           | MPLS On-Demand Connectivity          |Tool | RFC 6426 |
   |           | Verification and Route Tracing       |     |          |
   |           +--------------------------------------+-----+----------+
   |           | MPLS Fault Management Operations,    |Tool | RFC 6427 |
   |           | Administration, and Maintenance (OAM)|     |          |
   |           +--------------------------------------+-----+----------+
   |           | MPLS Transport Profile Lock Instruct |Tool | RFC 6435 |
   |           | and Loopback Functions               |     |          |
   |           +--------------------------------------+-----+----------+
   |           | Packet Loss and Delay Measurement for|Tool | RFC 6374 |
   |           | MPLS Networks                        |     |          |
   |           +--------------------------------------+-----+----------+
   |           | A Packet Loss and Delay Measurement  |Prof.| RFC 6375 |
   |           | Profile for MPLS-Based Transport     |     |          |
   |           | Networks                             |     |          |
   |PW VCCV    | Pseudowire Virtual Circuit           |Inf. | RFC 5085 |
   |           | Connectivity Verification (VCCV):    |     |          |
   |           | A Control Channel for Pseudowires    |     |          |
   |IPPM       | Framework for IP Performance Metrics |Misc.| RFC 2330 |
   |           +--------------------------------------+-----+----------+
   |           | IPPM Metrics for Measuring           |Misc.| RFC 2678 |
   |           | Connectivity                         |     |          |
   |           +--------------------------------------+-----+----------+
   |           | A One-way Delay Metric for IPPM      |Misc.| RFC 2679 |
   |           +--------------------------------------+-----+----------+
   |           | A One-way Packet Loss Metric for IPPM|Misc.| RFC 2680 |
   |           +--------------------------------------+-----+----------+
   |           | A Round-trip Delay Metric for IPPM   |Misc.| RFC 2681 |
   |           +--------------------------------------+-----+----------+
   |           | A One-way Active Measurement Protocol|Tool | RFC 4656 |
   |           | (OWAMP)                              |     |          |
   |           +--------------------------------------+-----+----------+
   |           | A Two-Way Active Measurement Protocol|Tool | RFC 5357 |
   |           | (TWAMP)                              |     |          |
               Table 1 Summary of IETF OAM Related Standards

1.4. Non-IETF OAM Standards

   In addition to the OAM mechanisms defined by the IETF, the IEEE and
   ITU-T have also defined various OAM mechanisms that focus on
   Ethernet, and various other transport network environments. These
   various mechanisms, 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 mechanisms for MPLS LSPs,
   [ITU-T Y.1711]
   [ITU-T-Y.1711] and [LSP Ping]. [LSP-Ping]. The following OAM standards by the
   IEEE and ITU-T are to some extent linked to IETF OAM mechanisms
   listed above and are mentioned here only as reference material:

   o OAM mechanisms for Ethernet based networks have been defined by
      both the ITU-T in [ITU-T Y.1731], [ITU-T-Y.1731], and by the IEEE in [IEEE [IEEE-
      802.1ag]. The IEEE 802.3 standard defines OAM for one-hop Ethernet
      links [IEEE 802.3ah]. [IEEE-802.3ah].

   o The ITU-T has defined OAM for MPLS LSPs in [ITU-T Y.1711]. [ITU-T-Y.1711].

   Table 2 summarizes the OAM standards mentioned in this document. This
   document focuses on IETF OAM standards, but these non-IETF standards
   are referenced where relevant.

   |           | Title                                |Standard/Draft |
   |ITU-T      | Operation & Maintenance mechanism    |[ITU-T Y.1711]    |[ITU-T-Y.1711] |
   |MPLS OAM   | for MPLS networks                    |               |
   |           +--------------------------------------+---------------+
   |           | Assignment of the 'OAM Alert Label'  | RFC 3429      |
   |           | for Multiprotocol Label Switching    |               |
   |           | Architecture (MPLS) Operation and    |               |
   |           | Maintenance (OAM) Functions          |               |
   |           |                                      |               |
   |           |  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 Y.1711.                          |               |
   |ITU-T      | OAM Functions and Mechanisms for     |[ITU-T Y.1731]     |[ITU-T-Y.1731] |
   |Ethernet   | Ethernet-based Networks              |               |
   |OAM        |                                      |               |
   |IEEE       | Connectivity Fault Management        |[IEEE 802.1ag]        |[IEEE-802.1ag] |
   |CFM        |                                      |               |
   |IEEE       | Media Access Control Parameters,     |[IEEE 802.3ah]     |[IEEE-802.3ah] |
   |802.3      | Physical Layers, and Management      |               |
   |link level | Parameters for Subscriber Access     |               |
   |OAM        | Networks                             |               |
         Table 2 Non-IETF OAM Standards Mentioned in this Document

2. Basic Terminology

2.1. Abbreviations

   ACH    Associated Channel Header

   AIS    Alarm Indication Signal

   BFD    Bidirectional Forwarding Detection

   CC     Continuity Check

   CCM    Continuity Check Message

   CV     Connectivity Verification

   DM     Delay Measurement

   FEC    Forwarding Equivalence Class

   GAL    Generic Associated Label

   ICMP   Internet Control Message Protocol

   L2TP   Layer Two Tunneling Protocol

   LCCE   L2TP Control Connection Endpoint

   LDP    Label Distribution Protocol

   LM     Loss Measurement

   LOC    Loss Of Continuity
   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

   PE     Provider Edge

   PW     Pseudowire

   PWE3   Pseudowire Emulation Edge-to-Edge

   RDI    Remote Defect Indication

   TTL    Time To Live

   VCCV   Virtual Circuit Connectivity Verification

2.2. Terminology used in OAM Standards

2.2.1. General Terms

   A wide variety of terms is used in various OAM standards. Each of the
   OAM standards listed in the reference section includes a section that
   defines terms relevant to that tool. A thesaurus of terminology for
   MPLS-TP terms is presented in [MPLS-TP Term], [MPLS-TP-Term], and provides a good
   summary of some of the OAM related terminology.

   This section presents a comparison of the terms used in various OAM
   standards, without fully quoting the definition of each term. For a
   formal definition of each term, refer to the references at the end of
   this document.

2.2.2. OAM Maintenance Entities

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

   The following related terms are also quoted from [TP OAM FW]: [TP-OAM-FW]:

   o MEP: The two points that define a maintenance entity.

   o MEG: The collection of one or more MEs that belongs to the same
      transport path and that are maintained and monitored as a group
      are known as a Maintenance Entity Group (MEG).

   o MIP: In between MEPs, there are zero or more intermediate points,
      called Maintenance Entity Group Intermediate Points (MIPs).

   A pair of MEPs engaged in an ME are connected by a communication
   link, which may be one of several types of connection, e.g. a single
   physical connection, a set of physical connections, or a virtual link
   such as an MPLS LSP.

   The term Maintenance Entity (ME) is used in ITU-T Recommendations
   (e.g. [ITU-T Y.1731]), [ITU-T-Y.1731]), as well as in the MPLS-TP terminology ([TP OAM
   FW]). ([TP-
   OAM-FW]). Various terms are used to refer to an ME. For example, BFD
   does not explicitly use a term that is equivalent to ME, but rather
   uses the term "session", referring to the relationship between two
   nodes using a BFD protocol. The MPLS LSP Ping ([LSP Ping]) ([LSP-Ping])
   terminology simply uses the term "LSP" in this context.

   MPLS-TP has defined the terms ME and Maintenance Entity Group (MEG)
   in [TP OAM FW], [TP-OAM-FW], similar to the terms defined by ITU-T.  A MEG allows
   the monitoring of a compound set of MEs, for example when monitoring
   a p2mp MEG that is considered to be the set of MEs between the root
   and each individual destination MEP.

2.2.3. OAM Maintenance Points

   A Maintenance Point (MP) is a functional entity that is defined at a
   node in the network, and either initiates or reacts to OAM messages.
   A Maintenance End Point (MEP) is one of the end points of an ME, and
   can initiate OAM messages and respond to them. A Maintenance
   Intermediate Point (MIP) is an intermediate point between two MEPs,
   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 value of the TTL field in the OAM packet. The
   term Maintenance Point is a general term for MEPs and MIPs.

   The 802.1ag defines a finer distinction between Up MPs and Down MPs.
   An MP is a bridge interface, that is monitored by an OAM protocol
   either in the direction facing the network, or in the direction
   facing the bridge. A Down MP is an MP that receives OAM packets from,
   and transmits them to the direction of the network. An Up MP receives
   OAM packets from, and transmits them to the direction of the bridging

   MPLS-TP ([TP OAM FW]) ([TP-OAM-FW]) uses a similar distinction on the placement of
   the MP - either at the ingress, egress, or forwarding function of the
   node (Down / Up MPs).  This placement is important for localization
   of a connection failure.

2.2.4. Proactive and On-demand activation

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

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

   o On-demand activation - indicates that the tool is activated
      "manually" to detect a specific anomaly.  In this activation a
      small number of OAM messages are sent by a MEP and the reply
      message is received.

2.2.5. 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], [MPLS-TP-OAM], and is
   used similarly in this document.

   Continuity checks are used to verify the liveness of a connection or
   a path between two MPs, and are typically sent proactively, though
   they can be invoked on-demand as well.

   A connectivity verification function allows an MP to check whether it
   is connected to a peer MP or not. This function also allows the MP to
   verify that messages from the peer MP 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. This allows detection of unexpected topology changes. 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 and continuity checks are considered
   complementary mechanisms, and are often used in conjunction with each

2.2.6. Failures

   The terms Failure, Fault, and Defect are used interchangeably in the
   standards, referring to a malfunction that can be detected by a
   connectivity or a continuity check. In some standards, such as [IEEE [IEEE-
   802.1ag], there is no distinction between these terms, while in other
   standards each of these terms refers to a different type of

   The terminology used in IETF MPLS-TP OAM takes after the ITU-T, which
   distinguishes between these terms in [ITU-T G.806]; [ITU-T-G.806]; The term Fault
   refers to an inability to perform a required action, e.g., an
   unsuccessful attempt to deliver a packet. The term Defect refers to
   an interruption in the normal operation, such as a consecutive period
   of time where no packets are delivered successfully. 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 Tools

3.1. ICMP Ping

   ICMP provides a connectivity verification 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.

3.2. Traceroute

   Traceroute ([TCPIP Tools]) ([TCPIP-Tools]) is an application that allows users to
   discover the path between an IP source and an IP destination.
   Traceroute sends a sequence of UDP packets to UDP port 33434 at the
   destination. By default, Traceroute begins by sending three packets,
   each with an IP Time-To-Live (TTL) value of one to the destination.

   These packets expire as soon as they reach the first router in the
   path. That router responds by sending three ICMP Time Exceeded
   Messages 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.

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

3.3. Bidirectional Forwarding Detection (BFD)

3.3.1. Overview

   While multiple OAM mechanisms 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 mechanism
   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]), ([BFD-IP], [BFD-Multi]), for MPLS LSPs [BFD LSP], [BFD-LSP], and for PWE3
   [BFD VCCV].
   [BFD-VCCV]. The usage of BFD in MPLS-TP is defined in [MPLS-TP CC [MPLS-TP-CC-

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

3.3.2. 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 packet have been received during a predetermined
      period of time, a failure is detected.

   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
      verify the liveness of the session. BFD control packets are sent
      independently in each direction.

   Each of the end-points of the monitored path maintains its own
   session identification, called a Discriminator, both of which are
   included in the BFD Control Packets that are exchanged between the
   end-points.  At the time of session establishment, the Discriminators
   are exchanged between the two-end points.  In addition, the
   transmission (and reception) rate is negotiated between the two end-
   points, 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. no failures are
   detected, the BFD session is in the Up state.  If no BFD Control
   packets are received during a fixed period of time, called the
   Detection Time, the session is declared to be Down. The detection
   time is a function of the negotiated transmission time, 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.

3.3.3. 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
   ([BFD-IP]), but is not used in BFD for MPLS LSPs, PWs, or in BFD for MPLS-

3.4. LSP Ping

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

   LSP Ping is based on ICMP Ping and just like its predecessor 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

   LSP Ping extends the basic ICMP Ping operation (of data-plane
   connectivity verification) with functionality to verify data-plane
   vs. control-plane consistency for a Forwarding Equivalence Class
   (FEC) and also Maximum Transmission Unit (MTU) problems. The
   traceroute functionality may be used to isolate and localize the 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.

   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 easily extensible to
   include additional information needed to support new functionality,
   by use of Type-Length-Value (TLV) constructs. The usage of TLVs is
   typically not easy to perform in hardware, and is thus typically
   handled by the control plane.

   LSP Ping supports both asynchronous, as well as, on-demand

3.5. PWE3 Virtual Circuit Connectivity Verification (VCCV)

   VCCV, as defined in [VCCV], provides a means for end-to-end fault
   detection and diagnostics tools to be extended for PWs (regardless of
   the underlying tunneling technology). The VCCV switching function
   provides a control channel associated with each PW (based on the PW
   Associated Channel Header (ACH) which is defined in [PW ACH]), [PW-ACH]), and
   allows transmitting the OAM packets in-band with PW data (using CC
   Type 1: In-band VCCV).

   VCCV currently supports the following OAM mechanisms: ICMP Ping, LSP
   Ping, and BFD. ICMP and LSP Ping are IP encapsulated before being
   sent over the PW ACH. BFD for 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 pseudo wire (FEC),
   eliminating the need to exchange Discriminator values.

   VCCV consists of two components: (1) signaled component to
   communicate VCCV capabilities as part of VC label, and (2) 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 negotiation 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.

3.6. IP Performance Metrics (IPPM)

3.6.1. Overview

   The IPPM working group in the IETF defines common criteria and
   metrics for measuring performance of IP traffic ([IPPM FW]). ([IPPM-FW]). Some of
   the key RFCs published by this working group have defined metrics for
   measuring connectivity [IPPM Con], [IPPM-Con], delay ([IPPM 1DM], [IPPM 2DM]), ([IPPM-1DM], [IPPM-2DM]),
   and packet loss [IPPM 1LM]. [IPPM-1LM].

   Alternative protocols for performance measurement are defined, for
   example, in MPLS-TP OAM ([MPLS LM DM], [TP LM DM]), ([MPLS-LM-DM], [TP-LM-DM]), and in Ethernet
   OAM [ITU-T Y.1731]. [ITU-T-Y.1731].

   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] define a method and
   protocol for measuring delay and packet loss 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
   end points.

   TWAMP [TWAMP] is a similar protocol that enables measurement of two-
   way (round trip) characteristics.  TWAMP does not require accurate
   time of day, and, furthermore, allows the use of a simple session
   reflector, making it an attractive alternative to OWAMP.

   OWAMP and TWAMP use two separate protocols: a Control plane protocol,
   and a Test plane protocol.

3.6.2. 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 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 pseudo-random). Statistics
   recorded conform to the relevant IPPM RFCs.

   OWAMP and TWAMP test traffic is designed with security in mind.  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.

3.6.3. 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 playing the roles of Server and

   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 modes.  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 and the Server acknowledges.  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.  Once finished, the Fetch-Client sends a
   fetch request to the server, which responds with an acknowledgement
   and immediately thereafter the result data.

3.6.4. 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 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 insertion of


3.7.1. Overview

   The MPLS working group is currently working on defining 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], [MPLS-TP-OAM], and
   include both general requirements for the behavior of the OAM
   mechanisms 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], [TP-OAM-FW], which describes the general architecture of the OAM
   system as well as giving overviews of the functionality of the OAM

   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 and 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 user-plane ones. 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.

3.7.2. 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 and 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), that uses a format similar to
      the PW Control Word, is a 4-byte header that is prepended to OAM

   o A Generic Associated 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.

3.7.3. 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
   mechanisms and their ability to fulfill the required functionality.
   The conclusions of this analysis are documented in [OAM Analysis]. [OAM-Analysis].
   The MPLS working group currently plans to use a mixture of OAM
   mechanisms that are based on various existing standards, and adapt
   them to the requirements of [MPLS-TP OAM]. [MPLS-TP-OAM]. Some of the main building
   blocks of this solution are based on:

   o Bidirectional Forwarding Detection ([BFD], [BFD LSP]) [BFD-LSP]) for
      proactive continuity check and connectivity verification.

   o LSP Ping as defined in [LSP Ping] [LSP-Ping] for on-demand connectivity

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

   o Performance measurement protocols that are based on the
      functionality that is described in [ITU-T Y.1731]. [ITU-T-Y.1731].

   The following sub-sections describe the OAM tools defined for MPLS-TP
   as described in [TP OAM FW]. [TP-OAM-FW]. Continuity Check and Connectivity Verification

   Continuity Check and Connectivity Verification are presented in
   Section 2.2.5 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 [MPLS-TP CC CV] [MPLS-TP-CC-CV] while the on-demand tool is defined in
   [OnDemand CV].Proactively [MPLS-TP OAM]
   [OnDemand-CV].Proactively [MPLS-TP-OAM] states that the function
   should allow the MEPs to monitor the liveness and connectivity of a
   transport path. In on-demand mode, this function should support
   monitoring between the MEPs and, in addition, between a MEP and MIP.

   [TP OAM FW]

   [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

   The proactive tool [MPLS-TP CC CV] [MPLS-TP-CC-CV] is based on extensions to BFD (see
   Section 3.3) with the additional limitation that the transmission and
   receiving rates are based on configuration by the operator.  The on-
   demand tool [OnDemand CV] [OnDemand-CV] is an adaptation of LSP Ping (See Section
   3.4) for the required behavior of MPLS-TP. Route Tracing


   [MPLS-TP-OAM] defines that there is a need for functionality that
   would allow a path end-point to identify the intermediate and end-
   points of the path. This function would be used in on-demand mode.
   Normally, this path will be used for bidirectional PW, LSP, 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 3.4) functionality and is described in [OnDemand CV]. [OnDemand-CV]. Lock Instruct

   The Lock Instruct function is used to notify a transport path end-
   point 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, Diagnostic
   testing, to minimize the side-effect on user data traffic. Lock Reporting

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

   Alarm Reporting is a function used by an intermediate point of a
   path, that becomes aware of a fault on the path, to report to the
   end-points of the path. [TP OAM FW] [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]. [TP-OAM-FW]. Remote Defect Indication

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

   Client Failure Indication (CFI) is defined in [MPLS-TP OAM] [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. Packet Loss Measurement

   Packet Loss Measurement is a function used to verify the quality of
   the service. This function indicates the ratio of packets that are
   not delivered out of all packets that are transmitted by the path

   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.

   o Sending delimiting messages for 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. Packet Delay Measurement

   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
   end-points of a path (PW, LSP, or Section). Where:

   o One-way packet delay 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

   o Two-way packet delay 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 loop-backed packet by the
      same source node, when the loopback is performed at the packet's
      destination node.

   Similarly to the packet loss measurement this could be performed in
   either of the two ways outlined above.

3.8. Summary of OAM Functions

   Table 3 summarizes the OAM functions that are supported in each of
   the standards that were analyzed in this section.

   | Standard  |Continu|Connecti|Path    |Defect     |Perform|Other   |
   |           |ity    |vity    |Discover|Indications|ance   |Function|
   |           |Check  |Verifica|y       |           |Monitor|s       |
   |           |       |tion    |        |           |ing    |        |
   |ICMP Ping  |       |Echo    |        |           |       |        |
   + --------- + ----- + ------ + ------ + --------- + ----- + ------ +
   |Traceroute |       |        |Tracerou|           |       |        |
   |           |       |        |te      |           |       |        |
   + --------- + ----- + ------ + ------ + --------- + ----- + ------ +
   |BFD        |BFD    |BFD     |        |           |       |        |
   |           |Control|Echo    |        |           |       |        |
   + --------- + ----- + ------ + ------ + --------- + ----- + ------ +
   |LSP Ping   |       |"Ping"  |"Tracero|           |       |        |
   |           |       |mode    |ute"    |           |       |        |
   |           |       |        |mode    |           |       |        |
   + --------- + ----- + ------ + ------ + --------- + ----- + ------ +
   |IPPM       |       |        |        |           |-Delay |        |
   |           |       |        |        |           | measur|        |
   |           |       |        |        |           | ement |        |
   |           |       |        |        |           |-Packet|        |
   |           |       |        |        |           | loss  |        |
   |           |       |        |        |           | measur|        |
   |           |       |        |        |           | ement |        |
   + --------- + ----- + ------ + ------ + --------- + ----- + ------ +
   |MPLS-TP    |CC     |CV/pro- |Route   |-Alarm     |-LM    |-Diagnos|
   |OAM        |       |active  |Tracing | Reporting |-DM    | tic Tes|
   |           |       |or on-  |        |-Client    |       | t      |
   |           |       |demand  |        | Failure   |       |-Lock   |
   |           |       |        |        | Indication|       |        |
   |           |       |        |        |-Remote    |       |        |
   |           |       |        |        | Defect    |       |        |
   |           |       |        |        | Indication|       |        |
                     Table 3 Summary of OAM Functions

4. Security Considerations

   This memo presents an overview of existing OAM mechanisms, and
   proposes no new OAM mechanisms. Therefore, this document introduces
   no security considerations. However, the OAM mechanism reviewed in
   this document can and do present security issues. The reader is
   encouraged to review the Security Considerations section of each
   document reference by this memo.

5. IANA Considerations

   There are no new IANA considerations implied by this document.

6. Acknowledgments

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

7. References

7.1. Normative References

   [LSP Ping]

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


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


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

   [OAM Label]

   [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.


   [MPLS-TP-OAM] Vigoureux, M., Ward, D., Betts, M., "Requirements for
                 OAM in MPLS Transport Networks", RFC 5860, May 2010.

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

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

   [PW ACH]

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

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

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

   [TCPIP Tools]

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

   [IPPM FW]

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

   [IPPM Con]

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

   [IPPM 1DM]

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

   [IPPM 1LM]

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

   [IPPM 2DM]

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

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

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

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

   [BFD IP]

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

   [BFD Gen]

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

   [BFD Multi]

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

   [BFD LSP]

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


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

   [TP OAM FW]

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


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

   [OnDemand CV]

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


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

   [TP LM DM]

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

   [MPLS-TP Fault]

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

   [TP Lock Loop]

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

7.2. Informative References

   [OAM Def]

   [OAM-Def]     Andersson, L., Van Helvoort, H., Bonica, R., Romascanu,
                 D., Mansfield, S., "Guidelines for the use of the OAM
                 acronym in the IETF ", RFC 6291, June 2011.

   [OAM Analysis]Sprecher,

   [OAM-Analysis]Sprecher, N., Fang, L., "An Overview of the OAM Tool
                 Set for  MPLS based Transport Networks", work-in-
                 progress, draft-ietf-mpls-tp-oam-analysis, March RFC 6669,
                 July 2012.

   [MPLS-TP Term]Van

   [MPLS-TP-Term]Van Helvoort, H., Andersson, L., Sprecher, N., "A
                 Thesaurus for the Terminology used in Multiprotocol
                 Label Switching Transport Profile (MPLS-TP)
                 drafts/RFCs and ITU-T's Transport Network
                 Recommendations", work-in-progress, draft-ietf-mpls-
                 tp-rosetta-stone, January 2012.

   [IEEE 802.1ag]"Connectivity

   [IEEE-802.1ag]"Connectivity Fault Management", December 2007.

   [ITU-T Y.1731]"OAM

   [ITU-T-Y.1731]"OAM Functions and Mechanisms for Ethernet-based
                 Networks", February 2008.

   [ITU-T Y.1711]"Operation

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

   [IEEE 802.3ah]"Media

   [IEEE-802.3ah]"Media Access Control Parameters, Physical Layers, and
                 Management Parameters for Subscriber Access Networks",
                 clause 57, September 2004.

   [ITU-T G.806]

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

Authors' Addresses

   Tal Mizrahi
   6 Hamada St.
   Yokneam, 20692

   Email: talmi@marvell.com

   Nurit Sprecher
   Nokia Siemens Networks
   3 Hanagar St. Neve Ne'eman B
   Hod Hasharon,   45241

   Email: nurit.sprecher@nsn.com

   Elisa Bellagamba
   6 Farogatan St.
   Stockholm,   164 40

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

   Yaacov Weingarten
   Nokia Siemens Networks
   3 Hanagar
   34 Hagefen St. Neve Ne'eman B
   Hod Hasharon,   45241
   Karnei Shomron,   4485500

   Phone: +972-9-775 1827

   Email: yaacov.weingarten@nsn.com wyaacov@gmail.com