Operations and Management Area Working Group                 T. Mizrahi
Internet Draft                                                 Marvell
Intended status: Informational                            N. Sprecher
Expires: September November 2011                          Nokia Siemens Networks
                                                         E. Bellagamba
                                                         Y. Weingarten
                                                Nokia Siemens Networks
                                                        March 29,
                                                          May 16, 2011

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

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   Operations, Administration, and Maintenance (OAM) is a general term
   that refers to a toolset that can be used for fault detection and
   localization, 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, as well as
   a comparison to other OAM mechanisms that have been defined by the
   IEEE and ITU-T.

Table of Contents

   1. Introduction................................................4
   2. Conventions used in this document............................8
   3. Basic Terminology...........................................8
      3.1. Abbreviations..........................................8
      3.2. Terminology used in OAM Standards.......................9
         3.2.1. General Terms......................................9
         3.2.2. OAM Maintenance Entities and Communication Links...10
         3.2.3. OAM Maintenance Points............................10
         3.2.4. Connectivity Verification and Continuity Checks....11
         3.2.5. Link Failures.....................................11
         3.2.6. Summary of OAM Terms used in the Standards.........12
   4. OAM Functions..............................................13
      4.1. ICMP Ping.............................................13
      4.2. Bidirectional Forwarding Detection (BFD)...............14
         4.2.1. Overview.........................................14
         4.2.2. BFD Control.......................................14
         4.2.3. BFD Echo.........................................15
      4.3. LSP Ping..............................................15
      4.4. PWE3 Virtual Circuit Connectivity Verification (VCCV)...16
      4.5. IP Performance Metrics (IPPM)..........................16
         4.5.1. Overview.........................................16
         4.5.2. Control and Test Protocols........................17
         4.5.3. OWAMP............................................17
         4.5.4. TWAMP............................................18
      4.6. ITU-T Y.1711..........................................18
         4.6.1. Overview.........................................18
         4.6.2. Connectivity Verification (CV)....................19
         4.6.3. Fast Failure Detection (FFD)......................19
         4.6.4. Forward Defect Indication (FDI)...................19
         4.6.5. Backward Defect Indication (BDI)..................20
      4.7. ITU-T Y.1731..........................................20
         4.7.1. Overview.........................................20
         4.7.2. ETH-CC...........................................20
         4.7.3. ETH-LB...........................................21
         4.7.4. ETH-TST..........................................21
         4.7.5. ETH-LT...........................................21
         4.7.6. ETH-AIS..........................................21
         4.7.7. ETH-LCK..........................................21
         4.7.8. ETH-RDI..........................................22
         4.7.9. ETH-APS..........................................22
         4.7.10. ETH-LM..........................................22
         4.7.11. ETH-DM..........................................22
      4.8. IEEE 802.1ag..........................................23
         4.8.1. Overview.........................................23
         4.8.2. Continuity Check..................................23
         4.8.3. Loopback.........................................23
         4.8.4. Linktrace........................................24
      4.9. IEEE 802.3ah..........................................24
         4.9.1. Overview.........................................24
         4.9.2. Remote Failure Indication.........................24
         4.9.3. Remote Loopback...................................24
         4.9.4. Link Monitoring...................................24
      4.10. MPLS-TP OAM..........................................24
         4.10.1. Overview........................................24
         4.10.2. Generic Associated Channel.......................25
         4.10.3. MPLS-TP OAM Toolset..............................25
   Continuity Check and Connectivity Verification26
   Diagnostic Tests............................26
   Route Tracing...............................26
   Lock Instruct...............................27
   Lock Reporting..............................27
   Alarm Reporting.............................27
   Remote Defect Indication....................27
   Client Failure Indication...................27
   Packet Loss Measurement.....................27
   Packet Delay Measurement...................28
      4.11. Summary of OAM Functions..............................28
      4.12. Summary of Continuity Check Mechanisms................30
   5. Security Considerations.....................................31
   6. IANA Considerations........................................31
   7. Acknowledgments............................................31
   8. References.................................................31
      8.1. Normative References...................................31
      8.2. Informative References.................................33

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 Soup].
   In the context of this document OAM refers to Operations,
   Administration, and Maintenance, i.e., this document refers to OAM in
   the context of monitoring communication entities, e.g., nodes, paths,
   physical links, or logical links. Other aspects associated with the
   OAM acronym, such as management, are outside the scope of this

   OAM was originally used in the world of telephony, and has been
   adopted in packet based networks. OAM mechanisms are used in various
   layers in the protocol stack, and are applied to a variety of
   different protocols.

   The IETF has defined OAM for several protocols, and is currently
   working on defining several new OAM protocols. A summary of these
   protocols, old and new, is listed below:

   o MPLS LSP Ping, as defined in [LSP Ping] is an OAM mechanism for
      point to point MPLS LSPs. The IETF is currently working on an
      extension to the LSP Ping for point to multipoint MPLS - [P2MP

   o Virtual Circuit Connectivity Check (VCCV) for Pseudowires, as
      defined in [VCCV].

   o 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, and is not traditionally associated with OAM,
      but it is presented in this document for the sake of completeness,
      since both LSP Ping and VCCV are to some extent based on ICMP

   o 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

   o The OAM requirements for MPLS Transport Profile (MPLS-TP) are
      defined in [MPLS-TP OAM], and the toolset is described in [MPLS-TP
      OAM FW]. The OAM toolset for MPLS-TP is currently being defined in
      the MPLS working group.

   o 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.
      Alternative protocols for performance measurement are defined, for
      example, in MPLS-TP OAM [MPLS-TP OAM], and in Ethernet OAM [ITU-T

   In addition to the OAM mechanisms defined by the IETF, the IEEE and
   ITU-T have also defined various OAM mechanisms. 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] and [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 also discussed in this document:

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

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

   This document summarizes the OAM mechanisms defined in the standards
   above. The focus is on OAM mechanisms defined by the IETF. These
   mechanisms will be compared with the relevant OAM mechanisms defined
   by the ITU-T and IEEE, where applicable. We first present a
   comparison of the terminology used in various OAM standards, and then
   summarize the OAM functions that each OAM standard provides.

   Table 1 summarizes the OAM standards discussed in this document.

   |           | Title                                |Standard/Draft |
   |ICMPv4 Ping| Internet Control Message Protocol    | RFC 792       |
   |           |                                      |               |
   |ICMPv6 Ping| Internet Control Message Protocol    | RFC 4443      |
   |           | (ICMPv6) for the Internet Protocol   |               |
   |           | Version 6 (IPv6) Specification       |               |
   |BFD        | Bidirectional Forwarding Detection   | RFC 5880      |
   |           +--------------------------------------+---------------+
   |           | Bidirectional Forwarding Detection   | RFC 5881      |
   |           | (BFD) for IPv4 and IPv6 (Single Hop) |               |
   |           +--------------------------------------+---------------+
   |           | Generic Application of Bidirectional | RFC 5882      |
   |           | Forwarding Detection                 |               |
   |           +--------------------------------------+---------------+
   |           | Bidirectional Forwarding Detection   | RFC 5883      |
   |           | (BFD) for Multihop Paths             |               |
   |           +--------------------------------------+---------------+
   |           | Bidirectional Forwarding Detection   | RFC 5884      |
   |           | for MPLS Label Switched Paths (LSPs) |               |
   |           +--------------------------------------+---------------+
   |           | Bidirectional Forwarding Detection   | RFC 5885      |
   |           | for the Pseudowire Virtual Circuit   |               |
   |           | Connectivity Verification (VCCV)     |               |
   |IETF MPLS  | Operations and Management (OAM)      | RFC 4377      |
   |OAM        | Requirements for Multi-Protocol Label|               |
   |(LSP Ping) | Switched (MPLS) Networks             |               |
   |           +--------------------------------------+---------------+
   |           | A Framework for Multi-Protocol       | RFC 4378      |
   |           | Label Switching (MPLS) Operations    |               |
   |           | and Management (OAM)                 |               |
   |           +--------------------------------------+---------------+
   |           | Detecting Multi-Protocol Label       | RFC 4379      |
   |           | Switched (MPLS) Data Plane Failures  |               |
   |           +--------------------------------------+---------------+
   |           | Operations and Management (OAM)      | RFC 4687      |
   |           | Requirements for Point-to-Multipoint |               |
   |           | MPLS Networks                        |               |
   |MPLS-TP    | Requirements for OAM in MPLS-TP      | RFC 5860      |
   |OAM        +--------------------------------------+---------------+
   |           | MPLS Generic Associated Channel      | RFC 5586      |
   |           +--------------------------------------+---------------+
   |           | MPLS-TP OAM Framework                |[MPLS-TP OAM FW|
   |           |                                      |] - work in    |
   |           |                                      |progress       |
   |           +--------------------------------------+---------------+
   |           | MPLS-TP OAM Analysis                 |[OAM Analysis] |
   |           |                                      | - work in     |
   |           |                                      |progress       |
   |PW VCCV    | Pseudowire Virtual Circuit           | RFC 5085      |
   |           | Connectivity Verification (VCCV):    |               |
   |           | A Control Channel for Pseudowires    |               |
   |IPPM       | Framework for IP Performance Metrics | RFC 2330      |
   |           +--------------------------------------+---------------+
   |           | IPPM Metrics for Measuring           | RFC 2678      |
   |           | Connectivity                         |               |
   |           +--------------------------------------+---------------+
   |           | A One-way Delay Metric for IPPM      | RFC 2679      |
   |           +--------------------------------------+---------------+
   |           | A One-way Packet Loss Metric for IPPM| RFC 2680      |
   |           +--------------------------------------+---------------+
   |           | A Round-trip Delay Metric for IPPM   | RFC 2681      |
   |           +--------------------------------------+---------------+
   |           | A One-way Active Measurement Protocol| RFC 4656      |
   |           | (OWAMP)                              |               |
   |           +--------------------------------------+---------------+
   |           | A Two-Way Active Measurement Protocol| RFC 5357      |
   |           | (TWAMP)                              |               |
   |ITU-T      | Operation & Maintenance mechanism    |[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          |               |
   |ITU-T      | OAM Functions and Mechanisms for     |[ITU-T Y.1731] |
   |Ethernet   | Ethernet-based Networks              |               |
   |OAM        |                                      |               |
   |IEEE       | Connectivity Fault Management        |[IEEE 802.1ag] |
   |CFM        |                                      |               |
   |IEEE       | Media Access Control Parameters,     |[IEEE 802.3ah] |
   |802.3      | Physical Layers, and Management      |               |
   |link level | Parameters for Subscriber Access     |               |
   |OAM        | Networks                             |               |
                     Table 1 Summary of OAM Standards

2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [KEYWORDS].

3. Basic Terminology

3.1. Abbreviations

   AIS    Alarm Indication Signal

   APS    Automatic Protection Switching

   BDI    Backward Defect Indication

   BFD    Bidirectional Forwarding Detection

   CC     Continuity Check

   CCM    Continuity Check Message

   CV     Connectivity Verification

   DM     Delay Measurement

   DTE    Data Terminal Equipment

   FDI    Forward Defect Indication

   FFD    Fast Failure Detection

   ICMP   Internet Control Message Protocol

   L2TP   Layer Two Tunneling Protocol

   LCCE   L2TP Control Connection Endpoint
   LM     Loss Measurement

   LSP    Label Switching Path

   LSR    Label Switching Router

   MA     Maintenance Association

   ME     Maintenance Entity

   MEG    Maintenance Entity Group

   MEP    Maintenance End Point

   MHF    MIP Half Function

   MIP    Maintenance Intermediate Point

   MP     Maintenance Point

   MPLS   Multiprotocol Label Switching

   MPLS-TP MPLS Transport Profile

   OAM    Operations, Administration, and Maintenance

   PE     Provider Edge

   PW     Pseudowire

   PWE3   Pseudowire Emulation Edge-to-Edge

   RDI    Remote Defect Indication

   TTL    Time To Live

   TTSI   Trail Termination Source Identifier

   VCCV   Virtual Circuit Connectivity Verification

3.2. Terminology used in OAM Standards

3.2.1. 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 the relevant terms. A thesaurus of terminology for MPLS-TP
   terms is presented in [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. The comparison focuses on three basic terms, and is
   summarized in section 3                             ..2.6. 3.2.6.

3.2.2. OAM Maintenance Entities and Communication Links

   A Maintenance Entity (ME) is a point-to-point relationship between
   two Maintenance Points (MP). The connectivity between these
   Maintenance Points is managed and monitored by the OAM protocol.

   A pair of MPs engaged in an ME are connected by a communication Link.
   The term "Link" in this context is a generic term that may refer to
   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 Link is used throughout this document to refer
   to the connection between the MPs that is monitored by an OAM

   The term Maintenance Entity (ME) is defined in ITU-T standards (e.g.
   [ITU-T Y.1731]). Various terms are used to refer to an ME. For
   example, in MPLS LSP Ping ([LSP Ping]) terminology, an ME is simply
   referred to as an LSP. 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.

   MPLS-TP has defined the terms ME and Maintenance Entity Group (MEG)
   in [MPLS-TP OAM FW], similar to the terms defined by ITU-T.

3.2.3. 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 initiate OAM frames, but is able to respond to OAM
   frames that are destined to it, and to forward others.

   The terms MEP and MIP are defined in ITU-T standards (e.g. [ITU-T
   Y.1731]). The term Maintenance Point is a general term for MEPs and
   MIPs, and is used in [IEEE 802.1ag].

   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 has defined the terms MEP and MIP and their functional
   characteristics in [MPLS-TP OAM FW], similar to the terms defined by

3.2.4. 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 checks are used to verify the liveness of a link, and are
   typically sent proactively, though they can be invoked on-demand as

   A connectivity verification function allows an MP to check whether it
   is connected to a peer MP or not. 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

3.2.5. Link Failures

   The terms Failure, Fault, and Defect are intermittently used in the
   standards, referring to a malfunction that can be detected by a
   connectivity or a continuity check. In some standards, such as [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 ITU-T distinguishes between these terms in [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.

3.2.6. Summary of OAM Terms used in the Standards

   Table 2 provides a comparison of the terminology used in different
   OAM standards.

   |           |Maintenance  |Maintenance|Link Failure Terminology    |
   |           |Point        |Entity     |                            |
   |           |Terminology  |Terminology|                            |
   |ICMPv4 Ping|-Host        |           |                            |
   |           |-Gateway     |           |                            |
   + --------- + ----------- + --------- + -------------------------- +
   |ICMPv6 Ping| Node        |           |                            |
   + --------- + ----------- + --------- + -------------------------- +
   |BFD        | System      | Session   |-Failure                    |
   |           |             |           |-Session is declared down   |
   + --------- + ----------- + --------- + -------------------------- +
   |LSP Ping   | LSR         | LSP       |-Failure                    |
   |           |             |           |-Fault = typically a local  |
   |           |             |           | isolated failure           |
   + --------- + ----------- + --------- + -------------------------- +
   |PW VCCV    |-PE          | PW        |-Failure                    |
   |           |-LCCE        |           |-Fault                      |
   + --------- + ----------- + --------- + -------------------------- +
   |IPPM       |-Host        |-Path      | Connectivity is indicated  |
   |           |-End system  |-Measuremen| by a Boolean value. Thus,  |
   |           |             | t session | a failure is referred to as|
   |           |             |           | a path with a measurement  |
   |           |             |           | value "false".             |
   + --------- + ----------- + --------- + -------------------------- +
   |ITU-T      | LSR         | LSP       |-Fault, Defect, Failure: as |
   |Y.1711     |             |           | defined in [ITU-T G.806]   |
   + --------- + ----------- + --------- + -------------------------- +
   |ITU-T      |-MEP         | ME        |-Fault, Defect, Failure: as |
   |Y.1731     |-MIP         |           | defined in [ITU-T G.806]   |
   |           |             |           |                            |
   + --------- + ----------- + --------- + -------------------------- +
   |MPLS-TP    |-End Point,  |-LSP       |-Fault, Defect, Failure: as |
   |OAM        | MEP         |-PW        | defined in [ITU-T G.806]   |
   |           |-Intermediate|-Section   |                            |
   |           | Point, MIP  |           |                            |
   + --------- + ----------- + --------- + -------------------------- +
   |IEEE       |-MP (Down,Up)| ME        |-Failure                    |
   |802.1ag    |  -MEP       |           |-Fault                      |
   |           |  -MIP       |           |-Defect                     |
   |           |  -MHF       |           |                            |
   + --------- + ----------- + --------- + -------------------------- +
   |IEEE       | DTE         | Link      |-Failure                    |
   |802.3ah    |             |           |-Fault                      |
                       Table 2 Summary of OAM Terms

4. OAM Functions

4.1. ICMP Ping

   ICMP provides a connectivity verification function for the Internet
   Protocol. The originator transmits an 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.

   ICMP is also used in Traceroute for path discovery. Traceroute allows
   a host to detect the path to a destination host, as follows:

   o The originator host repeatedly transmits an ICMP message to the
      destination host. At first, the value of the Time To Live (TTL)
      field in the ICMP message is 1, and is then repeatedly incremented
      by 1.

   o In turn, each router on the traversing path returns an ICMP
      message to the originator with an ICMP Time Exceeded error

   o Finally, the destination router replies with an ICMP Echo Reply.

4.2. Bidirectional Forwarding Detection (BFD)

4.2.1. 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]), for MPLS LSPs [BFD LSP], and for PWE3
   [BFD VCCV]. BFD for MPLS-TP is currently evolving in the MPLS working
   group (e.g. [MPLS-TP Ping BFD]).

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

4.2.2. 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: 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 link. BFD control packets are sent independently in
      each direction of the link.

   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.

4.2.3. BFD Echo

   The echo function is used for connectivity verification. 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.

4.3. LSP Ping

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

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

   LSP Ping extends the basic ICMP Ping operation (of data-plane
   connectivity and continuity check) 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 does support 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
   activation. In addition, extensions for LSP Ping are being defined
   for point-to-multipoint LSPs in [P2MP LSP Ping] and for MPLS Tunnels
   in [MPLS LSP Ping].

4.4. PWE3 Virtual Circuit Connectivity Verification (VCCV)

   VCCV, as defined in [VCCV], provides end-to-end fault detection
   and diagnostics 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]), and allows sending 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.

4.5. IP Performance Metrics (IPPM)

4.5.1. Overview

   The IPPM working group [IPPM FW] in the IETF defines common criteria
   and metrics for measuring performance of IP traffic. Some of the key
   RFCs published by this working group have defined metrics for
   measuring connectivity [rfc2678], [IPPM Con], delay [RFC2679, RFC 2681], ([IPPM 1DM], [IPPM 2DM]),
   and packet loss [RFC2681]. [IPPM 1LM].

   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.

4.5.2. 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.

4.5.3. 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.

4.5.4. 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

4.6. ITU-T Y.1711

4.6.1. Overview

   As mentioned above (4.3.), the IETF defined LSP Ping as an OAM
   mechanism for MPLS. The ITU-T has also defined an OAM protocol for
   MPLS, defined in recommendation [ITU-T Y.1711]. This recommendation
   defines mechanisms for connectivity verification and fast failure
   detection, as well as mechanism for reporting defects that have been
   identified in an LSP.

   MPLS OAM packets per Y.1711 are detected by a reserved MPLS label
   value. The reserved value is 14, and is defined in [OAM Label] as the
   'OAM Alert Label'.

4.6.2. Connectivity Verification (CV)

   The CV function is used to detect connectivity defects in an LSP. CV
   frames are sent proactively at a rate of 1 per second. Each frame
   contains the Trail-Termination Source Identifier (TTSI), indicating
   the identity of the transmitting LSR.

   The CV function can detect any of the following defect conditions.

   o Loss of Connectivity Verification (LOCV): A loss of connectivity
      is detected when no CV OAM packets are received in a period of 3
      consecutive transmission periods.
      It should be noted that the LOCV defect is in fact loss of
      continuity when using the terminology defined in 3                                                          ..2.4. 3.2.4.

   o TTSI Mismatch: A TTSI mismatch is detected when a CV frame with an
      unexpected TTSI is received.

   o TTSI Mismerge: A TTSI mismerge is detected when the CV frames
      received in a given LSP contain some frame with an expected TTSI,
      and some frames with an unexpected TTSI.

   o Excess: An excess is detected when at least 5 CV frames are
      received during a period of 3 consecutive transmission periods.

4.6.3. Fast Failure Detection (FFD)

   The FFD function is a proactive function, used for fast detection of
   connectivity defects. While CV is typically sufficient for path
   failure detection and reporting, protection switching mechanisms
   typically require faster detection. FFD is very similar to CV in
   terms of the packet format, and the possible defect conditions, but
   FFD allows a configurable transmission frequency. The default
   transmission rate of FFD frames is 20 per second, i.e., every 50 ms,
   allowing fast detection for protection switching applications.

4.6.4. Forward Defect Indication (FDI)

   The FDI function is used by an LSR to report a defect to affected
   client layers, allowing them to suppress alarms about this defect.
   In MPLS-TP OAM this function is referred to as Client Failure

   FDI packets are sent at a rate of 1 per second.

4.6.5. Backward Defect Indication (BDI)

   The BDI function is used by an LSR to inform a peer LSR about a
   defect condition on an LSP for which they are the end points of.
   In MPLS-TP OAM this function is referred to as Remote Defect

   BDI packets are sent at the same transmission rate as FDI.

4.7. ITU-T Y.1731

4.7.1. Overview

   The [ITU-T Y.1731] defines a protocol for Ethernet OAM. It is
   presented in this document as a reference point. Y.1731 defines
   various OAM functions, including continuity and connectivity
   verification, and functions for performance monitoring.

4.7.2. ETH-CC

   The Ethernet Continuity Check function is a proactive function that
   allows a MEP to detect loss of continuity with any of the other MEPs
   in the MEG. This function also allows detection of other defect
   conditions, such as unintended connectivity between two MEGs (also
   known as a mismerge). The ETH-CC function is used for one of three
   possible applications: fault management, performance monitoring (see
   4.6.10.), and protection switching.

   Continuity Check Messages (CCM) are transmitted periodically at a
   constant rate. There are 7 possible transmission periods, from 3.33
   ms to 10 min. When the ETH-CC function detects a defect, it reports
   one of the following defect conditions:

   o Loss of continuity (LOC): Occurs when at least when no CCM
      messages have been received from a peer MEP during a period of 3.5
      times the configured transmission period.

   o Unexpected MEG level: The MEG level is a 3-bit number that defines
      the level of hierarchy of the MEG. This defect condition occurs
      when a CCM is received from a peer MEP with a MEG level that is
      lower than the expected MEG level.

   o Mismerge: Occurs when a CCM is received from a peer MEP with an
      unexpected MEG ID.

   o Unexpected MEP: Occurs when a CCM is received from a peer MEP with
      an unexpected transmitting MEP ID.

   o Unexpected period: Occurs when the transmission period field in
      the CCM does not match the expected transmission period value.

4.7.3. ETH-LB

   The Ethernet loopback function verifies connectivity with a peer MEP
   or MIP. The loopback function is performed on-demand, by sending a
   loopback message (LBM) to the peer MEP or MIP. The peer node then
   responds with a loopback reply (LBR).

   More precisely, it is used for one of two purposes:

   o Bidirectional connectivity test.

   o Bidirectional in-service / out-of-service test. The in-service
      mode refers to a test that is run under traffic, while the out-of-
      service test requires other traffic to be halted.

4.7.4. ETH-TST

   The test function is very similar to the loopback function, but is
   unidirectional, i.e., the ETH-TST PDUs are terminated by the receiver
   rather than being looped back to the sender.

4.7.5. ETH-LT

   The Ethernet linktrace is an on-demand function that is used for path
   discovery to a given target, or for locating a failure in a broken

4.7.6. ETH-AIS

   The Alarm Indication Signal indicates that a MEG should suppress
   alarms about a defect condition at a lower MEG level, i.e., since a
   defect has occurred in a lower hierarchy in the network, it should
   not be reported by the current node.

   A MEP that detects a failure periodically sends AIS messages to
   higher hierarchies. AIS messages are sent periodically at a
   recommended rate of 1 packet per second, until the defect condition
   is resolved.

4.7.7. ETH-LCK

   The lock function is used for administrative locking. A MEP can
   initiate administrative locking, resulting in interruption of data,
   e.g., for out-of-service ETH-LB or ETH-TST.

   A MEP that initiates an administrative locking notifies its peer MEPs
   to halt all relevant traffic until administrative/diagnostic
   condition is removed. ETH-LCK frames are used to report to higher MEG
   levels about the lock. The LCK frame, much like an AIS frame,
   indicates to the receiving MEP that it should suppress alarms about
   the locked link.

4.7.8. ETH-RDI

   The Remote Defect Indication allows the sender to indicate that it
   encountered a defect conditions. The receiving MEPs are then aware
   that there is a defect condition in the MEG.

4.7.9. ETH-APS

   The Y.1731 standard defines the frame format for Automatic Protection
   Switching frames. The protection switching operations are defined in
   other ITU-T standards.

4.7.10. ETH-LM

   The loss measurement function allows a MEP to measure the packet loss
   rate from/to a given MEP in the MEG. Each MEP maintains counters of
   transmitted and received in-profile packets to/from each of its peer
   MEPs. These counters are incorporated in the ETH-LM frames, allowing
   the MEPs to compute the packet loss rate.

   The ETH-LM function measures the far-end loss, referring to traffic
   FROM the MEP to its peer, as well as the near-end loss, referring to
   traffic from the peer MEP TO the local MEP.

   ETH-LM is performed in one of two possible modes:

   o Single-ended LM: in this mode loss measurement is performed on-
      demand. The initiator sends an LM message (LMM) to its peer MEP,
      and the peer responds with an LM reply (LMR).

   o Dual-ended LM: in this mode loss measurement is performed
      proactively. The continuity check message (CCM) is used for
      proactive LM. The LM counters are piggy-backed into the CCM, and
      allow proactive loss measurement.

4.7.11. ETH-DM

   The delay measurement function is an on-demand function that allows a
   MEP to measure the frame delay and frame delay variation to a peer

   ETH-DM can be performed in one of two modes of operation:

   o One-way DM: in this mode, a MEP transmits a 1DM frame containing
      the time of its transmission, TxTimeStampf. The receiving MEP
      receives the 1DM frame and records the time of reception, RxTimef.
      The receiving MEP can then compute the one-way delay by: RxTimef -

   o Two-way DM: in this mode, a MEP transmits a delay measurement
      message (DMM) containing its transmission time, TxTimeStampf. The
      peer MEP receives the DMM and responds with a delay measurement
      reply (DMR). Upon receiving the DMR, the initiating MEP records
      the time of its reception, RxTimef, and computes the round trip
      delay by: RxTimef - TxTimeStampf.

   Each MEP maintains a time-of-day clock that is used for timestamping
   delay measurement frames. It should be noted that in one-way DM it is
   implicitly assumed that the clocks of the two peer MEPs are
   synchronized by a time synchronization protocol.

4.8. IEEE 802.1ag

4.8.1. Overview

   While the [ITU-T Y.1731] was defined in the ITU-T, the IEEE defined
   the [IEEE 802.1ag] as a standard for connectivity fault management in
   Ethernet based networks. While the two standards are to some extent
   overlapping, they can also be viewed as two complementary parts of a
   single Ethernet OAM picture. The two standards use a common packet
   format. There are a few differences between the two standards in
   terms of terminology: the term MEG level, used in Y.1731, as referred
   to as Maintenance Domain level in 802.1ag; the Y.1731 standard uses
   the term MEG, while the 802.1ag equivalent is Maintenance Association

   While Y.1731 defines multiple OAM functions (see section 4.6), the
   802.1ag standard focuses on three main OAM functions: continuity
   check, loopback, and linktrace, and defines them with great detail.

4.8.2. Continuity Check

   See 4.6.2.

4.8.3. Loopback

   See 4.6.3.

4.8.4. Linktrace

   See 4.6.5.

4.9. IEEE 802.3ah

4.9.1. Overview

   The [IEEE 802.3ah] defines Ethernet for the Last Mile (EFM). With
   respect to OAM, this standard was designed as an Ethernet link-layer
   OAM, for single-hop Ethernet links, allowing to monitor remote
   networking devices that are not managed by a centralized management
   system. The OAM functions in this standard are described below.

4.9.2. Remote Failure Indication

   This function allows a node to notify a peer about a defect in the
   receive path. Some physical interfaces allow unidirectional traffic,
   where even if one direction of the link fails, the reverse direction
   can still be used to convey the remote failure indication.

4.9.3. Remote Loopback

   The remote loopback function provides a diagnostic mode that is used
   to verify the link connectivity, and to measure the packet loss rate.
   When a bridge interface is configured to loopback mode, all incoming
   traffic through the interface is looped and sent back to the

4.9.4. Link Monitoring

   Link monitoring provides an event notification function, allowing
   peer devices to communicate defect conditions and diagnostic


4.10.1. Overview

   The MPLS working group is currently working on defining the OAM
   toolset that fulfill 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
   mechanisms and a set of operations that should be supported by the
   OAM toolset.  The set of mechanisms required are further elaborated
   in [MPLS-TP OAM FW], that describes the general architecture of the
   OAM system as well as giving 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 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.

4.10.2. 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 added to OAM

   o A Generic Associated Label (GAL). The GAL is a reserved MPLS label
      value. The reserved value is 13, and indicates the existence of
      the ACH immediately after it.

4.10.3. 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].
   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]. 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

   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].

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

   Continuity Check and Connectivity Verification (CC-V) are OAM
   operations generally used in tandem, and compliment each other. These
   functions are generally run proactively, but may also be used on-
   demand, either due to bandwidth considerations or for diagnoses of a
   specific condition. 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.[MPLS-TP OAM FW] highlights 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 function, both
   proactively and in on-demand mode, need to be transmitted at regular
   rates pre-configured by the operator. Diagnostic Tests

   Diagnostic testing is a protocol that allows a network to send
   special test data on a transport path.  For example, this could be
   used as part of bandwidth utilization measurement. 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. 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. [MPLS-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 [MPLS-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] points out that
   this function may be applied to a unidirectional LSP only if there a
   return path exists.  [MPLS-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] 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.

4.11. 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    |Tracerou|           |       |        |
   |           |       |        |te      |           |       |        |
   + --------- + ----- + ------ + ------ + --------- + ----- + ------ +
   |BFD        |BFD    |BFD     |        |           |       |        |
   |           |Control|Echo    |        |           |       |        |
   + --------- + ----- + ------ + ------ + --------- + ----- + ------ +
   |LSP Ping   |       |"Ping"  |"Tracero|           |       |        |
   |           |       |mode    |ute"    |           |       |        |
   |           |       |        |mode    |           |       |        |
   + --------- + ----- + ------ + ------ + --------- + ----- + ------ +
   |PW VCCV    |       |VCCV    |        |           |       |        |
   + --------- + ----- + ------ + ------ + --------- + ----- + ------ +
   |IPPM       |       |        |        |           |-Delay |        |
   |           |       |        |        |           | measur|        |
   |           |       |        |        |           | ement |        |
   |           |       |        |        |           |-Packet|        |
   |           |       |        |        |           | loss  |        |
   |           |       |        |        |           | measur|        |
   |           |       |        |        |           | ement |        |
   + --------- + ----- + ------ + ------ + --------- + ----- + ------ +
   |ITU-T      |-CV    |        |        |           |       |        |
   |Y.1711     |-FFD   |        |        |           |       |        |
   + --------- + ----- + ------ + ------ + --------- + ----- + ------ +
   |Y.1731     |       |        |        |-ETH-AIS   |-ETH-DM|-ETH-APS|
   |           |       |        |        |           |       |-ETH-TST|
   + --------- + ----- + ------ + ------ + --------- + ----- + ------ +
   |IEEE       |CC     |Loopback|Linktrac|           |       |        |
   |802.1ag    |       |        |e       |           |       |        |
   + --------- + ----- + ------ + ------ + --------- + ----- + ------ +
   |IEEE       |       |Remote  |        |-Remote    |       |        |
   |802.3ah    |       |Loopback|        | Failure   |       |        |
   |           |       |        |        | Indication|       |        |
   |           |       |        |        |-Link      |       |        |
   |           |       |        |        | Monitoring|       |        |
   + --------- + ----- + ------ + ------ + --------- + ----- + ------ +
   |MPLS-TP    |CC     |CV      |Route   |-Alarm     |-LM    |-Diagnos|
   |OAM        |       |        |Tracing | Reporting |-DM    | tic Tes|
   |           |       |        |        |-Client    |       | s      |
   |           |       |        |        | Failure   |       |-Lock   |
   |           |       |        |        | Indication|       |        |
   |           |       |        |        |-Remote    |       |        |
   |           |       |        |        | Defect    |       |        |
   |           |       |        |        | Indication|       |        |
                     Table 3 Summary of OAM Functions

4.12. Summary of Continuity Check Mechanisms

   A key element in some of the OAM standards that are analyzed in this
   document is the continuity check. It is thus interesting to present a
   more detailed comparison of the connectivity check mechanisms defined
   in OAM standards. Table 4 can be viewed as an extension of Table 3,
   but is presented separately for convenience. The table compares the
   OAM standards that support a continuity check. MPLS-TP is not
   included in the comparison, as the continuity check mechanism in
   MPLS-TP has not yet been defined.

   The "Tx Interval" column in the table specifies the period between
   two consequent message transmissions, while the "Source Identifier"
   column specifies the name of the field in the OAM packet that is used
   as the identifier of the transmitter. The "Error Codes" column
   specifies the possible error codes when the unidirectional
   connectivity check detects a failure.

   |           |Mechani|Tx      |UC/|Source  | Error                  |
   |           |sm     |Interval|MC |Identifi| Codes                  |
   |           |       |        |   |er      |                        |
   |BFD        |BFD    |Negotiat|UC |My Discr| Control Detection Time |
   |           |Control|ed durin|   |iminator| Expired                |
   |           |       |g sessio|   |        |                        |
   |           |       |n       |   |        |                        |
   + --------- + ----- + ------ + - + ------ + ---------------------- +
   |ITU-T      |CV     |CV: 1s  |UC |TTSI    |-Loss of CV (LOCV)      |
   |Y.1711     |FFD    |FFD: par|   |        |-TTSI Mismatch          |
   |           |       |ameter, |   |        |-TTSI Mismerge          |
   |           |       |default:|   |        |-Excess                 |
   |           |       |50 ms   |   |        |                        |
   + --------- + ----- + ------ + - + ------ + ---------------------- +
   |ITU-T      |CC     |7 possib|UC/|MEP ID  |-Loss of Continuity(LOC)|
   |Y.1731 /   |       |le perio|MC |        |-Unexpected MEG level   |
   |IEEE       |       |ds:     |   |        |-Mismerge               |
   |802.1ag    |       |3 1/3 ms|   |        |-Unexpected MEP         |
   |           |       |10 ms   |   |        |-Unexpected period      |
   |           |       |100 ms  |   |        |                        |
   |           |       |1 s     |   |        |                        |
   |           |       |10 s    |   |        |                        |
   |           |       |1 min   |   |        |                        |
   |           |       |10 min  |   |        |                        |
                       Table 4 Summary of OAM Terms

5. Security Considerations

   There are no security implications imposed by this document.

6. IANA Considerations

   There are no new IANA considerations implied by this document.

7. Acknowledgments

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

8. References

8.1. Normative References

   [KEYWORDS]    Bradner, S., "Key words for use in RFCs to Indicate
                 Requirement Levels", BCP 14, RFC 2119, March 1997.

   [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.

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

   [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]      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.

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

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

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

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

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

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

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

   [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

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

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

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

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

8.2. Informative References

   [OAM Soup]    Andersson, L., Van Helvoort, H., Bonica, R., Romascanu,
                 D., Mansfield, S., " Guidelines for the use of the OAM
                 acronym in the IETF ", work-in-progress, draft-ietf-
                 opsawg-mpls-tp-oam-def, September, 2010.

   [OAM Analysis] Sprecher, N., Bellagamba, E., Weingarten, Y., "OAM
                 functions in MPLS based transport network", work-in-
                 progress, draft-ietf-mpls-tp-oam-analysis, January,

   [MPLS-TP OAM FW] Busi, I., Niven-Jenkins, B., Allan, D., "
                 Operations, "Operations,
                 Administration and Maintenance Framework for MPLS-based MPLS-
                 based Transport Networks ", work-in-progress,
                 draft-ietf-mpls-tp-oam-framework, draft-
                 ietf-mpls-tp-oam-framework, February, 2011.

   [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, November, 2010.

   [MPLS-TP Ping BFD] Bahadur, N., Aggarwal, R., Ward, D., Nadeau, T.,
                 Sprecher, N., Weingarten, Y., "LSP-Ping and BFD
                 encapsulation over ACH", draft-ietf-mpls-tp-lsp-ping-
                 bfd-procedures, work-in-progress, August, 2010.

   [P2MP Ping]   Saxena, S., Farrel, A. , Yasukawa, S., "Detecting Data
                 Plane Failures in Point-to-Multipoint Multiprotocol
                 Label Switching (MPLS) - Extensions to LSP Ping",
                 work-in-progress, draft-ietf-mpls-p2mp-lsp-ping,
                 March, 2011.

   [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 St. Neve Ne'eman B
   Hod Hasharon,   45241

   Phone: +972-9-775 1827
   Email: yaacov.weingarten@nsn.com