draft-ietf-opsawg-oam-overview-01.txt   draft-ietf-opsawg-oam-overview-02.txt 
Operations and Management Area Working Group T. Mizrahi Operations and Management Area Working Group T. Mizrahi
Internet Draft Marvell Internet Draft Marvell
Intended status: Informational July 12, 2010 Intended status: Informational N. Sprecher
Expires: January 2011 Expires: April 2011 Nokia Siemens Networks
E. Bellagamba
Ericsson
Y. Weingarten
Nokia Siemens Networks
October 7, 2010
An Overview of An Overview of
Operations, Administration, and Maintenance (OAM) Mechanisms Operations, Administration, and Maintenance (OAM) Mechanisms
draft-ietf-opsawg-oam-overview-01.txt draft-ietf-opsawg-oam-overview-02.txt
Status of this Memo Status of this Memo
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Abstract Abstract
Operations, Administration, and Maintenance (OAM) is a general term Operations, Administration, and Maintenance (OAM) is a general term
that refers to detecting and reporting link failures. OAM mechanisms that refers to a toolset that can be used for detecting and reporting
have been defined for various layers in the protocol stack, and are connection failures or measurement of connection performance
used with a variety of protocols. parameters. 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 This document presents an overview of the OAM mechanisms that have
been defined and are currently being defined by the IETF, as well as 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 a comparison to other OAM mechanisms that have been defined by the
IEEE and ITU-T. IEEE and ITU-T.
Table of Contents Table of Contents
1. Introduction................................................4 1. Introduction................................................4
2. Conventions used in this document............................8 2. Conventions used in this document............................8
3. Basic Terminology...........................................8 3. Basic Terminology...........................................8
3.1. Abbreviations..........................................8 3.1. Abbreviations..........................................8
3.2. Terminology used in OAM Standards.......................9 3.2. Terminology used in OAM Standards.......................9
3.2.1. General Terms......................................9 3.2.1. General Terms......................................9
3.2.2. OAM Maintenance Entities...........................9 3.2.2. OAM Maintenance Entities and Communication Links...10
3.2.3. OAM Maintenance Points............................10 3.2.3. OAM Maintenance Points............................10
3.2.4. OAM Link Failures.................................10 3.2.4. Link Failures.....................................11
3.2.5. Summary of OAM Terms used in the Standards.........10 3.2.5. Connectivity Verification and Continuity Checks....11
4. OAM Functions..............................................12 3.2.6. Summary of OAM Terms used in the Standards.........11
4.1. ICMP Ping.............................................12 4. OAM Functions..............................................13
4.2. Bidirectional Forwarding Detection (BFD)...............12 4.1. ICMP Ping.............................................13
4.2.1. Overview.........................................12 4.2. Bidirectional Forwarding Detection (BFD)...............13
4.2.2. BFD Control.......................................12 4.2.1. Overview.........................................13
4.2.3. BFD Echo.........................................13 4.2.2. BFD Control.......................................13
4.3. LSP Ping..............................................13 4.2.3. BFD Echo.........................................14
4.4. PWE3 Virtual Circuit Connectivity Verification (VCCV)...13 4.3. LSP Ping..............................................14
4.5. IP Performance Metrics (IPPM)..........................14 4.4. PWE3 Virtual Circuit Connectivity Verification (VCCV)...15
4.5.1. Overview.........................................14 4.5. IP Performance Metrics (IPPM)..........................15
4.5.2. OWAMP/TWAMP Control...............................14 4.5.1. Overview.........................................15
4.5.3. OWAMP/TWAMP Test..................................14 4.5.2. Control and Test Protocols........................16
4.6. ITU-T Y.1711..........................................14 4.5.3. OWAMP............................................16
4.6.1. Overview.........................................14 4.5.4. TWAMP............................................17
4.6.2. Connectivity Verification (CV)....................15 4.6. ITU-T Y.1711..........................................17
4.6.3. Fast Failure Detection (FFD)......................15 4.6.1. Overview.........................................17
4.6.4. Forward Defect Indication (FDI)...................15 4.6.2. Connectivity Verification (CV)....................18
4.6.5. Backward Defect Indication (BDI)..................15 4.6.3. Fast Failure Detection (FFD)......................18
4.6.4. Forward Defect Indication (FDI)...................18
4.7. ITU-T Y.1731..........................................16 4.6.5. Backward Defect Indication (BDI)..................19
4.7.1. Overview.........................................16 4.7. ITU-T Y.1731..........................................19
4.7.2. ETH-CC...........................................16 4.7.1. Overview.........................................19
4.7.3. ETH-LB...........................................17 4.7.2. ETH-CC...........................................19
4.7.4. ETH-TST..........................................17 4.7.3. ETH-LB...........................................20
4.7.5. ETH-LT...........................................17 4.7.4. ETH-TST..........................................20
4.7.6. ETH-AIS..........................................17 4.7.5. ETH-LT...........................................20
4.7.7. ETH-LCK..........................................17 4.7.6. ETH-AIS..........................................20
4.7.8. ETH-RDI..........................................18 4.7.7. ETH-LCK..........................................20
4.7.9. ETH-APS..........................................18 4.7.8. ETH-RDI..........................................21
4.7.10. ETH-LM..........................................18 4.7.9. ETH-APS..........................................21
4.7.11. ETH-DM..........................................18 4.7.10. ETH-LM..........................................21
4.8. IEEE 802.1ag..........................................19 4.7.11. ETH-DM..........................................21
4.8.1. Overview.........................................19 4.8. IEEE 802.1ag..........................................22
4.8.2. Continuity Check..................................19 4.8.1. Overview.........................................22
4.8.3. Loopback.........................................19 4.8.2. Continuity Check..................................22
4.8.4. Linktrace........................................20 4.8.3. Loopback.........................................22
4.9. IEEE 802.3ah..........................................20 4.8.4. Linktrace........................................23
4.9.1. Overview.........................................20 4.9. IEEE 802.3ah..........................................23
4.9.2. Remote Failure Indication.........................20 4.9.1. Overview.........................................23
4.9.3. Remote Loopback...................................20 4.9.2. Remote Failure Indication.........................23
4.9.4. Link Monitoring...................................20 4.9.3. Remote Loopback...................................23
4.10. MPLS-TP OAM..........................................20 4.9.4. Link Monitoring...................................23
4.10.1. Overview........................................20 4.10. MPLS-TP OAM..........................................23
4.10.2. Continuity Checks................................21 4.10.1. Overview........................................23
4.10.3. Connectivity Verification........................21 4.10.2. Generic Associated Channel.......................24
4.10.4. Diagnostic Tests.................................21 4.10.3. MPLS-TP OAM Toolset..............................24
4.10.5. Route Tracing....................................22 4.10.3.1. Continuity Check and Connectivity Verification25
4.10.6. Lock Instruct....................................22 4.10.3.2. Diagnostic Tests............................25
4.10.7. Lock Reporting...................................22 4.10.3.3. Route Tracing...............................25
4.10.8. Alarm Reporting..................................22 4.10.3.4. Lock Instruct...............................25
4.10.9. Remote Defect Indication.........................22 4.10.3.5. Lock Reporting..............................26
4.10.10. Client Failure Indication.......................22 4.10.3.6. Alarm Reporting.............................26
4.10.11. Packet Loss Measurement.........................22 4.10.3.7. Remote Defect Indication....................26
4.10.12. Packet Delay Measurement........................22 4.10.3.8. Client Failure Indication...................26
4.11. Summary of OAM Functions..............................22 4.10.3.9. Packet Loss Measurement.....................26
4.12. Summary of Unidirectional Connectivity Check Mechanisms24 4.10.3.10. Packet Delay Measurement...................27
5. Security Considerations.....................................25 4.11. Summary of OAM Functions..............................27
6. IANA Considerations........................................25 4.12. Summary of Continuity Check Mechanisms................29
7. Acknowledgments............................................25 5. Security Considerations.....................................30
8. References.................................................25 6. IANA Considerations........................................30
8.1. Normative References...................................25 7. Acknowledgments............................................30
8.2. Informative References.................................28 8. References.................................................30
8.1. Normative References...................................30
8.2. Informative References.................................32
1. Introduction 1. Introduction
OAM is a general term that refers to detecting and reporting link OAM is a general term that refers to a toolset that can be used for
failures and defects. The term OAM has been used over the years in detecting and reporting connection failures or measurement of
several different contexts, as discussed in [OAM Soup]. In the connection performance parameters. The term OAM has been used over
context of this document OAM refers to Operations, Administration, the years in several different contexts, as discussed in [OAM Soup].
and Maintenance, i.e., this document refers to OAM in the context of In the context of this document OAM refers to Operations,
monitoring communication links. Other aspects associated with the OAM Administration, and Maintenance, i.e., this document refers to OAM in
acronym, such as management, are not described in this document. the context of monitoring communication links. Other aspects
associated with the OAM acronym, such as management, are not
described in this document.
OAM was originally used in the world of telephony, and has been OAM was originally used in the world of telephony, and has been
adopted in packet based networks. OAM mechanisms are used in various adopted in packet based networks. OAM mechanisms are used in various
layers in the protocol stack, and are applied to a variety of layers in the protocol stack, and are applied to a variety of
different protocols. different protocols.
The IETF has defined OAM for several protocols, and is currently The IETF has defined OAM for several protocols, and is currently
working on defining several new OAM protocols. A summary of these working on defining several new OAM protocols. A summary of these
protocols, old and new, is listed below: protocols, old and new, is listed below:
skipping to change at page 4, line 39 skipping to change at page 4, line 42
o Virtual Circuit Connectivity Check (VCCV) for Pseudowires, as o Virtual Circuit Connectivity Check (VCCV) for Pseudowires, as
defined in [VCCV]. defined in [VCCV].
o ICMP Echo request, also known as Ping, as defined in [ICMPv4], and o ICMP Echo request, also known as Ping, as defined in [ICMPv4], and
[ICMPv6]. ICMP Ping is a very simple and basic mechanism in [ICMPv6]. ICMP Ping is a very simple and basic mechanism in
failure diagnosis, and is not traditionally associated with OAM, failure diagnosis, and is not traditionally associated with OAM,
but it is presented in this document for the sake of completeness, 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 since both LSP Ping and VCCV are to some extent based on ICMP
Ping. Ping.
o Bidirectional Forwarding Detection (BFD) is a family of standards o Bidirectional Forwarding Detection (BFD) is defined in [BFD] as a
that are currently being defined by the IETF. BFD is intended to framework for a lightweight generic OAM mechanism. The intention
be a generic OAM mechanism that can be used with various is to define a base mechanism that can be used with various
encapsulation types, and in various medium types. encapsulation types, network environments, and in various medium
types.
o OAM for MPLS-TP is currently being defined in the MPLS working o The OAM requirements for MPLS Transport Profile (MPLS-TP) are
group. 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 o IP Performance Metrics (IPPM) is a working group in the IETF that
defined common metrics for performance measurement, as well as a defined common metrics for performance measurement, as well as a
protocol for measuring delay and packet loss in IP networks. protocol for measuring delay and packet loss in IP networks.
While performance measurement is not directly related to link Alternative protocols for performance measurement are defined, for
failures, it is often associated with OAM. Alternative protocols example, in MPLS-TP OAM [MPLS-TP OAM], and in Ethernet OAM [ITU-T
for performance measurement are defined, for example, in MPLS-TP Y.1731].
OAM [MPLS-TP OAM], and in Ethernet OAM [ITU-T Y.1731].
In addition to the OAM mechanisms defined by the IETF, the IEEE and In addition to the OAM mechanisms defined by the IETF, the IEEE and
ITU-T have also defined various OAM mechanisms. These various ITU-T have also defined various OAM mechanisms. These various
mechanisms defined by the three standard organizations are often mechanisms defined by the three standard organizations are often
tightly coupled, and have had a mutual effect on each other. For tightly coupled, and have had a mutual effect on each other. The ITU-
example, the emerging MPLS-TP OAM is in many ways based on [ITU-T T and IETF have both defined OAM mechanisms for MPLS LSPs, [ITU-T
Y.1731]. The ITU-T and IETF have both defined OAM mechanisms for MPLS Y.1711] and [LSP Ping]. The following OAM standards by the IEEE and
LSPs, [ITU-T Y.1711] and [LSP Ping]. The following OAM standards by ITU-T are to some extent linked to IETF OAM mechanisms listed above,
the IEEE and ITU-T are to some extent linked to IETF OAM mechanisms and are also discussed in this document:
listed above, and are also discussed in this document:
o OAM mechanisms for Ethernet based networks have been defined by 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 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 802.1ag]. The IEEE 802.3 standard defines OAM for one-hop Ethernet
links [IEEE 802.3ah]. links [IEEE 802.3ah].
o The ITU-T has defined OAM for MPLS LSPs in [ITU-T Y.1711]. 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 This document summarizes the OAM mechanisms defined in the standards
above. The focus is on OAM mechanisms defined by the IETF, compared above. The focus is on OAM mechanisms defined by the IETF. These
with the relevant OAM mechanisms defined by the ITU-T and IEEE. We mechanisms will be compared with the relevant OAM mechanisms defined
first present a comparison of the terminology used in various OAM by the ITU-T and IEEE, where applicable. We first present a
standards, and then summarize the OAM functions that each OAM comparison of the terminology used in various OAM standards, and then
standard provides. summarize the OAM functions that each OAM standard provides.
Table 1 summarizes the OAM standards discussed in this document. Table 1 summarizes the OAM standards discussed in this document.
+-----------+--------------------------------------+---------------+ +-----------+--------------------------------------+---------------+
| | Title |Standard | | | Title |Standard/Draft |
+-----------+--------------------------------------+---------------+ +-----------+--------------------------------------+---------------+
|ICMPv4 Ping| Internet Control Message Protocol | RFC 792 | |ICMPv4 Ping| Internet Control Message Protocol | RFC 792 |
| | | | | | | |
+-----------+--------------------------------------+---------------+ +-----------+--------------------------------------+---------------+
|ICMPv6 Ping| Internet Control Message Protocol | RFC 4443 | |ICMPv6 Ping| Internet Control Message Protocol | RFC 4443 |
| | (ICMPv6) for the Internet Protocol | | | | (ICMPv6) for the Internet Protocol | |
| | Version 6 (IPv6) Specification | | | | Version 6 (IPv6) Specification | |
+-----------+--------------------------------------+---------------+ +-----------+--------------------------------------+---------------+
|BFD | Bidirectional Forwarding Detection | RFC 5880 | |BFD | Bidirectional Forwarding Detection | RFC 5880 |
| +--------------------------------------+---------------+ | +--------------------------------------+---------------+
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| | Label Switching (MPLS) Operations | | | | Label Switching (MPLS) Operations | |
| | and Management (OAM) | | | | and Management (OAM) | |
| +--------------------------------------+---------------+ | +--------------------------------------+---------------+
| | Detecting Multi-Protocol Label | RFC 4379 | | | Detecting Multi-Protocol Label | RFC 4379 |
| | Switched (MPLS) Data Plane Failures | | | | Switched (MPLS) Data Plane Failures | |
| +--------------------------------------+---------------+ | +--------------------------------------+---------------+
| | Operations and Management (OAM) | RFC 4687 | | | Operations and Management (OAM) | RFC 4687 |
| | Requirements for Point-to-Multipoint | | | | Requirements for Point-to-Multipoint | |
| | MPLS Networks | | | | 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 | |PW VCCV | Pseudowire Virtual Circuit | RFC 5085 |
| | Connectivity Verification (VCCV): | | | | Connectivity Verification (VCCV): | |
| | A Control Channel for Pseudowires | | | | A Control Channel for Pseudowires | |
+-----------+--------------------------------------+---------------+ +-----------+--------------------------------------+---------------+
|IPPM | Framework for IP Performance Metrics | RFC 2330 | |IPPM | Framework for IP Performance Metrics | RFC 2330 |
| +--------------------------------------+---------------+ | +--------------------------------------+---------------+
| | IPPM Metrics for Measuring | RFC 2678 | | | IPPM Metrics for Measuring | RFC 2678 |
| | Connectivity | | | | Connectivity | |
| +--------------------------------------+---------------+ | +--------------------------------------+---------------+
| | A One-way Delay Metric for IPPM | RFC 2679 | | | A One-way Delay Metric for IPPM | RFC 2679 |
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| +--------------------------------------+---------------+ | +--------------------------------------+---------------+
| | Assignment of the 'OAM Alert Label' | RFC 3429 | | | Assignment of the 'OAM Alert Label' | RFC 3429 |
| | for Multiprotocol Label Switching | | | | for Multiprotocol Label Switching | |
| | Architecture (MPLS) Operation and | | | | Architecture (MPLS) Operation and | |
| | Maintenance (OAM) Functions | | | | Maintenance (OAM) Functions | |
+-----------+--------------------------------------+---------------+ +-----------+--------------------------------------+---------------+
|ITU-T | OAM Functions and Mechanisms for |[ITU-T Y.1731] | |ITU-T | OAM Functions and Mechanisms for |[ITU-T Y.1731] |
|Ethernet | Ethernet-based Networks | | |Ethernet | Ethernet-based Networks | |
|OAM | | | |OAM | | |
+-----------+--------------------------------------+---------------+ +-----------+--------------------------------------+---------------+
|MPLS-TP | Requirements for OAM in MPLS | RFC 5860 |
|OAM +--------------------------------------+---------------+
| | MPLS Generic Associated Channel | RFC 5586 |
+-----------+--------------------------------------+---------------+
|IEEE | Connectivity Fault Management |[IEEE 802.1ag] | |IEEE | Connectivity Fault Management |[IEEE 802.1ag] |
|CFM | | | |CFM | | |
+-----------+--------------------------------------+---------------+ +-----------+--------------------------------------+---------------+
|IEEE | Media Access Control Parameters, |[IEEE 802.3ah] | |IEEE | Media Access Control Parameters, |[IEEE 802.3ah] |
|802.3 | Physical Layers, and Management | | |802.3 | Physical Layers, and Management | |
|link level | Parameters for Subscriber Access | | |link level | Parameters for Subscriber Access | |
|OAM | Networks | | |OAM | Networks | |
+-----------+--------------------------------------+---------------+ +-----------+--------------------------------------+---------------+
Table 1 Summary of OAM Standards Table 1 Summary of OAM Standards
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A wide variety of terms is used in various OAM standards. Each of the 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 OAM standards listed in the reference section includes a section that
defines the relevant terms. A thesaurus of terminology for MPLS-TP defines the relevant terms. A thesaurus of terminology for MPLS-TP
terms is presented in [MPLS-TP Term], and provides a good summary of terms is presented in [MPLS-TP Term], and provides a good summary of
some of the OAM related terminology. some of the OAM related terminology.
This section presents a comparison of the terms used in various OAM This section presents a comparison of the terms used in various OAM
standards, without fully quoting the definition of each term. For a standards, without fully quoting the definition of each term. For a
formal definition of each term, refer to the references at the end of formal definition of each term, refer to the references at the end of
this document. The comparison focuses on three basic terms, and is this document. The comparison focuses on three basic terms, and is
summarized in section 3 ..2.5. summarized in section 3 ..2.6.
3.2.2. OAM Maintenance Entities 3.2.2. OAM Maintenance Entities and Communication Links
A Maintenance Entity (ME) can be either a point-to-point or a point- A Maintenance Entity (ME) can be either a point-to-point or a point-
to-multipoint relationship between two or more Maintenance Points. to-multipoint relationship between two or more Maintenance Points
(MP). The connectivity between these Maintenance Points is managed
and monitored by the OAM protocol.
The connectivity between these Maintenance Points is mangaged and A pair of MPs engaged in an ME are connected by a communication Link.
monitored by the OAM protocol. Link in this context may refer to a physical connection, or to a
logical path 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 protocol.
The term Maintenance Entity (ME) is defined in ITU-T standards (e.g. 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 [ITU-T Y.1731]). Various terms are used to refer to an ME. For
example, in MPLS terminology, an ME is simply referred to as an LSP. example, in MPLS terminology, an ME is simply referred to as an LSP.
BFD does not explicitly use a term that is equivalent to ME, but BFD does not explicitly use a term that is equivalent to ME, but
rather uses the term "session", referring to the relationship between rather uses the term "session", referring to the relationship between
two nodes using a BFD protocol. 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 3.2.3. OAM Maintenance Points
A Maintenance Point (MP) is a node that uses an OAM protocol. A A Maintenance Point (MP) is a function that is defined at a node in
Maintenance End Point (MEP) is one of the end points of an ME. A the network, and either initiates or reacts to OAM messages. A
Maintenance Intermediate Point (MIP) is a point between two MEPs, Maintenance End Point (MEP) is one of the end points of an ME, and
that is able to respond to OAM frames, but does not initiate them. can initiate OAM messages and respond to them. A Maintenance
Intermediate Point (MIP) is a point between two MEPs, that is able to
respond to OAM frames, but does not initiate them.
The terms MEP and MIP are defined in ITU-T standards (e.g. [ITU-T 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 Y.1731]). The term Maintenance Point is a general term for MEPs and
MIPs, and is used in [IEEE 802.1ag]. MIPs, and is used in [IEEE 802.1ag].
3.2.4. OAM Link Failures MPLS-TP has defined the terms MEP and MIP and their functional
characteristics in [MPLS-TP OAM FW], similar to the terms defined by
ITU-T.
3.2.4. Link Failures
The terms Failure, Fault, and Defect are intermittently used in the The terms Failure, Fault, and Defect are intermittently used in the
standards. In some standards, such as [IEEE 802.1ag], there is no standards. In some standards, such as [IEEE 802.1ag], there is no
distinction between these terms, while in other standards each of distinction between these terms, while in other standards each of
these terms refers to a different type of malfunction. these terms refers to a different type of malfunction.
The ITU-T distinguishes between these terms in [ITU-T G.806]. The 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., term Fault refers to an inability to perform a required action, e.g.,
an unsuccessful attempt to deliver a packet. The term Defect refers an unsuccessful attempt to deliver a packet. The term Defect refers
to an interruption in the normal operation, such as a consecutive to an interruption in the normal operation, such as a consecutive
period of time where no packets are delivered successfully. The term period of time where no packets are delivered successfully. The term
Failure refers to the termination of the required function. While a Failure refers to the termination of the required function. While a
Defect typically refers to a limited period of time, a failure refers Defect typically refers to a limited period of time, a failure refers
to a long period of time. to a long period of time.
3.2.5. Summary of OAM Terms used in the Standards 3.2.5. 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], 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
well.
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
other.
3.2.6. Summary of OAM Terms used in the Standards
Table 2 provides a comparison of the terminology used in different Table 2 provides a comparison of the terminology used in different
OAM standards. OAM standards.
+-----------+-------------+-----------+----------------------------+ +-----------+-------------+-----------+----------------------------+
| |Maintenance |Maintenance|Link Failure Terminology | | |Maintenance |Maintenance|Link Failure Terminology |
| |Point |Entity | | | |Point |Entity | |
| |Terminology |Terminology| | | |Terminology |Terminology| |
+-----------+-------------+-----------+----------------------------+ +-----------+-------------+-----------+----------------------------+
|ICMPv4 Ping|-Host | | | |ICMPv4 Ping|-Host | | |
skipping to change at page 11, line 33 skipping to change at page 12, line 33
| | | | a path with a measurement | | | | | a path with a measurement |
| | | | value "false". | | | | | value "false". |
+ --------- + ----------- + --------- + -------------------------- + + --------- + ----------- + --------- + -------------------------- +
|ITU-T | LSR | LSP |-Fault, Defect, Failure: as | |ITU-T | LSR | LSP |-Fault, Defect, Failure: as |
|Y.1711 | | | defined in [ITU-T G.806] | |Y.1711 | | | defined in [ITU-T G.806] |
+ --------- + ----------- + --------- + -------------------------- + + --------- + ----------- + --------- + -------------------------- +
|ITU-T |-MEP | ME |-Fault, Defect, Failure: as | |ITU-T |-MEP | ME |-Fault, Defect, Failure: as |
|Y.1731 |-MIP | | defined in [ITU-T G.806] | |Y.1731 |-MIP | | defined in [ITU-T G.806] |
| | | | | | | | | |
+ --------- + ----------- + --------- + -------------------------- + + --------- + ----------- + --------- + -------------------------- +
|MPLS-TP |-End Point |-LSP |-Fault, Defect, Failure: as | |MPLS-TP |-End Point, |-LSP |-Fault, Defect, Failure: as |
|OAM |-Intermediate|-PW | defined in [ITU-T G.806] | |OAM | MEP |-PW | defined in [ITU-T G.806] |
| |Point |-Section | | | |-Intermediate|-Section | |
| | Point, MIP | | |
+ --------- + ----------- + --------- + -------------------------- + + --------- + ----------- + --------- + -------------------------- +
|IEEE |-MEP | ME |-Failure | |IEEE |-MEP | ME |-Failure |
|802.1ag |-MIP | |-Fault | |802.1ag |-MIP | |-Fault |
| |-MP | |-Defect | | |-MP | |-Defect |
+ --------- + ----------- + --------- + -------------------------- + + --------- + ----------- + --------- + -------------------------- +
|IEEE | DTE | Link |-Failure | |IEEE | DTE | Link |-Failure |
|802.3ah | | |-Fault | |802.3ah | | |-Fault |
+-----------+-------------+-----------+----------------------------+ +-----------+-------------+-----------+----------------------------+
Table 2 Summary of OAM Terms Table 2 Summary of OAM Terms
4. OAM Functions 4. OAM Functions
4.1. ICMP Ping 4.1. ICMP Ping
ICMP provides a bidirectional connectivity check for the Internet ICMP provides a connectivity verification function for the Internet
Protocol. The originator transmits an echo request packet, and the Protocol. The originator transmits an echo request packet, and the
receiver replies with an echo reply. ICMP ping is defined in two receiver replies with an echo reply. ICMP ping is defined in two
variants, [ICMPv4] is used for IPv4, and [ICMPv6] is used for IPv6. variants, [ICMPv4] is used for IPv4, and [ICMPv6] is used for IPv6.
4.2. Bidirectional Forwarding Detection (BFD) 4.2. Bidirectional Forwarding Detection (BFD)
4.2.1. Overview 4.2.1. Overview
While multiple OAM mechanisms have been defined for various protocols While multiple OAM mechanisms have been defined for various protocols
in the protocol stack, Bidirectional Forwarding Detection [BFD], in the protocol stack, Bidirectional Forwarding Detection [BFD],
skipping to change at page 12, line 32 skipping to change at page 13, line 33
various medium types. The IETF has defined variants of the protocol 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 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 [BFD VCCV]. BFD for MPLS-TP is currently evolving in the MPLS working
group (e.g. [MPLS-TP Ping BFD]). group (e.g. [MPLS-TP Ping BFD]).
BFD includes two main OAM functions, using two types of BFD packets: BFD includes two main OAM functions, using two types of BFD packets:
BFD Control packets, and BFD Echo packets. BFD Control packets, and BFD Echo packets.
4.2.2. BFD Control 4.2.2. BFD Control
BFD supports a unidirectional connectivity check, using BFD control BFD supports a bidirectional continuity check, using BFD control
packets. BFD control packets are be sent in one of two modes: 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 o Asynchronous mode: in this mode BFD control packets are sent
periodically. When the receiver detects that no BFD control packet periodically. When the receiver detects that no BFD control packet
have been received during a predetermined period of time, a have been received during a predetermined period of time, a
failure is detected. failure is detected.
o Demand mode: in this mode, BFD control packets are sent on-demand. 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 Upon need, a system initiates a series of BFD control packets to
verify the link. BFD control packets are sent independently in verify the link. BFD control packets are sent independently in
each direction of the link. each direction of the link.
The transmission interval of BFD packets that are sent periodically, Each of the end-points of the monitored path maintains its own
is a result of negotiation between the two systems. Each BFD Control session identification, called a Discriminator, both of which are
packet includes the desired transmission interval, and the desired included in the BFD Control Packets that are exchanged between the
reception interval, allowing the two systems to agree on common end-points. At the time of session establishment, the Discriminators
intervals. 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.
If no BFD Control packets are received during a fixed period of time During normal operation of the session, i.e. no failures are
called the Detection Time, the session is declared to be down. The detected, the BFD session is in the Up state. If no BFD Control
detection time is a function of the negotiated transmission time, and packets are received during a fixed period of time, called the
a parameter called Detect Mult. Detect Mult determines the number of 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 missing BFD Control packets that cause the session to be declared as
down. This parameter is included in the BFD Control packet. Down. This parameter is included in the BFD Control packet.
The BFD Control packet also includes two fields that specify the
transmitting and receiving systems, called My Discriminator and Your
Discriminator, respectively.
4.2.3. BFD Echo 4.2.3. BFD Echo
The echo function is a bidirectional connectivity check. A 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 packet is sent to a peer system, and is looped back to the
originator. The echo function can be used proactively, or on-demand. originator. The echo function can be used proactively, or on-demand.
4.3. LSP Ping 4.3. LSP Ping
The IETF MPLS working group has defined OAM for MPLS LSPs. The The IETF MPLS working group has defined OAM for MPLS LSPs. The
requirements and framework of this effort was defined in [MPLS OAM requirements and framework of this effort was defined in [MPLS OAM
FW] and [MPLS OAM], respectively. The corresponding OAM mechanism FW] and [MPLS OAM], respectively. The corresponding OAM mechanism
that was defined in this context is LSP Ping [LSP Ping]. LSP ping is defined, in this context, is LSP Ping [LSP Ping].
used to detect data plain failures in MPLS LSPs. The transmitting LSR
sends an echo request to a remote LSR, and in turn receives an echo LSP Ping is based on ICMP Ping and just like its predecessor may be
reply. LSP ping is used in one of two modes: used in one of two modes:
o "Ping" mode: In this mode LSP ping is used for end-to-end o "Ping" mode: In this mode LSP ping is used for end-to-end
connectivity verification between two LSRs. connectivity verification between two LSRs.
o "Traceroute" mode: This mode is used for hop-by-hop fault o "Traceroute" mode: This mode is used for hop-by-hop fault
localization. localization.
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.
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) 4.4. PWE3 Virtual Circuit Connectivity Verification (VCCV)
VCCV, as defined in [VCCV], maintains the connectivity status of a VCCV, as defined in [VCCV], provides end-to-end fault detection
pseudowire. VCCV is supported for both MPLS PWs and L2TPv3 PWs. 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 supports two possible Connectivity Verification (CV) types, VCCV currently supports the following OAM mechanisms: ICMP Ping, LSP
i.e., two modes of operation: 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.
o ICMP Ping: In this mode the CV is performed using an ICMP ping VCCV consists of two components: (1) signaled component to
packet format, as defined in [ICMPv4] or [ICMPv6]. communicate VCCV capabilities as part of VC label, and (2) switching
component to cause the PW payload to be treated as a control packet.
o LSP Ping: In this mode the LSP Ping packet format, as defined in VCCV is not directly dependent upon the presence of a control plane.
[LSP Ping] is used for CV. 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. IP Performance Metrics (IPPM)
4.5.1. Overview 4.5.1. Overview
The IPPM working group [IPPM FW] in the IETF defines common criteria The IPPM working group [IPPM FW] in the IETF defines common criteria
and metrics for measuring performance of IP traffic. Some of the key and metrics for measuring performance of IP traffic. Some of the key
RFCs published by this working group have defined metrics for RFCs published by this working group have defined metrics for
measuring connectivity [rfc2678], delay [RFC2679, RFC 2681], and measuring connectivity [rfc2678], delay [RFC2679, RFC 2681], and
packet loss [RFC2681]. packet loss [RFC2681].
The IPPM working group has defined not only metrics for performance The IPPM working group has defined not only metrics for performance
measurement, but also protocols that define how the measurement is measurement, but also protocols that define how the measurement is
carried out. The One-way Active Measurement Protocol [OWAMP] and the carried out. The One-way Active Measurement Protocol [OWAMP] and the
Two-Way Active Measurement Protocol [TWAMP] define a method and Two-Way Active Measurement Protocol [TWAMP] define a method and
protocol for measuring delay and packet loss in IP networks. 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, OWAMP and TWAMP use two separate protocols: a Control plane protocol,
and a Test plane protocol. and a Test plane protocol.
4.5.2. OWAMP/TWAMP Control 4.5.2. Control and Test Protocols
Each of these standards defines a Control protocol. This protocol is OWAMP and TWAMP control protocols run over TCP, while the test
layered over TCP, and is used to initiate measurement sessions, and protocols run over UDP. The purpose of the control protocols is to
to communicate their results. 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.
4.5.3. OWAMP/TWAMP Test 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.
The Test protocol is layered over UDP, and is used to measure delay 4.5.3. OWAMP
and packet loss between the session endpoints. The Test session is
initiated by a Request/Response negotiation, followed by a set of OWAMP defines the following logical roles: Session-Sender, Session-
active test packets that are used for the measurement. 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
Session-Receiver.
In a typical OWAMP session the Control-Client establishes a TCP
connection to port 861 of the Server, which responds with a server
greeting message indicating supported security/integrity modes. The
Control-Client responds with the chosen communications mode and the
Server accepts the 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
timestamps.
4.6. ITU-T Y.1711 4.6. ITU-T Y.1711
4.6.1. Overview 4.6.1. Overview
As mentioned above (4.3.), the IETF defined LSP Ping as an OAM 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 mechanism for MPLS. The ITU-T has also defined an OAM protocol for
MPLS, defined in [ITU-T Y.1711]. The standard defines mechanisms for MPLS, defined in recommendation [ITU-T Y.1711]. This recommendation
connectivity verification and fast failure detection, as well as defines mechanisms for connectivity verification and fast failure
mechanism for reporting defects that have been identified in an LSP. 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 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 value. The reserved value is 14, and is defined in [OAM Label] as the
'OAM Alert Label'. 'OAM Alert Label'.
4.6.2. Connectivity Verification (CV) 4.6.2. Connectivity Verification (CV)
The CV function is used to detect connectivity defects in an LSP. 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 frames are sent proactively at a rate of 1 per second. Each frame
contains the Trail-Termination Source Identifier (TTSI), indicating contains the Trail-Termination Source Identifier (TTSI), indicating
skipping to change at page 16, line 9 skipping to change at page 19, line 17
The BDI function is used to inform the LSR at an LSP trail The BDI function is used to inform the LSR at an LSP trail
termination source point about a defect condition in the forward termination source point about a defect condition in the forward
direction of an LSP. The LSR at the LSP trail termination sink point direction of an LSP. The LSR at the LSP trail termination sink point
transmits the BDI to the upstream LSR through the return path. BDI transmits the BDI to the upstream LSR through the return path. BDI
packets are sent at the same transmission rate as FDI. packets are sent at the same transmission rate as FDI.
4.7. ITU-T Y.1731 4.7. ITU-T Y.1731
4.7.1. Overview 4.7.1. Overview
The [ITU-T Y.1731] is a protocol for Ethernet OAM. It is presented in The [ITU-T Y.1731] defines a protocol for Ethernet OAM. It is
this document as a reference point, since the OAM mechanisms that are presented in this document as a reference point. Y.1731 defines
currently being defined by the IETF for MPLS-TP are in many ways various OAM functions, including continuity and connectivity
based on this standard. The standard defines various OAM functions, verification, and functions for performance monitoring.
including unidirectional and bidirectional continuity check, and
functions for performance monitoring.
4.7.2. ETH-CC 4.7.2. ETH-CC
The Ethernet Continuity Check function is a proactive function that The Ethernet Continuity Check function is a proactive function that
allows a MEP to detect loss of continuity with any of the other MEPs 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 in the MEG. This function also allows detection of other defect
conditions, such as unintended connectivity between two MEGs. The conditions, such as unintended connectivity between two MEGs. The
ETH-CC function is used for one of three possible applications: fault ETH-CC function is used for one of three possible applications: fault
management, performance monitoring (see 4.6.10.), and protection management, performance monitoring (see 4.6.10.), and protection
switching. switching.
skipping to change at page 20, line 43 skipping to change at page 23, line 43
Link monitoring provides an event notification function, allowing Link monitoring provides an event notification function, allowing
peer devices to communicate defect conditions and diagnostic peer devices to communicate defect conditions and diagnostic
information. information.
4.10. MPLS-TP OAM 4.10. MPLS-TP OAM
4.10.1. Overview 4.10.1. Overview
The MPLS working group is currently working on defining the OAM The MPLS working group is currently working on defining the OAM
requirements and mechanisms for MPLS-TP. The requirements of MPLS-TP toolset that fulfill the requirements for MPLS-TP OAM. The full set
OAM are defined in [MPLS-TP OAM], and are described below. 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.
MPLS-TP OAM traffic uses a Generic Associated Channel (G-ACh), Some of the basic requirements for the OAM toolset for MPLS-TP are:
defined in [G-ACh]. This standard defines that MPLS-TP OAM traffic
uses:
o An Associated Channel Header (ACH), also known as a Control Word o MPLS-TP OAM must be able to support both an IP based and non-IP
in the PWE3 terminology, is a 4-byte header that is added to OAM 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
packets. packets.
o A Generic Associated Label (GAL). The GAL is a reserved MPLS label o A Generic Associated Label (GAL). The GAL is a reserved MPLS label
value. The reserved value is 13, and identifies the packet as an value. The reserved value is 13, and indicates the existence of
MPLS-TP OAM packet. A GAL indicates the existence of the ACH the ACH immediately after it.
immediately after it.
The analysis in [OAM Analysis] discusses various OAM mechanism that 4.10.3. MPLS-TP OAM Toolset
were considered in order to satisfy the requirements in [MPLS-TP
OAM]. The MPLS working group currently plans to use a mixture of OAM 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 mechanisms that are based on various existing standards, and adapt
them to the requirements of [MPLS-TP OAM]. Some of the main building them to the requirements of [MPLS-TP OAM]. Some of the main building
blocks of this solution are based on: blocks of this solution are based on:
o Bidirectional Forwarding Detection ([BFD], [BFD LSP]) for o Bidirectional Forwarding Detection ([BFD], [BFD LSP]) for
proactive connectivity verification. proactive continuity check and connectivity verification.
o LSP Ping as defined in [LSP Ping] for on-demand connectivity o LSP Ping as defined in [LSP Ping] for on-demand connectivity
verification. verification.
o Y.1731 per the [ITU-T Y.1731], mainly for performance measurement. o New protocol packets, using G-ACH, to address different
functionality.
The requirements of MPLS-TP OAM are summarized below. o Performance measurement protocols that are based on the
functionality that is described in [ITU-T Y.1731].
4.10.2. Continuity Checks The following sub-sections describe the OAM tools that will be
defined for MPLS-TP as described in [MPLS-TP OAM FW].
The continuity check is a proactive function that allows an End Point 4.10.3.1. Continuity Check and Connectivity Verification
to determine whether or not it receives traffic from its peer End
Points.
4.10.3. 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.
The connectivity verification is a function that allows an End Point 4.10.3.2. Diagnostic Tests
to verify its connectivity to a peer node. The connectivity check is
performed by sending a connectivity verification PDU to the peer
node, and receiving a reply within an expected time frame. This
function can be performed proactively or on-demand.
4.10.4. 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.
This function allows an End Point to perform an on-demand test, e.g., 4.10.3.3. Route Tracing
for bandwidth measurement.
4.10.5. 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.
This on-demand function is used for path discovery and for locating 4.10.3.4. Lock Instruct
link failures.
4.10.6. 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.
The lock instruct function allows an End Point to instruct its peers 4.10.3.5. Lock Reporting
to enter an administrative status where all traffic is halted except
the test traffic and OAM PDUs.
4.10.7. 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.
This function allows an Intermediate Point to report to an End Point 4.10.3.6. Alarm Reporting
about a lock condition.
4.10.8. 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].
This function allows an Intermediate Point to report to an End Point 4.10.3.7. Remote Defect Indication
about a defect condition.
4.10.9. 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.
This is a proactive function that allows the sender to indicate that 4.10.3.8. Client Failure Indication
it encountered a defect conditions.
4.10.10. 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.
This function allows the MPLS-TP network to relay information about a 4.10.3.9. Packet Loss Measurement
fault condition in a client network, allowing the failure indication
to propagate from end to end over the MPLS-TP network.
4.10.11. 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
source.
This function measures the packet loss ratio between two peer End There are two possible ways of determining this measurement:
Points. It can be performed proactively or on-demand.
4.10.12. Packet Delay 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.
This function measures the frame delay between two peer End Points. o Sending delimiting messages for the start and end of a measurement
Two modes of operation are supported, one-way DM, and two-way DM. period during which the source and sink of the path count the
packets transmitted and received. After the end delimiter, the
ratio would be calculated by the path OAM entity.
4.10.3.10. 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
node.
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 4.11. Summary of OAM Functions
Table 3 summarizes the OAM functions that are supported in each of Table 3 summarizes the OAM functions that are supported in each of
the standards that were analyzed in this section. the standards that were analyzed in this section.
+-----------+-------+--------+--------+-----------+-------+--------+ +-----------+-------+--------+--------+-----------+-------+--------+
| Standard |Unidire|Bidirect|Path |Defect |Perform|Other | | Standard |Continu|Connecti|Path |Defect |Perform|Other |
| |ctional|ional |Discover|Indications|ance |Function| | |ity |vity |Discover|Indications|ance |Function|
| |Connect|Connecti|y | |Monitor|s | | |Check |Verifica|y | |Monitor|s |
| |ivity |vity | | |ing | | | | |tion | | |ing | |
| |Check |Check | | | | |
+-----------+-------+--------+--------+-----------+-------+--------+ +-----------+-------+--------+--------+-----------+-------+--------+
|ICMP Ping | | Echo | | | | | |ICMP Ping | |Echo | | | | |
+ --------- + ----- + ------ + ------ + --------- + ----- + ------ + + --------- + ----- + ------ + ------ + --------- + ----- + ------ +
|BFD |BFD |BFD | | | | | |BFD |BFD |BFD | | | | |
| |Control|Echo | | | | | | |Control|Echo | | | | |
+ --------- + ----- + ------ + ------ + --------- + ----- + ------ + + --------- + ----- + ------ + ------ + --------- + ----- + ------ +
|LSP Ping | |"Ping" |"Tracero| | | | |LSP Ping | |"Ping" |"Tracero| | | |
| | |mode |ute" | | | | | | |mode |ute" | | | |
| | | |mode | | | | | | | |mode | | | |
+ --------- + ----- + ------ + ------ + --------- + ----- + ------ + + --------- + ----- + ------ + ------ + --------- + ----- + ------ +
|PW VCCV | |VCCV | | | | | |PW VCCV | |VCCV | | | | |
+ --------- + ----- + ------ + ------ + --------- + ----- + ------ + + --------- + ----- + ------ + ------ + --------- + ----- + ------ +
skipping to change at page 24, line 16 skipping to change at page 29, line 5
|OAM | | |Tracing | Reporting |-DM | tic Tes| |OAM | | |Tracing | Reporting |-DM | tic Tes|
| | | | |-Client | | s | | | | | |-Client | | s |
| | | | | Failure | |-Lock | | | | | | Failure | |-Lock |
| | | | | Indication| | | | | | | | Indication| | |
| | | | |-Remote | | | | | | | |-Remote | | |
| | | | | Defect | | | | | | | | Defect | | |
| | | | | Indication| | | | | | | | Indication| | |
+-----------+-------+--------+--------+-----------+-------+--------+ +-----------+-------+--------+--------+-----------+-------+--------+
Table 3 Summary of OAM Functions Table 3 Summary of OAM Functions
4.12. Summary of Unidirectional Connectivity Check Mechanisms 4.12. Summary of Continuity Check Mechanisms
A key element in some of the OAM standards that are analyzed in this A key element in some of the OAM standards that are analyzed in this
document is the unidirectional connectivity check. It is thus document is the continuity check. It is thus interesting to present a
interesting to present a more detailed comparison of the connectivity more detailed comparison of the connectivity check mechanisms defined
check mechanisms defined in OAM standards. Table 4 can be viewed as in OAM standards. Table 4 can be viewed as an extension of Table 3,
an extension of Table 3, but is presented separately for convenience. but is presented separately for convenience. The table compares the
The table compares the OAM standards that support a unidirectional OAM standards that support a continuity check. MPLS-TP is not
connectivity check. MPLS-TP is not included in the comparison, as the included in the comparison, as the continuity check mechanism in
continuity check mechanism in MPLS-TP has not yet been defined. MPLS-TP has not yet been defined.
The "Tx Interval" column in the table specifies the period between The "Tx Interval" column in the table specifies the period between
two consequent message transmissions, while the "Source Identifier" two consequent message transmissions, while the "Source Identifier"
column specifies the name of the field in the OAM packet that is used column specifies the name of the field in the OAM packet that is used
as the identifier of the transmitter. The "Error Codes" column as the identifier of the transmitter. The "Error Codes" column
specifies the possible error codes when the unidirectional specifies the possible error codes when the unidirectional
connectivity check detects a failure. connectivity check detects a failure.
+-----------+-------+--------+---+--------+------------------------+ +-----------+-------+--------+---+--------+------------------------+
| |Mechani|Tx |UC/|Source | Error | | |Mechani|Tx |UC/|Source | Error |
skipping to change at page 28, line 7 skipping to change at page 32, line 39
[ITU-T Y.1711]"Operation & Maintenance mechanism for MPLS networks", [ITU-T Y.1711]"Operation & Maintenance mechanism for MPLS networks",
February 2004. February 2004.
[IEEE 802.3ah]"Media Access Control Parameters, Physical Layers, and [IEEE 802.3ah]"Media Access Control Parameters, Physical Layers, and
Management Parameters for Subscriber Access Networks", Management Parameters for Subscriber Access Networks",
clause 57, September 2004. clause 57, September 2004.
8.2. Informative References 8.2. Informative References
[P2MP Ping] Saxena, S., Farrel, A. , Yasukawa, S., "Detecting Data
Plane Failures in Point-to-Multipoint Multiprotocol
Label Switching (MPLS) - Extensions to LSP Ping",
draft-ietf-mpls-p2mp-lsp-ping, March 2010.
[OAM Soup] Andersson, L., Van Helvoort, H., Bonica, R., Romascanu, [OAM Soup] Andersson, L., Van Helvoort, H., Bonica, R., Romascanu,
D., Mansfield, S., "The OAM Acronym Soup", draft-ietf- D., Mansfield, S., "The OAM Acronym Soup", draft-ietf-
opsawg-mpls-tp-oam-def, June 2010. opsawg-mpls-tp-oam-def, June 2010.
[ITU-T G.806] "Characteristics of transport equipment - Description [OAM Analysis] Sprecher, N., Bellagamba, E., Weingarten, Y., "MPLS-TP
methodology and generic functionality", January 2009. OAM Analysis", draft-ietf-mpls-tp-oam-analysis, July
2010.
[MPLS-TP OAM FW] Busi, I., Niven-Jenkins, B., Allan, D., "MPLS-TP OAM
Framework", work-in-progress, draft-ietf-mpls-tp-oam-
framework, July, 2010.
[MPLS-TP Term]Van Helvoort, H., Andersson, L., Sprecher, N., "A [MPLS-TP Term]Van Helvoort, H., Andersson, L., Sprecher, N., "A
Thesaurus for the Terminology used in Multiprotocol Thesaurus for the Terminology used in Multiprotocol
Label Switching Transport Profile (MPLS-TP) Label Switching Transport Profile (MPLS-TP)
drafts/RFCs and ITU-T's Transport Network drafts/RFCs and ITU-T's Transport Network
Recommendations", draft-ietf-mpls-tp-rosetta-stone, Recommendations", draft-ietf-mpls-tp-rosetta-stone,
May 2010. May 2010.
[MPLS-TP Ping BFD] Bahadur, N., Aggarwal, R., Ward, D., Nadeau, T., [MPLS-TP Ping BFD] Bahadur, N., Aggarwal, R., Ward, D., Nadeau, T.,
Sprecher, N., Weingarten, Y., "LSP-Ping and BFD Sprecher, N., Weingarten, Y., "LSP-Ping and BFD
encapsulation over ACH", draft-ietf-mpls-tp-lsp-ping- encapsulation over ACH", draft-ietf-mpls-tp-lsp-ping-
bfd-procedures, March 2010. bfd-procedures, March 2010.
[OAM Analysis] Sprecher, N., Bellagamba, E., Weingarten, Y., "MPLS-TP [P2MP Ping] Saxena, S., Farrel, A. , Yasukawa, S., "Detecting Data
OAM Analysis", draft-ietf-mpls-tp-oam-analysis, July Plane Failures in Point-to-Multipoint Multiprotocol
2010. Label Switching (MPLS) - Extensions to LSP Ping",
draft-ietf-mpls-p2mp-lsp-ping, March 2010.
[ITU-T G.806] "Characteristics of transport equipment - Description
methodology and generic functionality", January 2009.
Authors' Addresses Authors' Addresses
Tal Mizrahi Tal Mizrahi
Marvell Marvell
6 Hamada St.
Yokneam, 20692
Israel
Email: talmi@marvell.com Email: talmi@marvell.com
Nurit Sprecher
Nokia Siemens Networks
3 Hanagar St. Neve Ne'eman B
Hod Hasharon, 45241
Israel
Email: nurit.sprecher@nsn.com
Elisa Bellagamba
Ericsson
6 Farogatan St.
Stockholm, 164 40
Sweden
Phone: +46 761440785
Email: elisa.bellagamba@ericsson.com
Yaacov Weingarten
Nokia Siemens Networks
3 Hanagar St. Neve Ne'eman B
Hod Hasharon, 45241
Israel
Phone: +972-9-775 1827
Email: yaacov.weingarten@nsn.com
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