Requirements for OAM in MPLS Transport Networks
draft-ietf-mpls-tp-oam-requirements-03

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Abstract

This document lists architectural and functional requirements for the Operations, Administration and Maintenance of MPLS Transport Profile. These requirements apply to pseudowires, Label Switched Paths, and Sections.

Table of Contents

1.  Introduction
    1.1.  Scope of this Document
    1.2.  Requirements Language and Terminology
2.  OAM Requirements
    2.1.  Architectural Requirements
        2.1.1.  Scope of OAM
        2.1.2.  Independence
        2.1.3.  OAM and IP Capabilities
        2.1.4.  Interoperability and Interworking
        2.1.5.  Data Plane
        2.1.6.  Configuration
    2.2.  Functional Requirements
        2.2.1.  General Requirements
        2.2.2.  Continuity Checks
        2.2.3.  Connectivity Verifications
        2.2.4.  Diagnostic Tests
        2.2.5.  Route Tracing
        2.2.6.  Lock Instruct
        2.2.7.  Lock Reporting
        2.2.8.  Alarm Reporting
        2.2.9.  Remote Defect Indication
        2.2.10.  Client Failure Indication
        2.2.11.  Packet Loss Measurement
        2.2.12.  Packet Delay Measurement
3.  Congestion Considerations
4.  Security Considerations
5.  IANA Considerations
6.  Acknowledgements
7.  References
    7.1.  Normative References
    7.2.  Informative References
§  Authors' Addresses

1.  Introduction

In the context of MPLS Transport Profile (MPLS-TP, see [5] (Bocci, M., Bryant, S., Frost, D., Levrau, L., and L. Berger, “A Framework for MPLS in Transport Networks,” April 2010.) and [6] (Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., and S. Ueno, “MPLS-TP Requirements,” August 2009.)), the rationales for Operations, Administration and Maintenance (OAM) are twofold as it can serve:

• as a network-oriented functionality, used by a transport network operator to monitor his network infrastructure and to implement internal mechanisms in order to enhance the general behaviour and the level of performance of his network (e.g., protection mechanism in case of node or link failure). As an example, fault localization is typically associated with this use case.
• as a service-oriented functionality, used by a transport service provider to monitor services offered to end customers in order to be able to react rapidly in case of a problem and to be able to verify some of the Service Level Agreements (SLAs) parameters (e.g., using performance monitoring) negotiated with the end customers. Note that a transport service could be provided over several networks or administrative domains that may not all be owned and managed by the same transport service provider.

More generally, OAM is an important and fundamental functionality in transport networks as it contributes to:

• the reduction of operational complexity and costs, by allowing for efficient and automatic detection, localisation, handling and diagnosis of defects, as well as by minimizing service interruptions and operational repair times.
• the enhancement of network availability, by ensuring that defects, for example resulting in misdirected customer traffic, and faults, are detected, diagnosed and dealt with before a customer reports the problem.
• meeting service and performance objectives, as the OAM functionality allows for SLA verification in a multi-maintenance domain environment and allows for the determination of service degradation due, for example, to packet delay or packet loss.

1.1.  Scope of this Document

This document lists architectural and functional requirements for the OAM functionality of MPLS-TP. These requirements apply to pseudowires (PWs), Label Switched Paths (LSPs) and Sections.

These requirements are derived from the set of requirements specified by ITU-T and published in the ITU-T Supplement Y.Sup4 [7] (ITU-T Supplement Y.Sup4, “ITU-T Y.1300-series: Supplement on transport requirements for T-MPLS OAM and considerations for the application of IETF MPLS technology,” 2008.).

By covering transport specificities, these requirements complement those identified in RFC 4377 [8] (Nadeau, T., Morrow, M., Swallow, G., Allan, D., and S. Matsushima, “Operations and Management (OAM) Requirements for Multi-Protocol Label Switched (MPLS) Networks,” February 2006.), yet some requirements may be similar.

This document only lists architectural and functional OAM requirements. It does not detail the implications of their applicability to the various types (e.g., point-to-point, point-to-multipoint, unidirectional, bidirectional ...) of PWs, LSPs and Sections. Furthermore, this document does not provide requirements on how the protocol solution(s) should behave to achieve the functional objectives. Please see [9] (Allan, D., Busi, I., Niven-Jenkins, B., Fulignoli, A., Hernandez-Valencia, E., Levrau, L., Mohan, D., Sestito, V., Sprecher, N., Helvoort, H., Vigoureux, M., Weingarten, Y., and R. Winter, “MPLS-TP OAM Framework,” April 2010.) for further information.

Note that the OAM functions identified in this document may be used for fault management, performance monitoring and/or protection switching applications. For example, connectivity verification can be used for fault management by detecting failure conditions, but may also be used for performance monitoring through its contribution to the evaluation of performance metrics (e.g., unavailability time). Nevertheless, it is outside the scope of this document to specify which function should be used for which application.

1.2.  Requirements Language and Terminology

Although this document is not a protocol specification, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in RFC 2119 [1] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) and are to be interpreted as instructions to the protocol designers producing solutions that satisfy the requirements set out in this document.

In this document we refer to the inability of a function to perform a required action, as a fault. This does not include an inability due to preventive maintenance, lack of external resources, or planned actions. See also ITU-T G.806 [2] (ITU-T Recommendation G.806, “Characteristics of transport equipment - Description methodology and generic functionality,” 2009.).

In this document we refer to the situation in which the density of anomalies has reached a level where the ability to perform a required function has been interrupted, as a defect. See also ITU-T G.806 [2] (ITU-T Recommendation G.806, “Characteristics of transport equipment - Description methodology and generic functionality,” 2009.).

In this document we refer to a Label Edge Router (LER), for a given LSP or Section, and to a PW Terminating Provider Edge (T-PE), for a given PW, as an End Point. Further, we refer to a Label Switching Router (LSR), for a given LSP, and to a PW Switching Provider Edge (S-PE), for a given PW, as an Intermediate Point. This document does not make a distinction between End Points (e.g., source and destination) as it can be inferred from the context of the sentences.

In this document we use the term "node" as a general reference to End Points and Intermediate Points.

In this document we refer to both segment and concatenated segments as segments (see [6] (Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., and S. Ueno, “MPLS-TP Requirements,” August 2009.) for definitions relating to the term "segment" as well as for other definitions relating to MPLS-TP).

In this document we refer to both single segment PWs and multi-segment PWs as PWs.

In this document we refer to both bidirectional associated LSPs and bidirectional co-routed LSPs as bidirectional LSPs.

2.  OAM Requirements

This section lists the requirements by which the OAM functionality of MPLS-TP should abide.

The requirements listed below may be met by one or more OAM protocols; the definition or selection of these protocols is outside the scope of this document.

2.1.  Architectural Requirements

2.1.1.  Scope of OAM

The protocol solution(s) developed to meet the requirements identified in this document MUST at least be applicable to point-to-point bidirectional PWs, point-to-point co-routed bidirectional LSPs, and point-to-point bidirectional Sections. Section 2.2 (Functional Requirements) provides additional information with regards to the applicability to point-to-point associated bidirectional LSPs, point-to-point undirectional LSPs and point-to-multipoint LSPs.

The service emulated by a PW may span multiple domains. An LSP may also span multiple domains. The protocol solution(s) MUST be applicable end-to-end and to segments. More generally, it MUST be possible to operate OAM functions on a per domain basis and across multiple domains.

Since LSPs may be stacked, the protocol solution(s) MUST be applicable on any LSP, regardless of the label stack depth. Furthermore it MUST be possible to estimate OAM fault and performance metrics of a single PW or LSP segment or of an aggregate of PWs or LSPs segments.

2.1.2.  Independence

The protocol solution(s) SHOULD be independent of the underlying tunnelling or point-to-point technology or transmission media.

The protocol solution(s) SHOULD be independent of the service a PW may emulate.

Any OAM function operated on a PW, LSP or Section SHOULD be independent of the OAM function(s) operated on a different PW, LSP or Section. In other words, only the OAM functions operated on e.g., a given LSP should be used to achieve the OAM objectives for that LSP.

The protocol solution(s) MUST support the capability to be concurrently and independently operated end-to-end and on segments. Therefore, any OAM function applied to segment(s) of a PW or LSP SHOULD be independent of the OAM function(s) operated on the end-to-end PW or LSP. It SHOULD also be possible to distinguish an OAM packet running over a segment of a PW or LSP from another OAM packet running on the end-to-end PW or LSP.

Furthermore, any OAM function applied to segment(s) of a PW or LSP SHOULD be independent of the OAM function(s) applied to other segment(s) of the same PW or LSP.

Note:

Independence should not be understood in terms of isolation as there can be interactions between OAM functions operated on e.g., an LSP, and on another LSP or a PW.

2.1.3.  OAM and IP Capabilities

The OAM functionality may be deployed in various environments.

• In some environments (e.g., IP/MPLS environments), IP routing and forwarding capabilities are inherently present in the data plane.
• In some environments (e.g., MPLS-TP environments), IP routing and forwarding capabilities may not necessarily be present in the data plane.

In the former case, it MUST be possible to operate the OAM functions by relying on IP routing and forwarding capabilities (e.g., encapsulation in IP header for (de)multiplexing purposes) while in the latter case it MUST be possible to operate the OAM functions without relying on IP routing and forwarding capabilities.

For certain functions, OAM messages need to incorporate identification information (e.g., of source and/or destination nodes). The protocol solution(s) MUST at least support identification information in the form of an IP addressing structure and MUST also be extensible to support additional identification schemes.

2.1.4.  Interoperability and Interworking

It is REQUIRED that OAM interoperability is achieved between distinct domains materializing the environments described in Section 2.1.3 (OAM and IP Capabilities). It is also REQUIRED that the first two requirements of Section 2.1.3 (OAM and IP Capabilities) still hold and MUST still be met when interoperability is achieved.

When MPLS-TP is run with IP routing and forwarding capabilities, it MUST be possible to operate any of the existing IP/MPLS and PW OAM protocols (e.g., LSP-Ping [3] (Kompella, K. and G. Swallow, “Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures,” February 2006.), MPLS-BFD [10] (Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, “BFD For MPLS LSPs,” June 2008.), VCCV [4] (Nadeau, T. and C. Pignataro, “Pseudowire Virtual Circuit Connectivity Verification (VCCV): A Control Channel for Pseudowires,” December 2007.) and VCCV-BFD [11] (Nadeau, T. and C. Pignataro, “Bidirectional Forwarding Detection (BFD) for the Pseudowire Virtual Circuit Connectivity Verification (VCCV),” July 2009.)).

2.1.5.  Data Plane

OAM functions operate in the data plane. OAM packets MUST run in-band; that is, OAM packets for a specific PW, LSP or Section MUST follow the exact same data path as user traffic of that PW, LSP or Section. This is often referred to as fate sharing.

It MUST be possible to discriminate user traffic from OAM packets. This includes a means to differentiate OAM packets from user traffic as well as the capability to apply specific treatment to OAM packets, at the nodes processing these OAM packets.

As part of the design of OAM protocol solution(s) for MPLS-TP, a mechanism, for enabling the encapsulation and differentiation of OAM messages on a PW, LSP or Section, MUST be provided. Such mechanism SHOULD also support the encapsulation and differentiation of existing IP/MPLS and PW OAM messages.

2.1.6.  Configuration

OAM functions MUST operate and be configurable even in the absence of a control plane. Conversely, it SHOULD be possible to configure as well as enable/disable the capability to operate OAM functions as part of connectivity management and it SHOULD also be possible to configure as well as enable/disable the capability to operate OAM functions after connectivity has been established.

In the latter case, the customer MUST NOT perceive service degradation as a result of OAM enabling/disabling. Ideally OAM enabling/disabling should take place without introducing any customer impairments (e.g., no customer packet losses). Procedures aimed to prevent any traffic impairment MUST be defined for the enabling/disabling of OAM functions.

Means for configuring OAM functions and for connectivity management are outside the scope of this document.

2.2.  Functional Requirements

Hereafter are listed the required functionalities composing the MPLS-TP OAM toolset. The list may not be exhaustive and as such the OAM mechanisms developed in support of the identified requirements SHALL be extensible and thus SHALL NOT preclude the definition of additional OAM functionalities, in the future.

The design of OAM mechanisms for MPLS-TP, MUST allow for the ability to support experimental OAM functions. These functions MUST be disabled by default.

The use of any OAM function MUST be optional and it MUST be possible to select the set of OAM function(s) to use on any PW, LSP or Section.

It is RECOMMENDED that any protocol solution, meeting one or more functional requirement(s), be the same for PWs, LSPs and Sections.

It is RECOMMENDED that any protocol solution, meeting one or more functional requirement(s), effectively provides a fully featured function; that is, a function which is applicable to all the cases identified for that functionality. In that context, protocol solution(s) MUST state their applicability.

Unless otherwise stated, the OAM functionalities MUST NOT rely on user traffic; that is, only OAM messages MUST be used to achieve the objectives.

2.2.1.  General Requirements

If a defect or fault occurs on a PW, LSP or Section, mechanisms MUST be provided to detect it, diagnose it, localize it, and notify the appropriate nodes. Mechanisms SHOULD exist such that corrective actions can be taken.

Furthermore, mechanisms MUST be available for a service provider to be aware of a fault or defect affecting the service(s) he provides, even if the fault or defect is located outside of his domain.

Protocol solution(s) developed to meet these requirements may rely on information exchange. Information exchange between various nodes involved in the operation of an OAM function SHOULD be reliable such that, for example, defects or faults are properly detected or that state changes are effectively known by the appropriate nodes.

2.2.2.  Continuity Checks

The MPLS-TP OAM toolset MUST provide a function to enable an End Point to determine whether or not it receives traffic on a PW, LSP or Section.

This function SHOULD be performed between End Points of PWs, LSPs and Sections.

This function SHOULD be performed pro-actively.

The protocol solution(s) developed to perform this function MUST also apply to point-to-point associated bidirectional LSPs, point-to-point unidirectional LSPs and point-to-multipoint LSPs.

2.2.3.  Connectivity Verifications

The MPLS-TP OAM toolset MUST provide a function to enable an End Point of a PW, LSP or Section to determine whether or not the connectivity provided to an other node through a PW, LSP or Section is effective (i.e., that a packet sent on that PW, LSP or Section, reaches the expected node).

This function SHOULD be performed pro-actively between End Points of PWs, LSPs and Sections.

This function SHOULD be performed on-demand between End Points and Intermediate Points of PWs and LSPs, and between End Points of PWs, LSPs and Sections.

The protocol solution(s) developed to perform this function pro-actively MUST also apply to point-to-point associated bidirectional LSPs, point-to-point unidirectional LSPs and point-to-multipoint LSPs.

The protocol solution(s) developed to perform this function on-demand MAY also apply to point-to-point associated bidirectional LSPs, to point-to-point unidirectional LSPs and point-to-multipoint LSPs in case a return path exists.

2.2.4.  Diagnostic Tests

The MPLS-TP OAM toolset MUST provide a function to enable conducting diagnostic tests on a PW, LSP or Section. An example of such diagnostic test consists in looping the traffic at an Intermediate Point back to the originating End Point. Another example of such diagnostic test consists in estimating the bandwidth of e.g., an LSP.

This function SHOULD be performed on-demand.

This function SHOULD be performed between End Points and Intermediate Points of PWs and LSPs, and between End Points of PWs, LSPs and Sections.

The protocol solution(s) developed to perform this function MAY also apply to point-to-point associated bidirectional LSPs, to point-to-point unidirectional LSPs and point-to-multipoint LSPs in case a return path exists.

2.2.5.  Route Tracing

The MPLS-TP OAM toolset MUST provide functionality to enable an End Point to discover the Intermediate (if any) and End Point(s) along a PW, LSP or Section, and more generally to trace the route of a PW, LSP or Section. The information collected MUST include identifiers related to the nodes and interfaces composing that route.

This function SHOULD be performed on-demand.

This function SHOULD be performed between End Points and Intermediate Points of PWs and LSPs, and between End Points of PWs, LSPs and Sections.

The protocol solution(s) developed to perform this function MAY also apply to point-to-point associated bidirectional LSPs, to point-to-point unidirectional LSPs and point-to-multipoint LSPs in case a return path exists.

2.2.6.  Lock Instruct

The MPLS-TP OAM toolset MUST provide functionality to enable an End Point of a PW, LSP or Section to instruct its associated End Point(s) to lock the PW, LSP or Section. Note that lock corresponds to an administrative status in which it is expected that only test traffic, if any, and OAM (dedicated to the PW, LSP or Section) can be mapped on that PW, LSP or Section.

This function SHOULD be performed on-demand.

This function SHOULD be performed between End Points of PWs, LSPs and Sections.

The protocol solution(s) developed to perform this function MUST also apply to point-to-point associated bidirectional LSPs, point-to-point unidirectional LSPs and point-to-multipoint LSPs.

2.2.7.  Lock Reporting

Based on the tunnelling capabilities of MPLS, there are cases where Intermediate Point(s) of a PW or of an LSP coincide with End Point(s) of another LSP on which the former is mapped/tunnelled. Further, it may happen that the tunnel LSP be out of service as a result of a lock action on that tunnel LSP. By means outside of the scope of this document, the Intermediate Point(s) of the PW or LSP may be aware of this condition. The MPLS-TP OAM toolset MUST provide a function to enable an Intermediate Point of a PW or LSP to report, to an End Point of that same PW or LSP, a lock condition indirectly affecting that PW or LSP.

This function SHOULD be performed pro-actively.

This function SHOULD be performed between Intermediate Points and End Points of PWs and LSPs.

The protocol solution(s) developed to perform this function MUST also apply to point-to-point associated bidirectional LSPs, point-to-point unidirectional LSPs and point-to-multipoint LSPs.

2.2.8.  Alarm Reporting

Based on the tunnelling capabilities of MPLS, there are cases where Intermediate Point(s) of a PW or of an LSP coincide with End Point(s) of another LSP on which the former is mapped/tunnelled. Further, it may happen that the tunnel LSP be out of service as a result of a fault on that tunnel LSP. By means outside of the scope of this document, the Intermediate Point(s) of the PW or LSP may be aware of this condition. The MPLS-TP OAM toolset MUST provide functionality to enable an Intermediate Point of a PW or LSP to report, to an End Point of that same PW or LSP, a fault or defect condition indirectly affecting that PW or LSP.

This function SHOULD be performed pro-actively.

This function SHOULD be performed between Intermediate Points and End Points of PWs and LSPs.

The protocol solution(s) developed to perform this function MUST also apply to point-to-point associated bidirectional LSPs, point-to-point unidirectional LSPs and point-to-multipoint LSPs.

2.2.9.  Remote Defect Indication

The MPLS-TP OAM toolset MUST provide a function to enable an End Point to report, to its associated End Point, a fault or defect condition that it detects on a PW, LSP or Section for which they are the End Points.

This function SHOULD be performed pro-actively.

This function SHOULD be performed between End Points of PWs, LSPs and Sections.

The protocol solution(s) developed to perform this function MUST also apply to point-to-point associated bidirectional LSPs and MAY also apply to point-to-point unidirectional LSPs and point-to-multipoint LSPs in case a return path exists.

2.2.10.  Client Failure Indication

The MPLS-TP OAM toolset MUST provide a function to enable the propagation, from edge to edge of an MPLS-TP network, of information pertaining to a client (i.e., external to the MPLS-TP network) defect or fault condition detected at an End Point of a PW or LSP, if the client layer OAM functionality does not provide an alarm notification/propagation functionality.

This function SHOULD be performed pro-actively.

This function SHOULD be performed between End Points of PWs and LSPs.

The protocol solution(s) developed to perform this function MUST also apply to point-to-point associated bidirectional LSPs, point-to-point unidirectional LSPs and point-to-multipoint LSPs.

2.2.11.  Packet Loss Measurement

The MPLS-TP OAM toolset MUST provide a function to enable the quantification of packet loss ratio over a PW, LSP or Section.

Note that packet loss ratio is the ratio of the user packets not delivered to the total number of user packets transmitted during a defined time interval. The number of user packets not delivered is the difference between the number of user packets transmitted by an End Point and the number of user packets received at an End Point.

This function MAY either be performed pro-actively or on-demand.

This function SHOULD be performed between End Points of PWs, LSPs and Sections.

It SHOULD be possible to rely on user traffic to perform that functionality.

The protocol solution(s) developed to perform this function MUST also apply to point-to-point associated bidirectional LSPs, point-to-point unidirectional LSPs and point-to-multipoint LSPs.

2.2.12.  Packet Delay Measurement

The MPLS-TP OAM toolset MUST provide a function to enable the quantification of the one-way, and if appropriate, the two-way, delay of a PW, LSP or Section.

• One-way delay is the time elapsed from the start of transmission of the first bit of a packet by an End Point until the reception of the last bit of that packet by the other End Point.
• Two-way delay is the time elapsed from the start of transmission of the first bit of a packet by a End Point until the reception of the last bit of that packet by the same End Point, when loopback is performed at the other End Point.

This function SHOULD be performed on-demand and MAY be performed pro-actively.

This function SHOULD be performed between End Points of PWs, LSPs and Sections.

The protocol solution(s) developed to perform this function MUST also apply to point-to-point associated bidirectional LSPs, point-to-point unidirectional LSPs and point-to-multipoint LSPs but only to enable the quantification of the one-way delay.

3.  Congestion Considerations

A mechanism (e.g., rate limiting) MUST be provided to prevent OAM packets from causing congestion in the Packet Switched Network.

4.  Security Considerations

This document, in itself, does not imply any security consideration but OAM, as such, is subject to several security considerations. OAM messages can reveal sensitive information such as passwords, performance data and details about e.g., the network topology.

The nature of OAM therefore suggests having some form of authentication, authorization and encryption in place. This will prevent unauthorized access to MPLS-TP equipment and it will prevent third parties from learning about sensitive information about the transport network.

In general, mechanisms SHOULD be provided to ensure that OAM functions cannot be accessed unauthorized.

Further, OAM messages MAY be authenticated to prove their origin and to make sure that they are destined for the receiving node.

An OAM packet received over a PW, LSP or Section MUST NOT be forwarded beyond the End Point of that PW, LSP or Section, so as to avoid that the OAM packet leaves the current administrative domain.

5.  IANA Considerations

There are no IANA actions required by this draft.

6.  Acknowledgements

The editors gratefully acknowledge the contributions of Matthew Bocci, Italo Busi, Thomas Dietz, Annamaria Fulignoli, Huub van Helvoort, Wataru Imajuku, Marc Lasserre, Lieven Levrau, Han Li, Julien Meuric, Philippe Niger, Benjamin Niven-Jenkins, Jing Ruiquan, Nurit Sprecher, Yuji Tochio, Satoshi Ueno and Yaacov Weingarten.

The authors would like to thank all members of the teams (the Joint Working Team, the MPLS Interoperability Design Team in IETF and the MPLS-TP Ad Hoc Group in ITU-T) involved in the definition and specification of MPLS-TP.

7.  References

7.1. Normative References

7.2. Informative References

Authors' Addresses