Operations, Administration, and Maintenance Framework for MPLS-Based Transport Networks
draft-ietf-mpls-tp-oam-framework-11
The information below is for an old version of the document that is already published as an RFC.
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| Authors | David Allan , Italo Busi | ||
| Last updated | 2020-01-21 (Latest revision 2011-02-11) | ||
| Replaces | draft-busi-mpls-tp-oam-framework | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Informational | ||
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draft-ietf-mpls-tp-oam-framework-11
MPLS Working Group I. Busi (Ed)
Internet Draft Alcatel-Lucent
Intended status: Informational D. Allan (Ed)
Ericsson
Expires: August 11, 2011 February 11, 2011
Operations, Administration and Maintenance Framework for
MPLS-based Transport Networks
draft-ietf-mpls-tp-oam-framework-11.txt
Abstract
The Transport Profile of Multi-Protocol Label Switching
(MPLS-TP) is a packet-based transport technology based on the
MPLS Traffic Engineering (MPLS-TE) and Pseudowire (PW) data
plane architectures.
This document describes a framework to support a comprehensive
set of Operations, Administration and Maintenance (OAM)
procedures that fulfill the MPLS-TP OAM requirements for fault,
performance and protection-switching management and that do not
rely on the presence of a control plane.
This document is a product of a joint Internet Engineering Task
Force (IETF) / International Telecommunications Union
Telecommunication Standardization Sector (ITU-T) effort to
include an MPLS Transport Profile within the IETF MPLS and PWE3
architectures to support the capabilities and functionalities of
a packet transport network as defined by the ITU-T.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance
with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet
Engineering Task Force (IETF), its areas, and its working
groups. Note that other groups may also distribute working
documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other
documents at any time. It is inappropriate to use Internet-
Drafts as reference material or to cite them other than as "work
in progress".
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The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
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This Internet-Draft will expire on August 11, 2011.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with
respect to this document. Code Components extracted from this
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without warranty as described in the Simplified BSD License.
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Table of Contents
1. Introduction..................................................5
1.1. Contributing Authors.....................................7
2. Conventions used in this document.............................7
2.1. Terminology..............................................7
2.2. Definitions..............................................9
3. Functional Components........................................12
3.1. Maintenance Entity and Maintenance Entity Group.........12
3.2. MEG Nesting: SPMEs and Tandem Connection Monitoring.....14
3.3. MEG End Points (MEPs)...................................16
3.4. MEG Intermediate Points (MIPs)..........................20
3.5. Server MEPs.............................................22
3.6. Configuration Considerations............................23
3.7. P2MP considerations.....................................23
3.8. Further considerations of enhanced segment monitoring...24
4. Reference Model..............................................26
4.1. MPLS-TP Section Monitoring (SMEG).......................28
4.2. MPLS-TP LSP End-to-End Monitoring Group (LMEG)..........29
4.3. MPLS-TP PW Monitoring (PMEG)............................29
4.4. MPLS-TP LSP SPME Monitoring (LSMEG).....................30
4.5. MPLS-TP MS-PW SPME Monitoring (PSMEG)...................31
4.6. Fate sharing considerations for multilink...............33
5. OAM Functions for proactive monitoring.......................33
5.1. Continuity Check and Connectivity Verification..........34
5.1.1. Defects identified by CC-V.........................37
5.1.2. Consequent action..................................39
5.1.3. Configuration considerations.......................40
5.2. Remote Defect Indication................................42
5.2.1. Configuration considerations.......................43
5.3. Alarm Reporting.........................................43
5.4. Lock Reporting..........................................44
5.5. Packet Loss Measurement.................................46
5.5.1. Configuration considerations.......................47
5.5.2. Sampling skew......................................48
5.5.3. Multilink issues...................................48
5.6. Packet Delay Measurement................................48
5.6.1. Configuration considerations.......................49
5.7. Client Failure Indication...............................49
5.7.1. Configuration considerations.......................50
6. OAM Functions for on-demand monitoring.......................50
6.1. Connectivity Verification...............................51
6.1.1. Configuration considerations.......................52
6.2. Packet Loss Measurement.................................52
6.2.1. Configuration considerations.......................53
6.2.2. Sampling skew......................................53
6.2.3. Multilink issues...................................53
6.3. Diagnostic Tests........................................53
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6.3.1. Throughput Estimation..............................53
6.3.2. Data plane Loopback................................55
6.4. Route Tracing...........................................57
6.4.1. Configuration considerations.......................57
6.5. Packet Delay Measurement................................57
6.5.1. Configuration considerations.......................58
7. OAM Functions for administration control.....................58
7.1. Lock Instruct...........................................58
7.1.1. Locking a transport path...........................59
7.1.2. Unlocking a transport path.........................59
8. Security Considerations......................................60
9. IANA Considerations..........................................61
10. Acknowledgments.............................................61
11. References..................................................62
11.1. Normative References...................................62
11.2. Informative References.................................63
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Editors' Note:
This Informational Internet-Draft is aimed at achieving IETF
Consensus before publication as an RFC and will be subject to an
IETF Last Call.
[RFC Editor, please remove this note before publication as an
RFC and insert the correct Streams Boilerplate to indicate that
the published RFC has IETF Consensus.]
1. Introduction
As noted in the multi-protocol label switching (MPLS-TP) Framework
RFCs (RFC 5921 [8] and [9]), MPLS-TP is a packet-based transport
technology based on the MPLS Traffic Engineering (MPLS-TE) and Pseudo
Wire (PW) data plane architectures defined in RFC 3031 [1], RFC 3985
[2] and RFC 5659 [4].
MPLS-TP supports a comprehensive set of Operations,
Administration and Maintenance (OAM) procedures for fault,
performance and protection-switching management that do not rely
on the presence of a control plane.
In line with [15], existing MPLS OAM mechanisms will be used
wherever possible and extensions or new OAM mechanisms will be
defined only where existing mechanisms are not sufficient to
meet the requirements. Some extensions discussed in this
framework may end up as aspirational capabilities and may be
determined to be not tractably realizable in some
implementations. Extensions do not deprecate support for
existing MPLS OAM capabilities.
The MPLS-TP OAM framework defined in this document provides a
protocol neutral description of the required OAM functions and
of the data plane OAM architecture to support a comprehensive
set of OAM procedures that satisfy the MPLS-TP OAM requirements
of RFC 5860 [11]. In this regard, it defines similar OAM
functionality as for existing SONET/SDH and OTN OAM mechanisms
(e.g. [19]).
The MPLS-TP OAM framework is applicable to sections, Label
Switched Paths (LSPs), Multi-Segment Pseudowires (MS-)PWs and
Sub Path Maintenance Entities (SPMEs). It supports co-routed and
associated bidirectional p2p transport paths as well as
unidirectional p2p and p2mp transport paths.
OAM packets that instrument a particular direction of a
transport path are subject to the same forwarding treatment
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(i.e. fate-share) as the user data packets and in some cases,
where Explicitly TC-encoded-PSC LSPs (E-LSPs) are employed, may
be required to have common Per-hop Behavior (PHB) scheduling
class (PSC) E2E with the class of traffic monitored. In case of
Label-Only-Inferred-PSC LSP (L-LSP), only one class of traffic
needs to be monitored and therefore the OAM packets have common
PSC with the monitored traffic class.
OAM packets can be distinguished from the used data packets
using the GAL and ACH constructs of RFC 5586 [7] for LSP, SPME
and Section or the ACH construct of RFC 5085 [3] and RFC 5586
[7] for (MS-)PW. OAM packets are never fragmented and are not
combined with user data in the same packet payload.
This framework makes certain assumptions as to the utility and
frequency of different classes of measurement that naturally
suggest different functions are implemented as distinct OAM
flows or packets. This is dictated by the combination of the
class of problem being detected and the need for timeliness of
network response to the problem. For example fault detection is
expected to operate on an entirely different time base than
performance monitoring which is also expected to operate on an
entirely different time base than in-band management
transactions.
The remainder of this memo is structured as follow:
Section 2 covers the definitions and terminology used in this
memo.
Section 3 describes the functional component that generates and
processes OAM packets.
Section 4 describes the reference models for applying OAM
functions to Sections, LSP, MS-PW and their SPMEs.
Sections 5, 6 and 7 provide a protocol-neutral description of
the OAM functions, defined in RFC 5860 [11], aimed at clarifying
how the OAM protocol solutions will behave to achieve their
functional objectives.
Section 8 discusses the security implications of OAM protocol
design in the MPLS-TP context.
The OAM protocol solutions designed as a consequence of this
document are expected to comply with the functional behavior
described in sections 5, 6 and 7. Alternative solutions to
required functional behaviors may also be defined.
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OAM specifications following this OAM framework may be provided
in different documents to cover distinct OAM functions.
This document is a product of a joint Internet Engineering Task
Force (IETF) / International Telecommunication Union
Telecommunication Standardization Sector (ITU-T) effort to
include an MPLS Transport Profile within the IETF MPLS and PWE3
architectures to support the capabilities and functionalities of
a packet transport network as defined by the ITU-T.
1.1. Contributing Authors
Dave Allan, Italo Busi, Ben Niven-Jenkins, Annamaria Fulignoli,
Enrique Hernandez-Valencia, Lieven Levrau, Vincenzo Sestito,
Nurit Sprecher, Huub van Helvoort, Martin Vigoureux, Yaacov
Weingarten, Rolf Winter
2. Conventions used in this document
2.1. Terminology
AC Attachment Circuit
AIS Alarm indication signal
CC Continuity Check
CC-V Continuity Check and/or Connectivity Verification
CV Connectivity Verification
DBN Domain Border Node
E-LSP Explicitly TC-encoded-PSC LSP
ICC ITU Carrier Code
LER Label Edge Router
LKR Lock Report
L-LSP Label-Only-Inferred-PSC LSP
LM Loss Measurement
LME LSP Maintenance Entity
LMEG LSP ME Group
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LSP Label Switched Path
LSR Label Switching Router
LSME LSP SPME ME
LSMEG LSP SPME ME Group
ME Maintenance Entity
MEG Maintenance Entity Group
MEP Maintenance Entity Group End Point
MIP Maintenance Entity Group Intermediate Point
NMS Network Management System
PE Provider Edge
PHB Per-hop Behavior
PM Performance Monitoring
PME PW Maintenance Entity
PMEG PW ME Group
PSC PHB Scheduling Class
PSME PW SPME ME
PSMEG PW SPME ME Group
PW Pseudowire
SLA Service Level Agreement
SME Section Maintenance Entity
SMEG Section ME Group
SPME Sub-path Maintenance Element
S-PE Switching Provider Edge
TC Traffic Class
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T-PE Terminating Provider Edge
2.2. Definitions
This document uses the terms defined in RFC 5654 [5].
This document uses the term 'Per-hop Behavior' as defined in RFC
2474 [16].
This document uses the term LSP to indicate either a service LSP
or a transport LSP (as defined in RFC 5921 [8]).
This document uses the term Sub Path Maintenance Element (SPME)
as defined in RFC 5921 [8].
This document uses the term traffic profile as defined in RFC
2475 [13].
Where appropriate, the following definitions are aligned with
ITU-T recommendation Y.1731 [21] in order to have a common,
unambiguous terminology. They do not however intend to imply a
certain implementation but rather serve as a framework to
describe the necessary OAM functions for MPLS-TP.
Adaptation function: The adaptation function is the interface
between the client (sub)-layer and the server (sub-)layer.
Branch Node: A node along a point-to-multipoint transport path
that is connected to more than one downstream node.
Bud Node: A node along a point-to-multipoint transport path that
is at the same time a branch node and a leaf node for this
transport path.
Data plane loopback: An out-of-service test where a transport
path at either an intermediate or terminating node is placed
into a data plane loopback state, such that all traffic
(including both payload and OAM) received on the looped back
interface is sent on the reverse direction of the transport
path.
Note - The only way to send an OAM packet to a node that has been put
into data plane loopback mode is via TTL expiry, irrespective of
whether the node is hosting MIPs or MEPs.
Domain Border Node (DBN): An intermediate node in an MPLS-TP LSP
that is at the boundary between two MPLS-TP OAM domains. Such a
node may be present on the edge of two domains or may be
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connected by a link to the DBN at the edge of another OAM
domain.
Down MEP: A MEP that receives OAM packets from, and transmits
them towards, the direction of a server layer.
Forwarding Engine: An abstract functional component, residing in
an LSR, that forwards the packets from an ingress interface
toward the egress interface(s).
In-Service: The administrative status of a transport path when
it is unlocked.
Interface: An interface is the attachment point to a server
(sub-)layer e.g., MPLS-TP section or MPLS-TP tunnel.
Intermediate Node: An intermediate node transits traffic for an
LSP or a PW. An intermediate node may originate OAM flows
directed to downstream intermediate nodes or MEPs.
Loopback: See data plane loopback and OAM loopback definitions.
Maintenance Entity (ME): Some portion of a transport path that
requires management bounded by two points (called MEPs), and the
relationship between those points to which maintenance and
monitoring operations apply (details in section 3.1).
Maintenance Entity Group (MEG): The set of one or more
maintenance entities that maintain and monitor a section or a
transport path in an OAM domain.
MEP: A MEG end point (MEP) is capable of initiating (Source MEP)
and terminating (sink MEP) OAM packets for fault management and
performance monitoring. MEPs define the boundaries of an ME
(details in section 3.3).
MIP: A MEG intermediate point (MIP) terminates and processes OAM
packets that are sent to this particular MIP and may generate
OAM packets in reaction to received OAM packets. It never
generates unsolicited OAM packets itself. A MIP resides within a
MEG between MEPs (details in section 3.3).
MPLS-TP Section: As defined in [8], it is a link that can be
traversed by one or more MPLS-TP LSPs.
OAM domain: A domain, as defined in [5], whose entities are
grouped for the purpose of keeping the OAM confined within that
domain. An OAM domain contains zero or more MEGs.
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Note - within the rest of this document the term "domain" is
used to indicate an "OAM domain"
OAM flow: Is the set of all OAM packets originating with a
specific source MEP that instrument one direction of a MEG (or
possibly both in the special case of data plane loopback).
OAM loopback: The capability of a node to be directed by a
received OAM packet to generate a reply back to the sender. OAM
loopback can work in-service and can support different OAM
functions (e.g., bidirectional on-demand connectivity
verification).
OAM Packet: A packet that carries OAM information between MEPs
and/or MIPs in MEG to perform some OAM functionality (e.g.
connectivity verification).
Originating MEP: A MEP that originates an OAM transaction packet
(toward a target MIP/MEP) and expects a reply, either in-band or
out-of-band, from that target MIP/MEP. The originating MEP
always generates the OAM request packets in-band and expects and
processes only OAM reply packets returned by the target MIP/MEP.
Out-of-Service: The administrative status of a transport path
when it is locked. When a path is in a locked condition, it is
blocked from carrying client traffic.
Path Segment: It is either a segment or a concatenated segment,
as defined in RFC 5654 [5].
Signal Degrade: A condition declared by a MEP when the data
forwarding capability associated with a transport path has
deteriorated, as determined by performance monitoring (PM). See also
ITU-T recommendation G.806 [14].
Signal Fail: A condition declared by a MEP when the data
forwarding capability associated with a transport path has
failed, e.g. loss of continuity. See also ITU-T recommendation
G.806 [14].
Sink MEP: A MEP acts as a sink MEP for an OAM packet when it
terminates and processes the packets received from its
associated MEG.
Source MEP: A MEP acts as source MEP for an OAM packet when it
originates and inserts the packet into the transport path for
its associated MEG.
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Tandem Connection: A tandem connection is an arbitrary part of a
transport path that can be monitored (via OAM) independent of
the end-to-end monitoring (OAM). The tandem connection may also
include the forwarding engine(s) of the node(s) at the
boundaries of the tandem connection. Tandem connections may be
nested but cannot overlap. See also ITU-T recommendation G.805
[20].
Target MEP/MIP: A MEP or a MIP that is targeted by OAM
transaction packets and that replies to the originating MEP that
initiated the OAM transactions. The target MEP or MIP can reply
either in-band or out-of-band. The target sink MEP function
always receives the OAM request packets in-band while the target
source MEP function only generates the OAM reply packets that
are sent in-band.
Up MEP: A MEP that transmits OAM packets towards, and receives
them from, the direction of the forwarding engine.
3. Functional Components
MPLS-TP is a packet-based transport technology based on the MPLS
and PW data plane architectures ([1], [2] and [4]) and is
capable of transporting service traffic where the
characteristics of information transfer between the transport
path endpoints can be demonstrated to comply with certain
performance and quality guarantees.
In order to describe the required OAM functionality, this
document introduces a set of functional components.
3.1. Maintenance Entity and Maintenance Entity Group
MPLS-TP OAM operates in the context of Maintenance Entities
(MEs) that define a relationship between two points of a
transport path to which maintenance and monitoring operations
apply. The two points that define a maintenance entity are
called Maintenance Entity Group (MEG) End Points (MEPs). The
collection of one or more MEs that belongs to the same transport
path and that are maintained and monitored as a group are known
as a maintenance entity group (MEG). In between MEPs, there are
zero or more intermediate points, called Maintenance Entity
Group Intermediate Points (MIPs). MEPs and MIPs are associated
with the MEG and can be shared by more than one ME in a MEG.
An abstract reference model for an ME is illustrated in Figure 1
below:
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+-+ +-+ +-+ +-+
|A|----|B|----|C|----|D|
+-+ +-+ +-+ +-+
Figure 1 ME Abstract Reference Model
The instantiation of this abstract model to different MPLS-TP
entities is described in section 4. In Figure 1, nodes A and D
can be LERs for an LSP or the Terminating Provider Edges (T-PEs)
for a MS-PW, nodes B and C are LSRs for a LSP or Switching PEs
(S-PEs) for a MS-PW. MEPs reside in nodes A and D while MIPs
reside in nodes B and C and may reside in A and D. The links
connecting adjacent nodes can be physical links, (sub-)layer
LSPs/SPMEs, or server layer paths.
This functional model defines the relationships between all OAM
entities from a maintenance perspective and it allows each
Maintenance Entity to provide monitoring and management for the
(sub-)layer network under its responsibility and efficient
localization of problems.
An MPLS-TP Maintenance Entity Group may be defined to monitor
the transport path for fault and/or performance management.
The MEPs that form a MEG bound the scope of an OAM flow to the
MEG (i.e. within the domain of the transport path that is being
monitored and managed). There are two exceptions to this:
1) A misbranching fault may cause OAM packets to be delivered to
a MEP that is not in the MEG of origin.
2) An out-of-band return path may be used between a MIP or a MEP
and the originating MEP.
In case of unidirectional point-to-point transport paths, a
single unidirectional Maintenance Entity is defined to monitor
it.
In case of associated bi-directional point-to-point transport
paths, two independent unidirectional Maintenance Entities are
defined to independently monitor each direction. This has
implications for transactions that terminate at or query a MIP,
as a return path from MIP to originating MEP does not
necessarily exist in the MEG.
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In case of co-routed bi-directional point-to-point transport
paths, a single bidirectional Maintenance Entity is defined to
monitor both directions congruently.
In case of unidirectional point-to-multipoint transport paths, a
single unidirectional Maintenance entity for each leaf is
defined to monitor the transport path from the root to that
leaf.
In all cases, portions of the transport path may be monitored by
the instantiation of SPMEs (see section 3.2).
The reference model for the p2mp MEG is represented in Figure 2.
+-+
/--|D|
/ +-+
+-+
/--|C|
+-+ +-+/ +-+\ +-+
|A|----|B| \--|E|
+-+ +-+\ +-+ +-+
\--|F|
+-+
Figure 2 Reference Model for p2mp MEG
In case of p2mp transport paths, the OAM measurements are
independent for each ME (A-D, A-E and A-F):
o Fault conditions - some faults may impact more than one ME
depending from where the failure is located;
o Packet loss - packet dropping may impact more than one ME
depending from where the packets are lost;
o Packet delay - will be unique per ME.
Each leaf (i.e. D, E and F) terminates OAM flows to monitor the
ME between itself and the root while the root (i.e. A) generates
OAM packets common to all the MEs of the p2mp MEG. All nodes may
implement a MIP in the corresponding MEG.
3.2. MEG Nesting: SPMEs and Tandem Connection Monitoring
In order to verify and maintain performance and quality
guarantees, there is a need to not only apply OAM functionality
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on a transport path granularity (e.g. LSP or MS-PW), but also on
arbitrary parts of transport paths, defined as Tandem
Connections, between any two arbitrary points along a transport
path.
Sub-path Maintenance Elements (SPMEs), as defined in [8], are
hierarchical LSPs instantiated to provide monitoring of a
portion of a set of transport paths (LSPs or MS-PWs) that follow
the same path between the ingress and the egress of the SPME.
The operational aspects of instantiating SPMEs are out of scope
of this memo.
SPMEs can also be employed to meet the requirement to provide
tandem connection monitoring (TCM), as defined by ITU-T
Recommendation G.805 [20].
TCM for a given path segment of a transport path is implemented
by creating an SPME that has a 1:1 association with the path
segment of the transport path that is to be monitored.
In the TCM case, this means that the SPME used to provide TCM
can carry one and only one transport path thus allowing direct
correlation between all fault management and performance
monitoring information gathered for the SPME and the monitored
path segment of the end-to-end transport path.
There are a number of implications to this approach:
1) The SPME would use the uniform model [23] of Traffic Class
(TC) code point copying between sub-layers for diffserv such
that the E2E markings and PHB treatment for the transport
path was preserved by the SPMEs.
2) The SPME normally would use the short-pipe model for TTL
handling [6] (no TTL copying between sub-layer) such that the
TTL distance to the MIPs for the E2E entity would not be
impacted by the presence of the SPME, but it should be
possible for an operator to specify use of the uniform model.
Note that points 1 and 2 above assume that the TTL copying mode
and TC copying modes are independently configurable for an LSP.
The TTL distance to the MIPs plays a critical role for
delivering packets to these MIPs as described in section 3.4.
There are specific issues with the use of the uniform model of
TTL copying for an SPME:
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1. A MIP in the SPME sub-layer is not part of the transport path MEG,
hence only an out of band return path for OAM originating in the
transport path MEG that addressed an SPME MIP might be available.
2. The instantiation of a lower level MEG or protection switching
actions within a lower level MEG may change the TTL distances to
MIPs in the higher level MEGs.
The endpoints of the SPME are MEPs and limit the scope of an OAM
flow within the MEG that the MEPs belong to (i.e. within the
domain of the SPME that is being monitored and managed).
When considering SPMEs, it is important to consider that the
following properties apply to all MPLS-TP MEGs (regardless of
whether they instrument LSPs, SPMEs or MS-PWs):
o They can be nested but not overlapped, e.g. a MEG may cover a
path segment of another MEG, and may also include the
forwarding engine(s) of the node(s) at the edge(s) of the
path segment. However when MEGs are nested, the MEPs and MIPs
in the SPME are no longer part of the encompassing MEG.
o It is possible that MEPs of MEGs that are nested reside on a
single node but again implemented in such a way that they do
not overlap.
o Each OAM flow is associated with a single MEG
o When a SPME is instantiated after the transport path has been
instantiated the TTL distance to the MIPs may change for the
short-pipe model of TTL copying, and may change for the
uniform model if the SPME is not co-routed with the original
path.
3.3. MEG End Points (MEPs)
MEG End Points (MEPs) are the source and sink points of a MEG.
In the context of an MPLS-TP LSP, only LERs can implement MEPs
while in the context of an SPME, any LSR of the MPLS-TP LSP can
be an LER of SPMEs that contributes to the overall monitoring
infrastructure of the transport path. Regarding PWs, only T-PEs
can implement MEPs while for SPMEs supporting one or more PWs
both T-PEs and S-PEs can implement SPME MEPs. Any MPLS-TP LSR
can implement a MEP for an MPLS-TP Section.
MEPs are responsible for originating almost all of the proactive
and on-demand monitoring OAM functionality for the MEG. There is
a separate class of notifications (such as Lock report (LKR) and
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Alarm indication signal (AIS)) that are originated by
intermediate nodes and triggered by server layer events. A MEP
is capable of originating and terminating OAM packets for fault
management and performance monitoring. These OAM packets are
carried within the G-ACh with the proper encapsulation and an
appropriate channel type as defined in RFC 5586 [7]. A MEP
terminates all the OAM packets it receives from the MEG it
belongs to and silently discards those that do not (note in the
particular case of Connectivity Verification (CV) processing a
CV packet from an incorrect MEG will result in a
mis-connectivity defect and there are further actions taken).
The MEG the OAM packet belongs to is associated with the MPLS or
PW label. Whether the label is used to infer the MEG or the
content of the OAM packet is an implementation choice. In the
case of an MPLS-TP section, the MEG is inferred from the port on
which an OAM packet was received with the GAL at the top of the
label stack.
OAM packets may require the use of an available "out-of-band"
return path (as defined in [8]). In such cases sufficient
information is required in the originating transaction such that
the OAM reply packet can be constructed and properly forwarded
to the originating MEP (e.g. IP address).
Each OAM solution document will further detail the applicability
of the tools it defines as a pro-active or on-demand mechanism
as well as its usage when:
o The "in-band" return path exists and it is used;
o An "out-of-band" return path exists and it is used;
o Any return path does not exist or is not used.
Once a MEG is configured, the operator can configure which
proactive OAM functions to use on the MEG but the MEPs are
always enabled.
MEPs terminate all OAM packets received from the associated MEG.
As the MEP corresponds to the termination of the forwarding path
for a MEG at the given (sub-)layer, OAM packets never leak
outside of a MEG in a properly configured fault-free
implementation.
A MEP of an MPLS-TP transport path coincides with transport path
termination and monitors it for failures or performance
degradation (e.g. based on packet counts) in an end-to-end
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scope. Note that both source MEP and sink MEP coincide with
transport paths' source and sink terminations.
The MEPs of an SPME are not necessarily coincident with the
termination of the MPLS-TP transport path. They are used to
monitor a path segment of the transport path for failures or
performance degradation (e.g. based on packet counts) only
within the boundary of the MEG for the SPME.
An MPLS-TP sink MEP passes a fault indication to its client
(sub-)layer network as a consequent action of fault detection.
When the client layer is not MPLS TP, the consequent actions in
the client layer (e.g., ignore or generate client layer specific
OAM notifications) are outside the scope of this document.
A node hosting a MEP can either support per-node MEP or per-
interface MEP(s). A per-node MEP resides in an unspecified
location within the node while a per-interface MEP resides on a
specific side of the forwarding engine. In particular a per-
interface MEP is called "Up MEP" or "Down MEP" depending on its
location relative to the forwarding engine. An "Up MEP"
transmits OAM packets towards, and receives them from, the
direction of the forwarding engine, while a "Down MEP" receives
OAM packets from, and transmits them towards, the direction of a
server layer.
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Source node Up MEP Destination node Up MEP
------------------------ ------------------------
| | | |
|----- -----| |----- -----|
| MEP | | | | | | MEP |
| | ---- | | | | ---- | |
| In |->-| FW |->-| Out |->- ->-| In |->-| FW |->-| Out |
| i/f | ---- | i/f | | i/f | ---- | i/f |
|----- -----| |----- -----|
| | | |
------------------------ ------------------------
(1) (2)
Source node Down MEP Destination node Down MEP
------------------------ ------------------------
| | | |
|----- -----| |----- -----|
| | | MEP | | MEP | | |
| | ---- | | | | ---- | |
| In |->-| FW |->-| Out |->- ->-| In |->-| FW |->-| Out |
| i/f | ---- | i/f | | i/f | ---- | i/f |
|----- -----| |----- -----|
| | | |
------------------------ ------------------------
(3) (4)
Figure 3 Examples of per-interface MEPs
Figure 3 describes four examples of per-interface Up MEPs: an Up
Source MEP in a source node (case 1), an Up Sink MEP in a
destination node (case 2), a Down Source MEP in a source node
(case 3) and a Down Sink MEP in a destination node (case 4).
The usage of per-interface Up MEPs extends the coverage of the
ME for both fault and performance monitoring closer to the edge
of the domain and allows the isolation of failures or
performance degradation to being within a node or either the
link or interfaces.
Each OAM solution document will further detail the implications
of the tools it defines when used with per-interface or per-node
MEPs, if necessary.
It may occur that multiple MEPs for the same MEG are on the same
node, and are all Up MEPs, each on one side of the forwarding
engine, such that the MEG is entirely internal to the node.
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It should be noted that a ME may span nodes that implement per
node MEPs and per-interface MEPs. This guarantees backward
compatibility with most of the existing LSRs that can implement
only a per-node MEP as in current implementations label
operations are largely performed on the ingress interface, hence
the exposure of the GAL as top label will occur at the ingress
interface.
Note that a MEP can only exist at the beginning and end of a
(sub-)layer in MPLS-TP. If there is a need to monitor some
portion of that LSP or PW, a new sub-layer in the form of an
SPME must be created which permits MEPs and associated MEGs to
be created.
In the case where an intermediate node sends an OAM packet to a
MEP, it uses the top label of the stack at that point.
3.4. MEG Intermediate Points (MIPs)
A MEG Intermediate Point (MIP) is a function located at a point
between the MEPs of a MEG for a PW, LSP or SPME.
A MIP is capable of reacting to some OAM packets and forwarding all
the other OAM packets while ensuring fate sharing with user data
packets. However, a MIP does not initiate unsolicited OAM packets,
but may be addressed by OAM packets initiated by one of the MEPs of
the MEG. A MIP can generate OAM packets only in response to OAM
packets that it receives from the MEG it belongs to. The OAM packets
generated by the MIP are sent to the originating MEP.
An intermediate node within a MEG can either:
o Support per-node MIP (i.e. a single MIP per node in an
unspecified location within the node);
o Support per-interface MIP (i.e. two or more MIPs per node on
both sides of the forwarding engine).
Support of per-interface of per-node MIPs is an implementation
choice. It is also possible that a node support per-interface
MIPs on some MEGs and per-node MIPs on other MEGs for which it
is a transit node.
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Intermediate node
------------------------
| |
|----- -----|
| MIP | | MIP |
| | ---- | |
->-| In |->-| FW |->-| Out |->-
| i/f | ---- | i/f |
|----- -----|
| |
------------------------
Figure 4 Example of per-interface MIPs
Figure 4 describes an example of two per-interface MIPs at an
intermediate node of a point-to-point MEG.
The usage of per-interface MIPs allows the isolation of failures
or performance degradation to being within a node or either the
link or interfaces.
When sending an OAM packet to a MIP, the source MEP should set
the TTL field to indicate the number of hops necessary to reach
the node where the MIP resides.
The source MEP should also include target MIP information in the
OAM packets sent to a MIP to allow proper identification of the
MIP within the node. The MEG the OAM packet belongs to is
associated with the MPLS label. Whether the label is used to
infer the MEG or the content of the OAM packet is an
implementation choice. In the latter, the MPLS label is checked
to be the expected one.
The use of TTL expiry to deliver OAM packets to a specific MIP
is not a fully reliable delivery mechanism because the TTL
distance of a MIP from a MEP can change. Any MPLS-TP node
silently discards any OAM packet received with an expired TTL
and that it is not addressed to any of its MIPs or MEPs. An
MPLS-TP node that does not support OAM is also expected to
silently discard any received OAM packet.
Packets directed to a MIP may not necessarily carry specific MIP
identification information beyond that of TTL distance. In this
case a MIP would promiscuously respond to all MEP queries on its
MEG. This capability could be used for discovery functions
(e.g., route tracing as defined in section 6.4) or when it is
desirable to leave to the originating MEP the job of correlating
TTL and MIP identifiers and noting changes or irregularities
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(via comparison with information previously extracted from the
network).
MIPs are associated to the MEG they belong to and their identity
is unique within the MEG. However, their identity is not
necessarily unique to the MEG: e.g. all nodal MIPs in a node can
have a common identity.
A node hosting a MEP can also support per-interface Up MEPs and
per-interface MIPs on either side of the forwarding engine.
Once a MEG is configured, the operator can enable/disable the
MIPs on the nodes within the MEG. All the intermediate nodes and
possibly the end nodes host MIP(s). Local policy allows them to
be enabled per function and per MEG. The local policy is
controlled by the management system, which may delegate it to
the control plane. A disabled MIP silently discards any received
OAM packets.
3.5. Server MEPs
A server MEP is a MEP of a MEG that is either:
o Defined in a layer network that is "below", which is to say
encapsulates and transports the MPLS-TP layer network being
referenced, or
o Defined in a sub-layer of the MPLS-TP layer network that is
"below" which is to say encapsulates and transports the
sub-layer being referenced.
A server MEP can coincide with a MIP or a MEP in the client
(MPLS-TP) (sub-)layer network.
A server MEP also provides server layer OAM indications to the
client/server adaptation function between the client (MPLS-TP)
(sub-)layer network and the server (sub-)layer network. The
adaptation function maintains state on the mapping of MPLS-TP
transport paths that are setup over that server (sub-)layer's
transport path.
For example, a server MEP can be either:
o A termination point of a physical link (e.g. 802.3), an SDH
VC or OTN ODU, for the MPLS-TP Section layer network, defined
in section 4.1;
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o An MPLS-TP Section MEP for MPLS-TP LSPs, defined in section
4.2;
o An MPLS-TP LSP MEP for MPLS-TP PWs, defined in section 4.3;
o An MPLS-TP SPME MEP used for LSP path segment monitoring, as
defined in section 4.4, for MPLS-TP LSPs or higher-level
SPMEs providing LSP path segment monitoring;
o An MPLS-TP SPME MEP used for PW path segment monitoring, as
defined in section 4.5, for MPLS-TP PWs or higher-level SPMEs
providing PW path segment monitoring.
The server MEP can run appropriate OAM functions for fault detection
within the server (sub-)layer network, and provides a fault
indication to its client MPLS-TP layer network via the client/server
adaptation function. When the server layer is not MPLS-TP, server MEP
OAM functions are simply assumed to exist but are outside the scope
of this document.
3.6. Configuration Considerations
When a control plane is not present, the management plane configures
these functional components. Otherwise they can be configured either
by the management plane or by the control plane.
Local policy allows disabling the usage of any available "out-
of-band" return path, as defined in [8], irrespective of what is
requested by the node originating the OAM packet.
SPMEs are usually instantiated when the transport path is
created by either the management plane or by the control plane
(if present). Sometimes an SPME can be instantiated after the
transport path is initially created.
3.7. P2MP considerations
All the traffic sent over a p2mp transport path, including OAM
packets generated by a MEP, is sent (multicast) from the root to
all the leaves. As a consequence:
o To send an OAM packet to all leaves, the source MEP can
send a single OAM packet that will be delivered by the
forwarding plane to all the leaves and processed by all the
leaves. Hence a single OAM packet can simultaneously
instrument all the MEs in a p2mp MEG.
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o To send an OAM packet to a single leaf, the source MEP
sends a single OAM packet that will be delivered by the
forwarding plane to all the leaves but contains sufficient
information to identify a target leaf, and therefore is
processed only by the target leaf and ignored by the other
leaves.
o To send an OAM packet to a single MIP, the source MEP sends
a single OAM packet with the TTL field indicating the
number of hops necessary to reach the node where the MIP
resides. This packet will be delivered by the forwarding
plane to all intermediate nodes at the same TTL distance of
the target MIP and to any leaf that is located at a shorter
distance. The OAM packet must contain sufficient
information to identify the target MIP and therefore is
processed only by the target MIP.
o In order to send an OAM packet to M leaves (i.e., a subset
of all the leaves), the source MEP sends M different OAM
packets targeted to each individual leaf in the group of M
leaves. Aggregated or sub setting mechanisms are outside
the scope of this document.
A bud node with a Down MEP or a per-node MEP will both terminate
and relay OAM packets. Similar to how fault coverage is
maximized by the explicit utilization of Up MEPs, the same is
true for MEPs on a bud node.
P2MP paths are unidirectional; therefore any return path to an
originating MEP for on-demand transactions will be out-of-band.
A mechanism to target "on-demand" transactions to a single MEP
or MIP is required as it relieves the originating MEP of an
arbitrarily large processing load and of the requirement to
filter and discard undesired responses as normally TTL
exhaustion will address all MIPs at a given distance from the
source, and failure to exhaust TTL will address all MEPs.
3.8. Further considerations of enhanced segment monitoring
Segment monitoring, like any in-service monitoring, in a
transport network should meet the following network objectives:
1. The monitoring and maintenance of existing transport paths has to
be conducted in service without traffic disruption.
2. Segment monitoring must not modify the forwarding of the segment
portion of the transport path.
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SPMEs defined in section 3.2 meet the above two objectives, when
they are pre-configured or pre-instantiated as exemplified in
section 3.6. However, pre-design and pre-configuration of all
the considered patterns of SPME are not sometimes preferable in
real operation due to the burden of design works, a number of
header consumptions, bandwidth consumption and so on.
When SPMEs are configured or instantiated after the transport
path has been created, network objective (1) can be met:
application and removal of SPME to a faultless monitored
transport entity can be performed in such a way as not to
introduce any loss of traffic, e.g., by using non-disruptive
"make before break" technique.
However, network objective (2) cannot be met due to new
assignment of MPLS labels. As a consequence, generally speaking,
the results of SPME monitoring are not necessarily correlated
with the behaviour of traffic in the monitored entity when it
does not use SPME. For example, application of SPME to a
problematic/faulty monitoring entity might "fix" the problem
encountered by the latter - for as long as SPME is applied. And
vice versa, application of SPME to a faultless monitored entity
may result in making it faulty - again, as long as SPME is
applied.
Support for a more sophisticated segment monitoring mechanism
(temporal and hitless segment monitoring) to efficiently meet
the two network objectives may be necessary.
One possible option to instantiate non-intrusive segment
monitoring without the use of SPMEs would require the MIPs
selected as monitoring endpoints to implement enhanced
functionality and state for the monitored transport path.
For example the MIPs need to be configured with the TTL distance
to the peer or with the address of the peer, when out-of-band
return paths are used.
A further issue that would need to be considered is events that
result in changing the TTL distance to the peer monitoring
entity such as protection events that may temporarily invalidate
OAM information gleaned from the use of this technique.
Further considerations on this technique are outside the scope
of this document.
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4. Reference Model
The reference model for the MPLS-TP OAM framework builds upon
the concept of a MEG, and its associated MEPs and MIPs, to
support the functional requirements specified in RFC 5860 [11].
The following MPLS-TP MEGs are specified in this document:
o A Section Maintenance Entity Group (SMEG), allowing
monitoring and management of MPLS-TP Sections (between MPLS
LSRs).
o An LSP Maintenance Entity Group (LMEG), allowing monitoring
and management of an end-to-end LSP (between LERs).
o A PW Maintenance Entity Group (PMEG), allowing monitoring and
management of an end-to-end SS/MS-PWs (between T-PEs).
o An LSP SPME ME Group (LSMEG), allowing monitoring and
management of an SPME (between a given pair of LERs and/or
LSRs along an LSP).
o A PW SPME ME Group (PSMEG), allowing monitoring and
management of an SPME (between a given pair of T-PEs and/or
S-PEs along an (MS-)PW).
The MEGs specified in this MPLS-TP OAM framework are compliant
with the architecture framework for MPLS-TP [8] that includes
both MS-PWs [4] and LSPs [1].
Hierarchical LSPs are also supported in the form of SPMEs. In
this case, each LSP in the hierarchy is a different sub-layer
network that can be monitored, independently from higher and
lower level LSPs in the hierarchy, on an end-to-end basis (from
LER to LER) by a SPME. It is possible to monitor a portion of a
hierarchical LSP by instantiating a hierarchical SPME between
any LERs/LSRs along the hierarchical LSP.
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Native |<------------------ MS-PW1Z ---------------->| Native
Layer | | Layer
Service | |<LSP13>| |<-LSP3X->| |<LSPXZ>| | Service
(AC1) V V V V V V V V (AC2)
+----+ +---+ +----+ +----+ +---+ +----+
+----+ |T-PE| |LSR| |S-PE| |S-PE| |LSR| |T-PE| +----+
| | | 1 | | 2 | | 3 | | X | | Y | | Z | | |
| | | |=======| |=========| |=======| | | |
| CE1|--|.......PW13......|...PW3X..|......PWXZ.......|---|CE2 |
| | | |=======| |=========| |=======| | | |
| | | | | | | | | | | | | | | |
+----+ | | | | | | | | | | | | +----+
+----+ +---+ +----+ +----+ +---+ +----+
. . . .
| | | |
|<--- Domain 1 -->| |<--- Domain Z -->|
^----------------- PW1Z PMEG ----------------^
^--- PW13 PSMEG --^ ^--- PWXZ PSMEG --^
^-------^ ^-------^
LSP13 LMEG LSPXZ LMEG
^--^ ^--^ ^---------^ ^--^ ^--^
Sec12 Sec23 Sec3X SecXY SecYZ
SMEG SMEG SMEG SMEG SMEG
^---^ ME
^ MEP
==== LSP
.... PW
T-PE1: Terminating Provider Edge 1
LSR: Label Switching Router 2
S-PE3: Switching Provider Edge 3
T-PEX: Terminating Provider Edge X
LSRY: Label Switching Router Y
S-PEZ: Switching Provider Edge Z
Figure 5 Reference Model for the MPLS-TP OAM Framework
Figure 5 depicts a high-level reference model for the MPLS-TP
OAM framework. The figure depicts portions of two MPLS-TP
enabled network domains, Domain 1 and Domain Z. In Domain 1,
LSR1 is adjacent to LSR2 via the MPLS-TP Section Sec12 and LSR2
is adjacent to LSR3 via the MPLS-TP Section Sec23. Similarly, in
Domain Z, LSRX is adjacent to LSRY via the MPLS-TP Section SecXY
and LSRY is adjacent to LSRZ via the MPLS-TP Section SecYZ. In
addition, LSR3 is adjacent to LSRX via the MPLS-TP Section 3X.
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Figure 5 also shows a bi-directional MS-PW (PW1Z) between AC1 on
T-PE1 and AC2 on T-PEZ. The MS-PW consists of three
bi-directional PW path segments: 1) PW13 path segment between
T-PE1 and S-PE3 via the bi-directional LSP13 LSP, 2) PW3X path
segment between S-PE3 and S-PEX, via the bi-directional LSP3X
LSP, and 3) PWXZ path segment between S-PEX and T-PEZ via the
bi-directional LSPXZ LSP.
The MPLS-TP OAM procedures that apply to a MEG are expected to
operate independently from procedures on other MEGs. Yet, this
does not preclude that multiple MEGs may be affected
simultaneously by the same network condition, for example, a
fiber cut event.
Note that there are no constrains imposed by this OAM framework
on the number, or type (p2p, p2mp, LSP or PW), of MEGs that may
be instantiated on a particular node. In particular, when
looking at Figure 5, it should be possible to configure one or
more MEPs on the same node if that node is the endpoint of one
or more MEGs.
Figure 5 does not describe a PW3X PSMEG because typically SPMEs
are used to monitor an OAM domain (like PW13 and PWXZ PSMEGs)
rather than the segment between two OAM domains. However the OAM
framework does not pose any constraints on the way SPMEs are
instantiated as long as they are not overlapping.
The subsections below define the MEGs specified in this MPLS-TP
OAM architecture framework document. Unless otherwise stated,
all references to domains, LSRs, MPLS-TP Sections, LSPs,
pseudowires and MEGs in this section are made in relation to
those shown in Figure 5.
4.1. MPLS-TP Section Monitoring (SMEG)
An MPLS-TP Section MEG (SMEG) is an MPLS-TP maintenance entity
intended to monitor an MPLS-TP Section as defined in RFC 5654
[5]. An SMEG may be configured on any MPLS-TP section. SMEG OAM
packets must fate-share with the user data packets sent over the
monitored MPLS-TP Section.
An SMEG is intended to be deployed for applications where it is
preferable to monitor the link between topologically adjacent
(next hop in this layer network) MPLS-TP LSRs rather than
monitoring the individual LSP or PW path segments traversing the
MPLS-TP Section and the server layer technology does not provide
adequate OAM capabilities.
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Figure 5 shows five Section MEGs configured in the network
between AC1 and AC2:
1. Sec12 MEG associated with the MPLS-TP Section between LSR 1
and LSR 2,
2. Sec23 MEG associated with the MPLS-TP Section between LSR 2
and LSR 3,
3. Sec3X MEG associated with the MPLS-TP Section between LSR 3
and LSR X,
4. SecXY MEG associated with the MPLS-TP Section between LSR X
and LSR Y, and
5. SecYZ MEG associated with the MPLS-TP Section between LSR Y
and LSR Z.
4.2. MPLS-TP LSP End-to-End Monitoring Group (LMEG)
An MPLS-TP LSP MEG (LMEG) is an MPLS-TP maintenance entity group
intended to monitor an end-to-end LSP between its LERs. An LMEG
may be configured on any MPLS LSP. LMEG OAM packets must
fate-share with user data packets sent over the monitored MPLS-
TP LSP.
An LMEG is intended to be deployed in scenarios where it is
desirable to monitor an entire LSP between its LERs, rather
than, say, monitoring individual PWs.
Figure 5 depicts two LMEGs configured in the network between AC1
and AC2: 1) the LSP13 LMEG between LER 1 and LER 3, and 2) the
LSPXZ LMEG between LER X and LER Y. Note that the presence of a
LSP3X LMEG in such a configuration is optional, hence, not
precluded by this framework. For instance, the SPs may prefer to
monitor the MPLS-TP Section between the two LSRs rather than the
individual LSPs.
4.3. MPLS-TP PW Monitoring (PMEG)
An MPLS-TP PW MEG (PMEG) is an MPLS-TP maintenance entity
intended to monitor a SS-PW or MS-PW between its T-PEs. A PMEG
can be configured on any SS-PW or MS-PW. PMEG OAM packets must
fate-share with the user data packets sent over the monitored
PW.
A PMEG is intended to be deployed in scenarios where it is
desirable to monitor an entire PW between a pair of MPLS-TP
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enabled T-PEs rather than monitoring the LSP aggregating
multiple PWs between PEs.
Figure 5 depicts a MS-PW (MS-PW1Z) consisting of three path
segments: PW13, PW3X and PWXZ and its associated end-to-end PMEG
(PW1Z PMEG).
4.4. MPLS-TP LSP SPME Monitoring (LSMEG)
An MPLS-TP LSP SPME MEG (LSMEG) is an MPLS-TP SPME with an
associated maintenance entity group intended to monitor an
arbitrary part of an LSP between the MEPs instantiated for the
SPME independent from the end-to-end monitoring (LMEG). An LSMEG
can monitor an LSP path segment and it may also include the
forwarding engine(s) of the node(s) at the edge(s) of the path
segment.
When SPME is established between non-adjacent LSRs, the edges of
the SPME becomes adjacent at the LSP sub-layer network and any
LSR that were previously in between becomes an LSR for the SPME.
Multiple hierarchical LSMEGs can be configured on any LSP. LSMEG
OAM packets must fate-share with the user data packets sent over
the monitored LSP path segment.
A LSME can be defined between the following entities:
o The LER and LSR of a given LSP.
o Any two LSRs of a given LSP.
An LSMEG is intended to be deployed in scenarios where it is
preferable to monitor the behavior of a part of an LSP or set of
LSPs rather than the entire LSP itself, for example when there
is a need to monitor a part of an LSP that extends beyond the
administrative boundaries of an MPLS-TP enabled administrative
domain.
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|<-------------------- PW1Z ------------------->|
| |
| |<-------------LSP1Z LSP------------->| |
| |<-LSP13->| |<LSP3X>| |<-LSPXZ->| |
V V V V V V V V
+----+ +---+ +----+ +----+ +---+ +----+
+----+ | PE | |LSR| |DBN | |DBN | |LSR| | PE | +----+
| | | 1 | | 2 | | 3 | | X | | Y | | Z | | |
| |AC1| |=====================================| |AC2| |
| CE1|---|.....................PW1Z......................|---|CE2 |
| | | |=====================================| | | |
| | | | | | | | | | | | | | | |
+----+ | | | | | | | | | | | | +----+
+----+ +---+ +----+ +----+ +---+ +----+
. . . .
| | | |
|<---- Domain 1 --->| |<---- Domain Z --->|
^---------^ ^---------^
LSP13 LSMEG LSPXZ LSMEG
^-------------------------------------^
LSP1Z LMEG
DBN: Domain Border Node
Figure 6 MPLS-TP LSP SPME MEG (LSMEG)
Figure 6 depicts a variation of the reference model in Figure 5
where there is an end-to-end LSP (LSP1Z) between PE1 and PEZ.
LSP1Z consists of, at least, three LSP Concatenated Segments:
LSP13, LSP3X and LSPXZ. In this scenario there are two separate
LSMEGs configured to monitor the LSP1Z: 1) a LSMEG monitoring
the LSP13 Concatenated Segment on Domain 1 (LSP13 LSMEG), and 2)
a LSMEG monitoring the LSPXZ Concatenated Segment on Domain Z
(LSPXZ LSMEG).
It is worth noticing that LSMEGs can coexist with the LMEG
monitoring the end-to-end LSP and that LSMEG MEPs and LMEG MEPs
can be coincident in the same node (e.g. PE1 node supports both
the LSP1Z LMEG MEP and the LSP13 LSMEG MEP).
4.5. MPLS-TP MS-PW SPME Monitoring (PSMEG)
An MPLS-TP MS-PW SPME Monitoring MEG (PSMEG) is an MPLS-TP SPME
with an associated maintenance entity group intended to monitor
an arbitrary part of an MS-PW between the MEPs instantiated for
the SPME independently of the end-to-end monitoring (PMEG). A
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PSMEG can monitor a PW path segment and it may also include the
forwarding engine(s) of the node(s) at the edge(s) of the path
segment. A PSMEG is no different than an SPME, it is simply
named as such to discuss SPMEs specifically in a PW context.
When SPME is established between non-adjacent S-PEs, the edges
of the SPME becomes adjacent at the MS-PW sub-layer network and
any S-PEs that were previously in between becomes an LSR for the
SPME.
S-PE placement is typically dictated by considerations other
than OAM. S-PEs will frequently reside at operational boundaries
such as the transition from distributed control plane (CP) to
centralized Network Management System (NMS) control or at a
routing area boundary. As such the architecture would appear not
to have the flexibility that arbitrary placement of SPME
segments would imply. Support for an arbitrary placement of
PSMEG would require the definition of additional PW
sub-layering.
Multiple hierarchical PSMEGs can be configured on any MS-PW.
PSMEG OAM packets fate-share with the user data packets sent
over the monitored PW path Segment.
A PSMEG does not add hierarchical components to the MPLS
architecture, it defines the role of existing components for the
purposes of discussing OAM functionality.
A PSME can be defined between the following entities:
o T-PE and any S-PE of a given MS-PW
o Any two S-PEs of a given MS-PW.
Note that, in line with the SPME description in section 3.2, when a
PW SPME is instantiated after the MS-PW has been instantiated, the
TTL distance of the MIPs may change and MIPs in the PW SPME are no
longer part of the encompassing MEG. This means that the S-PE nodes
hosting these MIPs are no longer S-PEs but P nodes at the SPME LSP
level. The consequences are that the S-PEs hosting the PSMEG MEPs
become adjacent S-PEs. This is no different than the operation of
SPMEs in general.
A PSMEG is intended to be deployed in scenarios where it is
preferable to monitor the behavior of a part of a MS-PW rather
than the entire end-to-end PW itself, for example to monitor an
MS-PW path segment within a given network domain of an inter-
domain MS-PW.
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Figure 5 depicts a MS-PW (MS-PW1Z) consisting of three path
segments: PW13, PW3X and PWXZ with two separate PSMEGs: 1) a
PSMEG monitoring the PW13 MS-PW path segment on Domain 1 (PW13
PSMEG), and 2) a PSMEG monitoring the PWXZ MS-PW path segment on
Domain Z with (PWXZ PSMEG).
It is worth noticing that PSMEGs can coexist with the PMEG
monitoring the end-to-end MS-PW and that PSMEG MEPs and PMEG
MEPs can be coincident in the same node (e.g. T-PE1 node
supports both the PW1Z PMEG MEP and the PW13 PSMEG MEP).
4.6. Fate sharing considerations for multilink
Multilink techniques are in use today and are expected to
continue to be used in future deployments. These techniques
include Ethernet Link Aggregation [22] and the use of Link
Bundling for MPLS [18] where the option to spread traffic over
component links is supported and enabled. While the use of Link
Bundling can be controlled at the MPLS-TP layer, use of Link
Aggregation (or any server layer specific multilink) is not
necessarily under control of the MPLS-TP layer. Other techniques
may emerge in the future. These techniques frequently share the
characteristic that an LSP may be spread over a set of component
links and therefore be reordered but no flow within the LSP is
reordered (except when very infrequent and minimally disruptive
load rebalancing occurs).
The use of multilink techniques may be prohibited or permitted
in any particular deployment. If multilink techniques are used,
the deployment can be considered to be only partially MPLS-TP
compliant, however this is unlikely to prevent its use.
The implications for OAM are that not all components of a
multilink will be exercised, independent server layer OAM being
required to exercise the aggregated link components. This has
further implications for MIP and MEP placement, as per-interface
MIPs or "down" MEPs on a multilink interface are akin to a layer
violation, as they instrument at the granularity of the server
layer. The implications for reduced OAM loss measurement
functionality are documented in sections 5.5.3 and 6.2.3.
5. OAM Functions for proactive monitoring
In this document, proactive monitoring refers to OAM operations
that are either configured to be carried out periodically and
continuously or preconfigured to act on certain events such as
alarm signals.
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Proactive monitoring is usually performed "in-service". Such
transactions are universally MEP to MEP in operation while
notifications can be node to node (e.g. some MS-PW transactions)
or node to MEPs (e.g., AIS). The control and measurement
considerations are:
1. Proactive monitoring for a MEG is typically configured at
transport path creation time.
2. The operational characteristics of in-band measurement
transactions (e.g., CV, Loss Measurement (LM) etc.) are
configured at the MEPs.
3. Server layer events are reported by OAM packets originating
at intermediate nodes.
4. The measurements resulting from proactive monitoring are
typically reported outside of the MEG (e.g. to a management
system) as notifications events such as faults or indications
of performance degradations (such as signal degrade
conditions).
5. The measurements resulting from proactive monitoring may be
periodically harvested by an NMS.
Pro-active fault reporting is assumed to be subject to
unreliable delivery, soft-state and need to operate also in
cases where a return path is not available or faulty. Therefore
periodic repetition is assumed to be used for reliability,
instead of handshaking.
Delay measurement requires periodic repetition also to allow
estimation of the packet delay variation for the MEG.
For statically provisioned transport paths the above information
is statically configured; for dynamically established transport
paths the configuration information is signaled via the control
plane or configured via the management plane.
The operator may enable/disable some of the consequent actions
defined in section 5.1.2.
5.1. Continuity Check and Connectivity Verification
Proactive Continuity Check functions, as required in section
2.2.2 of RFC 5860 [11], are used to detect a loss of continuity
defect (LOC) between two MEPs in a MEG.
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Proactive Connectivity Verification functions, as required in
section 2.2.3 of RFC 5860 [11], are used to detect an unexpected
connectivity defect between two MEGs (e.g. mismerging or
misconnection), as well as unexpected connectivity within the
MEG with an unexpected MEP.
Both functions are based on the (proactive) generation, at the
same rate, of OAM packets by the source MEP that are processed
by the peer sink MEP(s). As a consequence, in order to save OAM
bandwidth consumption, CV, when used, is linked with CC into
Continuity Check and Connectivity Verification (CC-V) OAM
packets.
In order to perform pro-active Connectivity Verification, each
CC-V OAM packet also includes a globally unique Source MEP
identifier, whose value needs to be configured on the source MEP
and on the peer sink MEP(s). In some cases, to avoid the need to
configure the globally unique Source MEP identifier, it is
preferable to perform only pro-active Continuity Check. In this
case, the CC-V OAM packet does not need to include any globally
unique Source MEP identifier. Therefore, an MEG can be monitored
only for CC or for both CC and CV. CC-V OAM packets used for CC-
only monitoring are called CC OAM packets while CC-V OAM packets
used for both CC and CV are called CV OAM packets.
As a consequence, it is not possible to detect misconnections
between two MEGs monitored only for continuity as neither the
OAM packet type nor the OAM packet content provides sufficient
information to disambiguate an invalid source. To expand:
o For CC OAM packet leaking into a CC monitored MEG -
undetectable.
o For CV OAM packet leaking into a CC monitored MEG - reception
of CV OAM packets instead of a CC OAM packets (e.g., with the
additional Source MEP identifier) allows detecting the fault.
o For CC OAM packet leaking into a CV monitored MEG - reception
of CC OAM packets instead of CV OAM packets (e.g., lack of
additional Source MEP identifier) allows detecting the fault.
o For CV OAM packet leaking into a CV monitored MEG - reception
of CV OAM packets with different Source MEP identifier
permits fault to be identified.
Having a common packet format for CC-V OAM packets would
simplify parsing in a sink MEP to properly detect all the
mis-configuration cases described above.
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Different formats of MEP identifiers are defined in [10] to
address different environments. When an alternative to IP
addressing is desired (e.g., MPLS-TP is deployed in transport
network environments where consistent operations with other
transport technologies defined by the ITU-T are required), the
ITU Carrier Code (ICC)-based format for MEP identification is
used. When MPLS-TP is deployed in an environment where IP
capabilities are available and desired for OAM, the IP-based MEP
identification is used.
CC-V OAM packets are transmitted at a regular, operator
configurable, rate. The default CC-V transmission periods are
application dependent (see section 5.1.3).
Proactive CC-V OAM packets are transmitted with the "minimum
loss probability PHB" within the transport path (LSP, PW) they
are monitoring. For E-LSPs, this PHB is configurable on network
operator's basis while for L-LSPs this is determined as per RFC
3270 [23]. PHBs can be translated at the network borders by the
same function that translates it for user data traffic. The
implication is that CC-V fate-shares with much of the forwarding
implementation, but not all aspects of PHB processing are
exercised. Either on-demand tools are used for finer grained
fault finding or an implementation may utilize a CC-V flow per
PHB to ensure a CC-V flow fate-shares with each individual PHB.
In a co-routed or associated, bidirectional point-to-point
transport path, when a MEP is enabled to generate pro-active
CC-V OAM packets with a configured transmission rate, it also
expects to receive pro-active CC-V OAM packets from its peer MEP
at the same transmission rate as a common SLA applies to all
components of the transport path. In a unidirectional transport
path (either point-to-point or point-to-multipoint), the source
MEP is enabled only to generate CC-V OAM packets while each sink
MEP is configured to expect these packets at the configured
rate.
MIPs, as well as intermediate nodes not supporting MPLS-TP OAM,
are transparent to the pro-active CC-V information and forward
these pro-active CC-V OAM packets as regular data packets.
During path setup and tear down, situations arise where CC-V
checks would give rise to alarms, as the path is not fully
instantiated. In order to avoid these spurious alarms the
following procedures are recommended. At initialization, the
source MEP function (generating pro-active CC-V packets) should
be enabled prior to the corresponding sink MEP function
(detecting continuity and connectivity defects). When disabling
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the CC-V proactive functionality, the sink MEP function should
be disabled prior to the corresponding source MEP function.
It should be noted that different encapsulations are possible
for CC-V packets and therefore it is possible that in case of
mis-configurations or mis-connectivity, CC-V packets are
received with an unexpected encapsulation.
There are practical limitations to detecting unexpected
encapsulation. It is possible that there are mis-configuration
or mis-connectivity scenarios where OAM packets can alias as
payload, e.g., when a transport path can carry an arbitrary
payload without a pseudo wire.
When CC-V packets are received with an unexpected encapsulation
that can be parsed by a sink MEP, the CC-V packet is processed
as it were received with the correct encapsulation and if it is
not a manifestation of a mis-connectivity defect a warning is
raised (see section 5.1.1.4). Otherwise the CC-V packet may be
silently discarded as unrecognized and a LOC defect may be
detected (see section 5.1.1.1).
The defect conditions are described in no specific order.
5.1.1. Defects identified by CC-V
Pro-active CC-V functions allow a sink MEP to detect the defect
conditions described in the following sub-sections. For all of
the described defect cases, a sink MEP should notify the
equipment fault management process of the detected defect.
Sequential consecutive loss of CC-V packets is considered
indicative of an actual break and not congestive loss or
physical layer degradation. The loss of 3 packets in a row
(implying a 3.5 insertion time detection interval) is
interpreted as a true break and a condition that will not clear
by itself.
A CC-V OAM packet is considered to carry an unexpected globally
unique Source MEP identifier if it is a CC OAM packet received
by a sink MEP monitoring the MEG for CV; it is a CV OAM packet
received by a sink MEP monitoring the MEG for CC or it is a CV
OAM packet received by a sink MEP monitoring the MEG for CV but
carrying a unique Source MEP identifier that is different that
the expected one. Conversely, the CC-V packet is considered to
have an expected globally unique Source MEP identifier where it
is a CC OAM packet received by a sink MEP monitoring the MEG for
CC or it is a it is a CV OAM packet received by a sink MEP
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monitoring the MEG for CV and carrying a unique Source MEP
identifier that is equal to the expected one.
5.1.1.1. Loss Of Continuity defect
When proactive CC-V is enabled, a sink MEP detects a loss of
continuity (LOC) defect when it fails to receive pro-active CC-V
OAM packets from the source MEP.
o Entry criteria: If no pro-active CC-V OAM packets from the
source MEP (and in the case of CV, this includes the
requirement to have the expected globally unique Source MEP
identifier) are received within the interval equal to 3.5
times the receiving MEP's configured CC-V reception period.
o Exit criteria: A pro-active CC-V OAM packet from the source
MEP (and again in the case of CV, with the expected globally
unique Source MEP identifier) is received.
5.1.1.2. Mis-connectivity defect
When a pro-active CC-V OAM packet is received, a sink MEP
identifies a mis-connectivity defect (e.g. mismerge,
misconnection or unintended looping) when the received packet
carries an unexpected globally unique Source MEP identifier.
o Entry criteria: The sink MEP receives a pro-active CC-V OAM
packet with an unexpected globally unique Source MEP
identifier or with an unexpected encapsulation.
o Exit criteria: The sink MEP does not receive any pro-active
CC-V OAM packet with an unexpected globally unique Source MEP
identifier for an interval equal at least to 3.5 times the
longest transmission period of the pro-active CC-V OAM
packets received with an unexpected globally unique Source
MEP identifier since this defect has been raised. This
requires the OAM packet to self identify the CC-V periodicity
as not all MEPs can be expected to have knowledge of all
MEGs.
5.1.1.3. Period Misconfiguration defect
If pro-active CC-V OAM packets are received with the expected
globally unique Source MEP identifier but with a transmission
period different than the locally configured reception period,
then a CC-V period mis-configuration defect is detected.
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o Entry criteria: A MEP receives a CC-V pro-active packet with
the expected globally unique Source MEP identifier but with a
transmission period different than its own CC-V configured
transmission period.
o Exit criteria: The sink MEP does not receive any pro-active
CC-V OAM packet with the expected globally unique Source MEP
identifier and an incorrect transmission period for an
interval equal at least to 3.5 times the longest transmission
period of the pro-active CC-V OAM packets received with the
expected globally unique Source MEP identifier and an
incorrect transmission period since this defect has been
raised.
5.1.1.4. Unexpected encapsulation defect
If pro-active CC-V OAM packets are received with the expected
globally unique Source MEP identifier but with an unexpected
encapsulation, then a CC-V unexpected encapsulation defect is
detected.
It should be noted that there are practical limitations to
detecting unexpected encapsulation (see section 5.1.1).
o Entry criteria: A MEP receives a CC-V pro-active packet with
the expected globally unique Source MEP identifier but with
an unexpected encapsulation.
o Exit criteria: The sink MEP does not receive any pro-active
CC-V OAM packet with the expected globally unique Source MEP
identifier and an unexpected encapsulation for an interval
equal at least to 3.5 times the longest transmission period
of the pro-active CC-V OAM packets received with the expected
globally unique Source MEP identifier and an unexpected
encapsulation since this defect has been raised.
5.1.2. Consequent action
A sink MEP that detects any of the defect conditions defined in
section 5.1.1 declares a defect condition and performs the
following consequent actions.
If a MEP detects a mis-connectivity defect, it blocks all the
traffic (including also the user data packets) that it receives
from the misconnected transport path.
If a MEP detects LOC defect that is not caused by a period
mis-configuration, it should block all the traffic (including
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also the user data packets) that it receives from the transport
path, if this consequent action has been enabled by the
operator.
It is worth noticing that the OAM requirements document [11]
recommends that CC-V proactive monitoring be enabled on every
MEG in order to reliably detect connectivity defects. However,
CC-V proactive monitoring can be disabled by an operator for a
MEG. In the event of a misconnection between a transport path
that is pro-actively monitored for CC-V and a transport path
which is not, the MEP of the former transport path will detect a
LOC defect representing a connectivity problem (e.g. a
misconnection with a transport path where CC-V proactive
monitoring is not enabled) instead of a continuity problem, with
a consequent wrong traffic delivering. For these reasons, the
traffic block consequent action is applied even when a LOC
condition occurs. This block consequent action can be disabled
through configuration. This deactivation of the block action may
be used for activating or deactivating the monitoring when it is
not possible to synchronize the function activation of the two
peer MEPs.
If a MEP detects a LOC defect (section 5.1.1.1), a
mis-connectivity defect (section 5.1.1.2) it declares a signal
fail condition of the ME.
It is a matter if local policy if a MEP that detects a period
misconfiguration defect (section 5.1.1.3) declares a signal fail
condition of the ME.
The detection of an unexpected encapsulation defect does not
have any consequent action: it is just a warning for the network
operator. An implementation able to detect an unexpected
encapsulation but not able to verify the source MEP ID may
choose to declare a mis-connectivity defect.
5.1.3. Configuration considerations
At all MEPs inside a MEG, the following configuration
information needs to be configured when a proactive CC-V
function is enabled:
o MEG ID; the MEG identifier to which the MEP belongs;
o MEP-ID; the MEP's own identity inside the MEG;
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o list of the other MEPs in the MEG. For a point-to-point MEG
the list would consist of the single MEP ID from which the
OAM packets are expected. In case of the root MEP of a p2mp
MEG, the list is composed by all the leaf MEP IDs inside the
MEG. In case of the leaf MEP of a p2mp MEG, the list is
composed by the root MEP ID (i.e. each leaf needs to know the
root MEP ID from which it expect to receive the CC-V OAM
packets).
o PHB for E-LSPs; it identifies the per-hop behavior of CC-V
packet. Proactive CC-V packets are transmitted with the
"minimum loss probability PHB" previously configured within a
single network operator. This PHB is configurable on network
operator's basis. PHBs can be translated at the network
borders.
o transmission rate; the default CC-V transmission periods are
application dependent (depending on whether they are used to
support fault management, performance monitoring, or
protection switching applications):
o Fault Management: default transmission period is 1s (i.e.
transmission rate of 1 packet/second).
o Performance Management: default transmission period is
100ms (i.e. transmission rate of 10 packets/second). CC-V
contributes to the accuracy of performance monitoring
(PM) statistics by permitting the defect free periods to
be properly distinguished as described in sections 5.5.1
and 5.6.1.
o Protection Switching: If protection switching with CC-V
defect entry criteria of 12ms is required (for example,
in conjunction with the requirement to support 50ms
recovery time as indicated in RFC 5654 [5]), then an
implementation should use a default transmission period
of 3.33ms (i.e., transmission rate of 300
packets/second). Sometimes, the requirement of 50ms
recovery time is associated with the requirement for a
CC-V defect entry criteria period of 35 ms: in these
cases a transmission period of 10ms (i.e., transmission
rate of 100 packets/second) can be used. Furthermore,
when there is no need for so small CC-V defect entry
criteria periods, larger transmission period can be used.
It should be possible for the operator to configure these
transmission rates for all applications, to satisfy specific
network requirements.
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Note that the reception period is the same as the configured
transmission rate.
For management provisioned transport paths the above parameters
are statically configured; for dynamically signaled transport
paths the configuration information are distributed via the
control plane.
The operator should be able to enable/disable some of the
consequent actions. Which consequent action can be
enabled/disabled are described in section 5.1.2.
5.2. Remote Defect Indication
The Remote Defect Indication (RDI) function, as required in
section 2.2.9 of RFC 5860 [11], is an indicator that is
transmitted by a sink MEP to communicate to its source MEP that
a signal fail condition exists. In case of co-routed and
associated bidirectional transport paths, RDI is associated with
proactive CC-V and the RDI indicator can be piggy-backed onto
the CC-V packet. In case of unidirectional transport paths, the
RDI indicator can be sent only using an out-of-band return path
if it exists and its usage is enabled by policy actions.
When a MEP detects a signal fail condition (e.g. in case of a
continuity or connectivity defect), it should begin transmitting
an RDI indicator to its peer MEP. When incorporated into CC-V,
the RDI information will be included in all pro-active CC-V
packets that it generates for the duration of the signal fail
condition's existence.
A MEP that receives packets from a peer MEP with the RDI
information should determine that its peer MEP has encountered a
defect condition associated with a signal fail condition.
MIPs as well as intermediate nodes not supporting MPLS-TP OAM
are transparent to the RDI indicator and forward OAM packets
that include the RDI indicator as regular data packets, i.e. the
MIP should not perform any actions nor examine the indicator.
When the signal fail condition clears, the MEP should stop
transmitting the RDI indicator to its peer MEP. When
incorporated into CC-V, the RDI indicator will be cleared from
subsequent transmission of pro-active CC-V packets. A MEP
should clear the RDI defect upon reception of an RDI indicator
cleared.
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5.2.1. Configuration considerations
In order to support RDI indication, the indication may be
carried in a unique OAM packet or may be embedded in a CC-V
packet. The in-band RDI transmission rate and PHB of the OAM
packets carrying RDI should be the same as that configured for
CC-V to allow both far-end and near-end defect conditions being
resolved in a timeframe that has the same order of magnitude.
This timeframe is application specific as described in section
5.1.3. Methods of the out-of-band return paths will dictate how
out-of-band RDI indications are transmitted.
5.3. Alarm Reporting
The Alarm Reporting function, as required in section 2.2.8 of
RFC 5860 [11], relies upon an Alarm Indication Signal (AIS)
packet to suppress alarms following detection of defect
conditions at the server (sub-)layer.
When a server MEP asserts a signal fail condition, it notifies
that to the co-located MPLS-TP client/server adaptation function
which then generates OAM packets with AIS information in the
downstream direction to allow the suppression of secondary
alarms at the MPLS-TP MEP in the client (sub-)layer.
The generation of packets with AIS information starts
immediately when the server MEP asserts a signal fail condition.
These periodic OAM packets, with AIS information, continue to be
transmitted until the signal fail condition is cleared.
It is assumed that to avoid spurious alarm generation a MEP
detecting a loss of continuity defect (see section 5.1.1.1) will
wait for a hold off interval prior to asserting an alarm to the
management system. Therefore, upon receiving an OAM packet with
AIS information an MPLS-TP MEP enters an AIS defect condition
and suppresses reporting of alarms to the NMS on the loss of
continuity with its peer MEP but does not block traffic received
from the transport path. A MEP resumes loss of continuity alarm
generation upon detecting loss of continuity defect conditions
in the absence of AIS condition.
MIPs, as well as intermediate nodes, do not process AIS
information and forward these AIS OAM packets as regular data
packets.
For example, let's consider a fiber cut between LSR 1 and LSR 2
in the reference network of Figure 5. Assuming that all of the
MEGs described in Figure 5 have pro-active CC-V enabled, a LOC
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defect is detected by the MEPs of Sec12 SMEG LSP13 LMEG, PW1
PSMEG and PW1Z PMEG, however in a transport network only the
alarm associated to the fiber cut needs to be reported to an NMS
while all secondary alarms should be suppressed (i.e. not
reported to the NMS or reported as secondary alarms).
If the fiber cut is detected by the MEP in the physical layer
(in LSR2), LSR2 can generate the proper alarm in the physical
layer and suppress the secondary alarm associated with the LOC
defect detected on Sec12 SMEG. As both MEPs reside within the
same node, this process does not involve any external protocol
exchange. Otherwise, if the physical layer has not enough OAM
capabilities to detect the fiber cut, the MEP of Sec12 SMEG in
LSR2 will report a LOC alarm.
In both cases, the MEP of Sec12 SMEG in LSR 2 notifies the
adaptation function for LSP13 LMEG that then generates AIS
packets on the LSP13 LMEG in order to allow its MEP in LSR3 to
suppress the LOC alarm. LSR3 can also suppress the secondary
alarm on PW13 PSMEG because the MEP of PW13 PSMEG resides within
the same node as the MEP of LSP13 LMEG. The MEP of PW13 PSMEG in
LSR3 also notifies the adaptation function for PW1Z PMEG that
then generates AIS packets on PW1Z PMEG in order to allow its
MEP in LSRZ to suppress the LOC alarm.
The generation of AIS packets for each MEG in the MPLS-TP client
(sub-)layer is configurable (i.e. the operator can
enable/disable the AIS generation).
AIS condition is cleared if no AIS packet has been received in
3.5 times the AIS transmission period.
The AIS transmission period is traditionally one per second but
an option to configure longer periods would be also desirable.
As a consequence, OAM packets need to self-identify the
transmission period such that proper exit criteria can be
established.
AIS packets are transmitted with the "minimum loss probability
PHB" within a single network operator. For E-LSPs, this PHB is
configurable on network operator's basis, while for L-LSPs, this
is determined as per RFC 3270 [23].
5.4. Lock Reporting
The Lock Reporting function, as required in section 2.2.7 of RFC
5860 [11], relies upon a Locked Report (LKR) packet used to
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suppress alarms following administrative locking action in the
server (sub-)layer.
When a server MEP is locked, the MPLS-TP client (sub-)layer
adaptation function generates packets with LKR information to
allow the suppression of secondary alarms at the MEPs in the
client (sub-)layer. Again it is assumed that there is a hold off
for any loss of continuity alarms in the client layer MEPs
downstream of the node originating the locked report. In case of
client (sub-)layer co-routed bidirectional transport paths, the
LKR information is sent on both directions. In case of client
(sub-)layer unidirectional transport paths, the LKR information
is sent only in the downstream direction. As a consequence, in
case of client (sub-)layer point-to-multipoint transport paths,
the LKR information is sent only to the MEPs that are downstream
to the server (sub-)layer that has been administratively locked.
Client (sub-)layer associated bidirectional transport paths
behave like co-routed bidirectional transport paths if the
server (sub-)layer that has been administratively locked is used
by both directions; otherwise they behave like unidirectional
transport paths.
The generation of packets with LKR information starts
immediately when the server MEP is locked. These periodic
packets, with LKR information, continue to be transmitted until
the locked condition is cleared.
Upon receiving a packet with LKR information an MPLS-TP MEP
enters an LKR defect condition and suppresses loss of continuity
alarm associated with its peer MEP but does not block traffic
received from the transport path. A MEP resumes loss of
continuity alarm generation upon detecting loss of continuity
defect conditions in the absence of LKR condition.
MIPs, as well as intermediate nodes, do not process the LKR
information and forward these LKR OAM packets as regular data
packets.
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For example, let's consider the case where the MPLS-TP Section
between LSR 1 and LSR 2 in the reference network of Figure 5 is
administrative locked at LSR2 (in both directions).
Assuming that all the MEGs described in Figure 5 have pro-active
CC-V enabled, a LOC defect is detected by the MEPs of LSP13
LMEG, PW1 PSMEG and PW1Z PMEG, however in a transport network
all these secondary alarms should be suppressed (i.e. not
reported to the NMS or reported as secondary alarms).
The MEP of Sec12 SMEG in LSR 2 notifies the adaptation function
for LSP13 LMEG that then generates LKR packets on the LSP13 LMEG
in order to allow its MEPs in LSR1 and LSR3 to suppress the LOC
alarm. LSR3 can also suppress the secondary alarm on PW13 PSMEG
because the MEP of PW13 PSMEG resides within the same node as
the MEP of LSP13 LMEG. The MEP of PW13 PSMEG in LSR3 also
notifies the adaptation function for PW1Z PMEG that then
generates AIS packets on PW1Z PMEG in order to allow its MEP in
LSRZ to suppress the LOC alarm.
The generation of LKR packets for each MEG in the MPLS-TP client
(sub-)layer is configurable (i.e. the operator can
enable/disable the LKR generation).
Locked condition is cleared if no LKR packet has been received
for 3.5 times the transmission period.
The LKR transmission period is traditionally one per second but
an option to configure longer periods would be also desirable.
As a consequence, OAM packets need to self-identify the
transmission period such that proper exit criteria can be
established.
LKR packets are transmitted with the "minimum loss probability
PHB" within a single network operator. For E-LSPs, this PHB is
configurable on network operator's basis, while for L-LSPs, this
is determined as per RFC 3270 [23].
5.5. Packet Loss Measurement
Packet Loss Measurement (LM) is one of the capabilities
supported by the MPLS-TP Performance Monitoring (PM) function in
order to facilitate reporting of QoS information for a transport
path as required in section 2.2.11 of RFC 5860 [11]. LM is used
to exchange counter values for the number of ingress and egress
packets transmitted and received by the transport path monitored
by a pair of MEPs.
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Proactive LM is performed by periodically sending LM OAM packets
from a MEP to a peer MEP and by receiving LM OAM packets from
the peer MEP (if a co-routed or associated bidirectional
transport path) during the life time of the transport path. Each
MEP performs measurements of its transmitted and received user
data packets. These measurements are then correlated in real
time with the peer MEP in the ME to derive the impact of packet
loss on a number of performance metrics for the ME in the MEG.
The LM transactions are issued such that the OAM packets will
experience the same PHB scheduling class as the measured traffic
while transiting between the MEPs in the ME.
For a MEP, near-end packet loss refers to packet loss associated
with incoming data packets (from the far-end MEP) while far-end
packet loss refers to packet loss associated with egress data
packets (towards the far-end MEP).
Pro-active LM can be operated in two ways:
o One-way: a MEP sends LM OAM packet to its peer MEP containing
all the required information to facilitate near-end packet
loss measurements at the peer MEP.
o Two-way: a MEP sends LM OAM packet with a LM request to its
peer MEP, which replies with a LM OAM packet as a LM
response. The request/response LM OAM packets containing all
the required information to facilitate both near-end and
far-end packet loss measurements from the viewpoint of the
originating MEP.
One-way LM is applicable to both unidirectional and
bidirectional (co-routed or associated) transport paths while
two-way LM is applicable only to bidirectional (co-routed or
associated) transport paths.
MIPs, as well as intermediate nodes, do not process the LM
information and forward these pro-active LM OAM packets as
regular data packets.
5.5.1. Configuration considerations
In order to support proactive LM, the transmission rate and, for
E-LSPs, the PHB class associated with the LM OAM packets
originating from a MEP need be configured as part of the LM
provisioning. LM OAM packets should be transmitted with the PHB
that yields the lowest drop precedence within the measured PHB
Scheduling Class (see RFC 3260 [17]), in order to maximize
reliability of measurement within the traffic class.
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If that PHB class is not an ordered aggregate where the ordering
constraint is all packets with the PHB class being delivered in
order, LM can produce inconsistent results.
Performance monitoring (e.g., LM) is only relevant when the
transport path is defect free. CC-V contributes to the accuracy
of PM statistics by permitting the defect free periods to be
properly distinguished. Therefore support of pro-active LM has
implications on the CC-V transmission period (see section
5.1.3).
5.5.2. Sampling skew
If an implementation makes use of a hardware forwarding path
which operates in parallel with an OAM processing path, whether
hardware or software based, the packet and byte counts may be
skewed if one or more packets can be processed before the OAM
processing samples counters. If OAM is implemented in software
this error can be quite large.
5.5.3. Multilink issues
If multilink is used at the LSP ingress or egress, there may be
no single packet processing engine where to inject or extract a
LM packet as an atomic operation to which accurate packet and
byte counts can be associated with the packet.
In the case where multilink is encountered in the LSP path, the
reordering of packets within the LSP can cause inaccurate LM
results.
5.6. Packet Delay Measurement
Packet Delay Measurement (DM) is one of the capabilities
supported by the MPLS-TP PM function in order to facilitate
reporting of QoS information for a transport path as required in
section 2.2.12 of RFC 5860 [11]. Specifically, pro-active DM is
used to measure the long-term packet delay and packet delay
variation in the transport path monitored by a pair of MEPs.
Proactive DM is performed by sending periodic DM OAM packets
from a MEP to a peer MEP and by receiving DM OAM packets from
the peer MEP (if a co-routed or associated bidirectional
transport path) during a configurable time interval.
Pro-active DM can be operated in two ways:
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o One-way: a MEP sends DM OAM packet to its peer MEP containing
all the required information to facilitate one-way packet
delay and/or one-way packet delay variation measurements at
the peer MEP. Note that this requires precise time
synchronisation at either MEP by means outside the scope of
this framework.
o Two-way: a MEP sends DM OAM packet with a DM request to its
peer MEP, which replies with a DM OAM packet as a DM
response. The request/response DM OAM packets containing all
the required information to facilitate two-way packet delay
and/or two-way packet delay variation measurements from the
viewpoint of the originating MEP.
One-way DM is applicable to both unidirectional and
bidirectional (co-routed or associated) transport paths while
two-way DM is applicable only to bidirectional (co-routed or
associated) transport paths.
MIPs, as well as intermediate nodes, do not process the DM
information and forward these pro-active DM OAM packets as
regular data packets.
5.6.1. Configuration considerations
In order to support pro-active DM, the transmission rate and,
for E-LSPs, the PHB associated with the DM OAM packets
originating from a MEP need be configured as part of the DM
provisioning. DM OAM packets should be transmitted with the PHB
that yields the lowest drop precedence within the measured PHB
Scheduling Class (see RFC 3260 [17]).
Performance monitoring (e.g., DM) is only relevant when the
transport path is defect free. CC-V contributes to the accuracy
of PM statistics by permitting the defect free periods to be
properly distinguished. Therefore support of pro-active DM has
implications on the CC-V transmission period (see section
5.1.3).
5.7. Client Failure Indication
The Client Failure Indication (CFI) function, as required in
section 2.2.10 of RFC 5860 [11], is used to help process client
defects and propagate a client signal defect condition from the
process associated with the local attachment circuit where the
defect was detected (typically the source adaptation function
for the local client interface) to the process associated with
the far-end attachment circuit (typically the source adaptation
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function for the far-end client interface) for the same
transmission path in case the client of the transport path does
not support a native defect/alarm indication mechanism, e.g.
AIS.
A source MEP starts transmitting a CFI indication to its peer
MEP when it receives a local client signal defect notification
via its local CSF function. Mechanisms to detect local client
signal fail defects are technology specific. Similarly
mechanisms to determine when to cease originating client signal
fail indication are also technology specific.
A sink MEP that has received a CFI indication report this
condition to its associated client process via its local CFI
function. Consequent actions toward the client attachment
circuit are technology specific.
Either there needs to be a 1:1 correspondence between the client
and the MEG, or when multiple clients are multiplexed over a
transport path, the CFI packet requires additional information
to permit the client instance to be identified.
MIPs, as well as intermediate nodes, do not process the CFI
information and forward these pro-active CFI OAM packets as
regular data packets.
5.7.1. Configuration considerations
In order to support CFI indication, the CFI transmission rate
and, for E-LSPs, the PHB of the CFI OAM packets should be
configured as part of the CFI configuration.
6. OAM Functions for on-demand monitoring
In contrast to proactive monitoring, on-demand monitoring is
initiated manually and for a limited amount of time, usually for
operations such as diagnostics to investigate a defect
condition.
On-demand monitoring covers a combination of "in-service" and
"out-of-service" monitoring functions. The control and
measurement implications are:
1. A MEG can be directed to perform an "on-demand" functions at
arbitrary times in the lifetime of a transport path.
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2. "out-of-service" monitoring functions may require a-priori
configuration of both MEPs and intermediate nodes in the MEG
(e.g., data plane loopback) and the issuance of notifications
into client layers of the transport path being removed from
service (e.g., lock-reporting)
3. The measurements resulting from on-demand monitoring are
typically harvested in real time, as these are frequently
initiated manually. These do not necessarily require
different harvesting mechanisms that for harvesting proactive
monitoring telemetry.
The functions that are exclusively out-of-service are those
described in section 6.3. The remainder are applicable to both
in-service and out-of-service transport paths.
6.1. Connectivity Verification
On demand connectivity verification function, as required in
section 2.2.3 of RFC 5860 [11], is a transaction that flows from
the originating MEP to a target MIP or MEP to verify the
connectivity between these points.
Use of on-demand CV is dependent on the existence of either a
bi-directional ME, or an associated return ME, or the
availability of an out-of-band return path because it requires
the ability for target MIPs and MEPs to direct responses to the
originating MEPs.
One possible use of on-demand CV would be to perform fault
management without using proactive CC-V, in order to preserve
network resources, e.g. bandwidth, processing time at switches.
In this case, network management periodically invokes on-demand
CV.
An additional use of on-demand CV would be to detect and locate
a problem of connectivity when a problem is suspected or known
based on other tools. In this case the functionality will be
triggered by the network management in response to a status
signal or alarm indication.
On-demand CV is based upon generation of on-demand CV packets
that should uniquely identify the MEG that is being checked.
The on-demand functionality may be used to check either an
entire MEG (end-to-end) or between the originating MEP and a
specific MIP. This functionality may not be available for
associated bidirectional transport paths or unidirectional
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paths, as the MIP may not have a return path to the originating
MEP for the on-demand CV transaction.
When on-demand CV is invoked, the originating MEP issues a
sequence of on-demand CV packets that uniquely identifies the
MEG being verified. The number of packets and their
transmission rate should be pre-configured at the originating
MEP, to take into account normal packet-loss conditions. The
source MEP should use the mechanisms defined in sections 3.3 and
3.4 when sending an on-demand CV packet to a target MEP or
target MIP respectively. The target MEP/MIP shall return a reply
on-demand CV packet for each packet received. If the expected
number of on-demand CV reply packets is not received at
originating MEP, this is an indication that a connectivity
problem may exist.
On-demand CV should have the ability to carry padding such that
a variety of MTU sizes can be originated to verify the MTU
transport capability of the transport path.
MIPs that are not targeted by on-demand CV packets, as well as
intermediate nodes, do not process the CV information and
forward these on-demand CV OAM packets as regular data packets.
6.1.1. Configuration considerations
For on-demand CV the originating MEP should support the
configuration of the number of packets to be
transmitted/received in each sequence of transmissions and their
packet size.
In addition, when the CV packet is used to check connectivity
toward a target MIP, the number of hops to reach the target MIP
should be configured.
For E-LSPs, the PHB of the on-demand CV packets should be
configured as well. This permits the verification of correct
operation of QoS queuing as well as connectivity.
6.2. Packet Loss Measurement
On-demand Packet Loss Measurement (LM) is one of the
capabilities supported by the MPLS-TP Performance Monitoring
function in order to facilitate the diagnosis of QoS
performances for a transport path, as required in section 2.2.11
of RFC 5860 [11].
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On-demand LM is very similar to pro-active LM described in
section 5.5. This section focuses on the differences between on-
demand and pro-active LM.
On-demand LM is performed by periodically sending LM OAM packets
from a MEP to a peer MEP and by receiving LM OAM packets from
the peer MEP (if a co-routed or associated bidirectional
transport path) during a pre-defined monitoring period. Each MEP
performs measurements of its transmitted and received user data
packets. These measurements are then correlated to evaluate the
packet loss performance metrics of the transport path.
Use of packet loss measurement in an out-of-service transport
path requires a traffic source such as a test device that can
inject synthetic traffic.
6.2.1. Configuration considerations
In order to support on-demand LM, the beginning and duration of
the LM procedures, the transmission rate and, for E-LSPs, the
PHB class associated with the LM OAM packets originating from a
MEP must be configured as part of the on-demand LM provisioning.
LM OAM packets should be transmitted with the PHB that yields
the lowest drop precedence as described in section 5.5.1.
6.2.2. Sampling skew
The same considerations described in section 5.5.2 for the
pro-active LM are also applicable to on-demand LM
implementations.
6.2.3. Multilink issues
Multi-link Issues are as described in section 5.5.3.
6.3. Diagnostic Tests
Diagnostic tests are tests performed on a MEG that has been taken
out-of-service.
6.3.1. Throughput Estimation
Throughput estimation is an on-demand out-of-service function,
as required in section 2.2.5 of RFC 5860 [11], that allows
verifying the bandwidth/throughput of an MPLS-TP transport path
(LSP or PW) before it is put in-service.
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Throughput estimation is performed between MEPs and between MEP
and MIP. It can be performed in one-way or two-way modes.
According to RFC 2544 [12], this test is performed by sending
OAM test packets at increasing rate (up to the theoretical
maximum), computing the percentage of OAM test packets received
and reporting the rate at which OAM test packets begin to drop.
In general, this rate is dependent on the OAM test packet size.
When configured to perform such tests, a source MEP inserts OAM
test packets with a specified packet size and transmission
pattern at a rate to exercise the throughput.
The throughput test can create congestion within the network
impacting other transport paths. However, the test traffic
should comply with the traffic profile of the transport path
under test, so the impact of the test will not be worst than the
impact caused by the customers, whose traffic would be sent over
that transport path, sending the traffic at the maximum rate
allowed by their traffic profiles. Therefore, throughput tests
are not applicable to transport paths that do not have a defined
traffic profile, such as for instance, LSPs in a context where
statistical multiplexing is leveraged for network capacity
dimensioning.
For a one-way test, the remote sink MEP receives the OAM test
packets and calculates the packet loss. For a two-way test, the
remote MEP loopbacks the OAM test packets back to original MEP
and the local sink MEP calculates the packet loss.
It is worth noting that two-way throughput estimation is only
applicable to bidirectional (co-routed or associated) transport
paths and can only evaluate the minimum of available throughput
of the two directions. In order to estimate the throughput of
each direction uniquely, two one-way throughput estimation
sessions have to be setup. One-way throughput estimation
requires coordination between the transmitting and receiving
test devices as described in section 6 of RFC 2544 [12].
It is also worth noting that if throughput estimation is
performed on transport paths that transit oversubscribed links,
the test may not produce comprehensive results if viewed in
isolation because the impact of the test on the surrounding
traffic needs to also be considered. Moreover, the estimation
will only reflect the bandwidth available at the moment when the
measure is made.
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MIPs that are not target by on-demand test OAM packets, as well
as intermediate nodes, do not process the throughput test
information and forward these on-demand test OAM packets as
regular data packets.
6.3.1.1. Configuration considerations
Throughput estimation is an out-of-service tool. The diagnosed
MEG should be put into a Lock status before the diagnostic test
is started.
A MEG can be put into a Lock status either via an NMS action or
using the Lock Instruct OAM tool as defined in section 7.
At the transmitting MEP, provisioning is required for a test
signal generator, which is associated with the MEP. At a
receiving MEP, provisioning is required for a test signal
detector which is associated with the MEP.
In order to ensure accurate measurement, care needs to be taken
to enable throughput estimation only if all the MEPs within the
MEG can process OAM test packets at the same rate as the payload
data rates (see section 6.3.1.2).
6.3.1.2. Limited OAM processing rate
If an implementation is able to process payload at much higher
data rates than OAM test packets, then accurate measurement of
throughput using OAM test packets is not achievable. Whether
OAM packets can be processed at the same rate as payload is
implementation dependent.
6.3.1.3. Multilink considerations
If multilink is used, then it may not be possible to perform
throughput measurement, as the throughput test may not have a
mechanism for utilizing more than one component link of the
aggregated link.
6.3.2. Data plane Loopback
Data plane loopback is an out-of-service function, as required
in section 2.2.5 of RFC 5860 [11]. This function consists in
placing a transport path, at either an intermediate or
terminating node, into a data plane loopback state, such that
all traffic (including both payload and OAM) received on the
looped back interface is sent on the reverse direction of the
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transport path. The traffic is looped back unmodified other than
normal per hop processing such as TTL decrement.
The data plane loopback function requires that the MEG is locked
such that user data traffic is prevented from entering/exiting
that MEG. Instead, test traffic is inserted at the ingress of
the MEG. This test traffic can be generated from an internal
process residing within the ingress node or injected by external
test equipment connected to the ingress node.
It is also normal to disable proactive monitoring of the path as
the MEP located upstream with respect to the node set in the
data plane loopback mode will see all the OAM packets,
originated by itself and this may interfere with other
measurements.
The only way to send an OAM packet (e.g., to remove the data
plane loopback state) to the MIPs or MEPs hosted by a node set
in the data plane loopback mode is via TTL expiry. It should
also be noted that MIPs can be addressed with more than one TTL
value on a co-routed bi-directional path set into data plane
loopback.
If the loopback function is to be performed at an intermediate
node it is only applicable to co-routed bi-directional paths. If
the loopback is to be performed end to end, it is applicable to
both co-routed bi-directional or associated bi-directional
paths.
It should be noted that data plane loopback function itself is
applied to data plane loopback points that can resides on
different interfaces from MIPs/MEPs. Where a node implements
data plane loopback capability and whether it implements it in
more than one point is implementation dependent.
6.3.2.1. Configuration considerations
Data plane loopback is an out-of-service tool. The MEG which
defines a diagnosed transport path should be put into a locked
state before the diagnostic test is started. However, a means is
required to permit the originated test traffic to be inserted at
ingress MEP when data plane loopback is performed.
A transport path, at either an intermediate or terminating node,
can be put into data plane loopback state via an NMS action or
using an OAM tool for data plane loopback configuration.
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If the data plane loopback point is set somewhere at an
intermediate point of a co-routed bidirectional transport path,
the side of loop back function (one side or both side) needs to
be configured.
6.4. Route Tracing
It is often necessary to trace a route covered by a MEG from an
originating MEP to the peer MEP(s) including all the MIPs in-
between, and may be conducted after provisioning an MPLS-TP
transport path for, e.g., trouble shooting purposes such as
fault localization.
The route tracing function, as required in section 2.2.4 of RFC
5860 [11], is providing this functionality. Based on the fate
sharing requirement of OAM flows, i.e. OAM packets receive the
same forwarding treatment as data packet, route tracing is a
basic means to perform connectivity verification and, to a much
lesser degree, continuity check. For this function to work
properly, a return path must be present.
Route tracing might be implemented in different ways and this
document does not preclude any of them.
Route tracing should always discover the full list of MIPs and
of the peer MEPs. In case a defect exists, the route trace
function will only be able to trace up to the defect, and needs
to be able to return the incomplete list of OAM entities that it
was able to trace such that the fault can be localized.
6.4.1. Configuration considerations
The configuration of the route trace function must at least
support the setting of the number of trace attempts before it
gives up.
6.5. Packet Delay Measurement
Packet Delay Measurement (DM) is one of the capabilities
supported by the MPLS-TP PM function in order to facilitate
reporting of QoS information for a transport path, as required
in section 2.2.12 of RFC 5860 [11]. Specifically, on-demand DM
is used to measure packet delay and packet delay variation in
the transport path monitored by a pair of MEPs during a pre-
defined monitoring period.
On-Demand DM is performed by sending periodic DM OAM packets
from a MEP to a peer MEP and by receiving DM OAM packets from
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the peer MEP (if a co-routed or associated bidirectional
transport path) during a configurable time interval.
On-demand DM can be operated in two modes:
o One-way: a MEP sends DM OAM packet to its peer MEP containing
all the required information to facilitate one-way packet
delay and/or one-way packet delay variation measurements at
the peer MEP. Note that this requires precise time
synchronisation at either MEP by means outside the scope of
this framework.
o Two-way: a MEP sends DM OAM packet with a DM request to its
peer MEP, which replies with an DM OAM packet as a DM
response. The request/response DM OAM packets containing all
the required information to facilitate two-way packet delay
and/or two-way packet delay variation measurements from the
viewpoint of the originating MEP.
MIPs, as well as intermediate nodes, do not process the DM
information and forward these on-demand DM OAM packets as
regular data packets.
6.5.1. Configuration considerations
In order to support on-demand DM, the beginning and duration of
the DM procedures, the transmission rate and, for E-LSPs, the
PHB associated with the DM OAM packets originating from a MEP
need be configured as part of the DM provisioning. DM OAM
packets should be transmitted with the PHB that yields the
lowest drop precedence within the measured PHB Scheduling Class
(see RFC 3260 [17]).
In order to verify different performances between long and short
packets (e.g., due to the processing time), it should be
possible for the operator to configure the packet size of the
on-demand OAM DM packet.
7. OAM Functions for administration control
7.1. Lock Instruct
Lock Instruct (LKI) function, as required in section 2.2.6 of
RFC 5860 [11], is a command allowing a MEP to instruct the peer
MEP(s) to put the MPLS-TP transport path into a locked
condition.
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This function allows single-side provisioning for
administratively locking (and unlocking) an MPLS-TP transport
path.
Note that it is also possible to administratively lock (and
unlock) an MPLS-TP transport path using two-side provisioning,
where the NMS administratively puts both MEPs into an
administrative lock condition. In this case, the LKI function is
not required/used.
MIPs, as well as intermediate nodes, do not process the lock
instruct information and forward these on-demand LKI OAM packets
as regular data packets.
7.1.1. Locking a transport path
A MEP, upon receiving a single-side administrative lock command
from an NMS, sends an LKI request OAM packet to its peer MEP(s).
It also puts the MPLS-TP transport path into a locked state and
notifies its client (sub-)layer adaptation function upon the
locked condition.
A MEP, upon receiving an LKI request from its peer MEP, can
either accept or reject the instruction and replies to the peer
MEP with an LKI reply OAM packet indicating whether or not it
has accepted the instruction. This requires either an in-band or
out-of-band return path. The LKI reply is needed to allow the
MEP to properly report to the NMS the actual result of the
single-side administrative lock command.
If the lock instruction has been accepted, it also puts the
MPLS-TP transport path into a locked state and notifies its
client (sub-)layer adaptation function upon the locked
condition.
Note that if the client (sub-)layer is also MPLS-TP, Lock
Reporting (LKR) generation at the client MPLS-TP (sub-)layer is
started, as described in section 5.4.
7.1.2. Unlocking a transport path
A MEP, upon receiving a single-side administrative unlock
command from NMS, sends an LKI removal request OAM packet to its
peer MEP(s).
The peer MEP, upon receiving an LKI removal request, can either
accept or reject the removal instruction and replies with an LKI
removal reply OAM packet indicating whether or not it has
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accepted the instruction. The LKI removal reply is needed to
allow the MEP to properly report to the NMS the actual result of
the single-side administrative unlock command.
If the lock removal instruction has been accepted, it also
clears the locked condition on the MPLS-TP transport path and
notifies this event to its client (sub-)layer adaptation
function.
The MEP that has initiated the LKI clear procedure, upon
receiving a positive LKI removal reply, also clears the locked
condition on the MPLS-TP transport path and notifies this event
to its client (sub-)layer adaptation function.
Note that if the client (sub-)layer is also MPLS-TP, Lock
Reporting (LKR) generation at the client MPLS-TP (sub-)layer is
terminated, as described in section 5.4.
8. Security Considerations
A number of security considerations are important in the context
of OAM applications.
OAM traffic can reveal sensitive information such as performance
data and details about the current state of the network.
Insertion of, or modifications to OAM transactions can mask the
true operational state of the network and in the case of
transactions for administration control, such as Lock or data
plane loopback instructions, these can be used for explicit
denial of service attacks. The effect of such attacks is
mitigated only by the fact that, for in-band messaging, the
managed entities whose state can be masked is limited to those
that transit the point of malicious access to the network
internals due to the fate sharing nature of OAM messaging. This
is not true when an out of band return path is employed.
The sensitivity of OAM data therefore suggests that one solution
is that some form of authentication, authorization and
encryption is in place. This will prevent unauthorized access to
vital equipment and it will prevent third parties from learning
about sensitive information about the transport network. However
it should be observed that the combination of the frequency of
some OAM transactions, the need for timeliness of OAM
transaction exchange and all permutations of unique MEP to MEP,
MEP to MIP, and intermediate system originated transactions
mitigates against the practical establishment and maintenance of
a large number of security associations per MEG either in
advance or as required.
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For this reason it is assumed that the internal links of the
network is physically secured from malicious access such that
OAM transactions scoped to fault and performance management of
individual MEGs are not encumbered with additional security.
Further it is assumed in multi-provider cases where OAM
transactions originate outside of an individual providers
trusted domain that filtering mechanisms or further
encapsulation will need to constrain the potential impact of
malicious transactions. Mechanisms that the framework does not
specify might be subject to additional security considerations.
In case of mis-configuration, some nodes can receive OAM packets
that they cannot recognize. In such a case, these OAM packets
should be silently discarded in order to avoid malfunctions
whose effect may be similar to malicious attacks (e.g., degraded
performance or even failure). Further considerations about data
plane attacks via G-ACh are provided in RFC 5921 [8].
9. IANA Considerations
This memo does not have any IANA considerations.
10. Acknowledgments
The authors would like to thank all members of the teams (the
Joint Working Team, the MPLS Interoperability Design Team in
IETF and the Ad Hoc Group on MPLS-TP in ITU-T) involved in the
definition and specification of MPLS Transport Profile.
The editors gratefully acknowledge the contributions of Adrian
Farrel, Yoshinori Koike, Luca Martini, Yuji Tochio and Manuel
Paul for the definition of per-interface MIPs and MEPs.
The editors gratefully acknowledge the contributions of Malcolm
Betts, Yoshinori Koike, Xiao Min, and Maarten Vissers for the
lock report and lock instruction description.
The authors would also like to thank Alessandro D'Alessandro,
Loa Andersson, Malcolm Betts, Dave Black, Stewart Bryant, Rui
Costa, Xuehui Dai, John Drake, Adrian Farrel, Dan Frost, Xia
Liang, Liu Gouman, Peng He, Russ Housley, Feng Huang, Su Hui,
Yoshionori Koike, Thomas Morin, George Swallow, Yuji Tochio,
Curtis Villamizar, Maarten Vissers and Xuequin Wei for their
comments and enhancements to the text.
This document was prepared using 2-Word-v2.0.template.dot.
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11. References
11.1. Normative References
[1] Rosen, E., Viswanathan, A., Callon, R., "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001
[2] Bryant, S., Pate, P., "Pseudo Wire Emulation Edge-to-Edge
(PWE3) Architecture", RFC 3985, March 2005
[3] Nadeau, T., Pignataro, S., "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for
Pseudowires", RFC 5085, December 2007
[4] Bocci, M., Bryant, S., "An Architecture for Multi-Segment
Pseudo Wire Emulation Edge-to-Edge", RFC 5659, October
2009
[5] Niven-Jenkins, B., Brungard, D., Betts, M., sprecher, N.,
Ueno, S., "MPLS-TP Requirements", RFC 5654, September 2009
[6] Agarwal, P., Akyol, B., "Time To Live (TTL) Processing in
Multiprotocol Label Switching (MPLS) Networks", RFC 3443,
January 2003
[7] Vigoureux, M., Bocci, M., Swallow, G., Ward, D., Aggarwal,
R., "MPLS Generic Associated Channel", RFC 5586, June 2009
[8] Bocci, M., et al., "A Framework for MPLS in Transport
Networks", RFC 5921, July 2010
[9] Bocci, M., et al., " MPLS Transport Profile User-to-Network and
Network-to-Network Interfaces", draft-ietf-mpls-tp-uni-nni-03
(work in progress), January 2011
[10] Swallow, G., Bocci, M., "MPLS-TP Identifiers", draft-ietf-
mpls-tp-identifiers-03 (work in progress), October 2010
[11] Vigoureux, M., Betts, M., Ward, D., "Requirements for OAM
in MPLS Transport Networks", RFC 5860, May 2010
[12] Bradner, S., McQuaid, J., "Benchmarking Methodology for
Network Interconnect Devices", RFC 2544, March 1999
[13] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
Weiss, W., "An Architecture for Differentiated Services",
RFC 2475, December 1998
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[14] ITU-T Recommendation G.806 (01/09), "Characteristics of
transport equipment - Description methodology and generic
functionality ", January 2009
11.2. Informative References
[15] Sprecher, N., Nadeau, T., van Helvoort, H., Weingarten,
Y., "MPLS-TP OAM Analysis", draft-ietf-mpls-tp-oam-
analysis-03 (work in progress), January 2011
[16] Nichols, K., Blake, S., Baker, F., Black, D., "Definition
of the Differentiated Services Field (DS Field) in the
IPv4 and IPv6 Headers", RFC 2474, December 1998
[17] Grossman, D., "New terminology and clarifications for
Diffserv", RFC 3260, April 2002.
[18] Kompella, K., Rekhter, Y., Berger, L., "Link Bundling in
MPLS Traffic Engineering (TE)", RFC 4201, October 2005
[19] ITU-T Recommendation G.707/Y.1322 (01/07), "Network node
interface for the synchronous digital hierarchy (SDH)",
January 2007
[20] ITU-T Recommendation G.805 (03/00), "Generic functional
architecture of transport networks", March 2000
[21] ITU-T Recommendation Y.1731 (02/08), "OAM functions and
mechanisms for Ethernet based networks", February 2008
[22] IEEE Standard 802.1AX-2008, "IEEE Standard for Local and
Metropolitan Area Networks - Link Aggregation", November
2008
[23] Le Faucheur et.al., "Multi-Protocol Label Switching (MPLS)
Support of Differentiated Services", RFC 3270, May 2002.
Authors' Addresses
Dave Allan
Ericsson
Email: david.i.allan@ericsson.com
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Italo Busi
Alcatel-Lucent
Email: Italo.Busi@alcatel-lucent.com
Ben Niven-Jenkins
Velocix
Email: ben@niven-jenkins.co.uk
Annamaria Fulignoli
Ericsson
Email: annamaria.fulignoli@ericsson.com
Enrique Hernandez-Valencia
Alcatel-Lucent
Email: Enrique.Hernandez@alcatel-lucent.com
Lieven Levrau
Alcatel-Lucent
Email: Lieven.Levrau@alcatel-lucent.com
Vincenzo Sestito
Alcatel-Lucent
Email: Vincenzo.Sestito@alcatel-lucent.com
Nurit Sprecher
Nokia Siemens Networks
Email: nurit.sprecher@nsn.com
Huub van Helvoort
Huawei Technologies
Email: hhelvoort@huawei.com
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Martin Vigoureux
Alcatel-Lucent
Email: Martin.Vigoureux@alcatel-lucent.com
Yaacov Weingarten
Nokia Siemens Networks
Email: yaacov.weingarten@nsn.com
Rolf Winter
NEC
Email: Rolf.Winter@nw.neclab.eu
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