MPLS Working Group I. Busi (Ed)
Internet Draft Alcatel-Lucent
Intended status: Informational B. Niven-Jenkins (Ed)
BT
D. Allan (Ed)
Ericsson
Expires: October 21, 2010 April 21, 2010
MPLS-TP OAM Framework
draft-ietf-mpls-tp-oam-framework-06.txt
Abstract
Multi-Protocol Label Switching (MPLS) Transport Profile (MPLS-
TP) is based on a profile of the MPLS and pseudowire (PW)
procedures as specified in the MPLS Traffic Engineering (MPLS-
TE), PW and multi-segment PW (MS-PW) architectures complemented
with additional Operations, Administration and Maintenance (OAM)
procedures for fault, performance and protection-switching
management for packet transport applications that do not rely on
the presence of a control plane.
This document describes a framework to support a comprehensive
set of OAM procedures that fulfill the MPLS-TP OAM requirements.
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-
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Drafts as reference material or to cite them other than as "work
in progress".
The list of current Internet-Drafts can be accessed at
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This Internet-Draft will expire on October 21, 2010.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction...................................................5
1.1. Contributing Authors......................................6
2. Conventions used in this document..............................6
2.1. Terminology...............................................6
2.2. Definitions...............................................7
3. Functional Components..........................................9
3.1. Maintenance Entity and Maintenance Entity Group...........9
3.2. Nested MEGs: Path Segment Tunnels and Tandem Connection
Monitoring....................................................11
3.3. MEG End Points (MEPs)....................................13
3.4. MEG Intermediate Points (MIPs)...........................15
3.5. Server MEPs..............................................17
3.6. Configuration Considerations.............................18
3.7. P2MP considerations......................................18
4. Reference Model...............................................19
4.1. MPLS-TP Section Monitoring (SME).........................21
4.2. MPLS-TP LSP End-to-End Monitoring (LME)..................22
4.3. MPLS-TP PW Monitoring (PME)..............................23
4.4. MPLS-TP LSP Path Segment Tunnel Monitoring (LPSTME)......23
4.5. MPLS-TP MS-PW Path Segment Tunnel Monitoring (PPSTME)....25
4.6. Fate sharing considerations for multilink................26
5. OAM Functions for proactive monitoring........................27
5.1. Continuity Check and Connectivity Verification...........28
5.1.1. Defects identified by CC-V..........................29
5.1.2. Consequent action...................................31
5.1.3. Configuration considerations........................32
5.2. Remote Defect Indication.................................33
5.2.1. Configuration considerations........................34
5.3. Alarm Reporting..........................................34
5.4. Lock Reporting...........................................35
5.5. Packet Loss Measurement..................................36
5.5.1. Configuration considerations........................37
5.5.2. Sampling skew.......................................37
5.5.3. Multilink issues....................................37
5.6. Packet Delay Measurement.................................37
5.6.1. Configuration considerations........................38
5.7. Client Failure Indication................................38
5.7.1. Configuration considerations........................39
6. OAM Functions for on-demand monitoring........................39
6.1. Connectivity Verification................................40
6.1.1. Configuration considerations........................41
6.2. Packet Loss Measurement..................................41
6.2.1. Configuration considerations........................42
6.2.2. Sampling skew.......................................42
6.2.3. Multilink issues....................................42
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6.3. Diagnostic Tests.........................................42
6.3.1. Throughput Estimation...............................42
6.3.2. Data plane Loopback.................................43
6.4. Route Tracing............................................44
6.4.1. Configuration considerations........................44
6.5. Packet Delay Measurement.................................45
6.5.1. Configuration considerations........................45
7. OAM Functions for administration control......................46
7.1. Lock Instruct............................................46
7.1.1. Locking a transport path............................46
7.1.2. Unlocking a transport path..........................46
8. Security Considerations.......................................47
9. IANA Considerations...........................................47
10. Acknowledgments..............................................48
11. References...................................................49
11.1. Normative References....................................49
11.2. Informative References..................................49
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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 [5], the multi protocol label switching (MPLS)
transport profile (MPLS-TP) defines a profile of the MPLS-
Traffic Engineering (MPLS-TE) and Multi-segment Pseudo Wire
(MS-PW) architectures defined in RFC 3031 [1], RFC 3985 [2] and
RFC 5659 [4] which is complemented with additional OAM
mechanisms and procedures for alarm, fault, performance and
protection-switching management for packet transport
applications.
In line with [10], 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. Extensions do not deprecate support for
existing MPLS OAM capabilities.
The MPLS-TP OAM framework defined in this document provides a
comprehensive set of OAM procedures that satisfy the MPLS-TP OAM
requirements [8]. In this regard, it defines similar OAM
functionality as for existing SONET/SDH and OTN OAM mechanisms
(e.g. [13]).
The MPLS-TP OAM framework is applicable to both LSPs and
(MS-)PWs and supports co-routed and associated bidirectional p2p
transport paths as well as unidirectional p2p and p2mp transport
paths.
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.
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1.1. Contributing Authors
Dave Allan, Italo Busi, Ben Niven-Jenkins, Annamaria Fulignoli,
Enrique Hernandez-Valencia, Lieven Levrau, Dinesh Mohan,
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
DBN Domain Border Node
LER Label Edge Router
LME LSP Maintenance Entity Group
LSP Label Switched Path
LSR Label Switching Router
LPSTME LSP path segment tunnel ME Group
ME Maintenance Entity
MEG Maintenance Entity Group
MEP Maintenance Entity Group End Point
MIP Maintenance Entity Group Intermediate Point
PHB Per-hop Behavior
PME PW Maintenance Entity Group
PPSTME PW path segment tunnel ME Group
PST Path Segment Tunnel
PW Pseudowire
SLA Service Level Agreement
SME Section Maintenance Entity Group
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2.2. Definitions
Note - the definitions in this section are aligned with ITU-T
recommendation Y.1731 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.
Data plane loopback: it is an out-of-service test where an
interface at either an intermediate or terminating node in a
path is placed into a data plane loopback state, such that all
traffic (including user data and OAM) received on the looped
back interface is sent on the reverse direction of the transport
path.
Domain Border Node (DBN): An LSP intermediate MPLS-TP node (LSR)
that is at the boundary of an MPLS-TP OAM domain. Such a node
may be present on the edge of two domains or may be connected by
a link to an MPLS-TP node in another OAM domain.
Down MEP: A MEP residing in a node that receives OAM packets
from, and transmits them towards, the direction of a server
layer.
In-Service: the administrative status of a transport path when
it is unlocked.
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, 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 transport path
in an OAM domain.
MEP: A MEG end point (MEP) is capable of initiating (MEP Source)
and terminating (MEP Sink) OAM messages for fault management and
performance monitoring. MEPs define the boundaries of an ME
(details in section 3.3).
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MEP Source: A MEP acts as MEP source for an OAM message when it
originates and inserts the message into the transport path for
its associated MEG.
MEP Sink: A MEP acts as a MEP sink for an OAM message when it
terminates and processes the messages received from its
associated MEG.
MIP: A MEG intermediate point (MIP) terminates and processes OAM
messages and may generate OAM messages in reaction to received
OAM messages. It never generates unsolicited OAM messages
itself. A MIP resides within a MEG between MEPs (details in
section 3.3).
OAM domain: A domain, as defined in [5], whose entities are
grouped for the purpose of keeping the OAM confined within that
domain.
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 messages originating with a
specific MEP source that instrument one direction of a MEG.
OAM information element: An atomic piece of information
exchanged between MEPs in MEG used by an OAM application.
OAM loopback: it is the capability of a node to intercepts some
specific OAM packets and to generate a reply back to their
sender. OAM loopback can work in-service and can support
different OAM functions (e.g., bidirectional on-demand
connectivity verification).
OAM Message: One or more OAM information elements that when
exchanged between MEPs or between MEPs and MIPs performs some
OAM functionality (e.g. connectivity verification)
OAM Packet: A packet that carries one or more OAM messages (i.e.
OAM information elements).
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].
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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 [9].
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.
Up MEP: A MEP residing in a node that transmits OAM packets
towards, and receives them from, the direction of the forwarding
engine.
This document uses the terms defined in RFC 5654 [5].
This document uses the term 'Per-hop Behavior' as defined in
[11].
This document uses the term LSP to indicate either a service LSP
or a transport LSP (as defined in [5]).
3. Functional Components
MPLS-TP defines a profile of the MPLS and PW architectures ([1],
[2] and [4]) that is required to transport 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 high-level functional components.
3.1. Maintenance Entity and Maintenance Entity Group
MPLS-TP OAM operates in the context of Maintenance Entities
(MEs) that are a relationship between any two points of a
transport path to which maintenance and monitoring operations
apply. 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) and the two
points that define a maintenance entity are called Maintenance
Entity Group (MEG) End Points (MEPs). In between these two
points zero or more intermediate points, called Maintenance
Entity Group Intermediate Points (MIPs), can exist and can be
shared by more than one ME in a MEG.
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The abstract reference model for an ME with MEPs and MIPs is
described in Figure 1 below:
+-+ +-+ +-+ +-+
|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 this model, nodes A, B, C
and D can be LER/LSR for an LSP or the {S|T}-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/PSTs, or serving layer
paths.
This functional model defines the relationships between all OAM
entities from a maintenance perspective, to allow each
Maintenance Entity to monitor and manage the (sub-)layer network
under its responsibility and to localize problems efficiently.
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 are configured and managed to limit the
scope of an OAM flow within the MEG that the MEPs belong to
(i.e. within the domain of the transport path that is being
monitored and managed). A misbranching fault may cause OAM
packets to be delivered to a MEP that is not in the MEG of
origin.
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 source MEP does not necessarily
exist in the MEG.
In case of co-routed bi-directional point-to-point transport
paths, a single bidirectional Maintenance Entity is defined to
monitor both directions congruently.
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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.
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 operations 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 from itself and the root while the root (i.e. A) generates
OAM messages common to all the MEs of the p2mp MEG. All nodes
may implement a MIP in the corresponding MEG.
3.2. Nested MEGs: Path Segment Tunnels and Tandem Connection
Monitoring
In order to verify and maintain performance and quality
guarantees, there is a need to not only apply OAM functionality
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.
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Path segment tunnels (PSTs), as defined in [5], are instantiated
to provide monitoring of a portion of a set of co-routed
transport paths (LSPs or MS-PWs). Path segment tunnels can also
be employed to meet the requirement to provide tandem connection
monitoring (TCM).
TCM for a given path segment of a transport path is implemented
by creating a path segment tunnel that has a 1:1 association
with the path segment of the transport path that is to be
uniquely monitored. This means that the PST used to provide TCM
can carry only one and only one transport path thus allowing
direct correlation between all fault management and performance
monitoring information gathered for the PST and the monitored
path segment of the end-to-end transport path. The PST is
monitored using normal LSP monitoring.
There are a number of implications to this approach:
1) The PST would use the uniform model of 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
PST.
2) The PST would use the pipe model for TTL handling such that
MIP addressing for the E2E entity would be not be impacted by
the presence of the PST.
3) PM statistics need to be adjusted for the encapsulation
overhead of the additional PST sub-layer.
A PST is instantiated to create a MEG that monitors a path
segment of a transport path (LSP or PW). The endpoints of the
PST are MEPs and limit the scope of an OAM flow within the MEG
the MEPs belong to (i.e. within the domain of the PST that is
being monitored and managed).
The following properties apply to all MPLS-TP MEGs:
o They can be nested but not overlapped, e.g. a MEG may cover a
segment or a concatenated segment of another MEG, and may
also include the forwarding engine(s) of the node(s) at the
edge(s) of the segment or concatenated segment. However when
MEGs are nested, the MEPs and MIPs in the nested MEG are no
longer part of the encompassing MEG.
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o It is possible that MEPs of nested MEGs 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 Maintenance Entity
Group.
o OAM packets that instrument a particular direction of a
transport path are subject to the same forwarding treatment
(i.e. fate share) as the data traffic and in some cases may
be required to have common queuing discipline E2E with the
class of traffic monitored. OAM packets can be distinguished
from the data traffic using the GAL and ACH constructs [6]
for LSP and Section or the ACH construct [3]and [6] for
(MS-)PW.
o When a PST is instantiated after the transport path has been
instantiated the addressing of the MIPs will change.
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 a path segment tunnel (PST) LSRs for the
MPLS-TP LSP can be LERs for PSTs that contribute to the overall
monitoring infrastructure for the transport path. Regarding
MPLS-TP PW, only T-PEs can implement MEPs while for PSTs
supporting a PW both T-PEs and S-PEs can implement MEPs. In the
context of MPLS-TP Section, any MPLS-TP LSR can implement a MEP
for a serving (sub-)layer PST.
MEPs are responsible for activating and controlling all of the
proactive and on demand monitoring OAM functionality for the
MEG. There is a separate class of server layer originated
notifications (such as LKR and AIS) that are originated by
intermediate nodes. A MEP is capable of originating and
terminating OAM messages for fault management and performance
monitoring. These OAM messages are encapsulated into an OAM
packet using the G-ACh as defined in RFC 5586 [6]: in this case
the G-ACh message is an OAM message and the channel type
indicates an OAM message. A MEP terminates all the OAM packets
it receives from the MEG it belongs to. The MEG the OAM packet
belongs to is inferred from the MPLS or PW label or, in case of
MPLS-TP section, the MPLS-TP port the OAM packet has been
received with the GAL at the top of the label stack.
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OAM packets may require the use of an available "out-of-band"
return path (as defined in [5]). In such cases sufficient
information is required in the originating transaction such that
the OAM reply packet can be constructed (e.g. IP address).
Each OAM solution will further detail its applicability as a
pro-active or on-demand measurement 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. A node at the edge of a MEG always supports a
MEP.
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
scope. Note that both MEP source and MEP sink coincide with
transport paths' source and sink terminations.
The MEPs of a path segment tunnel are not necessarily coincident
with the termination of the MPLS-TP transport path and 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 path segment tunnel.
An MPLS-TP MEP sink passes a fault indication to its client
(sub-)layer network as a consequent action of fault detection.
A node at the edge of a MEG 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.
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Source node Destination node
------------------------ ------------------------
| | | |
|----- -----| |----- -----|
| MEP | | | | | | MEP |
| | ---- | | | | ---- | |
| In |->-| FW |->-| Out |->- ->-| In |->-| FW |->-| Out |
| i/f | ---- | i/f | | i/f | ---- | i/f |
|----- -----| |----- -----|
| | | |
------------------------ ------------------------
(1) (2)
Figure 3 Example of per-interface Up MEPs
Figure 3 describes two examples of per-interface Up MEPs: an Up
Source MEP in a source node (case 1) and an Up Sink MEP in a
destination node (case 2).
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 will further detail the implications when used
with per-interface or per-node MEPs, if necessary.
It may occur that the Up MEPs of a path segment tunnel are set
on both sides of the forwarding engine such that the MEG is
entirely internal to the node.
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 a path
segment tunnel is created which permits MEPs and an associated
MEG to be created.
In the case where an intermediate node sends a message 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 PST.
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A MIP is capable of reacting to some OAM packets and forwarding
all the other OAM packets while ensuring fate sharing with data
plane 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 are sent on the MEG it belongs to.
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).
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. It is always assumed that the
"pipe"/"short pipe" model of TTL handling is used by the MPLS
transport profile.
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 is associated with
is inferred from the MPLS label.
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A node at the edge of a MEG 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.
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 interacts with 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;
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 PST MEP used for LSP path segment monitoring, as
defined in section 4.4, for MPLS-TP LSPs or higher-level PSTs
providing LSP path segment monitoring;
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o An MPLS-TP PST MEP used for PW path segment monitoring, as
defined in section 4.5, for MPLS-TP PWs or higher-level PSTs
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. Server MEP
OAM functions 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 to disable the usage of any available "out-
of-band" return path, as defined in [5], to generate OAM reply
packets, irrespectively on what is requested by the node
originating the OAM packet triggering the request.
PSTs are usually instantiated when the transport path is created
by either the management plane or by the control plane (if
present). Sometimes PST can be instantiated after the transport
path is initially created (e.g. PST).
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.
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
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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 message must contain sufficient
information to identify the target MIP and therefore is
processed only by the target MIP. The source MEP should
also include Target MIP information in the OAM packet to
allow proper identification of the node and the MIP the OAM
packet is addressed to.
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. Better mechanisms are outside the scope of this
document.
P2MP paths are unidirectional, therefore any return path to a
source MEP for on demand transactions will be out of band. A
mechanism to scope the set of MEPs or MIPs expected to respond
to a given "on demand" transaction is useful as it relieves the
source MEP of the requirement to filter and discard undesired
responses as normally TTL exhaust will address all MIPs at a
given distance from the source, and failure to exhaust TTL will
address all MEPs.
4. Reference Model
The reference model for the MPLS-TP framework builds upon the
concept of a MEG, and its associated MEPs and MIPs, to support
the functional requirements specified in [8].
The following MPLS-TP MEGs are specified in this document:
o A Section Maintenance Entity Group (SME), allowing monitoring
and management of MPLS-TP Sections (between MPLS LSRs).
o An LSP Maintenance Entity Group (LME), allowing monitoring
and management of an end-to-end LSP (between LERs).
o A PW Maintenance Entity Group (PME), allowing monitoring and
management of an end-to-end SS/MS-PWs (between T-PEs).
o An LSP Path Segment Tunnel ME Group (LPSTME), allowing
monitoring and management of a path segment tunnel (between
any LERs/LSRs along an LSP).
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o A PW Path Segment Tunnel ME Group (PPSTME), allowing
monitoring and management of an MPLS-TP path segment tunnel
(between any T-PEs/S-PEs along the (MS-)PW).
The MEGs specified in this MPLS-TP framework are compliant with
the architecture framework for MPLS-TP MS-PWs [4] and LSPs [1].
Hierarchical LSPs are also supported in the form of path segment
tunnels. 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 PSTME. It is possible to monitor a
portion of a hierarchical LSP by instantiating a hierarchical
PSTME between any LERs/LSRs along the hierarchical LSP.
Native |<------------------- MS-PW1Z ------------------->| Native
Layer | | Layer
Service | |<-LSP13->| |<-LSP3X->| |<-LSPXZ->| | Service
(AC1) V V LSP V V LSP V V LSP V V (AC2)
+----+ +-+ +----+ +----+ +-+ +----+
+----+ |TPE1| | | |SPE3| |SPEX| | | |TPEZ| +----+
| | | |=========| |=========| |=========| | | |
| CE1|---|........PW13.......|...PW3X..|........PWXZ.......|---|CE2 |
| | | |=========| |=========| |=========| | | |
+----+ | 1 | |2| | 3 | | X | |Y| | Z | +----+
+----+ +-+ +----+ +----+ +-+ +----+
. . . .
| | | |
|<---- Domain 1 --->| |<---- Domain Z --->|
^------------------- PW1Z PME -------------------^
^---- PW13 PPSTME---^ ^---- PWXZ PPSTME---^
^---------^ ^---------^
LSP13 LME LSPXZ LME
^---^ ^---^ ^---------^ ^---^ ^---^
Sec12 Sec23 Sec3X SecXY SecYZ
SME SME SME SME SME
TPE1: Terminating Provider Edge 1 SPE2: Switching Provider Edge 3
TPEX: Terminating Provider Edge X SPEZ: Switching Provider Edge Z
^---^ ME ^ MEP ==== LSP .... PW
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
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enabled network domains, Domain 1 and Domain Z. In Domain 1,
LSR1 is adjacent to LSR2 via the MPLS Section Sec12 and LSR2 is
adjacent to LSR3 via the MPLS Section Sec23. Similarly, in
Domain Z, LSRX is adjacent to LSRY via the MPLS Section SecXY
and LSRY is adjacent to LSRZ via the MPLS Section SecYZ. In
addition, LSR3 is adjacent to LSRX via the MPLS Section 3X.
Figure 5 also shows a bi-directional MS-PW (PW1Z) between AC1 on
TPE1 and AC2 on TPEZ. 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 3, 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 PPSTME because typically PSTs
are used to monitor an OAM domain (like PW13 and PWXZ PPSTMEs)
rather than the segment between two OAM domains. However the OAM
framework does not pose any constraints on the way PSTs 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 Sections, LSPs,
pseudowires and MEGs in this section are made in relation to
those shown in Figure 5.
4.1. MPLS-TP Section Monitoring (SME)
An MPLS-TP Section ME (SME) is an MPLS-TP maintenance entity
intended to an MPLS Section as defined in [5]. An SME may be
configured on any MPLS section. SME OAM packets must fate share
with the user data packets sent over the monitored MPLS Section.
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An SME 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 (and MPLS-TP enabled) LSRs
rather than monitoring the individual LSP or PW path segments
traversing the MPLS Section and the server layer technology does
not provide adequate OAM capabilities.
Figure 5 shows 5 Section MEs configured in the network between
AC1 and AC2:
1. Sec12 ME associated with the MPLS Section between LSR 1 and
LSR 2,
2. Sec23 ME associated with the MPLS Section between LSR 2 and
LSR 3,
3. Sec3X ME associated with the MPLS Section between LSR 3 and
LSR X,
4. SecXY ME associated with the MPLS Section between LSR X and
LSR Y, and
5. SecYZ ME associated with the MPLS Section between LSR Y and
LSR Z.
4.2. MPLS-TP LSP End-to-End Monitoring (LME)
An MPLS-TP LSP ME (LME) is an MPLS-TP maintenance entity
intended to monitor an end-to-end LSP between two LERs. An LME
may be configured on any MPLS LSP. LME OAM packets must fate
share with user data packets sent over the monitored MPLS-TP
LSP.
An LME 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 2 LMEs configured in the network between AC1
and AC2: 1) the LSP13 LME between LER 1 and LER 3, and 2) the
LSPXZ LME between LER X and LER Y. Note that the presence of a
LSP3X LME 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.
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4.3. MPLS-TP PW Monitoring (PME)
An MPLS-TP PW ME (PME) is an MPLS-TP maintenance entity intended
to monitor a SS-PW or MS-PW between a pair of T-PEs. A PME can
be configured on any SS-PW or MS-PW. PME OAM packets must fate
share with the user data packets sent over the monitored PW.
A PME is intended to be deployed in scenarios where it is
desirable to monitor an entire PW between a pair of MPLS-TP
enabled T-PEs rather than monitoring the LSP aggregating
multiple PWs between PEs.
|<------------------- MS-PW1Z ------------------->|
| |
| |<-LSP13->| |<-LSP3X->| |<-LSPXZ->| |
V V LSP V V LSP V V LSP V V
+----+ +-+ +----+ +----+ +-+ +----+
+----+ |TPE1| | | |SPE3| |SPEX| | | |TPEZ| +----+
| |AC1| |=========| |=========| |=========| |AC2| |
| CE1|---|........PW13.......|...PW3X..|........PWXZ.......|---|CE2 |
| | | |=========| |=========| |=========| | | |
+----+ | 1 | |2| | 3 | | X | |Y| | Z | +----+
+----+ +-+ +----+ +----+ +-+ +----+
^---------------------PW1Z PME--------------------^
Figure 6 MPLS-TP PW ME (PME)
Figure 6 depicts a MS-PW (MS-PW1Z) consisting of three path
segments: PW13, PW3X and PWXZ and its associated end-to-end PME
(PW1Z PME).
4.4. MPLS-TP LSP Path Segment Tunnel Monitoring (LPSTME)
An MPLS-TP LSP Path Segment Tunnel ME (LPSTME) is an MPLS-TP LSP
with associated maintenance entity intended to monitor an
arbitrary part of an LSP between the pair of MEPs instantiated
for the PST independent from the end-to-end monitoring (LME). An
LPSTMEE can monitor an LSP segment or concatenated segment and
it may also include the forwarding engine(s) of the node(s) at
the edge(s) of the segment or concatenated segment.
Multiple LPSTMEs can be configured on any LSP. The LSRs that
terminate the LPSTME may or may not be immediately adjacent at
the MPLS-TP layer. LPSTME OAM packets must fate share with the
user data packets sent over the monitored LSP path segment.
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A LPSTME can be defined between the following entities:
o The end node and any intermediate node of a given LSP.
o Any two intermediate nodes of a given LSP.
An LPSTME is intended to be deployed in scenarios where it is
preferable to monitor the behaviour 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.
|<--------------------- PW1Z -------------------->|
| |
| |<--------------LSP1Z LSP-------------->| |
| |<-LSP13->| |<-LSP3X->| |<-LSPXZ->| |
V V S-LSP V V S-LSP V V S-LSP V V
+----+ +-+ +----+ +----+ +-+ +----+
+----+ | PE1| | | |DBN3| |DBNX| | | | PEZ| +----+
| |AC1| |=======================================| |AC2| |
| CE1|---|......................PW1Z.......................|---|CE2 |
| | | |=======================================| | | |
+----+ | 1 | |2| | 3 | | X | |Y| | Z | +----+
+----+ +-+ +----+ +----+ +-+ +----+
. . . .
| | | |
|<---- Domain 1 --->| |<---- Domain Z --->|
^---------^ ^---------^
LSP13 LPSTME LSPXZ LPSTME
^---------------------------------------^
LSP1Z LME
DBN: Domain Border Node
Figure 7 MPLS-TP LSP Path Segment Tunnel ME (LPSTME)
Figure 7 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
LPSTMEs configured to monitor the LSP1Z: 1) a LPSTME monitoring
the LSP13 Concatenated Segment on Domain 1 (LSP13 LPSTME), and
2) a LPSTME monitoring the LSPXZ Concatenated Segment on Domain
Z (LSPXZ LPSTME).
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It is worth noticing that LPSTMEs can coexist with the LME
monitoring the end-to-end LSP and that LPSTME MEPs and LME MEPs
can be coincident in the same node (e.g. PE1 node supports both
the LSP1Z LME MEP and the LSP13 LPSTME MEP).
4.5. MPLS-TP MS-PW Path Segment Tunnel Monitoring (PPSTME)
An MPLS-TP MS-PW Path Segment Tunnel Monitoring ME (PPSTME) is
an MPLS-TP maintenance entity intended to monitor an arbitrary
part of an MS-PW between a given pair of PEs independently from
the end-to-end monitoring (PME). A PPSTME can monitor a PW
segment or concatenated segment and it may also include the
forwarding engine(s) of the node(s) at the edge(s) of the
segment or concatenated segment.
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 (CP) to centralized
(NMS) control or at a routing area boundary. As such the
architecture would superficially appear not to have the
flexibility that arbitrary placement of PST segments would
imply. More arbitrary placement of MEs for a PW would require
additional hierarchical components, beyond the PSTs between PEs
Multiple PPSTMEs can be configured on any MS-PW. The PEs may or
may not be immediately adjacent at the MS-PW layer. PPSTME OAM
packets fate share with the user data packets sent over the
monitored PW path Segment.
A PPSTME 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. It can span several PW
segments.
A PPSTME is intended to be deployed in scenarios where it is
preferable to monitor the behaviour 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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|<------------------- MS-PW1Z ------------------->|
| |
| |<-LSP13->| |<-LSP3X->| |<-LSPXZ->| |
V V LSP V V LSP V V LSP V V
+----+ +-+ +----+ +----+ +-+ +----+
+----+ |TPE1| | | |SPE3| |SPEX| | | |TPEZ| +----+
| |AC1| |=========| |=========| |=========| |AC2| |
| CE1|---|........PW13.......|...PW3X..|........PWXZ.......|---|CE2 |
| | | |=========| |=========| |=========| | | |
+----+ | 1 | |2| | 3 | | X | |Y| | Z | +----+
+----+ +-+ +----+ +----+ +-+ +----+
^---- PW1 PPSTME----^ ^---- PW5 PPSTME----^
^---------------------PW1Z PME--------------------^
Figure 8 MPLS-TP MS-PW Path Segment Tunnel Monitoring (PPSTME)
Figure 8 depicts the same MS-PW (MS-PW1Z) between AC1 and AC2 as
in Figure 6. In this scenario there are two separate PPSTMEs
configured to monitor MS-PW1Z: 1) a PPSTME monitoring the PW13
MS-PW path segment on Domain 1 (PW13 PPSTME), and 2) a PPSTME
monitoring the PWXZ MS-PW path segment on Domain Z with (PWXZ
PPSTME).
It is worth noticing that PPSTMEs can coexist with the PME
monitoring the end-to-end MS-PW and that PPSTME MEPs and PME
MEPs can be coincident in the same node (e.g. TPE1 node supports
both the PW1Z PME MEP and the PW13 PPSTME 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 Aggregations [14], the use of Link
Bundling for MPLS [13] 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 share in common 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,
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the deployment can be considered to be only partially MPLS-TP
compliant, however this is unlikely to prevent its use.
The implications for OAM is 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 is 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.
Proactive monitoring is frequently "in-service" monitoring. The
control and measurement implications 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, LM etc.) are configured at the MEPs.
3. Server layer events are reported by transactions originating
at intermediate nodes.
4. The measurements resulting from proactive monitoring are
typically only reported outside of the MEG as unsolicited
notifications for "out of profile" events, such as faults or
loss measurement indication of excessive impairment of
information transfer capability.
5. The measurements resulting from proactive monitoring may be
periodically harvested by an EMS/NMS.
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 enables/disables some of the consequent actions
defined in section 5.1.2.
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5.1. Continuity Check and Connectivity Verification
Proactive Continuity Check functions, as required in section
2.2.2 of [8], are used to detect a loss of continuity defect
(LOC) between two MEPs in a MEG.
Proactive Connectivity Verification functions, as required in
section 2.2.3 of [8], 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 of OAM
packets by the source MEP that are processed by the sink MEP. As
a consequence these two functions are grouped together into
Continuity Check and Connectivity Verification (CC-V) OAM
packets.
In order to perform pro-active Connectivity Verification
function, each CC-V OAM packet also includes a globally unique
Source MEP identifier. When used to perform only pro-active
Continuity Check function, the CC-V OAM packet will not include
any globally unique Source MEP identifier. Different formats of
MEP identifiers are defined in [7] to address different
environments. When MPLS-TP is deployed in transport network
environments where IP addressing is not used in the forwarding
plane, the ICC-based format for MEP identification is used. When
MPLS-TP is deployed in IP-based environment, the IP-based MEP
identification is used.
As a consequence, it is not possible to detect misconnections
between two MEGs monitored only for continuity as neither the
OAM message type nor OAM message content provides sufficient
information to disambiguate an invalid source. To expand:
o For CC leaking into a CC monitored MEG - undetectable
o For CV leaking into a CC monitored MEG - presence of
additional Source MEP identifier allows detecting the fault
o For CC leaking into a CV monitored MEG - lack of additional
Source MEP identifier allows detecting the fault.
o For CV leaking into a CV monitored MEG - different Source MEP
identifier permits fault to be identified.
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CC-V OAM packets are transmitted at a regular, operator's
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. This PHB is configurable on network operator's
basis. 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 with the entire E-LSP fate sharing with any individual PHB.
In a 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), only the source MEP is
enabled to generate CC-V OAM packets and only the 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 MEP
source function (generating pro-active CC-V packets) should be
enabled prior to the corresponding MEP sink function (detecting
continuity and connectivity defects). When disabling the CC-V
proactive functionality, the MEP sink function should be
disabled prior to the corresponding MEP source function.
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, the sink MEP should notify the
equipment fault management process of the detected defect.
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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 peer MEP.
o Entry criteria: if no pro-active CC-V OAM packets from the
peer MEP with the correct encapsulation (and in the case of
CV, this includes the requirement to have a correct 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 peer MEP
with the correct encapsulation (and again in the case of CV,
with the correct 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) with its peer source MEP
when the received packet carries an incorrect globally unique
Source MEP identifier.
o Entry criteria: the sink MEP receives a pro-active CC-V OAM
packet with an incorrect globally unique Source MEP
identifier.
o Exit criteria: the sink MEP does not receive any pro-active
CC-V OAM packet with an incorrect 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 incorrect globally unique Source MEP
identifier since this defect has been raised. This requires
the OAM message 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 a correct
globally unique Source MEP identifier but with a transmission
period different than the locally configured reception period,
then a CV period mis-configuration defect is detected.
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o Entry criteria: a MEP receives a CC-V pro-active packet with
correct globally unique Source MEP identifier but with a
Period field value 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 a correct 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 a
correct globally unique Source MEP identifier and an
incorrect transmission period since this defect has been
raised.
5.1.2. Consequent action
A sink MEP that detects one of the defect conditions defined in
section 5.1.1 performs the following consequent actions.
If a MEP detects an unexpected globally unique Source MEP
Identifier, 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
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 [8]
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.
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If a MEP detects a LOC defect (section 5.1.1.1), a
mis-connectivity defect (section 5.1.1.2) or a period
misconfiguration defect (section 5.1.1.3), it declares a signal
fail condition at the transport path level.
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;
o list of peer MEPs inside the MEG. For a point-to-point MEG
the list would consist of the single peer 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; it identifies the per-hop behaviour 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 Monitoring: default transmission period is
100ms (i.e. transmission rate of 10 packets/second).
Performance monitoring 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.
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o Protection Switching: default transmission period is
3.33ms (i.e. transmission rate of 300 packets/second), in
order to achieve sub-50ms the CC-V defect entry criteria
should resolve in less than 10msec, and complete a
protection switch within a subsequent period of 50 msec.
It is also possible to lengthen the transmission period
to 10ms (i.e. transmission rate of 100 packets/second):
in this case the CC-V defect entry criteria resolves is
longer (i.e. 30msec).
It should be possible for the operator to configure these
transmission rates for all applications, to satisfy his internal
requirements.
Note that the reception period is the same as the configured
transmission rate.
For statically provisioned transport paths the above information
are statically configured; for dynamically established transport
paths the configuration information are signaled via the control
plane.
The operator should be able to enable/disable some of the
consequent actions defined in section 5.1.2.
5.2. Remote Defect Indication
The Remote Defect Indication (RDI) function, as required in
section 2.2.9 of [8], is an indicator that is transmitted by a
MEP to communicate to its peer MEPs that a signal fail condition
exists. RDI is only used for bidirectional connections and is
associated with proactive CC-V activation. The RDI indicator is
piggy-backed onto the CC-V packet.
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. 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 the packets with the RDI information should
determine that its peer MEP has encountered a defect condition
associated with a signal fail.
MIPs as well as intermediate nodes not supporting MPLS-TP OAM
are transparent to the RDI indicator and forward these proactive
CC-V packets that include the RDI indicator as regular data
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packets, i.e. the MIP should not perform any actions nor examine
the indicator.
When the signal fail defect condition clears, the MEP should
clear the RDI indicator from subsequent transmission of pro-
active CC-V packets. A MEP should clear the RDI defect upon
reception of a pro-active CC-V packet from the source MEP with
the RDI indicator cleared.
5.2.1. Configuration considerations
In order to support RDI indication, this may be a unique OAM
message or an OAM information element embedded in a CV message.
In this case the RDI transmission rate and PHB of the OAM
packets carrying RDI should be the same as that configured for
CC-V.
5.3. Alarm Reporting
The Alarm Reporting function, as required in section 2.2.8 of
[8], relies upon an Alarm Indication Signal (AIS) message to
suppress alarms following detection of defect conditions at the
server (sub-)layer.
When a server MEP asserts signal fail, the MPLS-TP client
(sub-)layer adaptation function generates packets with AIS
information in the downstream direction to allow the suppression
of secondary alarms at the MEP in the client (sub-)layer.
The generation of packets with AIS information starts
immediately when the server MEP asserts signal fail. These
periodic packets, with AIS information, continue to be
transmitted until the signal fail condition is cleared.
Upon receiving a packet with AIS information an MPLS-TP MEP
enters an AIS defect condition and suppresses loss of continuity
alarms associated with its peer MEP. A MEP resumes loss of
continuity alarm generation upon detecting loss of continuity
defect conditions in the absence of AIS condition.
For example, let's consider a fiber cut between LSR 1 and LSR 2
in the reference network of Figure 5. Assuming that all the MEGs
described in Figure 5 have pro-active CC-V enabled, a LOC defect
is detected by the MEPs of Sec12 SME, LSP13 LME, PW1 PPSTME and
PW1Z PME, however in transport network only the alarm associate
to the fiber cut needs to be reported to NMS while all these
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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 SME. 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 SME in
LSR2 will report a LOC alarm.
In both cases, the MEP of Sec12 SME in LSR 2 notifies the
adaptation function for LSP13 LME that then generates AIS
packets on the LSP13 LME in order to allow its MEP in LSR3 to
suppress the LOC alarm. LSR3 can also suppress the secondary
alarm on PW13 PPSTME because the MEP of PW13 PPSTME resides
within the same node as the MEP of LSP13 LME. The MEP of PW13
PPSTME in LSR3 also notifies the adaptation function for PW1Z
PME that then generates AIS packets on PW1Z PME 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 packets are transmitted with the "minimum loss probability
PHB" within a single network operator. This PHB is configurable
on network operator's basis.
A MIP is transparent to packets with AIS information and
therefore does not require any information to support AIS
functionality.
5.4. Lock Reporting
The Lock Reporting function, as required in section 2.2.7 of
[8], relies upon a Locked Report (LKR) message used to suppress
alarms following administrative locking action in the server
(sub-)layer.
When a server MEP is locked or receives a lock report, the
MPLS-TP client (sub-)layer adaptation function generates packets
with LKR information in both directions to allow the suppression
of secondary alarms at the MEPs in the client (sub-)layer.
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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. A MEP resumes loss of
continuity alarm generation upon detecting loss of continuity
defect conditions in the absence of LKR condition.
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).
LKR packets are transmitted with the "minimum loss probability
PHB" within a single network operator. This PHB is configurable
on network operator's basis.
A MIP is transparent to packets with LKR information and
therefore does not require any information to support LKR
functionality.
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 [8]. 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.
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 bidirectional transport path) during the life
time of the transport path. Each MEP performs measurements of
its transmitted and received packets. These measurements are
then transactionally correlated 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 queuing
discipline as the measured traffic while transiting between the
MEPs in the ME.
In order to support proactive LM, the transmission rate and PHB
associated with the LM OAM packets originating from a MEP need
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be configured as part of the LM provisioning procedures. LM OAM
packets are transmitted with the same PHB class that the LM is
intended to measure. If that PHB 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.
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).
5.5.1. Configuration considerations
In order to support proactive LM, the transmission rate and PHB
associated with the LM OAM packets originating from a MEP need
be configured as part of the LM provisioning procedures. LM OAM
packets should be transmitted with the same PHB class that the
LM is intended to measure. If that PHB is not an ordered
aggregate where the ordering constraint is all packets with the
PHB being delivered in order, LM can produce inconsistent
results.
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
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section 2.2.12 of [8]. 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 bidirectional transport path) during a
configurable time interval.
Pro-active DM can be operated in two ways:
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 synchronized precision
time 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 source MEP.
5.6.1. Configuration considerations
In order to support pro-active DM, the transmission rate and PHB
associated with the DM OAM packets originating from a MEP need
be configured as part of the DM provisioning procedures. DM OAM
packets should be transmitted with the PHB that yields the
lowest packet loss performance among the PHB Scheduling Classes
or Ordered Aggregates (see RFC 3260 [12]) in the monitored
transport path for the relevant network domain(s).
5.7. Client Failure Indication
The Client Failure Indication (CFI) function, as required in
section 2.2.10 of [8], 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 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.
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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.
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 message requires additional information
to permit the client instance to be identified.
5.7.1. Configuration considerations
In order to support CFI indication, the CFI transmission rate
and PHB of the CFI OAM message/information element 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 e.g. diagnostics to investigate into 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.
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
craftsperson initiated and attended. These do not necessarily
require different harvesting mechanisms that that for
harvesting proactive monitoring telemetry.
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The functions that are exclusive 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
In order to preserve network resources, e.g. bandwidth,
processing time at switches, it may be preferable to not use
proactive CC-V. In order to perform fault management functions,
network management may invoke periodic on-demand bursts of on-
demand CV packets, as required in section 2.2.3 of [8].
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.
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 a MEP to a specific MIP. This
functionality may not be available for associated bidirectional
transport paths or unidirectional paths, as the MIP may not have
a return path to the source MEP for the on-demand CV
transaction.
On-demand CV may generate a one-time burst of on-demand CV
packets, or be used to invoke periodic, non-continuous, bursts
of on-demand CV packets. The number of packets generated in
each burst is configurable at the MEPs, and should take into
account normal packet-loss conditions.
When invoking a periodic check of the MEG, the source MEP should
issue a burst of on-demand CV packets that uniquely identifies
the MEG being verified. The number of packets and their
transmission rate should be pre-configured and known to both the
source MEP and the target MEP or MIP. 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
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each packet received. If the expected number of on-demand CV
reply packets is not received at source MEP, the LOC defect
state is entered.
On demand CV should have the ability to carry padding such that
a variety of MTU sizes can be originated to verify the MTU
capacity of the transport path.
6.1.1. Configuration considerations
For on-demand CV the MEP should support the configuration of the
number of packets to be transmitted/received in each burst of
transmissions and their packet size. The transmission rate
should be configured between the different nodes.
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.
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 diagnostic of QoS performance
for a transport path, as required in section 2.2.11 of [8]. As
proactive LM, on-demand 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.
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 bidirectional transport path) during a pre-
defined monitoring period. Each MEP performs measurements of its
transmitted and received packets. These measurements are then
correlated 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 tester.
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6.2.1. Configuration considerations
In order to support on-demand LM, the beginning and duration of
the LM procedures, the transmission rate and PHB associated with
the LM OAM packets originating from a MEP must be configured as
part of the on-demand LM provisioning procedures. LM OAM packets
should be transmitted with the PHB that yields the lowest packet
loss performance among the PHB Scheduling Classes or Ordered
Aggregates (see RFC 3260 [12]) in the monitored transport path
for the relevant network domain(s).
6.2.2. 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.
6.2.3. Multilink issues
Multi-link Issues are as described in section 5.5.3.
6.3. Diagnostic Tests
6.3.1. Throughput Estimation
Throughput estimation is an on-demand out-of-service function,
as required in section 2.2.5 of [8], that allows verifying the
bandwidth/throughput of an MPLS-TP transport path (LSP or PW)
before it is put in-service.
Throughput estimation is performed between MEPs and can be
performed in one-way or two-way modes.
This test is performed by sending OAM test packets at increasing
rate (up to the theoretical maximum), graphing 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 MEP source inserts OAM
test packets with test information with specified throughput,
packet size and transmission patterns.
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For one-way test, remote MEP sink receives the OAM test packets
and calculates the packet loss. For two-way test, the remote MEP
loopbacks the OAM test packets back to original MEP and the
local MEP sink calculates the packet loss. However, a two-way
test will return the minimum of available throughput in the two
directions. Alternatively it is possible to run two individual
one-way tests to get a distinct measurement in the two
directions.
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 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.
A MIP is transparent to the OAM test packets sent for throught
estimation and therefore does not require any provisioning to
support MPLS-TP throughput estimation.
6.3.1.2. Limited OAM processing rate
If an implementation is able to process payload at much higher
data rates than OAM packets, then accurate measurement of
throughput using OAM 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 [8], that permits all traffic (including
user data and OAM) originated at the ingress of a transport path
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or inserted by the test equipment to be looped back in the
direction of the point of origin by an interface at either an
intermediate node or a terminating node. TTL is decremented
normally during this process.
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.
Where a node implements data plane loopback capability and
whether it implements more than one point is implementation
dependent.
6.4. Route Tracing
It is often necessary to trace a route covered by a MEG from a
source MEP to the sink MEP including all the MIPs in-between
after e.g., provisioning an MPLS-TP transport path or for
trouble shooting purposes, it.
The route tracing function, as required in section 2.2.4 of [8],
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 exist, the route trace
function needs to be able to detect it and stop automatically
returning the incomplete list of OAM entities that it was able
to trace.
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.
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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 [8]. 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
the peer MEP (if a bidirectional transport path) during a
configurable time interval.
On-demand DM can be operated in two ways:
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.
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 source MEP.
6.5.1. Configuration considerations
In order to support on-demand DM, the beginning and duration of
the DM procedures, the transmission rate and PHB associated with
the DM OAM packets originating from a MEP need be configured as
part of the LM provisioning procedures. DM OAM packets should be
transmitted with the PHB that yields the lowest packet delay
performance among the PHB Scheduling Classes or Ordering
Aggregates (see RFC 3260 [12]) in the monitored transport path
for the relevant network domain(s).
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 of the on-demand OAM DM
packet.
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7. OAM Functions for administration control
7.1. Lock Instruct
Lock Instruct (LKI) function, as required in section 2.2.6 of
[8], is a command allowing a MEP to instruct the peer MEP(s) to
put the MPLS-TP transport path into a locked condition.
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 put both MEPs into ad
administrative lock condition. In this case, the LKI function is
not required/used.
7.1.1. Locking a transport path
A MEP, upon receiving a single-side administrative lock command
from NMS, sends an LKI request OAM packet to its peer MEP(s). It
also puts the MPLS-TP transport path into a locked and notify
its client (sub-)layer adaptation function upon the locked
condition.
A MEP, upon receiving an LKI request from its peer MEP, can
accept or not the instruction and replies to the peer MEP with
an LKI reply OAM packet indicating whether it has accepted or
not the instruction.
If the lock instruction has been accepted, it also puts the
MPLS-TP transport path into a locked and notify 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 accept
or not the removal instruction and replies with an LKI removal
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reply OAM packet indicating whether it has accepted or not the
instruction.
If the lock removal instruction has been accepted, it also
clears the locked condition on the MPLS-TP transport path and
notify 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 notify 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 passwords,
performance data and details about e.g. the network topology.
The nature of OAM data therefore suggests to have some form of
authentication, authorization and encryption 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 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.
For this reason it is assumed that the network is physically
secured against man in the middle attacks. Further, this
document describes OAM functions that, if a man in the middle
attack was possible, could be exploited to significantly disrupt
proper operation of the network.
Mechanisms that the framework does not specify might be subject
to additional security considerations.
9. IANA Considerations
No new IANA considerations.
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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 Loa Andersson, Malcolm
Betts, Stewart Bryant, Rui Costa, Xuehui Dai, John Drake, Adrian
Farrel, Liu Gouman, Feng Huang, Yoshionori Koike, 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] Vigoureux, M., Bocci, M., Swallow, G., Ward, D., Aggarwal,
R., "MPLS Generic Associated Channel", RFC 5586, June 2009
[7] Swallow, G., Bocci, M., "MPLS-TP Identifiers", draft-ietf-
mpls-tp-identifiers-01 (work in progress), April 2010
[8] Vigoureux, M., Betts, M., Ward, D., "Requirements for OAM
in MPLS Transport Networks", draft-ietf-mpls-tp-oam-
requirements-06 (work in progress), March 2010
[9] ITU-T Recommendation G.806 (01/09), "Characteristics of
transport equipment - Description methodology and generic
functionality ", January 2009
11.2. Informative References
[10] Sprecher, N., Nadeau, T., van Helvoort, H., Weingarten,
Y., "MPLS-TP OAM Analysis", draft-ietf-mpls-tp-oam-
analysis-01 (work in progress), March 2010
[11] 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
[12] Grossman, D., "New terminology and clarifications for
Diffserv", RFC 3260, April 2002.
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[13] Kompella, K., Rekhter, Y., Berger, L., "Link Bundling in
MPLS Traffic Engineering (TE)", RFC 4201, October 2005
[14] IEEE Standard 802.1AX-2008, "IEEE Standard for Local and
Metropolitan Area Networks - Link Aggregation", November
2008
Authors' Addresses
Dave Allan
Ericsson
Email: david.i.allan@ericsson.com
Italo Busi
Alcatel-Lucent
Email: Italo.Busi@alcatel-lucent.com
Ben Niven-Jenkins
BT
Email: benjamin.niven-jenkins@bt.com
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
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Dinesh Mohan
Nortel
Email: mohand@nortel.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
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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