One document matched: draft-ietf-mpls-tp-oam-framework-04.txt
Differences from draft-ietf-mpls-tp-oam-framework-03.txt
MPLS Working Group I. Busi (Ed)
Internet Draft Alcatel-Lucent
Intended status: Informational B. Niven-Jenkins (Ed)
BT
D. Allan (Ed)
Ericsson
Expires: June 2010 December 10, 2009
MPLS-TP OAM Framework
draft-ietf-mpls-tp-oam-framework-04.txt
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress".
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
Busi et al. Expires June 10, 2010 [Page 1]
Internet-Draft MPLS-TP OAM Framework December 2009
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), pseudowire (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 fulfills the MPLS-TP OAM requirements [12].
This document is a product of a joint Internet Engineering Task Force
(IETF) / International Telecommunications Union Telecommunications
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.
Busi et al. Expires June 10, 2010 [Page 2]
Internet-Draft MPLS-TP OAM Framework December 2009
Table of Contents
1. Introduction..................................................5
1.1. Contributing Authors.....................................5
1.2. Editors Issues...........................................6
2. Conventions used in this document.............................9
2.1. Terminology..............................................9
2.2. Definitions.............................................10
3. Functional Components........................................12
3.1. Maintenance Entity and Maintenance Entity Group.........13
3.2. MEG End Points (MEPs)...................................16
3.3. MEG Intermediate Points (MIPs)..........................19
3.4. Server MEPs.............................................20
3.5. Path Segment Tunnels and Tandem Connection Monitoring...21
4. Reference Model..............................................21
4.1. MPLS-TP Section Monitoring..............................23
4.2. MPLS-TP LSP End-to-End Monitoring.......................24
4.3. MPLS-TP LSP Path Segment Tunnel Monitoring..............25
4.4. MPLS-TP PW Monitoring...................................27
4.5. MPLS-TP MS-PW Path Segment Tunnel Monitoring............27
5. OAM Functions for proactive monitoring.......................28
5.1. Continuity Check and Connectivity Verification..........29
5.1.1. Defects identified by CC-V.........................30
5.1.2. Consequent action..................................31
5.1.3. Configuration considerations.......................32
5.1.4. Applications for proactive CC-V....................33
5.2. Remote Defect Indication................................34
5.2.1. Configuration considerations.......................34
5.2.2. Applications for Remote Defect Indication..........35
5.3. Alarm Reporting.........................................35
5.4. Lock Reporting..........................................36
5.5. Packet Loss Monitoring..................................36
5.5.1. Configuration considerations.......................37
5.5.2. Applications for Packet Loss Monitoring............37
5.6. Client Signal Failure Indication........................38
5.6.1. Configuration considerations.......................38
5.6.2. Applications for Client Signal Failure Indication..38
5.7. Delay Measurement.......................................39
5.7.1. Configuration considerations.......................39
5.7.2. Applications for Delay Measurement.................40
6. OAM Functions for on-demand monitoring.......................40
6.1. Connectivity Verification...............................40
6.1.1. Configuration considerations.......................41
6.2. Packet Loss Monitoring..................................42
6.2.1. Configuration considerations.......................42
6.2.2. Applications for On-demand Packet Loss Monitoring..42
6.3. Diagnostic..............................................42
Busi et al. Expires June 10, 2010 [Page 3]
Internet-Draft MPLS-TP OAM Framework December 2009
6.4. Route Tracing...........................................43
6.5. Delay Measurement.......................................44
6.5.1. Configuration considerations.......................44
6.5.2. Applications for Delay Measurement.................45
6.6. Lock Instruct...........................................45
7. Security Considerations......................................45
8. IANA Considerations..........................................45
9. Acknowledgments..............................................46
10. References..................................................47
10.1. Normative References...................................47
10.2. Informative References.................................47
Busi et al. Expires June 10, 2010 [Page 4]
Internet-Draft MPLS-TP OAM Framework December 2009
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 [8], MPLS-TP defines a profile of the MPLS-TE and (MS-)PW
architectures defined in RFC 3031 [2], RFC 3985 [5] and [7] which is
complemented with additional OAM mechanisms and procedures for alarm,
fault, performance and protection-switching management for packet
transport applications.
In line with [13], 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.
The MPLS-TP OAM framework defined in this document provides a
comprehensive set of OAM procedures that satisfy the MPLS-TP OAM
requirements [12]. In this regard, it defines similar OAM
functionality as for existing SONET/SDH and OTN OAM mechanisms (e.g.
[16]).
The MPLS-TP OAM framework is applicable to both LSPs and (MS-)PWs and
supports co-routed and 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 Telecommunications Union Telecommunications
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.
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
Busi et al. Expires June 10, 2010 [Page 5]
Internet-Draft MPLS-TP OAM Framework December 2009
1.2. Editors Issues
Editor's Note:
This section is to be removed prior to submission to the RFC editor.
1) ME architecture needs further discussion/clarification
Agreement (call 24 November):
o Co-routed bidirectional p2p transport entity: one bidirectional
ME
o Associated bidirectional p2p transport entity: two
unidirectional MEs
o Unidirectional p2p transport entity: one unidirectional ME
o Unidirectional p2mp (with N leaves) transport entity: N
unidirectional ME
Clarify that in a p2mp transport entity all the traffic (including
OAM packets) is sent (multicast) from the root to all the leaves. As
a consequence:
o To send an OAM packet to all leaves, it is required to 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, it is required to send a
single OAM packet that will be delivered by the forwarding plane
to all the leaves and processed only by the target leaf and
ignored by the other leaves.
o In order to send an OAM packet to M leaves (i.e., a subset of
all the leaves), the current working assumption is to send M
different (multicast) OAM packets targeted to each individual
leaf in the group of M leaves. Better mechanisms are under
investigation and might be added in future versions of this
draft.
2) Use of terms LTCME and PTCME, should these be genericised for
PSTs.
Agreement (call 24 November): the editors of the framework document
will make sure that the framework document is aligned with the
Busi et al. Expires June 10, 2010 [Page 6]
Internet-Draft MPLS-TP OAM Framework December 2009
decision to use the term PST. This document will be aligned with this
decision.
3) CV refers to using an ME ID for misbranching detection. This does
not align with p2mp LSPs where a CV would then be required to
carry all the MEs in the MEG.
Agreement (call 24 November): we are going to use the term MEG ID in
the document. ME ID has been used in older versions of the document
and its use is legacy.
For pro-active CC-V (both p2p and p2mp), the globally unique MEP ID
information needs to be carried: section on pro-active CC-V needs to
be updated accordingly.
4) Discussions of PW monitoring and PW tandem connection monitoring
seem to be rendered out of scope by the layering decision at
Hiroshima.
Discussion points (call 24 November) - No agreement reached on this
issue
PW OAM architecture: based on the architecture defined in this
document using MEP and MIPs
PW TCM concept: just a specific application of the architecture of
the TP-LSP (1:1 mapped with the monitored PW) carrying a PW segment
in the MS-PW architecture.
Generic clarifications (to be added) [terminology based on RFC 5654]:
o before a TCM is setup, we can have a concatenated LSP
segment. After the TCM (that is a TP-LSP) is setup, we have a
single LSP segment between the TCM end-points;
o before a TCM is setup, we can have a concatenated PW segment.
After the TCM (that is a TP-LSP) is setup, we have a single
PW segment between the TCM end-points.
Problems with PW TCM are the implications of removing S-PEs from the
PW path. Need further discussion. It is not obvious to Dave that
removing an LSR from a path can be done hitlessly either ... by
slipping a PST under it ...
Action (Italo): check which requirements cannot be met if PW TCM
between non-adjacent PEs cannot be supported and whether this is a
showstopper issue or not.
Busi et al. Expires June 10, 2010 [Page 7]
Internet-Draft MPLS-TP OAM Framework December 2009
Action (Italo): describe the PW TCM as an LSP and circulate the
description to the mailing list for review. If needed, another call
will be setup to finalize the discussion.
Action (Matthew, Italo): Develop a couple of diagrams showing how the
mechanism works for LSPs and PWs.
5) Concerns have been raised against the idea of having MIPs capable
to generate spontaneous messages. AIS/Lock Indication packets are
generated by the adaptation functions. This point needs
clarifying.
Agreement (9 December):
AIS/Lock Indication are generate by a MIP node (to be define as a
node hosting a MIP) w/o saying that they are generated by a MIP.
The general framework will describe the mechanism for intermediate
nodes to insert packets and each specific framework document (e.g.,
OAM framework) will describe the usage of this capability on a case-
by-case basis. When you provision bw between two end-points you must
allow enough bw for any additional traffic, including traffic from
MEPs and MIPs.
OAM framework will describe that a MIP node may insert OAM packets
into a LSP and this will be described on a function-by-function
basis. It will also describe the functions that require a MIP to
generate OAM packets (e.g., on-demand CV).
6) Presence or absence of MIPs is a bizarre point. At least one MIP
in every node is addressed by TTL, and gaps in the enablement of
MIPs would produce spurious test results. A convention of "MIPs
exist at any node on a transport path that has a return path to a
source MEP" would make sense vs. discussing manual
enable/disable/configuration of MIPs.
Note - the annotated text ("If the set of MIPs is actually sparse
(i.e. not every hop is a MIP), then it has to be intermediate nodes
to do some operations") needs further clarification.
Agreement (9 December):
All the intermediate nodes host MIP(s). Local policy allows them to
be enabled per function and per LSP. The local policy is controlled
by the management system, which may delegate it to the control plane.
Busi et al. Expires June 10, 2010 [Page 8]
Internet-Draft MPLS-TP OAM Framework December 2009
7) Discussions in Hiroshima and subsequent calls have suggested use
of alternative return paths "if available", not all of which will
be GAL/GACH encapsulated? This point needs clarifying.
Agreement (9 December):
When the return path is not an MPLS-TP path, the reply message does
not need to be GAL/ACH encapsulated.
The request message needs to carry sufficient information to allow
the target MIP/MEP to reply when a non MPLS-TP return path is used.
8) Data plane loopback
Action (17 November): check on the mailing list (both ITU-T and IETF
to get inputs from both types of operators).
9) Review the draft to check that all the known implications related
to the support of p2mp transport paths have been described.
This check will be done in the next version after the current open
points/comments have been resolved.
10)Given layering discussion in Hiroshima, it is not very clear
whether MPLS TP is a sub layer network within the MPLS layer
network or a layer network by its own.
This issue should be resolved in the context of the MPLS TP Framework
draft but has impacts on this draft as well.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [1].
2.1. Terminology
AC Attachment Circuit
DBN Domain Border Node
FDI Forward Defect Indication
LER Label Edge Router
LME LSP Maintenance Entity
Busi et al. Expires June 10, 2010 [Page 9]
Internet-Draft MPLS-TP OAM Framework December 2009
LSP Label Switched Path
LSR Label Switch Router
LPSTME LSP packet segment tunnel ME
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
PPSTME PW path segment tunnel ME
PST Path Segment Tunnel
PSN Packet Switched Network
PW Pseudowire
SLA Service Level Agreement
SME Section Maintenance Entity
2.2. Definitions
Note - the definitions in this section are intended to be in line
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.
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.
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).
Busi et al. Expires June 10, 2010 [Page 10]
Internet-Draft MPLS-TP OAM Framework December 2009
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 reside at the boundaries of an ME
(details in section 3.2).
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 an MEG between MEPs (details in section 3.2).
OAM domain: A domain, as defined in [11], 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 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 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).
Path: See Transport Path
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.
Busi et al. Expires June 10, 2010 [Page 11]
Internet-Draft MPLS-TP OAM Framework December 2009
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.
This document uses the terms defined in RFC 5654 [11].
This document uses the term 'Per-hop Behavior' as defined in [14].
3. Functional Components
MPLS-TP defines a profile of the MPLS and PW architectures ([2], [5]
and [7]) that is designed 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 verify and maintain these 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 path.
In order to describe the required OAM functionality, this document
introduces a set of high-level functional components. [Note -
discussion in Munich -tues concluded that TCM not possible with PWs -
can monitor a single PW segment - but attempting to monitor more than
one segment converts the PW into an LSP and therefore the intervening
SPEs are unable to see the PW as a PW due to the differences in how
OAM flows are disambiguated.] [editors: if true this IMO is a huge
problem as the one place I would really want TCM is a multi-domain
MS-PW, else I have to control plane peer at two layers, pending
resolution of discussion item 4 in section 1.2]
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.
These functional components should be instantiated when the path is
created by either the management plane or by the control plane (if
present). Some components may be instantiated after the path is
initially created (e.g. PST).
[Dave: are we discussing the same issue for LSP PSTs as for PWs, an
S-PE cannot easily be removed, certainly not hitlessly, how is an LSP
different?]
Busi et al. Expires June 10, 2010 [Page 12]
Internet-Draft MPLS-TP OAM Framework December 2009
3.1. Maintenance Entity and Maintenance Entity Group
MPLS-TP OAM operates in the context of Maintenance Entities (MEs)
that are a relationship between two points of a point to point
transport path or a root and a leaf of a point to multipoint
transport path to which maintenance and monitoring operations apply.
These two points 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), MAY exist
and can be shared by more than one ME in a MEG.
The MEPs that form an 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 or segment, in the specific
sub-layer of the MPLS layer network, 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.
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. The links
connecting adjacent nodes can be physical links, or sub-layer
LSPs/PSTs.
This functional model defines the relationships between all OAM
entities from a maintenance perspective, to allow each Maintenance
Entity to monitor and manage the layer network under its
responsibility and to localize problems efficiently.
[Editor's note - MEG are sub-layers. Need to check the document for
consistency with this agreement]
An MPLS-TP maintenance entity group can cover either the whole end-
to-end path or a path segment tunnel supporting some portion of the
transport path. A Maintenance Entity Group may be defined to monitor
the transport path for fault and/or performance management.
Busi et al. Expires June 10, 2010 [Page 13]
Internet-Draft MPLS-TP OAM Framework December 2009
In case of associated bi-directional paths, two independent
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 exist
in a unidirectional ME.
The following properties apply to all MPLS-TP MEGs:
o They can be nested but not overlapped, e.g. an 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, but all its MEPs and MIPs are
no longer part of the encompassing MEG. It is possible that MEPs
of nested MEGs reside on a single node.
o Each OAM flow is associated with a single Maintenance Entity
Group.
o OAM packets that instrument a particular direction of an LSP 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 [9] for LSP and Section or the ACH construct
[6]and [9] for (MS-)PW.
[Editor's note: A key point in the definition of an ME is the end-
points are defined by location of the logical function MEP
Later in the framework we will discuss the precision with which we
can identify the location of a MEP/MIP i.e, ingress i/f, egress i/f
or node.
We need to distinguish between the point of interception of an OAM
msg and the point where the action takes place.
Action: look at the text in the framework document regarding the
location of the functional components (MEPs and MIPs).]
[Editors' note: Somewhere we need to distinguish between the OAM
control function and the OAM measurement function. i.e. we set up a
loop back (a control function, in which case the OAM message may be
intercepted and actioned anywhere convenient), and the measurement
function (i.e. looping the packet to determine that it reached a
particular part of the network) which needs to be actioned at a
precisely know and stipulated point in the network/equipment.
Busi et al. Expires June 10, 2010 [Page 14]
Internet-Draft MPLS-TP OAM Framework December 2009
Action (Dave) - add some text on the subject.]
Note that not all functionality / processing of an OAM pkt needs to
take place at the point of measurement. [editors: this comment is not
clear. For discussion during revision call]
[Editors' note - Address this comment while addressing the control
and measurement issue above.
We considered that an OAM function can be decomposed into the
following components
- Instruction or command
- Execution
- Addressing (node, interface etc) is ttl/LSP enough - do we need
sub-addressing to cause execution on a specific component in the
node - i.e. egress interface
- Response via OAM
- Reporting to mgt interface]
[Editor's note: the MPLS-TP framework will describe how it is
possible to inject OAM packets on intermediate nodes. We need to
describe how this capability is used within the OAM framework and to
reference to the MPLS-TP framework for the description of this
capability]
Another OAM construct is referred to as Maintenance Entity Group,
which is a collection of one or more MEs that belongs to the same
transport path and that are maintained and monitored as a group.
A use case for an MEG with more than one ME is point-to-multipoint
OAM. The reference model for the p2mp MEG is represented in Figure 2.
Busi et al. Expires June 10, 2010 [Page 15]
Internet-Draft MPLS-TP OAM Framework December 2009
+-+
/--|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 - depending on different paths
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. Nodes B and C MAY
implement a MIP in the corresponding MEG.
3.2. MEG End Points (MEPs)
MEG End Points (MEPs) are the source and sink points of an MEG. In
the context of an MPLS-TP LSP, only LERs can implement MEPs while in
the context of a path segment tunnel (PST) both LERs and LSRs can
implement MEPs 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 NE can implement a MEP.
[Munich: See note about PW Tandem monitoring earlier, and whether a
PW can be a tandem connection - for further discussion (discussion
point 4 in section 1.2)]
MEPs are responsible for activating and controlling all of the OAM
functionality for the MEG. A MEP is capable of originating and
Busi et al. Expires June 10, 2010 [Page 16]
Internet-Draft MPLS-TP OAM Framework December 2009
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 [9]: 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.[Editors: given the discussion about alternative
return paths, is a GAL/GaCH always present ...?. For discussion on
the IETF review calls]
Once an MEG is configured, the operator can configure which OAM
functions to use on the MEG but the MEPs are always enabled. A node
at the edge of an MEG always supports a MEP.
MEPs terminate all OAM packets received from the associated transport
path or path segment tunnel [Editors: the PST definition in the
framework should be augmented to clarity that the clients of a PST
should always be LSPs or PWs]. As the MEP corresponds to the
termination of the forwarding path for an MEG at the given sub-level,
OAM packets never "leaks" outside of a MEG in a fault free
implementation.
A MEP of an MPLS-TP transport path (Section, LSP or PW) 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 (LSP or PW) and monitor
some portion 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.
It may occur that the 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 i.e. an LSP or PW. If we need to monitor some portion of
that LSP or PW [editor: mention of PW in this context needs to be
revised after agreement on discussion point 4 in section 1.2], a new
sub-layer in the form of a path segment tunnel MUST be created which
permits MEPs and an associated MEG to be created.
Busi et al. Expires June 10, 2010 [Page 17]
Internet-Draft MPLS-TP OAM Framework December 2009
[Editor: We need to describe the migration process for adding a path
segment tunnel.]
[Editor's note: Update the draft to capture the agreements below
after the discussion points 5, 6 and 7 in section 1.2 are resolved
(to maintain consistency):
We have the case of a MIP sending msg to a MEP. To do this it uses
the LSP label - i.e. the top label of the stack at that point.
[editors: move and clarify in section 3.3 - for further discuss.
If the set of MIPs is actually sparse (i.e. not every hop is a MIP),
then it has to be intermediate nodes to do some operations.]
Agreement (10 November): An intermediate node can send an OAM packet.
Clarify that we need to provide enough bandwidth on the transport
paths to support OAM traffic (throughout the framework document).
From IETF point of view no distinction between MIPs and adaptation
functions.
Lou question about how triggered response OAM packets are sent by
MIPs/MEPs.
Agreement (call 9 December):
o bidirectional co-routed: use the reverse path (thus checking
both the forward and backward directions of the transport
path). Co-routed bidirectional transport paths can have a
minimum bandwidth return path.
o unidirectional p2p and p2mp: no ability to support triggered
response OAM message
Non MPLS-TP LSP/PW return path MAY be requested by the OAM message
triggering the reply and the target MIP/MEP MAY attempt to reply
using the requested return path.
In this case, only the forward direction of the MPLS-TP transport
path is checked and the connectivity to the source MEP via the
requested return path is not guaranteed.
Agreement (call 17 November) to use as a working assumption the same
MEP/MIP model in MS-PW OAM architecture. In order to validate this
working assumption we need to understand how to describe the PW
Status information: this information is propagated on a hop-by-hop
Busi et al. Expires June 10, 2010 [Page 18]
Internet-Draft MPLS-TP OAM Framework December 2009
basis between adjacent PEs using LDP (dynamic PW segments) or ACH
Status PW (static PW segments).]
3.3. MEG Intermediate Points (MIPs)
A MEG Intermediate Point (MIP) is a point between the MEPs of an MEG.
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 - editors:
this text was removed in the commented .rtf document from Munich but
not tracked as a revision, validate this change after MIP/MEP
discussion (discussion point 5 in section 1.2)] 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 point-to-point MEG can either:
o not support MPLS-TP OAM (i.e. no MIPs per node)
o support per-node MIP (i.e. a single MIP per node)
o support per-interface MIP (i.e. two MIPs per node on both sides of
the forwarding engine)
[Editor's note - Need to describe MIPs for p2mp MEGs]
[Editor's note - Add a Figure to describe how the two options can be
support]
A node at the edge of an MEG can also support a MEP and a
per-interface MIP at the two sides of the forwarding engine.
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.
Once an MEG is configured, the operator can enable/disable the MIPs
on the nodes within the MEG. [Editors': review this paragraph after
discussion point 6 in section 1.2 is resolved]
Busi et al. Expires June 10, 2010 [Page 19]
Internet-Draft MPLS-TP OAM Framework December 2009
3.4. Server MEPs
A server MEP is a MEP of an 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)
layer network.
[Editors' note: review the text above pending discussion of whether
MPLS-TP is a sub-layer network within the MPLS layer network or a
layer network by its own (discussion point 10 in section 1.2)]
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 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 4.4;
o An MPLS-TP PST MEP for higher-level PSTs, defined in section 4.3;
o An MPLS-TP PW Tandem Connection MEP for higher-level PTCMEs,
defined in section 4.5. [Editor: update this bullet after the
discussion on PW TCM (discussion point 4 in section 1.2)]
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.
Busi et al. Expires June 10, 2010 [Page 20]
Internet-Draft MPLS-TP OAM Framework December 2009
3.5. Path Segment Tunnels and Tandem Connection Monitoring
Path segment tunnels (PSTs) are instantiated to provide monitoring of
a portion of a set of co-routed transport paths. Path segment tunnels
can also be employed to meet the requirement to provide tandem
connection monitoring (TCM).
TCM for a given portion of a transport path is implemented by first
creating a path segment tunnel that that has a 1:1 association with
portion of the transport path that is to be uniquely monitored. This
means there is direct correlation between all FM and PM information
gathered for the PST AND the monitored portion of the E2E 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 EXP 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.
4. Reference Model
The reference model for the MPLS-TP framework builds upon the concept
of an MEG, and its associated MEPs and MIPs, to support the
functional requirements specified in [12].
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 A 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 A PST Maintenance Entity Group (PSTME), allowing monitoring and
management of a path segment tunnel (between any LERs/LSRs along
an LSP).
Busi et al. Expires June 10, 2010 [Page 21]
Internet-Draft MPLS-TP OAM Framework December 2009
o A MS-PW Tandem Connection Maintenance Entity (PTCME), allowing
monitoring and management of a PW Tandem Connection (between any
T-PEs/S-PEs along the (MS-)PW) [Editors': update this bullet after
resolution of PW TCM discussion (discussion point 4 in section
1.2]
The MEGs specified in this MPLS-TP framework are compliant with the
architecture framework for MPLS-TP MS-PWs [7] and LSPs [2].
Hierarchical LSPs are also supported in the form of path segment
tunnels. In this case, each LSP Tunnel in the hierarchy is a
different sub-layer network that can be monitored, independently from
higher and lower level LSP tunnels 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 | |<-PSN13->| |<-PSN3X->| |<-PSNXZ->| | 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---^
^---------^ ^---------^
PSN13 LME PSNXZ 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 3 Reference Model for the MPLS-TP OAM Framework
Busi et al. Expires June 10, 2010 [Page 22]
Internet-Draft MPLS-TP OAM Framework December 2009
Figure 3 depicts a high-level reference model for the MPLS-TP OAM
framework. The figure depicts portions of two MPLS-TP enabled network
domains, Domain 1 and Domain Z. In Domain 1, LSR1 is adjacent to LSR2
via the MPLS 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 3 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
Segments: 1) PW13 segment between T-PE1 and S-PE3 via the bi-
directional PSN13 LSP, 2) PW3X segment between S-PE3 and S-PEX, via
the bi-directional PSN3X LSP, and 3) PWXZ segment between S-PEX and
T-PEZ via the bi-directional PSNXZ LSP.
The MPLS-TP OAM procedures that apply to an MEG of a given transport
path are expected to operate independently from procedures on other
MEGs of the same transport path and certainly MEGs of other transport
paths. 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 3 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 3.
4.1. MPLS-TP Section Monitoring
An MPLS-TP Section ME (SME) is an MPLS-TP maintenance entity intended
to an MPLS Section as defined in [11]. 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.
Busi et al. Expires June 10, 2010 [Page 23]
Internet-Draft MPLS-TP OAM Framework December 2009
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 segments traversing the MPLS
Section and the server layer technology does not provide adequate OAM
capabilities.
|<------------------- MS-PW1Z ------------------->|
| |
| |<-PSN13->| |<-PSN3X->| |<-PSNXZ->| |
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 | +----+
+----+ +-+ +----+ +----+ +-+ +----+
^--^ ^--^ ^---------^ ^---^ ^---^
Sec12 Sec23 Sec3X SecXY SecYZ
SME SME SME SME SME
Figure 4 Reference Example of MPLS-TP Section MEs (SME)
Figure 4 shows 5 Section MEs configured in the path 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
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.
Busi et al. Expires June 10, 2010 [Page 24]
Internet-Draft MPLS-TP OAM Framework December 2009
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.
|<------------------- MS-PW1Z ------------------->|
| |
| |<-PSN13->| |<-PSN3X->| |<-PSNXZ->| |
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 | +----+
+----+ +-+ +----+ +----+ +-+ +----+
^---------^ ^---------^
PSN13 LME PSNXZ LME
Figure 5 Examples of MPLS-TP LSP MEs (LME)
Figure 5 depicts 2 LMEs configured in the path between AC1 and AC2:
1) the PSN13 LME between LER 1 and LER 3, and 2) the PSNXZ LME
between LER X and LER Y. Note that the presence of a PSN3X 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.
4.3. MPLS-TP LSP Path Segment Tunnel Monitoring
An MPLS-TP LSP Path Segment Tunnel ME (LPSTME) is an MPLS-TP
maintenance entity intended to monitor an arbitrary part of an LSP
between a given pair of LSRs independently 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 MAY 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 segment.
A LPSTME can be defined between the following entities:
o LER and any LSR of a given LSP.
o Any two LSRs of a given LSP.
Busi et al. Expires June 10, 2010 [Page 25]
Internet-Draft MPLS-TP OAM Framework December 2009
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 -------------------->|
| |
| |<--------------PSN1Z LSP-------------->| |
| |<-PSN13->| |<-PSN3X->| |<-PSNXZ->| |
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 --->|
^---------^ ^---------^
PSN13 LPSTME PSNXZ LPSTME
^---------------------------------------^
PSN1Z LME
DBN: Domain Border Node
Figure 6 MPLS-TP LSP Path Segment Tunnel ME (LPSTME)
Figure 6 depicts a variation of the reference model in Figure 3 where
there is an end-to-end PSN LSP (PSN1Z LSP) between PE1 and PEZ. PSN1Z
LSP consists of, at least, three LSP Concatenated Segments: PSN13,
PSN3X and PSNXZ. In this scenario there are two separate LTCMEs
configured to monitor the PSN1Z LSP: 1) a LPSTME monitoring the PSN13
LSP Concatenated Segment on Domain 1 (PSN13 LPSTME), and 2) a LPSTME
monitoring the PSNXZ LSP Concatenated Segment on Domain Z (PSNXZ
LPSTME).
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 PSN1Z
LME MEP and the PSN13 LPSTME MEP).
Busi et al. Expires June 10, 2010 [Page 26]
Internet-Draft MPLS-TP OAM Framework December 2009
4.4. MPLS-TP PW Monitoring
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 MAY 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 ------------------->|
| |
| |<-PSN13->| |<-PSN3X->| |<-PSNXZ->| |
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 7 MPLS-TP PW ME (PME)
Figure 7 depicts a MS-PW (MS-PW1Z) consisting of three segments:
PW13, PW3X and PWXZ and its associated end-to-end PME (PW1Z PME).
4.5. MPLS-TP MS-PW Path Segment Tunnel Monitoring
[Editors' note: revise this section after the discussion on PW TCM is
closed (discussion item 4 in section 1.2)]
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.
Multiple PPSTMEs MAY 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
Segment.
Busi et al. Expires June 10, 2010 [Page 27]
Internet-Draft MPLS-TP OAM Framework December 2009
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
Segment within a given network domain of an inter-domain MS-PW.
|<------------------- MS-PW1Z ------------------->|
| |
| |<-PSN13->| |<-PSN3X->| |<-PSNXZ->| |
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 7. In this scenario there are two separate PPSTMEs configured
to monitor MS-PW1Z: 1) a PPSTME monitoring the PW13 MS-PW Segment on
Domain 1 (PW13 PPSTME), and 2) a PTCME monitoring the PWXZ MS-PW
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).
5. OAM Functions for proactive monitoring
[Editors' note: at the beginning of each section, reference the
section in the OAM Requirements document and explicitly list
additional detailed requirements wrt the OAM Requirements document]
Busi et al. Expires June 10, 2010 [Page 28]
Internet-Draft MPLS-TP OAM Framework December 2009
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.
5.1. Continuity Check and Connectivity Verification
Proactive Continuity Check functions are used to detect a loss of
continuity defect (LOC) between two MEPs in an MEG.
Proactive Connectivity Verification functions 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 MUST also include a globally unique Source MEP
identifier. When used to perform only pro-active Continuity Check
function, the CC-V OAM packet MAY not include any globally unique
Source MEP identifier identifier. Different formats of MEP
identifiers are defined in [10] 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 while it is possible to detect
any misconnection between two MEGs monitored for Continuity and
Connectivity or between an MEG monitored for Continuity and
Connectivity and one MEG monitored only for Continuity.
[Editor's note - Rephrase the previous paragraph: describe the four
cases.]
CC-V OAM packets MUST be transmitted at a regular, operator's
configurable, rate. The default CC-V transmission periods are
application dependent (see section 5.1.4).
Proactive CC-V OAM packets are transmitted with the "minimum loss
probability PHB" within a single network operator. This PHB is
configurable on network operator's basis. PHBs can be translated at
Busi et al. Expires June 10, 2010 [Page 29]
Internet-Draft MPLS-TP OAM Framework December 2009
the network borders by the same function that translates it for user
data traffic.
[Editor's note - Describe the relation between the previous paragraph
and the fate sharing requirement. Need to clarify also in the
requirement document that for proactive CC-V the fate sharing is
related to the forwarding behavior and not to the QoS behavior]
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.
It is desirable to not generate spurious alarms during initialization
or tear down; hence 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.
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 (i.e. with the 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.
Busi et al. Expires June 10, 2010 [Page 30]
Internet-Draft MPLS-TP OAM Framework December 2009
o Exit criteria: a pro-active CC-V OAM packet from the peer MEP
(i.e. 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.
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
[editors: IMO this would be better folded into the specific defect
types, If agreed I will edit accordingly]
Busi et al. Expires June 10, 2010 [Page 31]
Internet-Draft MPLS-TP OAM Framework December 2009
A sink MEP that detects one of the defect conditions defined in
section 5.1.1 MUST perform the following consequent actions. Some of
these consequent actions SHOULD be enabled/disabled by the operator
depending upon the application used (see section 5.1.4).
If a MEP detects an unexpected globally unique Source MEP Identifier,
it MUST block 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 [12]
recommends that CC-V proactive monitoring is enabled on every MEG in
order to reliably detect connectivity defects. However, CC-V
proactive monitoring MAY be disabled by an operator on an 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 MAY be disabled through configuration. This deactivation of
the block action may be used for activating or deactivating the
monitoring when it is not possible to synchronize the function
activation of the two peer MEPs.
If a MEP detects a LOC defect (section 5.1.1.1), a mis-connectivity
defect (section 5.1.1.2) or a period misconfiguration defect (section
5.1.1.3), it MUST declare a signal fail condition at the transport
path level.
[Editor's note - Transport equipment also performs defect correlation
(as defined in G.806) in order to properly report failures to the
transport NMS]. The current working assumption, to be further
investigated, is that defect correlations are outside the scope of
this document and to be defined in ITU-T documents.]
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:
Busi et al. Expires June 10, 2010 [Page 32]
Internet-Draft MPLS-TP OAM Framework December 2009
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 MUST know the root MEP ID from which it
expect to receive the CC-V OAM packets).
o transmission rate; the default CC-V transmission periods are
application dependent (see section 5.1.4)
Note that the reception period is the same as the configured
transmission rate.
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.
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.
5.1.4. Applications for proactive CC-V
CC-V is applicable for 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.
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.
Busi et al. Expires June 10, 2010 [Page 33]
Internet-Draft MPLS-TP OAM Framework December 2009
It SHOULD be possible for the operator to configure these
transmission rates for all applications, to satisfy his internal
requirements.
In addition, the operator should be able to define the consequent
action to be performed for each of these applications.
5.2. Remote Defect Indication
The Remote Defect Indication (RDI) 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.
[Editor's note - Add some forward compatibility information to cover
the case where future OAM mechanisms that contributes to the signal
fail detection (and RDI generation) are defined.]
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 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.
Busi et al. Expires June 10, 2010 [Page 34]
Internet-Draft MPLS-TP OAM Framework December 2009
5.2.2. Applications for Remote Defect Indication
RDI is applicable for the following applications:
o Single-ended fault management - A MEP that receives an RDI
indication from its peer MEP, can report a far-end defect
condition (i.e. the peer MEP has detected a signal fail condition
in the traffic direction from the MEP that receives the RDI
indication to the peer MEP that has sent the RDI information).
o Contribution to far-end performance monitoring - The indication of
the far-end defect condition is used as a contribution to the
bidirectional performance monitoring process.
5.3. Alarm Reporting
The Alarm Reporting function relies upon an Alarm Indication Signal
(AIS) message used to suppress alarms following detection of defect
conditions at the server (sub-)layer.
o A server MEP that detects a signal fail conditions in the server
(sub-)layer, will notify the MPLS-TP client (sub-)layer adaptation
function, which can generate packets with AIS information in a
direction opposite to its peers MEPs to allow the suppression of
secondary alarms at the MEP in the client (sub-)layer.
A server MEP is responsible for notifying the MPLS-TP layer network
adaptation function upon fault detection in the server layer network
to which the server MEP is associated.
Only the client layer adaptation function at an intermediate node
will issue MPLS-TP packets with AIS information. Upon receiving
notification of a signal fail condition the adaptation function
SHOULD immediately start transmitting periodic packets with AIS
information. 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 3. Assuming that all the MEGs
described in Figure 3 have pro-active CC-V enabled, a LOC defect is
detected by the MEPs of Sec12 SME, PSN13 LME, PW1 PTCME and PW1Z PME,
Busi et al. Expires June 10, 2010 [Page 35]
Internet-Draft MPLS-TP OAM Framework December 2009
however in transport network only the alarm associate to the fiber
cut needs to be reported to NMS while all these 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 PSN13 LME that then generates AIS packets on the PSN13
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 PSN13 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 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
To be incorporated in a future revision of this document
5.5. Packet Loss Monitoring
Packet Loss Monitoring (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. 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.
Busi et al. Expires June 10, 2010 [Page 36]
Internet-Draft MPLS-TP OAM Framework December 2009
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.
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 PHB that yields the lowest packet loss
performance among the PHB Scheduling Classes or Ordered Aggregates
(see RFC 3260 [15]) in the monitored transport path for the relevant
network domain(s).
5.5.2. Applications for Packet Loss Monitoring
LM is relevant for the following applications:
o Single or double-end performance monitoring: determination of the
packet loss performance of a transport path for Service Level
Agreement (SLA) verification purposes.
o Single or double-end performance monitoring: determination of the
packet loss performance of a PHB Scheduling Class or Ordered
Aggregate within a transport path.
o Contribution to service unable time. Both near-end and far-end
packet loss measurements contribute to performance metrics such as
near-end severely errored seconds (Near-End SES) and far-end
severely errored seconds (Far-End SES) respectively, which
together contribute to unavailable time, in a manner similar to
Recommendation G.826 [19] and Recommendation G.7710 [20].
Busi et al. Expires June 10, 2010 [Page 37]
Internet-Draft MPLS-TP OAM Framework December 2009
5.6. Client Signal Failure Indication
The Client Signal Failure Indication (CSF) function 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 transmission path does not support a native
defect/alarm indication mechanism, e.g. FDI/AIS.
[Editor's note - The need to support this function on the LSP layer
(and not only at the PW layer) needs to be further investigated.
Pending discussion on MPLS-TP clients in the main framework
document.]
A source MEP starts transmitting a CSF 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 CSF indication report this condition
to its associated client process via its local CSF 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 CSF message requires additional information to permit the
client instance to be identified.
5.6.1. Configuration considerations
In order to support CSF indication, the CSF transmission rate and PHB
of the CSF OAM message/information element should be configured as
part of the CSF configuration.
5.6.2. Applications for Client Signal Failure Indication
CSF is applicable for the following applications:
o Single-ended fault management - A MEP that receives a CSF
indication from its peer MEP, can report a far-end client defect
condition (i.e. the peer MEP has been informed of local client
signal fail condition in the traffic direction from the client to
the peer MEP that transmitted the CSF).
Busi et al. Expires June 10, 2010 [Page 38]
Internet-Draft MPLS-TP OAM Framework December 2009
o Contribution to far-end performance monitoring - The indication of
the far-end defect condition may be used to account on network
operator contribution to the bidirectional performance monitoring
process.
CSF supports the application described in Appendix VIII of ITU-T
G.806 [18].
5.7. Delay Measurement
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. 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.
5.7.1. 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 [15]) in the monitored transport path for the relevant
network domain(s).
Busi et al. Expires June 10, 2010 [Page 39]
Internet-Draft MPLS-TP OAM Framework December 2009
5.7.2. Applications for Delay Measurement
DM is relevant for the following applications:
o Single or double-end performance monitoring: determination of the
delay performance of a transport path for SLA verification
purposes.
o Single or double-end performance monitoring: determination of the
delay performance of a PHB Scheduling Class or Ordered Aggregate
within a transport path
6. OAM Functions for on-demand monitoring
[Editors' note: at the beginning of each section, reference the
section in the OAM Requirements document and explicitly list
additional detailed requirements wrt the OAM Requirements document]
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.
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.
Use of on-demand CV is dependent on the existence of a bi-directional
MEG, because it requires the presence of a return path in the data
plane.[Editors': needs to be revised on the basis of the return path
discussion (discussion item 7 in section 1.2]
[Editor's note - Clarify in the sentence above and within the
paragraph that on-demand CV requires a return path to send back the
reply to on-demand CV packets]
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-
Busi et al. Expires June 10, 2010 [Page 40]
Internet-Draft MPLS-TP OAM Framework December 2009
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 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 TTL field to
indicate the number of hops necessary, when targeting a MIP and use
the default value when performing an end-to-end check [IB => This is
quite generic for addressing packets to MIPs and MEPs so it is better
to move this text in section 2]. The target MEP/MIP shall return a
reply on-demand CV packet for each packet received. If the expected
number of on-demand CV reply packets is not received at source MEP,
the LOC defect state is entered.
[Editor's note - We need to add some text for the usage of on-demand
CV with different packet sizes, e.g. to discover MTU problems.]
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.
[Editor's note - We need to be better define the reason for such
configuration]
Busi et al. Expires June 10, 2010 [Page 41]
Internet-Draft MPLS-TP OAM Framework December 2009
6.2. Packet Loss Monitoring
On-demand Packet Loss (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 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.
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 [15]) in the monitored transport path for the relevant
network domain(s).
6.2.2. Applications for On-demand Packet Loss Monitoring
On-demand LM is relevant for the following applications:
o Single-end performance monitoring: diagnostic of the packet loss
performance of a transport path for SLA trouble shooting purposes.
o Single-end performance monitoring: diagnostic of the packet loss
performance of a PHB Scheduling Class or Ordering Aggregate within
a transport path for QoS trouble shooting purposes.
6.3. Diagnostic
To be incorporated in a future revision of this document
[Editors' note: describe an OAM tool for throughput estimation (out-
of-service): works in one-way and two-way modes]
[Editors' note: Need further investigation about the need to support
a data-plane loopback. If needed, which layer does have to support
Busi et al. Expires June 10, 2010 [Page 42]
Internet-Draft MPLS-TP OAM Framework December 2009
this function (i.e. the MPLS-TP layer or its server layer?) It is
also needed to understand whether it is needed to specify where this
data-plane loopback takes place within the equipment]
[Munich: Need to describe the two types of loopback - LBM/LBR and
traffic loopback enhanced with variable sized packets in the on
demand cases.
One objective of diags is fault location, we need to make clear how
we apply the tools to fault location.
At the top of each section we need to describe the detailed
requirements and then in the rest of the section describe how it is
met.]
6.4. Route Tracing
[Editors' note: The framework needs to say what you need to trace and
not how you do it (remove the description of the solution).]
[Editors' note: Need to investigate if we need both tracing options:
describe why and a sketch of the two options and their properties.
Possible reasons for both options:
o TTL incremental tells whether the CP is correct or not
o the second one (path discovery) is ...
Action: check on the mailing list the need to support both modes of
operations.]
After e.g. provisioning an MPLS-TP LSP or for trouble shooting
purposes, it is often necessary to trace a route covered by an ME
from a source MEP to the sink MEP including all the MIPs in-between.
The route tracing function 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 CV and, to a much lesser degree, CC. 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 trace could be
implemented e.g. by an MPLS traceroute-like function [RFC4379].
However, route tracing should always return the full list of MIPs and
the peer MEP in it answer(s). In case a defect exist, the route trace
function needs to be able to detect it and stop automatically
Busi et al. Expires June 10, 2010 [Page 43]
Internet-Draft MPLS-TP OAM Framework December 2009
returning the incomplete list of OAM entities that it was able to
trace.
The configuration of the route trace function must at least support
the setting of the trace depth (number of hops)_and the number of
trace attempts before it gives up. Default setting need to be
configurable by the operator, too.
6.5. Delay Measurement
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. 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 [15]) in the
monitored transport path for the relevant network domain(s).
Busi et al. Expires June 10, 2010 [Page 44]
Internet-Draft MPLS-TP OAM Framework December 2009
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.
6.5.2. Applications for Delay Measurement
DM is relevant for the following applications:
o Single or double-end performance monitoring: determination of the
packet delay and/or delay variation performance of a transport
path for SLA verification purposes.
o Single or double-end performance monitoring: determination of the
packet delay and/or delay variation a PHB Scheduling Class or
Ordering Aggregate within a transport path
o Contribution to service unable time. Packet delay measurements may
contribute to performance metrics such as near-end severely
errored seconds (Near-End SES) and far-end severely errored
seconds (Far-End SES), which together contribute to unavailable
time.
6.6. Lock Instruct
To be incorporated in a future revision of this document
7. 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.
Mechanisms that the framework does not specify might be subject to
additional security considerations.
8. IANA Considerations
No new IANA considerations.
Busi et al. Expires June 10, 2010 [Page 45]
Internet-Draft MPLS-TP OAM Framework December 2009
9. 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
T-MPLS Ad Hoc Group in ITU-T) involved in the definition and
specification of MPLS Transport Profile.
This document was prepared using 2-Word-v2.0.template.dot.
Busi et al. Expires June 10, 2010 [Page 46]
Internet-Draft MPLS-TP OAM Framework December 2009
10. References
10.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997
[2] Rosen, E., Viswanathan, A., Callon, R., "Multiprotocol Label
Switching Architecture", RFC 3031, January 2001
[3] Rosen, E., et al., "MPLS Label Stack Encoding", RFC 3032,
January 2001
[4] Agarwal, P., Akyol, B., "Time To Live (TTL) Processing in
Multi-Protocol Label Switching (MPLS) Networks", RFC 3443,
January 2003
[5] Bryant, S., Pate, P., "Pseudo Wire Emulation Edge-to-Edge
(PWE3) Architecture", RFC 3985, March 2005
[6] Nadeau, T., Pignataro, S., "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for
Pseudowires", RFC 5085, December 2007
[7] Bocci, M., Bryant, S., "An Architecture for Multi-Segment
Pseudo Wire Emulation Edge-to-Edge", draft-ietf-pwe3-ms-pw-
arch-05 (work in progress), September 2008
[8] Bocci, M., et al., "A Framework for MPLS in Transport
Networks", draft-ietf-mpls-tp-framework-06 (work in progress),
October 2009
[9] Vigoureux, M., Bocci, M., Swallow, G., Ward, D., Aggarwal, R.,
"MPLS Generic Associated Channel", RFC 5586, June 2009
[10] Swallow, G., Bocci, M., "MPLS-TP Identifiers", draft-ietf-mpls-
tp-identifiers-00 (work in progress), November 2009
10.2. Informative References
[11] Niven-Jenkins, B., Brungard, D., Betts, M., sprecher, N., Ueno,
S., "MPLS-TP Requirements", RFC 5654, September 2009
[12] Vigoureux, M., Betts, M., Ward, D., "Requirements for OAM in
MPLS Transport Networks", draft-ietf-mpls-tp-oam-requirements-
03 (work in progress), August 2009
Busi et al. Expires June 10, 2010 [Page 47]
Internet-Draft MPLS-TP OAM Framework December 2009
[13] Sprecher, N., Nadeau, T., van Helvoort, H., Weingarten, Y.,
"MPLS-TP OAM Analysis", draft-ietf-mpls-tp-oam-analysis-00
(work in progress), November 2009
[14] 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
[15] Grossman, D., "New terminology and clarifications for
Diffserv", RFC 3260, April 2002.
[16] ITU-T Recommendation G.707/Y.1322 (01/07), "Network node
interface for the synchronous digital hierarchy (SDH)", January
2007
[17] ITU-T Recommendation G.805 (03/00), "Generic functional
architecture of transport networks", March 2000
[18] ITU-T Recommendation G.806 (01/09), "Characteristics of
transport equipment - Description methodology and generic
functionality ", January 2009
[19] ITU-T Recommendation G.826 (12/02), "End-to-end error
performance parameters and objectives for international,
constant bit-rate digital paths and connections", December 2002
[20] ITU-T Recommendation G.7710 (07/07), "Common equipment
management function requirements", July 2007
[21] ITU-T Recommendation Y.2611 (06/12), " High-level architecture
of future packet-based networks", 2006
Authors' Addresses
Dave Allan (Editor)
Ericsson
Email: david.i.allan@ericsson.com
Italo Busi (Editor)
Alcatel-Lucent
Email: Italo.Busi@alcatel-lucent.com
Busi et al. Expires June 10, 2010 [Page 48]
Internet-Draft MPLS-TP OAM Framework December 2009
Ben Niven-Jenkins (Editor)
BT
Email: benjamin.niven-jenkins@bt.com
Contributing Authors' Addresses
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
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
Busi et al. Expires June 10, 2010 [Page 49]
Internet-Draft MPLS-TP OAM Framework December 2009
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
Busi et al. Expires June 10, 2010 [Page 50]
| PAFTECH AB 2003-2026 | 2026-04-22 17:05:22 |