draft-ietf-mpls-tp-linear-protection-04.txt   draft-ietf-mpls-tp-linear-protection-05.txt 
Network Working Group S. Bryant, Ed. Network Working Group S. Bryant, Ed.
Internet-Draft E. Osborne Internet-Draft E. Osborne
Intended status: Standards Track Cisco Intended status: Standards Track Cisco
Expires: July 30, 2011 N. Sprecher, Ed. Expires: September 14, 2011 N. Sprecher, Ed.
Nokia Siemens Networks Nokia Siemens Networks
A. Fulignoli, Ed. A. Fulignoli, Ed.
Ericsson Ericsson
Y. Weingarten Y. Weingarten
Nokia Siemens Networks Nokia Siemens Networks
January 26, 2011 March 13, 2011
MPLS-TP Linear Protection MPLS-TP Linear Protection
draft-ietf-mpls-tp-linear-protection-04.txt draft-ietf-mpls-tp-linear-protection-05.txt
Abstract Abstract
The Transport Profile for Multiprotocol Label Switching (MPLS-TP) is The Transport Profile for Multiprotocol Label Switching (MPLS-TP) is
being specified jointly by IETF and ITU-T. This document addresses being specified jointly by IETF and ITU-T. This document addresses
the functionality described in the MPLS-TP Survivability Framework the functionality described in the MPLS-TP Survivability Framework
document [SurvivFwk] and defines a protocol that may be used to document [SurvivFwk] and defines a protocol that may be used to
fulfill the function of the Protection State Coordination for linear fulfill the function of the Protection State Coordination for linear
protection, as described in that document. protection, as described in that document.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 30, 2011. This Internet-Draft will expire on September 14, 2011.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Protection architectures . . . . . . . . . . . . . . . . . 4 1.1. Protection architectures . . . . . . . . . . . . . . . . . 4
1.2. Scope of the document . . . . . . . . . . . . . . . . . . 5 1.2. Scope of the document . . . . . . . . . . . . . . . . . . 5
1.3. Contributing authors . . . . . . . . . . . . . . . . . . . 6 1.3. Contributing authors . . . . . . . . . . . . . . . . . . . 6
2. Conventions used in this document . . . . . . . . . . . . . . 6 2. Conventions used in this document . . . . . . . . . . . . . . 6
2.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2. Definitions and Terminology . . . . . . . . . . . . . . . 7 2.2. Definitions and Terminology . . . . . . . . . . . . . . . 7
3. Protection switching control logic . . . . . . . . . . . . . . 7 3. Protection switching control logic . . . . . . . . . . . . . . 7
3.1. Protection switching control logical architecture . . . . 7 3.1. Local Request Logic . . . . . . . . . . . . . . . . . . . 8
3.1.1. Local Request Logic . . . . . . . . . . . . . . . . . 8 3.2. Remote Requests . . . . . . . . . . . . . . . . . . . . . 10
3.1.2. Remote Requests . . . . . . . . . . . . . . . . . . . 10 3.3. PSC Control Logic . . . . . . . . . . . . . . . . . . . . 11
3.1.3. PSC Control Logic . . . . . . . . . . . . . . . . . . 11 3.4. PSC Message Generator . . . . . . . . . . . . . . . . . . 12
3.1.4. PSC Message Generator . . . . . . . . . . . . . . . . 12 3.5. Wait-to-Restore (WTR) timer . . . . . . . . . . . . . . . 12
3.1.5. Wait-to-Restore (WTR) timer . . . . . . . . . . . . . 12 3.6. PSC Control States . . . . . . . . . . . . . . . . . . . . 12
3.1.6. PSC Control States . . . . . . . . . . . . . . . . . . 12 3.6.1. Local and Remote state . . . . . . . . . . . . . . . . 13
4. Protection state coordination (PSC) protocol . . . . . . . . . 14 4. Protection state coordination (PSC) protocol . . . . . . . . . 14
4.1. Transmission and acceptance of PSC control packets . . . . 14 4.1. Transmission and acceptance of PSC control packets . . . . 15
4.2. Protocol format . . . . . . . . . . . . . . . . . . . . . 15 4.2. Protocol format . . . . . . . . . . . . . . . . . . . . . 15
4.2.1. PSC Ver field . . . . . . . . . . . . . . . . . . . . 16 4.2.1. PSC Ver field . . . . . . . . . . . . . . . . . . . . 16
4.2.2. PSC Request field . . . . . . . . . . . . . . . . . . 16 4.2.2. PSC Request field . . . . . . . . . . . . . . . . . . 16
4.2.3. Protection Type (PT) . . . . . . . . . . . . . . . . . 17 4.2.3. Protection Type (PT) . . . . . . . . . . . . . . . . . 17
4.2.4. Revertive (R) field . . . . . . . . . . . . . . . . . 17 4.2.4. Revertive (R) field . . . . . . . . . . . . . . . . . 18
4.2.5. Fault path (FPath) field . . . . . . . . . . . . . . . 18 4.2.5. Fault path (FPath) field . . . . . . . . . . . . . . . 18
4.2.6. Data path (Path) field . . . . . . . . . . . . . . . . 18 4.2.6. Data path (Path) field . . . . . . . . . . . . . . . . 18
4.3. Principles of Operation . . . . . . . . . . . . . . . . . 18 4.3. Principles of Operation . . . . . . . . . . . . . . . . . 19
4.3.1. Basic operation . . . . . . . . . . . . . . . . . . . 19 4.3.1. Basic operation . . . . . . . . . . . . . . . . . . . 19
4.3.2. Priority of inputs . . . . . . . . . . . . . . . . . . 20 4.3.2. Priority of inputs . . . . . . . . . . . . . . . . . . 20
4.3.3. Operation of PSC States . . . . . . . . . . . . . . . 20 4.3.3. Operation of PSC States . . . . . . . . . . . . . . . 21
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31
6. Security Considerations . . . . . . . . . . . . . . . . . . . 31 6. Security Considerations . . . . . . . . . . . . . . . . . . . 31
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 31 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 31
Appendix A. PSC state machine tables . . . . . . . . . . . . . . 31 Appendix A. PSC state machine tables . . . . . . . . . . . . . . 31
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 35 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 36
8.1. Normative References . . . . . . . . . . . . . . . . . . . 35 8.1. Normative References . . . . . . . . . . . . . . . . . . . 36
8.2. Informative References . . . . . . . . . . . . . . . . . . 35 8.2. Informative References . . . . . . . . . . . . . . . . . . 36
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 36 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 37
1. Introduction 1. Introduction
The MPLS Transport Profile (MPLS-TP) [TPFwk] is a framework for the The MPLS Transport Profile (MPLS-TP) [TPFwk] is a framework for the
construction and operation of packet-switched transport networks construction and operation of packet-switched transport networks
based on the architectures for MPLS ([RFC3031] and [RFC3032]) and for based on the architectures for MPLS ([RFC3031] and [RFC3032]) and for
Pseudowires (PWs) ([RFC3985] and [RFC5659]) and the requirements of Pseudowires (PWs) ([RFC3985] and [RFC5659]) and the requirements of
[RFC5654]. [RFC5654].
Network survivability is the ability of a network to recover traffic Network survivability is the ability of a network to recover traffic
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switching. In a mesh network, linear protection provides a very switching. In a mesh network, linear protection provides a very
suitable protection mechanism because it can operate between any pair suitable protection mechanism because it can operate between any pair
of points within the network. It can protect against a defect in an of points within the network. It can protect against a defect in an
intermediate node, a span, a transport path segment, or an end-to-end intermediate node, a span, a transport path segment, or an end-to-end
transport path. transport path.
1.1. Protection architectures 1.1. Protection architectures
Protection switching is a fully allocated survivability mechanism. Protection switching is a fully allocated survivability mechanism.
It is fully allocated in the sense that the route and bandwidth of It is fully allocated in the sense that the route and bandwidth of
the recovery path is reserved for a selected working path or set of the protection path is reserved for a selected working path or set of
working paths. It provides a fast and simple survivability working paths. It provides a fast and simple survivability
mechanism, that allows the network operator to easily grasp the mechanism, that allows the network operator to easily grasp the
active state of the network, compared to other survivability active state of the network, compared to other survivability
mechanisms. mechanisms.
As specified in the Survivability Framework document [SurvivFwk], As specified in the Survivability Framework document [SurvivFwk],
protection switching is applied to a protection domain. For the protection switching is applied to a protection domain. For the
purposes of this document, we define the protection domain of a P2P purposes of this document, we define the protection domain of a P2P
LSP as consisting of two Label Edge Routers (LER) and the transport LSP as consisting of two Label Edge Routers (LER) and the transport
paths that connect them. For a P2MP LSP the protection domain paths that connect them. For a P2MP LSP the protection domain
includes the root (or source) LER, the destination (or sink) LERs, includes the root (or source) LER, the destination (or sink) LERs,
and the transport paths that connect them. and the transport paths that connect them.
In 1+1 unidirectional architecture as presented in [SurvivFwk], a In 1+1 unidirectional architecture as presented in [SurvivFwk], a
recovery transport path is dedicated to the working transport path. protection transport path is dedicated to the working transport path.
Normal traffic is bridged (as defined in [RFC4427])and fed to both Normal traffic is bridged (as defined in [RFC4427])and fed to both
the working and the recovery transport entities by a permanent bridge the working and the protection paths by a permanent bridge at the
at the source of the protection domain. The sink of the protection source of the protection domain. The sink of the protection domain
domain selects which of the working or recovery entities to receive selects which of the working or protection paths to receive the
the traffic from, based on a predetermined criteria, e.g. server traffic from, based on a predetermined criteria, e.g. server defect
defect indication. When used for bidirectional switching the 1+1 indication. When used for bidirectional switching the 1+1 protection
protection architecture must also support a Protection State architecture must also support a Protection State Coordination (PSC)
Coordination (PSC) protocol. This protocol is used to help protocol. This protocol is used to help coordinate between both ends
coordinate between both ends of the protection domain in selecting of the protection domain in selecting the proper traffic flow.
the proper traffic flow.
In the 1:1 architecture, a recovery transport path is dedicated to In the 1:1 architecture, a protection transport path is dedicated to
the working transport path of a single service and the traffic is the working transport path of a single service and the traffic is
only transmitted either on the working or the recovery path, by using only transmitted either on the working or the protection path, by
a selector bridge at the source of the protection domain. A selector using a selector bridge at the source of the protection domain. A
at the sink of the protection domain then selects the path that selector at the sink of the protection domain then selects the path
carries the normal traffic. Since the source and sink need to be that carries the normal traffic. Since the source and sink need to
coordinated to ensure that the selector bridge at both ends select be coordinated to ensure that the selector bridge at both ends select
the same path, this architecture must support a PSC protocol. the same path, this architecture must support a PSC protocol.
The 1:n protection architecture extends the 1:1 architecture above by The 1:n protection architecture extends the 1:1 architecture above by
sharing the recovery path among n services. Again, the recovery path sharing the protection path among n services. Again, the protection
is fully allocated and disjoint from any of the n working transport path is fully allocated and disjoint from any of the n working
paths that it is being used to protect. The normal data traffic for transport paths that it is being used to protect. The normal data
each service is transmitted either on the normal working path for traffic for each service is transmitted either on the normal working
that service or, in cases that trigger protection switching (as path for that service or, in cases that trigger protection switching
defined in [SurvivFwk]), may be sent on the recovery path. The (as defined in [SurvivFwk]), may be sent on the protection path. The
switching action is similar to the 1:1 case where a selector bridge switching action is similar to the 1:1 case where a selector bridge
is used at the source. It should be noted that in cases where is used at the source. It should be noted that in cases where
multiple working path services have triggered protection switching multiple working path services have triggered protection switching
that some services, dependent upon their Service Level Agreement that some services, dependent upon their Service Level Agreement
(SLA), may not be transmitted as a result of limited resources on the (SLA), may not be transmitted as a result of limited resources on the
recovery path. In this architecture there may be a need for protection path. In this architecture there may be a need for
coordination of the protection switching, and also for resource coordination of the protection switching, and also for resource
allocation negotiation. The procedures for this are for further allocation negotiation. The procedures for this are for further
study and may be addressed in future documents. study and may be addressed in future documents.
1.2. Scope of the document 1.2. Scope of the document
As was pointed out in the Survivability Framework [SurvivFwk] and As was pointed out in the Survivability Framework [SurvivFwk] and
highlighted above, there is a need for coordination between the end highlighted above, there is a need for coordination between the end
points of the protection domain when employing bidirectional points of the protection domain when employing bidirectional
protection schemes. This is especially true when there is a need to protection schemes. This is especially true when there is a need to
maintain traffic over a co-routed bidirectional LSP. maintain traffic over a co-routed bidirectional LSP.
The scope of this draft is to present a protocol for the Protection The scope of this draft is to present a protocol for the Protection
State Coordination of Linear Protection. The protocol addresses the State Coordination of Linear Protection. The protocol addresses the
protection of LSPs in an MPLS-TP network as required by [RFC5654] (in protection of LSPs in an MPLS-TP network as required by [RFC5654] (in
particular requirements 63-67 and 74-79) and described in particular requirements 63-65 and 74-79) and described in
[SurvivFwk]. The basic protocol is designed for use in conjunction [SurvivFwk]. The basic protocol is designed for use in conjunction
with the 1:1 protection architecture (for both unidirectional and with the 1:1 protection architecture bidirectional protection and for
bidirectional protection) and for 1+1 protection of a bidirectional 1+1 protection of a bidirectional path (for both unidirectional and
path (for both unidirectional and bidirectional protection bidirectional protection switching). Applicability of the protocol
switching). Applicability of the protocol for 1:n protection schemes for 1:1 unidirectional protection and for 1:n protection schemes may
may be documented in a future document. The applicability of this be documented in a future document. The applicability of this
protocol to additional MPLS-TP constructs and topologies may be protocol to additional MPLS-TP constructs and topologies may be
documented in future documents. documented in future documents.
While the unidirectional 1+1 protection architecture does not require While the unidirectional 1+1 protection architecture does not require
the use of a coordination protocol, the protocol may be used by the the use of a coordination protocol, the protocol may be used by the
ingress node of the path to notify the far-side end point that a ingress node of the path to notify the far-side end point that a
switching condition has occurred and verify the consistency of the switching condition has occurred and verify the consistency of the
end point configuration. This use may be especially useful for end point configuration. This use may be especially useful for
point-to-multipoint transport paths, that are unidirectional by point-to-multipoint transport paths, that are unidirectional by
definition of [RFC5654]. definition of [RFC5654].
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"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2.1. Acronyms 2.1. Acronyms
This draft uses the following acronyms: This draft uses the following acronyms:
DNR Do not revert DNR Do not revert
FS Forced Switch FS Forced Switch
G-ACh Generic Associated Channel Header G-ACh Generic Associated Channel Header
LER Label Switching Router LER Label Edge Router
LO Lockout of protection
MPLS-TP Transport Profile for MPLS MPLS-TP Transport Profile for MPLS
MS Manual Switch MS Manual Switch
NR No Request
P2P Point-to-point P2P Point-to-point
P2MP Point-to-multipoint P2MP Point-to-multipoint
PSC Protection State Coordination Protocol PSC Protection State Coordination Protocol
PST Path Segment Tunnel
SD Signal Degrade SD Signal Degrade
SF Signal Fail SF Signal Fail
SLA Service Level Agreement SLA Service Level Agreement
WTR Wait-to-Restore WTR Wait-to-Restore
2.2. Definitions and Terminology 2.2. Definitions and Terminology
The terminology used in this document is based on the terminology The terminology used in this document is based on the terminology
defined in [RFC4427] and further adapted for MPLS-TP in [SurvivFwk]. defined in [RFC4427] and further adapted for MPLS-TP in [SurvivFwk].
In addition, we use the term LER to refer to a MPLS-TP Network In addition, we use the term LER to refer to a MPLS-TP Network
Element, whether it is a LSR, LER, T-PE, or S-PE. Element, whether it is a LSR, LER, T-PE, or S-PE.
3. Protection switching control logic 3. Protection switching control logic
3.1. Protection switching control logical architecture
Protection switching processes the local triggers described in Protection switching processes the local triggers described in
requirements 74-79 of [RFC5654] together with inputs received from requirements 74-79 of [RFC5654] together with inputs received from
the far-end LER. Based on these inputs the LER will take certain the far-end LER. Based on these inputs the LER will take certain
protection switching actions, e.g. switching the Selector Bridge to protection switching actions, e.g. switching the Selector Bridge to
select the working or protection path, and transmit different select the working or protection path, and transmit different
protocol messages. protocol messages.
The following figure shows the logical decomposition of the PSC The following figure shows the logical decomposition of the
Control Logic into different logical processing units. These Protection Switching Control Logic into different logical processing
processing units are presented in subsequent subsections of this units. These processing units are presented in subsequent
document. subsections of this document. This logical decomposition is only
intended for descriptive purposes, any implementation that produces
the external behavior described in section 4 is acceptable.
Server Indication Control Plane Indication Server Indication Control Plane Indication
-----------------+ +------------- -----------------+ +-------------
Operator Command | | OAM Indication Operator Command | | OAM Indication
----------------+ | | +--------------- ----------------+ | | +---------------
| | | | | | | |
V V V V V V V V
+---------------+ +-------+ +---------------+ +-------+
| Local Request |<--------| WTR | | Local Request |<--------| WTR |
| logic |WTR Exps | Timer | | logic |WTR Exps | Timer |
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from the OAM, external operator commands, from the local control from the OAM, external operator commands, from the local control
plane (when present), and the Wait-to-Restore timer. By considering plane (when present), and the Wait-to-Restore timer. By considering
all of these local request sources it determines the highest priority all of these local request sources it determines the highest priority
local request. This high-priority request is passed to the PSC local request. This high-priority request is passed to the PSC
Control logic, that will cross-check this local request with the Control logic, that will cross-check this local request with the
information received from the far-end LER. The PSC Control logic information received from the far-end LER. The PSC Control logic
uses this input to determine what actions need to be taken, e.g. uses this input to determine what actions need to be taken, e.g.
local actions at the LER, or what message should be sent to the far- local actions at the LER, or what message should be sent to the far-
end LER, and the current status of the protection domain. end LER, and the current status of the protection domain.
3.1.1. Local Request Logic 3.1. Local Request Logic
The protection switching logic processes input triggers from five The Local Request logic processes input triggers from five sources:
sources:
o Operator command - the network operator may issue commands that o Operator command - the network operator may issue local
trigger protection switching. The supported commands are Forced administrative commands on the LER that trigger protection
Switch, Manual Switch, Clear, Lockout of Protection, (see switching. The supported commands are Forced Switch, Manual
definitions in [RFC4427]). Switch, Clear, Lockout of Protection, (see definitions in
[RFC4427]).
o Server layer alarm indication - the underlying server layer of the o Server layer alarm indication - the underlying server layer of the
network detects failure conditions at the underlying layer and may network detects failure conditions at the underlying layer and may
issue an indication to the MPLS-TP layer. The server layer may issue an indication to the MPLS-TP layer. The server layer may
employ its own protection switching mechanism, and therefore this employ its own protection switching mechanism, and therefore this
input MAY be controlled by a holdoff-timer that SHOULD be input MAY be controlled by a holdoff-timer that SHOULD be
configurable by the network operator. configurable by the network operator.
o Control plane - if there is a control plane active in the network o Control plane - if there is a control plane active in the network
(either signaling or routing), it MAY trigger protection switching (either signaling or routing), it MAY trigger protection switching
based on conditions detected by the control plane. If the control based on conditions detected by the control plane. If the control
plane is based on GMPLS [RFC3945] then the recovery process SHALL plane is based on GMPLS [RFC3945] then the recovery process SHALL
comply with the process described in [RFC4872]. comply with the process described in [RFC4872].
o OAM indication - OAM fault management or performance measurement o OAM indication - OAM fault management or performance measurement
tools may detect a failure or degrade condition on the MPLS-TP tools may detect a failure or degrade condition on either the
transport path and this SHOULD input an indication to the Local working or protection transport path and this SHOULD input an
Request Logic. indication to the Local Request Logic.
o WTR expires - The Wait-to-Restore timer is used in conjunction o WTR expires - The Wait-to-Restore timer is used in conjunction
with recovery from failure conditions on the working path in with recovery from failure conditions on the working path in
revertive mode. The timer SHALL signal the PSC control process revertive mode. The timer SHALL signal the PSC control process
when it expires and the end point SHOULD revert to the normal when it expires and the end point SHOULD revert to the normal
transmission of the user data traffic. transmission of the user data traffic.
The Local request logic SHALL process these different input sources The Local request logic SHALL process these different input sources
and, based on the priorities between them (see section 4.3.2), SHALL and, based on the priorities between them (see section 4.3.2), shall
produce a current local request. If more than one local input source produce a current local request. If more than one local input source
generates an indicator, then the Local request logic SHALL select the generates an indicator, then the Local request logic shall select the
higher priority indicator and block any lower priority indicator. As higher priority indicator and block any lower priority indicator. As
a result, there is a single current local request that is passed to a result, there is a single current local request that is passed to
the PSC Control logic. The different local requests that may be the PSC Control logic. The different local requests that may be
output from the Local Request Logic are: output from the Local Request Logic are:
o Clear - if the operator cancels an active local administrative o Clear - if the operator cancels an active local administrative
command, i.e. LO/FS/MS. command, i.e. LO/FS/MS.
o Lockout of Protection (LO) - if the operator requested to disable o Lockout of Protection (LO) - if the operator requested to prevent
the protection path. switching data traffic to the protection path, for any purpose.
o Signal Fail (SF) - if any of the Server Layer, Control plane, or o Signal Fail (SF) - if any of the Server Layer, Control plane, or
OAM indications signaled a failure condition on either the OAM indications signaled a failure condition on either the
protection path or one of the working paths. protection path or one of the working paths.
o Signal Degrade (SD) - if any of the Server Layer, Control plane, o Signal Degrade (SD) - if any of the Server Layer, Control plane,
or OAM indications signaled a degraded transmission condition on or OAM indications signaled a degraded transmission condition on
either the protection path or one of the working paths either the protection path or one of the working paths. The
determination and actions for SD are for further study and may
appear in a separate document. All references to SD input are
place-holders for this extension.
o Clear Signal Fail - if all of the Server Layer, Control plane, or o Clear Signal Fail - if all of the Server Layer, Control plane, or
OAM indications are no longer indicating a failure condition on a OAM indications are no longer indicating a failure condition on a
path that was previously indicating a failure condition. path that was previously indicating a failure condition.
o Forced Switch (FS) - if the operator requested that traffic be o Forced Switch (FS) - if the operator requested that traffic be
switched from one of the working paths to the protection path. switched from one of the working paths to the protection path.
o Manual Switch (MS) - if the operator requested that traffic be o Manual Switch (MS) - if the operator requested that traffic be
switched from its current path to the other path. This is only switched from the working path to the protection path. This is
relevant if there is no currently active Fault condition or only relevant if there is no currently active fault condition or
Operator command. Operator command.
o WTR Expires - generated by the WTR timer completing its period. o WTR Expires - generated by the WTR timer completing its period.
If none of the input sources have generated any input then the Local If none of the input sources have generated any input then the Local
request logic SHALL generate a No Request (NR) request as the current request logic should generate a No Request (NR) request as the
local request . current local request .
3.1.2. Remote Requests 3.2. Remote Requests
In addition to the local requests, generated as a result of the local In addition to the local requests, generated as a result of the local
triggers, indicated in the previous subsection, the PSC Control Logic triggers, indicated in the previous subsection, the PSC Control Logic
SHALL accept PSC messages from the far-end LER of the transport path. SHALL accept PSC messages from the far-end LER of the transport path.
These remote messages indicate the status of the transport path from These remote messages indicate the status of the transport path from
the viewpoint of the far-end LER, and may indicate if the local MEP the viewpoint of the far-end LER, and may indicate if the local MEP
SHOULD initiate a protection switch operation. SHOULD initiate a protection switch operation.
The following remote requests may be received by the PSC process: The following remote requests may be received by the PSC process:
skipping to change at page 11, line 28 skipping to change at page 11, line 29
o Remote DNR - indicates that the remote end point has determined o Remote DNR - indicates that the remote end point has determined
that the failure condition has recovered and will continue that the failure condition has recovered and will continue
transporting traffic on the protection path due to operator transporting traffic on the protection path due to operator
configuration that prevents automatic reversion to the Normal configuration that prevents automatic reversion to the Normal
state. state.
o Remote NR - indicates that the remote end point has no abnormal o Remote NR - indicates that the remote end point has no abnormal
condition to report. condition to report.
3.1.3. PSC Control Logic 3.3. PSC Control Logic
The PSC Control Logic SHALL accept as input - The PSC Control Logic SHALL accept as input -
a. the current local request output from the Local Request Logic a. the current local request output from the Local Request Logic
(see section 3.1.1), (see section 3.1),
b. the remote request message from the remote end point of the b. the remote request message from the remote end point of the
transport path, and transport path (see section 3.2), and
c. the current state of the PSC Control Logic (maintained internally c. the current state of the PSC Control Logic (maintained internally
by the PSC Control Logic). by the PSC Control Logic).
Based on the priorities between the different inputs, the PSC Control Based on the priorities between the different inputs, the PSC Control
Logic SHALL determine the new state of the PSC Control Logic and what Logic SHALL determine the new state of the PSC Control Logic and what
actions need to be taken. actions need to be taken.
The new state information SHALL be retained by the PSC Control Logic, The new state information SHALL be retained by the PSC Control Logic,
while the requested action SHALL be sent to the PSC Message Generator while the requested action should be sent to the PSC Message
(see subsection 3.1.4) to generate and transmit the proper PSC Generator (see subsection 3.4) to generate and transmit the proper
message to be transmitted to the remote end point of the protection PSC message to be transmitted to the remote end point of the
domain. protection domain.
3.1.4. PSC Message Generator 3.4. PSC Message Generator
Based on the action output from the Control Logic this unit formats Based on the action output from the PSC Control Logic this unit
the PSC protocol message that is transmitted to the remote end point formats the PSC protocol message that is transmitted to the remote
of the protection domain. When the PSC information has changed, end point of the protection domain. When the PSC control state (see
three PSC messages SHOULD be transmitted in quick succession, and section 3.6) has changed, three PSC messages SHOULD be transmitted in
subsequent messages should be transmitted continually at a lower quick succession, and subsequent messages should be transmitted
frequency. continually at a lower frequency.
The transmission of three rapid packets allows for fast protection The transmission of three rapid packets allows for fast protection
switching even if one or two PSC messages are lost or corrupted. For switching even if one or two PSC messages are lost or corrupted. For
protection switching within 50ms, it is RECOMMENDED that the default protection switching within 50ms, it is RECOMMENDED that the default
interval of the first three PSC messages SHOULD be no larger than interval of the first three PSC messages SHOULD be no larger than
3.3ms. The subsequent messages SHOULD be transmitted with an 3.3ms. The subsequent messages SHOULD be transmitted with an
interval of 5 sec, to avoid traffic congestion. interval of 5 sec, to avoid traffic congestion.
3.1.5. Wait-to-Restore (WTR) timer 3.5. Wait-to-Restore (WTR) timer
The WTR timer is used to delay reversion to Normal state when The WTR timer is used to delay reversion to Normal state when
recovering from a failure condition on the working path and the recovering from a failure condition on the working path and the
protection domain is configured for revertive behavior. The WTR may protection domain is configured for revertive behavior. The length
be in one of two states - either Running or Stopped. The WTR timer of the timer may be provisioned by the operator. The WTR may be in
MAY be started or stopped by the PSC Control Logic. one of two states - either Running or Stopped. The control of the
WTR timer is managed by the PSC Control Logic, by use of internal
signals to start and stop, i.e. reset, the WTR timer.
If the WTR timer expires prior to being stopped it SHALL generate a If the WTR timer expires prior to being stopped it shall generate a
WTR Expires local signal that shall be processed by the Local Request WTR Expires local signal that shall be processed by the Local Request
Logic. If the WTR timer is running, sending a Stop command SHALL Logic. If the WTR timer is running, sending a Stop command shall
reset the timer but SHALL NOT generate a WTR Expires local signal. reset the timer, and put the WTR timer into Stopped state, but shall
If the WTR timer is not running, a Stop command SHALL be ignored. not generate a WTR Expires local signal. If the WTR timer is
stopped, a Stop command shall be ignored.
3.1.6. PSC Control States 3.6. PSC Control States
The PSC Control Logic SHOULD maintain information on the current The PSC Control Logic SHOULD maintain information on the current
state of the protection domain. The state information SHALL include state of the protection domain. Information on the state of the
information of the current state and an indication of the cause for domain is maintained by each LER within the protection domain. The
the current state (e.g. unavailable due to local LO command, state information SHALL include information of the current state of
protecting due to remote FS). In particular, the state information the protection domain, an indication of the cause for the current
SHOULD include an indication if the state is related to a remote or state (e.g. unavailable due to local LO command, protecting due to
local condition. If there are both a local indicator and remote remote FS), and, for each LER, SHOULD include an indication if the
indicator for the state then the state shall be considered a local state is related to a remote or local condition. If there are both a
state. For example, if the LER enters into a Protecting failure local indicator and remote indicator for the state then the state
state due to a remote SF input, and then a local SF indication is shall be considered a local state. For example, if the protection
domain enters into a Protecting failure state and the LER identifies
this due to a remote SF input, and then a local SF indication is
received then even though this was initially a remote Protecting received then even though this was initially a remote Protecting
failure state, by receiving the local SF input the LER is considered failure state, by receiving the local SF input the LER is considered
to be in local Protecting failure state. to be in local Protecting failure state.
It should be noted that when referring to the "transport" of the data It should be noted that when referring to the "transport" of the data
traffic, in the following descriptions and later in the document that traffic, in the following descriptions and later in the document that
the data will be transmitted on both the working and the protection the data will be transmitted on both the working and the protection
paths when using 1+1 protection, and on either the working or the paths when using 1+1 protection, and on either the working or the
protection path exclusively when using 1:1 protection. When using protection path exclusively when using 1:1 protection. When using
1+1 protection, the receiving LER should select the proper 1+1 protection, the receiving LER should select the proper
transmission, according to the state of the protection domain. transmission, according to the state of the protection domain.
The states that are supported by the PSC Control Logic are: The protection domain states that are supported by the PSC Control
Logic are:
o Normal state - Both the protection and working paths are fully o Normal state - Both the protection and working paths are fully
allocated and active, data traffic is being transported over (or allocated and active, data traffic is being transported over (or
selected from) the working path, and no trigger events are selected from) the working path, and no trigger events are
reported within the domain. reported within the domain.
o Unavailable state - The protection path is unavailable - either as o Unavailable state - The protection path is unavailable - either as
a result of an operator Lockout command or a failure/degrade a result of an operator Lockout command or a failure condition
condition detected on the protection path. detected on the protection path.
o Protecting failure state - The working path has reported a o Protecting failure state - The working path has reported a
failure/degrade condition and the user traffic is being failure/degrade condition and the user traffic is being
transported (or selected) on the protection path. transported (or selected) on the protection path.
o Protecting administrative state - The operator has issued a o Protecting administrative state - The operator has issued a
command switching the user traffic to the protection path. command switching the user traffic to the protection path.
o Wait-to-restore state - The protection domain is recovering from a o Wait-to-restore state - The protection domain is recovering from a
SF/SD condition on the working path that is being controlled by SF/SD condition on the working path that is being controlled by
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o Do-not-revert state - The protection domain is recovering from a o Do-not-revert state - The protection domain is recovering from a
Protecting state, but the operator has configured the protection Protecting state, but the operator has configured the protection
domain to not automatically revert to the Normal state upon domain to not automatically revert to the Normal state upon
recovery. The protection domain SHALL remain in this state until recovery. The protection domain SHALL remain in this state until
the operator issues a command to revert to the Normal state or the operator issues a command to revert to the Normal state or
there is a new trigger to switch to a different state. there is a new trigger to switch to a different state.
See section 4.3.3 for details on what actions are taken by the PSC See section 4.3.3 for details on what actions are taken by the PSC
Process Logic for each state and the relevant input. Process Logic for each state and the relevant input.
3.1.6.1. Local and Remote state 3.6.1. Local and Remote state
An end-point may be in a given state as a result of either a local An end-point may be in a given state as a result of either a local
input indicator, e.g. OAM, WTR timer, or as a result of receiving a input indicator, e.g. OAM, WTR timer, or as a result of receiving a
PSC message from the far-end LER. If the state is entered as a PSC message from the far-end LER. If the state is entered as a
result of a local input indicator, then the state SHOULD be result of a local input indicator, then the state SHOULD be
considered a local state. If the state is entered as a result of a considered a local state. If the state is entered as a result of a
PSC message, in the absence of a local input, then the state SHOULD PSC message, in the absence of a local input, then the state SHOULD
be considered a remote state. This differentiation affects how the be considered a remote state. This differentiation affects how the
LER should react to different inputs, as described in section 4.3.3. LER should react to different inputs, as described in section 4.3.3.
The PSC Control logic should maintain, together with the current The PSC Control logic should maintain, together with the current
state, an indication of whether this is a local or remote state. protection domain state, an indication of whether this is a local or
remote state, for this LER.
In any instance where the LER has both a local and remote indicators In any instance where the LER has both a local and remote indicators
that cause the PSC Control logic to enter a particular state, then that cause the protection domain to enter a particular state, then
the state SHOULD be considered a local state, regardless of the order the state SHOULD be considered a local state, regardless of the order
in which the indicators were processed. If, however, the LER has in which the indicators were processed. If, however, the LER has
local and remote indicators that would cause the PSC Control logic to local and remote indicators that would cause the protection domain to
enter different states, e.g. a Local SF on working and a Remote enter different states, e.g. a Local SF on working and a Remote
Lockout message, then the state with the higher importance will be Lockout message, then the input with the higher priority (see section
the deciding factor and the source of that indicator will determine 4.3.2) will be the deciding factor and the source of that indicator
whether it is local or remote. In the given example the result would will determine whether it is local or remote. In the given example
be a Remote Unavailable state transmitting SF(1,0) messages. the result would be a Remote Unavailable state transmitting SF(1,0)
messages.
4. Protection state coordination (PSC) protocol 4. Protection state coordination (PSC) protocol
Bidirectional protection switching, as well as unidirectional 1:1 Bidirectional protection switching, as well as unidirectional 1:1
protection, requires coordination between the two end points in protection, requires coordination between the two end points in
determining which of the two possible paths, the working or recovery determining which of the two possible paths, the working or
path, is transmitting the data traffic in any given situation. When protection path, is transmitting the data traffic in any given
protection switching is triggered as described in section 3.1, the situation. When protection switching is triggered as described in
end points must inform each other of the switch-over from one path to section 3, the end points must inform each other of the switch-over
the other in a coordinated fashion. from one path to the other in a coordinated fashion.
There are different possibilities for the type of coordinating There are different possibilities for the type of coordinating
protocol. One possibility is a two-phased coordination in which the protocol. One possibility is a two-phased coordination in which the
LER that is initiating the protection switching sends a protocol LER that is initiating the protection switching sends a protocol
message indicating the switch but the actual switch-over is performed message indicating the switch but the actual switch-over is performed
only after receiving an 'Ack' from the far-end LER. The other only after receiving an 'Ack' from the far-end LER. The other
possibility is a single-phased coordination, in which the initiating possibility is a single-phased coordination, in which the initiating
LER performs the protection switchover to the alternate path and LER performs the protection switchover to the alternate path and
informs the far-end LER of the switch, and the far-end LER MUST informs the far-end LER of the switch, and the far-end LER MUST
complete the switchover. complete the switchover.
This protocol is a single-phase protocol, as described above. In the This protocol is a single-phased protocol, as described above. In
following subsections we describe the protocol messages that SHALL be the following subsections we describe the protocol messages that
used between the two end points of the protection domain. SHALL be used between the two end points of the protection domain.
4.1. Transmission and acceptance of PSC control packets 4.1. Transmission and acceptance of PSC control packets
The PSC control packets SHALL be transmitted over the protection path The PSC control packets SHALL be transmitted over the protection path
only. This allows the transmission of the messages without affecting only. This allows the transmission of the messages without affecting
the normal data traffic in the most prevalent case, i.e. the Normal the normal data traffic in the most prevalent case, i.e. the Normal
state. In addition, limiting the transmission to a single path state. In addition, limiting the transmission to a single path
avoids possible conflicts and race conditions that could develop if avoids possible conflicts and race conditions that could develop if
the PSC messages were sent on both paths. the PSC messages were sent on both paths.
When the PSC information is changed due to a local input, three PSC When the protection domain state is changed due to a local input,
messages SHOULD be transmitted as quickly as possible, to allow for three PSC messages SHOULD be transmitted as quickly as possible, to
rapid protection switching. This set of three rapid messages allows allow for rapid protection switching. This set of three rapid
for fast protection switching even if one or two of these packets are messages allows for fast protection switching even if one or two of
lost or corrupted. When the PSC information changes due to a remote these packets are lost or corrupted. When the protection domain
message there is no need for the aforementioned rapid transmission of state changes due to a remote message there is no need for the
three messages. The exception (e.g. when the rapid transmission is aforementioned rapid transmission of three messages. The exception
still required) is when going from WTR state to Normal state as a (e.g. when the rapid transmission is still required) is when going
result of a remote NR message. from WTR state to Normal state as a result of a remote NR message.
The frequency of the three rapid messages and the separate frequency The frequency of the three rapid messages and the separate frequency
of the continual transmission SHOULD be configurable by the operator. of the continual transmission SHOULD be configurable by the operator.
For protection switching within 50ms, the default interval of the For protection switching within 50ms, it is RECOMMENDED that the
first three PSC messages is RECOMMENDED to be no larger than 3.3ms. default interval of the first three PSC messages SHOULD be no larger
The continuous transmission interval is RECOMMENDED to be 5 seconds. than 3.3ms. The subsequent messages SHOULD be continuously
transmitted with an interval of 5 seconds.
If no valid PSC specific information is received, the last valid If no valid PSC message is received, the last valid received message
received information remains applicable. In the event a signal fail remains applicable.
condition is detected on the protection path, the received PSC
specific information should be evaluated.
4.2. Protocol format 4.2. Protocol format
The protocol messages SHALL be sent over the G-ACh as described in The protocol messages SHALL be sent over the G-ACh as described in
[RFC5586]. There is a single channel type for the set of PSC [RFC5586]. There is a single channel type for the set of PSC
messages [to be assigned by IANA]. The actual message function SHALL messages [to be assigned by IANA]. The actual message function SHALL
be identified by the Request field of the ACH payload as described be identified by the Request field of the ACH payload as described
below. The following figure shows the format for the complete PSC below. The following figure shows the format for the complete PSC
message:. message:.
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o (0110) Signal Fail - indicates that the transmitting end point has o (0110) Signal Fail - indicates that the transmitting end point has
identified a signal fail condition on either the working or identified a signal fail condition on either the working or
protection path. The Fpath field SHALL identify the path that is protection path. The Fpath field SHALL identify the path that is
reporting the failure condition (i.e. if protection path then reporting the failure condition (i.e. if protection path then
Fpath is set to 0 and if working path then Fpath is set to 1), and Fpath is set to 0 and if working path then Fpath is set to 1), and
the Path field SHALL indicate where the data traffic is being the Path field SHALL indicate where the data traffic is being
transported (i.e. if protection path is blocked then Path is set transported (i.e. if protection path is blocked then Path is set
to 0 and if working path is blocked then Path is set to 1). to 0 and if working path is blocked then Path is set to 1).
o (0101) Signal Defect - indicates that that the transmitting end o (0101) Signal Degrade - indicates that that the transmitting end
point has identified a degradation of the signal, or integrity of point has identified a degradation of the signal, or integrity of
the packet transmission on either the working or protection path. the packet transmission on either the working or protection path.
The specifics for the method of identifying this degradation is This request is presented here only as a place-holder. The
out-of-scope for this document. The details of the actions to be specifics for the method of identifying this degradation is out-
of-scope for this document. The details of the actions to be
taken for this situation is left for future specification. taken for this situation is left for future specification.
o (0100) Manual switch - indicates that the transmitting end point o (0100) Manual switch - indicates that the transmitting end point
has switched traffic as a result of an administrative Manual has switched traffic to the protection path as a result of an
Switch command. The Fpath field SHALL indicate that the working administrative Manual Switch command. The Fpath field SHALL
path is being blocked (i.e. Fpath set to 1), and the Path field indicate that the working path is being blocked (i.e. Fpath set
SHALL indicate that user data traffic is being transported on the to 1), and the Path field SHALL indicate that user data traffic is
protection path (i.e. Path set to 1). being transported on the protection path (i.e. Path set to 1).
o (0011) Wait to restore - indicates that the transmitting end point o (0011) Wait to restore - indicates that the transmitting end point
is recovering from a failure condition of the working path and has is recovering from a failure condition of the working path and has
started the Wait-to-Restore timer. Fpath SHALL be set to 0 and started the Wait-to-Restore timer. Fpath SHALL be set to 0 and
ignored upon receipt. Path SHALL indicate the working path that ignored upon receipt. Path SHALL indicate the working path that
is currently being protected (i.e. Path set to 1). is currently being protected (i.e. Path set to 1).
o (0010) Do not revert - indicates that the transmitting end point o (0010) Do not revert - indicates that the transmitting end point
is recovering from a failure/blocked condition, but due to the is recovering from a failure/blocked condition, but due to the
local settings is requesting that the protection domain continues local settings is requesting that the protection domain continues
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ends of the protection domain. If an inconsistency is detected then ends of the protection domain. If an inconsistency is detected then
an alarm SHALL be sent to the management system. The following are an alarm SHALL be sent to the management system. The following are
the possible values: the possible values:
o 11: bidirectional switching using a permanent bridge o 11: bidirectional switching using a permanent bridge
o 10: bidirectional switching using a selector bridge o 10: bidirectional switching using a selector bridge
o 01: unidirectional switching using a permanent bridge o 01: unidirectional switching using a permanent bridge
o 00: unidirectional switching using a selector bridge o 00: for future extensions
As described in the introduction (section 1.1) a 1+1 protection As described in the introduction (section 1.1) a 1+1 protection
architecture is characterized by the use of a permanent bridge at the architecture is characterized by the use of a permanent bridge at the
source node, whereas the 1:1 and 1:n protection architectures are source node, whereas the 1:1 and 1:n protection architectures are
characterized by the use of a selector bridge at the source node. characterized by the use of a selector bridge at the source node.
4.2.4. Revertive (R) field 4.2.4. Revertive (R) field
This field indicates that the transmitting end point is configured to This field indicates that the transmitting end point is configured to
work in revertive mode. If there is an inconsistency between the two work in revertive mode. If there is an inconsistency between the two
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path]. The coordination between the end points is expressed by the path]. The coordination between the end points is expressed by the
value of the Path field [indicating where the user data traffic is value of the Path field [indicating where the user data traffic is
being transmitted]. The value of the Path field SHOULD be identical being transmitted]. The value of the Path field SHOULD be identical
for both end points at any particular time. The values of the for both end points at any particular time. The values of the
Request and Fpath fields may not be identical between the two end Request and Fpath fields may not be identical between the two end
points. In particular it should be noted that a remote message MAY points. In particular it should be noted that a remote message MAY
not cause the end point to change the Request field that is being not cause the end point to change the Request field that is being
transmitted while it does affect the Path field (see details in the transmitted while it does affect the Path field (see details in the
following subsections). following subsections).
The protocol is a single-phase protocol. Single-phase implies that The protocol is a single-phased protocol. Single-phased implies that
each end point notifies its peer of a change in the operation each end point notifies its peer of a change in the operation
(switching to or from the protection path) and makes the switch (switching to or from the protection path) and makes the switch
without waiting for acknowledgement. without waiting for acknowledgement.
The following subsections will identify the messages that SHALL be The following subsections will identify the messages that SHALL be
transmitted by the end point in different scenarios. The messages transmitted by the end point in different scenarios. The messages
are described as REQ(FP, P) - where REQ is the value of the Request are described as REQ(FP, P) - where REQ is the value of the Request
field, FP is the value of the Fpath field, and P is the value of the field, FP is the value of the Fpath field, and P is the value of the
Path field. All examples assume a protection domain between LER-A Path field. All examples assume a protection domain between LER-A
and LER-Z with a single working path and single protection path (as and LER-Z with a single working path and single protection path (as
shown in figure 3). Again it should be noted that when using 1:1 shown in figure 3). Again it should be noted that when using 1:1
protection the data traffic will be transmitted exclusively on either protection the data traffic will be transmitted exclusively on either
the protection or working path, while when using 1+1 protection the the protection or working path, while when using 1+1 protection the
traffic will be transmitted on both paths and the receiving LER traffic will be transmitted on both paths and the receiving LER
should select the appropriate signal based on the state. The text should select the appropriate signal based on the state. The text
will refer to this transmission/selection as "transport" of the data will refer to this transmission/selection as "transport" of the data
traffic. traffic.
4.3.2. Priority of inputs 4.3.2. Priority of inputs
As noted above (in section 3.1.1) the PSC Control Process accepts As noted above (in section 3.1) the PSC Control Process accepts input
input from five local input sources. There is a definition of from five local input sources. There is a definition of priority
priority between the different inputs that may be triggered locally. between the different inputs that may be triggered locally. The list
The list of local requests in order of priority are (from highest to of local requests in order of priority are (from highest to lowest
lowest priority): priority):
1. Clear (Operator command) 1. Clear (Operator command)
2. Lockout of protection (Operator command) 2. Lockout of protection (Operator command)
3. Signal Fail on protection (OAM/Control Plane/Server Indication) 3. Signal Fail on protection (OAM/Control Plane/Server Indication)
4. Forced switch (Operator command) 4. Forced switch (Operator command)
5. Signal Fail on working (OAM/Control Plane/Server Indication) 5. Signal Fail on working (OAM/Control Plane/Server Indication)
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7. Clear Signal Fail/Degrade (OAM/Control Plane/Server Indication) 7. Clear Signal Fail/Degrade (OAM/Control Plane/Server Indication)
8. Manual switch (Operator command) 8. Manual switch (Operator command)
9. WTR expires (WTR Timer) 9. WTR expires (WTR Timer)
10. No request (default) 10. No request (default)
As was noted above, the Local request logic SHALL always select the As was noted above, the Local request logic SHALL always select the
local input indicator with the highest priority as the current local local input indicator with the highest priority as the current local
request. All local inputs with lower priority than this current request, i.e. only the highest priority local input will be used to
local request will be blocked. affect the control logic. All local inputs with lower priority than
this current local request will be ignored.
The determination of whether a remote message is accepted or ignored The remote message from the far-end LER is assigned a priority just
is a function of the current state of the local LER and the current below the similar local input. For example, a remote Signal Fail on
local request (see section 3.1.3). Part of this consideration will protection would have a priority just below a local Signal Fail on
be included in the following subsections describing the operation in protection but above a local Forced Switch input. As mentioned in
the different states. section 3.6.1, the state transition is determined by the higher
priority input between the highest priority local input and the
remote message. This also determines the classification of the state
as local or remote. The following subsections detail the transition
based on the current state and the higher priority of these two
inputs.
4.3.3. Operation of PSC States 4.3.3. Operation of PSC States
The following sub-sections present the operation of the different The following sub-sections present the operation of the different
states defined in section 3.1.6. For each state we define the states defined in section 3.6. For each state we define the
reaction, i.e. the new state and the message to transmit, to each reaction, i.e. the new state and the message to transmit, to each
possible input - either the highest priority local input or the PSC possible input - either the highest priority local input or the PSC
message from the remote LER. If the definition states to "ignore" message from the remote LER. It should be noted that the new state
the message, the intention is that the LER should remain in its of the protection domain is described from the point of view of the
current state and continue transmitting (as presented in section 4.1) LER that is reporting the state, therefore, the language of "the LER
the current PSC message. goes into a state" is referring to the LER reporting that the
protection domain is now in this new state. If the definition states
to "ignore" the message, the intention is that the protection domain
should remain in its current state and the LER should continue
transmitting (as presented in section 4.1) the current PSC message.
4.3.3.1. Normal State 4.3.3.1. Normal State
When the protection domain has no special condition in effect, the When the protection domain has no special condition in effect, the
ingress LER SHALL forward the user data along the working path, and, ingress LER SHALL forward the user data along the working path, and,
in the case of 1+1 protection, the Permanent Bridge will bridge the in the case of 1+1 protection, the Permanent Bridge will bridge the
data to the recovery path as well. The receiving LER SHALL read the data to the protection path as well. The receiving LER SHALL read
data from the working path. the data from the working path.
When the end point is in Normal State it SHALL transmit a NR(0,0) When the protection domain is in Normal State the end-point SHALL
message, indicating - Nothing to report and data traffic is being transmit a NR(0,0) message, indicating - Nothing to report and data
transported on the working path. traffic is being transported on the working path.
When the LER (assume LER-A) is in Normal State the following When the protection domain is in Normal State the following
transitions are relevant in reaction to a local input (new state transitions are relevant in reaction to a local input (new state
SHOULD be marked as local): SHOULD be marked as local) to the LER:
o A local Lockout of protection input SHALL cause the LER to go into o A local Lockout of protection input SHALL cause the LER to go into
local Unavailable State and begin transmission of a LO(0,0) local Unavailable State and begin transmission of a LO(0,0)
message. message.
o A local Forced switch input SHALL cause the LER to go into local o A local Forced switch input SHALL cause the LER to go into local
Protecting administrative state and begin transmission of a Protecting administrative state and begin transmission of a
FS(1,1) message. FS(1,1) message.
o A local Signal Fail indication on the protection path SHALL cause o A local Signal Fail indication on the protection path SHALL cause
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protection path - then the protection domain is in the unavailable protection path - then the protection domain is in the unavailable
state. In this state, the data traffic is transported on the working state. In this state, the data traffic is transported on the working
path and is not protected. When the domain is in unavailable state path and is not protected. When the domain is in unavailable state
the PSC messages may not get through and therefore the protection is the PSC messages may not get through and therefore the protection is
more dependent on the local inputs rather than the remote messages more dependent on the local inputs rather than the remote messages
(that may not be received). (that may not be received).
The protection domain will exit the unavailable state and revert to The protection domain will exit the unavailable state and revert to
the normal state when, either the operator clears the Lockout command the normal state when, either the operator clears the Lockout command
or the protection path recovers from the signal fail or degraded or the protection path recovers from the signal fail or degraded
situation. Both ends will resume sending the PSC packets over the situation. Both ends will continue to send the PSC messages over the
protection path, as a result of this recovery. protection path, as a result of this recovery.
When the LER (assume LER-A) is in Unavailable State the following When the LER (assume LER-A) is in Unavailable State the following
transitions are relevant in reaction to a local input (new state transitions are relevant in reaction to a local input (new state
SHOULD be marked as local): SHOULD be marked as local):
o A local Clear input SHOULD be ignored if the LER is in remote o A local Clear input SHOULD be ignored if the LER is in remote
Unavailable state. If in local Unavailable state due to a Lockout Unavailable state. If in local Unavailable state due to a Lockout
command, then the input SHALL cause the LER to go to Normal state command, then the input SHALL cause the LER to go to Normal state
and begin transmitting a NR(0,0) message. and begin transmitting a NR(0,0) message.
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o A local Lockout of protection input SHALL cause the LER to go into o A local Lockout of protection input SHALL cause the LER to go into
local Unavailable state and begin transmission of a LO(0,0) local Unavailable state and begin transmission of a LO(0,0)
message. message.
o A local Forced switch input SHALL cause the LER to remain in local o A local Forced switch input SHALL cause the LER to remain in local
Protecting administrative state and transmit a FS(1,1) message. Protecting administrative state and transmit a FS(1,1) message.
o A local Signal Fail indication on the protection path SHALL cause o A local Signal Fail indication on the protection path SHALL cause
the LER to go into local Unavailable state (i.e. overriding the MS the LER to go into local Unavailable state (i.e. overriding the MS
related Protection administrative state) and begin transmission of or FS related Protection administrative state) and begin
a SF(0,0) message. transmission of a SF(0,0) message.
o A local Signal Fail indication on the working path SHALL cause the o A local Signal Fail indication on the working path SHALL cause the
LER to go into local Protecting failure state and begin LER to go into local Protecting failure state and begin
transmitting a SF(1,1) message, if the current state is due to a transmitting a SF(1,1) message, if the current state is due to a
(local or remote) Manual switch operator command. If the LER is (local or remote) Manual switch operator command. If the LER is
in remote Protecting administrative state due to a remote Forced in remote Protecting administrative state due to a remote Forced
Switch command, then this local indication SHALL cause the LER to Switch command, then this local indication SHALL cause the LER to
remain in remote Protecting administrative state and transmit a remain in remote Protecting administrative state and transmit a
SF(1,1) message. If the LER is in local Protecting administrative SF(1,1) message. If the LER is in local Protecting administrative
state due to a local Forced Switch command then this indication state due to a local Forced Switch command then this indication
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o All other remote messages SHOULD be ignored. o All other remote messages SHOULD be ignored.
4.3.3.4. Protecting failure state 4.3.3.4. Protecting failure state
When the protection mechanism has been triggered and the protection When the protection mechanism has been triggered and the protection
domain has performed a protection switch, the domain is in the domain has performed a protection switch, the domain is in the
protecting failure state. In this state the normal data traffic is protecting failure state. In this state the normal data traffic is
transported on the protection path. When an LER is in this state it transported on the protection path. When an LER is in this state it
implies that there was either a local SF condition or received a implies that there was either a local SF condition or received a
remote SF PCS message. The SF condition or message indicated that remote SF PSC message. The SF condition or message indicated that
the failure is on the working path. the failure is on the working path.
This state may be overridden by the Unavailable state triggers, i.e. This state may be overridden by the Unavailable state triggers, i.e.
Lockout of Protection or SF on the protection path, or by issuing a Lockout of Protection or SF on the protection path, or by issuing a
FS operator command. This state will be cleared when the SF FS operator command. This state will be cleared when the SF
condition is cleared. In order to prevent flapping due to an condition is cleared. In order to prevent flapping due to an
intermittent fault, the LER SHOULD employ a Wait-to-restore timer to intermittent fault, the LER SHOULD employ a Wait-to-restore timer to
delay return to Normal state until the network has stabilized (see delay return to Normal state until the network has stabilized (see
section 3.1.5) section 3.5)
The following describe the reaction to local input: The following describe the reaction to local input:
o A local Clear SF SHALL be ignored if in remote Protecting failure o A local Clear SF SHALL be ignored if in remote Protecting failure
state. If the Clear SF indicates that the protection path is now state. If in local Protecting failure state and the LER is
cleared (but working is still in SF condition) then the indication configured for revertive behavior then this input SHALL cause the
SHALL be ignored. If in local Protecting failure state and the LER to go into Wait-to-restore state, start the WTR timer, and
LER is configured for revertive behavior then this input SHALL begin transmitting a WTR(0,1) message. If in local Protecting
cause the LER to go into Wait-to-restore state, start the WTR failure state and the LER is configured for non-revertive behavior
timer, and begin transmitting a WTR(0,1) message. If in local then this input SHALL cause the LER to go into Do-not-revert state
Protecting failure state and the LER is configured for non- and begin transmitting a DNR(0,1) message.
revertive behavior then this input SHALL cause the LER to go into
Do-not-revert state and begin transmitting a DNR(0,1) message.
o A local Lockout of protection input SHALL cause the LER to go into o A local Lockout of protection input SHALL cause the LER to go into
Unavailable state and begin transmission of a LO(0,0) message. Unavailable state and begin transmission of a LO(0,0) message.
o A local Forced switch input SHALL cause the LER to go into o A local Forced switch input SHALL cause the LER to go into
Protecting administrative state and begin transmission of a Protecting administrative state and begin transmission of a
FS(1,1) message. FS(1,1) message.
o A local Signal Fail indication on the protection path SHALL cause o A local Signal Fail indication on the protection path SHALL cause
the LER to go into Unavailable state and begin transmission of a the LER to go into Unavailable state and begin transmission of a
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user data since the working path is still in a failure condition. user data since the working path is still in a failure condition.
o If in remote Protecting failure state, a remote Wait-to-Restore o If in remote Protecting failure state, a remote Wait-to-Restore
message SHALL cause the LER to go into remote Wait-to-Restore message SHALL cause the LER to go into remote Wait-to-Restore
state and continue transmission of the current message. state and continue transmission of the current message.
o If in remote Protecting failure state, a remote Do-not-revert o If in remote Protecting failure state, a remote Do-not-revert
message SHALL cause the LER to go into remote Do-not-revert state message SHALL cause the LER to go into remote Do-not-revert state
and continue transmission of the current message. and continue transmission of the current message.
o If in remote Protecting failure state, a remote NR(0,0) SHALL
cause the LER to go to Normal state and transmit an NR(0,0)
message.
o All other remote messages SHOULD be ignored. o All other remote messages SHOULD be ignored.
4.3.3.5. Wait-to-restore state 4.3.3.5. Wait-to-restore state
The Wait-to-Restore state is used by the PSC protocol to delay The Wait-to-Restore state is used by the PSC protocol to delay
reverting to the normal state, when recovering from a failure reverting to the normal state, when recovering from a failure
condition on the working path, for the period of the WTR timer to condition on the working path, for the period of the WTR timer to
allow the recovering failure to stabilize. While in the Wait-to- allow the recovering failure to stabilize. While in the Wait-to-
Restore state the data traffic SHALL continue to be transported on Restore state the data traffic SHALL continue to be transported on
the protection path. The natural transition from the Wait-to-Restore the protection path. The natural transition from the Wait-to-Restore
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o A remote Signal Fail message for the working path SHALL cause the o A remote Signal Fail message for the working path SHALL cause the
LER to Stop the WTR timer, go into remote Protecting failure LER to Stop the WTR timer, go into remote Protecting failure
state, and begin transmission of a NR(0,1) message. state, and begin transmission of a NR(0,1) message.
o A remote Manual switch message SHALL cause the LER to Stop the WTR o A remote Manual switch message SHALL cause the LER to Stop the WTR
timer, go into remote Protecting administrative state and begin timer, go into remote Protecting administrative state and begin
transmission of a NR(0,1) message. transmission of a NR(0,1) message.
o If the WTR timer is running then a remote NR message SHALL be o If the WTR timer is running then a remote NR message SHALL be
ignored. If the WTR timer is no longer running then a remote NR ignored. If the WTR timer is stopped then a remote NR message
message SHALL cause the LER to go into Normal state and begin SHALL cause the LER to go into Normal state and begin transmitting
transmitting a NR(0,0) message. a NR(0,0) message.
o All other remote messages SHOULD be ignored. o All other remote messages SHOULD be ignored.
4.3.3.6. Do-not-revert state 4.3.3.6. Do-not-revert state
Do-not-revert state is a continuation of the Protecting failure Do-not-revert state is a continuation of the Protecting failure
state. When the protection domain is configured for non-revertive state. When the protection domain is configured for non-revertive
behavior. While in Do-not-revert state, data traffic continues to be behavior. While in Do-not-revert state, data traffic continues to be
transported on the protection path until the administrator sends a transported on the protection path until the administrator sends a
command to revert to the Normal state. It should be noted that there command to revert to the Normal state. It should be noted that there
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Working Team, the MPLS Interoperability Design Team in IETF and the Working Team, the MPLS Interoperability Design Team in IETF and the
T-MPLS Ad Hoc Group in ITU-T) involved in the definition and T-MPLS Ad Hoc Group in ITU-T) involved in the definition and
specification of MPLS Transport Profile. specification of MPLS Transport Profile.
Appendix A. PSC state machine tables Appendix A. PSC state machine tables
The PSC state machine is described in section 4.3.3. This appendix The PSC state machine is described in section 4.3.3. This appendix
provides the same information but in tabular format. In the event of provides the same information but in tabular format. In the event of
a mismatch between these tables and the text in section 4.3.3, the a mismatch between these tables and the text in section 4.3.3, the
text is authoritative. Note that this appendix is intended to be a text is authoritative. Note that this appendix is intended to be a
functional description, not an implmentation specification. functional description, not an implementation specification.
For the sake of clarity of the table the six states listed in the For the sake of clarity of the table the six states listed in the
text are split into thirteen states. The logic of the split is to text are split into thirteen states. The logic of the split is to
differentiate between the different cases given in the conditional differentiate between the different cases given in the conditional
statements in the descriptions of each state in the text. In statements in the descriptions of each state in the text. In
addition, the remote and local states were split for the Unavailable, addition, the remote and local states were split for the Unavailable,
Protecting failure, and Protecting administrative states. Protecting failure, and Protecting administrative states.
There is only one table for the PSC state machine, but it is broken There is only one table for the PSC state machine, but it is broken
into two parts for space reasons. The first part lists the thirteen into two parts for space reasons. The first part lists the thirteen
skipping to change at page 33, line 4 skipping to change at page 33, line 21
UA:LO:R NR(0,0) UA:LO:R NR(0,0)
UA:P:R NR(0,0) UA:P:R NR(0,0)
PF:W:L SF(1,1) PF:W:L SF(1,1)
PF:W:R NR(0,1) PF:W:R NR(0,1)
PA:F:L FS(1,1) PA:F:L FS(1,1)
PA:M:L MS(1,1) PA:M:L MS(1,1)
PA:F:R NR(0,1) PA:F:R NR(0,1)
PA:M:R NR(0,1) PA:M:R NR(0,1)
WTR WTR(0,1) WTR WTR(0,1)
DNR DNR(0,1) DNR DNR(0,1)
The top row in each table is the list of possible inputs. The local The top row in each table is the list of possible inputs. The local
inputs are: inputs are:
NR No Request NR No Request
OC Operator Clear OC Operator Clear
LO Lockout of protection LO Lockout of protection
SF-P Signal Fail on protection path SF-P Signal Fail on protection path
SF-W Signal Fail on working path SF-W Signal Fail on working path
FS Forced Switch FS Forced Switch
CSF Clear Signal Fail SFc Clear Signal Fail
MS Manual Switch MS Manual Switch
WTRExp WTR Expired WTRExp WTR Expired
and the remote inputs are: and the remote inputs are:
LO remote LO message LO remote LO message
SF-P remote SF message indicating protection path SF-P remote SF message indicating protection path
SF-W remote SF message indicating working path SF-W remote SF message indicating working path
FS remote FS message FS remote FS message
MS remote MS message MS remote MS message
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means that the state represented in the Unavailable rows in the table means that the state represented in the Unavailable rows in the table
of remote sources is by definition a remote Unavailable state. of remote sources is by definition a remote Unavailable state.
Each cell in the table below contains either a state, a footnote, or Each cell in the table below contains either a state, a footnote, or
the letter 'i'. 'i' stands for Ignore, and is an indication to the letter 'i'. 'i' stands for Ignore, and is an indication to
continue with the current behavior. See section 4.3.3. The continue with the current behavior. See section 4.3.3. The
footnotes are listed below the table. footnotes are listed below the table.
Part 1: Local input state machine Part 1: Local input state machine
| OC | LO | SF-P | FS | SF-W | CSF | MS | WTRExp | OC | LO | SF-P | FS | SF-W | SFc | MS | WTRExp
--------+-----+-------+------+------+------+------+------+------- --------+-----+-------+------+------+------+------+------+-------
N | i |UA:LO:L|UA:P:L|PA:F:L|PF:W:L| i |PA:M:L| i N | i |UA:LO:L|UA:P:L|PA:F:L|PF:W:L| i |PA:M:L| i
UA:LO:L | N | i | i | i | i | i | i | i UA:LO:L | N | i | i | i | i | i | i | i
UA:P:L | i |UA:LO:L| i | i | i | [5] | i | i UA:P:L | i |UA:LO:L| i | i | i | [5] | i | i
UA:LO:R | i |UA:LO:L| [1] | i | [2] | [6] | i | i UA:LO:R | i |UA:LO:L| [1] | i | [2] | [6] | i | i
UA:P:R | i |UA:LO:L|UA:P:L| i | [3] | [6] | i | i UA:P:R | i |UA:LO:L|UA:P:L| i | [3] | [6] | i | i
PF:W:L | i |UA:LO:L|UA:P:L|PA:F:L| i | [7] | i | i PF:W:L | i |UA:LO:L|UA:P:L|PA:F:L| i | [7] | i | i
PF:W:R | i |UA:LO:L|UA:P:L|PA:F:L|PF:W:L| i | i | i PF:W:R | i |UA:LO:L|UA:P:L|PA:F:L|PF:W:L| i | i | i
PA:F:L | N |UA:LO:L|UA:P:L| i | i | i | i | i PA:F:L | N |UA:LO:L|UA:P:L| i | i | i | i | i
PA:M:L | N |UA:LO:L|UA:P:L|PA:F:L|PF:W:L| i | i | i PA:M:L | N |UA:LO:L|UA:P:L|PA:F:L|PF:W:L| i | i | i
skipping to change at page 34, line 33 skipping to change at page 35, line 15
Part 2: Remote messages state machine Part 2: Remote messages state machine
| LO | SF-P | FS | SF-W | MS | WTR | DNR | NR | LO | SF-P | FS | SF-W | MS | WTR | DNR | NR
--------+-------+------+------+------+------+------+------+------ --------+-------+------+------+------+------+------+------+------
N |UA:LO:R|UA:P:R|PA:F:R|PF:W:R|PA:M:R| i | i | i N |UA:LO:R|UA:P:R|PA:F:R|PF:W:R|PA:M:R| i | i | i
UA:LO:L | i | i | i | i | i | i | i | i UA:LO:L | i | i | i | i | i | i | i | i
UA:P:L | [10] | i | i | i | i | i | i | i UA:P:L | [10] | i | i | i | i | i | i | i
UA:LO:R | i | i | i | i | i | i | i | [16] UA:LO:R | i | i | i | i | i | i | i | [16]
UA:P:R |UA:LO:R| i | i | i | i | i | i | [16] UA:P:R |UA:LO:R| i | i | i | i | i | i | [16]
PF:W:L | [11] | [12] |PA:F:R| i | i | i | i | i PF:W:L | [11] | [12] |PA:F:R| i | i | i | i | i
PF:W:R |UA:LO:R|UA:P:R|PA:F:R| i | i | [14] | [15] | i PF:W:R |UA:LO:R|UA:P:R|PA:F:R| i | i | [14] | [15] | N
PA:F:L |UA:LO:R|UA:P:R| i | i | i | i | i | i PA:F:L |UA:LO:R|UA:P:R| i | i | i | i | i | i
PA:M:L |UA:LO:R|UA:P:R|PA:F:R| [13] | i | i | i | i PA:M:L |UA:LO:R|UA:P:R|PA:F:R| [13] | i | i | i | i
PA:F:R |UA:LO:R|UA:P:R| i | i | i | i | i | N PA:F:R |UA:LO:R|UA:P:R| i | i | i | i | i | N
PA:M:R |UA:LO:R|UA:P:R|PA:F:R| [13] | i | i | i | N PA:M:R |UA:LO:R|UA:P:R|PA:F:R| [13] | i | i | i | N
WTR |UA:LO:R|UA:P:R|PA:F:R|PF:W:R|PA:M:R| i | i | [17] WTR |UA:LO:R|UA:P:R|PA:F:R|PF:W:R|PA:M:R| i | i | [17]
DNR |UA:LO:R|UA:P:R|PA:F:R|PF:W:R|PA:M:R| i | i | i DNR |UA:LO:R|UA:P:R|PA:F:R|PF:W:R|PA:M:R| i | i | i
The following are the footnotes for the table: The following are the footnotes for the table:
[1] Remain in the current state (UA:LO:R) and transmit SF(0,0) [1] Remain in the current state (UA:LO:R) and transmit SF(0,0)
[2] Remain in the current state (UA:LO:R) and transmit SF(1,0) [2] Remain in the current state (UA:LO:R) and transmit SF(1,0)
[3] Remain in the current state (UA:P:R) and transmit SF(1,0) [3] Remain in the current state (UA:P:R) and transmit SF(1,0)
[4] Remain in the current state (PA:F:R) and transmit SF(1,1) [4] Remain in the current state (PA:F:R) and transmit SF(1,1)
[5] If the SF being cleared is SF-P, Transition to N. If it's SF-W, [5] If the SF being cleared is SF-P, Transition to N. If it's SF-W,
ignore the clear. ignore the clear.
[6] Remain in current state (UA:x:R), if the CSF corresponds to a [6] Remain in current state (UA:x:R), if the SFc corresponds to a
previous SF then begin transmitting NR(0,0). previous SF then begin transmitting NR(0,0).
[7] If the SF being cleared is SF-P, ignore the clear. If it's SF-W, [7] If domain configured for revertive behavior transition to WTR,
transition to WTR, start the WTR timer, and send WTR(1,1) else transition to DNR
[8] Remain in PA:F:R and transmit NR(0,1) [7] Remain in PA:F:R and transmit NR(0,1)
[9] Remain in WTR, send NR(0,1) [8] Remain in WTR, send NR(0,1)
[10] Transition to UA:LO:R continue sending SF(0,0) [9] Transition to UA:LO:R continue sending SF(0,0)
[11] Transition to UA:LO:R and send SF(1,0) [10] Transition to UA:LO:R and send SF(1,0)
[12] Transition to UA and send SF(1,0) [11] Transition to UA and send SF(1,0)
[13] Transition to PF:W:R and send NR(0,1) [12] Transition to PF:W:R and send NR(0,1)
[14] Transition to WTR state and continue to send the current [13] Transition to WTR state and continue to send the current
message. message.
[15] Transition to DNR state and continue to send the current [14] Transition to DNR state and continue to send the current
message. message.
[16] Transition to N state and continue to send the current message. [15] Transition to N state and continue to send the current message.
[17] If the receiving node's WTR timer has expired, transition to N. [16] If the receiving node's WTR timer is running, maintain current
If not, maintain current state and message. state and message. If the WTR timer is stopped, transition to N.
8. References 8. References
8.1. Normative References 8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5654] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., [RFC5654] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N.,
and S. Ueno, "Requirements of an MPLS Transport Profile", and S. Ueno, "Requirements of an MPLS Transport Profile",
 End of changes. 98 change blocks. 
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