draft-ietf-mpls-tp-linear-protection-07.txt   draft-ietf-mpls-tp-linear-protection-08.txt 
Network Working Group S. Bryant Network Working Group S. Bryant
Internet-Draft E. Osborne Internet-Draft E. Osborne
Intended status: Standards Track Cisco Intended status: Standards Track Cisco
Expires: December 4, 2011 N. Sprecher Expires: January 26, 2012 N. Sprecher
Nokia Siemens Networks Nokia Siemens Networks
A. Fulignoli, Ed. A. Fulignoli, Ed.
Ericsson Ericsson
Y. Weingarten, Ed. Y. Weingarten, Ed.
Nokia Siemens Networks Nokia Siemens Networks
June 2, 2011 July 25, 2011
MPLS-TP Linear Protection MPLS-TP Linear Protection
draft-ietf-mpls-tp-linear-protection-07.txt draft-ietf-mpls-tp-linear-protection-08.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 December 4, 2011. This Internet-Draft will expire on January 26, 2012.
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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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. Local Request Logic . . . . . . . . . . . . . . . . . . . 8 3.1. Local Request Logic . . . . . . . . . . . . . . . . . . . 8
3.2. Remote Requests . . . . . . . . . . . . . . . . . . . . . 10 3.2. Remote Requests . . . . . . . . . . . . . . . . . . . . . 10
3.3. PSC Control Logic . . . . . . . . . . . . . . . . . . . . 11 3.3. PSC Control Logic . . . . . . . . . . . . . . . . . . . . 11
3.4. PSC Message Generator . . . . . . . . . . . . . . . . . . 12 3.4. PSC Message Generator . . . . . . . . . . . . . . . . . . 12
3.5. Wait-to-Restore (WTR) timer . . . . . . . . . . . . . . . 12 3.5. Wait-to-Restore (WTR) timer . . . . . . . . . . . . . . . 12
3.6. PSC Control States . . . . . . . . . . . . . . . . . . . . 12 3.6. PSC Control States . . . . . . . . . . . . . . . . . . . . 12
3.6.1. Local and Remote state . . . . . . . . . . . . . . . . 14 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 . . . . 15 4.1. Transmission and acceptance of PSC control packets . . . . 15
4.2. Protocol format . . . . . . . . . . . . . . . . . . . . . 15 4.2. Protocol format . . . . . . . . . . . . . . . . . . . . . 16
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) . . . . . . . . . . . . . . . . . 18
4.2.4. Revertive (R) field . . . . . . . . . . . . . . . . . 18 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 . . . . . . . . . . . . . . . . 19
4.2.7. Additional TLV information . . . . . . . . . . . . . . 19 4.2.7. Additional TLV information . . . . . . . . . . . . . . 19
4.3. Principles of Operation . . . . . . . . . . . . . . . . . 19 4.3. Principles of Operation . . . . . . . . . . . . . . . . . 20
4.3.1. Basic operation . . . . . . . . . . . . . . . . . . . 19 4.3.1. Basic operation . . . . . . . . . . . . . . . . . . . 20
4.3.2. Priority of inputs . . . . . . . . . . . . . . . . . . 20 4.3.2. Priority of inputs . . . . . . . . . . . . . . . . . . 21
4.3.3. Operation of PSC States . . . . . . . . . . . . . . . 21 4.3.3. Operation of PSC States . . . . . . . . . . . . . . . 22
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
5.1. Pseudowire Associated Channel Type . . . . . . . . . . . . 32 5.1. Pseudowire Associated Channel Type . . . . . . . . . . . . 32
5.2. PSC Request Field . . . . . . . . . . . . . . . . . . . . 32 5.2. PSC Request Field . . . . . . . . . . . . . . . . . . . . 33
5.3. Additional TLVs . . . . . . . . . . . . . . . . . . . . . 33
6. Security Considerations . . . . . . . . . . . . . . . . . . . 33 6. Security Considerations . . . . . . . . . . . . . . . . . . . 33
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 33 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 34
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 33 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 35
8.1. Normative References . . . . . . . . . . . . . . . . . . . 33 8.1. Normative References . . . . . . . . . . . . . . . . . . . 35
8.2. Informative References . . . . . . . . . . . . . . . . . . 33 8.2. Informative References . . . . . . . . . . . . . . . . . . 35
Appendix A. PSC state machine tables . . . . . . . . . . . . . . 35 Appendix A. PSC state machine tables . . . . . . . . . . . . . . 36
Appendix B. Exercising the protection domain . . . . . . . . . . 39 Appendix B. Exercising the protection domain . . . . . . . . . . 40
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 40 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41
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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[SurvivFwk]. Linear protection provides rapid and simple protection [SurvivFwk]. Linear protection provides rapid and simple protection
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 resources of
the protection path is reserved for a selected working path or set of the protection path are reserved for a selected working path or set
working paths. It provides a fast and simple survivability of 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, that can operate between any pair of
mechanisms. points within the network.
As specified in the Survivability Framework document [SurvivFwk], As described 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
LSP as consisting of two Label Edge Routers (LER) and the transport point-to-point LSP as consisting of two Label Edge Routers (LER) and
paths that connect them (see Figure 3 below). For a P2MP LSP the the transport paths that connect them (see Figure 3 below). For a
protection domain includes the root (or source) LER, the destination point-to-multipoint LSP the protection domain includes the root (or
(or sink) LERs, and the transport paths that connect them. source) LER, the destination (or sink) LERs, 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
protection 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 protection paths by a permanent bridge at the the working and the protection paths by a permanent bridge at the
source of the protection domain. The sink of the protection domain source of the protection domain. The sink of the protection domain
uses a selector to select either the working or protection paths to uses a selector to select either the working or protection paths to
receive the traffic from, based on a predetermined criteria, e.g. receive the traffic from, based on a predetermined criteria, e.g.
server defect indication. When used for bidirectional switching the server defect indication. When used for bidirectional switching the
1+1 protection architecture must also support a Protection State 1+1 protection architecture must also support a Protection State
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carries the normal traffic. Since the source and sink need to be carries the normal traffic. Since the source and sink need to be
coordinated to ensure that the selector at both ends select the same coordinated to ensure that the selector at both ends select the same
path, this architecture must support a PSC protocol. 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 protection path among n services. Again, the protection sharing the protection path among n services. Again, the protection
path is fully allocated and disjoint from any of the n working path is fully allocated and disjoint from any of the n working
transport paths that it is being used to protect. The normal data transport paths that it is being used to protect. The normal data
traffic for each service is transmitted either on the normal working traffic for each service is transmitted either on the normal working
path for that service or, in cases that trigger protection switching path for that service or, in cases that trigger protection switching
(as defined in [SurvivFwk]), may be sent on the protection path. The (as listed in [SurvivFwk]), may be sent on the protection path. The
switching action is similar to the 1:1 case where a selector is used switching action is similar to the 1:1 case where a selector is used
at the source. It should be noted that in cases where multiple at the source. It should be noted that in cases where multiple
working path services have triggered protection switching that some working path services have triggered protection switching that some
services, dependent upon their Service Level Agreement (SLA), may not services, dependent upon their Service Level Agreement (SLA), may not
be transmitted as a result of limited resources on the protection be transmitted as a result of limited resources on the protection
path. In this architecture there may be a need for coordination of path. In this architecture there may be a need for coordination of
the protection switching, and also for resource allocation the protection switching, and also for resource allocation
negotiation. The procedures for this are for further study and may negotiation. The procedures for this are for further study and may
be addressed in future documents. 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. verify that the traffic continues to be transported on a bi-
directional LSP that is co-routed.
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 63-65 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 bidirectional protection and for with the 1:1 protection architecture bidirectional protection and for
1+1 protection of a bidirectional path (for both unidirectional and 1+1 protection of a bidirectional path (for both unidirectional and
bidirectional protection switching). Applicability of the protocol bidirectional protection switching). Applicability of the protocol
for 1:1 unidirectional protection and for 1:n protection schemes may for 1:1 unidirectional protection and for 1:n protection schemes may
be documented in a future document. The applicability of this be documented in a future document and are out of scope for this
protocol to additional MPLS-TP constructs and topologies may be document. The applicability of this protocol to additional MPLS-TP
documented in future documents. constructs and topologies may be 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]. The use of this protocol for point-to-
multipoint paths is out of scope for this document and may be
addressed in a future applicability document.
1.3. Contributing authors 1.3. Contributing authors
Hao Long (Huawei), Dan Frost (Cisco), Davide Chiara (Ericsson), Hao Long (Huawei), Dan Frost (Cisco), Davide Chiara (Ericsson),
Francesco Fondelli (Ericsson), Francesco Fondelli (Ericsson),
2. Conventions used in this document 2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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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 G-ACh Generic Associated Channel
LER Label Edge Router LER Label Edge Router
LO Lockout of protection 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 NR No Request
P2P Point-to-point
P2MP Point-to-multipoint
PSC Protection State Coordination Protocol PSC Protection State Coordination Protocol
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].
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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. Local Request Logic 3.1. Local Request Logic
The Local Request logic processes input triggers from five sources: The Local Request logic processes input triggers from five sources:
o Operator command - the network operator may issue local o Operator command - the network operator may issue local
administrative commands on the LER that trigger protection administrative commands on the LER that trigger protection
switching. The supported commands are Forced Switch, Manual switching. The commands Forced Switch, Manual Switch, Clear,
Switch, Clear, Lockout of Protection, (see definitions in Lockout of Protection (see definitions in [RFC4427]) MUST be
[RFC4427]). An implementation MAY provide additional commands for supported. An implementation MAY provide additional commands for
operator use; providing that these commands do not introduce operator use; providing that these commands do not introduce
incompatable behavior between two arbitrary implementations, they incompatable behavior between two arbitrary implementations, they
are outside the scope of this document. For example, an are outside the scope of this document. For example, an
implementation could provide a command to manually trigger a "WTR implementation could provide a command to manually trigger a "WTR
expires" trigger (see below) input without waiting for the expires" trigger (see below) input without waiting for the
duration of the WTR timer; as this merely hastens the transition duration of the WTR timer; as this merely hastens the transition
from one state to another and has no impact on the state machine from one state to another and has no impact on the state machine
itself, it would be perfectly valid. itself, it would be perfectly valid.
o Server layer alarm indication - the underlying server layer of the o Server layer alarm indication - the underlying server layer of the
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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. The holdoff-timer is configurable by the network operator. The holdoff-timer is
described in greater detail in [SurvivFwk]. described in greater detail in [SurvivFwk].
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] and [RFC4873].
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 either the tools may detect a failure or degrade condition on either the
working or protection transport path and this SHOULD input an working or protection transport path and this must input an
indication to the Local 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 SHALL 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 processes these different input sources and,
and, based on the priorities between them (see section 4.3.2), shall based on the priorities between them (see section 4.3.2), produces a
produce a current local request. If more than one local input source current local request. If more than one local input source generates
generates an indicator, then the Local request logic shall select the an indicator, then the Local request logic selects the higher
higher priority indicator and block any lower priority indicator. As priority indicator and blocks any lower priority indicator. As a
a result, there is a single current local request that is passed to result, there is a single current local request that is passed to the
the PSC Control logic. The different local requests that may be PSC Control logic. The different local requests that may be output
output from the Local Request Logic are: 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 prevent o Lockout of Protection (LO) - if the operator requested to prevent
switching data traffic to the protection path, for any purpose. 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. The either the protection path or one of the working paths. The
determination and actions for SD are for further study and may determination and actions for SD are for further study and may
appear in a separate document. All references to SD input are appear in a separate document. All references to SD input are
place-holders for this extension. place-holders for this extension.
o Clear Signal Fail - if all of the Server Layer, Control plane, or o Clear Signal Fail (SFc) - if all of the Server Layer, Control
OAM indications are no longer indicating a failure condition on a plane, or OAM indications are no longer indicating a failure
path that was previously indicating a failure condition. condition on a 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 the working path to the protection path. This is switched from the working path to the protection path. This is
only 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 should generate a No Request (NR) request as the request logic should generate a No Request (NR) request as the
current local request . current local request .
3.2. 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 Remote messages indicate the status of the transport path from the
the viewpoint of the far-end LER, and may indicate if the local MEP viewpoint of the far-end LER. These messages may drive state changes
SHOULD initiate a protection switch operation. on the local MEP, as defined later in this document. When using 1+1
unidirectional protection, an LER that receives a remote request
SHALL NOT perform any protection switching action, i.e. will continue
to select traffic from the working path and transport traffic on both
paths.
The following remote requests may be received by the PSC process: The following remote requests may be received by the PSC process:
o Remote LO - indicates that the remote end point is in Unavailable o Remote LO - indicates that the remote end point is in Unavailable
state due to a Lockout of Protection operator command. state due to a Lockout of Protection operator command.
o Remote SF - indicates that the remote end point has detected a o Remote SF - indicates that the remote end point has detected a
Signal Fail condition on one of the transport paths in the Signal Fail condition on one of the transport paths in the
protection domain. This remote message SHALL include an protection domain. This remote message includes an indication of
indication of which transport path is affected by the SF which transport path is affected by the SF condition. In
condition. In addition, it should be noted that the SF condition addition, it should be noted that the SF condition may be either a
may be either a unidirectional or a bidirectional failure, even if unidirectional or a bidirectional failure, even if the transport
the transport path is bidirectional. path is bidirectional.
o Remote SD - indicates that the remote end point has detected a o Remote SD - indicates that the remote end point has detected a
Signal Degrade condition on one of the transport paths in the Signal Degrade condition on one of the transport paths in the
protection domain. This remote message SHALL include an protection domain. This remote message includes an indication of
indication of which transport path is affected by the SD which transport path is affected by the SD condition. In
condition. In addition, it should be noted that the SD condition addition, it should be noted that the SD condition may be either a
may be either a unidirectional or a bidirectional failure, even if unidirectional or a bidirectional failure, even if the transport
the transport path is bidirectional. path is bidirectional.
o Remote FS - indicates that the remote end point is operating under o Remote FS - indicates that the remote end point is operating under
an operator command to switch the traffic to the protection path. an operator command to switch the traffic to the protection path.
o Remote MS - indicates that the remote end point is operating under o Remote MS - indicates that the remote end point is operating under
an operator command to switch the traffic to the path that was not an operator command to switch the traffic from the working path to
being used previously. the protection path.
o Remote WTR - indicates that the remote end point has determined o Remote WTR - indicates that the remote end point has determined
that the failure condition has recovered and has started its WTR that the failure condition has recovered and has started its WTR
timer in preparation for reverting to the Normal state. timer in preparation for reverting to the Normal state.
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.
3.3. PSC Control Logic 3.3. PSC Control Logic
The PSC Control Logic SHALL accept as input - The PSC Control Logic accepts the following 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), (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 (see section 3.2), 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 determines 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 is retained by the PSC Control Logic, while
while the requested action should be sent to the PSC Message the requested action should be sent to the PSC Message Generator (see
Generator (see subsection 3.4) to generate and transmit the proper Section 3.4) to generate and transmit the proper PSC message to be
PSC message to be transmitted to the remote end point of the transmitted to the remote end point of the protection domain.
protection domain.
3.4. PSC Message Generator 3.4. PSC Message Generator
Based on the action output from the PSC Control Logic this unit Based on the action output from the PSC Control Logic this unit
formats the PSC protocol message that is transmitted to the remote formats the PSC protocol message that is transmitted to the remote
end point of the protection domain. This message may either be the end point of the protection domain. This message may either be the
same as the previously transmitted message or change when the PSC same as the previously transmitted message or change when the PSC
control state (see section 3.6) has changed. The messages should be control state (see section 3.6) has changed. The messages are
transmitted as described in section 4.1 of this document. transmitted as described in section 4.1 of this document.
3.5. 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 length protection domain is configured for revertive behavior. The length
of the timer may be provisioned by the operator. The WTR may be in of the timer may be provisioned by the operator. The WTR may be in
one of two states - either Running or Stopped. The control of the 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 WTR timer is managed by the PSC Control Logic, by use of internal
signals to start and stop, i.e. reset, the WTR timer. 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 is 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, and put the WTR timer into Stopped state, but shall reset the timer, and put the WTR timer into Stopped state, but SHALL
not generate a WTR Expires local signal. If the WTR timer is NOT generate a WTR Expires local signal. If the WTR timer is
stopped, a Stop command shall be ignored. stopped, a Stop command SHALL be ignored.
3.6. 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. Information on the state of the state of the protection domain. Information on the state of the
domain is maintained by each LER within the protection domain. The domain is maintained by each LER within the protection domain. The
state information SHALL include information of the current state of state information would include information of the current state of
the protection domain, an indication of the cause for the current the protection domain, an indication of the cause for the current
state (e.g. unavailable due to local LO command, protecting due to state (e.g. unavailable due to local LO command, protecting due to
remote FS), and, for each LER, SHOULD include an indication if the remote FS), and, for each LER, should include an indication if the
state is related to a remote or local condition. If there are both a state is related to a remote or local condition.
local indicator and remote indicator for the state then the state
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
failure state, by receiving the local SF input the LER is considered
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 protection domain states that are supported by the PSC Control The protection domain states that are supported by the PSC Control
skipping to change at page 13, line 40 skipping to change at page 13, line 36
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
the Wait-to-Restore (WTR) timer. the Wait-to-Restore (WTR) timer.
o Do-not-revert state - The protection domain is recovering from a o Do-not-revert state - The protection domain has recovered 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.
3.6.1. 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 is considered a
considered a local state. If the state is entered as a result of a local state. If the state is entered as a result of a PSC message,
PSC message, in the absence of a local input, then the state SHOULD in the absence of a local input, then the state is considered a
be considered a remote state. This differentiation affects how the remote state. This differentiation affects how the LER reacts to
LER should react to different inputs, as described in section 4.3.3. different inputs, as described in Section 4.3.3. The PSC Control
The PSC Control logic should maintain, together with the current logic should maintain, together with the current protection domain
protection domain state, an indication of whether this is a local or state, an indication of whether this is a local or remote state, for
remote state, for this LER. 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 protection domain 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 is considered a local state, regardless of the order in
in which the indicators were processed. If, however, the LER has which the indicators were processed. If, however, the LER has local
local and remote indicators that would cause the protection domain to and remote indicators that would cause the protection domain to enter
enter different states, e.g. a Local SF on working and a Remote different states, e.g. a Local SF on working and a Remote Lockout
Lockout message, then the input with the higher priority (see section message, then the input with the higher priority (see section 4.3.2)
4.3.2) will be the deciding factor and the source of that indicator will be the deciding factor and the source of that indicator will
will determine whether it is local or remote. In the given example determine whether it is local or remote. In the given example the
the result would be a Remote Unavailable state transmitting SF(1,0) result would be a Remote Unavailable state transmitting PSC messages
messages. that indicate a SF condition on the working path and that the
protection path is not being used to transport protected traffic (as
described in the next section).
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 determining which of the two possible paths, the working or
protection path, is transmitting the data traffic in any given protection path, is transmitting the data traffic in any given
situation. When protection switching is triggered as described in situation. When protection switching is triggered as described in
section 3, the end points must inform each other of the switch-over section 3, the end points must inform each other of the switch-over
from one path to 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 will
complete the switchover. complete the switchover.
This protocol is a single-phased protocol, as described above. In This protocol is a single-phased protocol, as described above. In
the following subsections we describe the protocol messages that the following subsections we describe the protocol messages that are
SHALL be used between the two end points of the protection domain. 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 protection domain state is changed due to a local input, When the protection domain state is changed due to a local input,
three PSC messages SHOULD be transmitted as quickly as possible, to three PSC messages SHALL be transmitted as quickly as possible, to
allow for rapid protection switching. This set of three rapid allow for rapid protection switching. This set of three rapid
messages allows for fast protection switching even if one or two of messages allows for fast protection switching even if one or two of
these packets are lost or corrupted. When the protection domain these packets are lost or corrupted. When the protection domain
state changes due to a remote message the LER MAY send the three state changes due to a remote message the LER MAY send the three
rapid messages, but is not required to. However, when the LER rapid messages, but is not required to. However, when the LER
tranfers from WTR state to Normal state as a result of a remote NR tranfers from WTR state to Normal state as a result of a remote NR
message, the three rapid messages SHOULD be transmitted. message, the three rapid messages SHALL be transmitted. After the
transmission of the three rapid messages, the LER MUST retransmit the
most recently transmitted PSC message on a continual basis.
The frequency of the three rapid messages and the separate frequency An implementation that is concerned about the potential for end
of the continual transmission SHOULD be configurable by the operator. points to become out of sync as a result of lost messages MAY choose
For protection switching within 50ms, it is RECOMMENDED that the to send messages more frequently at every state change. Such
default interval of the first three PSC messages SHOULD be no larger behavior is consistent with the protocol specified here and will be
than 3.3ms. The subsequent messages SHOULD be continuously handled correctly by the receiver.
transmitted with an interval of 5 seconds.
If no valid PSC message is received, the last valid received message Both the default frequency of the three rapid messages as well as the
remains applicable. default frequency of the continual message transmission SHALL be
configurable by the operator. The actual frequencies used may be
configurable, at the time of establishment, for each individual
protected LSP. For management purposes, the operator should be able
to retrieve the current default frequency values as well as the
actual values for any specific LSP. For protection switching within
50ms, it is RECOMMENDED that the default interval of the first three
rapid PSC messages SHOULD be no larger than 3.3ms. Using this
frequency would allow the far-end to be guaranteed of receiving the
trigger indication within 10ms and completion of the switching
operation within 50ms. Subsequent messages SHOULD be continuously
transmitted with a default interval of 5 seconds. The purpose of the
continual messages is to verify that the PSC session is still alive.
If no valid PSC message is received, over a period of several
continual messages intervals, the last valid received message remains
applicable.
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. The actual message function SHALL be identified by the messages. The actual message function SHALL be identified by the
Request field of the ACH payload as described below. Request field of the ACH payload as described below.
The channel type for the PSC messages SHALL be PSC-CT=0xHH (to be The channel type for the PSC messages SHALL be PSC-CT=0xHH (to be
assigned by IANA) assigned by IANA)
The following figure shows the format for the complete PSC message: The following figure shows the format for the complete PSC message:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|Version| Reserved | PSC-CT | |0 0 0 1|Version| Reserved | PSC-CT |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ver|Request|PT |R| Reserved | FPath | Path | |Ver|Request|PT |R| Reserved1 | FPath | Path |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLV Length | Reserved | | TLV Length | Reserved2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Optional TLVs ~ ~ Optional TLVs ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Format of PSC packet with a G-ACh header Figure 2: Format of PSC packet with a G-ACh header
Where: Where:
o The following subsections describe the fields of the PSC payload. o Both Reserved1 and Reserved2 fields MUST be set to 0 and ignored
upon receipt.
o The following subsections describe the remaining fields of the PSC
payload.
4.2.1. PSC Ver field 4.2.1. PSC Ver field
The Ver field identifies the version of the protocol. For this The Ver field identifies the version of the protocol. For this
version of the document the value SHALL be 1. version of the document the value SHALL be 1.
4.2.2. PSC Request field 4.2.2. PSC Request field
The PSC protocol SHALL support transmission of the following requests The PSC protocol SHALL support transmission of the following requests
between the two end points of the protection domain: between the two end points of the protection domain:
o (1110) Lockout of protection - indicates that the end point has o (14) Lockout of protection - indicates that the end point has
disabled the protection path as a result of an administrative disabled the protection path as a result of an administrative
command. Both the FPath and Path fields SHALL be set to 0. command. Both the FPath and Path fields SHALL be set to 0.
o (1100) Forced switch - indicates that the transmitting end point o (12) Forced switch - indicates that the transmitting end point has
has switched traffic to the protection path as a result of an switched traffic to the protection path as a result of an
administrative command. The Fpath field SHALL indicate that the administrative command. The Fpath field SHALL indicate that the
working path is being blocked (i.e. Fpath set to 1), and the Path working path is being blocked (i.e. Fpath set to 1), and the Path
field SHALL indicate that user data traffic is being transported field SHALL indicate that user data traffic is being transported
on the protection path (i.e. Path set to 1). on the protection path (i.e. Path set to 1).
o (1010) Signal Fail - indicates that the transmitting end point has o (10) 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 (0111) Signal Degrade - indicates that that the transmitting end o (7) 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.
This request is presented here only as a place-holder. The This request is presented here only as a place-holder. The
specifics for the method of identifying this degradation is out- specifics for the method of identifying this degradation is out-
of-scope for this document. The details of the actions to be 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 (0101) Manual switch - indicates that the transmitting end point o (5) Manual switch - indicates that the transmitting end point has
has switched traffic to the protection path as a result of an switched traffic to the protection path as a result of an
administrative Manual Switch command. The Fpath field SHALL administrative Manual Switch command. The Fpath field SHALL
indicate that the working path is being blocked (i.e. Fpath set indicate that the working path is being blocked (i.e. Fpath set
to 1), and the Path field SHALL indicate that user data traffic is to 1), and the Path field SHALL indicate that user data traffic is
being transported on the protection path (i.e. Path set to 1). being transported on the protection path (i.e. Path set to 1).
o (0100) Wait to restore - indicates that the transmitting end point o (4) Wait to restore - indicates that the transmitting end point is
is recovering from a failure condition of the working path and has 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 (0001) Do not revert - indicates that the transmitting end point o (1) Do not revert - indicates that the transmitting end point has
is recovering from a failure/blocked condition, but due to the recovered from a failure/blocked condition, but due to the local
local settings is requesting that the protection domain continues settings is is requesting that the protection domain continues to
to transmit data over the protection path, rather than revert to transport the data as if it is in a protecting state, rather than
the Normal state. Fpath SHALL be set to 0 and ignored upon revert to the Normal state. Fpath SHALL be set to 0 and ignored
receipt. Path SHALL indicate the working path that is currently upon receipt. Path SHALL indicate the working path that is
being protected (i.e. Path set to 1). currently being protected (i.e. Path set to 1).
o (0000) No request - indicates that the transmitting end point has o (0) No request - indicates that the transmitting end point has
nothing to report, Fpath and Path fields SHALL be set to according nothing to report, Fpath and Path fields SHALL be set to according
to the state of the end point, see section 4.3.3 for detailed to the state of the end point, see section 4.3.3 for detailed
scenarios. scenarios.
All other values are for future extensions (to be administered by
IANA) and SHALL be ignored upon receipt.
4.2.3. Protection Type (PT) 4.2.3. Protection Type (PT)
The PT field indicates the currently configured protection The PT field indicates the currently configured protection
architecture type, this SHOULD be validated to be consistent for both architecture type, this SHOULD be validated to be consistent for both
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 3: bidirectional switching using a permanent bridge
o 10: bidirectional switching using a selector bridge o 2: bidirectional switching using a selector bridge
o 01: unidirectional switching using a permanent bridge o 1: unidirectional switching using a permanent bridge
o 00: for future extensions
o 0: 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
skipping to change at page 18, line 27 skipping to change at page 18, line 46
system SHOULD be notified. Possible values are: system SHOULD be notified. Possible values are:
o 0 - non-revertive mode o 0 - non-revertive mode
o 1 - revertive mode o 1 - revertive mode
4.2.5. Fault path (FPath) field 4.2.5. Fault path (FPath) field
The Fpath field indicates which path (i.e. working or protection) is The Fpath field indicates which path (i.e. working or protection) is
identified to be in a fault condition or affected by an identified to be in a fault condition or affected by an
administrative command. The following are the possible values: administrative command, when a fault or command is indicated by the
Request field to be in effect. The following are the possible
values:
o 0: indicates that the anomaly condition is on the protection path o 0: indicates that the anomaly condition is on the protection path
o 1: indicates that the anomaly condition is on the working path o 1: indicates that the anomaly condition is on the working path
o 2-255: for future extensions o 2-255: for future extensions and SHALL be ignored by this version
of the protocol.
4.2.6. Data path (Path) field 4.2.6. Data path (Path) field
The Path field indicates which data is being transmitted on the The Path field indicates which data is being transported on the
protection path. Under normal conditions, the protection path protection path. Under normal conditions, the protection path
(especially in 1:1 or 1:n architecture) does not need to carry any (especially in 1:1 or 1:n architecture) does not need to carry any
user data traffic. If there is a failure/degrade condition on one of user data traffic. If there is a failure/degrade condition on one of
the working paths, then that working path's data traffic will be the working paths, then that working path's data traffic will be
transmitted over the protection path. The following are the possible transported over the protection path. The following are the possible
values: values:
o 0: indicates that the protection path is not transporting user o 0: indicates that the protection path is not transporting user
data traffic (in 1:n architecture) or transporting redundant user data traffic (in 1:n architecture) or transporting redundant user
data traffic (in 1+1 architecture). data traffic (in 1+1 architecture).
o 1: indicates that the protection path is transmitting user traffic o 1: indicates that the protection path is transmitting user traffic
replacing the use of the working path. replacing the use of the working path.
o 2-255: for future extensions o 2-255: for future extensions and SHALL be ignored by this version
of the protocol.
4.2.7. Additional TLV information 4.2.7. Additional TLV information
It may be necessary for future applications of the protocol to It may be necessary for future applications of the protocol to
include additional information for the proper processing of the include additional information for the proper processing of the
requests. For this purpose, we provide for optional additional requests. For this purpose, we provide for optional additional
information to be included in the PSC payload. This information MUST information to be included in the PSC payload. This information MUST
include a header that indicates the total length (in bytes) of the include a header that indicates the total length (in bytes) of the
additional information. additional information.
This information includes the following fields: This information includes the following fields:
o TLV Length -- indicates the number of bytes included in the o TLV Length -- indicates the number of bytes included in the
optional TLV information. For the basic PSC protocol operation optional TLV information. For the basic PSC protocol operation
described in this document this value SHOULD be 0. described in this document this value MUST be 0.
o Reserved -- this field SHALL be 0.
o Optional TLVs -- this includes any additional information o Optional TLVs -- this includes any additional information
formatted as TLV units. There are no TLV units defined for the formatted as TLV units. There are no TLV units defined for the
basic PSC operation. basic PSC operation.
4.3. Principles of Operation 4.3. Principles of Operation
In all of the following subsections, assume a protection domain In all of the following subsections, assume a protection domain
between LER-A and LER-Z, using paths W (working) and P (protection) between LER-A and LER-Z, using paths W (working) and P (protection)
as shown in figure 3. as shown in figure 3.
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4.3.1. Basic operation 4.3.1. Basic operation
The purpose of the PSC protocol is to allow an end point of the The purpose of the PSC protocol is to allow an end point of the
protection domain to notify its peer of the status of the domain that protection domain to notify its peer of the status of the domain that
is known at the end point and coordinate the transmission of the data is known at the end point and coordinate the transmission of the data
traffic. The current state of the end point is expressed in the traffic. The current state of the end point is expressed in the
values of the Request field [reflecting the local requests at that values of the Request field [reflecting the local requests at that
end point] and the Fpath field [reflecting knowledge of a blocked end point] and the Fpath field [reflecting knowledge of a blocked
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]. Except during a protection switch, the value of
for both end points at any particular time. The values of the the Path field should be identical for both end points at any
Request and Fpath fields may not be identical between the two end particular time. The values of the Request and Fpath fields may not
points. In particular it should be noted that a remote message MAY be identical between the two end points. In particular it should be
not cause the end point to change the Request field that is being noted that a remote message may not cause the end point to change the
transmitted while it does affect the Path field (see details in the Request field that is being transmitted while it does affect the Path
following subsections). field (see details in the following subsections).
The protocol is a single-phased protocol. Single-phased 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. As a side-effect of using a
single-phased protocol, there will be a short period during state
transitions of one-sided triggers (e.g. operator commands, or
unidirectional SF) when one LER may be transporting/selecting the
data from one transport path while the other end point is
transporting/selecting from the other transport path. This should
become coordinated once the remote message is received and the far-
end LER performs the protection switching operation.
The following subsections will identify the messages that SHALL be The following subsections will identify the messages that will 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. For 1+1 unidirectional protection, the state of the
selector will only be switched in reaction to a local message. When
receiving a remote message, a LER that is configured for 1+1
unidirectional protection, will transfer to the new remote state,
however it will continue to select data according to the latest known
local state.
4.3.2. Priority of inputs 4.3.2. Priority of inputs
As noted above (in section 3.1) the PSC Control Process accepts input As noted above (in section 3.1) the PSC Control Process accepts input
from five local input sources. There is a definition of priority from five local input sources. There is a definition of priority
between the different inputs that may be triggered locally. The list between the different inputs that may be triggered locally. The list
of local requests in order of priority are (from highest to lowest of local requests in order of priority are (from highest to lowest
priority): priority):
1. Clear (Operator command) 1. Clear (Operator command)
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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 continue to send the PSC messages 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 SHALL 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.
o A local Lockout of protection input SHALL cause the LER to remain o A local Lockout of protection input SHALL cause the LER to remain
in local Unavailable State and transmit a LO(0,0) message to the in local Unavailable State and transmit a LO(0,0) message to the
far-end LER (LER-Z). far-end LER (LER-Z).
o A local Clear SF of the protection path in local Unavailable state o A local Clear SF of the protection path in local Unavailable state
that is due to a SF on the protection path SHALL cause the LER to that is due to a SF on the protection path SHALL cause the LER to
go to Normal state and begin transmitting a NR(0,0) message. If go to Normal state and begin transmitting a NR(0,0) message. If
the LER is in remote Unavailable state but has an active local SF the LER is in remote Unavailable state but has an active local SF
condition, then the local Clear SF SHALL clear the SF local condition, then the local Clear SF SHALL clear the SF local
condition and the LER SHALL remain in remote Unavailable state and condition and the LER SHALL remain in remote Unavailable state and
begin transmitting NR(0,0) messages. In all other cases the local begin transmitting NR(0,0) messages. In all other cases the local
Clear SF SHOULD be ignored. Clear SF SHALL be ignored.
o A local Forced switch SHALL be ignored by the PSC Control Logic. o A local Forced switch SHALL be ignored by the PSC Control Logic.
o A local Signal Fail on the protection path input when in local o A local Signal Fail on the protection path input when in local
Unavailable state [by implication this is due to a local SF on Unavailable state [by implication this is due to a local SF on
protection] SHALL cause the LER to remain in local Unavailable protection] SHALL cause the LER to remain in local Unavailable
state and transmit a SF(0,0) message. state and transmit a SF(0,0) message.
o A local Signal Fail on the working path input when in remote o A local Signal Fail on the working path input when in remote
Unavailable state SHALL cause the LER to remain in remote Unavailable state SHALL cause the LER to remain in remote
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the protection path, while the working path is blocked due to an the protection path, while the working path is blocked due to an
operator command, i.e. Forced Switch or Manual Switch. The operator command, i.e. Forced Switch or Manual Switch. The
difference between a local FS and local MS affects what local difference between a local FS and local MS affects what local
indicators may be received - the Local request logic will block any indicators may be received - the Local request logic will block any
local SF when under the influence of a local FS, whereas the SF would local SF when under the influence of a local FS, whereas the SF would
override a local MS. In general, a MS will be canceled in case of override a local MS. In general, a MS will be canceled in case of
either a local or remote SF or LO condition. either a local or remote SF or LO condition.
The following describe the reaction to local input: The following describe the reaction to local input:
o A local Clear SHOULD be ignored if in remote Protecting o A local Clear SHALL be ignored if in remote Protecting
administrative state. If in local Protecting administrative state administrative state. If in local Protecting administrative state
then this input SHALL cause the LER to go into Normal state and then this input SHALL cause the LER to go into Normal state and
begin transmitting a NR(0,0) message. begin transmitting a NR(0,0) 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
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.
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(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
SHALL be ignored (i.e. the indication should have been blocked by SHALL be ignored (i.e. the indication should have been blocked by
the Local request logic). the Local request logic).
o A local Clear SF when in remote Protecting administrative state o A local Clear SF when in remote Protecting administrative state
SHOULD clear any local SF condition that may exist. The LER SHALL SHALL clear any local SF condition that may exist. The LER SHALL
stop transmitting the SF(x,1) message and begin transmitting an stop transmitting the SF(x,1) message and begin transmitting an
NR(0,1) message. NR(0,1) message.
o A local Manual switch input SHALL be ignored if in remote o A local Manual switch input SHALL be ignored if in remote
Protecting administrative state is due to a remote Forced switch Protecting administrative state is due to a remote Forced switch
command. If the current state is due to a (local or remote) command. If the current state is due to a (local or remote)
Manual switch operator command, it SHALL cause the LER to remain Manual switch operator command, it SHALL cause the LER to remain
in local Protecting administrative state and transmit a MS(1,1) in local Protecting administrative state and transmit a MS(1,1)
message. message.
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While in Protecting administrative state the LER may receive and While in Protecting administrative state the LER may receive and
react as follows to remote PSC messages: react as follows to remote PSC messages:
o A remote Lockout of protection message SHALL cause the LER to go o A remote Lockout of protection message SHALL cause the LER to go
into remote Unavailable state and begin transmitting a NR(0,0) into remote Unavailable state and begin transmitting a NR(0,0)
message. It should be noted that this automatically cancels the message. It should be noted that this automatically cancels the
current Forced switch or Manual switch command and data traffic is current Forced switch or Manual switch command and data traffic is
reverted to the working path. reverted to the working path.
o A remote Forced switch message SHOULD be ignored by the PSC o A remote Forced switch message SHALL be ignored by the PSC Process
Process Logic if there is an active local Forced switch operator Logic if there is an active local Forced switch operator command.
command. If the Protecting administrative state is due to a If the Protecting administrative state is due to a remote Forced
remote Forced switch message then the LER SHALL remain in remote switch message then the LER SHALL remain in remote Protecting
Protecting administrative state and continue transmitting the last administrative state and continue transmitting the last message.
message. If the Protecting administrative state is due to either If the Protecting administrative state is due to either a local or
a local or remote Manual switch then the LER SHALL remain in remote Manual switch then the LER SHALL remain in remote
remote Protecting administrative state (updating the state Protecting administrative state (updating the state information
information with the proper relevant information) and begin with the proper relevant information) and begin transmitting a
transmitting a NR(0,1) message. NR(0,1) message.
o A remote Signal Fail message indicating a failure on the o A remote Signal Fail message indicating a failure on the
protection path SHALL cause the LER to go into remote Unavailable protection path SHALL cause the LER to go into remote Unavailable
state and begin transmitting a NR(0,0) message. It should be state and begin transmitting a NR(0,0) message. It should be
noted that this automatically cancels the current Forced switch or noted that this automatically cancels the current Forced switch or
Manual switch command and data traffic is reverted to the working Manual switch command and data traffic is reverted to the working
path. path.
o A remote Signal Fail message indicating a failure on the working o A remote Signal Fail message indicating a failure on the working
path SHALL be ignored if there is an active local Forced switch path SHALL be ignored if there is an active local Forced switch
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transmitting the current message. transmitting the current message.
o A remote NR(0,0) message SHALL be ignored if in local Protecting o A remote NR(0,0) message SHALL be ignored if in local Protecting
administrative state. If in remote Protecting administrative administrative state. If in remote Protecting administrative
state and there is no active local Signal Fail indication then the state and there is no active local Signal Fail indication then the
LER SHALL go to Normal state and begin transmitting a NR(0,0) LER SHALL go to Normal state and begin transmitting a NR(0,0)
message. If there is a local Signal Fail on the working path, the message. If there is a local Signal Fail on the working path, the
LER SHALL go to local Protecting failure state and begin LER SHALL go to local Protecting failure state and begin
transmitting a SF(1,1) message. transmitting a SF(1,1) message.
o All other remote messages SHOULD be ignored. o All other remote messages SHALL 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 PSC 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.
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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
SF(0,0) message. 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 remain in local Protecting failure state and transmit a LER to remain in local Protecting failure state and transmit a
SF(1,1) message. SF(1,1) message.
o All other local inputs SHOULD be ignored. o All other local inputs SHALL be ignored.
While in Protecting failure state the LER may receive and react as While in Protecting failure state the LER may receive and react as
follows to remote PSC messages: follows to remote PSC messages:
o A remote Lockout of protection message SHALL cause the LER to go o A remote Lockout of protection message SHALL cause the LER to go
into remote Unavailable state and if in local Protecting failure into remote Unavailable state and if in local Protecting failure
state then the LER SHALL transmit a SF(1,0) message, otherwise it state then the LER SHALL transmit a SF(1,0) message, otherwise it
SHALL transmit a NR(0,0) message. It should be noted that this SHALL transmit a NR(0,0) message. It should be noted that this
may cause loss of user data since the working path is still in a may cause loss of user data since the working path is still in a
failure condition. failure condition.
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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 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) cause the LER to go to Normal state and transmit an NR(0,0)
message. message.
o All other remote messages SHOULD be ignored. o All other remote messages SHALL 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
state to Normal state will occur when the WTR timer expires. state to Normal state will occur when the WTR timer expires.
skipping to change at page 29, line 47 skipping to change at page 30, line 34
LER to Stop the WTR timer, go into local Protecting failure state, LER to Stop the WTR timer, go into local Protecting failure state,
and begin transmission of a SF(1,1) message. and begin transmission of a SF(1,1) message.
o A local Manual switch input SHALL cause the LER to Stop the WTR o A local Manual switch input SHALL cause the LER to Stop the WTR
timer, go into local Protecting administrative state and begin timer, go into local Protecting administrative state and begin
transmission of a MS(1,1) message. transmission of a MS(1,1) message.
o A local WTR expires input SHALL cause the LER to remain in Wait- o A local WTR expires input SHALL cause the LER to remain in Wait-
to-Restore state and begin transmitting a NR(0,1) message. to-Restore state and begin transmitting a NR(0,1) message.
o All other local inputs SHOULD be ignored. o All other local inputs SHALL be ignored.
When in Wait-to-Restore state the following describe the reaction to When in Wait-to-Restore state the following describe the reaction to
remote messages: remote messages:
o A remote Lockout of protection message SHALL cause the LER to Stop o A remote Lockout of protection message SHALL cause the LER to Stop
the WTR timer, go into remote Unavailable state, and begin the WTR timer, go into remote Unavailable state, and begin
transmitting a NR(0,0) message. transmitting a NR(0,0) message.
o A remote Forced switch message SHALL cause the LER to Stop the WTR o A remote Forced 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
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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 stopped then a remote NR message ignored. If the WTR timer is stopped then a remote NR message
SHALL cause the LER to go into Normal state and begin transmitting SHALL cause the LER to go into Normal state and begin transmitting
a NR(0,0) message. a NR(0,0) message.
o All other remote messages SHOULD be ignored. o All other remote messages SHALL 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
is a fundamental difference between this state and Normal - whereas is a fundamental difference between this state and Normal - whereas
Forced Switch in Normal state actually causes a switch in the Forced Switch in Normal state actually causes a switch in the
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of a SF(0,0) message. 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
transmission of a SF(1,1) message. transmission of a SF(1,1) message.
o A local Manual switch input SHALL cause the LER to go into local o A local Manual 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
MS(1,1) message. MS(1,1) message.
o All other local inputs SHOULD be ignored. o All other local inputs SHALL be ignored.
When in Do-not-revert state the following describe the reaction to When in Do-not-revert state the following describe the reaction to
remote messages: remote messages:
o A remote Lockout of protection message SHALL cause the LER to go o A remote Lockout of protection message SHALL cause the LER to go
into remote Unavailable state and begin transmitting a NR(0,0) into remote Unavailable state and begin transmitting a NR(0,0)
message. message.
o A remote Forced switch message SHALL cause the LER to go into o A remote Forced switch message SHALL cause the LER to go into
remote Protecting administrative state and begin transmission of a remote Protecting administrative state and begin transmission of a
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of a NR(0,0) message. of a NR(0,0) message.
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 go into remote Protecting failure state, and begin LER to go into remote Protecting failure state, and begin
transmission of a NR(0,1) message. transmission of a NR(0,1) message.
o A remote Manual switch message SHALL cause the LER to go into o A remote Manual switch message SHALL cause the LER to go into
remote Protecting administrative state and begin transmission of a remote Protecting administrative state and begin transmission of a
NR(0,1) message. NR(0,1) message.
o All other remote messages SHOULD be ignored. o All other remote messages SHALL be ignored.
5. IANA Considerations 5. IANA Considerations
5.1. Pseudowire Associated Channel Type 5.1. Pseudowire Associated Channel Type
In the "Pseudowire Name Spaces (PWE3) IANA" maintains the " In the "Pseudowire Name Spaces (PWE3) IANA" maintains the "
Pseudowire Associated Channel Types Registry". Pseudowire Associated Channel Types Registry".
IANA is requested to assign a new code point from this registry. The IANA is requested to assign a new code point from this registry. The
code point shall be assigned form the code point space that requires code point shall be assigned form the code point space that requires
"IETF Review" as follows: "IETF Review" as follows:
Registry: Registry:
skipping to change at page 32, line 24 skipping to change at page 33, line 16
Value Description TLV Follows Reference Value Description TLV Follows Reference
----- ----------------------- ----------- --------------- ----- ----------------------- ----------- ---------------
0xHH Protection State no [this document] 0xHH Protection State no [this document]
Coordination Protocol - Coordination Protocol -
Channel Type (PSC-CT) Channel Type (PSC-CT)
5.2. PSC Request Field 5.2. PSC Request Field
The IANA is instructed to create and maintain a new registry within The IANA is instructed to create and maintain a new registry within
the "Multiprotocol Label Switching Architecture (MPLS)" called "MPLS the "Multiprotocol Label Switching Architecture (MPLS)" namespace
PSC Request Registry". All code points within this registry shall be called "MPLS PSC Request Registry". All code points within this
allocated according to the "Standards Action" procedures as specified registry shall be allocated according to the "Standards Action"
in [RFC5226]. procedures as specified in [RFC5226].
The PSC Request Field is 4 bits and the values shall be allocated as The PSC Request Field is 4 bits and the values shall be allocated as
follows: follows:
Value Description Reference Value Description Reference
------------- --------------------- --------------- ----- --------------------- ---------------
b0000 No Request [this document] 0 No Request [this document]
b0001 Do not revert [this document] 1 Do not revert [this document]
b0010 - b0011 Unassigned 2 - 3 Unassigned
b0100 Wait to restore [this document] 4 Wait to restore [this document]
b0101 Manual switch [this document] 5 Manual switch [this document]
b0110 Unassigned 6 Unassigned
b0111 Signal Degrade [this document] 7 Signal Degrade [this document]
b1000 - b1001 Unassigned 8 - 9 Unassigned
b1010 Signal Fail [this document] 10 Signal Fail [this document]
b1011 Unassigned 11 Unassigned
b1100 Forced switch [this document] 12 Forced switch [this document]
b1101 Unassigned 13 Unassigned
b1110 Lockout of protection [this document] 14 Lockout of protection [this document]
b1111 Unassigned 15 Unassigned
5.3. Additional TLVs
The IANA is instructed to create and maintain a new registry within
the "Multiprotocol Label Switching Architecture (MPLS)" namespace
called "MPLS PSC TLV Registry". All code points within this registry
shall be allocated according to the "IETF Review" procedures as
specified in [RFC5226].
6. Security Considerations 6. Security Considerations
The generic security considerations for the data-plane of MPLS-TP are MPLS-TP is a subset of MPLS and so builds upon many of the aspects of
described in the security framework document [SecureFwk] together the security model of MPLS. MPLS networks make the assumption that
with the required mechanisms needed to address them. The security it is very hard to inject traffic into a network, and equally hard to
considerations for the generic associated control channel are cause traffic to be directed outside the network. The control plane
described in [RFC5586]. The security considerations for protection protocols utilize hop-by-hop security, and assume a "chain-of-trust"
and recovery aspects of MPLS-TP are addressed in [SurvivFwk]. model such that end-to-end control plane security is not used. For
more information on the generic aspects of MPLS security, see
[RFC5920].
The protocol described in this document is based on the use of the This document describes a protocol carried in the G-ACh [RFC5586],
Generic Associated Channel as defined in [RFC5586]. Any new security and so is dependent on the security of the G-ACh, itself. The G-ACh
risk introduced may be in the treatment of corrupted protocol units. is a generalization of the Associated Channel defined in [RFC4385].
Thus, this document relies heavily on the security mechanisms
provided for the Associated Channel and described in those two
documents.
A specific concern for the G-ACh is that is can be used to provide a
covert channel. This problem is wider than the scope of this
document and does not need to be addressed here, but it should be
noted that the channel provides end-to-end connectivity and SHOULD
NOT be policed by transit nodes. Thus, there is no simple way of
preventing any traffic being carried between in the G-ACh consenting
nodes.
A good discussion of the data plane security of an associated channel
may be found in [RFC5085]. That document also describes some
mitigation techniques.
It should be noted that the G-ACh is essentially connection-oriented
so injection or modification of control messages specified in this
document require the subversion of a transit node. Such subversion
is generally considered hard in MPLS networks, and impossible to
protect against at the protocol level. Management level techniques
are more appropriate.
However, a new concern for this document is the accidental corruption
of messages (through faulty implementations, or random corruption).
The main concern is around the Request, FPath and Path fields as a The main concern is around the Request, FPath and Path fields as a
change to these fields would change the behavior of the peer change to these fields would change the behavior of the peer end
endpoint. Although there is no way to avoid a change in network point. Although this document does not define a way to avoid a
behavior upon receipt of a message indicating a change in protection change in network behavior upon receipt of a message indicating a
status, the transition between states will converge on a known and change in protection status, the transition between states will
stable behavior in the face of messages which do not match reality. converge on a known and stable behavior in the face of messages which
do not match reality.
7. Acknowledgements 7. Acknowledgements
The authors would like to thank all members of the teams (the Joint The authors would like to thank all members of the teams (the Joint
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.
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",
RFC 5654, September 2009. RFC 5654, September 2009.
[RFC5586] Vigoureux,, M., Bocci, M., Swallow, G., Aggarwal, R., and
D. Ward, "MPLS Generic Associated Channel", RFC 5586,
May 2009.
[RFC4385] Bryant, S., Swallow, G., Martini, L., and D. McPherson,
"Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
Use over an MPLS PSN", RFC 4385, Feb 2006.
8.2. Informative References 8.2. Informative References
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, Jan 2001. Label Switching Architecture", RFC 3031, Jan 2001.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, Jan 2001. Encoding", RFC 3032, Jan 2001.
[RFC5659] Bocci, M. and S. Bryant, "An Architecture for Multi- [RFC5659] Bocci, M. and S. Bryant, "An Architecture for Multi-
Segment Pseudowire Emulation Edge-to-Edge", RFC 5659, Segment Pseudowire Emulation Edge-to-Edge", RFC 5659,
October 2009. October 2009.
[RFC5920] Fang, Luyuan., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, July 2010.
[RFC3985] Bryant, S. and P. Pate, "Pseudowire Emulation Edge-to-Edge [RFC3985] Bryant, S. and P. Pate, "Pseudowire Emulation Edge-to-Edge
(PWE3) Architecture", RFC 3985, March 2005. (PWE3) Architecture", RFC 3985, March 2005.
[RFC5085] Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit [RFC5085] Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for Connectivity Verification (VCCV): A Control Channel for
Pseudowires", RFC 5085, December 2007. Pseudowires", RFC 5085, December 2007.
[TPFwk] Bocci, M., Bryant, S., and L. Levrau, "A Framework for [TPFwk] Bocci, M., Bryant, S., Frost, D., Levrau, L., and L.
MPLS in Transport Networks",
ID draft-ietf-mpls-tp-framework-06.txt, July 2009.
[RFC5586] Vigoureux,, M., Bocci, M., Swallow, G., Aggarwal, R., and Berger, "A Framework for MPLS in Transport Networks",
D. Ward, "MPLS Generic Associated Channel", RFC 5586, RFC 5921, July 2010.
May 2009.
[RFC4427] Mannie, E. and D. Papadimitriou, "Recovery Terminology for [RFC4427] Mannie, E. and D. Papadimitriou, "Recovery Terminology for
Generalized Multi-Protocol Label Switching", RFC 4427, Generalized Multi-Protocol Label Switching", RFC 4427,
Mar 2006. Mar 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226, IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008. May 2008.
[SurvivFwk] [SurvivFwk]
Sprecher, N., Farrel, A., and H. Shah, "Multi-protocol Sprecher, N., Farrel, A., and H. Shah, "Multi-protocol
Label Switching Transport Profile Survivability Label Switching Transport Profile Survivability
Framework", ID draft-ietf-mpls-tp-survive-fwk-02.txt, Framework", ID draft-ietf-mpls-tp-survive-fwk-06.txt,
Feb 2009. June 2010.
[SecureFwk]
Fang, L., Niven-Jenkins, B., Mansfield, S., Zhang, R.,
Bitar, N., Daikoku, M., and L. Wang, "MPLS-TP Security
Framework",
ID draft-ietf-mpls-tp-security-framework-00.txt, Feb 2011.
[RFC4872] Lang, J., Papadimitriou, D., and Y. Rekhter, "RSVP-TE [RFC4872] Lang, J., Papadimitriou, D., and Y. Rekhter, "RSVP-TE
Extensions in Support of End-to-End Generalized Multi- Extensions in Support of End-to-End Generalized Multi-
Protocol Label Switching (GMPLS) Recovery", RFC 4872, Protocol Label Switching (GMPLS) Recovery", RFC 4872,
May 2007. May 2007.
[RFC4873] Berger, L., Bryskin, I., Papadimitriou, D., and A. Farrel,
"GMPLS Segment Recovery", RFC 4873, May 2007.
[RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching [RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching
(GMPLS) Architecture", RFC 3945, Oct 2004. (GMPLS) Architecture", RFC 3945, Oct 2004.
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 implementation specification. functional description, not an implementation specification.
 End of changes. 98 change blocks. 
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