draft-ietf-mpls-tp-psc-itu-00.txt   draft-ietf-mpls-tp-psc-itu-01.txt 
MPLS Working Group J. Ryoo, Ed. MPLS Working Group J. Ryoo, Ed.
Internet-Draft ETRI Internet-Draft ETRI
Updates: 6378 (if approved) E. Gray, Ed. Updates: 6378 (if approved) E. Gray, Ed.
Intended status: Standards Track Ericsson Intended status: Standards Track Ericsson
Expires: May 31, 2014 H. van Helvoort Expires: July 23, 2014 H. van Helvoort
Huawei Technologies Huawei Technologies
A. D'Alessandro A. D'Alessandro
Telecom Italia Telecom Italia
T. Cheung T. Cheung
ETRI ETRI
E. Osborne E. Osborne
Cisco Systems, Inc. Cisco Systems, Inc.
November 27, 2013 January 19, 2014
MPLS Transport Profile (MPLS-TP) Linear Protection in Support of ITU-T's MPLS Transport Profile (MPLS-TP) Linear Protection to Match the
Requirements Operational Expectations of SDH, OTN and Ethernet Transport Network
draft-ietf-mpls-tp-psc-itu-00.txt Operators
draft-ietf-mpls-tp-psc-itu-01.txt
Abstract Abstract
This document introduces alternate ways to perform certain operations This document describes alternate mechanisms to perform some of the
defined in RFC6378, "MPLS Transport Profile (MPLS-TP) Linear sub-functions of MPLS Transport Profile (MPLS-TP) linear protection
Protection", and also defines additional behaviors. This set of defined in RFC 6378, and also defines additional mechanisms. The
modified and additional behaviors together with the protocol defined purpose of these alternate and additional mechanisms is to provide
in RFC6378 meets the ITU-T's protection switching requirements. operator control and experience that more closely models the behavior
of linear protection seen in other transport networks.
This document introduces capabilities and modes. A capability is an This document also introduces capabilities and modes for linear
individual behavior. The capabilities of a node are advertised using protection. A capability is an individual behavior, and a mode is a
the method given in this document. A mode is a particular particular combination of capabilities. Two modes are defined in
combination of capabilities. Two modes are defined in this document: this document: Protection State Coordination (PSC) mode and Automatic
Protection State Coordination (PSC) mode and Automatic Protection Protection Switching (APS) mode.
Switching (APS) mode.
This document describes the behavior of the PSC protocol including This document describes the behavior of the PSC protocol including
priority logic and state machine when all the capabilities associated priority logic and state machine when all the capabilities associated
with the APS mode are enabled. with the APS mode are enabled.
This document updates RFC6378 in that the capability advertisement This document updates RFC 6378 in that the capability advertisement
method defined here is an addition to that document. method defined here is an addition to that document.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
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This Internet-Draft will expire on May 31, 2014. This Internet-Draft will expire on July 23, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 4 2. Conventions Used in This Document . . . . . . . . . . . . . . 5
3. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Capability 1: Priority Modification . . . . . . . . . . . . . 5 4. Capability 1: Priority modification . . . . . . . . . . . . . 6
4.1. Motivations for swapping priorities of FS and SF-P . . . 5 4.1. Motivations for swapping priorities of FS and SF-P . . . 6
4.2. Motivation for raising the priority of Clear SF . . . . . 6 4.2. Motivation for raising the priority of SFc . . . . . . . 7
4.3. Motivation for introducing Freeze command . . . . . . . . 6 4.3. Motivation for introducing Freeze command . . . . . . . . 7
4.4. Updates to the PSC RFC . . . . . . . . . . . . . . . . . 6 4.4. Modifications to RFC 6378 . . . . . . . . . . . . . . . . 7
5. Capability 2: Modification of Non-revertive Operation . . . . 7 5. Capability 2: Modification of non-revertive operation . . . . 8
6. Capability 3: Support of Manual Switch to Working Command . . 7 6. Capability 3: Support of MS-W command . . . . . . . . . . . . 8
6.1. Motivation for adding Manual Switch to Working . . . . . 7 6.1. Motivation for adding MS-W . . . . . . . . . . . . . . . 8
6.2. Terms modified to support MS-W . . . . . . . . . . . . . 8 6.2. Terms modified to support MS-W . . . . . . . . . . . . . 9
6.3. Behavior of MS-P and MS-W . . . . . . . . . . . . . . . . 8 6.3. Behavior of MS-P and MS-W . . . . . . . . . . . . . . . . 9
6.4. Equal priority resolution for MS . . . . . . . . . . . . 8 6.4. Equal priority resolution for MS . . . . . . . . . . . . 9
7. Capability 4: Support of protection against Signal Degrade . 9 7. Capability 4: Support of protection against SD . . . . . . . 10
7.1. Motivation for supporting protection against Signal 7.1. Motivation for supporting protection against SD . . . . . 10
Degrade . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.2. Terms modified to support SD . . . . . . . . . . . . . . 10
7.2. Terms modified to support SD . . . . . . . . . . . . . . 9 7.3. Behavior of protection against SD . . . . . . . . . . . . 10
7.3. Behavior of protection against SD . . . . . . . . . . . . 9
7.4. Equal priority resolution . . . . . . . . . . . . . . . . 11 7.4. Equal priority resolution . . . . . . . . . . . . . . . . 11
8. Capability 5: Support of Exercise Command . . . . . . . . . . 12
9. Capabilities and Modes . . . . . . . . . . . . . . . . . . . 13 8. Capability 5: Support of EXER command . . . . . . . . . . . . 13
9.1. Capabilities . . . . . . . . . . . . . . . . . . . . . . 13 9. Capabilities and modes . . . . . . . . . . . . . . . . . . . 14
9.1.1. Sending the Capabilities TLV . . . . . . . . . . . . 14 9.1. Capabilities . . . . . . . . . . . . . . . . . . . . . . 14
9.1.2. Receiving the Capabilities TLV . . . . . . . . . . . 14 9.1.1. Sending the Capabilities TLV . . . . . . . . . . . . 15
9.1.2. Receiving the Capabilities TLV . . . . . . . . . . . 15
9.1.3. Handling Capabilities TLV errors . . . . . . . . . . 15 9.1.3. Handling Capabilities TLV errors . . . . . . . . . . 15
9.2. Modes . . . . . . . . . . . . . . . . . . . . . . . . . . 16 9.2. Modes . . . . . . . . . . . . . . . . . . . . . . . . . . 16
9.2.1. PSC Mode . . . . . . . . . . . . . . . . . . . . . . 16 9.2.1. PSC Mode . . . . . . . . . . . . . . . . . . . . . . 16
9.2.2. APS Mode . . . . . . . . . . . . . . . . . . . . . . 16 9.2.2. APS Mode . . . . . . . . . . . . . . . . . . . . . . 16
9.3. Backward compatibility . . . . . . . . . . . . . . . . . 16 9.3. Backward compatibility . . . . . . . . . . . . . . . . . 17
10. PSC Protocol in APS Mode . . . . . . . . . . . . . . . . . . 17 10. PSC Protocol in APS Mode . . . . . . . . . . . . . . . . . . 17
10.1. Request field in PSC protocol message . . . . . . . . . 17 10.1. Request field in PSC protocol message . . . . . . . . . 17
10.2. Priorities of local inputs and remote requests . . . . . 17 10.2. Priorities of local inputs and remote requests . . . . . 18
11. State Transition Tables in APS Mode . . . . . . . . . . . . . 19 10.3. Acceptance and retention of local inputs . . . . . . . . 20
11.1. State transition by local inputs . . . . . . . . . . . . 21 11. State Transition Tables in APS Mode . . . . . . . . . . . . . 21
11.2. State transition by remote messages . . . . . . . . . . 22 11.1. State transition by local inputs . . . . . . . . . . . . 23
12. Security considerations . . . . . . . . . . . . . . . . . . . 24 11.2. State transition by remote messages . . . . . . . . . . 25
13. IANA considerations . . . . . . . . . . . . . . . . . . . . . 24 11.3. State transition for 1+1 unidirectional
13.1. PSC Request Field . . . . . . . . . . . . . . . . . . . 24 protection . . . . . . . . . . . . . . . . . . . . . . . 27
13.2. PSC TLV . . . . . . . . . . . . . . . . . . . . . . . . 25 12. Provisioning mismatch and protocol failure
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25 in the APS mode . . . . . . . . . . . . . . . . . . . . . . . 28
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 25 13. Security considerations . . . . . . . . . . . . . . . . . . . 28
15.1. Normative References . . . . . . . . . . . . . . . . . . 25 14. IANA considerations . . . . . . . . . . . . . . . . . . . . . 28
15.2. Informative References . . . . . . . . . . . . . . . . . 25 14.1. MPLS PSC Request Registry . . . . . . . . . . . . . . . 29
Appendix A. An example of out-of-service scenarios . . . . . . . 26 14.2. MPLS PSC TLV Registry . . . . . . . . . . . . . . . . . 29
14.3. MPLS PSC Capability Flag Registry . . . . . . . . . . . 29
15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 30
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 30
16.1. Normative References . . . . . . . . . . . . . . . . . . 30
16.2. Informative References . . . . . . . . . . . . . . . . . 30
Appendix A. An example of out-of-service scenarios . . . . . . . 31
Appendix B. An example of sequence diagram showing Appendix B. An example of sequence diagram showing
the problem with the priority level of Clear SF . . 27 the problem with the priority level of SFc . . . . . 32
Appendix C. Freeze Command . . . . . . . . . . . . . . . . . . . 28 Appendix C. Freeze Command . . . . . . . . . . . . . . . . . . . 33
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29 Appendix D. Operation examples of the APS mode . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 38
1. Introduction 1. Introduction
This document introduces alternate ways to perform certain operations Linear protection mechanisms for the MPLS Transport Profile (MPLS-TP)
defined in [RFC6378], "MPLS Transport Profile (MPLS-TP) Linear are described in RFC 6378 [RFC6378] to meet the requirements
Protection", and also defines additional behaviors. This set of described in RFC 5654 [RFC5654].
modified and additional behaviors together with the protocol defined
in [RFC6378] meets the ITU-T's protection switching requirements.
Alternative behaviors are defined for the following capabilities: This document describes alternate mechanisms to perform some of the
sub-functions of linear protection, and also defines additional
mechanisms. The purpose of these alternate and additional mechanisms
is to provide operator control and experience that more closely
models the behavior of linear protection seen in other transport
networks, such as Synchronous Digital Hierarchy (SDH), Optical
Transport Network (OTN) and Ethernet transport networks. Linear
protection for SDH, OTN, and Ethernet transport networks are defined
in ITU-T Recommendations G.841 [G841], G.873.1 [G873.1] and G.8031
[G8031], respectively.
The reader of this document is assumed to be familiar with RFC 6378.
The alternative mechanisms described in this document are for the
following capabilities:
1. Priority modification, 1. Priority modification,
2. non-revertive behavior modification, 2. non-revertive behavior modification,
and the following capabilities have been added to define additional and the following capabilities have been added to define additional
behaviors: mechanisms:
3. support of Manual Switch to Working path (MS-W) command,
3. support of Manual Switch to Working (MS-W) command,
4. support of protection against Signal Degrade (SD), and 4. support of protection against Signal Degrade (SD), and
5. support of Exercise command. 5. support of Exercise (EXER) command.
Priority modification includes priority swapping between Signal Fail Priority modification includes priority swapping between Signal Fail
on the Protection path (SF-P) and Forced Switch (FS), and raising the on Protection path (SF-P) and Forced Switch (FS), and raising the
priority level of Clear SF. priority level of Clear Signal Fail (SFc).
Non-revertive behavior is modified to align with the behavior defined Non-revertive behavior is modified to align with the behavior defined
in [RFC4427] as well as to meet the ITU-T's protection switching in RFC 4427 [RFC4427] as well as to follow the behavior of linear
requirements. protection seen in other transport networks.
Support of Manual Switch to Working (MS-W) command to revert traffic Support of MS-W command to revert traffic to the working path in non-
to the working path in non-revertive operation is covered in this revertive operation is covered in this document.
document.
Support of protection switching protocol against Signal Degrade (SD) Support of protection switching protocol against SD is covered in
is covered in this document. The specifics for the method of this document. The specifics for the method of identifying SD is out
identifying SD is out of the scope of this document similarly to SF of the scope of this document similarly to Signal Fail (SF) for RFC
for [RFC6378]. 6378.
Support of Exercise command to test if the Protection State Support of EXER command to test if the Protection State Coordination
Coordination (PSC) communication is operating correctly is also (PSC) communication is operating correctly is also covered in this
covered in this document. More specifically, the Exercise tests and document. More specifically, EXER command tests and validates the
validates the linear protection mechanism and PSC protocol including linear protection mechanism and PSC protocol including the aliveness
the aliveness of the Local Request logic, the PSC state machine and of the priority logic, the PSC state machine and the PSC message
the PSC message generation and reception, and the integrity of the generation and reception, and the integrity of the protection path,
protection path, without triggering the actual traffic switching. without triggering the actual traffic switching.
This document introduces capabilities and modes. A capability is an This document introduces capabilities and modes. A capability is an
individual behavior, The capabilities of a node are advertised using individual behavior. The capabilities of a node are advertised using
the method given in this document. A mode is a particular the method given in this document. A mode is a particular
combination of capabilities. Two modes are defined in this document: combination of capabilities. Two modes are defined in this document:
PSC mode and Automatic Protection Switching (APS) mode. PSC mode and Automatic Protection Switching (APS) mode.
This document describes the behavior of the PSC protocol including This document describes the behavior of the PSC protocol including
priority logic and state machine when all the capabilities associated the priority logic and the state machine when all the capabilities
with the APS mode are enabled. associated with the APS mode are enabled.
This document updates [RFC6378] in that the capability advertisement This document updates RFC 6378 in that the capability advertisement
method defined here is an addition to that document. For an existing method defined here is an addition to that document. For an existing
implementation of [RFC6378], it is recommended to be updated with the implementation of RFC 6378, it is recommended to be updated with the
bug-fixes in [I-D.ietf-mpls-psc-updates] and the capability bug-fixes in [I-D.ietf-mpls-psc-updates] and the capability
adevertisement in this document. advertisement in this document.
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
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Acronyms 3. Acronyms
This document uses the following acronyms: This document uses the following acronyms:
APS Automatic Protection Switching APS Automatic Protection Switching
DNR Do-not-Revert
EXER Exercise EXER Exercise
FS Forced Switch FS Forced Switch
LER Label Edge Router
LO Lockout of protection LO Lockout of protection
MS Manual Switch MS Manual Switch
MS-P Manual Switch to Protection MS-P Manual Switch to Protection path
MS-W Manual Switch to Working MS-W Manual Switch to Working path
MPLS-TP MPLS Transport Profile MPLS-TP MPLS Transport Profile
NR No Request NR No Request
OC Operator Clear OC Operator Clear
OTN Optical Transport Network
PSC Protection State Coordination PSC Protection State Coordination
RR Reverse Request RR Reverse Request
SD Signal Degrade SD Signal Degrade
SD-P Signal Degrade on the Protection path SDH Synchronous Digital Hierarchy
SD-W Signal Degrade on the Working path SD-P Signal Degrade on Protection path
SD-W Signal Degrade on Working path
SF Signal Fail SF Signal Fail
SFc Clear Signal Fail SFc Clear Signal Fail
SF-P Signal Fail on the Protection path SFDc Clear Signal Fail or Degrade
SF-W Signal Fail on the Working path SF-P Signal Fail on Protection path
SF-W Signal Fail on Working path
WTR Wait to Restore WTR Wait to Restore
4. Capability 1: Priority Modification 4. Capability 1: Priority modification
In this document, the priorities of Forced Switch (FS) and Signal In this document, the priorities of FS and SF-P are swapped and the
Fail on the Protection path (SF-P) are swapped and the priority of priority of Clear SF (SFc) is raised. In addition to the priority
Clear SF (SFc) is raised. In addition to the priority modification, modification, this document introduces the use of Freeze command in
this document introduces the use of a Freeze command in Appendix C. Appendix C. The reasons for these changes are explained in the
The reasons for these changes are explained in the following sub- following sub-sections from technical and network operational
sections from technical and network operational aspects. aspects.
4.1. Motivations for swapping priorities of FS and SF-P 4.1. Motivations for swapping priorities of FS and SF-P
Defining the priority of FS higher than that of Signal Fail on the Defining the priority of FS higher than that of SF-P can result in a
Protection path (SF-P) can result in a situation where the protected situation where the protected traffic is taken out-of-service.
traffic is taken out-of-service. Setting the priority of any input Setting the priority of any input that is supposed to be signaled to
that is supposed to be signalled to the other end to be higher than the other end to be higher than that of SF-P can result in
that of SF-P can result in unpredictable protection switching state, unpredictable protection switching state, when the protection path
when the protection path has failed and consequently the PSC has failed and consequently the PSC communication stopped. An
communication stopped. An example of the out-of-service scenarios is example of the out-of-service scenarios is shown in Appendix A.
shown in Appendix A
According to Section 2.4 of [RFC5654] it MUST be possible to operate
an MPLS-TP network without using a control plane. This means that
external switch commands, e.g., FS, can be transferred to the far end
only by using the PSC communication channel and should not rely on
the presence of a control plane.
As the priority of SF-P has been higher than FS in optical transport According to Section 2.4 of RFC 5654 [RFC5654] it MUST be possible to
networks and Ethernet transport networks, for network operators it is operate an MPLS-TP network without using a control plane. This means
important that the MPLS-TP protection switching preserves the network that external switch commands, e.g., FS, can be transferred to the
operation behavior to which network operators have become accustomed. remote Label Edge Router (LER) only by using the PSC communication
Typically, the FS command is issued before network maintenance jobs, channel and should not rely on the presence of a control plane.
(e.g., replacing optical cables or other network components). When
an operator pulls out a cable on the protection path by mistake, the
traffic should be protected and the operator expects this behavior
based on his/her experience on the traditional transport network
operations.
4.2. Motivation for raising the priority of Clear SF As the priority of SF-P has been higher than FS in other transport
networks, such as SDH, OTN and Ethernet transport networks, for
network operators it is important that the MPLS-TP protection
switching preserves the network operation behavior to which network
operators have become accustomed. Typically, FS command is issued
before network maintenance jobs, (e.g., replacing optical cables or
other network components). When an operator pulls out a cable on the
protection path by mistake, the traffic should be protected and the
operator expects this behavior based on his/her experience on the
traditional transport network operations.
The priority level of SFc defined in [RFC6378] can cause traffic 4.2. Motivation for raising the priority of SFc
disruption when a node that has experienced local signal fails on
both working and protection paths is recovering from these failures. The priority level of SFc defined in RFC 6378 [RFC6378] can cause
traffic disruption when a node that has experienced local signal
fails on both the working and the protection paths is recovering from
these failures.
An example of sequence diagram showing the problem with the priority An example of sequence diagram showing the problem with the priority
level of SFc as defined in [RFC6378] is shown in Appendix B. level of SFc as defined in RFC 6378 is shown in Appendix B.
4.3. Motivation for introducing Freeze command 4.3. Motivation for introducing Freeze command
With the priority swapping between FS and SF-P, the traffic is always With the priority swapping between FS and SF-P, the traffic is always
moved back to the working path when SF-P occurs in Protecting moved back to the working path when SF-P occurs in Protecting
Administrative state. In the case that network operators need an administrative state. In the case that network operators need an
option to control their networks so that the traffic can remain on option to control their networks so that the traffic can remain on
the protection path even when the PSC communication channel is the protection path even when the PSC communication channel is
broken, the Freeze command, which is a local command (i.e., not broken, the Freeze command, which is a local command (i.e., not
signalled to the other end) can be used. The use of the Freeze signaled to the other end) can be used. The use of the Freeze
command is described in Appendix C. command is described in Appendix C.
4.4. Updates to the PSC RFC 4.4. Modifications to RFC 6378
The list of local requests in order of priority should be modified as The list of local requests in order of priority SHALL be modified as
follows: follows:
(from higher to lower) (from higher to lower)
o Clear Signal Fail/Degrade o Clear Signal Fail
o Signal Fail on the Protection path o Signal Fail on Protection path
o Forced Switch o Forced Switch
o Signal Fail on the Working path o Signal Fail on Working path
The change of the PSC control logic including state machine due to The change of the PSC Control logic including the state machine due
this priority modification is incorporated in the PSC control logic to this priority modification is incorporated in the PSC Control
description when all the capabilities are enabled in Section 10 and logic description in Section 10 and Section 11 when all the
Section 11. capabilities are enabled.
5. Capability 2: Modification of Non-revertive Operation 5. Capability 2: Modification of non-revertive operation
Non-revertive mode of protection switching is defined in [RFC4427]. Non-revertive mode of protection switching is defined in RFC 4427
In this mode, the traffic does not return to the working path when [RFC4427]. In this mode, the traffic does not return to the working
switch-over requests are terminated. path when switch-over requests are terminated.
However, PSC protocol defined in [RFC6378] supports this operation However, PSC protocol defined in RFC 6378 [RFC6378] supports this
only when recovering from a defect condition, but does not operate as operation only when recovering from a defect condition, but does not
non-revertive when an operator's switch-over command such as Forced operate as non-revertive when an operator's switch-over command such
Switch or Manual Switch is cleared. To be aligned with legacy as FS or Manual Switch (MS) is cleared. To be aligned with legacy
transport network behavior and [RFC4427], a node should go into the transport network behavior and RFC 4427, a node should go into the
Do-not-Revert (DNR) state not only when a failure condition on a Do-not-Revert (DNR) state not only when a failure condition on the
working path is cleared but also when an operator command requesting working path is cleared but also when an operator command requesting
switch-over is cleared. switch-over is cleared.
The change of the PSC control logic including state machine due to The change of the PSC Control logic including the state machine due
the modification of non-revertive operation is incorporated into the to the modification of non-revertive operation is incorporated into
PSC control logic description when all the capabilities are enabled the PSC Control logic description in Section 10 and Section 11 when
in Section 10 and Section 11. all the capabilities are enabled.
6. Capability 3: Support of Manual Switch to Working Command 6. Capability 3: Support of MS-W command
6.1. Motivation for adding Manual Switch to Working 6.1. Motivation for adding MS-W
Changing the non-revertive operation introduces necessity of a new Changing the non-revertive operation introduces necessity of a new
operator command to revert traffic to the working path when in Do- operator command to revert traffic to the working path when in the
not-Revert (DNR) state. When the traffic is on the protection path DNR state. When the traffic is on the protection path in the DNR
in DNR state, a Manual Switch to Working (MS-W) command is issued to state, a Manual Switch to Working (MS-W) command is issued to switch
switch the normal traffic back to the working path. According to the normal traffic back to working path. According to
Section 4.3.3.6 (Do-not-Revert State) in [RFC6378], "to revert back Section 4.3.3.6 (Do-not-Revert State) in RFC 6378 [RFC6378], "to
to Normal state, the administrator SHALL issue a Lockout of revert back to Normal state, the administrator SHALL issue a Lockout
protection (LO) command followed by a Clear command." However, using of protection (LO) command followed by a Clear command." However,
LO command introduces the potential risk of an unprotected situation using LO command introduces the potential risk of an unprotected
while the Lockout of protection is in effect. situation while the LO is in effect.
Manual Switch-over for recovery LSP/span command, defined in Manual Switch-over for recovery LSP/span command, defined in RFC 4427
[RFC4427] and also defined in [RFC5654], Requirement 83, as one of [RFC4427] and also defined in RFC 5654 [RFC5654], Requirement 83, as
the mandatory external commands, should be used for this purpose, but one of the mandatory external commands, should be used for this
is not included in [RFC6378]. Note that the "Manual Switch-over for purpose, but is not included in RFC 6378. Note that the "Manual
recovery LSP/span" command is the same as MS-W command. Switch-over for recovery LSP/span" command is the same as MS-W
command.
6.2. Terms modified to support MS-W 6.2. Terms modified to support MS-W
The term "Manual Switch" and its acronym "MS" used in [RFC6378] are The term "Manual Switch" and its acronym "MS" used in RFC 6378 are
replaced respectively by "Manual Switch to Protection" and "MS-P" by replaced respectively by "Manual Switch to Protection path" and
this document to avoid confusion with "Manual Switch to Working" and "MS-P" by this document to avoid confusion with "Manual Switch to
its acronym "MS-W". Working path" and its acronym "MS-W".
Also, the term "Protecting administrative state" used in [RFC6378] is Also, the term "Protecting administrative state" used in RFC 6378 is
replaced by "Switching administrative state" by this document to replaced by "Switching administrative state" by this document to
include the case where traffic is switched back to the working path include the case where traffic is switched back to the working path
by administrative Manual Switch to Working command. by administrative MS-W command.
6.3. Behavior of MS-P and MS-W 6.3. Behavior of MS-P and MS-W
The MS-P and MS-W commands SHALL have the same priority. If one of The MS-P and MS-W commands SHALL have the same priority. If one of
these commands is already issued and accepted, and the other command these commands is already issued and accepted, then the other command
that is issued afterwards SHALL be ignored. If two LERs are that is issued afterwards SHALL be ignored. If two LERs are
requesting opposite operations simultaneously, i.e. one LER is requesting opposite operations simultaneously, i.e. one LER is
sending MS-P while the other LER is sending MS-W, the MS-W SHALL be sending MS-P while the other LER is sending MS-W, the MS-W SHALL be
considered to have a higher priority than MS-P, and MS-P SHALL be considered to have a higher priority than MS-P, and MS-P SHALL be
ignored. ignored and cancelled.
Two commands, MS-P and MS-W are represented by the same Request Field Two commands, MS-P and MS-W are represented by the same Request Field
value, but differentiated by the FPath value. When traffic is value, but differentiated by the FPath value. When traffic is
switched to the protection path, the FPath field SHALL indicate that switched to the protection path, the FPath field SHALL indicate that
the working path is being blocked (i.e., FPath set to 1), and the the working path is being blocked (i.e., FPath set to 1), and the
Path field SHALL indicate that user data traffic is being transported Path field SHALL indicate that user data traffic is being transported
on the protection path (i.e., Path set to 1). When traffic is on the protection path (i.e., Path set to 1). When traffic is
switched to the working path, the FPath field SHALL indicate that the switched to the working path, the FPath field SHALL indicate that the
protection path is being blocked (i.e., FPath set to 0), and the Path protection path is being blocked (i.e., FPath set to 0), and the Path
field SHALL indicate that user data traffic is being transported on field SHALL indicate that user data traffic is being transported on
the working path (i.e., Path set to 0). the working path (i.e., Path set to 0).
6.4. Equal priority resolution for MS 6.4. Equal priority resolution for MS
[RFC6378] defines only one rule for equal priority condition in RFC 6378 defines only one rule for equal priority condition in
Section 4.3.2 as "The remote message from the far-end LER is assigned Section 4.3.2 as "The remote message from the remote LER is assigned
a priority just below the similar local input." In order to support a priority just below the similar local input." In order to support
the manual switch behavior described in Section 6.3, additional rules the manual switch behavior described in Section 6.3, additional rules
for equal priority resolution are required. Since the support of for equal priority resolution are required. Since the support of
protection against signal degrades also requires a similar equal protection against signal degrade also requires a similar equal
priority resolution, the rules are described in Section 7.4. priority resolution, the rules are described in Section 7.4.
The change of the PSC control logic including state machine due to The change of the PSC Control logic including the state machine due
the support of MS-W command is incorporated into the PSC control to the support of MS-W command is incorporated into the PSC Control
logic description when all the capabilities are enabled in Section 10 logic description in Section 10 and Section 11 when all the
and Section 11. capabilities are enabled
7. Capability 4: Support of protection against Signal Degrade 7. Capability 4: Support of protection against SD
7.1. Motivation for supporting protection against Signal Degrade 7.1. Motivation for supporting protection against SD
In MPLS-TP survivability framework [RFC6372], fault conditions In MPLS-TP survivability framework [RFC6372], fault conditions
include both Signal Fail (SF) and Signal Degrade (SD) that can be include both SF and SD that can be used to trigger protection
used to trigger protection switching. switching.
[RFC6378], which defines the Protection State Coordination (PSC) RFC 6378 [RFC6378], which defines the protection switching protocol
protocol, does not specify how the SF and SD are declared and for MPLS-TP does not specify how the SF and SD are detected, and
specifies the protection switching protocol associated with SF only. specifies the protection switching protocol associated with SF only.
The protection switching protocol associated with SD is covered in The PSC protocol associated with SD is covered in this document, and
this document, and the specifics for the method of identifying SD is the specifics for the method of identifying SD is out of the scope of
out of the scope of PSC protocol similarly to how to detect SF and the protection protocol similar to the facts that how SF is detect
how MS and FS commands are initiated in a management system and and how MS and FS commands are initiated in a management system and
signalled to PSC. signaled to protection switching are out of its scope.
7.2. Terms modified to support SD 7.2. Terms modified to support SD
Clear Signal Fail (SFc) includes the clearance of a degraded Instead of SFc, Clear Signal Fail or Degrade (SFDc) is used to
condition in addition to the clearance of a failure condition indicate the clearance of either a degraded condition or a failure
condition.
The second paragraph of Section 4.3.3.2 Unavailable State in The second paragraph of Section 4.3.3.2 Unavailable state in RFC 6378
[RFC6378] shows the intention of including Signal Degrade on the shows the intention of including Signal Degrade on Protection path
Protection path (SD-P) in the Unavailable state. Even though the (SD-P) in the Unavailable state. Even though the protection path can
protection path can be partially available under the condition of the be partially available under the condition of SD-P, this document
Signal Degrade on the Protection path, this document follows the same follows the same state grouping as RFC 6378 for SD-P.
state grouping as [RFC6378] for SD on the protection path.
The bullet item "Protecting failure state" in Section 3.6. PSC The bullet item "Protecting failure state" in Section 3.6 in RFC 6378
Control States in [RFC6378] includes the degraded condition in includes the degraded condition in Protecting failure state. This
Protection Failure state. This document follows the same state document follows the same state grouping as RFC 6378 for Signal
grouping as [RFC6378] for Signal Degrade on the Working path (SD-W). Degrade on Working path (SD-W).
7.3. Behavior of protection against SD 7.3. Behavior of protection against SD
In order to maintain the network operation behavior to which In order to maintain the network operation behavior to which
transport network operators have become accustomed, the priorities of transport network operators have become accustomed, the priorities of
SD-P and SD-W are defined to be equal as in other transport networks, SD-P and SD-W are defined to be equal as in other transport networks,
such as OTN and Ethernet. Once a switch has been completed due to such as SDH, OTN and Ethernet transport networks. Once a switch has
Signal Degrade on one path, it will not be overridden by Signal been completed due to SD on one path, it will not be overridden by SD
Degrade on the other path (first come, first served behavior), to on the other path (first come, first served behavior), to avoid
avoid protection switching that cannot improve signal quality and protection switching that cannot improve signal quality.
flapping.
Signal Degrade (SD) indicates that the transmitting end point has SD indicates that the transmitting end point has identified a
identified a degradation of the signal, or integrity of the packet degradation of the signal, or integrity of the packet transmission on
transmission on either the working or protection path. The FPath either the working path or the protection path. The FPath field
field SHALL identify the path that is reporting the degrade condition SHALL identify the path that is reporting the degrade condition
(i.e., if protection path, then FPath is set to 0; if working path, (i.e., if the protection path, then FPath is set to 0; if the working
then FPath is set to 1), and the Path field SHALL indicate where the path, then FPath is set to 1), and the Path field SHALL indicate
data traffic is being transported (i.e., if working path is selected, where the data traffic is being transported (i.e., if the working
then Path is set to 0; if protection path is selected, then Path is path is selected, then Path is set to 0; if the protection path is
set to 1). selected, then Path is set to 1).
The Wait to Restore (WTR) timer is used when the protected domain is The Wait to Restore (WTR) timer is used when the protected domain is
configured for revertive behavior and started at the node that configured for revertive behavior and started at the node that
recovers from a local degraded condition on the working path. recovers from a local degraded condition on the working path.
If the detection of a SD depends on the presence of user data Protection switching against SD is always provided by a selector
packets, such a condition declared on the working path is cleared bridge duplicating user data traffic and feeding it to both the
following protection switching to the protection path if a selector working path and the protection path under SD condition. When a
bridge is used, possibly resulting in flapping. To avoid flapping, local or remote SD occurs on either the working path or the
the selector bridge should duplicate the user data traffic and feed protection path, the LER SHALL duplicate user data traffic and SHALL
it to both working and protection paths under SD condition. In feed to both the working path and the protection path. The packet
revertive mode, when WTR timer expires the packet duplication will be duplication SHALL continue as long as any SD condition exists in the
stopped and the user data traffic will be transported on the working protected domain, and SHALL stop when there is no SD condition.
path only. In non-revertive mode, when SD is cleared the packet Additionally, the packet duplication SHALL continue in the WTR state
duplication will be stopped and the user data traffic will be in revertive mode. In non-revertive mode, the packet duplication
transported on the protection path only. SHALL stop when there is no SD condition.
When multiple SDs are detected simultaneously, either as local or
remote requests on both working and protection paths, the SD on the
standby path (the path from which the selector does not select the
user data traffic) is considered as having higher priority than the
SD on the active path (the path from which the selector selects the
user data traffic). Therefore, no unnecessary protection switching
is performed and the user data traffic continues to be selected from
the active path.
In the preceding paragraph, "simultaneously" relates to the The selector bridge with the packet duplication under SD condition,
occurrence of SD on both the active and standby paths at input to the which is a non-permanent bridge, is considered to be a 1:1 protection
Protection State Control Logic in Figure 1 of [RFC6378] at the same architecture.
time, or as long as a SD request has not been acknowledged by the
remote end in bidirectional protection switching. In other words,
when a local node that has transmitted a SD message receives a SD
message that indicates a different value of data path (Path) field
than the value of the Path field in the transmitted SD message, both
the local and the remote SD requests are considered to occur
simultaneously.
7.4. Equal priority resolution 7.4. Equal priority resolution
In order to support the manual switch behavior described in In order to support the manual switch behavior described in
Section 6.3 and the protection against Signal Degrade described in Section 6.3 and the protection against Signal Degrade described in
Section 7.3, the rules to resolve the equal priority requests are Section 7.3, the rules to resolve the equal priority requests are
required. required.
For local inputs with same priority, such as MS and SD, first-come, For the equal priority local inputs, such as MS and SD, first-come,
first-served rule is applied. Once a local input is determined as first-served rule is applied. Once a local input is determined as
the highest priority local input, then a subsequent equal priority the highest priority local input, then a subsequent equal priority
local input requesting a different action, i.e., the same PSC Request local input requesting a different action, i.e., the action results
Field but different FPath value, to the PSC control logic will not be in the same PSC Request Field but different FPath value, will not be
presented to the PSC control logic as the highest local request. presented to the PSC Control logic as the highest local request.
Furthermore, in the case of MS, the subsequent MS local input Furthermore, in the case of MS command, the subsequent local MS
requesting a different action will be cancelled. command requesting a different action will be cancelled.
The remote message from the far-end LER is assigned a priority just
below the similar local input. For example, a remote Forced Switch
would have a priority just below a local Forced Switch but above a
local Signal Fail on working input assuming that the priority
modification is in place as in Section 4.4
However, if the LER is in a remote state due to a remote message, a If the LER is in a remote state due to a remote SD (or MS) message, a
subsequent local input having the same priority but requesting subsequent local input having the same priority but requesting
different action to the control logic, will be considered as having different action to the PSC Control logic, will be considered as
lower priority than the remote message, and will be ignored. For having lower priority than the remote message, and will be ignored.
example, if the LER is in remote Unavailable state due to a remote If the LER is in remote Switching administrative state due to a
SD-P, then subsequent local SD-W input will be ignored. Likewise, if remote MS-P, then subsequent local MS-W SHALL be ignored and
the LER is in remote Switching administrative state due to a remote automatically cancelled. If the LER is in remote Unavailable state
MS-P, then subsequent local MS-W will be ignored and automatically due to a remote SD-P, then subsequent local SD-W input will be
cancelled. ignored. However, the local SD-W SHALL appear in the Local Request
logic as long as the SD condition exists, but SHALL NOT be the top
priority global request, which determines the state transition at the
PSC Control logic.
It should be noted that there is a reverse case where one LER There is a case where one LER receives a local input and the other
receives a local input and the other LER receives, simultaneously, an LER receives, simultaneously, a local input with the same priority
input with the same priority but requesting different action. In but requesting different action. In this case, each of the two LERs
this case, each of the two LERs receives a subsequent remote message receives a subsequent remote message having the same priority but
having the same priority but requesting different action, while the requesting different action, while the LER is in a local state due to
LER is in a local state due to the local input. In this case, a the local input. When this case happens, a priority must be set for
priority must be set for the inputs with the same priority regardless the inputs with the same priority regardless of its origin (local
of its origin (local input or remote message). For example, one LER input or remote message).
receives SD-P as a local input and the other LER receives SP-W as a
local input, simultaneously. Likewise, one LER receives MS-P as a
local input and the other LER receives MS-W as a local input,
simultaneously.
When MS-W and MS-P occur simultaneously at both LERs, MS-W SHALL be When MS-W and MS-P occur simultaneously at both LERs, MS-W SHALL be
considered as having higher priority than MS-P at both LERs. considered as having higher priority than MS-P at both LERs.
When SD-W and SD-P occur simultaneously at both LERs, In this case, When SD-W and SD-P occur simultaneously at both LERs, the SD on the
the SD on the standby path (the path from which the selector does not standby path (the path from which the selector does not select the
select the user data traffic) is considered as having higher priority user data traffic) is considered as having higher priority than the
than the SD on the active path (the path from which the selector SD on the active path (the path from which the selector selects the
selects the user data traffic) regardless of its origin (local or user data traffic) regardless of its origin (local or remote
remote message). Therefore, no unnecessary protection switching is message). Therefore, no unnecessary protection switching is
performed and the user data traffic continues to be selected from the performed and the user data traffic continues to be selected from the
active path. Giving the higher priority to the SD on the standby active path.
path SHALL also be applied to the Local Request logic when two SDs
for different paths happen to be presented to the Local Request logic
exactly at the same time.
The change of the PSC control logic including state machine due to In the preceding paragraphs, the "simultaneously" refers to the case
the support of protection against SD is incorporated into the PSC a sent SD (or MS) request has not been confirmed by the remote end in
control logic description when all the capabilities are enabled in bidirectional protection switching. When a local node that has
Section 10 and Section 11. transmitted a SD message receives a SD (or MS) message that indicates
a different value of data path (Path) field than the value of the
Path field in the transmitted SD (or MS) message, both the local and
the remote SD requests are considered to occur simultaneously.
8. Capability 5: Support of Exercise Command The change of the PSC Control logic including the state machine due
to the support of protection against SD is incorporated into the PSC
Control logic description in Section 10 and Section 11 when all the
capabilities are enabled.
Exercise is a command to test if the PSC communication is operating 8. Capability 5: Support of EXER command
correctly. More specifically, the Exercise is to test and validate
the linear protection mechanism and PSC protocol including the
aliveness of the Local Request logic, the PSC state machine and the
PSC message generation and reception, and the integrity of the
protection path, without triggering the actual traffic switching. It
is used while the working path is either carrying the traffic or not.
It is lower priority than any "real" switch request. It is only
valid in bidirectional switching, since this is the only place where
one can get a meaningful test by looking for a response.
This command is documented in R84 of [RFC5654] and it has been EXER is a command to test if the PSC communication is operating
identified as a requirement from ITU-T. correctly. More specifically, EXER is to test and validate the
linear protection mechanism and PSC protocol including the aliveness
of the Local Request logic, the PSC state machine and the PSC message
generation and reception, and the integrity of the protection path,
without triggering the actual traffic switching. It is used while
the working path is either carrying the traffic or not. It has lower
priority than any "real" switch request. It is only valid in
bidirectional switching, since this is the only place where one can
get a meaningful test by looking for a response.
This command is documented in R84 of RFC 5654 [RFC5654].
A received EXER message indicates that the remote end point is A received EXER message indicates that the remote end point is
operating under an operator command to validate the protection operating under an operator command to validate the protection
mechanism and PSC protocol including the aliveness of the Local mechanism and PSC protocol including the aliveness of the Local
Request logic, the PSC state machine and the PSC message generation Request logic, the PSC state machine and the PSC message generation
and reception, and the integrity of the protection path, without and reception, and the integrity of the protection path, without
triggering the actual traffic switching. The valid response to EXER triggering the actual traffic switching. The valid response to EXER
message will be an Reverse Request (RR) with the corresponding FPath message is an Reverse Request (RR) with the corresponding FPath and
and Path numbers. The near end will signal a Reverse Request (RR) Path numbers. The local LER SHALL signal a RR only in response to an
only in response to an EXER command from the far end. EXER command from the remote LER.
When Exercise commands are input at both ends, an EXER, instead of When Exercise commands are input at both ends, an EXER, instead of
RR, is transmitted from both ends. RR, SHALL be transmitted from both ends.
The following PSC Requests should be added to PSC Request field to The following PSC Requests SHALL be added to PSC Request field to
support Exercise: support Exercise:
(TBD2) Exercise - indicates that the transmitting end point is (3) Exercise - indicates that the transmitting end point is
exercising the protection channel and mechanism. FPath and Path exercising the protection channel and mechanism. FPath and Path
are set to the same value of the NR, RR or DNR request that EXER are set to the same value of the No Request (NR), RR or DNR
replaces. request that EXER replaces.
(TBD1) Reverse Request - indicates that the transmitting end point (2) Reverse Request - indicates that the transmitting end point is
is responding to an EXER command from the far end. FPath and Path responding to an EXER command from the remote LER. FPath and Path
are set to the same value of the NR, RR or DNR request that EXER are set to the same value of the NR or DNR request that RR
replaces. replaces.
The priority of Exercise should be inserted between the priorities of The priority of Exercise SHALL be inserted between the priorities of
WTR Expires and No Request. WTR Expires and No Request.
9. Capabilities and Modes 9. Capabilities and modes
9.1. Capabilities 9.1. Capabilities
A Capability is an individual behavior whose use is signalled in a A Capability is an individual behavior whose use is signaled in a
Capabilities TLV, which is placed in Optional TLVs field inside PSC Capabilities TLV, which is placed in Optional TLVs field inside the
messages shown in Figure 2 of [RFC6378]. The format of the PSC message shown in Figure 2 of RFC 6378 [RFC6378]. The format of
Capabilities TLV is: the Capabilities TLV is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = Capabilities | Length | | Type = Capabilities | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value = Options | | Value = Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The value of the Type field is TBD3 pending IANA allocation. Figure 1: Format of Capabilities TLV
The value of the Length field is the length of the Options Value, and The value of the Type field is TBD pending IANA allocation.
is in octets.
The Value of the Capabilities TLV can be any length, as long as it is The value of the Length field is the length of the Flags field in
a multiple of 4 octets. The length of the Value field MUST be the octets. The length of the Flags field MUST be a multiple of 4 octets
minimum required to signal all the required capabilities. Section 4 and MUST be the minimum required to signal all the required
to Section 8 discuss five capabilities that are signalled using the 5 capabilities.
most significant bits; if a node wishes to signal these five
capabilities, it MUST send an Options Value of 4 octets. A node Section 4 to Section 8 discuss five capabilities that are signaled
would send an Options Value greater than 4 octets only if it had more using the five most significant bits; if a node wishes to signal
than 32 Capabilities to indicate. All unused bits MUST be set to these five capabilities, it MUST send a Flags field of 4 octets. A
zero. node would send a Flags field greater than 4 octets only if it had
more than 32 Capabilities to indicate. All unused bits MUST be set
to zero.
If the bit assigned for an individual capability is set to 1, it If the bit assigned for an individual capability is set to 1, it
indicates the sending node's intent to use that capability in the indicates the sending node's intent to use that capability in the
protected domain. If a bit is set to 0, the sending node does not protected domain. If a bit is set to 0, the sending node does not
intend to use the indicated capability in the protected domain. Note intend to use the indicated capability in the protected domain. Note
that it is not possible to distinguish between the intent not to use that it is not possible to distinguish between the intent not to use
a capability and a node's complete non-support (i.e. lack of a capability and a node's complete non-support (i.e., lack of
implementation) of a given capability. implementation) of a given capability.
This document defines five specific capabilities that are described This document defines five specific capabilities that are described
from Section 4 to Section 8. Each capability is assigned bit as from Section 4 to Section 8. Each capability is assigned bit as
follows: follows:
0x80000000: priority modification 0x80000000: priority modification
0x40000000: modification of non-revertive behavior 0x40000000: non-revertive behavior modification
0x20000000: support of MS-W command
0x20000000: support of Manual Switch to Working (MS-W) command 0x10000000: support of protection against SD
0x10000000: support of protection against Signal Degrade (SD) 0x08000000: support of EXER command
0x08000000: support of Exercise command If all the five capabilities should be used, an LER SHALL set
0xF8000000 in the Flags field.
9.1.1. Sending the Capabilities TLV 9.1.1. Sending the Capabilities TLV
PSC sends messages in response to external events and in periodic PSC sends messages in response to external events and in periodic
retransmission of current status. It may be expensive to send and to retransmission of current status. It may be expensive to send and to
parse an Capabilities TLV attached to a packet intended to trigger a parse an Capabilities TLV attached to a packet intended to trigger a
protection switch or other real- time behavior. However, if a node protection switch or other real-time behavior. However, if a node
does not periodically send its Capabilities TLV, the receiving node does not periodically send its Capabilities TLV, the receiving node
cannot discriminate a deliberate omission of the Capabilities TLV for cannot discriminate a deliberate omission of the Capabilities TLV for
performance reasons from an accidental omission due to an performance reasons from an accidental omission due to an
implementation issue. To guard against this, a node MUST include its implementation issue. To guard against this, a node MUST include its
Capabilities TLV in every PSC message that it sends. Capabilities TLV in every PSC message that it sends.
9.1.2. Receiving the Capabilities TLV 9.1.2. Receiving the Capabilities TLV
A node MUST establish a receive timer for the Capabilities TLV. By A node MUST establish a receive timer for the Capabilities TLV. By
default this MUST be 3.5 times the periodic retransmission timer of default this MUST be 3.5 times the periodic retransmission timer of
five seconds - i.e., 17.5 seconds. Both the periodic retransmission five seconds - i.e., 17.5 seconds. Both the periodic retransmission
time and the timeout SHOULD be configurable by the operator. When a time and the timeout SHOULD be configurable by the operator. When a
node receives a Capabilities TLV it resets the timer to 17.5 seconds. node receives a Capabilities TLV it resets the timer to 17.5 seconds.
If the timer expires, the node behaves as in Section 9.1.3. If the timer expires, the node behaves as in Section 9.1.3.
[Editor's note: In other packet transport protection technologies,
Failure of Protocol defect (dFOP) is declared when no protocol
message is received on the protection path during at least 3.5 times
the periodic message transmission interval (i.e., at least 17.5
seconds) and there is no defect on the protection transport entity.
As the "Capabilities TLV" is included in the PSC message, this error
of not receiving the Capabilities TLV can be covered by dFOP. To be
discussed.]
When a node receives a Capabilities TLV it MUST compare it to its When a node receives a Capabilities TLV it MUST compare it to its
most recent transmitted Capabilities TLV. If the two are equal, the most recent transmitted Capabilities TLV. If the two are equal, the
protected domain is said to be running in the mode indicated by that protected domain is said to be running in the mode indicated by that
set of capabilities (see Section 9.2). If the sent and received set of capabilities (see Section 9.2). If the sent and received
Capabilities TLVs are not equal, this indicates a capabilities Capabilities TLVs are not equal, this indicates a capabilities
mismatch. When this happens, the node MUST alert the operator and mismatch. When this happens, the node MUST alert the operator and
MUST behave as in Section 9.1.3. MUST behave as in Section 9.1.3.
9.1.3. Handling Capabilities TLV errors 9.1.3. Handling Capabilities TLV errors
This section covers the two possible errors - a TLV timeout and a TLV This section covers the two possible errors - a TLV timeout and a TLV
mismatch - and the error handling procedures in both cases. mismatch - and the error handling procedures in both cases.
9.1.3.1. Capabilities TLV Timeout 9.1.3.1. Capabilities TLV Timeout
If the Capabilities TLV receive timer expires, a node is said to have If the Capabilities TLV receive timer expires and there is no defect
timed out. When this happens, the node MUST alert the operator and on the protection path, the node MUST alert the operator and MUST
MUST behave as in Section 9.1.3.3. behave as in Section 9.1.3.3.
9.1.3.2. Capabilities TLV Mismatch 9.1.3.2. Capabilities TLV Mismatch
If the sent and received Capabilities TLVs are not equal, this If the sent and received Capabilities TLVs are not equal, this
indicates a capabilities mismatch. When this happens, the node MUST indicates a capabilities mismatch. When this happens, the node MUST
alert the operator and MUST behave as in Section 9.1.3.3. A node MAY alert the operator and MUST behave as in Section 9.1.3.3. A node MAY
retain the received TLV for logging, alert or debug purposes. retain the received TLV for logging, alert or debug purposes.
9.1.3.3. Handling Capabilities TLV error conditions 9.1.3.3. Handling Capabilities TLV error conditions
When a node enters in Capabilities protocol error conditions, the When a node enters in Capabilities protocol error conditions, the
following actions MUST be taken: following actions MUST be taken:
1. Indicate the error condition (e.g., either mismatch or timeout) 1. Indicate the error condition (e.g., either mismatch or timeout)
to the operator by the usual alert mechanisms (e.g., syslog). to the operator by the usual alert mechanisms (e.g., syslog).
2. Not make any state transitions based on the contents of any PSC 2. Not make any state transitions based on the contents of any PSC
Messages messages
To expand on point 2 - assume node A is receiving NR(0,0) from its To expand on point 2 - assume node A is receiving NR(0,0) from its
PSC peer node Z and is also receiving a mismatched set of PSC peer node Z and is also receiving a mismatched set of
capabilities (e.g., received 0x4, transmitted 0x5). If node Z capabilities (e.g., received 0x20000000, transmitted 0xA0000000). If
detects a local SF-W and wants to initiate a protection switch (that node Z detects a local SF-W and wants to initiate a protection switch
is, by sending SF(1,1)), node A MUST NOT react to this input by (that is, by sending SF(1,1)), node A MUST NOT react to this input by
changing its state. A node MAY increase the severity or urgency of changing its state. A node MAY increase the severity or urgency of
its alarms to the operator, but until the operator resolves the its alarms to the operator, but until the operator resolves the
mismatch in the Capabilities TLV the protected domain will likely mismatch in the Capabilities TLV the protected domain will likely
operate in an inconsistent state. operate in an inconsistent state.
9.2. Modes 9.2. Modes
A Mode is a given set of Capabilities. Modes are shorthand; A Mode is a given set of Capabilities. Modes are shorthand;
referring to a set of capabilities by their individual values or by referring to a set of capabilities by their individual values or by
the name of their mode does not change the protocol behavior. This the name of their mode does not change the protocol behavior. This
document defines two modes - PSC and APS. document defines two modes - PSC and APS.
9.2.1. PSC Mode 9.2.1. PSC Mode
PSC Mode is defined as the lack of any Capabilities - that is, a PSC Mode is defined as the lack of any Capabilities - that is, a
Capabilities set of 0x0. It is the behavior specified in RFC6378. Capabilities set of 0x0. It is the behavior specified in RFC 6378.
There are two ways to declare PSC Mode. A node can send a There are two ways to declare PSC Mode. A node can send a
Capabilities TLV of 0x0, or it can send no Capabilities TLV at all. Capabilities TLV of 0x0, or it can send no Capabilities TLV at all.
This is further explored in Section 9.3. This is further explored in Section 9.3.
9.2.2. APS Mode 9.2.2. APS Mode
APS Mode is defined as the use of all of the five specific APS Mode is defined as the use of all the five specific capabilities,
capabilities, which are described from Section 4 to Section 8 in this which are described from Section 4 to Section 8 in this document.
document. APS Mode is indicated with a Value of 0xF8000000. APS Mode is indicated with the Flags value of 0xF8000000.
9.3. Backward compatibility 9.3. Backward compatibility
As defined in Section 9.2.1, PSC Mode is indicated either with a As defined in Section 9.2.1, PSC Mode is indicated either with a
Capabilities TLV of 0x0 or the lack of Capabilities TLV. This is to Capabilities TLV of 0x0 or the lack of Capabilities TLV. This is to
allow backward compatibility between two nodes - one which can send allow backward compatibility between two nodes - one which can send
the Capabilities TLV, and one which cannot. the Capabilities TLV, and one which cannot.
[RFC6378] does not define how to handle an unrecognized TLV. There RFC 6378 does not define how to handle an unrecognized TLV. There
may be some implementations that silently discard an unrecognized may be some implementations that silently discard an unrecognized
TLV, and some that take more drastic steps like refusing to allow PSC TLV, and some that take more drastic steps like refusing to allow PSC
to operate. Thus, a node which has the ability to send and receive to operate. Thus, a node which has the ability to send and receive
the PSC Mode Capabilities TLV MUST be able to both send the PSC Mode the PSC Mode Capabilities TLV MUST be able to both send the PSC Mode
Capabilities TLV and send no Capabilities TLV at all. An Capabilities TLV and send no Capabilities TLV at all. An
implementation MUST be configurable between these two choices. implementation MUST be configurable between these two choices.
One question that arises from this dual definition of PSC Mode is, One question that arises from this dual definition of PSC Mode is,
what happens if a node which was sending a non-null Capabilities TLV what happens if a node which was sending a non-null Capabilities TLV
(e.g., APS Mode) sends PSC packets without any Capabilities TLV? (e.g., APS Mode) sends PSC packets without any Capabilities TLV?
This case is handled as follows: This case is handled as follows:
If a node has never, during the life of a PSC session, received a If a node has never, during the life of a PSC session, received a
Capabilities TLV from a neighbour, the lack of a Capabilities TLV is Capabilities TLV from its peer, the lack of a Capabilities TLV is
treated as receipt of a PSC Capabilities TLV. This allows for treated as receipt of a PSC Capabilities TLV. This allows for
interop between nodes which support the PSC Mode TLV and nodes which interoperability between nodes which support the PSC Mode TLV and
do not, and are thus implicitly operating in PSC Mode. nodes which do not, and are thus implicitly operating in PSC Mode.
If a node has received a non-null Capabilities TLV (e.g., APS Mode) If a node has received a non-null Capabilities TLV (e.g., APS Mode)
during the life of a PSC session and then receives a PSC packet with during the life of a PSC session and then receives a PSC packet with
no Capabilities TLV, the receiving node MUST treat the lack of no Capabilities TLV, the receiving node MUST treat the lack of
Capabilities TLV as simply a lack of refresh. That is, the receipt Capabilities TLV as simply a lack of refresh. That is, the receipt
of a PSC packet with no Capabilities TLV simply does not reset the of a PSC packet with no Capabilities TLV simply does not reset the
receive timer defined in Section 9.1.2. receive timer defined in Section 9.1.2.
10. PSC Protocol in APS Mode 10. PSC Protocol in APS Mode
This section and Section 11 defines the behavior of PSC protocol when This section and Section 11 define the behavior of PSC protocol when
all of the aforementioned capabilities are enabled, i.e., APS mode. all of the aforementioned capabilities are enabled, i.e., APS mode.
10.1. Request field in PSC protocol message 10.1. Request field in PSC protocol message
The values of "Request" field in the PSC protocol message, which is The values of "Request" field in PSC protocol message, which is shown
shown in Figure 2 of [RFC6378], are defined as follows: in Figure 2 of RFC 6378 [RFC6378], are redefined as follows:
(14) Lockout of protection (14) Lockout of protection
(12) Forced Switch (12) Forced Switch
(10) Signal Fail (10) Signal Fail
(7) Signal Degrade (7) Signal Degrade
(5) Manual Switch (5) Manual Switch
(4) Wait-to-Restore (4) Wait-to-Restore
(TBD2) Exercise (3) Exercise
(TBD1) Reverse Request (2) Reverse Request
(1) Do-not-Revert (1) Do-not-Revert
(0) No Request (0) No Request
10.2. Priorities of local inputs and remote requests 10.2. Priorities of local inputs and remote requests
Based on the description in Section 3 and Section 4.3.2 in [RFC6378], Based on the description in Section 3 and Section 4.3.2 in RFC 6378,
the priorities of multiple outstanding local inputs are evaluated in the priorities of multiple outstanding local inputs are evaluated in
Local Request logic unit, where the highest priority local request is the Local Request logic, where the highest priority local input
determined. This high-priority local request is passed to the PSC (highest local request) is determined. This highest local request is
Control logic, that will determine the higher priority input (top passed to the PSC Control logic, that will determine the higher
priority global request) between the highest priority local input and priority input (top priority global request) between the highest
the last received remote message. When a remote message comes to the local request and the last received remote message. When a remote
PSC Control logic, the top priority global request is determined message comes to the PSC Control logic, the top priority global
between this remote message and the highest priority local input request is determined between this remote message and the highest
which is present. The top priority global request is used to local request which is present. The top priority global request is
determine the state transition, which is described in Section 11. used to determine the state transition, which is described in
Section 11.
The priorities for both local and remote requests are defined as The priorities for both local and remote requests are defined as
follows from highest to lowest: follows from highest to lowest:
o Operator Clear (Local only) o Operator Clear (Local only)
o Lockout of protection (Local and Remote) o Lockout of protection (Local and Remote)
o Clear Signal Fail/Degrade (Local only) o Clear Signal Fail or Degrade (Local only)
o Signal Fail on Protection path (Local and Remote) o Signal Fail on Protection path (Local and Remote)
o Forced Switch (Local and Remote) o Forced Switch (Local and Remote)
o Signal Fail on Working path (Local and Remote) o Signal Fail on Working path (Local and Remote)
o Signal Degrade on either Protection path or Working path (Local o Signal Degrade on either Protection path or Working path (Local
and Remote) and Remote)
skipping to change at page 18, line 40 skipping to change at page 19, line 20
o WTR (Remote only) o WTR (Remote only)
o Exercise (Local and Remote) o Exercise (Local and Remote)
o Reverse Request (Remote only) o Reverse Request (Remote only)
o Do-Not-Revert (Remote only) o Do-Not-Revert (Remote only)
o No Request (Remote and Local) o No Request (Remote and Local)
The remote request from the far-end LER is assigned a priority just Note that the "Local only" requests are not signaled to the remote
LER. Likewise, the "Remote only" requests do not exist in the Local
Request logic as local inputs. For example, the priority of WTR only
applies to the received WTR message, which is generated from the
remote LER. The remote LER that is running the WTR timer in the WTR
state has no local request.
The remote request from the remote LER is assigned a priority just
below the same local request. However, for the equal priority below the same local request. However, for the equal priority
requests, such as Signal Degrade on either Working or protection and requests, such as SD and MS, the following equal priority resolution
Manual Switch to either Protection or Working path, the following rules are defined:
equal priority resolution rules are defined:
o If two local inputs having same priority but requesting different o If two local inputs having the same priority but requesting
action come to the Local Request logic, then the input coming different action come to the Local Request logic, then the input
first SHALL be considered to have a higher priority than the other coming first SHALL be considered to have a higher priority than
coming later (first-come, first-served). the other coming later (first-come, first-served).
o If the LER receives both a local input and a remote message with o If the PSC Control logic has both the highest local request and a
the same priority and requesting the same action, i.e., the same remote message with the same priority and requesting the same
PSC Request Field and the same FPath value, then the local input action, i.e., the same PSC Request Field and the same FPath value,
SHALL be considered to have a higher priority than the remote then the local input SHALL be considered to have a higher priority
message. than the remote message.
o If the LER receives both a local input and a remote message with o If the PSC Control logic has both the highest local request and a
the same priority but requesting different actions, i.e., the same remote message with the same priority but requesting different
PSC Request Field but different FPath value, then the first-come, action and the remote message exists when the highest local
first-served rule SHALL be applied. If the remote message comes request comes to the PSC Control logic, the highest local request
first, then the state SHALL be a remote state and subsequent local is ignored and the remote Request SHALL be the top priority global
input is ignored. However, if the local input comes first, the request.
first-come, first-served rule cannot be applied and must be viewed
as simultaneous condition. This is because the subsequent remote
message will not be an acknowledge of the local input by the far-
end node. In this case, the priority SHALL be determined by rules
for each simultaneous condition.
o If the LER receives both MS-P and MS-W requests as both local o If the PSC Control logic has both the highest local request and a
input and remote message and the LER is in a local Switching remote message with the same priority but requesting different
administrative state, then the MS-W request SHALL be considered to action and the highest local request exists when the remote
have a higher priority than the MS-P request. message comes to the PSC Control logic, the top priority global
request SHALL be determined by the following rules for each
simultaneous condition:
o If the LER receives both SD-P and SD-W requests as both local o For simultaneous MS requests, the MS-W request SHALL be considered
input and remote message and the LER is in a local state, then the to have a higher priority than the MS-P request. The LER that has
SD on the standby path (the path from which the selector does not local MS-W request SHALL maintain the local MS-W request as the
select the user data traffic) SHALL be considered as having higher top priority global request, but the other LER that has local MS-P
priority than the SD on the active path (the path from which the request SHALL clear the MS-P command and internally generate
selector selects the user data traffic) regardless of its origin "Operator Clear" request.
(local or remote message). This rule of giving the higher
priority to the SD on the standby path SHALL also be applied to o For simultaneous SD requests, the SD on the standby path (the path
the Local Request logic when two SDs for different paths happen to from which the selector does not select the user data traffic)
be presented to the Local Request logic exactly at the same time. SHALL be considered as having higher priority than the SD on the
active path (the path from which the selector selects the user
data traffic) regardless of its origin (local or remote message).
The LER that has the SD on the standby path SHALL maintain the
local SD on the standby path request as the top priority global
request. The other LER that has local SD on the active path SHALL
use the remote SD on the standby path as the top priority global
request to lookup the state transition table. The differentiation
of the active and standby paths is based upon which path had been
used for the user data traffic at the time just before an LER
selected its local SD as the top priority global request.
No Request is another exception to the rule of assigning a remote
request a priority just below the same local request. Since a
received NR message needs to be used in the state transition table
lookup when there is no outstanding local request, the received
remote NR request SHALL be the top priority global request when there
is no request in the local LER.
10.3. Acceptance and retention of local inputs
A local input indicating a defect, such as SF-P, SF-W, SD-P and SD-W,
SHALL be accepted and retained persistently in the Local Request
logic as long as the defect condition exists. If there is any higher
priority local input than the local defect input, the higher priority
local input is passed to the PSC Control logic as the highest local
request, but the local defect input cannot be removed but remains in
the Local Request logic. When the higher priority local input
disappears, the local defect will become the highest local request if
the defect condition still exists.
Operator Clear command, SFDc and WTR Expires are not persistent.
Once they appear to the Local Request logic and complete the
operation, they SHALL be disappeared.
Operator LO, FS, MS, and EXER commands SHALL be rejected if there is
any higher priority local input in the Local Request logic. If a new
operator command is accepted, any previous lower-priority local
operator command SHALL be cancelled. When any higher priority remote
request is received, a lower-priority local operator command SHALL be
cancelled. The cancelled operator command is forgotten and will
never return, unless the operator reissues the command.
11. State Transition Tables in APS Mode 11. State Transition Tables in APS Mode
When there is a change in the highest-priority local request or in When there is a change in the highest local request or in remote PSC
remote PSC messages, the top priority global request is evaluated and messages, the top priority global request SHALL be evaluated and the
the state transition tables are looked up in PSC control logic. The state transition tables SHALL be looked up in the PSC Control logic.
following rules are applied to the operation related to the state The following rules are applied to the operation related to the state
transition table lookup. transition table lookup.
o If the top priority global request, which determines the state o If the top priority global request, which determines the state
transition, is the highest priority local input, the local state transition, is the highest local request, the local state
transition table SHALL be used to decide the next state of the transition table in Section 11.1 SHALL be used to decide the next
LER. Otherwise, remote messages state transition table SHALL be state of the LER. Otherwise, remote messages state transition
used. table in Section 11.2 SHALL be used.
o If in remote state, the highest local defect condition (SF-P, o If in remote state, the highest local defect condition (SF-P,
SF-W, SD-P or SD-W) SHALL always be reflected in the Request Field SF-W, SD-P or SD-W) SHALL always be reflected in the Request Field
and Fpath. and Fpath.
o Operator Clear command, Clear SF/SD (SFc) and WTR Expires are not
persistent. Once they appear to the local priority logic and
complete the operation, they will be disappeared.
o For the LER currently in the local state, if the top priority o For the LER currently in the local state, if the top priority
global request is changed to OC or SFc causing the next state to global request is changed to OC or SFDc causing the next state to
be Normal, WTR or DNR, then all the local and remote requests be Normal, WTR or DNR, then all the local and remote requests
should be re-evaluated as if the LER is in the state specified in should be re-evaluated as if the LER is in the state specified in
the footnotes to the state transition tables, before deciding the the footnotes to the state transition tables, before deciding the
final state. This re-evaluation is an internal operation confined final state. This re-evaluation is an internal operation confined
within the local LER, and PSC messages are generated according to within the local LER, and PSC messages are generated according to
the final state. the final state.
o The WTR timer is started only when the LER which has recovered o The WTR timer is started only when the LER which has recovered
from a local failure/degradation enters the WTR state. An LER from a local failure/degradation enters the WTR state. An LER
which is entering into the WTR state due to a remote WTR message which is entering into the WTR state due to a remote WTR message
does not start the WTR timer. does not start the WTR timer. The WTR timer is stopped when any
local or remote request triggers the state change out of the WTR
state.
The extended states, as they appear in the table, are as follows: The extended states, as they appear in the table, are as follows:
N Normal state N Normal state
UA:LO:L Unavailable state due to local LO command UA:LO:L Unavailable state due to local LO command
UA:P:L Unavailable state due to local SF-P UA:P:L Unavailable state due to local SF-P
UA:DP:L Unavailable state due to local SD-P UA:DP:L Unavailable state due to local SD-P
UA:LO:R Unavailable state due to remote LO message UA:LO:R Unavailable state due to remote LO message
UA:P:R Unavailable state due to remote SF-P message UA:P:R Unavailable state due to remote SF-P message
UA:DP:L Unavailable state due to local SD-P UA:DP:R Unavailable state due to remote SD-P message
PF:W:L Protecting failure state due to local SF-W PF:W:L Protecting failure state due to local SF-W
PF:DW:L Protecting failure state due to local SD-W PF:DW:L Protecting failure state due to local SD-W
PF:W:R Protecting failure state due to remote SF-W message PF:W:R Protecting failure state due to remote SF-W message
PF:DW:R Protecting failure state due to remote SD-W message PF:DW:R Protecting failure state due to remote SD-W message
SA:F:L Switching administrative state due to local FS command SA:F:L Switching administrative state due to local FS command
SA:MW:L Switching administrative state due to local MS-W command SA:MW:L Switching administrative state due to local MS-W command
SA:MP:L Switching administrative state due to local MS-P command SA:MP:L Switching administrative state due to local MS-P command
SA:F:R Switching administrative state due to remote FS message SA:F:R Switching administrative state due to remote FS message
SA:MW:R Switching administrative state due to remote MS-W message SA:MW:R Switching administrative state due to remote MS-W message
SA:MP:R Switching administrative state due to remote MS-P message SA:MP:R Switching administrative state due to remote MS-P message
skipping to change at page 21, line 25 skipping to change at page 23, line 22
UA:P:R highest local request(local FPath,0) UA:P:R highest local request(local FPath,0)
UA:DP:R highest local request(local FPath,0) UA:DP:R highest local request(local FPath,0)
PF:W:L SF(1,1) PF:W:L SF(1,1)
PF:DW:L SD(1,1) PF:DW:L SD(1,1)
PF:W:R highest local request(local FPath,1) PF:W:R highest local request(local FPath,1)
PF:DW:R highest local request(local FPath,1) PF:DW:R highest local request(local FPath,1)
SA:F:L FS(1,1) SA:F:L FS(1,1)
SA:MW:L MS(0,0) SA:MW:L MS(0,0)
SA:MP:L MS(1,1) SA:MP:L MS(1,1)
SA:F:R highest local request(local FPath,1) SA:F:R highest local request(local FPath,1)
SA:MW:R highest local request(local FPath,0) SA:MW:R NR(0,0)
SA:MP:R highest local request(local FPath,1) SA:MP:R NR(0,1)
WTR WTR(0,1) WTR WTR(0,1)
DNR DNR(0,1) DNR DNR(0,1)
E::L EXER(0,x), where x is the existing Path value E::L EXER(0,x), where x is the existing Path value
when Exercise command is issued. when Exercise command is issued.
E::R RR(0,x), where x is the existing Path value E::R RR(0,x), where x is the existing Path value
when RR message is generated. when RR message is generated.
11.1. State transition by local inputs Some operation examples of the APS mode are shown in Appendix D.
| OC | LO | SFc | SF-P | FS | SF-W | 11.1. State transition by local inputs
--------+-----+---------+-----+--------+--------+--------+ | OC | LO | SFDc | SF-P | FS | SF-W |
N | i | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L | --------+-----+---------+------+--------+--------+--------+
UA:LO:L | (1) | i | i | i | i | i | N | i | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L |
UA:P:L | i | UA:LO:L | (1) | i | i | i | UA:LO:L | (1) | i | i | i | i | i |
UA:DP:L | i | UA:LO:L | (1) | UA:P:L | SA:F:L | PF:W:L | UA:P:L | i | UA:LO:L | (1) | i | i | i |
UA:LO:R | i | UA:LO:L | i | UA:P:L | i | PF:W:L | UA:DP:L | i | UA:LO:L | (1) | UA:P:L | SA:F:L | PF:W:L |
UA:P:R | i | UA:LO:L | i | UA:P:L | PF:W:L | PF:W:L | UA:LO:R | i | UA:LO:L | i | UA:P:L | i | PF:W:L |
UA:DP:R | i | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L | UA:P:R | i | UA:LO:L | i | UA:P:L | i | PF:W:L |
PF:W:L | i | UA:LO:L | (2) | UA:P:L | SA:F:L | i | UA:DP:R | i | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L |
PF:DW:L | i | UA:LO:L | (2) | UA:P:L | SA:F:L | PF:W:L | PF:W:L | i | UA:LO:L | (2) | UA:P:L | SA:F:L | i |
PF:W:R | i | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L | PF:DW:L | i | UA:LO:L | (2) | UA:P:L | SA:F:L | PF:W:L |
PF:DW:R | i | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L | PF:W:R | i | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L |
SA:F:L | (3) | UA:LO:L | i | UA:P:L | i | i | PF:DW:R | i | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L |
SA:MW:L | (1) | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L | SA:F:L | (3) | UA:LO:L | i | UA:P:L | i | i |
SA:MP:L | (3) | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L | SA:MW:L | (1) | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L |
SA:F:R | i | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L | SA:MP:L | (3) | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L |
SA:MW:R | i | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L | SA:F:R | i | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L |
SA:MP:R | i | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L | SA:MW:R | i | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L |
WTR | i | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L | SA:MP:R | i | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L |
DNR | i | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L | WTR | (4) | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L |
E::L | (4) | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L | DNR | i | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L |
E::R | i | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L | E::L | (5) | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L |
E::R | i | UA:LO:L | i | UA:P:L | SA:F:L | PF:W:L |
| SD-P | SD-W | MS-W | MS-P | WTRExp | EXER | SD-P | SD-W | MS-W | MS-P | WTRExp | EXER
--------+---------+---------+---------+---------+--------+------ --------+---------+---------+---------+---------+--------+------
N | UA:DP:L | PF:DW:L | SA:MW:L | SA:MP:L | i | E::L N | UA:DP:L | PF:DW:L | SA:MW:L | SA:MP:L | i | E::L
UA:LO:L | i | i | i | i | i | i UA:LO:L | i | i | i | i | i | i
UA:P:L | i | i | i | i | i | i UA:P:L | i | i | i | i | i | i
UA:DP:L | i | i | i | i | i | i UA:DP:L | i | i | i | i | i | i
UA:LO:R | UA:DP:L | PF:DW:L | i | i | i | i UA:LO:R | UA:DP:L | PF:DW:L | i | i | i | i
UA:P:R | UA:DP:L | PF:DW:L | i | i | i | i UA:P:R | UA:DP:L | PF:DW:L | i | i | i | i
UA:DP:R | UA:DP:L | PF:DW:L | i | i | i | i UA:DP:R | UA:DP:L | PF:DW:L | i | i | i | i
skipping to change at page 22, line 35 skipping to change at page 25, line 4
SA:F:L | i | i | i | i | i | i SA:F:L | i | i | i | i | i | i
SA:MW:L | UA:DP:L | PF:DW:L | i | i | i | i SA:MW:L | UA:DP:L | PF:DW:L | i | i | i | i
SA:MP:L | UA:DP:L | PF:DW:L | i | i | i | i SA:MP:L | UA:DP:L | PF:DW:L | i | i | i | i
SA:F:R | UA:DP:L | PF:DW:L | i | i | i | i SA:F:R | UA:DP:L | PF:DW:L | i | i | i | i
SA:MW:R | UA:DP:L | PF:DW:L | SA:MW:L | i | i | i SA:MW:R | UA:DP:L | PF:DW:L | SA:MW:L | i | i | i
SA:MP:R | UA:DP:L | PF:DW:L | i | SA:MP:L | i | i SA:MP:R | UA:DP:L | PF:DW:L | i | SA:MP:L | i | i
WTR | UA:DP:L | PF:DW:L | SA:MW:L | SA:MP:L | (6) | i WTR | UA:DP:L | PF:DW:L | SA:MW:L | SA:MP:L | (6) | i
DNR | UA:DP:L | PF:DW:L | SA:MW:L | SA:MP:L | i | E::L DNR | UA:DP:L | PF:DW:L | SA:MW:L | SA:MP:L | i | E::L
E::L | UA:DP:L | PF:DW:L | SA:MW:L | SA:MP:L | i | i E::L | UA:DP:L | PF:DW:L | SA:MW:L | SA:MP:L | i | i
E::R | UA:DP:L | PF:DW:L | SA:MW:L | SA:MP:L | i | E::L E::R | UA:DP:L | PF:DW:L | SA:MW:L | SA:MP:L | i | E::L
NOTES:
11.2. State transition by remote messages (1) Re-evaluate to determine final state as if the LER is in the
Normal state.
(2) In the case that both local input after SFDc and the last
received remote message are no requests, the LER enters into the
WTR state when the domain is configured for revertive behavior,
or the LER enters into the DNR state when the domain is
configured for non-revertive behavior. In all the other cases,
re-evaluate to determine the final state as if the LER is in the
Normal state.
(3) Re-evaluate to determine final state as if the LER is in the
Normal state when the domain is configured for revertive
behavior, or as if the LER is in the DNR state when the domain
is configured for non-revertive behavior,
(4) Remain in WTR and send NR(0,1). Stop the WTR timer if it is
running.
(5) If Path value is 0, re-evaluate to determine final state as if
the LER is in the Normal state. If Path value is 1, re-evaluate
to determine final state as if the LER is in the DNR state.
(6) Remain in WTR and send NR(0,1).
11.2. State transition by remote messages
| LO | SF-P | FS | SF-W | SD-P | SD-W | | LO | SF-P | FS | SF-W | SD-P | SD-W |
--------+---------+--------+--------+--------+---------+---------+ --------+---------+--------+--------+--------+---------+---------+
N | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R | N | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R |
UA:LO:L | i | i | i | i | i | i | UA:LO:L | i | i | i | i | i | i |
UA:P:L | UA:LO:R | i | i | i | i | i | UA:P:L | UA:LO:R | i | i | i | i | i |
UA:DP:L | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | i | (10) | UA:DP:L | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | i | (7) |
UA:LO:R | i | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R | UA:LO:R | i | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R |
UA:P:R | UA:LO:R | i | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R | UA:P:R | UA:LO:R | i | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R |
UA:DP:R | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | i | PF:DW:R | UA:DP:R | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | i | PF:DW:R |
PF:W:L | UA:LO:R | UA:P:R | SA:F:R | i | i | i | PF:W:L | UA:LO:R | UA:P:R | SA:F:R | i | i | i |
PF:DW:L | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | (11) | i | PF:DW:L | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | (8) | i |
PF:W:R | UA:LO:R | UA:P:R | SA:F:R | i | UA:DP:R | PF:DW:R | PF:W:R | UA:LO:R | UA:P:R | SA:F:R | i | UA:DP:R | PF:DW:R |
PF:DW:R | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R | PF:DW:R | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | i |
SA:F:L | UA:LO:R | UA:P:R | i | i | i | i | SA:F:L | UA:LO:R | UA:P:R | i | i | i | i |
SA:MW:L | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R | SA:MW:L | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R |
SA:MP:L | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R | SA:MP:L | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R |
SA:F:R | UA:LO:R | UA:P:R | i | PF:W:R | UA:DP:R | PF:DW:R | SA:F:R | UA:LO:R | UA:P:R | i | PF:W:R | UA:DP:R | PF:DW:R |
SA:MW:R | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R | SA:MW:R | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R |
SA:MP:R | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R | SA:MP:R | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R |
WTR | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R | WTR | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R |
DNR | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R | DNR | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R |
E::L | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R | E::L | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R |
E::R | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R | E::R | UA:LO:R | UA:P:R | SA:F:R | PF:W:R | UA:DP:R | PF:DW:R |
| MS-W | MS-P | WTR | EXER | RR | DNR | NR | MS-W | MS-P | WTR | EXER | RR | DNR | NR
--------+---------+---------+-----+------+----+-----+---- --------+---------+---------+-----+------+----+------+----
N | SA:MW:R | SA:MP:R | i | E::R | i | i | i N | SA:MW:R | SA:MP:R | i | E::R | i | i | i
UA:LO:L | i | i | i | i | i | i | i UA:LO:L | i | i | i | i | i | i | i
UA:P:L | i | i | i | i | i | i | i UA:P:L | i | i | i | i | i | i | i
UA:DP:L | i | i | i | i | i | i | i UA:DP:L | i | i | i | i | i | i | i
UA:LO:R | SA:MW:R | SA:MP:R | i | E::R | i | i | N UA:LO:R | SA:MW:R | SA:MP:R | i | E::R | i | i | N
UA:P:R | SA:MW:R | SA:MP:R | i | E::R | i | i | N UA:P:R | SA:MW:R | SA:MP:R | i | E::R | i | i | N
UA:DP:R | SA:MW:R | SA:MP:R | i | E::R | i | i | N UA:DP:R | SA:MW:R | SA:MP:R | i | E::R | i | i | N
PF:W:L | i | i | i | i | i | i | i PF:W:L | i | i | i | i | i | i | i
PF:DW:L | i | i | i | i | i | i | i PF:DW:L | i | i | i | i | i | i | i
PF:W:R | SA:MW:R | SA:MP:R | (7) | E::R | i | (8) | (5) PF:W:R | SA:MW:R | SA:MP:R | (9) | E::R | i | (10) | (11)
PF:DW:R | SA:MW:R | SA:MP:R | (7) | E::R | i | (8) | (5) PF:DW:R | SA:MW:R | SA:MP:R | (9) | E::R | i | (10) | (11)
SA:F:L | i | i | i | i | i | i | i SA:F:L | i | i | i | i | i | i | i
SA:MW:L | i | i | i | i | i | i | i SA:MW:L | i | i | i | i | i | i | i
SA:MP:L | i | i | i | i | i | i | i SA:MP:L | i | i | i | i | i | i | i
SA:F:R | SA:MW:R | SA:MP:R | i | E::R | i | DNR | N SA:F:R | SA:MW:R | SA:MP:R | i | E::R | i | DNR | N
SA:MW:R | i | SA:MP:R | i | E::R | i | i | N SA:MW:R | i | SA:MP:R | i | E::R | i | i | N
SA:MP:R | SA:MW:R | i | i | E::R | i | DNR | N SA:MP:R | SA:MW:R | i | i | E::R | i | DNR | N
WTR | SA:MW:R | SA:MP:R | i | i | i | i | (9) WTR | SA:MW:R | SA:MP:R | i | i | i | i | (12)
DNR | SA:MW:R | SA:MP:R | i | E::R | i | i | i DNR | SA:MW:R | SA:MP:R | i | E::R | i | i | i
E::L | SA:MW:R | SA:MP:R | i | i | i | i | i E::L | SA:MW:R | SA:MP:R | (13)| i | i | i | i
E::R | SA:MW:R | SA:MP:R | i | i | i | DNR | N E::R | SA:MW:R | SA:MP:R | i | i | i | DNR | N
NOTES: NOTES:
(1) Re-evaluate to determine final state as if the LER is in the (7) If the received SD-W message has Path=0, ignore the message. If
Normal state. the received SD-W message has Path=1, go to PF:DW:R state and
transmit SD(0,1)
(2) In the case that both local input and the last received remote (8) If the received SD-P message has Path=1, ignore the message. If
message are no request after the occurrence of SFc, the LER the received SD-P message has Path=0, go to UA:DP:R state and
enters into the WTR state when the domain is configured for transmit SD(1,0).
revertive behavior, or the LER enters into the DNR state when
the domain is configured for non-revertive behavior. In all the
other cases, re-evaluate to determine the final state as if the
LER is in the Normal state.
(3) Re-evaluate to determine final state as if the LER is in the (9) Transition to WTR state and continue to send the current
Normal state when the domain is configured for revertive message.
behavior, or as if the LER is in the DNR state when the domain
is configured for non-revertive behavior,
(4) If Path value is 0, re-evaluate to determine final state as if (10) Transition to DNR state and continue to send the current
the LER is in the Normal state. If Path value is 1, re-evaluate message.
to determine final state as if the LER is in the DNR state
(5) If the received NR message has Path=1, transition to WTR if (11) If the received NR message has Path=1, transition to WTR if
domain configured for revertive behavior, else transition to domain configured for revertive behavior, else transition to
DNR. DNR. If the received NR message has Path=0, transition to N.
(6) Remain in WTR, send NR(0,1). (12) If the receiving LER's WTR timer is running, maintain current
state and message. If the WTR timer is not running, transition
to N.
(7) Transition to WTR state and continue to send the current (13) Transit to WTR state and send NR(0,1) message. The WTR timer is
message. not initiated.
(8) Transition to DNR state and continue to send the current 11.3. State transition for 1+1 unidirectional protection
message.
(9) If the receiving LER's WTR timer is running, maintain current The state transition tables given in Section 11.1 and Section 11.2
state and message. If the WTR timer is not running, transition are for bidirectional protection switching, where remote PSC protocol
to N. messages are used to determine the protection switching actions. The
1+1 unidirectional protection switching does not require the remote
information in PSC protocol message and acts upon local inputs only.
The state transition by local inputs in Section 11.1 SHALL be reused
for the 1+1 unidirectional protection under the following conditions:
(10) If the active path just before the SD is selected as the highest o The value of Request field in the received remote message is
local input was the working path, then ignore. Otherwise, go to ignored and always assumed to be no request.
PF:DW:R and transmit SD(0,1)
(11) If the received SD-P message has Path=1, ignore the message. If o Replace footnote (4) with "Stop the WTR timer and transit to
the received SD-P message has Path=0 and the active path just Normal state."
before the SD is selected as the highest local input was the
working path, then go to UA:DP:R and transmit SD(1,0). If the
received SD-P message has Path=0 and the active path just before
the SD is selected as the highest local input was the protection
path, then ignore the received SD-P message.
12. Security considerations o Replace footnote (6) with "Transit to Normal state."
No specific security issue is raised in addition to those ones o Exercise is not applicable.
already documented in [RFC6378]
13. IANA considerations 12. Provisioning mismatch and protocol failure in the APS mode
13.1. PSC Request Field The remote PSC message that is received from the remote LER is
subject to the detection of provisioning mismatch and protocol
failure conditions. In the APS mode, provisioning mismatches are
handled as follows:
This document defines two new values in the "MPLS PSC Request o If the PSC message is received from the working path due to
Registry". working/protection path configuration mismatch, the node MUST
alert the operator and MUST NOT perform any protection switching.
The PSC Request Field is 4 bits, and the two new values have been o If the "Protection Type (PT)" field mismatches and two sides are
allocated as follows: unable to converge as described in Section 5.1 in
[I-D.ietf-mpls-psc-updates], the node MUST alert the operator and
MUST NOT perform any protection switching.
Value Description Reference o If the "Revertive (R)" bit mismatches, two sides will interwork
----- --------------------- --------------- and traffic is protected in the APS mode. The node MAY notify the
TBD1 Reverse Request [this document] operator of this event.
TBD2 Exercise [this document]
[to be removed upon publication: It is requested to assign 2 o If the Capabilities TLV mismatches, the node MUST alert the
(=TBD1)for the Reverse Request value and 3 (=TBD2) for the Exercise operator and MUST NOT perform any protection switching.
value to be aligned with the priority levels of those two requests
defined in this document.]
13.2. PSC TLV The followings are the protocol failure situations and the actions to
be taken:
o No match in sent "Data Path (Path)" and received "Data Path
(Path)" for more than 50 ms: The node MAY continue to perform
protection switching and SHOULD notify the operator of these
events:
o No PSC message is received on the protection path during at least
3.5 times the long PSC message interval (e.g. at least 17.5
seconds) and there is no defect on the protection path (The
Capabilities TLV Timeout error specifies in Section 9.1.3 is
included in this situation.): The node MUST alert the operator and
MUST NOT perform any protection switching.
13. Security considerations
No specific security issue is raised in addition to those ones
already documented in RFC 6378 [RFC6378]
14. IANA considerations
14.1. MPLS PSC Request Registry
In the "Multiprotocol Label Switching (MPLS) Operations,
Administration, and Management (OAM) Parameters" registry, IANA
maintains the "MPLS PSC Request Registry".
IANA is requested to assign two new code points from this registry.
The values shall be allocated as follows:
Value Description Reference
----- --------------------- ---------------
2 Reverse Request (this document)
3 Exercise (this document)
14.2. MPLS PSC TLV Registry
In the "Multiprotocol Label Switching (MPLS) Operations,
Administration, and Management (OAM) Parameters" registry, IANA
maintains the "MPLS PSC TLV Registry".
This document defines a new value for the Capabilities TLV type in This document defines a new value for the Capabilities TLV type in
the "MPLS PSC TLV Registry". the "MPLS PSC TLV Registry".
Type TLV Name Reference Value Description Reference
----- --------------------- --------------- ------ --------------------- ---------------
TBD3 Capabilities [this document] TBD Capabilities (this document)
[Editor's note: Need to specify a registry for Value (=options) 14.3. MPLS PSC Capability Flag Registry
inside the Capabilities TLV in a later version of this draft]
14. Acknowledgements IANA is requested to create and maintain a new registry within the
"Multiprotocol Label Switching (MPLS) Operations, Administration, and
Management (OAM) Parameters" registry called "MPLS PSC Capability
Flag Registry". All flags within this registry SHALL be allocated
according to the "Standards Action" procedures as specified in RFC
5226 [RFC5226].
15. References The length of the flags MUST be a multiple of 4 octets. This
document defines 4 octet flags. Flags greater than 4 octets SHALL be
used only if more than 32 Capabilities need to be defined. Flags
defined in this document are:
15.1. Normative References Bit Hex Value Capability Reference
---- ---------- ----------------------------------- ---------------
0 0x80000000 priority modification (this document)
1 0x40000000 non-revertive behavior modification (this document)
2 0x20000000 support of MS-W command (this document)
3 0x10000000 support of protection against SD (this document)
4 0x08000000 support of EXER command (this document)
5-31 Unassigned (this document)
15. Acknowledgements
16. References
16.1. 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.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[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.
[RFC6378] Weingarten, Y., Bryant, S., Osborne, E., Sprecher, N., and [RFC6378] Weingarten, Y., Bryant, S., Osborne, E., Sprecher, N., and
A. Fulignoli, "MPLS Transport Profile (MPLS-TP) Linear A. Fulignoli, "MPLS Transport Profile (MPLS-TP) Linear
Protection", RFC 6378, October 2011. Protection", RFC 6378, October 2011.
[I-D.ietf-mpls-psc-updates] [I-D.ietf-mpls-psc-updates]
Osborne, E., "Updates to PSC", draft-ietf-mpls-psc- Osborne, E., "Updates to PSC", draft-ietf-mpls-psc-
updates-00 (work in progress), October 2013. updates-00 (work in progress), October 2013.
15.2. Informative References 16.2. Informative References
[RFC4427] Mannie, E. and D. Papadimitriou, "Recovery (Protection and [RFC4427] Mannie, E. and D. Papadimitriou, "Recovery (Protection and
Restoration) Terminology for Generalized Multi-Protocol Restoration) Terminology for Generalized Multi-Protocol
Label Switching (GMPLS)", RFC 4427, March 2006. Label Switching (GMPLS)", RFC 4427, March 2006.
[RFC6372] Sprecher, N. and A. Farrel, "MPLS Transport Profile (MPLS- [RFC6372] Sprecher, N. and A. Farrel, "MPLS Transport Profile (MPLS-
TP) Survivability Framework", RFC 6372, September 2011. TP) Survivability Framework", RFC 6372, September 2011.
[G841] International Telecommunications Union, "Types and
characteristics of SDH network protection architectures",
ITU-T Recommendation G.841, October 1998.
[G873.1] International Telecommunications Union, "Optical Transport
Network (OTN): Linear protection", ITU-T Recommendation
G.873.1, July 2011.
[G8031] International Telecommunications Union, "Ethernet Linear
Protection Switching", ITU-T Recommendation G.8031/Y.1342,
June 2011.
Appendix A. An example of out-of-service scenarios Appendix A. An example of out-of-service scenarios
The sequence diagram shown is an example of the out-of-service The sequence diagram shown is an example of the out-of-service
scenerios based on the priority level defined in [RFC6378]. The scenarios based on the priority level defined in RFC 6378. The first
first PSC message which differs from the previous PSC message is PSC message which differs from the previous PSC message is shown.
shown.
A Z A Z
| | | |
(1) |-- NR(0,0) ------>| (1) (1) |-- NR(0,0) ------>| (1)
|<----- NR(0,0) ---| |<----- NR(0,0) ---|
| | | |
| | | |
| (FS issued at Z) | (2) | (FS issued at Z) | (2)
(3) |<------ FS(1,1) --| (3) |<------ FS(1,1) --|
|-- NR(0,1) ------>| |-- NR(0,1) ------>|
| | | |
| | | |
(4) | (SF on P(A<-Z)) | (4) | (SF on P(A<-Z)) |
| | | |
| | | |
| (Clear FS at Z) | (5) | (Clear FS at Z) | (5)
(6) | X <- NR(0,0) --| (6) | X <- NR(0,0) --|
| | | |
| | | |
(1) Each end is in Normal state, and transmits NR (0,0) messages. (1) Each end is in the Normal state, and transmits NR(0,0) messages.
(2) When a Forced Switch command is issued at node Z, node Z goes (2) When a FS command is issued at node Z, node Z goes into local
into local Protecting Administrative state (PA:F:L) and begins Protecting administrative state (PA:F:L) and begins transmission of
transmission of an FS (1,1) messages. an FS(1,1) messages.
(3) A remote Forced Switch message causes node A to go into remote (3) A remote FS message causes node A to go into remote Protecting
Protecting Administrative state (PA:F:R), and node A begins administrative state (PA:F:R), and node A begins transmitting NR(0,1)
transmitting NR (0,1) messages. messages.
(4) When node A detects a unidirectional Signal Fail on the (4) When node A detects a unidirectional SF-P, node A keeps sending
Protection path, node A keeps sending NR (0,1) message because SF-P NR(0,1) message because SF-P is ignored under the PA:F:R state.
is ignored under the state PA:F:R.
(5) When a Clear command is issued at node Z, node Z goes into Normal (5) When a Clear command is issued at node Z, node Z goes into the
state and begins transmission of NR (0,0) messages. Normal state and begins transmission of NR(0,0) messages.
(6) But node A cannot receive PSC message because of local (6) But, node A cannot receive PSC message because of local
unidirectional Signal Fail on the Protection path. Because no valid unidirectional SF-P. Because no valid PSC message is received, over
PSC message is received, over a period of several successive message a period of several successive message intervals, the last valid
intervals, the last valid received message remains applicable and the received message remains applicable and the node A continue to
node A continue to transmit an NR (0,1) message in the state of transmit an NR(0,1) message in the PA:F:R state.
PA:F:R.
Now, there exists a mismatch between the bridge/selector positions of Now, there exists a mismatch between the bridge/selector positions of
node A (transmitting an NR (0,1)) and node Z (transmitting an NR node A (transmitting an NR(0,1)) and node Z (transmitting an
(0,0)). It results in out-of-service even when there is neither NR(0,0)). It results in out-of-service even when there is neither
signal fail on working path nor FS. SF-W nor FS.
Appendix B. An example of sequence diagram showing the problem with the Appendix B. An example of sequence diagram showing the problem with the
priority level of Clear SF priority level of SFc
An example of sequence diagram showing the problem with the priority An example of sequence diagram showing the problem with the priority
level of Clear SF defined in [RFC6378] is given below. The following level of SFc defined in RFC 6378 is given below. The following
sequence diagram is depicted for the case of bidirectional signal sequence diagram is depicted for the case of bidirectional signal
fails. However, other cases with unidirectional signal fails can fails. However, other cases with unidirectional signal fails can
result in the same problem. The first PSC message which differs from result in the same problem. The first PSC message which differs from
the previous PSC message is shown. the previous PSC message is shown.
A Z A Z
| | | |
(1) |-- NR(0,0) ------>| (1) (1) |-- NR(0,0) ------>| (1)
|<----- NR(0,0) ---| |<----- NR(0,0) ---|
| | | |
| | | |
(2) | (SF on P(A<->Z)) | (2) (2) | (SF on P(A<->Z)) | (2)
|-- SF(0,0) ------>| |-- SF(0,0) ------>|
|<------ SF(0,0) --| |<------ SF(0,0) --|
| | | |
| | | |
(3) | (SF on W(A<->Z)) | (3) (3) | (SF on W(A<->Z)) | (3)
| | | |
| | | |
(4) | (Clear SF-P) | (4) (4) | (Clear SF-P) | (4)
| | | |
| | | |
(5) | (Clear SF-W) | (5) (5) | (Clear SF-W) | (5)
| | | |
| | | |
(1) Each end is in Normal state, and transmits NR (0,0) messages. (1) Each end is in the Normal state, and transmits NR(0,0) messages.
(2) When signal fail on protection (SF-P) occurs, each node enters (2) When SF-P occurs, each node enters into the UA:P:L state and
into [UA:P:L] state and transmits SF (0,0) messages. Traffic remains transmits SF(0,0) messages. Traffic remains on the working path.
on working path.
(3) When signal fail on working (SF-W) occurs, each node remains in (3) When SF-W occurs, each node remains in the UA:P:L state as SF-W
[UA:P:L] state as SF-W has a lower priority than SF-P. Traffic is has a lower priority than SF-P. Traffic is still on the working
still on the working path. Traffic cannot be delivered as both path. Traffic cannot be delivered as both the working path and the
working and protection paths are experiencing signal fails. protection path are experiencing signal fails.
(4) When the signal fail on protection is cleared, local "Clear SF-P" (4) When SF-P is cleared, local "Clear SF-P" request cannot be
request cannot be presented to the PSC control logic, which takes the presented to the PSC Control logic, which takes the highest local
highest priority local request and runs PSC state machine, as the request and runs PSC state machine, since the priority of "Clear
priority of "Clear SF-P" is lower than that of SF-W. Consequently, SF-P" is lower than that of SF-W. Consequently, there is no change
there is no change in state, and the selector and/or bridge keep in state, and the selector and/or bridge keep pointing at the working
pointing at the working path, which has signal fail condition. path, which has signal fail condition.
Now, traffic cannot be delivered while the protection path is Now, traffic cannot be delivered while the protection path is
recovered and available. It should be noted that the same problem recovered and available. It should be noted that the same problem
will occur in the case that the sequence of SF-P and SF-W events is will occur in the case that the sequence of SF-P and SF-W events is
changed. changed.
If we further continue with this sequence to see what will happen If we further continue with this sequence to see what will happen
after SF-W is cleared, after SF-W is cleared,
(5) When the signal fail on working is cleared, local "Clear SF-W" (5) When SF-W is cleared, local "Clear SF-W" request can be passed to
request can be passed to the PSC control logic (state machine) as the PSC Control logic as there is no higher priority local input, but
there is no higher priority local request, but this will be ignored this will be ignored in the PSC Control logic according to the state
in the PSC control logic according to the state transition definition transition definition in RFC 6378. There will be no change in state
in [RFC6378]. There will be no change in state or protocol message or protocol message transmitted.
transmitted.
As the signal fail on working is now cleared and the selector and/or As SF-W is now cleared and the selector and/or bridge are still
bridge are still pointing at the working path, traffic delivery is pointing at the working path, traffic delivery is resumed. However,
resumed. However, each node is in [UA:P:L] state and transmitting each node is the in UA:P:L state and transmitting SF(0,0) message,
SF(0,0) message, while there exists no outstanding request for while there exists no outstanding request for protection switching.
protection switching. Moreover, any future legitimate protection Moreover, any future legitimate protection switching requests, such
switching requests, such as SF-W, will be rejected as each node as SF-W, will be rejected as each node thinks the protection path is
thinks the protection path is unavailable. unavailable.
Appendix C. Freeze Command Appendix C. Freeze Command
The "Freeze" command applies only to the near end (local node) of the The "Freeze" command applies only to the local LER of the protection
protection group and is not signalled to the far end. This command group and is not signaled to the remote LER. This command freezes
freezes the state of the protection group. Until the Freeze is the state of the protection group. Until the Freeze is cleared,
cleared, additional near end commands are rejected and condition additional local commands are rejected and condition changes and
changes and received PSC information are ignored. received PSC information are ignored.
"Clear Freeze" command clears the local freeze. When the Freeze "Clear Freeze" command clears the local freeze. When the Freeze
command is cleared, the state of the protection group is recomputed command is cleared, the state of the protection group is recomputed
based on the persistent condition of the local triggers. based on the persistent condition of the local triggers.
Because the freeze is local, if the freeze is issued at one end only, Because the freeze is local, if the freeze is issued at one end only,
a failure of protocol can occur as the other end is open to accept a failure of protocol can occur as the other end is open to accept
any operator command or a fault condition. any operator command or a fault condition.
Appendix D. Operation examples of the APS mode
The sequence diagrams shown in this section are only a few examples
of the APS mode operations. The first PSC protocol message which
differs from the previous message is shown. The operation of hold-
off timer is omitted. The Request, FPath and Path fields, whose
values are changed during PSC message exchange are shown. For an
example, SF(1, 0) represents an PSC message with the following field
values: Request = SF, FPath = 1, and Path = 1. The values of the
other fields remain unchanged from the initial configuration.
W(A->Z) and P(A->Z) indicate the working path and the protection path
in the direction of A to Z, respectively.
Example 1. 1:1 bidirectional protection switching (revertive mode) -
Unidirectional SF case
A Z
| |
(1) |<---- NR(0,0)---->| (1)
| |
| |
(2) | (SF on W(Z->A)) |
|---- SF(1,1)----->| (3)
(4) |<----- NR(0,1)----|
| |
| |
(5) | (Clear SF-W) |
|---- WTR(0,1)---->|
/| |
| | |
WTR timer | |
| | |
\| |
(6) |---- NR(0,1)----->| (7)
(8) |<----- NR(0,0)----|
|---- NR(0,0)----->| (9)
| |
(1) The protection domain is operating without any defect, and the
working path is used for delivering the traffic in the Normal state.
(2) SF-W occurs in the Z to A direction. Node A enters into the
PF:W:L state and generates SF(1, 1) message. Selector and bridge of
node A are pointing at the protection path.
(3) Upon receiving SF(1, 1), node Z sets selector and bridge to the
protection path. As there is no local request in node Z, node Z
generates NR(0, 1) message in the PF:W:R state.
(4) Node A confirms that the remote LER is also selecting protection
path.
(5) Node A detects clearing of SF condition, starts the WTR timer,
and sends WTR(0, 1) message in the WTR state.
(6) At expiration of the WTR timer, node A sets selector and bridge
to the working path and sends NR(0, 1) message.
(7) Node Z is notified that the remote request has been cleared.
Node Z transits to the Normal state and sends NR(0,0) message.
(8) Upon receiving NR(0,0) message, node A transits to the Normal
state and sends NR(0,0) message.
(9) It is confirmed that the remote LER is also selecting the working
path.
Example 2. 1:1 bidirectional protection switching (revertive mode) -
Bidirectional SF case - Inconsistent WTR timers
A Z
| |
(1) |<---- NR(0,0)---->| (1)
| |
| |
(2) | (SF on W(A<->Z)) | (2)
|<---- SF(1,1)---->|
| |
| |
(3) | (Clear SF-W) | (3)
|<---- NR(0,1)---->|
(4) |<--- WTR(0,1) --->| (4)
/| |\
| | | |
WTR timer | | WTR timer
| | | |
| | |/
| |<------ NR(0,1)---| (5)
| | |
\| |
(6) |--- NR(0,1)------>|
|<------ NR(0,0)---| (7)
(8) |--- NR(0,0)------>|
| |
(1) Each end is in the Normal state, and transmits NR(0,0) messages.
(2) When SF-W occurs, each node enters into the PF:W:L state and
transmits SF(1,1) messages. Traffic is switched to the protection
path. Upon receiving SF(1,1), each node confirms that the remote LER
is also sending and receiving the traffic from the protection path.
(3) When SF-W is cleared, each node transits to the PF:W:R state and
transmits NR(0,1) messages as the last received message is SF-W.
(4) Upon receiving NR(0,1) messages, each node goes into the WTR
state, starts the WTR timer, and sends the WTR(0,1) messages.
(5) At expiration of the WTR timer in node Z, node Z sends NR(0,1) as
the last received APS message was WTR. When NR(0,1) arrives at node
A, node A maintains the WTR state and keeps sending current WTR
messages as described in the state transition table.
(6) At expiration of the WTR timer in node A, node A sends NR(0,1).
(7) When the NR(0,1) message arrives at node Z, node Z moves to the
Normal state, sets selector and bridge to the working path, and sends
NR(0, 0) message.
(8) The received NR(0,0) message causes node A to go to the Normal
state. Now, the traffic is switched back to the working path.
Example 3. 1:1 bidirectional protection switching - R bit mismatch
This example shows that both sides will interwork and the traffic is
protected when one side (node A) is configured as revertive mode and
the other (node Z) is configured as non-revertive mode. The
interworking is covered in the state transition tables.
(revertive) A Z (non-revertive)
| |
(1) |<---- NR(0,0)---->| (1)
| |
| |
(2) | (SF on W(A<->Z)) | (2)
|<---- SF(1,1)---->|
| |
| |
(3) | (Clear SF-W) | (3)
|<---- NR(0,1)---->|
(4) |<----- DNR(0,1)---| (4)
/|-- WTR(0,1)------>|
| |<----- NR(0,1)----| (5)
| | |
WTR timer | |
| | |
| | |
\| |
(6) |--- NR(0,1)------>|
|<------ NR(0,0)---| (7)
(8) |--- NR(0,0)------>|
| |
(1) Each end is in the Normal state, and transmits NR(0,0) messages.
(2) When SF-W occurs, each node enters into the PF:W:L state and
transmits SF(l,l) messages. Traffic is switched to the protection
path. Upon receiving SF(1,1), each node confirms that the remote LER
is also sending and receiving the traffic on the protection path.
(3) When SF-W is cleared, each node transits to the PF:W:R state and
transmits NR(0,1) messages as the last received message is SF-W.
(4) Upon receiving NR(0,1) messages, node A goes into the WTR state,
starts the WTR timer, and sends WTR(0,1) messages. At the same time,
node B transits to the DNR state and sends DNR(0,1) message.
(5) When the WTR message arrives at node Z, node Z transits to the
WTR state and send NR(0,1) message according to the state transition
table. At the same time, the DNR message arrived at node Z is
ignored according to the state transition table. Therefore, node Z,
which is configured as non-revertive mode, is operating as if in
revertive mode.
(6) At expiration of the WTR timer in node A, node A sends NR(0,1).
(7) When the NR(0,1) message arrives at node Z, node Z moves to the
Normal state, sets selector and bridge to the working path, and sends
NR(0, 0) message.
(8) The received NR(0,0) message causes node A to transits to the
Normal state. Now, the traffic is switched back to the working path.
Authors' Addresses Authors' Addresses
Jeong-dong Ryoo (editor) Jeong-dong Ryoo (editor)
ETRI ETRI
218 Gajeongno 218 Gajeongno
Yuseong-gu, Daejeon 305-700 Yuseong-gu, Daejeon 305-700
South Korea South Korea
Phone: +82-42-860-5384 Phone: +82-42-860-5384
Email: ryoo@etri.re.kr Email: ryoo@etri.re.kr
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