draft-ietf-mpls-tp-linear-protection-03.txt   draft-ietf-mpls-tp-linear-protection-04.txt 
Network Working Group S. Bryant, Ed. Network Working Group S. Bryant, Ed.
Internet-Draft E. Osborne Internet-Draft E. Osborne
Intended status: Standards Track Cisco Intended status: Standards Track Cisco
Expires: April 27, 2011 N. Sprecher, Ed. Expires: July 30, 2011 N. Sprecher, Ed.
Nokia Siemens Networks Nokia Siemens Networks
A. Fulignoli, Ed. A. Fulignoli, Ed.
Ericsson Ericsson
Y. Weingarten Y. Weingarten
Nokia Siemens Networks Nokia Siemens Networks
October 24, 2010 January 26, 2011
MPLS-TP Linear Protection MPLS-TP Linear Protection
draft-ietf-mpls-tp-linear-protection-03.txt draft-ietf-mpls-tp-linear-protection-04.txt
Abstract Abstract
The Transport Profile for Multiprotocol Label Switching (MPLS-TP) is The Transport Profile for Multiprotocol Label Switching (MPLS-TP) is
being specified jointly by IETF and ITU-T. This document addresses being specified jointly by IETF and ITU-T. This document addresses
the functionality described in the MPLS-TP Survivability Framework the functionality described in the MPLS-TP Survivability Framework
document [SurvivFwk] and defines a protocol that may be used to document [SurvivFwk] and defines a protocol that may be used to
fulfill the function of the Protection State Coordination for linear fulfill the function of the Protection State Coordination for linear
protection, as described in that document. protection, as described in that document.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 27, 2011. This Internet-Draft will expire on July 30, 2011.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
skipping to change at page 3, line 18 skipping to change at page 3, line 18
1.1. Protection architectures . . . . . . . . . . . . . . . . . 4 1.1. Protection architectures . . . . . . . . . . . . . . . . . 4
1.2. Scope of the document . . . . . . . . . . . . . . . . . . 5 1.2. Scope of the document . . . . . . . . . . . . . . . . . . 5
1.3. Contributing authors . . . . . . . . . . . . . . . . . . . 6 1.3. Contributing authors . . . . . . . . . . . . . . . . . . . 6
2. Conventions used in this document . . . . . . . . . . . . . . 6 2. Conventions used in this document . . . . . . . . . . . . . . 6
2.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2. Definitions and Terminology . . . . . . . . . . . . . . . 7 2.2. Definitions and Terminology . . . . . . . . . . . . . . . 7
3. Protection switching control logic . . . . . . . . . . . . . . 7 3. Protection switching control logic . . . . . . . . . . . . . . 7
3.1. Protection switching control logical architecture . . . . 7 3.1. Protection switching control logical architecture . . . . 7
3.1.1. Local Request Logic . . . . . . . . . . . . . . . . . 8 3.1.1. Local Request Logic . . . . . . . . . . . . . . . . . 8
3.1.2. Remote Requests . . . . . . . . . . . . . . . . . . . 10 3.1.2. Remote Requests . . . . . . . . . . . . . . . . . . . 10
3.1.3. PSC Process Logic . . . . . . . . . . . . . . . . . . 11 3.1.3. PSC Control Logic . . . . . . . . . . . . . . . . . . 11
3.1.4. PSC Message Generator . . . . . . . . . . . . . . . . 11 3.1.4. PSC Message Generator . . . . . . . . . . . . . . . . 12
3.1.5. Wait-to-Restore (WTR) timer . . . . . . . . . . . . . 12 3.1.5. Wait-to-Restore (WTR) timer . . . . . . . . . . . . . 12
3.1.6. PSC Control States . . . . . . . . . . . . . . . . . . 12 3.1.6. PSC Control States . . . . . . . . . . . . . . . . . . 12
4. Protection state coordination (PSC) protocol . . . . . . . . . 13 4. Protection state coordination (PSC) protocol . . . . . . . . . 14
4.1. Transmission and acceptance of PSC control packets . . . . 14 4.1. Transmission and acceptance of PSC control packets . . . . 14
4.2. Protocol format . . . . . . . . . . . . . . . . . . . . . 14 4.2. Protocol format . . . . . . . . . . . . . . . . . . . . . 15
4.2.1. PSC Ver field . . . . . . . . . . . . . . . . . . . . 15 4.2.1. PSC Ver field . . . . . . . . . . . . . . . . . . . . 16
4.2.2. PSC Request field . . . . . . . . . . . . . . . . . . 15 4.2.2. PSC Request field . . . . . . . . . . . . . . . . . . 16
4.2.3. Protection Type (PT) . . . . . . . . . . . . . . . . . 16 4.2.3. Protection Type (PT) . . . . . . . . . . . . . . . . . 17
4.2.4. Revertive (R) field . . . . . . . . . . . . . . . . . 17 4.2.4. Revertive (R) field . . . . . . . . . . . . . . . . . 17
4.2.5. Fault path (FPath) field . . . . . . . . . . . . . . . 17 4.2.5. Fault path (FPath) field . . . . . . . . . . . . . . . 18
4.2.6. Data path (Path) field . . . . . . . . . . . . . . . . 17 4.2.6. Data path (Path) field . . . . . . . . . . . . . . . . 18
4.3. Principles of Operation . . . . . . . . . . . . . . . . . 18 4.3. Principles of Operation . . . . . . . . . . . . . . . . . 18
4.3.1. Basic operation . . . . . . . . . . . . . . . . . . . 18 4.3.1. Basic operation . . . . . . . . . . . . . . . . . . . 19
4.3.2. Priority of inputs . . . . . . . . . . . . . . . . . . 19 4.3.2. Priority of inputs . . . . . . . . . . . . . . . . . . 20
4.3.3. Operation of PSC States . . . . . . . . . . . . . . . 20 4.3.3. Operation of PSC States . . . . . . . . . . . . . . . 20
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
6. Security Considerations . . . . . . . . . . . . . . . . . . . 29 6. Security Considerations . . . . . . . . . . . . . . . . . . . 31
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 29 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 31
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Appendix A. PSC state machine tables . . . . . . . . . . . . . . 31
8.1. Normative References . . . . . . . . . . . . . . . . . . . 29 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 35
8.2. Informative References . . . . . . . . . . . . . . . . . . 29 8.1. Normative References . . . . . . . . . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 30 8.2. Informative References . . . . . . . . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 36
1. Introduction 1. Introduction
The MPLS Transport Profile (MPLS-TP) [TPFwk] is a framework for the The MPLS Transport Profile (MPLS-TP) [TPFwk] is a framework for the
construction and operation of packet-switched transport networks construction and operation of packet-switched transport networks
based on the architectures for MPLS ([RFC3031] and [RFC3032]) and for based on the architectures for MPLS ([RFC3031] and [RFC3032]) and for
Pseudowires (PWs) ([RFC3985] and [RFC5659]) and the requirements of Pseudowires (PWs) ([RFC3985] and [RFC5659]) and the requirements of
[RFC5654]. [RFC5654].
Network survivability is the ability of a network to recover traffic Network survivability is the ability of a network to recover traffic
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In the 1:1 architecture, a recovery transport path is dedicated to In the 1:1 architecture, a recovery transport path is dedicated to
the working transport path of a single service and the traffic is the working transport path of a single service and the traffic is
only transmitted either on the working or the recovery path, by using only transmitted either on the working or the recovery path, by using
a selector bridge at the source of the protection domain. A selector a selector bridge at the source of the protection domain. A selector
at the sink of the protection domain then selects the path that at the sink of the protection domain then selects the path that
carries the normal traffic. Since the source and sink need to be carries the normal traffic. Since the source and sink need to be
coordinated to ensure that the selector bridge at both ends select coordinated to ensure that the selector bridge at both ends select
the same path, this architecture must support a PSC protocol. the same path, this architecture must support a PSC protocol.
The 1:n protection architecture extends the 1:1 architecture above by The 1:n protection architecture extends the 1:1 architecture above by
sharing the recovery path amongst n services. Again, the recovery sharing the recovery path among n services. Again, the recovery path
path is fully allocated and disjoint from any of the n working is fully allocated and disjoint from any of the n working transport
transport paths that it is being used to protect. The normal data paths that it is being used to protect. The normal data traffic for
traffic for each service is transmitted either on the normal working each service is transmitted either on the normal working path for
path for that service or, in cases that trigger protection switching that service or, in cases that trigger protection switching (as
(as defined in [SurvivFwk]), may be sent on the recovery path. The defined in [SurvivFwk]), may be sent on the recovery path. The
switching action is similar to the 1:1 case where a selector bridge switching action is similar to the 1:1 case where a selector bridge
is used at the source. It should be noted that in cases where is used at the source. It should be noted that in cases where
multiple working path services have triggered protection switching multiple working path services have triggered protection switching
that some services, dependent upon their Service Level Agreement that some services, dependent upon their Service Level Agreement
(SLA), may not be transmitted as a result of limited resources on the (SLA), may not be transmitted as a result of limited resources on the
recovery path. In this architecture there may be a need for recovery path. In this architecture there may be a need for
coordination of the protection switching, and also for resource coordination of the protection switching, and also for resource
allocation negotiation. The procedures for this are for further allocation negotiation. The procedures for this are for further
study and may be addressed in future documents. study and may be addressed in future documents.
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| | | | | | | |
V V V V V V V V
+---------------+ +-------+ +---------------+ +-------+
| Local Request |<--------| WTR | | Local Request |<--------| WTR |
| logic |WTR Exps | Timer | | logic |WTR Exps | Timer |
+---------------+ +-------+ +---------------+ +-------+
| ^ | ^
Highest local|request | Highest local|request |
V | Start/Stop V | Start/Stop
+-----------------+ | +-----------------+ |
Remote PSC | PSC Process |------------+ Remote PSC | PSC Control |------------+
------------>| logic | ------------>| logic |
Request +-----------------+ Request +-----------------+
| |
| Action +------------+ | Action +------------+
+---------------->| Message | +---------------->| Message |
| Generator | | Generator |
+------------+ +------------+
| |
Output PSC | Message Output PSC | Message
V V
Figure 1: Protection switching control logic Figure 1: Protection switching control logic
Figure 1 describes the logical architecture of the protection Figure 1 describes the logical architecture of the protection
switching control. The Local Request logic unit accepts the triggers switching control. The Local Request logic unit accepts the triggers
from the OAM, external operator commands, from the local control from the OAM, external operator commands, from the local control
plane (when present), and the Wait-to-Restore timer. By considering plane (when present), and the Wait-to-Restore timer. By considering
all of these local request sources it determines the highest priority all of these local request sources it determines the highest priority
local request. This high-priority request is passed to the PSC local request. This high-priority request is passed to the PSC
Process logic, that will cross-check this local request with the Control logic, that will cross-check this local request with the
information received from the far-end LER. The PSC Process logic information received from the far-end LER. The PSC Control logic
uses this input to determine what actions need to be taken, e.g. uses this input to determine what actions need to be taken, e.g.
local actions at the LER, or what message should be sent to the far- local actions at the LER, or what message should be sent to the far-
end LER, and the current status of the protection domain. end LER, and the current status of the protection domain.
3.1.1. Local Request Logic 3.1.1. Local Request Logic
The protection switching logic processes input triggers from five The protection switching logic processes input triggers from five
sources: sources:
o Operator command - the network operator may issue commands that o Operator command - the network operator may issue commands that
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transport path and this SHOULD input an indication to the Local transport path and this SHOULD input an indication to the Local
Request Logic. Request Logic.
o WTR expires - The Wait-to-Restore timer is used in conjunction o WTR expires - The Wait-to-Restore timer is used in conjunction
with recovery from failure conditions on the working path in with recovery from failure conditions on the working path in
revertive mode. The timer SHALL signal the PSC control process revertive mode. The timer SHALL signal the PSC control process
when it expires and the end point SHOULD revert to the normal when it expires and the end point SHOULD revert to the normal
transmission of the user data traffic. transmission of the user data traffic.
The Local request logic SHALL process these different input sources The Local request logic SHALL process these different input sources
and, based on the priorities between them, SHOULD produce a current and, based on the priorities between them (see section 4.3.2), SHALL
local request. The different local requests that may be output from produce a current local request. If more than one local input source
the Local Request Logic are: generates an indicator, then the Local request logic SHALL select the
higher priority indicator and block any lower priority indicator. As
a result, there is a single current local request that is passed to
the PSC Control logic. The different local requests that may be
output from the Local Request Logic are:
o Clear - if the operator cancels an active local administrative o Clear - if the operator cancels an active local administrative
command, i.e. LO/FS/MS. command, i.e. LO/FS/MS.
o Lockout of Protection (LO) - if the operator requested to disable o Lockout of Protection (LO) - if the operator requested to disable
the protection path. the protection path.
o Signal Fail (SF) - if any of the Server Layer, Control plane, or o Signal Fail (SF) - if any of the Server Layer, Control plane, or
OAM indications signaled a failure condition on either the OAM indications signaled a failure condition on either the
protection path or one of the working paths. protection path or one of the working paths.
o Signal Degrade (SD) - if any of the Server Layer, Control plane, o Signal Degrade (SD) - if any of the Server Layer, Control plane,
or OAM indications signaled a degraded transmission condition on or OAM indications signaled a degraded transmission condition on
either the protection path or one of the working paths either the protection path or one of the working paths
o Clear Signal Fail - if all of the Server Layer, Control plane, or o Clear Signal Fail - if all of the Server Layer, Control plane, or
OAM indications are no longer indicating a failure condition on a OAM indications are no longer indicating a failure condition on a
path that was peviously indicating a failure condition. path that was previously indicating a failure condition.
o Forced Switch (FS) - if the operator requested that traffic be o Forced Switch (FS) - if the operator requested that traffic be
switched from one of the working paths to the protection path. switched from one of the working paths to the protection path.
o Manual Switch (MS) - if the operator requested that traffic be o Manual Switch (MS) - if the operator requested that traffic be
switched from its current path to the other path. This is only switched from its current path to the other path. This is only
relevant if there is no currently active Fault condition or relevant if there is no currently active Fault condition or
Operator command. Operator command.
o WTR Expires - generated by the WTR timer completing its period. o WTR Expires - generated by the WTR timer completing its period.
If none of the input sources have generated any input then the If none of the input sources have generated any input then the Local
current local request SHALL be a No Request (NR) request. request logic SHALL generate a No Request (NR) request as the current
local request .
3.1.2. Remote Requests 3.1.2. Remote Requests
In addition to the local requests generated as a result of the local In addition to the local requests, generated as a result of the local
triggers indicated in the previous subsection, the PSC Control Logic triggers, indicated in the previous subsection, the PSC Control Logic
SHALL accept PSC messages from the far-end LER of the transport path. SHALL accept PSC messages from the far-end LER of the transport path.
These remote messages indicate the status of the transport path from These remote messages indicate the status of the transport path from
the viewpoint of the far-end LER, and may indicate if the local MEP the viewpoint of the far-end LER, and may indicate if the local MEP
SHOULD initiate a protection switch operation. SHOULD initiate a protection switch operation.
The following remote requests may be received by the PSC process: The following remote requests may be received by the PSC process:
o Remote LO - indicates that the remote end point is in Unavailable o Remote LO - indicates that the remote end point is in Unavailable
state due to a Lockout of Protection operator command. state due to a Lockout of Protection operator command.
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o Remote DNR - indicates that the remote end point has determined o Remote DNR - indicates that the remote end point has determined
that the failure condition has recovered and will continue that the failure condition has recovered and will continue
transporting traffic on the protection path due to operator transporting traffic on the protection path due to operator
configuration that prevents automatic reversion to the Normal configuration that prevents automatic reversion to the Normal
state. state.
o Remote NR - indicates that the remote end point has no abnormal o Remote NR - indicates that the remote end point has no abnormal
condition to report. condition to report.
3.1.3. PSC Process Logic 3.1.3. PSC Control Logic
The PSC Process Logic SHALL accept as input - The PSC Control Logic SHALL accept as input -
a. the Local request output from the Local Request Logic, a. the current local request output from the Local Request Logic
(see section 3.1.1),
b. the remote request message from the remote end point of the b. the remote request message from the remote end point of the
transport path, and transport path, and
c. the current state of the PSC Control Logic (maintained internally c. the current state of the PSC Control Logic (maintained internally
by the PSC Control Logic). by the PSC Control Logic).
Based on the priorities between the different inputs, the PSC Process Based on the priorities between the different inputs, the PSC Control
Logic SHALL determine the new state of the PSC Control Logic and what Logic SHALL determine the new state of the PSC Control Logic and what
actions need to be taken. actions need to be taken.
The new state information should be retained by the PSC Process The new state information SHALL be retained by the PSC Control Logic,
Logic, while the requested action SHALL be sent to the PSC Message while the requested action SHALL be sent to the PSC Message Generator
Generator (see subsection 3.1.4) to generate and transmit the proper (see subsection 3.1.4) to generate and transmit the proper PSC
PSC message to be transmitted to the remote end point of the message to be transmitted to the remote end point of the protection
protection domain. domain.
3.1.4. PSC Message Generator 3.1.4. PSC Message Generator
Based on the action output from the Process Logic this unit formats Based on the action output from the Control Logic this unit formats
the PSC protocol message that is transmitted to the remote end point the PSC protocol message that is transmitted to the remote end point
of the protection domain. When the PSC information has changed, of the protection domain. When the PSC information has changed,
three PSC messages SHOULD be transmitted in quick succession, and three PSC messages SHOULD be transmitted in quick succession, and
subsequent messages should be transmitted continually at a lower subsequent messages should be transmitted continually at a lower
rate. frequency.
The transmission of three rapid packets allows for fast protection The transmission of three rapid packets allows for fast protection
switching even if one or two PSC messages are lost or corrupted. For switching even if one or two PSC messages are lost or corrupted. For
protection switching within 50ms, it is RECOMMENDED that the default protection switching within 50ms, it is RECOMMENDED that the default
interval of the first three PSC messages SHOULD be no larger than interval of the first three PSC messages SHOULD be no larger than
3.3ms. The subsequent messages SHOULD be transmitted with an 3.3ms. The subsequent messages SHOULD be transmitted with an
interval of 5 sec, to avoid traffic congestion. interval of 5 sec, to avoid traffic congestion.
3.1.5. Wait-to-Restore (WTR) timer 3.1.5. Wait-to-Restore (WTR) timer
The WTR timer is used to delay reversion to Normal state when The WTR timer is used to delay reversion to Normal state when
recovering from a failure condition on the working path and the recovering from a failure condition on the working path and the
protection domain is configured for revertive behavior. The WTR may protection domain is configured for revertive behavior. The WTR may
be in one of two states - either Running or Stopped. The WTR timer be in one of two states - either Running or Stopped. The WTR timer
MAY be started or stopped by the PSC Process Logic. MAY be started or stopped by the PSC Control Logic.
If the WTR timer expires prior to being stopped it SHALL generate a If the WTR timer expires prior to being stopped it SHALL generate a
WTR Expires local signal that shall be processed by the Local Request WTR Expires local signal that shall be processed by the Local Request
Logic. If the WTR timer is running, sending a Stop command SHALL Logic. If the WTR timer is running, sending a Stop command SHALL
reset the timer but SHALL NOT generate a WTR Expires local signal. reset the timer but SHALL NOT generate a WTR Expires local signal.
If the WTR timer is not running, a Stop command SHALL be ignored. If the WTR timer is not running, a Stop command SHALL be ignored.
3.1.6. PSC Control States 3.1.6. PSC Control States
The PSC Control Logic SHOULD maintain information on the current The PSC Control Logic SHOULD maintain information on the current
state of the protection domain. The state information SHALL include state of the protection domain. The state information SHALL include
information of the current state and an indication of the cause for information of the current state and an indication of the cause for
the current state (e.g. unavailable due to local LO command, the current state (e.g. unavailable due to local LO command,
protecting due to remote FS). In particular, the state information protecting due to remote FS). In particular, the state information
SHOULD include an indication if the state is related to a remote or SHOULD include an indication if the state is related to a remote or
local condition. local condition. If there are both a local indicator and remote
indicator for the state then the state shall be considered a local
state. For example, if the LER enters into a Protecting failure
state due to a remote SF input, and then a local SF indication is
received then even though this was initially a remote Protecting
failure state, by receiving the local SF input the LER is considered
to be in local Protecting failure state.
It should be noted that when referring to the "transport" of the data It should be noted that when referring to the "transport" of the data
traffic, in the following descriptions and later in the document that traffic, in the following descriptions and later in the document that
the data will be transmitted on both the working and the protection the data will be transmitted on both the working and the protection
paths when using 1+1 protection, and on either the working or the paths when using 1+1 protection, and on either the working or the
protection path exclusively when using 1:1 protection. When using protection path exclusively when using 1:1 protection. When using
1+1 protection, the receiving LER should select the proper 1+1 protection, the receiving LER should select the proper
transmission, according to the state of the protection domain. transmission, according to the state of the protection domain.
The states that are supported by the PSC Control Logic are: The states that are supported by the PSC Control Logic are:
skipping to change at page 13, line 27 skipping to change at page 13, line 39
SF/SD condition on the working path that is being controlled by SF/SD condition on the working path that is being controlled by
the Wait-to-Restore (WTR) timer. the Wait-to-Restore (WTR) timer.
o Do-not-revert state - The protection domain is recovering from a o Do-not-revert state - The protection domain is recovering from a
Protecting state, but the operator has configured the protection Protecting state, but the operator has configured the protection
domain to not automatically revert to the Normal state upon domain to not automatically revert to the Normal state upon
recovery. The protection domain SHALL remain in this state until recovery. The protection domain SHALL remain in this state until
the operator issues a command to revert to the Normal state or the operator issues a command to revert to the Normal state or
there is a new trigger to switch to a different state. there is a new trigger to switch to a different state.
See section 4.3.1 for details on what actions are taken by the PSC See section 4.3.3 for details on what actions are taken by the PSC
Process Logic for each state and the relevant input. Process Logic for each state and the relevant input.
3.1.6.1. Local and Remote state
An end-point may be in a given state as a result of either a local
input indicator, e.g. OAM, WTR timer, or as a result of receiving a
PSC message from the far-end LER. If the state is entered as a
result of a local input indicator, then the state SHOULD be
considered a local state. If the state is entered as a result of a
PSC message, in the absence of a local input, then the state SHOULD
be considered a remote state. This differentiation affects how the
LER should react to different inputs, as described in section 4.3.3.
The PSC Control logic should maintain, together with the current
state, an indication of whether this is a local or remote state.
In any instance where the LER has both a local and remote indicators
that cause the PSC Control logic to enter a particular state, then
the state SHOULD be considered a local state, regardless of the order
in which the indicators were processed. If, however, the LER has
local and remote indicators that would cause the PSC Control logic to
enter different states, e.g. a Local SF on working and a Remote
Lockout message, then the state with the higher importance will be
the deciding factor and the source of that indicator will determine
whether it is local or remote. In the given example the result would
be a Remote Unavailable state transmitting SF(1,0) messages.
4. Protection state coordination (PSC) protocol 4. Protection state coordination (PSC) protocol
Bidirectional protection switching, as well as unidirectional 1:1 Bidirectional protection switching, as well as unidirectional 1:1
protection, requires coordination between the two end points in protection, requires coordination between the two end points in
determining which of the two possible paths, the working or recovery determining which of the two possible paths, the working or recovery
path, is transmitting the data traffic in any given situation. When path, is transmitting the data traffic in any given situation. When
protection switching is triggered as described in section 3.1, the protection switching is triggered as described in section 3.1, the
end points must inform each other of the switch-over from one path to end points must inform each other of the switch-over from one path to
the other in a coordinated fashion. the other in a coordinated fashion.
skipping to change at page 14, line 21 skipping to change at page 15, line 11
state. In addition, limiting the transmission to a single path state. In addition, limiting the transmission to a single path
avoids possible conflicts and race conditions that could develop if avoids possible conflicts and race conditions that could develop if
the PSC messages were sent on both paths. the PSC messages were sent on both paths.
When the PSC information is changed due to a local input, three PSC When the PSC information is changed due to a local input, three PSC
messages SHOULD be transmitted as quickly as possible, to allow for messages SHOULD be transmitted as quickly as possible, to allow for
rapid protection switching. This set of three rapid messages allows rapid protection switching. This set of three rapid messages allows
for fast protection switching even if one or two of these packets are for fast protection switching even if one or two of these packets are
lost or corrupted. When the PSC information changes due to a remote lost or corrupted. When the PSC information changes due to a remote
message there is no need for the aforementioned rapid transmission of message there is no need for the aforementioned rapid transmission of
three messages. The exception (e.g. when the rapid tranmission is three messages. The exception (e.g. when the rapid transmission is
still required) is when going from WTR state to Normal state as a still required) is when going from WTR state to Normal state as a
result of a remote NR message. result of a remote NR message.
The frequency of the three rapid messages and the separate frequency The frequency of the three rapid messages and the separate frequency
of the continual transmission SHOULD be configurable by the operator. of the continual transmission SHOULD be configurable by the operator.
For protection switching within 50ms, the default interval of the For protection switching within 50ms, the default interval of the
first three PSC messages is RECOMMENDED to be no larger than 3.3ms. first three PSC messages is RECOMMENDED to be no larger than 3.3ms.
The continuous transmission interval is RECOMMENDED to be 5 seconds. The continuous transmission interval is RECOMMENDED to be 5 seconds.
If no valid PSC specific information is received, the last valid If no valid PSC specific information is received, the last valid
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has switched traffic to the protection path as a result of an has switched traffic to the protection path as a result of an
administrative command. The Fpath field SHALL indicate that the administrative command. The Fpath field SHALL indicate that the
working path is being blocked (i.e. Fpath set to 1), and the Path working path is being blocked (i.e. Fpath set to 1), and the Path
field SHALL indicate that user data traffic is being transported field SHALL indicate that user data traffic is being transported
on the protection path (i.e. Path set to 1). on the protection path (i.e. Path set to 1).
o (0110) Signal Fail - indicates that the transmitting end point has o (0110) Signal Fail - indicates that the transmitting end point has
identified a signal fail condition on either the working or identified a signal fail condition on either the working or
protection path. The Fpath field SHALL identify the path that is protection path. The Fpath field SHALL identify the path that is
reporting the failure condition (i.e. if protection path then reporting the failure condition (i.e. if protection path then
Fpath set to 0 and if working path then Fpath set to 1), and the Fpath is set to 0 and if working path then Fpath is set to 1), and
Path field SHALL indicate where the data traffic is being the Path field SHALL indicate where the data traffic is being
transported (i.e. if protection path is blocked then Path set to 0 transported (i.e. if protection path is blocked then Path is set
and if working path is blocked then Path set to 1). to 0 and if working path is blocked then Path is set to 1).
o (0101) Signal Defect - indicates that that the transmitting end o (0101) Signal Defect - indicates that that the transmitting end
point has identified a degradation of the signal, or integrity of point has identified a degradation of the signal, or integrity of
the packet transmission on either the working or protection path. the packet transmission on either the working or protection path.
The specifics for the method of identifying this degradation is The specifics for the method of identifying this degradation is
out-of-scope for this document. The details of the actions to be out-of-scope for this document. The details of the actions to be
taken for this situation is left for future specification. taken for this situation is left for future specification.
o (0100) Manual switch - indicates that the transmitting end point o (0100) Manual switch - indicates that the transmitting end point
has switched traffic as a result of an administrative Manual has switched traffic as a result of an administrative Manual
skipping to change at page 18, line 33 skipping to change at page 19, line 18
| ?< | | >? | | ?< | | >? |
| \|\\ Protection Path //|/ | | \|\\ Protection Path //|/ |
+-----+ \\=======================// +-----+ +-----+ \\=======================// +-----+
|--------Protection Domain--------| |--------Protection Domain--------|
Figure 3: Protection domain Figure 3: Protection domain
4.3.1. Basic operation 4.3.1. Basic operation
The purpose of the PSC protocol is to allow the end points of the The purpose of the PSC protocol is to allow an end point of the
protection domain to notify their peer of the status of the domain protection domain to notify its peer of the status of the domain that
that is known at the end point and coordinate the transmission of the is known at the end point and coordinate the transmission of the data
data traffic. The current state of the end point is expressed in the traffic. The current state of the end point is expressed in the
values of the Request field [reflecting the local requests at that values of the Request field [reflecting the local requests at that
end point] and the Fpath field [reflecting knowledge of a blocked end point] and the Fpath field [reflecting knowledge of a blocked
path]. The coordination between the end points is expressed by the path]. The coordination between the end points is expressed by the
value of the Path field [indicating where the data traffic is being value of the Path field [indicating where the user data traffic is
transmitted]. The value of the Path field SHOULD be identical for being transmitted]. The value of the Path field SHOULD be identical
both end points at any particular time. The values of the Request for both end points at any particular time. The values of the
and Fpath fields may not be identical between the two end points.In Request and Fpath fields may not be identical between the two end
particular it should be noted that a remote message MAY not cause the points. In particular it should be noted that a remote message MAY
end point to change the Request field that is being transmitted while not cause the end point to change the Request field that is being
it does affect the Path field (see details in the following transmitted while it does affect the Path field (see details in the
subsections). following subsections).
The protocol is a single-phase protocol. Single-phase implies that The protocol is a single-phase protocol. Single-phase implies that
each end point notifies its peer of a change in the operation each end point notifies its peer of a change in the operation
(switching to or from the protection path) and makes the switch (switching to or from the protection path) and makes the switch
without waiting for acknowledgement. without waiting for acknowledgement.
The following subsections will identify the messages that SHALL be The following subsections will identify the messages that SHALL be
transmitted by the end point in different scenarios. The messages transmitted by the end point in different scenarios. The messages
are described as REQ(FP, P) - where REQ is the value of the Request are described as REQ(FP, P) - where REQ is the value of the Request
field, FP is the value of the Fpath field, and P is the value of the field, FP is the value of the Fpath field, and P is the value of the
skipping to change at page 19, line 28 skipping to change at page 20, line 13
traffic. traffic.
4.3.2. Priority of inputs 4.3.2. Priority of inputs
As noted above (in section 3.1.1) the PSC Control Process accepts As noted above (in section 3.1.1) the PSC Control Process accepts
input from five local input sources. There is a definition of input from five local input sources. There is a definition of
priority between the different inputs that may be triggered locally. priority between the different inputs that may be triggered locally.
The list of local requests in order of priority are (from highest to The list of local requests in order of priority are (from highest to
lowest priority): lowest priority):
1. Clear (Operator command) 1. Clear (Operator command)
2. Lockout of protection (Operator command) 2. Lockout of protection (Operator command)
3. Signal Fail on protection (OAM/Control Plane/Server Indication) 3. Signal Fail on protection (OAM/Control Plane/Server Indication)
4. Forced switch (Operator command) 4. Forced switch (Operator command)
5. Signal Fail on working (OAM/Control Plane/Server Indication) 5. Signal Fail on working (OAM/Control Plane/Server Indication)
6. Signal Degrade on working (OAM/Control Plane/Server Indication) 6. Signal Degrade on working (OAM/Control Plane/Server Indication)
7. Clear Signal Fail/Degrade (OAM/Control Plane/Server Indication) 7. Clear Signal Fail/Degrade (OAM/Control Plane/Server Indication)
8. Manual switch (Operator command) 8. Manual switch (Operator command)
9. WTR expires (WTR Timer) 9. WTR expires (WTR Timer)
10. No request (default)
As was noted above, the Local request logic SHALL always select the
local input indicator with the highest priority as the current local
request. All local inputs with lower priority than this current
local request will be blocked.
The determination of whether a remote message is accepted or ignored The determination of whether a remote message is accepted or ignored
is a function of the current state of the local LER and the current is a function of the current state of the local LER and the current
local request (see section 3.1.3). Part of this consideration will local request (see section 3.1.3). Part of this consideration will
be included in the following subsections describing the operation in be included in the following subsections describing the operation in
the different states. the different states.
4.3.3. Operation of PSC States 4.3.3. Operation of PSC States
The following sub-sections present the operation of the different
states defined in section 3.1.6. For each state we define the
reaction, i.e. the new state and the message to transmit, to each
possible input - either the highest priority local input or the PSC
message from the remote LER. If the definition states to "ignore"
the message, the intention is that the LER should remain in its
current state and continue transmitting (as presented in section 4.1)
the current PSC message.
4.3.3.1. Normal State 4.3.3.1. Normal State
When the protection domain has no special condition in effect, the When the protection domain has no special condition in effect, the
ingress LER SHALL forward the user data along the working path, and, ingress LER SHALL forward the user data along the working path, and,
in the case of 1+1 protection, the Permanent Bridge will bridge the in the case of 1+1 protection, the Permanent Bridge will bridge the
data to the recovery path as well. The receiving LER SHALL read the data to the recovery path as well. The receiving LER SHALL read the
data from the working path. data from the working path.
When the end point is in Normal State it SHALL transmit a NR(0,0) When the end point is in Normal State it SHALL transmit a NR(0,0)
message, indicating - Nothing to report and data traffic is being message, indicating - Nothing to report and data traffic is being
transported on the working path. transported on the working path.
When the LER (assume LER-A) is in Normal State the following When the LER (assume LER-A) is in Normal State the following
transitions are relevant in reaction to a local input (new state transitions are relevant in reaction to a local input (new state
SHOULD be marked as local): SHOULD be marked as local):
o A local Lockout of protection input SHALL cause the LER to go into o A local Lockout of protection input SHALL cause the LER to go into
Unavailable State and begin transmission of a LO(0,0) message to local Unavailable State and begin transmission of a LO(0,0)
the far-end LER (LER-Z). message.
o A local Forced switch input SHALL cause the LER to go into o A local Forced switch input SHALL cause the LER to go into local
Protecting administrative state and begin transmission of a Protecting administrative state and begin transmission of a
FS(1,1) message to the far-end LER (LER-Z). FS(1,1) message.
o A local Signal Fail indication on the protection path SHALL cause o A local Signal Fail indication on the protection path SHALL cause
the LER to go into Unavailable state and begin transmission of a the LER to go into local Unavailable state and begin transmission
SF(0,0) message to the far-end LER (LER-Z). of a SF(0,0) message.
o A local Signal Fail indication on the working path SHALL cause the o A local Signal Fail indication on the working path SHALL cause the
LER to go into Protecting failure state and begin transmission of LER to go into local Protecting failure state and begin
a SF(1,1) message to the far-end LER (LER-Z). transmission of a SF(1,1) message.
o A local Manual switch input SHALL cause the LER to go into o A local Manual switch input SHALL cause the LER to go into local
Protecting administrative state and begin transmission of a Protecting administrative state and begin transmission of a
MS(1,1) message to the far-end LER (LER-Z). MS(1,1) message.
o All other local inputs SHOULD be ignored. o All other local inputs SHALL be ignored.
In Normal state, remote messages would cause the following reaction In Normal state, remote messages would cause the following reaction
from the LER (new state SHOULD be marked as remote): from the LER (new state SHOULD be marked as remote):
o A remote Lockout of protection message SHALL cause the LER (LER-A) o A remote Lockout of protection message SHALL cause the LER to go
to go into Unavailable state, while continuing to transmit the into remote Unavailable state, while continuing to transmit the
NR(0,0) message. NR(0,0) message.
o A remote Forced switch message SHALL cause the LER (LER-A) to go o A remote Forced switch message SHALL cause the LER to go into
into Protecting administrative state, and transmit a NR(0,1) remote Protecting administrative state, and begin transmitting a
message. NR(0,1) message.
o A remote Signal Fail message that indicates that the failure is on o A remote Signal Fail message that indicates that the failure is on
the protection path SHALL cause the LER (LER-A) to go into the protection path SHALL cause the LER (LER-A) to go into remote
Unavailable state, while continuing to transmit the NR(0,0) Unavailable state, while continuing to transmit the NR(0,0)
message. message.
o A remote Signal Fail message that indicates that the failure is on o A remote Signal Fail message that indicates that the failure is on
the working path SHALL cause the LER (LER-A) to go into Protecting the working path SHALL cause the LER to go into remote Protecting
failure state, and transmit a NR(0,1) message. failure state, and transmit a NR(0,1) message.
o A remote Manual switch message SHALL cause the LER (LER-A) to go o A remote Manual switch message SHALL cause the LER to go into
into Protecting administrative state, and transmit a NR(0,1) remote Protecting administrative state, and transmit a NR(0,1)
message. message.
o All other remote messages SHOULD be ignored. o All other remote messages SHALL be ignored.
4.3.3.2. Unavailable State 4.3.3.2. Unavailable State
When the protection path is unavailable - either as a result of a When the protection path is unavailable - either as a result of a
Lockout operator command, or as a result of a SF or SD detected on Lockout operator command, or as a result of a SF detected on the
the protection path - then the protection domain is in the protection path - then the protection domain is in the unavailable
unavailable state. In this state, the data traffic is transported on state. In this state, the data traffic is transported on the working
the working path. path and is not protected. When the domain is in unavailable state
the PSC messages may not get through and therefore the protection is
more dependent on the local inputs rather than the remote messages
(that may not be received).
The protection domain will exit the unavailable state and revert to The protection domain will exit the unavailable state and revert to
the normal state when, either the operator clears the Lockout command the normal state when, either the operator clears the Lockout command
or the protection path recovers from the signal fail or degraded or the protection path recovers from the signal fail or degraded
situation. Both ends will resume sending the PSC packets over the situation. Both ends will resume sending the PSC packets over the
protection path, as a result of this recovery. protection path, as a result of this recovery.
When in unavailable state the data traffic is being transported on
the working path and is not protected. When the domain is in
unavailable state the PSC messages may not get through and therefore
the protection is more dependent on the local inputs rather than the
remote messages (that may not be received).
When the LER (assume LER-A) is in Unavailable State the following When the LER (assume LER-A) is in Unavailable State the following
transitions are relevant in reaction to a local input (new state transitions are relevant in reaction to a local input (new state
SHOULD be marked as local): SHOULD be marked as local):
o A local Clear input SHOULD be ignored if the LER is in remote o A local Clear input SHOULD be ignored if the LER is in remote
Unavailable state. If in local Unavailable state due to a Lockout Unavailable state. If in local Unavailable state due to a Lockout
command, then the input SHALL cause the LER to go to Normal state command, then the input SHALL cause the LER to go to Normal state
and begin transmitting a NR(0,0) message. and begin transmitting a NR(0,0) message.
o A local Lockout of protection input SHALL cause the LER to remain o A local Lockout of protection input SHALL cause the LER to remain
in Unavailable State and begin transmission of a LO(0,0) message in local Unavailable State and transmit a LO(0,0) message to the
to the far-end LER (LER-Z). far-end LER (LER-Z).
o A local Clear SF in local Unavailable state due to a Signal Fail o A local Clear SF of the protection path in local Unavailable state
on the protection path and the Clear SF indicates that the that is due to a SF on the protection path SHALL cause the LER to
protection path is now cleared, then the input SHALL cause the LER go to Normal state and begin transmitting a NR(0,0) message. If
to go to Normal state and begin transmitting a NR(0,0) message. the LER is in remote Unavailable state but has an active local SF
If the LER is in remote Unavailable state but is under a local SF
condition, then the local Clear SF SHALL clear the SF local condition, then the local Clear SF SHALL clear the SF local
condition and the LER SHALL begin transmitting NR(0,0) messages, condition and the LER SHALL remain in remote Unavailable state and
maintaining the remote Unavailable state. In all other cases the begin transmitting NR(0,0) messages. In all other cases the local
local Clear SF SHOULD be ignored. Clear SF SHOULD be ignored.
o A local Forced switch SHOULD be ignored by the PSC Process Logic. o A local Forced switch SHALL be ignored by the PSC Control Logic.
o A local Signal Fail indication on the protection path SHALL cause o A local Signal Fail on the protection path input when in local
the LER to remain in Unavailable state and begin transmission of a Unavailable state [by implication this is due to a local SF on
SF(0,0) message. protection] SHALL cause the LER to remain in local Unavailable
state and transmit a SF(0,0) message.
o All other local inputs SHOULD be ignored. o A local Signal Fail on the working path input when in remote
Unavailable state SHALL cause the LER to remain in remote
Unavailable state and transmit a SF(1,0) message.
o All other local inputs SHALL be ignored.
If remote messages are being received over the protection path then If remote messages are being received over the protection path then
they would have the following affect: they would have the following affect:
o A remote Lockout of protection message SHALL cause the LER to o A remote Lockout of protection message SHALL cause the LER to
remain in Unavailable state, and continue transmission of the remain in Unavailable state, (note that if the LER was previously
current message (either NR(0,0) or LO(0,0) or SF(0,0)) in local Unavailable state due to a Signal Fail on the protection
path, then it will now be in remote Unavailable state) and
continue transmission of the current message (either NR(0,0) or
LO(0,0) or SF(0,0))
o A remote Signal Fail message that indicates that the failure is on o A remote Signal Fail message that indicates that the failure is on
the protection path SHALL cause the LER to remain in Unavailable the protection path SHALL cause the LER to remain in Unavailable
state and continue transmission of the current message (either state and continue transmission of the current message (either
NR(0,0) or SF(0,0) or LO(0,0)). NR(0,0) or SF(0,0) or LO(0,0)).
o A remote No Request, when the LER is remote Unavailable state o A remote No Request, when the LER is in remote Unavailable state
SHALL cause the LER to go into Normal state and begin transmission SHALL cause the LER to go into Normal state and continue
of a NR(0,0) message. When in local Unavailable state, the transmission of the current message (either NR(0,0) or SF(0,0)).
message SHALL be ignored. If there is a local SF indicator this may cause an immediate state
change after switching into Normal state. When in local
Unavailable state, the remote message SHALL be ignored.
o All other remote messages SHOULD be ignored. o All other remote messages SHALL be ignored.
4.3.3.3. Protecting administrative state 4.3.3.3. Protecting administrative state
In the protecting state the user data traffic is being transported on In the protecting state the user data traffic is being transported on
the protection path, while the working path is blocked due to an the protection path, while the working path is blocked due to an
operator command, i.e. Forced Switch or Manual Switch. operator command, i.e. Forced Switch or Manual Switch. The
difference between a local FS and local MS affects what local
indicators may be received - the Local request logic will block any
local SF when under the influence of a local FS, whereas the SF would
override a local MS. In general, a MS will be canceled in case of
either a local or remote SF or LO condition.
The following describe the reaction to local input: The following describe the reaction to local input:
o A local Clear SHOULD be ignored if in remote Protecting state. If o A local Clear SHOULD be ignored if in remote Protecting
in local Protecting administrative state then this input SHALL administrative state. If in local Protecting administrative state
cause the LER to go into Normal state and begin transmitting a then this input SHALL cause the LER to go into Normal state and
NR(0,0) message. begin transmitting a NR(0,0) message.
o A local Lockout of protection input SHALL cause the LER to go into o A local Lockout of protection input SHALL cause the LER to go into
Unavailable state and begin transmission of a LO(0,0) message. local Unavailable state and begin transmission of a LO(0,0)
message.
o A local Forced switch input SHALL cause the LER to remain in o A local Forced switch input SHALL cause the LER to remain in local
Protecting administrative state and begin transmission of a Protecting administrative state and transmit a FS(1,1) message.
FS(1,1) message.
o A local Signal Fail indication on the protection path SHALL cause o A local Signal Fail indication on the protection path SHALL cause
the LER to go into Unavailable state and begin transmission of a the LER to go into local Unavailable state (i.e. overriding the MS
SF(0,0) message. related Protection administrative state) and begin transmission of
a SF(0,0) message.
o A local Signal Fail indication on the working path SHOULD be o A local Signal Fail indication on the working path SHALL cause the
filtered by the Local Request Logic if the protecting state was LER to go into local Protecting failure state and begin
entered due to an active local Forced switch operator command. If transmitting a SF(1,1) message, if the current state is due to a
the protecting state is due to a remote Forced switch message, (local or remote) Manual switch operator command. If the LER is
then this local indication SHOULD be filtered by the PSC Process in remote Protecting administrative state due to a remote Forced
Logic. If the current state is due to a (local or remote) Manual Switch command, then this local indication SHALL cause the LER to
switch operator command, it SHALL cause the LER to go into remain in remote Protecting administrative state and transmit a
Protecting failure state and begin transmitting a SF(1,1) message. SF(1,1) message. If the LER is in local Protecting administrative
state due to a local Forced Switch command then this indication
SHALL be ignored (i.e. the indication should have been blocked by
the Local request logic).
o A local Clear SF when in remote Protecting administrative state o A local Clear SF when in remote Protecting administrative state
SHOULD clear any local SF condition that may exist. The LER SHALL SHOULD clear any local SF condition that may exist. The LER SHALL
stop transmitting the SF(1,1) message and begin transmitting an stop transmitting the SF(x,1) message and begin transmitting an
NR(0,1) message. NR(0,1) message.
o A local Manual switch input SHALL be filtered by the Local Request o A local Manual switch input SHALL be ignored if in remote
Logic if there is an active local Forced switch. If the Protecting administrative state is due to a remote Forced switch
protecting state is due to a remote Forced switch command, then command. If the current state is due to a (local or remote)
this local indication SHOULD be filtered by the PSC Process Logic. Manual switch operator command, it SHALL cause the LER to remain
If the current state is due to a (local or remote) Manual switch in local Protecting administrative state and transmit a MS(1,1)
operator command, it SHALL cause the LER to remain in Protecting message.
administrative state and begin transmission of a MS(1,1) message.
o All other local inputs SHOULD be ignored. o All other local inputs SHALL be ignored.
While in Protecting administrative state the LER may receive and While in Protecting administrative state the LER may receive and
react as follows to remote PSC messages: react as follows to remote PSC messages:
o A remote Lockout of protection message SHALL cause the LER to go o A remote Lockout of protection message SHALL cause the LER to go
into Unavailable state and begin transmitting a NR(0,0) message. into remote Unavailable state and begin transmitting a NR(0,0)
It should be noted that this automatically cancels the current message. It should be noted that this automatically cancels the
Forced switch or Manual switch command and data traffic is current Forced switch or Manual switch command and data traffic is
reverted to the working path. reverted to the working path.
o A remote Forced switch message SHOULD be ignored by the PSC o A remote Forced switch message SHOULD be ignored by the PSC
Process Logic if there is an active local Forced switch operator Process Logic if there is an active local Forced switch operator
command. If the Protecting state is due to a remote Forced switch command. If the Protecting administrative state is due to a
message then the LER SHALL remain in Protecting administrative remote Forced switch message then the LER SHALL remain in remote
state and continue transmission of the last message. If the Protecting administrative state and continue transmitting the last
Protecting state is due to either a local or remote Manual switch message. If the Protecting administrative state is due to either
then the LER SHALL remain in Protecting administrative state a local or remote Manual switch then the LER SHALL remain in
(updating the state information with the proper relevant remote Protecting administrative state (updating the state
information) and begin transmitting a NR(0,1) message. information with the proper relevant information) and begin
transmitting a NR(0,1) message.
o A remote Signal Fail message indicating a failure on the o A remote Signal Fail message indicating a failure on the
protection path SHALL cause the LER to go into Unavailable state protection path SHALL cause the LER to go into remote Unavailable
and begin transmitting a NR(0,0) message. It should be noted that state and begin transmitting a NR(0,0) message. It should be
this automatically cancels the current Forced switch or Manual noted that this automatically cancels the current Forced switch or
switch command and data traffic is reverted to the working path. Manual switch command and data traffic is reverted to the working
path.
o A remote Signal Fail message indicating a failure on the working o A remote Signal Fail message indicating a failure on the working
path SHALL be ignored if there is an active local Forced switch path SHALL be ignored if there is an active local Forced switch
command. If the Protecting state is due to a local or remote command. If the Protecting state is due to a local or remote
Manual switch then the LER SHALL go to Protecting failure state Manual switch then the LER SHALL go to remote Protecting failure
and begin transmitting a NR(0,1) message. state and begin transmitting a NR(0,1) message.
o A remote Manual switch message SHALL be ignored by the PSC Process o A remote Manual switch message SHALL be ignored by the PSC Control
Logic if in Protecting state due to a local or remote Forced Logic if in Protecting administrative state due to a local or
switch. If in Protecting state due to a remote Manual switch then remote Forced switch. If in Protecting administrative state due
the LER SHALL remain in Protecting administrative state and to a remote Manual switch then the LER SHALL remain in remote
continue transmitting the current message. If in Protecting state Protecting administrative state and continue transmitting the
due to an active local Manual switch then the LER SHALL remain in current message. If in local Protecting administrative state due
to an active Manual switch then the LER SHALL remain in local
Protecting administrative state and continue transmission of the Protecting administrative state and continue transmission of the
MS(1,1) message. MS(1,1) message.
o A remote DNR(0,0) message SHALL be ignored if in Protecting state o A remote DNR(0,1) message SHALL be ignored if in local Protecting
due to a local input. If in Protecting state due to a remote administrative state. If in remote Protecting administrative
message then the LER SHALL go to Do-not-revert state and begin state then the LER SHALL go to Do-not-revert state and continue
transmitting a NR(0,0) message. transmitting the current message.
o A remote NR(0,0) message SHALL be ignored if in Protecting state o A remote NR(0,0) message SHALL be ignored if in local Protecting
due to a local input. If in Protecting state due to a remote administrative state. If in remote Protecting administrative
message then the LER SHALL go to Normal state and begin state then the LER SHALL go to Normal state and begin transmitting
transmitting a NR(0,0) message. a NR(0,0) message.
o All other remote messages SHOULD be ignored. o All other remote messages SHOULD be ignored.
4.3.3.4. Protecting failure state 4.3.3.4. Protecting failure state
When the protection mechanism has been triggered and the protection When the protection mechanism has been triggered and the protection
domain has performed a protection switch, the domain is in the domain has performed a protection switch, the domain is in the
protecting failure state. In this state the normal data traffic is protecting failure state. In this state the normal data traffic is
transported on the protection path. transported on the protection path. When an LER is in this state it
implies that there was either a local SF condition or received a
remote SF PCS message. The SF condition or message indicated that
the failure is on the working path.
This state may be overridden by the Unavailable state triggers, i.e.
Lockout of Protection or SF on the protection path, or by issuing a
FS operator command. This state will be cleared when the SF
condition is cleared. In order to prevent flapping due to an
intermittent fault, the LER SHOULD employ a Wait-to-restore timer to
delay return to Normal state until the network has stabilized (see
section 3.1.5)
The following describe the reaction to local input: The following describe the reaction to local input:
o A local Clear SF SHOULD be ignored if in remote Protecting state. o A local Clear SF SHALL be ignored if in remote Protecting failure
If the Clear SF indicates that the protection path is now cleared state. If the Clear SF indicates that the protection path is now
(but working is still in SF condition) then the indicateion SHOULD cleared (but working is still in SF condition) then the indication
be ignored. If in local Protecting failure state and the LER is SHALL be ignored. If in local Protecting failure state and the
configured for revertive behavior then this input SHALL cause the LER is configured for revertive behavior then this input SHALL
LER to go into Wait-to-restore state, start the WTR timer, and cause the LER to go into Wait-to-restore state, start the WTR
begin transmitting a WTR(0,1) message. If in local Protecting timer, and begin transmitting a WTR(0,1) message. If in local
failure state and the LER is configured for non-revertive behavior Protecting failure state and the LER is configured for non-
then this input SHALL cause the LER to go into Do-not-revert state revertive behavior then this input SHALL cause the LER to go into
and begin transmitting a DNR(0,1) message. Do-not-revert state and begin transmitting a DNR(0,1) message.
o A local Lockout of protection input SHALL cause the LER to go into o A local Lockout of protection input SHALL cause the LER to go into
Unavailable state and begin transmission of a LO(0,0) message. Unavailable state and begin transmission of a LO(0,0) message.
o A local Forced switch input SHALL cause the LER to go into o A local Forced switch input SHALL cause the LER to go into
Protecting administrative state and begin transmission of a Protecting administrative state and begin transmission of a
FS(1,1) message. FS(1,1) message.
o A local Signal Fail indication on the protection path SHALL cause o A local Signal Fail indication on the protection path SHALL cause
the LER to go into Unavailable state and begin transmission of a the LER to go into Unavailable state and begin transmission of a
SF(0,0) message. SF(0,0) message.
o A local Signal Fail indication on the working path SHALL cause the o A local Signal Fail indication on the working path SHALL cause the
LER to remain in Protecting failure state and begin transmitting a LER to remain in local Protecting failure state and transmit a
SF(1,1) message. SF(1,1) message.
o All other local inputs SHOULD be ignored. o All other local inputs SHOULD be ignored.
While in Protecting failure state the LER may receive and react as While in Protecting failure state the LER may receive and react as
follows to remote PSC messages: follows to remote PSC messages:
o A remote Lockout of protection message SHALL cause the LER to go o A remote Lockout of protection message SHALL cause the LER to go
into Unavailable state and if in protecting failure state due to a into remote Unavailable state and if in local Protecting failure
local SF condition then the LER SHALL begin transmitting a SF(1,0) state then the LER SHALL transmit a SF(1,0) message, otherwise it
message, otherwise it SHALL transmit a NR(0,0) message. It should SHALL transmit a NR(0,0) message. It should be noted that this
be noted that this may cause loss of user data since the working may cause loss of user data since the working path is still in a
path is still in a failure condition. failure condition.
o A remote Forced switch message SHALL cause the LER go into o A remote Forced switch message SHALL cause the LER go into remote
Protecting administrative state and if in protecting failure state Protecting administrative state and if in local Protecting failure
due to a local SF condition the LER SHALL begin transmitting the state the LER SHALL transmit the SF(1,1) message, otherwise it
SF(1,1) message, otherwise it SHALL begin transmitting NR(0,0). SHALL transmit NR(0,1).
o A remote Signal Fail message indicating a failure on the o A remote Signal Fail message indicating a failure on the
protection path SHALL cause the LER to go into Unavailable state protection path SHALL cause the LER to go into remote Unavailable
and if in protecting failure state due to a local SF condition state and if in local Protecting failure state then the LER SHALL
then the LER SHALL begin transmitting a SF(1,0) message, otherwise transmit a SF(1,0) message, otherwise it SHALL transmitting
it SHALL begin transmitting NR(0,0) message. It should be noted NR(0,0) message. It should be noted that this may cause loss of
that this may cause loss of user data since the working path is user data since the working path is still in a failure condition.
still in a failure condition.
o If in Protecting state due to a remote message, a remote Wait-to- o If in remote Protecting failure state, a remote Wait-to-Restore
Restore message SHALL cause the LER to go into Wait-to-Restore message SHALL cause the LER to go into remote Wait-to-Restore
state and continue transmission of the current message. state and continue transmission of the current message.
o If in Protecting state due to a remote message, a remote Do-not- o If in remote Protecting failure state, a remote Do-not-revert
revert message SHALL cause the LER to go into Do-not-revert state message SHALL cause the LER to go into remote Do-not-revert state
and continue transmission of the current message. and continue transmission of the current message.
o All other remote messages SHOULD be ignored. o All other remote messages SHOULD be ignored.
4.3.3.5. Wait-to-restore state 4.3.3.5. Wait-to-restore state
The Wait-to-Restore state is used by the PSC protocol to delay The Wait-to-Restore state is used by the PSC protocol to delay
reverting to the normal state, when recovering from a failure reverting to the normal state, when recovering from a failure
condition on the working path, for the period of the WTR timer to condition on the working path, for the period of the WTR timer to
allow the recovering failure to stabilize. While in the Wait-to- allow the recovering failure to stabilize. While in the Wait-to-
Restore state the data traffic SHALL continue to be transported on Restore state the data traffic SHALL continue to be transported on
the protection path. The natural transition from the Wait-to-Restore the protection path. The natural transition from the Wait-to-Restore
state to Normal state will occur when the WTR timer expires. state to Normal state will occur when the WTR timer expires.
When in Wait-to-Restore state the following describe the reaction to When in Wait-to-Restore state the following describe the reaction to
local inputs: local inputs:
o A local Lockout of protection command SHALL cause the LER to Stop o A local Lockout of protection command SHALL cause the LER to Stop
the WTR timer, go into Unavailable state, and begin transmitting a the WTR timer, go into local Unavailable state, and begin
LO(0,0) message. transmitting a LO(0,0) message.
o A local Forced switch command SHALL cause the LER to Stop the WTR o A local Forced switch command SHALL cause the LER to Stop the WTR
timer, go into Protecting administrative state, and begin timer, go into local Protecting administrative state, and begin
transmission of a FS(1,1) message. transmission of a FS(1,1) message.
o A local Signal Fail indication on the protection path SHALL cause o A local Signal Fail indication on the protection path SHALL cause
the LER to Stop the WTR timer, go into Unavailable state, and the LER to Stop the WTR timer, go into local Unavailable state,
begin transmission of a SF(0,0) message. and begin transmission of a SF(0,0) message.
o A local Signal Fail indication on the working path SHALL cause the o A local Signal Fail indication on the working path SHALL cause the
LER to Stop the WTR timer, go into Protecting failure state, and LER to Stop the WTR timer, go into local Protecting failure state,
begin transmission of a SF(1,1) message. and begin transmission of a SF(1,1) message.
o A local Manual switch input SHALL cause the LER to Stop the WTR o A local Manual switch input SHALL cause the LER to Stop the WTR
timer, go into Protecting administrative state and begin timer, go into local Protecting administrative state and begin
transmission of a MS(1,1) message. transmission of a MS(1,1) message.
o A local WTR expires input SHALL cause the LER to remain in Wait- o A local WTR expires input SHALL cause the LER to remain in Wait-
to-Restore state and begin transmitting a NR(0,1) message. to-Restore state and begin transmitting a NR(0,1) message.
o All other local inputs SHOULD be ignored. o All other local inputs SHOULD be ignored.
When in Wait-to-Restore state the following describe the reaction to When in Wait-to-Restore state the following describe the reaction to
remote messages: remote messages:
o A remote Lockout of protection message SHALL cause the LER to Stop o A remote Lockout of protection message SHALL cause the LER to Stop
the WTR timer, go into Unavailable state, and begin transmitting a the WTR timer, go into remote Unavailable state, and begin
NR(0,0) message. transmitting a NR(0,0) message.
o A remote Forced switch message SHALL cause the LER to Stop the WTR o A remote Forced switch message SHALL cause the LER to Stop the WTR
timer, go into Protecting administrative state, and begin timer, go into remote Protecting administrative state, and begin
transmission of a NR(0,1) message. transmission of a NR(0,1) message.
o A remote Signal Fail message for the protection path SHALL cause o A remote Signal Fail message for the protection path SHALL cause
the LER to Stop the WTR timer, go into Unavailable state, and the LER to Stop the WTR timer, go into remote Unavailable state,
begin transmission of a NR(0,0) message. and begin transmission of a NR(0,0) message.
o A remote Signal Fail message for the working path SHALL cause the o A remote Signal Fail message for the working path SHALL cause the
LER to Stop the WTR timer, go into Protecting failure state, and LER to Stop the WTR timer, go into remote Protecting failure
begin transmission of a NR(0,1) message. state, and begin transmission of a NR(0,1) message.
o A remote Manual switch message SHALL cause the LER to Stop the WTR o A remote Manual switch message SHALL cause the LER to Stop the WTR
timer, go into Protecting administrative state and begin timer, go into remote Protecting administrative state and begin
transmission of a NR(0,1) message. transmission of a NR(0,1) message.
o If the WTR timer is running then a remote NR message SHALL be o If the WTR timer is running then a remote NR message SHALL be
ignored. If the WTR timer is no longer running then a remote NR ignored. If the WTR timer is no longer running then a remote NR
message SHALL cause the LER to go into Normal state and begin message SHALL cause the LER to go into Normal state and begin
transmitting a NR(0,0) message. transmitting a NR(0,0) message.
o All other remote messages SHOULD be ignored. o All other remote messages SHOULD be ignored.
4.3.3.6. Do-not-revert state 4.3.3.6. Do-not-revert state
Do-not-revert state is a continuation of the protecting state when Do-not-revert state is a continuation of the Protecting failure
the protection domain is configured for non-revertive behavior. state. When the protection domain is configured for non-revertive
While in Do-not-revert state, data traffic continues to be behavior. While in Do-not-revert state, data traffic continues to be
transported on the protection path until the administrator sends a transported on the protection path until the administrator sends a
command to revert to the Normal state. It should be noted that there command to revert to the Normal state. It should be noted that there
is a fundemental difference between this state and Normal - whereas is a fundamental difference between this state and Normal - whereas
Forced Switch in Normal state actually causes a switch in the Forced Switch in Normal state actually causes a switch in the
transport path used, in Do-not-revert state the Forced switch just transport path used, in Do-not-revert state the Forced switch just
switches the state (to Protecting administrative state) but the switches the state (to Protecting administrative state) but the
traffic would continue to be transported on the protection path! The traffic would continue to be transported on the protection path! To
command to revert back to Normal state could either be a Lockout of revert back to Normal state the administrator SHALL issue a Lockout
protection (followed be a Clear command), a Clear command, or a new of protection command followed by a Clear command.
form of the Manual switch command [note: This would also require some
kind of agreement, although it seems to have been adopted by ITU-T in
G.8031 for Ethernet]. The following description of operation is
based on the Lockout/Clear option mentioned!
When in Do-not-revert state the following describe the reaction to When in Do-not-revert state the following describe the reaction to
local input: local input:
o A local Lockout of protection command SHALL cause the LER to go o A local Lockout of protection command SHALL cause the LER to go
into Unavailable state and begin transmitting a LO(0,0) message. into local Unavailable state and begin transmitting a LO(0,0)
message.
o A local Forced switch command SHALL cause the LER to go into o A local Forced switch command SHALL cause the LER to go into local
Protecting administrative state and begin transmission of a Protecting administrative state and begin transmission of a
FS(1,1) message. FS(1,1) message.
o A local Signal Fail indication on the protection path SHALL cause o A local Signal Fail indication on the protection path SHALL cause
the LER to go into Unavailable state and begin transmission of a the LER to go into local Unavailable state and begin transmission
SF(0,0) message. of a SF(0,0) message.
o A local Signal Fail indication on the working path SHALL cause the o A local Signal Fail indication on the working path SHALL cause the
LER to go into Protecting failure state and begin transmission of LER to go into local Protecting failure state and begin
a SF(1,1) message. transmission of a SF(1,1) message.
o A local Manual switch input SHALL cause the LER to go into o A local Manual switch input SHALL cause the LER to go into local
Protecting administrative state and begin transmission of a Protecting administrative state and begin transmission of a
MS(1,1) message. MS(1,1) message.
o All other local inputs SHOULD be ignored. o All other local inputs SHOULD be ignored.
When in Do-not-revert state the following describe the reaction to When in Do-not-revert state the following describe the reaction to
remote messages: remote messages:
o A remote Lockout of protection message SHALL cause the LER to go o A remote Lockout of protection message SHALL cause the LER to go
into Unavailable state and begin transmitting a NR(0,0) message. into remote Unavailable state and begin transmitting a NR(0,0)
message.
o A remote Forced switch message SHALL cause the LER to go into o A remote Forced switch message SHALL cause the LER to go into
Protecting administrative state and begin transmission of a remote Protecting administrative state and begin transmission of a
NR(0,1) message. NR(0,1) message.
o A remote Signal Fail message for the protection path SHALL cause o A remote Signal Fail message for the protection path SHALL cause
the LER to go into Unavailable state and begin transmission of a the LER to go into remote Unavailable state and begin transmission
NR(0,0) message. of a NR(0,0) message.
o A remote Signal Fail message for the working path SHALL cause the o A remote Signal Fail message for the working path SHALL cause the
LER to go into Protecting failure state, and begin transmission of LER to go into remote Protecting failure state, and begin
a NR(0,1) message. transmission of a NR(0,1) message.
o A remote Manual switch message SHALL cause the LER to go into o A remote Manual switch message SHALL cause the LER to go into
Protecting administrative state and begin transmission of a remote Protecting administrative state and begin transmission of a
NR(0,1) message. NR(0,1) message.
o All other remote messages SHOULD be ignored. o All other remote messages SHOULD be ignored.
5. IANA Considerations 5. IANA Considerations
To be added in future version. This draft requires the allocation of a Channel Code from the G-ACh
repository.
6. Security Considerations 6. Security Considerations
To be added in future version. To be added in future version.
7. Acknowledgements 7. Acknowledgements
The authors would like to thank all members of the teams (the Joint The authors would like to thank all members of the teams (the Joint
Working Team, the MPLS Interoperability Design Team in IETF and the Working Team, the MPLS Interoperability Design Team in IETF and the
T-MPLS Ad Hoc Group in ITU-T) involved in the definition and T-MPLS Ad Hoc Group in ITU-T) involved in the definition and
specification of MPLS Transport Profile. specification of MPLS Transport Profile.
Appendix A. PSC state machine tables
The PSC state machine is described in section 4.3.3. This appendix
provides the same information but in tabular format. In the event of
a mismatch between these tables and the text in section 4.3.3, the
text is authoritative. Note that this appendix is intended to be a
functional description, not an implmentation specification.
For the sake of clarity of the table the six states listed in the
text are split into thirteen states. The logic of the split is to
differentiate between the different cases given in the conditional
statements in the descriptions of each state in the text. In
addition, the remote and local states were split for the Unavailable,
Protecting failure, and Protecting administrative states.
There is only one table for the PSC state machine, but it is broken
into two parts for space reasons. The first part lists the thirteen
possible states, the eight possible local inputs (that is, inputs
which are generated by the node in question) and the action taken
when a given input is received when the node is in a particular
state. The second part of the table lists the thirteen possible
states and the eight remote inputs (inputs which come from a node
other than the one executing the state machine).
There are thirteen rows in the table, headers notwithstanding. These
rows are the thirteen possible extended states in the state machine.
The text in the first column is the current state. Those states
which have both source and cause are formatted as State:Cause:Source.
For example, the string UA:LO:L indicates that the current state is
'Unavailable', that the cause of the current state is a Lockoutof
protection that was a Local input. In contrast, the state N simply
is Normal; there is no need to track the cause for entry into Normal
state.
The thirteen extended states, as they appear in the table, are:
N Normal state
UA:LO:L Unavailable state due to local Lockout
UA:P:L Unavailable state due to local SF on protection path
UA:LO:R Unavailable state due to remote Lockout message
UA:P:R Unavailable state due to remote SF message on protection path
PF:W:L Protecting failure state due to local SF on working path
PF:W:R Protecting failure state due to remote SF message on working
path
PA:F:L Protecting administrative state due to local FS operator
command
PA:M:L Protecting administrative state due to local MS operator
command
PA:F:R Protecting administrative state due to remote FS message
PA:M:R Protecting administrative state due to remote MS message
WTR Wait-to-restore state
DNR Do-not-revert state
Each state corresponds to the transmission of a particular set of
Request, FPath and Path bits. The table below lists the message that
is generally sent in each particular state. If the message to be
sent in a particular state deviates from the table below, it is noted
in the footnotes to the state-machine table.
State REQ(FP,P)
------- ---------
N NR(0,0)
UA:LO:L LO(0,0)
UA:P:L SF(0,0)
UA:LO:R NR(0,0)
UA:P:R NR(0,0)
PF:W:L SF(1,1)
PF:W:R NR(0,1)
PA:F:L FS(1,1)
PA:M:L MS(1,1)
PA:F:R NR(0,1)
PA:M:R NR(0,1)
WTR WTR(0,1)
DNR DNR(0,1)
The top row in each table is the list of possible inputs. The local
inputs are:
NR No Request
OC Operator Clear
LO Lockout of protection
SF-P Signal Fail on protection path
SF-W Signal Fail on working path
FS Forced Switch
CSF Clear Signal Fail
MS Manual Switch
WTRExp WTR Expired
and the remote inputs are:
LO remote LO message
SF-P remote SF message indicating protection path
SF-W remote SF message indicating working path
FS remote FS message
MS remote MS message
WTR remote WTR message
DNR remote DNR message
NR remote NR message
Section 4.3.3 refers to some states as 'remote' and some as 'local'.
By definition, all states listed in the table of local sources are
local states, and all states listed in the table of remote sources
are remote states. For example, section 4.3.3.1 says "A local
Lockout of protection input SHALL cause the LER to go into local
Unavailable State". As the trigger for this state change is a local
one, 'local Unavailable State' is by definition displayed in the
table of local sources. Similarly, "A remote Lockout of protection
message SHALL cause the LER to go into remote Unavailable state"
means that the state represented in the Unavailable rows in the table
of remote sources is by definition a remote Unavailable state.
Each cell in the table below contains either a state, a footnote, or
the letter 'i'. 'i' stands for Ignore, and is an indication to
continue with the current behavior. See section 4.3.3. The
footnotes are listed below the table.
Part 1: Local input state machine
| OC | LO | SF-P | FS | SF-W | CSF | MS | WTRExp
--------+-----+-------+------+------+------+------+------+-------
N | i |UA:LO:L|UA:P:L|PA:F:L|PF:W:L| i |PA:M:L| i
UA:LO:L | N | i | i | i | i | i | i | i
UA:P:L | i |UA:LO:L| i | i | i | [5] | i | i
UA:LO:R | i |UA:LO:L| [1] | i | [2] | [6] | i | i
UA:P:R | i |UA:LO:L|UA:P:L| i | [3] | [6] | i | i
PF:W:L | i |UA:LO:L|UA:P:L|PA:F:L| i | [7] | i | i
PF:W:R | i |UA:LO:L|UA:P:L|PA:F:L|PF:W:L| i | i | i
PA:F:L | N |UA:LO:L|UA:P:L| i | i | i | i | i
PA:M:L | N |UA:LO:L|UA:P:L|PA:F:L|PF:W:L| i | i | i
PA:F:R | i |UA:LO:L|UA:P:L|PA:F:L| [4] | [8] | i | i
PA:M:R | i |UA:LO:L|UA:P:L|PA:F:L|PF:W:L| i |PA:M:L| i
WTR | i |UA:LO:L|UA:P:L|PA:F:L|PF:W:L| i |PA:M:L| [9]
DNR | i |UA:LO:L|UA:P:L|PA:F:L|PF:W:L| i |PA:M:L| i
Part 2: Remote messages state machine
| LO | SF-P | FS | SF-W | MS | WTR | DNR | NR
--------+-------+------+------+------+------+------+------+------
N |UA:LO:R|UA:P:R|PA:F:R|PF:W:R|PA:M:R| i | i | i
UA:LO:L | i | i | i | i | i | i | i | i
UA:P:L | [10] | i | i | i | i | i | i | i
UA:LO:R | i | i | i | i | i | i | i | [16]
UA:P:R |UA:LO:R| i | i | i | i | i | i | [16]
PF:W:L | [11] | [12] |PA:F:R| i | i | i | i | i
PF:W:R |UA:LO:R|UA:P:R|PA:F:R| i | i | [14] | [15] | i
PA:F:L |UA:LO:R|UA:P:R| i | i | i | i | i | i
PA:M:L |UA:LO:R|UA:P:R|PA:F:R| [13] | i | i | i | i
PA:F:R |UA:LO:R|UA:P:R| i | i | i | i | i | N
PA:M:R |UA:LO:R|UA:P:R|PA:F:R| [13] | i | i | i | N
WTR |UA:LO:R|UA:P:R|PA:F:R|PF:W:R|PA:M:R| i | i | [17]
DNR |UA:LO:R|UA:P:R|PA:F:R|PF:W:R|PA:M:R| i | i | i
The following are the footnotes for the table:
[1] Remain in the current state (UA:LO:R) and transmit SF(0,0)
[2] Remain in the current state (UA:LO:R) and transmit SF(1,0)
[3] Remain in the current state (UA:P:R) and transmit SF(1,0)
[4] Remain in the current state (PA:F:R) and transmit SF(1,1)
[5] If the SF being cleared is SF-P, Transition to N. If it's SF-W,
ignore the clear.
[6] Remain in current state (UA:x:R), if the CSF corresponds to a
previous SF then begin transmitting NR(0,0).
[7] If the SF being cleared is SF-P, ignore the clear. If it's SF-W,
transition to WTR, start the WTR timer, and send WTR(1,1)
[8] Remain in PA:F:R and transmit NR(0,1)
[9] Remain in WTR, send NR(0,1)
[10] Transition to UA:LO:R continue sending SF(0,0)
[11] Transition to UA:LO:R and send SF(1,0)
[12] Transition to UA and send SF(1,0)
[13] Transition to PF:W:R and send NR(0,1)
[14] Transition to WTR state and continue to send the current
message.
[15] Transition to DNR state and continue to send the current
message.
[16] Transition to N state and continue to send the current message.
[17] If the receiving node's WTR timer has expired, transition to N.
If not, maintain current state and message.
8. References 8. References
8.1. Normative References 8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5654] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., [RFC5654] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N.,
and S. Ueno, "Requirements of an MPLS Transport Profile", and S. Ueno, "Requirements of an MPLS Transport Profile",
RFC 5654, September 2009. RFC 5654, September 2009.
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