One document matched: draft-weingarten-mpls-tp-linear-protection-04.txt
Differences from draft-weingarten-mpls-tp-linear-protection-03.txt
Network Working Group S. Bryant, Ed.
Internet-Draft Cisco
Intended status: Standards Track N. Sprecher, Ed.
Expires: April 29, 2010 Nokia Siemens Networks
H. van Helvoort, Ed.
Huawei
A. Fulignoli, Ed.
Ericsson
Y. Weingarten
Nokia Siemens Networks
October 26, 2009
MPLS-TP Linear Protection
draft-weingarten-mpls-tp-linear-protection-04.txt
Status of this Memo
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Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Abstract
The MPLS Transport Profile (MPLS-TP) being specified jointly by IETF
and ITU-T includes requirements documents and framework documents.
The framework documents define the basic architecture that is needed
in order to support various aspects of the required behavior. This
document addresses the functionality described in the Survivability
Framework document [11] and defines a protocol that may be used to
fulfill the function of the Protection State Coordination for linear
protection, as described in that document.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Contributing authors . . . . . . . . . . . . . . . . . . . 5
2. Conventions used in this document . . . . . . . . . . . . . . 5
2.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Definitions and Terminology . . . . . . . . . . . . . . . 6
3. Protection switching logic . . . . . . . . . . . . . . . . . . 6
3.1. Protection switching trigger mechanisms . . . . . . . . . 6
3.2. Protection switching control logical architecture . . . . 7
3.2.1. PSC Status Module . . . . . . . . . . . . . . . . . . 8
4. Protection state coordination (PSC) protocol . . . . . . . . . 8
4.1. Transmission and acceptance of PSC control packets . . . . 9
4.2. Protocol format . . . . . . . . . . . . . . . . . . . . . 9
4.2.1. PSC Requests . . . . . . . . . . . . . . . . . . . . . 11
4.2.2. Path Fault Identifier . . . . . . . . . . . . . . . . 12
4.2.3. Active path indicator . . . . . . . . . . . . . . . . 12
4.2.4. Current Protection Type . . . . . . . . . . . . . . . 12
4.3. Principles of Operation . . . . . . . . . . . . . . . . . 13
4.3.1. PSC States . . . . . . . . . . . . . . . . . . . . . . 13
4.3.2. Failure or Degraded condition (Working path) . . . . . 14
4.3.3. Lockout of Protection . . . . . . . . . . . . . . . . 15
4.3.4. Failure or Degraded condition (Recovery path) . . . . 15
4.3.5. Operator Controlled Switching . . . . . . . . . . . . 16
4.3.6. Recovery from switching . . . . . . . . . . . . . . . 17
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
6. Security Considerations . . . . . . . . . . . . . . . . . . . 18
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1. Normative References . . . . . . . . . . . . . . . . . . . 18
8.2. Informative References . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
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1. Introduction
As noted in the architecture for Multi-Protocol Label Switching
Transport Profile (MPLS-TP) [7], the overall architecture framework
for MPLS-TP is based on a profile of the MPLS and Pseudowire (PW)
procedures as specified for the MPLS and (MS-)PW architectures
defined in RFC 3031 [3], RFC 3985 [5] and [6]. One of the basic
survivability functions, pointed out by the Survivability Framework
document [11], is that of simple and rapid protection switching
mechanisms for Label Switched Paths (LSP) and Pseudo-wires (PW).
Protection switching is a fully allocated survivability mechanism.
It is fully allocated in the sense that the route and bandwidth of
the recovery path is reserved for a selected working path. It
provides a fast and simple survivability mechanism, that allows the
network operator to easily grasp the active state of the network,
compared to other survivability mechanisms.
As specified in the Survivability Framework document [11], protection
switching is applied to a protection domain. For the purposes of
this document, we define the protection domain of a P2P LSP as
consisting of two Label Switching Relays (LSR) and the transport
paths that connect them. For a P2MP LSP the protection domain
includes the root (or source) LSR, the destination (or sink) LSRs,
and the transport paths that connect them.
In 1+1 unidirectional architecture as presented in [11], a recovery
transport path is dedicated to each working transport path. Normal
traffic is bridged and fed to both the working and the recovery
transport entities by a permanent bridge at the source of the
protection domain. The sink of the protection domain selects which
of the working or recovery entities to receive the traffic from,
based on a predetermined criteria, e.g. server defect indication.
When used for bidirectional switching the 1+1 protection architecture
must also support a Protection State Coordination (PSC) protocol.
This protocol is used to help synchronize the decisions of both ends
of the protection domain in selecting the proper traffic flow.
In the 1:1 architecture, a recovery transport path is dedicated to
the working transport path of a single service. However, the normal
traffic is transmitted only once, on either the working or the
recovery path, by using a selector bridge at the source of the
protection domain. A selector at the sink of the protection domain
then selects the path that carries the normal traffic. Since the
source and sink need to be coordinated to ensure that the selector
bridge at both ends select the same path, this architecture must
support the PSC protocol.
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The 1:n protection architecture extends this last architecture by
sharing the recovery path amongst n services. Again, the recovery
path is fully allocated and disjoint from any of the n working
transport paths that it is being used to protect. The normal data
traffic for each service is transmitted only once, either on the
normal working path for that service or, in cases that trigger
protection switching (as defined in [11]) may be sent on the recovery
path. It should be noted that in cases where multiple working path
services have triggered protection switching that some services,
dependent upon their Service Level Agreement (SLA), may not be
transmitted as a result of limited resources on the recovery path.
In this architecture there is a need for coordination of the
protection switching, and in addition there is need for resource
allocation negotiation. Due to the added complexity of this
architecture, the procedures for this will be delayed to a different
document and further study.
As was pointed out in the Survivability Framework [11] and
highlighted above, there is a need for coordination between the end-
points of the protection domain when employing bidirectional
protection schemes. This is especially true when there is a need to
maintain traffic over a co-routed bidirectional LSP. This document
presents a protocol and a set of procedures for activating this
coordination within the protection domain.
1.1. Contributing authors
Hao Long (Huawei)
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [1].
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2.1. Acronyms
This draft uses the following acronyms:
+---------+----------------------------------------+
| DNR | Do not revert |
| FS | Forced Switch |
| GACH | Generic Associated Channel Header |
| LSR | Label Switching relay |
| MPLS-TP | Transport Profile for MPLS |
| MS | Manual Switch |
| P2P | Point-to-point |
| P2MP | Point-to-multipoint |
| PDU | Packet Data Unit |
| PSC | Protection State Coordination Protocol |
| PST | Path Segment Tunnel |
| SD | Signal Degrade |
| SF | Signal Fail |
| SLA | Service Level Agreement |
| WTR | Wait-to-Restore |
+---------+----------------------------------------+
2.2. Definitions and Terminology
The terminology used in this document is based on the terminology
defined in [10] and further adapted for MPLS-TP in [11]. . In
addition, we use the term LSR to refer to a MPLS-TP Network Element,
whether it is a LSR, LER, T-PE, or S-PE.
3. Protection switching logic
3.1. Protection switching trigger mechanisms
The protection switching should be initiated in reaction to any of
the following triggers:
o Server layer indication - if any of the lower layers (e.g. the
physical layer) notifies the MPLS-TP layer that a failure has been
detected.
o OAM signalling - if the OAM continuity and connectivity
verification tools detect that there is a loss of continuity or
mis-connectivity or the performance monitoring indicates a
degradation of the utility of the working path for the current
transport path. In cases of signal degradation, switching to the
recovery path SHOULD only be activated if the recovery path can
guarantee better conditions than the degraded working path.
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o Control plane - if there is a control plane active in the network
(either signalling or routing), it MAY trigger protection
switching based on conditions detected by the control plane. If
the control-plane is based on GMPLS [13] then the recovery process
should comply with the process described in [12].
o Operator command - the network operator may issue commands that
trigger protection switching. The commands that are supported
include - Forced Switch, Manual Switch, Clear, Lockout of
Protection, (see definitions in [10]).
3.2. Protection switching control logical architecture
Protection switching processes the triggers described above together
with the inputs received from the far-end LSR. These inputs cause
the LSR to take certain actions, e.g. switching the Selector Bridge
to select the working or recovery path, and to transmit different
protocol messages.
+-------------+ Operator Command Local PSC +-----------+
| External |-----------------+ +-----------------| PSC Status|
| Interface | | | request +---| Module |
+-------------+ | | | +-----------+
V V V Prot. Stat. ^
+----------+ Local OAM +---------------+Highest +------------+ |
| OAM |----------->| Local Request |------->| PSC Mess. | |
| Module | request | logic |local R.| Generator | |
+----------+ +------->+---------------+ +------------+ |
+----------+ | | | |
| Svr/CP |---+ Highest local|request | |
+----------+ V V |
+-------------+ +-----------------+ PSC Message |
| Remote Req. | Remote PSC | global Request | |
| Receiver |------------>| logic | |
+-------------+ Request +-----------------+ |
^ | |
| Highest global request| |
| V |
| +-----------------+ PSC status |
Remote PSC message | PSC Process |-----------------+
| logic |--------> Action
| |
+-----------------+
Figure 1: Protection switching control logic
Figure 1 describes the logical architecture of the protection
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switching control. The Local Request logic unit accepts the triggers
from the OAM, external operator commands, and from the local control
plane (when present) and determines the highest priority request.
This high-priority request is passed to both the PSC Message
generator, that will generate the appropriate protocol message to be
sent to the far-end LSR, and the Global Request logic, that will
cross-check this local request with the information received from the
far-LSR. The Global Request logic then processes these two PSC
requests that determines the highest priority request that is passed
to the PSC Process logic. The PSC Process logic uses this input to
determine what actions need to be taken, e.g. switching the Selector
Bridge, and the current status of the protection domain.
3.2.1. PSC Status Module
The PSC Control Logic must retain the status of the protection
domain. The possible different states indicate the current status of
the protection environment, and can be in one of three states:
o Normal (Idle) state - When both the recovery and the working paths
are fully allocated and active, data traffic is being transmitted
over the working path, and there are no events being reported
within the domain.
o Protecting state - When either the working path has reported a
signal failure or degradation of signal, or the operator has
issued an operator command and the data traffic has been
redirected to the recovery path.
o Unavailable state - When the recovery path is unavailable, either
as a result of reporting a SF or SD condition, or as a result of
an administrative Lockout command.
This state may affect the actions taken by the control logic, and
therefore, the PSC Status Module transfers the current status to the
Local Request Logic.
See section 4.3.1 for details on what actions are affected by the PSC
state.
4. Protection state coordination (PSC) protocol
Bidirectional protection switching, as well as unidirectional 1:1
protection, requires coordination between the two end-points in
determining which of the two possible paths, the working or recovery
path, is operational in any given situation. When protection
switching is triggered as described in section 3.1, the end-points
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must inform each other of the switch-over from one path to the other
in a coordinated fashion.
There are different possibilities for the type of coordinating
protocol. One possibility is a two-phased coordination in which the
MEP that is initiating the protection switching sends a protocol
message indicating the switch but the actual switch-over is performed
only after receiving an 'Ack' from the far-end MEP. The other
possibility is a single-phased coordination, in which the initiating
MEP switches over to the alternate path and informs the far-end of
the switch, and the far-end must complete the switch-over.
In the following sub-sections we describe the protocol messages that
should be used between the two end-points of the protection domain.
For the sake of simplicity of the protocol, this protocol is based on
the single-phase approach described above.
4.1. Transmission and acceptance of PSC control packets
The PSC control packets should be transmitted over the recovery path
only. This allows the transmission of the messages without affecting
the normal traffic in the most prevalent case, i.e. the idle state.
In addition, limiting the transmission to a single path avoids
possible conflicts and race conditions that could develop if the PSC
messages were sent on both paths.
A new PSC control packets must be transmitted immediately when a
change in the transmitted status occurs.
The first three PSC packets should be transmitted as fast as possible
only if the PSC information to be transmitted has been changed so
that fast protection switching is possible even if one or two PSC
packets are lost or corrupted. For protection switching within 50ms,
the interval of the first three PSC signals should be 3.3ms. PSC
packets after the first three should be transmitted with an interval
of 5 seconds.
If no valid PSC specific information is received, the last valid
received information remains applicable. In the event a signal fail
condition is detected on the protection transport entity, the
received PSC specific information should be evaluated.
4.2. Protocol format
The protocol messages SHALL be sent over the GACH as described in
[8]. There is a single channel type for the set of PSC messages,
each message will be identified by the first field of the ACH payload
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as described below. PSC messages SHOULD support addressing by use of
the method described in [8]. The following figure shows the format
for the full PSC message.
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 0 0 1|0 0 0 0|0 0 0 0 0 0 0 0| MPLS-TP PSC Channel Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ACH TLV Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Addressing TLV +
: ... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ PSC Control Packet ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Format of PSC packet with a GACH header
Where:
o MPLS-TP PSC Channel Code is the GACH channel number assigned to
the PSC = TBD
o The ACH TLV Header is described in [8]
o The use of the Addressing TLV are for further study
o The following figure shows the format of the PSC Control message
that is the payload for the PSC packet.
Editor's note: There is a suggestion that this format should be
aligned with the format used by G.8031/G.8131/Y.1731 in ITU. The
argument being that this would make it easier to pass review from ITU
and allow easier transfer of technology.
The counter-argument is that the ITU format is based upon an attempt
to find a common format for different functionality and therefore
involves different fields that are not necessary for the protection
switching. Defining a new dedicated format would make for a simpler
and more intuitive protocol. End of editor's note.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ver|Request|Typ| FPath | Path | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Format of the PSC control packet
Where:
o Ver: is the version of the protocol, for this version the value
SHOULD be 0.
o Request: this field indicates the specific PSC request that is
being transmitted, the details are described in section 4.1.1
o Typ: indicates the type of protection scheme currently supported,
more details are given in section 4.1.4
o FPath: used to indicate the path that is reporting a failure
condition, the possible values are described in section 4.1.2
o Path: used to indicate the currently active path, possible values
are described in section 4.1.3
o Rsv, Reserved: these fields are reserved for possible future use.
These bits MUST be set to zero on transmission, and ignored upon
reception.
4.2.1. PSC Requests
The Protection Switching Coordination (PSC) protocol SHALL support
the following request types, in order of priority from highest to
lowest:
o (1111) Clear
o (1110) Lockout protection
o (1101) Forced switch
o (0110) Signal fault
o (0101) Signal degrade
o (0100) Manual switch
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o (0011) Wait to restore
o (0010) Do not revert (DNR)
o (0000) No request
See section 6.3 for a description of the operation of the different
requests.
4.2.2. Path Fault Identifier
The Fpath field of the PSC control SHALL be used only in a Signal
fault (0101) or Signal degrade (0100) control packet. Its value
indicates on which path the signal anomaly was detected. The
following are the possible values:
o 0: indicates that the fault condition is on the Recovery path
o 1: indicates that the fault condition is on the Working path
o 2-255: for future extensions
4.2.3. Active path indicator
The Path field of the PSC control SHALL be used to indicate which
path the source MEP is currently using for data transmission. The
MEP should compare the value of this bit with the path that is
locally selected for data transmission to verify that there is no
inconsistency between the two end-points of the protected domain. If
an inconsistency is detected then an alarm should be raised. The
following are the possible values:
o 0: indicates that normal traffic is being transmitted on the
Working path.
o 1: indicates the Recovery path is being used to transmit the
normal traffic from the Working path.
o 2-255: for future extensions
4.2.4. Current Protection Type
The Typ field indicates the currently configured protection
architecture type, this should be validated to be consistent for both
ends of the protected domain. If an inconsistency is detected then
an alarm should be raised. The following are the possible values:
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o 11: 1+1 bidirectional switching
o 10: 1:1 bidirectional switching
o 01: 1+1 unidirectional switching
o 00: 1:1 unidirectional switching
4.3. Principles of Operation
In all of the following sub-sections, assume a protected domain
between LSR-A and LSR-Z, using paths W (working) and R (recovery).
4.3.1. PSC States
4.3.1.1. Normal State
When the protected domain has no special condition in effect, the
ingress LSR SHOULD forward the user data along the working path, and,
in the case of 1+1 protection, the Permanent Bridge will bridge the
data to the recovery path as well. The receiving LSR SHOULD read the
data from the working path.
The ingress LSR MAY transmit a No Request PSC packet with the Path
field set to 0 for the recovery path.
4.3.1.2. Protecting State
When the protection mechanism has been triggered and the protected
domain has performed a protection switch, the domain is in the
protecting state. In this state the normal traffic is transmitted
and received on the recovery path.
If the protection domain is currently in a protecting state, then the
LSRs SHOULD NOT accept a Manual Switch request.
If the protection domain is currently in a protecting state, and a
Forced Switch is requested then the normal traffic SHALL continue to
be transmitted on the recovery path even if the original protection
trigger is cleared, and the Forced Switch condition will be signalled
by the PSC messages.
4.3.1.3. Unavailable State
When the recovery path is unavailable - either as a result of a
Lockout operator command (see section 4.3.3), or as a result of a SF
or SD detected on the recovery path (see section 4.3.4) - then the
protection domain is in the unavailable state. In this state, the
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normal traffic is transmitted and received on the working path.
While in unavailable state any event that would trigger a protection
switching SHOULD be ignored with the following exception - If a
Signal Degrade request is received, then protection switching will be
activated only if the recovery path can guarantee a better signal
than the working path.
The protection domain will exit the unavailable state and revert to
the normal state when, either the operator clears the Lockout command
or the recovery path recovers from the signal fault or degraded
situation. Both ends will resume sending the PCS packets over the
recovery path, as a result of this recovery.
4.3.2. Failure or Degraded condition (Working path)
If one of the LSRs (for example, LSR-A) detects a failure condition
or a serious degradation condition on the working path that warrants
invoking protection switching, then it SHOULD take the following
actions:
o Switch all traffic for LSR-Z to the recovery path only.
o Transmit a PCS control packet, using GACH, with the appropriate
Request code (either Signal fault or Signal degrade), the Fpath
set to 1, to indicate that the fault/degrade was detected on the
working path, and the Path set to 0, indicating that normal
traffic is now being transmitted on the recovery path.
o Verify that LSR-Z replies with a PCS control packet indicating
that it has switched to the recovery path. If this is not
received after xxx then send an alarm to the management system.
When the far-end LSR (in this example LSR-Z) receives the PCS packet
informing it that other LSR (LSR-A) has switched, it SHOULD perform
the following actions:
o Check priority of the request
o Switch all traffic addressed to LSR-A to the recovery path only.
o Begin transmission of a PCS control packet, using GACH, with the
appropriate Request code (either Signal fault or Signal degrade),
the Fpath set to 1, to indicate that the fault/degrade was
detected on the working path, and the Path set to 1, indicating
that traffic is now being transmitted on the recovery path.
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4.3.3. Lockout of Protection
If one of the LSRs (for example, LSR-A) receives a management command
indicating that the protection is disabled, then it SHOULD indicate
this to the far-end LSR (for example, LSR-Z) that it is not possible
to use the recovery path. The following actions MUST be taken:
Transmit a PCS control packet, using GACH, with the Request code
set to Lockout of protection (1110), the Fpath set to 0, and the
Path set to 0.
All normal traffic packets should be transmitted on the working
path only.
Verify that the far-end LSR (for example LSR-Z) is forwarding the
data packets on the working path. Raise alarm in case of
mismatch.
The PSC control logic should go into Unavailable state.
When the far-end LSR (in this example LSR-Z) receives the PCS packet
informing it that other LSR (LSR-A) has switched, it SHOULD perform
the following actions:
o Check priority of request
o Switch all normal traffic addressed to LSR-A to the working path
only.
o The PSC control logic should go into Unavailable status.
o Begin transmission of a PCS control packet, using GACH, with the
appropriate Request code (Lockout of protection), the Fpath set to
0, and the Path set to 0, indicating that traffic is now being
transmitted on the working path only.
4.3.4. Failure or Degraded condition (Recovery path)
If one of the LSRs (for example, LSR-A) detects a failure condition
or a serious degradation condition on the recovery path, then it
SHOULD take the following actions:
o Begin transmission of a PCS control packet with the appropriate
Request code (either Signal fault or Signal degrade), the Fpath
set to 0, to indicate that the fault/degrade was detected on the
recovery path, and the Path set to 0, indicating that traffic is
now being forwarded on the working path. Note that this will
actually reach the far-end if this is a unidirectional fault or
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recovery path is possibly in a degraded situation.
o The PSC control logic should go into Unavailable state.
o All traffic MUST be transmitted on the working path for the
duration of the SF/SD condition.
When the far-end LSR (in this example LSR-Z) receives the PCS packet
informing it that other LSR (LSR-A) has become Unavailable, it SHOULD
perform the following actions:
o Transmit all traffic on the working path for the duration of the
SF/SD condition
o The PSC Control logic should go into Unavailable state.
4.3.5. Operator Controlled Switching
If the management system indicated to one of the LSRs (for example
LSR-A) that a switch is necessary, e.g. either a Forced Switch or a
Manual Switch, then the LSR SHOULD switch the traffic to the recovery
path and perform the following actions:
o Switch all data traffic to the recovery path only.
o Transmit a PCS control packet, using GACH, with the appropriate
Request code (either Manual switch or Forced switch), the Fpath
set to 0, to indicate that the fault/degrade was detected on the
working path, and the Path set to 1, indicating that traffic is
now being forwarded on the recovery path.
o Verify that LSR-Z replies with a PCS control packet indicating
that it has switched to the recovery path. If this is not
received after xxx then send an alarm to the management system.
When the far-end LSR (in this example LSR-Z) receives the PCS packet
informing it that other LSR (LSR-A) has switched, it SHOULD perform
the following actions:
o Check priority of the request
o Switch all normal traffic addressed to LSR-A to the recovery path
only.
o Begin transmission of a PCS control packet, using GACH, with the
appropriate Request code (either Manual switch of Forced switch),
the Fpath set to 1, to indicate that the fault/degrade was
detected on the working path, and the Path set to 1, indicating
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that traffic is now being forwarded on the recovery path.
4.3.5.1. Clearing operator commands
The operator may clear the switching condition by issuing a Clear
request. This command will cause immediate recovery from the switch
that was initiated by any of the previous operator commands, i.e.
Forced Switch or Manual Switch. In addition, a Clear command after a
Lockout Protection command should clear the Unavailable state and
return the protection domain to the normal state.
If the Clear request is issued in the absence of a Manual Switch,
Forced Switch, or Lockout protection, then it SHALL be ignored. In
the presence of any of these commands, the Clear request SHALL clear
the state affected by the operator command.
4.3.6. Recovery from switching
When the condition that triggered the protection switching clears,
e.g. the cause of the failure condition has been corrected, or the
operator clears a Manual Switch, then the protection domain SHOULD
follow the following procedures:
o If the network is configured for non-revertive behaviour, then the
two LSRs SHOULD transmit DNR (Request code 0010) messages.
o If the network is recovering from an operator switching command
(in revertive mode), then both LSRs SHOULD return to using the
working transport path and transmit No request (Request code 0000)
messages.
o If the network is recovering from a failure or degraded condition
(in revertive mode), then the LSR that detects this recovery SHALL
activate a local Wait-to-restore (WTR) timer (see section 4.3.6.1)
to verify that there is not an intermittent failure. After the
WTR expires, the LSR SHOULD return to using the working transport
path and transmit No request (Request code 0000) messages.
4.3.6.1. Wait-to-restore timer
In revertive mode, in order to prevent frequent activation of
protection switching due to an intermittent defect, the working
transport path must become stable and fault-free before reverting to
the normal condition. In order to verify that this is the case a
fixed period of time must elapse before the normal traffic uses the
working transport path. This period, called the WTR period, should
be configurable by the operator in 1-minute intervals within the
range 1-12 minutes. The default value is 5 minutes.
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During this period, if a failure condition is detected on the working
transport path, then the WTR timer is cleared and the normal traffic
SHALL continue to be transported over the recovery transport path.
If the WTR timer expires without being pre-empted by a failure, then
the traffic SHOULD be returned to use the working transport path (as
above).
5. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
6. Security Considerations
This document does not by itself raise any particular security
considerations.
7. Acknowledgements
The authors would like to thank all members of the teams (the Joint
Working Team, the MPLS Interoperability Design Team in IETF and the
T-MPLS Ad Hoc Group in ITU-T) involved in the definition and
specification of MPLS Transport Profile.
8. References
8.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 792, March 1997.
[2] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., and
S. Ueno, "Requirements for the Trasport Profile of MPLS",
RFC 5654, June 2009.
8.2. Informative References
[3] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label
Switching Architecture", RFC 3031, Jan 2001.
[4] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., and T. Li,
"MPLS Label Stack Encoding", RFC 3032, January 2001", RFC 3032,
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Internet-Draft MPLS-TP LP October 2009
Jan 2001.
[5] Bryant, S. and P. Pate, "Pseudowire Emulation Edge-to-Edge
(PWE3) Architecture", RFC 3985, March 2005.
[6] Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for
Pseudowires", RFC 5085, December 2007.
[7] Bocci, M., Bryant, S., and L. Levrau, "A Framework for MPLS in
Transport Networks", ID draft-ietf-mpls-tp-framework-06.txt,
July 2009.
[8] Vigoureux,, M., Bocci, M., Swallow, G., Aggarwal, R., and D.
Ward, "MPLS Generic Associated Channel", RFC 5586, May 2009.
[9] Vigoureux, M., Betts, M., and D. Ward, "Requirements for OAM in
MPLS Transport Networks",
ID draft-ietf-mpls-tp-oam-requirements-03, April 2009.
[10] Mannie, E. and D. Papadimitriou, "Recovery Terminology for
Generalized Multi-Protocol Label Switching", RFC 4427,
Mar 2006.
[11] Sprecher, N., Farrel, A., and H. Shah, "Multi-protocol Label
Switching Transport Profile Survivability Framework",
ID draft-ietf-mpls-tp-survive-fwk-02.txt, Feb 2009.
[12] Lang, J., Papadimitriou, D., and Y. Rekhter, "RSVP-TE
Extensions in Support of End-to-End Generalized Multi-Protocol
Label Switching (GMPLS) Recovery", RFC 4872, May 2007.
[13] Mannie, E., "Generalized Multi-Protocol Label Switching (GMPLS)
Architecture", RFC 3945, Oct 2004.
Authors' Addresses
Stewart Bryant (editor)
Cisco
United Kingdom
Email: stbryant@cisco.com
Bryant, et al. Expires April 29, 2010 [Page 19]
Internet-Draft MPLS-TP LP October 2009
Nurit Sprecher (editor)
Nokia Siemens Networks
3 Hanagar St. Neve Ne'eman B
Hod Hasharon, 45241
Israel
Email: nurit.sprecher@nsn.com
Huub van Helvoort (editor)
Huawei
Kolkgriend 38, 1356 BC Almere
Netherlands
Phone: +31 36 5316076
Email: hhelvoort@huawei.com
Annamaria Fulignoli (editor)
Ericsson
Italy
Phone:
Email: annamaria.fulignoli@ericsson.com
Yaacov Weingarten
Nokia Siemens Networks
3 Hanagar St. Neve Ne'eman B
Hod Hasharon, 45241
Israel
Phone: +972-9-775 1827
Email: yaacov.weingarten@nsn.com
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