< draft-ietf-mpls-recovery-frmwrk-02.txt   draft-ietf-mpls-recovery-frmwrk-03.txt >
IETF Draft Vishal Sharma MPLS Working Group Vishal Sharma
Multi-Protocol Label Switching Jasmine Networks, Inc. Informational Track Metanoia, Inc.
Expires: August 2001 Expires: January 2002
Ben-Mack Crane Ben-Mack Crane
Srinivas Makam Srinivas Makam
Tellabs Operations, Inc. Tellabs Operations, Inc.
Ken Owens Ken Owens
Erlang Technology, Inc. Erlang Technology, Inc.
Changcheng Huang Changcheng Huang
Carleton University Carleton University
Fiffi Hellstrand Fiffi Hellstrand
Jon Weil Jon Weil
Loa Andersson Loa Andersson
Bilel Jamoussi Bilel Jamoussi
Nortel Networks Nortel Networks
Brad Cain Brad Cain
Mirror Image Internet Cereva Networks
Seyhan Civanlar Seyhan Civanlar
Coreon Networks Lemur Networks
Angela Chiu Angela Chiu
Celion Networks, Inc. Celion Networks, Inc.
March 2001 July 2001
Framework for MPLS-based Recovery Framework for MPLS-based Recovery
<draft-ietf-mpls-recovery-frmwrk-02.txt> <draft-ietf-mpls-recovery-frmwrk-03.txt>
Status of this memo Status of this memo
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Abstract Abstract
Multi-protocol label switching (MPLS) [1] integrates the label Multi-protocol label switching (MPLS) [1] integrates the label
swapping forwarding paradigm with network layer routing. To deliver swapping forwarding paradigm with network layer routing. To deliver
reliable service, MPLS requires a set of procedures to provide reliable service, MPLS requires a set of procedures to provide
protection of the traffic carried on different paths. This requires protection of the traffic carried on different paths. This requires
that the label switched routers (LSRs) support fault detection, fault that the label switched routers (LSRs) support fault detection, fault
notification, and fault recovery mechanisms, and that MPLS signaling notification, and fault recovery mechanisms, and that MPLS signaling
[2], [3], [4], [5], [6], [7] support the configuration of recovery. [2], [3], [4], [5], [6], [7] support the configuration of recovery.
With these objectives in mind, this document specifies a framework With these objectives in mind, this document specifies a framework
for MPLS based recovery. for MPLS based recovery.
Table of Contents Page Table of Contents
1.0 Introduction 3
1.1 Background 3
1.2 Motivations for MPLS-Based Recovery 3
1.3 Objectives 4
2.0 Overview 5
2.1 Recovery Models 6
2.2 Recovery Cycles 7
2.2.1 MPLS Recovery Cycle Model 7
2.2.2 MPLS Reversion Cycle Model 9
2.2.3 Dynamic Reroute Cycle Model 10
2.3 Definitions and Terminology 11
2.4 Abbreviations 15
3.0 MPLS Recovery Principles 15
3.1 Configuration of Recovery 15
3.2 Initiation of Path Setup 15
3.3 Initiation of Resource Allocation 16
3.4 Scope of Recovery 17
3.4.1 Topology 17
3.4.1.1 Local Repair 17
3.4.1.2 Global Repair 17
3.4.1.3 Alternate Egress Repair 18
3.4.1.4 Multi-Layer Repair 18
3.4.1.5 Concatenated Protection Domains 18
3.4.2 Path Mapping 18
3.4.3 Bypass Tunnels 19
3.4.4 Recovery Granularity 20
3.4.4.1 Selective Traffic Recovery 20
3.4.4.2 Bundling 20
3.4.5 Recovery Path Resource Use 20
3.5 Fault Detection 21
3.6 Fault Notification 21
3.7 Switch Over Operation 22
3.7.1 Recovery Trigger 22
3.7.2 Recovery Action 22
3.8 Post Recovery Operation 23
3.8.1 Fixed Protection Counterparts 23
3.8.2 Dynamic Protection Counterparts 24
3.8.3 Restoration and Notification 25
3.8.4 Reverting to Preferred Path 25
3.9 Performance 26
4.0 Recovery Requirements 26 1. Introduction.....................................................3
5.0 MPLS Recovery Options 27 1.1. Background......................................................3
6.0 Comparison Criteria 27 1.2. Motivation for MPLS-Based Recovery..............................4
7.0 Security Considerations 29 1.3. Objectives/Goals................................................5
8.0 Intellectual Property Considerations 29 2. Overview.........................................................6
9.0 Acknowledgements 29 2.1. Recovery Models.................................................7
10.0 Author's Addresses 30 2.1.1 Rerouting.......................................................7
11.0 References 30 2.1.2 Protection Switching............................................7
2.2. The Recovery Cycles.............................................8
2.2.1 MPLS Recovery Cycle Model.......................................8
2.2.2 MPLS Reversion Cycle Model......................................9
2.2.3 Dynamic Re-routing Cycle Model.................................11
2.3. Definitions and Terminology....................................12
2.3.1 General Recovery Terminology...................................12
2.3.2 Failure Terminology............................................15
2.4. Abbreviations..................................................16
3. MPLS-based Recovery Principles..................................16
3.1. Configuration of Recovery......................................16
3.2. Initiation of Path Setup.......................................17
3.3. Initiation of Resource Allocation..............................17
3.4. Scope of Recovery..............................................18
3.4.1 Topology.......................................................18
3.4.1.1 Local Repair................................................18
3.4.1.2 Global Repair...............................................19
3.4.1.3 Alternate Egress Repair.....................................19
3.4.1.4 Multi-Layer Repair..........................................19
3.4.1.5 Concatenated Protection Domains.............................19
3.4.2 Path Mapping...................................................20
3.4.3 Bypass Tunnels.................................................21
3.4.4 Recovery Granularity...........................................21
3.4.4.1 Selective Traffic Recovery..................................21
3.4.4.2 Bundling....................................................21
3.4.5 Recovery Path Resource Use.....................................21
3.5. Fault Detection................................................22
3.6. Fault Notification.............................................23
3.7. Switch-Over Operation..........................................23
3.7.1 Recovery Trigger...............................................23
3.7.2 Recovery Action................................................24
3.8. Post Recovery Operation........................................24
3.8.1 Fixed Protection Counterparts..................................24
3.8.1.1 Revertive Mode..............................................25
3.8.1.2 Non-revertive Mode..........................................25
3.8.2 Dynamic Protection Counterparts................................25
3.8.3 Restoration and Notification...................................26
3.8.4 Reverting to Preferred Path (or Controlled Rearrangement)......26
3.9. Performance....................................................27
4. MPLS Recovery Features..........................................27
5. Comparison Criteria.............................................28
6. Security Considerations.........................................30
7. Intellectual Property Considerations............................30
8. Acknowledgements................................................30
9. AuthorsÆ Addresses..............................................30
10. References......................................................31
1.0 Introduction 1. Introduction
This memo describes a framework for MPLS-based recovery. We provide a This memo describes a framework for MPLS-based recovery. We provide a
detailed taxonomy of recovery terminology, and discuss the motivation detailed taxonomy of recovery terminology, and discuss the motivation
for, the objectives of, and the requirements for MPLS-based recovery. for, the objectives of, and the requirements for MPLS-based recovery.
We outline principles for MPLS-based recovery, and also provide We outline principles for MPLS-based recovery, and also provide
comparison criteria that may serve as a basis for comparing and comparison criteria that may serve as a basis for comparing and
evaluating different recovery schemes. evaluating different recovery schemes.
1.1 Background 1.1. Background
Network routing deployed today is focussed primarily on connectivity Network routing deployed today is focussed primarily on connectivity
and typically supports only one class of service, the best effort and typically supports only one class of service, the best effort
class. Multi-protocol label switching, on the other hand, by class. Multi-protocol label switching, on the other hand, by
integrating forwarding based on label-swapping of a link local label integrating forwarding based on label-swapping of a link local label
with network layer routing allows flexibility in the delivery of new with network layer routing allows flexibility in the delivery of new
routing services. MPLS allows for using such media specific routing services. MPLS allows for using such media specific
forwarding mechanisms as label swapping. This enables more forwarding mechanisms as label swapping. This enables more
sophisticated features such as quality-of-service (QoS) and traffic sophisticated features such as quality-of-service (QoS) and traffic
engineering [8] to be implemented more effectively. An important engineering [8] to be implemented more effectively. An important
component of providing QoS, however, is the ability to transport data component of providing QoS, however, is the ability to transport data
reliably and efficiently. Although the current routing algorithms are reliably and efficiently. Although the current routing algorithms are
very robust and survivable, the amount of time they take to recover very robust and survivable, the amount of time they take to recover
from a fault can be significant, on the order of several seconds or from a fault can be significant, on the order of several seconds or
minutes, causing serious disruption of service for some applications minutes, causing serious disruption of service for some applications
in the interim. This is unacceptable to many organizations that aim in the interim. This is unacceptable to many organizations that aim
to provide a highly reliable service, and thus require recovery times to provide a highly reliable service, and thus require recovery times
on the order of tens of milliseconds, as specified, for example, in that are on the order of seconds down to 10's of milliseconds.
the GR253 specification for SONET.
MPLS recovery may be motivated by the notion that there are inherent MPLS recovery may be motivated by the notion that there are inherent
limitations to improving the recovery times of current routing limitations to improving the recovery times of current routing
algorithms. Additional improvement not obtainable by other means can algorithms. Additional improvement not obtainable by other means can
be obtained by augmenting these algorithms with MPLS recovery be obtained by augmenting these algorithms with MPLS recovery
mechanisms. Since MPLS is likely to be the technology of choice in mechanisms. Since MPLS is likely to be the technology of choice in
the future IP-based transport network, it is useful that MPLS be able the future IP-based transport network, it is useful that MPLS be able
to provide protection and restoration of traffic. MPLS may to provide protection and restoration of traffic. MPLS may
facilitate the convergence of network functionality on a common facilitate the convergence of network functionality on a common
control and management plane. Further, a protection priority could be control and management plane. Further, a protection priority could be
used as a differentiating mechanism for premium services that require used as a differentiating mechanism for premium services that require
high reliability. The remainder of this document provides a framework high reliability. The remainder of this document provides a framework
for MPLS based recovery. It is focused at a conceptual level and is for MPLS based recovery. It is focused at a conceptual level and is
meant to address motivation, objectives and requirements. Issues of meant to address motivation, objectives and requirements. Issues of
mechanism, policy, routing plans and characteristics of traffic mechanism, policy, routing plans and characteristics of traffic
carried by recovery paths are beyond the scope of this document. carried by recovery paths are beyond the scope of this document.
1.2 Motivation for MPLS-Based Recovery 1.2. Motivation for MPLS-Based Recovery
MPLS based protection of traffic (called MPLS-based Recovery) is MPLS based protection of traffic (called MPLS-based Recovery) is
useful for a number of reasons. The most important is its ability to useful for a number of reasons. The most important is its ability to
increase network reliability by enabling a faster response to faults increase network reliability by enabling a faster response to faults
than is possible with traditional Layer 3 (or IP layer) approaches than is possible with traditional Layer 3 (or IP layer) approaches
alone while still providing the visibility of the network afforded by alone while still providing the visibility of the network afforded by
Layer 3. Furthermore, a protection mechanism using MPLS could enable Layer 3. Furthermore, a protection mechanism using MPLS could enable
IP traffic to be put directly over WDM optical channels, without an IP traffic to be put directly over WDM optical channels and provide a
intervening SONET layer. This would facilitate the construction of recovery option without an intervening SONET layer. This would
IP-over-WDM networks. facilitate the construction of IP-over-WDM networks that request fast
recovery ability.
The need for MPLS-based recovery arises because of the following: The need for MPLS-based recovery arises because of the following:
I. Layer 3 or IP rerouting may be too slow for a core MPLS network I. Layer 3 or IP rerouting may be too slow for a core MPLS network
that needs to support high reliability/availability. that needs to support high reliability/availability.
II. Layer 0 (for example, optical layer) or Layer 1 (for example, II. Layer 0 (for example, optical layer) or Layer 1 (for example,
SONET) mechanisms may not be deployed in topologies that meet SONET) mechanisms may not be deployed in topologies that meet
carriers' protection goals. carriersÆ protection goals. Restoration at these layers may also be
wasteful use of resources.
III. The granularity at which the lower layers may be able to protect III. The granularity at which the lower layers may be able to protect
traffic may be too coarse for traffic that is switched using MPLS- traffic may be too coarse for traffic that is switched using MPLS-
based mechanisms. based mechanisms.
IV. Layer 0 or Layer 1 mechanisms may have no visibility into higher IV. Layer 0 or Layer 1 mechanisms may have no visibility into higher
layer operations. Thus, while they may provide, for example, link layer operations. Thus, while they may provide, for example, link
protection, they cannot easily provide node protection or protection protection, they cannot easily provide node protection or protection
of traffic transported at layer 3. of traffic transported at layer 3. Further, this may prevent the
lower layers from providing fast restoration for traffic that needs
it, while providing slower restoration (with possibly more optimal
use of resources) for traffic that does not require fast restoration.
In networks where the latter class of traffic is dominant, providing
fast restoration to all classes of traffic may not be cost effective
from a service providerÆs perspective.
V. MPLS has desirable attributes when applied to the purpose of V. MPLS has desirable attributes when applied to the purpose of
recovery for connectionless networks. Specifically that an LSP is recovery for connectionless networks. Specifically that an LSP is
source routed and a forwarding path for recovery can be "pinned" and source routed and a forwarding path for recovery can be "pinned" and
is not affected by transient instability in SPF routing brought on by is not affected by transient instability in SPF routing brought on by
failure scenarios. failure scenarios.
Furthermore there is a need for open standards. Furthermore, there is a need for open standards.
VI. Establishing interoperability of protection mechanisms between VI. Establishing interoperability of protection mechanisms between
routers/LSRs from different vendors in IP or MPLS networks is routers/LSRs from different vendors in IP or MPLS networks is desired
urgently required to enable the adoption of MPLS as a viable core to enable recovery mechanisms to work in a multivendor environment,
transport and traffic engineering technology. and to enable the transition of certain protected services to an MPLS
core.
1.3 Objectives/Goals 1.3. Objectives/Goals
We lay down the following objectives for MPLS-based recovery. The following are some important goals for MPLS-based recovery.
I. MPLS-based recovery mechanisms should facilitate fast (10's of ms) Ia. MPLS-based recovery mechanisms may be subject to the traffic
recovery times. engineering goal of optimal use of resources.
II. MPLS-based recovery should maximize network reliability and Ib. MPLS based recovery mechanisms should aim to facilitate
availability. MPLS-based recovery of traffic should minimize the restoration times that are sufficiently fast for the end user
number of single points of failure in the MPLS protected domain. application. That is, that better match the end-user applicationÆs
requirements. In some cases, this may be as short as 10s of
milliseconds.
III. MPLS-based recovery should enhance the reliability of the We observe that Ia and Ib are conflicting objectives, and a trade off
exists between them. The optimal choice depends on the end-user
application to restoration time and the cost impact of introducing
restoration in the network, as well as the end-user applicationÆs
sensitivity to cost.
II. MPLS-based recovery should aim to maximize network reliability
and availability. MPLS-based recovery of traffic should aim to
minimize the number of single points of failure in the MPLS protected
domain.
III. MPLS-based recovery should aim to enhance the reliability of the
protected traffic while minimally or predictably degrading the protected traffic while minimally or predictably degrading the
traffic carried by the diverted resources. traffic carried by the diverted resources.
IV. MPLS-based recovery techniques should be applicable for IV. MPLS-based recovery techniques should aim to be applicable for
protection of traffic at various granularities. For example, it protection of traffic at various granularities. For example, it
should be possible to specify MPLS-based recovery for a portion of should be possible to specify MPLS-based recovery for a portion of
the traffic on an individual path, for all traffic on an individual the traffic on an individual path, for all traffic on an individual
path, or for all traffic on a group of paths. Note that a path is path, or for all traffic on a group of paths. Note that a path is
used as a general term and includes the notion of a link, IP route or used as a general term and includes the notion of a link, IP route or
LSP. LSP.
V. MPLS-based recovery techniques may be applicable for an entire V. MPLS-based recovery techniques may be applicable for an entire
end-to-end path or for segments of an end-to-end path. end-to-end path or for segments of an end-to-end path.
VI. MPLS-based recovery actions should not adversely affect other VI. MPLS-based recovery mechanisms should aim to take into
network operations. consideration the recovery actions of lower layers. MPLS-based
mechanisms should not trigger lower layer protection switching.
VII. MPLS-based recovery actions in one MPLS protection domain
(defined in Section 2.2) should not adversely affect the recovery
actions in other MPLS protection domains.
VII. MPLS-based recovery mechanisms should be able to take into
consideration the recovery actions of lower layers.
VIII. MPLS-based recovery actions should avoid network-layering
violations. That is, defects in MPLS-based mechanisms should not
trigger lower layer protection switching.
IX. MPLS-based recovery mechanisms should minimize the loss of data VII. MPLS-based recovery mechanisms should aim to minimize the loss
and packet reordering during recovery operations. (The current MPLS of data and packet reordering during recovery operations. (The
specification has itself no explicit requirement on reordering). current MPLS specification itself has no explicit requirement on
reordering).
X. MPLS-based recovery mechanisms should minimize the state overhead VIII. MPLS-based recovery mechanisms should aim to minimize the state
incurred for each recovery path maintained. overhead incurred for each recovery path maintained.
XI. MPLS-based recovery mechanisms should be able to preserve the IX. MPLS-based recovery mechanisms should aim to preserve the
constraints on traffic after switchover, if desired. That is, if constraints on traffic after switchover, if desired. That is, if
desired, the recovery path should meet the resource requirements of, desired, the recovery path should meet the resource requirements of,
and achieve the same performance characteristics as the working path. and achieve the same performance characteristics as the working path.
2.0 Overview We observe that some of the above are conflicting goals, and real
deployment will often involve engineering compromises based on a
variety of factors such as cost, end-user application requirements,
network efficiency, and revenue considerations. Thus, these goals are
subject to tradeoffs based on the above considerations.
2. Overview
There are several options for providing protection of traffic using There are several options for providing protection of traffic using
MPLS. The most generic requirement is the specification of whether MPLS. The most generic requirement is the specification of whether
recovery should be via Layer 3 (or IP) rerouting or via MPLS recovery should be via Layer 3 (or IP) rerouting or via MPLS
protection switching or rerouting actions. protection switching or rerouting actions.
Generally network operators aim to provide the fastest and the best Generally network operators aim to provide the fastest and the best
protection mechanism that can be provided at a reasonable cost. The protection mechanism that can be provided at a reasonable cost. The
higher the level of protection, the more resources are consumed. higher the level of protection, the more resources are consumed.
Therefore it is expected that network operators will offer a spectrum Therefore it is expected that network operators will offer a spectrum
of service levels. MPLS-based recovery should give the flexibility to of service levels. MPLS-based recovery should give the flexibility to
select the recovery mechanism, choose the granularity at which select the recovery mechanism, choose the granularity at which
traffic is protected, and to also choose the specific types of traffic is protected, and to also choose the specific types of
traffic that are protected in order to give operators more control traffic that are protected in order to give operators more control
over that tradeoff. With MPLS-based recovery, it can be possible to over that tradeoff. With MPLS-based recovery, it can be possible to
provide different levels of protection for different classes of provide different levels of protection for different classes of
service, based on their service requirements. For example, using service, based on their service requirements. For example, using
approaches outlined below, a VLL service that supports real-time approaches outlined below, a Virtual Leased Line (VLL) service or
applications like VoIP may be supported using link/node protection real-time applications like Voice over IP (VoIP) may be supported
together with pre-established, pre-reserved path protection, while using link/node protection together with pre-established, pre-
best effort traffic may use established-on-demand path protection or reserved path protection. Best effort traffic, on the other hand, may
simply rely on IP re-route or higher layer recovery mechanisms. As use established-on-demand path protection or simply rely on IP re-
another example of their range of application, MPLS-based recovery route or higher layer recovery mechanisms. As another example of
strategies may be used to protect traffic not originally flowing on their range of application, MPLS-based recovery strategies may be
label switched paths, such as IP traffic that is normally routed hop- used to protect traffic not originally flowing on label switched
by-hop, as well as traffic forwarded on label switched paths. paths, such as IP traffic that is normally routed hop-by-hop, as well
as traffic forwarded on label switched paths.
2.1 Recovery Models 2.1. Recovery Models
There are two basic models for path recovery: rerouting and There are two basic models for path recovery: rerouting and
protection switching. protection switching.
Protection switching and rerouting, as defined below, may be used Protection switching and rerouting, as defined below, may be used
together. For example, protection switching to a recovery path may together. For example, protection switching to a recovery path may
be used for rapid restoration of connectivity while rerouting be used for rapid restoration of connectivity while rerouting
determines a new optimal network configuration, rearranging paths, as determines a new optimal network configuration, rearranging paths, as
needed, at a later time [9] [10]. needed, at a later time.
2.1.1 Rerouting 2.1.1 Rerouting
Recovery by rerouting is defined as establishing new paths or path Recovery by rerouting is defined as establishing new paths or path
segments on demand for restoring traffic after the occurrence of a segments on demand for restoring traffic after the occurrence of a
fault. The new paths may be based upon fault information, network fault. The new paths may be based upon fault information, network
routing policies, pre-defined configurations and network topology routing policies, pre-defined configurations and network topology
information. Thus, upon detecting a fault, paths or path segments to information. Thus, upon detecting a fault, paths or path segments to
bypass the fault are established using signaling. Reroute mechanisms bypass the fault are established using signaling. Reroute mechanisms
are inherently slower than protection switching mechanisms, since are inherently slower than protection switching mechanisms, since
more must be done following the detection of a fault. However reroute more must be done following the detection of a fault. However reroute
mechanisms are simpler and more frugal as no resources are committed mechanisms are simpler and more frugal as no resources are committed
skipping to change at page 7, line 9 skipping to change at page 7, line 38
Once the network routing algorithms have converged after a fault, it Once the network routing algorithms have converged after a fault, it
may be preferable, in some cases, to reoptimize the network by may be preferable, in some cases, to reoptimize the network by
performing a reroute based on the current state of the network and performing a reroute based on the current state of the network and
network policies. This is discussed further in Section 3.8. network policies. This is discussed further in Section 3.8.
In terms of the principles defined in section 3, reroute recovery In terms of the principles defined in section 3, reroute recovery
employs paths established-on-demand with resources reserved-on- employs paths established-on-demand with resources reserved-on-
demand. demand.
2.1.2 Protection Switching 2.1.2 Protection Switching
Protection switching recovery mechanisms pre-establish a recovery Protection switching recovery mechanisms pre-establish a recovery
path or path segment, based upon network routing policies, the path or path segment, based upon network routing policies, the
restoration requirements of the traffic on the working path, and restoration requirements of the traffic on the working path, and
administrative considerations. The recovery path may or may not be administrative considerations. The recovery path may or may not be
link and node disjoint with the working path[11], [14]. However if link and node disjoint with the working path[9], [14]. However if the
the recovery path shares sources of failure with the working path, recovery path shares sources of failure with the working path, the
the overall reliability of the construct is degraded. When a fault is overall reliability of the construct is degraded. When a fault is
detected, the protected traffic is switched over to the recovery detected, the protected traffic is switched over to the recovery
path(s) and restored. path(s) and restored.
In terms of the principles in section 3, protection switching employs In terms of the principles in section 3, protection switching employs
pre-established recovery paths, and if resource reservation is pre-established recovery paths, and, if resource reservation is
required on the recovery path, pre-reserved resources. required on the recovery path, pre-reserved resources. The various
sub-types of protection switching are detailed in Section 3.4 of this
2.1.2.1. Subtypes of Protection Switching document.
The resources (bandwidth, buffers, processing) on the recovery path
may be used to carry either a copy of the working path traffic or
extra traffic that is displaced when a protection switch occurs.
This leads to two subtypes of protection switching.
In 1+1 ("one plus one") protection, the resources (bandwidth,
buffers, processing capacity) on the recovery path are fully
reserved, and carry the same traffic as the working path. Selection
between the traffic on the working and recovery paths is made at the
path merge LSR (PML). In effect the PSL function is deprecated to
establishment of the working and recovery paths and a simple
replication function. The recovery intelligence is delegated to the
PML.
In 1:1 ("one for one") protection, the resources (if any) allocated
on the recovery path are fully available to preemptible low priority
traffic except when the recovery path is in use due to a fault on the
working path. In other words, in 1:1 protection, the protected
traffic normally travels only on the working path, and is switched to
the recovery path only when the working path has a fault. Once the
protection switch is initiated, the low priority traffic being
carried on the recovery path may be displaced by the protected
traffic. This method affords a way to make efficient use of the
recovery path resources.
This concept can be extended to 1:n (one for n) and m:n (m for n) 2.1.2.1
protection. 2.2. The Recovery Cycles
2.2 The Recovery Cycles
There are three defined recovery cycles; the MPLS Recovery Cycle, the There are three defined recovery cycles; the MPLS Recovery Cycle, the
MPLS Reversion Cycle and the Dynamic Re-routing Cycle. The first MPLS Reversion Cycle and the Dynamic Re-routing Cycle. The first
cycle detects a fault and restores traffic onto MPLS-based recovery cycle detects a fault and restores traffic onto MPLS-based recovery
paths. If the recovery path is non-optimal the cycle may be followed paths. If the recovery path is non-optimal the cycle may be followed
by any of the two latter to achieve an optimized network again. The by any of the two latter to achieve an optimized network again. The
reversion cycle applies for explicitly routed traffic that that does reversion cycle applies for explicitly routed traffic that that does
not rely on any dynamic routing protocols to be converged. The not rely on any dynamic routing protocols to be converged. The
dynamic re-routing cycle applies for traffic that is forwarded based dynamic re-routing cycle applies for traffic that is forwarded based
on hop-by-hop routing. on hop-by-hop routing.
2.2.1 MPLS Recovery Cycle Model 2.2.1 MPLS Recovery Cycle Model
The MPLS recovery cycle model is illustrated in Figure 1. The MPLS recovery cycle model is illustrated in Figure 1.
Definitions and a key to abbreviations follow. Definitions and a key to abbreviations follow.
--Network Impairment --Network Impairment
| --Fault Detected | --Fault Detected
| | --Start of Notification | | --Start of Notification
| | | -- Start of Recovery Operation | | | -- Start of Recovery Operation
| | | | --Recovery Operation Complete | | | | --Recovery Operation Complete
| | | | | --Path Traffic Restored | | | | | --Path Traffic Restored
skipping to change at page 9, line 35 skipping to change at page 9, line 40
Traffic Restoration Time Traffic Restoration Time
The time between the last recovery action and the time that the The time between the last recovery action and the time that the
traffic (if present) is completely recovered. This interval is traffic (if present) is completely recovered. This interval is
intended to account for the time required for traffic to once again intended to account for the time required for traffic to once again
arrive at the point in the network that experienced disrupted or arrive at the point in the network that experienced disrupted or
degraded service due to the occurrence of the fault (e.g. the PML). degraded service due to the occurrence of the fault (e.g. the PML).
This time may depend on the location of the fault, the recovery This time may depend on the location of the fault, the recovery
mechanism, and the propagation delay along the recovery path. mechanism, and the propagation delay along the recovery path.
2.2.2 MPLS Reversion Cycle Model 2.2.2 MPLS Reversion Cycle Model
Protection switching, revertive mode, requires the traffic to be Protection switching, revertive mode, requires the traffic to be
switched back to a preferred path when the fault on that path is switched back to a preferred path when the fault on that path is
cleared. The MPLS reversion cycle model is illustrated in Figure 2. cleared. The MPLS reversion cycle model is illustrated in Figure 2.
Note that the cycle shown below comes after the recovery cycle shown Note that the cycle shown below comes after the recovery cycle shown
in Fig. 1. in Fig. 1.
--Network Impairment Repaired --Network Impairment Repaired
| --Fault Cleared | --Fault Cleared
| | --Path Available | | --Path Available
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to-Restore Time period between fault clearing and the start of the to-Restore Time period between fault clearing and the start of the
reversion operation. reversion operation.
Reversion Operation Time Reversion Operation Time
The time between the first and last reversion actions. This may The time between the first and last reversion actions. This may
include message exchanges between the PSL and PML to coordinate include message exchanges between the PSL and PML to coordinate
reversion actions. reversion actions.
Traffic Restoration Time Traffic Restoration Time
The time between the last reversion action and the time that traffic The time between the last reversion action and the time that traffic
(if present) is completely restored on the preferred path. This (if present) is completely restored on the preferred path. This
interval is expected to be quite small since both paths are working interval is expected to be quite small since both paths are working
and care may be taken to limit the traffic disruption (e.g., using and care may be taken to limit the traffic disruption (e.g., using
"make before break" techniques and synchronous switch-over). "make before break" techniques and synchronous switch-over).
In practice, the only interesting times in the reversion cycle are In practice, the only interesting times in the reversion cycle are
the Wait-to-Restore Time and the Traffic Restoration Time (or some the Wait-to-Restore Time and the Traffic Restoration Time (or some
other measure of traffic disruption). Given that both paths are other measure of traffic disruption). Given that both paths are
available, there is no need for rapid operation, and a well- available, there is no need for rapid operation, and a well-
controlled switch-back with minimal disruption is desirable. controlled switch-back with minimal disruption is desirable.
2.2.3 Dynamic Re-routing Cycle Model 2.2.3 Dynamic Re-routing Cycle Model
Dynamic rerouting aims to bring the IP network to a stable state Dynamic rerouting aims to bring the IP network to a stable state
after a network impairment has occurred. A re-optimized network is after a network impairment has occurred. A re-optimized network is
achieved after the routing protocols have converged, and the traffic achieved after the routing protocols have converged, and the traffic
is moved from a recovery path to a (possibly) new working path. The is moved from a recovery path to a (possibly) new working path. The
steps involved in this mode are illustrated in Figure 3. steps involved in this mode are illustrated in Figure 3.
Note that the cycle shown below may be overlaid on the recovery Note that the cycle shown below may be overlaid on the recovery
cycle shown in Fig. 1 or the reversion cycle shown in Fig. 2, or both cycle shown in Fig. 1 or the reversion cycle shown in Fig. 2, or both
(in the event that both the recovery cycle and the reversion cycle (in the event that both the recovery cycle and the reversion cycle
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V. The PSL switches over the traffic from the working path to the V. The PSL switches over the traffic from the working path to the
recovery path recovery path
VI. The network enters a semi-stable state VI. The network enters a semi-stable state
VII. Dynamic routing protocols converge after the fault, and a new VII. Dynamic routing protocols converge after the fault, and a new
working path is calculated (based, for example, on some of the working path is calculated (based, for example, on some of the
criteria mentioned earlier in Section 2.1.1). criteria mentioned earlier in Section 2.1.1).
VIII. A new working path is established between the PSL and the PML VIII. A new working path is established between the PSL and the PML
(assumption is that PSL and PML have not changed) (assumption is that PSL and PML have not changed)
IX. Traffic is switched over to the new working path. IX. Traffic is switched over to the new working path.
2.3 Definitions and Terminology 2.3. Definitions and Terminology
This document assumes the terminology given in [1], and, in addition, This document assumes the terminology given in [1], and, in addition,
introduces the following new terms. introduces the following new terms.
2.3.1 General Recovery Terminology 2.3.1 General Recovery Terminology
Rerouting Rerouting
A recovery mechanism in which the recovery path or path segments are A recovery mechanism in which the recovery path or path segments are
created dynamically after the detection of a fault on the working created dynamically after the detection of a fault on the working
path. In other words, a recovery mechanism in which the recovery path path. In other words, a recovery mechanism in which the recovery path
is not pre-established. is not pre-established.
Protection Switching Protection Switching
A recovery mechanism in which the recovery path or path segments are A recovery mechanism in which the recovery path or path segments are
created prior to the detection of a fault on the working path. In created prior to the detection of a fault on the working path. In
other words, a recovery mechanism in which the recovery path is pre- other words, a recovery mechanism in which the recovery path is pre-
established. established.
Working Path Working Path
The protected path that carries traffic before the occurrence of a The protected path that carries traffic before the occurrence of a
fault. The working path exists between a PSL and PML. The working fault. The working path exists between a PSL and PML. The working
path can be of different kinds; a hop-by-hop routed path, a trunk, a path can be of different kinds; a hop-by-hop routed path, a trunk, a
link, an LSP or part of a multipoint-to-point LSP. link, an LSP or part of a multipoint-to-point LSP.
Synonyms for a working path are primary path and active path. Synonyms for a working path are primary path and active path.
Recovery Path Recovery Path
The path by which traffic is restored after the occurrence of a The path by which traffic is restored after the occurrence of a
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A path group that requires protection. A path group that requires protection.
Protected Traffic Portion (PTP) Protected Traffic Portion (PTP)
The portion of the traffic on an individual path that requires The portion of the traffic on an individual path that requires
protection. For example, code points in the EXP bits of the shim protection. For example, code points in the EXP bits of the shim
header may identify a protected portion. header may identify a protected portion.
Path Switch LSR (PSL) Path Switch LSR (PSL)
The PSL is responsible for switching or replicating the traffic
The PSL is responsible for switching or replicating the traffic
between the working path and the recovery path. between the working path and the recovery path.
Path Merge LSR (PML) Path Merge LSR (PML)
An LSR that receives both working path traffic and its corresponding An LSR that is responsible for receiving the recovery path traffic,
recovery path traffic, and either merges their traffic into a single and either merges the traffic back onto the working path, or, if it
outgoing path, or, if it is itself the destination, passes the is itself the destination, passes the traffic on to the higher layer
traffic on to the higher layer protocols. protocols.
Intermediate LSR Intermediate LSR
An LSR on a working or recovery path that is neither a PSL nor a PML An LSR on a working or recovery path that is neither a PSL nor a PML
for that path. for that path.
Bypass Tunnel Bypass Tunnel
A path that serves to back up a set of working paths using the label A path that serves to back up a set of working paths using the label
stacking approach [1]. The working paths and the bypass tunnel must stacking approach [1]. The working paths and the bypass tunnel must
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Non-revertive Mode Non-revertive Mode
A recovery mode in which traffic is not automatically switched back A recovery mode in which traffic is not automatically switched back
to the original working path after this path is restored to a fault- to the original working path after this path is restored to a fault-
free condition. (Depending on the configuration, the original working free condition. (Depending on the configuration, the original working
path may, upon moving to a fault-free condition, become the recovery path may, upon moving to a fault-free condition, become the recovery
path, or it may be used for new working traffic, and be no longer path, or it may be used for new working traffic, and be no longer
associated with its original recovery path). associated with its original recovery path).
MPLS Protection Domain MPLS Protection Domain
The set of LSRs over which a working path and its corresponding The set of LSRs over which a working path and its corresponding
recovery path are routed. recovery path are routed.
MPLS Protection Plan MPLS Protection Plan
The set of all LSP protection paths and the mapping from working to The set of all LSP protection paths and the mapping from working to
protection paths deployed in an MPLS protection domain at a given protection paths deployed in an MPLS protection domain at a given
time. time.
Liveness Message Liveness Message
A message exchanged periodically between two adjacent LSRs that A message exchanged periodically between two adjacent LSRs that
serves as a link probing mechanism. It provides an integrity check of serves as a link probing mechanism. It provides an integrity check of
the forward and the backward directions of the link between the two the forward and the backward directions of the link between the two
LSRs as well as a check of neighbor aliveness. LSRs as well as a check of neighbor aliveness.
Path Continuity Test Path Continuity Test
A test that verifies the integrity and continuity of a path or path A test that verifies the integrity and continuity of a path or path
segment. The details of such a test are beyond the scope of this segment. The details of such a test are beyond the scope of this
draft. (This could be accomplished, for example, by transmitting a draft. (This could be accomplished, for example, by transmitting a
control message along the same links and nodes as the data traffic or control message along the same links and nodes as the data traffic or
similarly could be measured by the absence of traffic and by similarly could be measured by the absence of traffic and by
providing feedback.) providing feedback.)
2.3.2 Failure Terminology 2.3.2 Failure Terminology
Path Failure (PF) Path Failure (PF)
Path failure is fault detected by MPLS-based recovery mechanisms, Path failure is fault detected by MPLS-based recovery mechanisms,
which is define as the failure of the liveness message test or a path which is define as the failure of the liveness message test or a path
continuity test, which indicates that path connectivity is lost. continuity test, which indicates that path connectivity is lost.
Path Degraded (PD) Path Degraded (PD)
Path degraded is a fault detected by MPLS-based recovery mechanisms Path degraded is a fault detected by MPLS-based recovery mechanisms
that indicates that the quality of the path is unacceptable. that indicates that the quality of the path is unacceptable.
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time. time.
Fault Recovery Signal (FRS) Fault Recovery Signal (FRS)
A signal that indicates a fault along a working path has been A signal that indicates a fault along a working path has been
repaired. Again, like the FIS, it is relayed by each intermediate LSR repaired. Again, like the FIS, it is relayed by each intermediate LSR
to its upstream or downstream neighbor, until is reaches the LSR that to its upstream or downstream neighbor, until is reaches the LSR that
performs recovery of the original path. . The FRS is transmitted performs recovery of the original path. . The FRS is transmitted
periodically by the node/nodes closest to the point of failure, for periodically by the node/nodes closest to the point of failure, for
some configurable length of time. some configurable length of time.
2.4 Abbreviations 2.4. Abbreviations
FIS: Fault Indication Signal. FIS: Fault Indication Signal.
FRS: Fault Recovery Signal. FRS: Fault Recovery Signal.
LD: Link Degraded. LD: Link Degraded.
LF: Link Failure. LF: Link Failure.
PD: Path Degraded. PD: Path Degraded.
PF: Path Failure. PF: Path Failure.
PML: Path Merge LSR. PML: Path Merge LSR.
PG: Path Group. PG: Path Group.
PPG: Protected Path Group. PPG: Protected Path Group.
PTP: Protected Traffic Portion. PTP: Protected Traffic Portion.
PSL: Path Switch LSR. PSL: Path Switch LSR.
3.0 MPLS-based Recovery Principles 3. MPLS-based Recovery Principles
MPLS-based recovery refers to the ability to effect quick and MPLS-based recovery refers to the ability to effect quick and
complete restoration of traffic affected by a fault in an MPLS- complete restoration of traffic affected by a fault in an MPLS-
enabled network. The fault may be detected on the IP layer or in enabled network. The fault may be detected on the IP layer or in
lower layers over which IP traffic is transported. Fastest MPLS lower layers over which IP traffic is transported. Fastest MPLS
recovery is assumed to be achieved with protection switching and may recovery is assumed to be achieved with protection switching and may
be viewed as the MPLS LSR switch completion time that is comparable be viewed as the MPLS LSR switch completion time that is comparable
to, or equivalent to, the 50 ms switch-over completion time of the to, or equivalent to, the 50 ms switch-over completion time of the
SONET layer. This section provides a discussion of the concepts and SONET layer. This section provides a discussion of the concepts and
principles of MPLS-based recovery. The concepts are presented in principles of MPLS-based recovery. The concepts are presented in
terms of atomic or primitive terms that may be combined to specify terms of atomic or primitive terms that may be combined to specify
recovery approaches. We do not make any assumptions about the recovery approaches. We do not make any assumptions about the
underlying layer 1 or layer 2 transport mechanisms or their recovery underlying layer 1 or layer 2 transport mechanisms or their recovery
mechanisms. mechanisms.
3.1 Configuration of Recovery 3.1. Configuration of Recovery
An LSR should allow for configuration of the following recovery An LSR may support any or all of the following recovery options:
options:
Default-recovery (No MPLS-based recovery enabled): Default-recovery (No MPLS-based recovery enabled):
Traffic on the working path is recovered only via Layer 3 or IP Traffic on the working path is recovered only via Layer 3 or IP
rerouting or by some lower layer mechanism such as SONET APS. This rerouting or by some lower layer mechanism such as SONET APS. This
is equivalent to having no MPLS-based recovery. This option may be is equivalent to having no MPLS-based recovery. This option may be
used for low priority traffic or for traffic that is recovered in used for low priority traffic or for traffic that is recovered in
another way (for example load shared traffic on parallel working another way (for example load shared traffic on parallel working
paths may be automatically recovered upon a fault along one of the paths may be automatically recovered upon a fault along one of the
working paths by distributing it among the remaining working paths). working paths by distributing it among the remaining working paths).
Recoverable (MPLS-based recovery enabled): Recoverable (MPLS-based recovery enabled):
This working path is recovered using one or more recovery paths, This working path is recovered using one or more recovery paths,
either via rerouting or via protection switching. either via rerouting or via protection switching.
3.2 Initiation of Path Setup 3.2. Initiation of Path Setup
There are three options for the initiation of the recovery path There are three options for the initiation of the recovery path
setup. setup.
Pre-established: Pre-established:
This is the same as the protection switching option. Here a recovery This is the same as the protection switching option. Here a recovery
path(s) is established prior to any failure on the working path. The path(s) is established prior to any failure on the working path. The
path selection can either be determined by an administrative path selection can either be determined by an administrative
centralized tool (online or offline), or chosen based on some centralized tool, or chosen based on some algorithm implemented at
algorithm implemented at the PSL and possibly intermediate nodes. To the PSL and possibly intermediate nodes. To guard against the
guard against the situation when the pre-established recovery path situation when the pre-established recovery path fails before or at
fails before or at the same time as the working path, the recovery the same time as the working path, the recovery path should have
path should have secondary configuration options as explained in secondary configuration options as explained in Section 3.3 below.
Section 3.3 below.
Pre Qualified: Pre Qualified:
A pre-established path need not be created, it may be pre-qualified. A pre-established path need not be created, it may be pre-qualified.
A pre-qualified recovery path is not created expressly for protecting A pre-qualified recovery path is not created expressly for protecting
the working path, but instead is a path created for other purposes the working path, but instead is a path created for other purposes
that is designated as a recovery path after determination that it is that is designated as a recovery path after determination that it is
an acceptable alternative for carrying the working path traffic. an acceptable alternative for carrying the working path traffic.
Variants include the case where an optical path or trail is Variants include the case where an optical path or trail is
configured, but no switches are set. configured, but no switches are set.
Established-on-Demand: Established-on-Demand:
This is the same as the rerouting option. Here, a recovery path is This is the same as the rerouting option. Here, a recovery path is
established after a failure on its working path has been detected and established after a failure on its working path has been detected and
notified to the PSL. notified to the PSL.
3.3 Initiation of Resource Allocation 3.3. Initiation of Resource Allocation
A recovery path may support the same traffic contract as the working A recovery path may support the same traffic contract as the working
path, or it may not. We will distinguish these two situations by path, or it may not. We will distinguish these two situations by
using different additive terms. If the recovery path is capable of using different additive terms. If the recovery path is capable of
replacing the working path without degrading service, it will be replacing the working path without degrading service, it will be
called an equivalent recovery path. If the recovery path lacks the called an equivalent recovery path. If the recovery path lacks the
resources (or resource reservations) to replace the working path resources (or resource reservations) to replace the working path
without degrading service, it will be called a limited recovery path. without degrading service, it will be called a limited recovery path.
Based on this, there are two options for the initiation of resource Based on this, there are two options for the initiation of resource
allocation: allocation:
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This option may apply either to rerouting or to protection switching. This option may apply either to rerouting or to protection switching.
Here a recovery path reserves the required resources after a failure Here a recovery path reserves the required resources after a failure
on the working path has been detected and notified to the PSL and on the working path has been detected and notified to the PSL and
before the traffic on the working path is switched over to the before the traffic on the working path is switched over to the
recovery path. recovery path.
Note that under both the options above, depending on the amount of Note that under both the options above, depending on the amount of
resources reserved on the recovery path, it could either be an resources reserved on the recovery path, it could either be an
equivalent recovery path or a limited recovery path. equivalent recovery path or a limited recovery path.
3.4 Scope of Recovery 3.4. Scope of Recovery
3.4.1 Topology 3.4.1 Topology
3.4.1.1 Local Repair 3.4.1.1 Local Repair
The intent of local repair is to protect against a link or neighbor The intent of local repair is to protect against a link or neighbor
node fault and to minimize the amount of time required for failure node fault and to minimize the amount of time required for failure
propagation. In local repair (also known as local recovery [12] [9]), propagation. In local repair (also known as local recovery [10] [9]),
the node immediately upstream of the fault is the one to initiate the node immediately upstream of the fault is the one to initiate
recovery (either rerouting or protection switching). Local repair can recovery (either rerouting or protection switching). Local repair can
be of two types: be of two types:
Link Recovery/Restoration Link Recovery/Restoration
In this case, the recovery path may be configured to route around a In this case, the recovery path may be configured to route around a
certain link deemed to be unreliable. If protection switching is certain link deemed to be unreliable. If protection switching is
used, several recovery paths may be configured for one working path, used, several recovery paths may be configured for one working path,
depending on the specific faulty link that each protects against. depending on the specific faulty link that each protects against.
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specific alternative FEC/LSP mappings with alternate egresses can be specific alternative FEC/LSP mappings with alternate egresses can be
formed. formed.
This may simplify enhancing the reliability of implicitly constructed This may simplify enhancing the reliability of implicitly constructed
MPLS topologies. A PSL may qualify LSP/FEC bindings as candidate MPLS topologies. A PSL may qualify LSP/FEC bindings as candidate
recovery paths as simply link and node disjoint with the immediate recovery paths as simply link and node disjoint with the immediate
downstream LSR of the working path. downstream LSR of the working path.
3.4.1.4 Multi-Layer Repair 3.4.1.4 Multi-Layer Repair
Multi-layer repair broadens the network designer's tool set for those Multi-layer repair broadens the network designerÆs tool set for those
cases where multiple network layers can be managed together to cases where multiple network layers can be managed together to
achieve overall network goals. Specific criteria for determining achieve overall network goals. Specific criteria for determining
when multi-layer repair is appropriate are beyond the scope of this when multi-layer repair is appropriate are beyond the scope of this
draft. draft.
3.4.1.5 Concatenated Protection Domains 3.4.1.5 Concatenated Protection Domains
A given service may cross multiple networks and these may employ A given service may cross multiple networks and these may employ
different recovery mechanisms. It is possible to concatenate different recovery mechanisms. It is possible to concatenate
protection domains so that service recovery can be provided end-to- protection domains so that service recovery can be provided end-to-
end. It is considered that the recovery mechanisms in different end. It is considered that the recovery mechanisms in different
domains may operate autonomously, and that multiple points of domains may operate autonomously, and that multiple points of
attachment may be used between domains (to ensure there is no single attachment may be used between domains (to ensure there is no single
point of failure). Alternate egress repair requires management of point of failure). Alternate egress repair requires management of
concatenated domains in that an explicit MPLS point of failure (the concatenated domains in that an explicit MPLS point of failure (the
PML) is by definition excluded. Details of concatenated protection PML) is by definition excluded. Details of concatenated protection
domains are beyond the scope of this draft. domains are beyond the scope of this draft.
3.4.2 Path Mapping 3.4.2 Path Mapping
Path mapping refers to the methods of mapping traffic from a faulty Path mapping refers to the methods of mapping traffic from a faulty
working path on to the recovery path. There are several options for working path on to the recovery path. There are several options for
this, as described below. Note that the options below should be this, as described below. Note that the options below should be
viewed as atomic terms that only describe how the working and viewed as atomic terms that only describe how the working and
protection paths are mapped to each other. The issues of resource protection paths are mapped to each other. The issues of resource
reservation along these paths, and how switchover is actually reservation along these paths, and how switchover is actually
performed lead to the more commonly used composite terms, such as 1+1 performed lead to the more commonly used composite terms, such as 1+1
and 1:1 protection, which were described in Section 2.1. and 1:1 protection, which were described in Section 2.1.
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carry the traffic of a working path based on a certain configurable carry the traffic of a working path based on a certain configurable
load splitting ratio. This is especially useful when no single load splitting ratio. This is especially useful when no single
recovery path can be found that can carry the entire traffic of the recovery path can be found that can carry the entire traffic of the
working path in case of a fault. Split path protection may require working path in case of a fault. Split path protection may require
handshaking between the PSL and the PML(s), and may require the handshaking between the PSL and the PML(s), and may require the
PML(s) to correlate the traffic arriving on multiple recovery paths PML(s) to correlate the traffic arriving on multiple recovery paths
with the working path. Although this is an attractive option, the with the working path. Although this is an attractive option, the
details of split path protection are beyond the scope of this draft, details of split path protection are beyond the scope of this draft,
and are for further study. and are for further study.
3.4.3 Bypass Tunnels 3.4.3 Bypass Tunnels
It may be convenient, in some cases, to create a "bypass tunnel" for It may be convenient, in some cases, to create a "bypass tunnel" for
a PPG between a PSL and PML, thereby allowing multiple recovery paths a PPG between a PSL and PML, thereby allowing multiple recovery paths
to be transparent to intervening LSRs [8]. In this case, one LSP to be transparent to intervening LSRs [8]. In this case, one LSP
(the tunnel) is established between the PSL and PML following an (the tunnel) is established between the PSL and PML following an
acceptable route and a number of recovery paths are supported through acceptable route and a number of recovery paths are supported through
the tunnel via label stacking. A bypass tunnel can be used with any the tunnel via label stacking. A bypass tunnel can be used with any
of the path mapping options discussed in the previous section. of the path mapping options discussed in the previous section.
As with recovery paths, the bypass tunnel may or may not have As with recovery paths, the bypass tunnel may or may not have
resource reservations sufficient to provide recovery without service resource reservations sufficient to provide recovery without service
degradation. It is possible that the bypass tunnel may have degradation. It is possible that the bypass tunnel may have
sufficient resources to recover some number of working paths, but not sufficient resources to recover some number of working paths, but not
all at the same time. If the number of recovery paths carrying all at the same time. If the number of recovery paths carrying
traffic in the tunnel at any given time is restricted, this is traffic in the tunnel at any given time is restricted, this is
similar to the 1 to n or m to n protection cases mentioned in Section similar to the 1 to n or m to n protection cases mentioned in Section
3.4.2. 3.4.2.
3.4.4 Recovery Granularity 3.4.4 Recovery Granularity
Another dimension of recovery considers the amount of traffic Another dimension of recovery considers the amount of traffic
requiring protection. This may range from a fraction of a path to a requiring protection. This may range from a fraction of a path to a
bundle of paths. bundle of paths.
3.4.4.1 Selective Traffic Recovery 3.4.4.1 Selective Traffic Recovery
This option allows for the protection of a fraction of traffic within This option allows for the protection of a fraction of traffic within
the same path. The portion of the traffic on an individual path that the same path. The portion of the traffic on an individual path that
requires protection is called a protected traffic portion (PTP). A requires protection is called a protected traffic portion (PTP). A
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3.4.4.2 Bundling 3.4.4.2 Bundling
Bundling is a technique used to group multiple working paths together Bundling is a technique used to group multiple working paths together
in order to recover them simultaneously. The logical bundling of in order to recover them simultaneously. The logical bundling of
multiple working paths requiring protection, each of which is routed multiple working paths requiring protection, each of which is routed
identically between a PSL and a PML, is called a protected path group identically between a PSL and a PML, is called a protected path group
(PPG). When a fault occurs on the working path carrying the PPG, the (PPG). When a fault occurs on the working path carrying the PPG, the
PPG as a whole can be protected either by being switched to a bypass PPG as a whole can be protected either by being switched to a bypass
tunnel or by being switched to a recovery path. tunnel or by being switched to a recovery path.
3.4.5 Recovery Path Resource Use 3.4.5 Recovery Path Resource Use
In the case of pre-reserved recovery paths, there is the question of In the case of pre-reserved recovery paths, there is the question of
what use these resources may be put to when the recovery path is not what use these resources may be put to when the recovery path is not
in use. There are two options: in use. There are two options:
Dedicated-resource: Dedicated-resource:
If the recovery path resources are dedicated, they may not be used If the recovery path resources are dedicated, they may not be used
for anything except carrying the working traffic. For example, in for anything except carrying the working traffic. For example, in
the case of 1+1 protection, the working traffic is always carried on the case of 1+1 protection, the working traffic is always carried on
the recovery path. Even if the recovery path is not always carrying the recovery path. Even if the recovery path is not always carrying
the working traffic, it may not be possible or desirable to allow the working traffic, it may not be possible or desirable to allow
other traffic to use these resources. other traffic to use these resources.
Extra-traffic-allowed: Extra-traffic-allowed:
If the recovery path only carries the working traffic when the If the recovery path only carries the working traffic when the
working path fails, then it is possible to allow extra traffic to use working path fails, then it is possible to allow extra traffic to use
the reserved resources at other times. Extra traffic is, by the reserved resources at other times. Extra traffic is, by
definition, traffic that can be displaced (without violating service definition, traffic that can be displaced (without violating service
agreements) whenever the recovery path resources are needed for agreements) whenever the recovery path resources are needed for
carrying the working path traffic. carrying the working path traffic.
3.5 Fault Detection Shared-resource:
A shared recovery resource is dedicated for use by multiple primary
resources that (according to SRLGs) are not expected to fail
simultaneously. Determining what resources that can be shared can be
accomplished by offline analysis or by techniques described in [14].
3.5. Fault Detection
MPLS recovery is initiated after the detection of either a lower MPLS recovery is initiated after the detection of either a lower
layer fault or a fault at the IP layer or in the operation of MPLS- layer fault or a fault at the IP layer or in the operation of MPLS-
based mechanisms. We consider four classes of impairments: Path based mechanisms. We consider four classes of impairments: Path
Failure, Path Degraded, Link Failure, and Link Degraded. Failure, Path Degraded, Link Failure, and Link Degraded.
Path Failure (PF) is a fault that indicates to an MPLS-based recovery Path Failure (PF) is a fault that indicates to an MPLS-based recovery
scheme that the connectivity of the path is lost. This may be scheme that the connectivity of the path is lost. This may be
detected by a path continuity test between the PSL and PML. Some, detected by a path continuity test between the PSL and PML. Some,
and perhaps the most common, path failures may be detected using a and perhaps the most common, path failures may be detected using a
skipping to change at page 22, line 43 skipping to change at page 23, line 4
continuity test must take the path merge points into consideration. continuity test must take the path merge points into consideration.
In the case of a bi-directional link implemented as two In the case of a bi-directional link implemented as two
unidirectional links, path failure could mean that either one or both unidirectional links, path failure could mean that either one or both
unidirectional links are damaged. unidirectional links are damaged.
Path Degraded (PD) is a fault that indicates to MPLS-based recovery Path Degraded (PD) is a fault that indicates to MPLS-based recovery
schemes/mechanisms that the path has connectivity, but that the schemes/mechanisms that the path has connectivity, but that the
quality of the connection is unacceptable. This may be detected by a quality of the connection is unacceptable. This may be detected by a
path performance monitoring mechanism, or some other mechanism for path performance monitoring mechanism, or some other mechanism for
determining the error rate on the path or some portion of the path. determining the error rate on the path or some portion of the path.
This is local to the LSR and consists of excessive discarding of This is local to the LSR and consists of excessive discarding of
packets at an interface, either due to label mismatch or due to TTL packets at an interface, either due to label mismatch or due to TTL
errors, for example. errors, for example.
Link Failure (LF) is an indication from a lower layer that the link Link Failure (LF) is an indication from a lower layer that the link
over which the path is carried has failed. If the lower layer over which the path is carried has failed. If the lower layer
supports detection and reporting of this fault (that is, any fault supports detection and reporting of this fault (that is, any fault
that indicates link failure e.g., SONET LOS), this may be used by the that indicates link failure e.g., SONET LOS), this may be used by the
MPLS recovery mechanism. In some cases, using LF indications may MPLS recovery mechanism. In some cases, using LF indications may
provide faster fault detection than using only MPLS_based fault provide faster fault detection than using only MPLSûbased fault
detection mechanisms. detection mechanisms.
Link Degraded (LD) is an indication from a lower layer that the link Link Degraded (LD) is an indication from a lower layer that the link
over which the path is carried is performing below an acceptable over which the path is carried is performing below an acceptable
level. If the lower layer supports detection and reporting of this level. If the lower layer supports detection and reporting of this
fault, it may be used by the MPLS recovery mechanism. In some cases, fault, it may be used by the MPLS recovery mechanism. In some cases,
using LD indications may provide faster fault detection than using using LD indications may provide faster fault detection than using
only MPLS-based fault detection mechanisms. only MPLS-based fault detection mechanisms.
3.6 Fault Notification 3.6. Fault Notification
MPLS-based recovery relies on rapid and reliable notification of MPLS-based recovery relies on rapid and reliable notification of
faults. Once a fault is detected, the node that detected the fault faults. Once a fault is detected, the node that detected the fault
must determine if the fault is severe enough to require path must determine if the fault is severe enough to require path
recovery. If the node is not capable of initiating direct action recovery. If the node is not capable of initiating direct action
(e.g. as a PSL) the node should send out a notification of the fault (e.g. as a PSL) the node should send out a notification of the fault
by transmitting a FIS to those of its upstream LSRs that were sending by transmitting a FIS to those of its upstream LSRs that were sending
traffic on the working path that is affected by the fault. This traffic on the working path that is affected by the fault. This
notification is relayed hop-by-hop by each subsequent LSR to its notification is relayed hop-by-hop by each subsequent LSR to its
upstream neighbor, until it eventually reaches a PSL. A PSL is the upstream neighbor, until it eventually reaches a PSL. A PSL is the
only LSR that can terminate the FIS and initiate a protection switch only LSR that can terminate the FIS and initiate a protection switch
of the working path to a recovery path. of the working path to a recovery path.
Since the FIS is a control message, it should be transmitted with Since the FIS is a control message, it should be transmitted with
high priority to ensure that it propagates rapidly towards the high priority to ensure that it propagates rapidly towards the
affected PSL(s). Depending on how fault notification is configured in affected PSL(s). Depending on how fault notification is configured in
the LSRs of an MPLS domain, the FIS could be sent either as a Layer 2 the LSRs of an MPLS domain, the FIS could be sent either as a Layer 2
or Layer 3 packet [13]. The use of a Layer 2-based notification or Layer 3 packet [11]. The use of a Layer 2-based notification
requires a Layer 2 path direct to the PSL. An example of a FIS could requires a Layer 2 path direct to the PSL. An example of a FIS could
be the liveness message sent by a downstream LSR to its upstream be the liveness message sent by a downstream LSR to its upstream
neighbor, with an optional fault notification field set or it can be neighbor, with an optional fault notification field set or it can be
implicitly denoted by a teardown message. Alternatively, it could be implicitly denoted by a teardown message. Alternatively, it could be
a separate fault notification packet. The intermediate LSR should a separate fault notification packet. The intermediate LSR should
identify which of its incoming links (upstream LSRs) to propagate the identify which of its incoming links (upstream LSRs) to propagate the
FIS on. In the case of 1+1 protection, the FIS should also be sent FIS on. In the case of 1+1 protection, the FIS should also be sent
downstream to the PML where the recovery action is taken. downstream to the PML where the recovery action is taken.
3.7 Switch-Over Operation 3.7. Switch-Over Operation
3.7.1 Recovery Trigger 3.7.1 Recovery Trigger
The activation of an MPLS protection switch following the detection The activation of an MPLS protection switch following the detection
or notification of a fault requires a trigger mechanism at the PSL. or notification of a fault requires a trigger mechanism at the PSL.
MPLS protection switching may be initiated due to automatic inputs or MPLS protection switching may be initiated due to automatic inputs or
external commands. The automatic activation of an MPLS protection external commands. The automatic activation of an MPLS protection
switch results from a response to a defect or fault conditions switch results from a response to a defect or fault conditions
detected at the PSL or to fault notifications received at the PSL. It detected at the PSL or to fault notifications received at the PSL. It
is possible that the fault detection and trigger mechanisms may be is possible that the fault detection and trigger mechanisms may be
combined, as is the case when a PF, PD, LF, or LD is detected at a combined, as is the case when a PF, PD, LF, or LD is detected at a
PSL and triggers a protection switch to the recovery path. In most PSL and triggers a protection switch to the recovery path. In most
cases, however, the detection and trigger mechanisms are distinct, cases, however, the detection and trigger mechanisms are distinct,
involving the detection of fault at some intermediate LSR followed by involving the detection of fault at some intermediate LSR followed by
the propagation of a fault notification back to the PSL via the FIS, the propagation of a fault notification back to the PSL via the FIS,
skipping to change at page 24, line 18 skipping to change at page 24, line 32
transmitter failures, or LSR fabric failures), as does the LF fault, transmitter failures, or LSR fabric failures), as does the LF fault,
with the difference that the LF is a lower layer impairment that may with the difference that the LF is a lower layer impairment that may
be communicated to - MPLS-based recovery mechanisms. The PD (or LD) be communicated to - MPLS-based recovery mechanisms. The PD (or LD)
fault, on the other hand, applies to soft defects (excessive errors fault, on the other hand, applies to soft defects (excessive errors
due to noise on the link, for instance). The PD (or LD) results in a due to noise on the link, for instance). The PD (or LD) results in a
fault declaration only when the percentage of lost packets exceeds a fault declaration only when the percentage of lost packets exceeds a
given threshold, which is provisioned and may be set based on the given threshold, which is provisioned and may be set based on the
service level agreement(s) in effect between a service provider and a service level agreement(s) in effect between a service provider and a
customer. customer.
3.7.2 Recovery Action 3.7.2 Recovery Action
After a fault is detected or FIS is received by the PSL, the recovery After a fault is detected or FIS is received by the PSL, the recovery
action involves either a rerouting or protection switching operation. action involves either a rerouting or protection switching operation.
In both scenarios, the next hop label forwarding entry for a recovery In both scenarios, the next hop label forwarding entry for a recovery
path is bound to the working path. path is bound to the working path.
3.8 Post Recovery Operation 3.8. Post Recovery Operation
When traffic is flowing on the recovery path decisions can be made to When traffic is flowing on the recovery path decisions can be made to
whether let the traffic remain on the recovery path and consider it whether let the traffic remain on the recovery path and consider it
as a new working path or do a switch to the old or a new working as a new working path or do a switch to the old or a new working
path. This post recovery operation has two styles, one where the path. This post recovery operation has two styles, one where the
protection counterparts, i.e. the working and recovery path, are protection counterparts, i.e. the working and recovery path, are
fixed or "pinned" to its route and one in which the PSL or other fixed or "pinned" to its route and one in which the PSL or other
network entity with real time knowledge of failure dynamically network entity with real time knowledge of failure dynamically
performs re-establishment or controlled rearrangement of the paths performs re-establishment or controlled rearrangement of the paths
comprising the protected service. comprising the protected service.
3.8.1 Fixed Protection Counterparts 3.8.1 Fixed Protection Counterparts
For fixed protection counterparts the PSL will be pre-configured with For fixed protection counterparts the PSL will be pre-configured with
the appropriate behavior to take when the original fixed path is the appropriate behavior to take when the original fixed path is
restored to service. The choices are revertive and non-revertive restored to service. The choices are revertive and non-revertive
mode. The choice will typically be depended on relative costs of the mode. The choice will typically be depended on relative costs of the
working and protection paths, and the tolerance of the service to the working and protection paths, and the tolerance of the service to the
effects of switching paths yet again. These protection modes indicate effects of switching paths yet again. These protection modes indicate
whether or not there is a preferred path for the protected traffic. whether or not there is a preferred path for the protected traffic.
3.8.1.1 Revertive Mode 3.8.1.1 Revertive Mode
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In the non-revertive mode of operation, the working traffic may or In the non-revertive mode of operation, the working traffic may or
may not be restored to a new optimal working path or to the original may not be restored to a new optimal working path or to the original
working path anyway. This is because it might be useful, in some working path anyway. This is because it might be useful, in some
cases, to either: (a) administratively perform a protection switch cases, to either: (a) administratively perform a protection switch
back to the original working path after gaining further assurances back to the original working path after gaining further assurances
about the integrity of the path, or (b) it may be acceptable to about the integrity of the path, or (b) it may be acceptable to
continue operation on the recovery path, or (c) it may be desirable continue operation on the recovery path, or (c) it may be desirable
to move the traffic to a new optimal working path that is calculated to move the traffic to a new optimal working path that is calculated
based on network topology and network policies. based on network topology and network policies.
3.8.2 Dynamic Protection Counterparts 3.8.2 Dynamic Protection Counterparts
For Dynamic protection counterparts when the traffic is switched over For Dynamic protection counterparts when the traffic is switched over
to a recovery path, the association between the original working path to a recovery path, the association between the original working path
and the recovery path may no longer exist, since the original path and the recovery path may no longer exist, since the original path
itself may no longer exist after the fault. Instead, when the network itself may no longer exist after the fault. Instead, when the network
reaches a stable state following routing convergence, the recovery reaches a stable state following routing convergence, the recovery
path may be switched over to a different preferred path either path may be switched over to a different preferred path either
optimization based on the new network topology and associated optimization based on the new network topology and associated
information or based on pre-configured information. information or based on pre-configured information.
Dynamic protection counterparts assume that upon failure, the PSL or Dynamic protection counterparts assume that upon failure, the PSL or
other network entity will establish new working paths if another other network entity will establish new working paths if another
switch-over will be performed. switch-over will be performed.
3.8.3 Restoration and Notification 3.8.3 Restoration and Notification
MPLS restoration deals with returning the working traffic from the MPLS restoration deals with returning the working traffic from the
recovery path to the original or a new working path. Reversion is recovery path to the original or a new working path. Reversion is
performed by the PSL either upon receiving notification, via FRS, performed by the PSL either upon receiving notification, via FRS,
that the working path is repaired, or upon receiving notification that the working path is repaired, or upon receiving notification
that a new working path is established. that a new working path is established.
For fixed counterparts in revertive mode, an LSR that detected the For fixed counterparts in revertive mode, an LSR that detected the
fault on the working path also detects the restoration of the working fault on the working path also detects the restoration of the working
path. If the working path had experienced a LF defect, the LSR path. If the working path had experienced a LF defect, the LSR
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along a recovery path towards a PSL and if the recovery path is an along a recovery path towards a PSL and if the recovery path is an
equivalent working path, it is possible for the working path and its equivalent working path, it is possible for the working path and its
recovery path to exchange roles once the original working path is recovery path to exchange roles once the original working path is
repaired following a fault. This is because, in that case, the repaired following a fault. This is because, in that case, the
recovery path effectively becomes the working path, and the restored recovery path effectively becomes the working path, and the restored
working path functions as a recovery path for the original recovery working path functions as a recovery path for the original recovery
path. This is important, since it affords the benefits of non- path. This is important, since it affords the benefits of non-
revertive switch operation outlined in Section 3.8.1, without leaving revertive switch operation outlined in Section 3.8.1, without leaving
the recovery path unprotected. the recovery path unprotected.
3.8.4 Reverting to Preferred Path (or Controlled Rearrangement) 3.8.4 Reverting to Preferred Path (or Controlled Rearrangement)
In the revertive mode, a "make before break" restoration switching In the revertive mode, a "make before break" restoration switching
can be used, which is less disruptive than performing protection can be used, which is less disruptive than performing protection
switching upon the occurrence of network impairments. This will switching upon the occurrence of network impairments. This will
minimize both packet loss and packet reordering. The controlled minimize both packet loss and packet reordering. The controlled
rearrangement of paths can also be used to satisfy traffic rearrangement of paths can also be used to satisfy traffic
engineering requirements for load balancing across an MPLS domain. engineering requirements for load balancing across an MPLS domain.
3.9 Performance 3.9. Performance
Resource/performance requirements for recovery paths should be Resource/performance requirements for recovery paths should be
specified in terms of the following attributes: specified in terms of the following attributes:
I. Resource class attribute: I. Resource class attribute:
Equivalent Recovery Class: The recovery path has the same resource Equivalent Recovery Class: The recovery path has the same resource
reservations and performance guarantees as the working path. In other reservations and performance guarantees as the working path. In other
words, the recovery path meets the same SLAs as the working path. words, the recovery path meets the same SLAs as the working path.
Limited Recovery Class: The recovery path does not have the same Limited Recovery Class: The recovery path does not have the same
resource reservations and performance guarantees as the working path. resource reservations and performance guarantees as the working path.
skipping to change at page 27, line 19 skipping to change at page 27, line 33
II. Priority Attribute: II. Priority Attribute:
The recovery path has a priority attribute just like the working path The recovery path has a priority attribute just like the working path
(i.e., the priority attribute of the associated traffic trunks). It (i.e., the priority attribute of the associated traffic trunks). It
can have the same priority as the working path or lower priority. can have the same priority as the working path or lower priority.
III. Preemption Attribute: III. Preemption Attribute:
The recovery path can have the same preemption attribute as the The recovery path can have the same preemption attribute as the
working path or a lower one. working path or a lower one.
4.0 MPLS Recovery Requirement 4. MPLS Recovery Features
The following are the MPLS recovery requirements: The following features are desirable from an operational point of
view:
I. MPLS recovery SHALL provide an option to identify protection I. It is highly desirable that MPLS recovery provides an option to
groups (PPGs) and protection portions (PTPs). identify protection groups (PPGs) and protection portions (PTPs).
II. Each PSL SHALL be capable of performing MPLS recovery upon the II. Each PSL should be capable of performing MPLS recovery upon the
detection of the impairments or upon receipt of notifications of detection of the impairments or upon receipt of notifications of
impairments. impairments.
III. A MPLS recovery method SHALL not preclude manual protection III. A MPLS recovery method should not preclude manual protection
switching commands. This implies that it would be possible under switching commands. This implies that it would be possible under
administrative commands to transfer traffic from a working path to a administrative commands to transfer traffic from a working path to a
recovery path, or to transfer traffic from a recovery path to a recovery path, or to transfer traffic from a recovery path to a
working path, once the working path becomes operational following a working path, once the working path becomes operational following a
fault. fault.
IV. A PSL SHALL be capable of performing either a switch back to the IV. A PSL may be capable of performing either a switch back to the
original working path after the fault is corrected or a switchover to original working path after the fault is corrected or a switchover to
a new working path, upon the discovery or establishment of a more a new working path, upon the discovery or establishment of a more
optimal working path. optimal working path.
V. The recovery model should take into consideration path merging at V. The recovery model should take into consideration path merging at
intermediate LSRs. If a fault affects the merged segment, all the intermediate LSRs. If a fault affects the merged segment, all the
paths sharing that merged segment should be able to recover. paths sharing that merged segment should be able to recover.
Similarly, if a fault affects a non-merged segment, only the path Similarly, if a fault affects a non-merged segment, only the path
that is affected by the fault should be recovered. that is affected by the fault should be recovered.
5.0 MPLS Recovery Options 5. Comparison Criteria
There SHOULD be an option for:
I. Configuration of the recovery path as excess or reserved, with
excess as the default. The recovery path that is configured as excess
SHALL provide lower priority preemptable traffic access to the
protection bandwidth, while the recovery path configured as reserved
SHALL not provide any other traffic access to the protection
bandwidth.
II. Configuring the protection alternatives as either rerouting or
protection switching.
III. Enabling restoration as either non-revertive or revertive, with
non-revertive as the default if fixed protection counterparts are
used.
6.0 Comparison Criteria
Possible criteria to use for comparison of MPLS-based recovery Possible criteria to use for comparison of MPLS-based recovery
schemes are as follows: schemes are as follows:
Recovery Time Recovery Time
We define recovery time as the time required for a recovery path to We define recovery time as the time required for a recovery path to
be activated (and traffic flowing) after a fault. Recovery Time is be activated (and traffic flowing) after a fault. Recovery Time is
the sum of the Fault Detection Time, Hold-off Time, Notification the sum of the Fault Detection Time, Hold-off Time, Notification
Time, Recovery Operation Time, and the Traffic Restoration Time. In Time, Recovery Operation Time, and the Traffic Restoration Time. In
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IV. Percentage of coverage: dependent on a scheme and its IV. Percentage of coverage: dependent on a scheme and its
implementation, a certain percentage of faults may be covered. This implementation, a certain percentage of faults may be covered. This
may be subdivided into percentage of link faults and percentage of may be subdivided into percentage of link faults and percentage of
node faults. node faults.
V. The number of protected paths may effect how fast the total set of V. The number of protected paths may effect how fast the total set of
paths affected by a fault could be recovered. The ratio of protected paths affected by a fault could be recovered. The ratio of protected
is n/N, where n is the number of protected paths and N is the total is n/N, where n is the number of protected paths and N is the total
number of paths. number of paths.
7.0 Security Considerations 6. Security Considerations
The MPLS recovery that is specified herein does not raise any The MPLS recovery that is specified herein does not raise any
security issues that are not already present in the MPLS security issues that are not already present in the MPLS
architecture. architecture.
8.0 Intellectual Property Considerations 7. Intellectual Property Considerations
The IETF has been notified of intellectual property rights claimed in The IETF has been notified of intellectual property rights claimed in
regard to some or all of the specification contained in this regard to some or all of the specification contained in this
document. For more information consult the online list of claimed document. For more information consult the online list of claimed
rights. rights.
9.0 Acknowledgements 8. Acknowledgements
We would like to thank members of the MPLS WG mailing list for their We would like to thank members of the MPLS WG mailing list for their
suggestions on the earlier versions of this draft. In particular, suggestions on the earlier versions of this draft. In particular,
Bora Akyol, Dave Allan, Neil Harrison, and Dave Danenberg whose Bora Akyol, Dave Allan, Neil Harrison, and Dave Danenberg whose
suggestions and comments were very helpful in revising the document. suggestions and comments were very helpful in revising the document.
10.0 Authors' Addresses The editors would like to give very special thanks to Curtis
Villamizar for his careful and extremely thorough reading of the
document and for taking the time to provide numerous suggestions,
which were very helpful in our latest revision of the document.
9. AuthorsÆ Addresses
Vishal Sharma Ben Mack-Crane Vishal Sharma Ben Mack-Crane
Jasmine Networks, Inc. Tellabs Operations, Inc. Metanoia, Inc. Tellabs Operations, Inc.
3061 B, Zanker Road 4951 Indiana Avenue 335 Elan Village Ln., Unit 203 4951 Indiana Avenue
San Jose, CA 95134 Lisle, IL 60532 San Jose, CA 95134 Lisle, IL 60532
Phone: 408-895-5030 Phone: 630-512-7255 Phone: 408-943-1794 Phone: 630-512-7255
vsharma@JasmineNetworks.com Ben.Mack-Crane@tellabs.com v.sharma@ieee.org Ben.Mack-Crane@tellabs.com
Srinivas Makam Ken Owens Srinivas Makam Ken Owens
Tellabs Operations, Inc. Erlang Technology, Inc. Tellabs Operations, Inc. Erlang Technology, Inc.
Lisle, IL 60532 St. Louis, MO 63119 Lisle, IL 60532 St. Louis, MO 63119
Phone: 630-512-7217 Phone: 630-512-7217 Phone: 314-918-1579
Srinivas.Makam@tellabs.com keno@erlangtech.com Srinivas.Makam@tellabs.com keno@erlangtech.com
Changcheng Huang Fiffi Hellstrand Changcheng Huang Fiffi Hellstrand
Dept. of Systems & Computer Engg. Nortel Networks Dept. of Systems & Computer Engg. Nortel Networks
Carleton University St Eriksgatan 115 Carleton University St Eriksgatan 115
Minto Center, Rm. 3082 PO Box 6701 Minto Center, Rm. 3082 PO Box 6701
1125 Colonial By Drive 113 85 Stockholm, Sweden 1125 Colonial By Drive 113 85 Stockholm, Sweden
Ottawa, Ontario K1S 5B6, Canada Phone: +46 8 5088 3687 Ottawa, Ontario K1S 5B6, Canada Phone: +46 8 5088 3687
Phone: 613 520-2600 x2477 Fiffi@nortelnetworks.com Phone: 613 520-2600 x2477 Fiffi@nortelnetworks.com
Changcheng.Huang@sce.carleton.ca Changcheng.Huang@sce.carleton.ca
Jon Weil Brad Cain Jon Weil Brad Cain
Nortel Networks Mirror Image Internet Nortel Networks Cereva Networks
Harlow Laboratories London Road 49 Dragon Ct. Harlow Laboratories London Road 3 Network Drive
Harlow Essex CM17 9NA, UK Woburn, MA 01801, USA Harlow Essex CM17 9NA, UK Marlborough, MA 01752
Phone: +44 (0)1279 403935 bcain@mirror-image.com Phone: +44 (0)1279 403935 Phone: 508-787-5000
jonweil@nortelnetworks.com jonweil@nortelnetworks.com bcain@cereva.com
Loa Andersson Bilel Jamoussi Loa Andersson Bilel Jamoussi
Nortel Networks Nortel Networks Utfors AB Nortel Networks
St Eriksgatan 115, PO Box 6701 3 Federal Street, BL3-03 R…sundav„gen 12, Box 525 3 Federal Street, BL3-03
113 85 Stockholm, Sweden Billerica, MA 01821, USA 169 29 Solna, Sweden Billerica, MA 01821, USA
Phone: +46 8 50 88 36 34 Phone:(978) 288-4506 Phone: +46 8 5270 5038 Phone:(978) 288-4506
loa.andersson@nortelnetworks.com jamoussi@nortelnetworks.com loa.andersson@utfors.se jamoussi@nortelnetworks.com
Seyhan Civanlar Angela Chiu Seyhan Civanlar Angela Chiu
Coreon, Inc. Celion Networks, Inc. Lemur Networks, Inc. Celion Networks, Inc.
1200 South Avenue, Suite 103 One Shiela Drive, Suite 2 135 West 20th Street, 5th Floor One Shiela Drive, Suite 2
Staten Island, NY 10314 Tinton Falls, NJ 07724 New York, NY 10011 Tinton Falls, NJ 07724
Phone: (718) 889 4203 Phone: (732) 345-3441 Phone: 212-367-7676 Phone: (732) 345-3441
scivanlar@coreon.net angela.chiu@celion.com scivanlar@lemurnetworks.com angela.chiu@celion.com
11.0 References
[1] Rosen, E., Viswanathan, A., and Callon, R., "Multiprotocol Label 10. References
Switching Architecture", RFC 3031, January 2001.
[2] Andersson, L., Doolan, P., Feldman, N., Fredette, A., Thomas, B., [1] Rosen, E., Viswanathan, A., and Callon, R., "Multiprotocol Label
"LDP Specification", RFC 3036, January 2001. Switching Architecture", RFC 3031, January 2001.
[3] Awduche, D. Hannan, A., and Xiao, X., "Applicability Statement for [2] Andersson, L., Doolan, P., Feldman, N., Fredette, A., Thomas, B.,
Extensions to RSVP for LSP-Tunnels", draft-ietf-mpls-rsvp-tunnel- "LDP Specification", RFC 3036, January 2001.
applicability-01.txt, work in progress, April 2000.
[4] Jamoussi, B. et al "Constraint-Based LSP Setup using LDP", Internet [3] Awduche, D. Hannan, A., and Xiao, X., "Applicability Statement
Draft draft-ietf-mpls-cr-ldp-04.txt, Work in Progress , July 2000. for Extensions to RSVP for LSP-Tunnels", draft-ietf-mpls-rsvp-
tunnel-applicability-02.txt, Work in Progress, April 2001.
[5] Braden, R., Zhang, L., Berson, S., Herzog, S., "Resource ReSerVation [4] Jamoussi, B. et al "Constraint-Based LSP Setup using LDP",
Protocol (RSVP) -- Version 1 Functional Specification", RFC 2205, Internet Draft draft-ietf-mpls-cr-ldp-05.txt, Work in Progress ,
September 1997. February 2001.
[6] Awduche, D. et al "Extensions to RSVP for LSP Tunnels", Internet [5] Braden, R., Zhang, L., Berson, S., Herzog, S., "Resource
Draft, draft-ietf-mpls-rsvp-lsp-tunnel-07.txt, Work in Progress, August ReSerVation Protocol (RSVP) -- Version 1 Functional
2000. Specification", RFC 2205, September 1997.
[7] Hellstrand, F., and Andersson, L., "Extensions to RSVP-TE and CR-LDP [6] Awduche, D. et al "Extensions to RSVP for LSP Tunnels", Internet
for setup of pre-established LSP Tunnels," Internet Draft, Work in Draft, draft-ietf-mpls-rsvp-lsp-tunnel-08.txt, Work in Progress,
Progress, draft-hellstrand-mpls-recovery-merge-01.txt, November 2000. February 2001.
[8] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., McManus, J., [7] Hellstrand, F., and Andersson, L., "Extensions to RSVP-TE and CR-
"Requirements for Traffic Engineering Over MPLS", RFC 2702, September LDP for setup of pre-established LSP Tunnels," Internet Draft,
1999. Work in Progress, draft-hellstrand-mpls-recovery-merge-01.txt,
November 2000.
[9] Kini, S, Lakshman, T. V., Villamizar, C., "Shared Backup Label [8] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., McManus, J.,
Switched Path Restoration, " Internet Draft, Work in Progress, draft- "Requirements for Traffic Engineering Over MPLS", RFC 2702,
kini-restoration-shared-backup-00.txt, October 2000. September 1999.
[10] Goguen, R. and Swallow, G., "RSVP Label Allocation for Backup [9] Kini, S., Lakshman, T. V., Villamizar, C., "Reservation Protocol
Tunnels", draft-swallow-rsvp-bypass-label-01.txt, work in progress, with Traffic Engineering Extensions: Extension for Label Switched
November 2000. Path Restoration," Internet Draft, Work in Progress, draft-kini-
rsvp-lsp-restoration-00.txt, November 2000.
[11] Kini, S., Lakshman, T. V., Villamizar, C., "Reservation Protocol [10] Haskin, D. and Krishnan R., "A Method for Setting an Alternative
with Traffic Engineering Extensions: Extension for Label Switched Path Label Switched Path to Handle Fast Reroute", Internet Draft draft-
Restoration," Internet Draft, Work in Progress, draft-kini-rsvp-lsp- haskin-mpls-fast-reroute-05.txt, November 2000, Work in progress.
restoration-00.txt, November 2000.
[12] Haskin, D. and Krishnan R., "A Method for Setting an Alternative [11] Owens, K., Makam, V., Sharma, V., Mack-Crane, B., and Haung, C.,
Label Switched Path to Handle Fast Reroute", Internet Draft draft- "A Path Protection/Restoration Mechanism for MPLS Networks",
haskin-mpls-fast-reroute-05.txt, November 2000, Work in progress. Internet Draft, draft-chang-mpls-path-protection-03.txt, Work in
Progress, July 2001.
[13] Owens, K., Makam, V., Sharma, V., Mack-Crane, B., and Haung, C., "A [14] Kini, S., Kodialam, M., Sengupta, S., Villamizar, C., "Shared
Path Protection/Restoration Mechanism for MPLS Networks", Internet Backup Label Switched Path Restoration", Internet Draft, draft-
Draft, draft-chang-mpls-path-protection-02.txt, Work in Progress kini-restoration-shared-backup-01.txt, Work in Progress May 2001.
November 2000.
 End of changes. 111 change blocks. 
289 lines changed or deleted 276 lines changed or added

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