draft-ietf-ccamp-gmpls-recovery-analysis-02.txt   draft-ietf-ccamp-gmpls-recovery-analysis-03.txt 
CCAMP Working Group CCAMP GMPLS P&R Design Team CCAMP Working Group CCAMP GMPLS P&R Design Team
Internet Draft Internet Draft
Category: Informational Dimitri Papadimitriou (Editor) Category: Informational Dimitri Papadimitriou (Editor)
Expiration Date: March 2004 Eric Mannie (Editor) Expiration Date: October 2004 Eric Mannie (Editor)
September 2003 April 2004
Analysis of Generalized Multi-Protocol Label Switching (GMPLS)-based Analysis of Generalized Multi-Protocol Label Switching (GMPLS)-based
Recovery Mechanisms (including Protection and Restoration) Recovery Mechanisms (including Protection and Restoration)
draft-ietf-ccamp-gmpls-recovery-analysis-02.txt draft-ietf-ccamp-gmpls-recovery-analysis-03.txt
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [1]. all provisions of Section 10 of RFC2026 [1].
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Internet-Drafts are draft documents valid for a maximum of Drafts. Internet-Drafts are draft documents valid for a maximum of
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This document provides an analysis grid to evaluate, compare and This document provides an analysis grid to evaluate, compare and
contrast the Generalized Multi-Protocol Label Switching (GMPLS) contrast the Generalized Multi-Protocol Label Switching (GMPLS)
protocol suite capabilities with respect to the recovery mechanisms protocol suite capabilities with respect to the recovery mechanisms
currently proposed at the IETF CCAMP Working Group. A detailed currently proposed at the IETF CCAMP Working Group. A detailed
analysis of each of the recovery phases is provided using the analysis of each of the recovery phases is provided using the
terminology defined in a companion document. This document focuses terminology defined in a companion document. This document focuses
on transport plane survivability and recovery issues and not on on transport plane survivability and recovery issues and not on
control plane resilience and related aspects. control plane resilience and related aspects.
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1. Table of Content Table of Content
Status of this Memo .............................................. 1 Status of this Memo .............................................. 1
Abstract ......................................................... 1 Abstract ......................................................... 1
1. Table of Content .............................................. 2 Table of Content ................................................. 2
2. Contributors .................................................. 3 1. Contributors .................................................. 3
2. Conventions used in this Document ............................. 3
3. Introduction .................................................. 4 3. Introduction .................................................. 4
4. Fault Management .............................................. 4 4. Fault Management .............................................. 4
4.1 Failure Detection ............................................ 4 4.1 Failure Detection ............................................ 4
4.2 Failure Localization and Isolation ........................... 7 4.2 Failure Localization and Isolation ........................... 7
4.3 Failure Notification ......................................... 7 4.3 Failure Notification ......................................... 7
4.4 Failure Correlation .......................................... 9 4.4 Failure Correlation .......................................... 9
5. Recovery Mechanisms .......................................... 10 5. Recovery Mechanisms .......................................... 10
5.1 Transport vs. Control Plane Responsibilities ................ 10 5.1 Transport vs. Control Plane Responsibilities ................ 10
5.2 Technology In/dependent Mechanisms .......................... 11 5.2 Technology In/dependent Mechanisms .......................... 11
5.2.1 OTN Recovery .............................................. 11 5.2.1 OTN Recovery .............................................. 11
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5.3.1 In-band vs. Out-of-band Signaling ......................... 12 5.3.1 In-band vs. Out-of-band Signaling ......................... 12
5.3.2 Uni- vs. Bi-directional Failures .......................... 13 5.3.2 Uni- vs. Bi-directional Failures .......................... 13
5.3.3 Partial vs. Full Span Recovery ............................ 15 5.3.3 Partial vs. Full Span Recovery ............................ 15
5.3.4 Difference between LSP, LSP Segment and Span Recovery ..... 15 5.3.4 Difference between LSP, LSP Segment and Span Recovery ..... 15
5.4 Difference between Recovery Type and Scheme ................. 16 5.4 Difference between Recovery Type and Scheme ................. 16
5.5 LSP Recovery Mechanisms ..................................... 18 5.5 LSP Recovery Mechanisms ..................................... 18
5.5.1 Classification ............................................ 18 5.5.1 Classification ............................................ 18
5.5.2 LSP Restoration ........................................... 19 5.5.2 LSP Restoration ........................................... 19
5.5.3 Pre-planned LSP Restoration ............................... 21 5.5.3 Pre-planned LSP Restoration ............................... 21
5.5.4 LSP Segment Restoration ................................... 22 5.5.4 LSP Segment Restoration ................................... 22
6. Normalization ................................................ 22 6. Reversion .................................................... 22
6.1 Wait-To-Restore (WTR) ....................................... 22 6.1 Wait-To-Restore (WTR) ....................................... 22
6.2 Revertive Mode Operation .................................... 23 6.2 Revertive Mode Operation .................................... 23
6.3 Orphans ..................................................... 23 6.3 Orphans ..................................................... 23
7. Hierarchies .................................................. 24 7. Hierarchies .................................................. 24
7.1 Horizontal Hierarchy (Partitions) ........................... 24 7.1 Horizontal Hierarchy (Partitions) ........................... 24
7.2 Vertical Hierarchy (Layers) ................................. 25 7.2 Vertical Hierarchy (Layers) ................................. 25
7.2.1 Recovery Granularity ...................................... 26
7.3 Escalation Strategies ....................................... 26 7.3 Escalation Strategies ....................................... 26
7.4 Disjointness ................................................ 27 7.4 Disjointness ................................................ 27
7.4.1 SRLG Disjointness ......................................... 27 7.4.1 SRLG Disjointness ......................................... 27
8. Recovery Mechanisms Analysis ................................. 28 8. Recovery Mechanisms Analysis ................................. 28
8.1 Fast Convergence (Detection/Correlation and Hold-off Time) .. 29 8.1 Fast Convergence (Detection/Correlation and Hold-off Time) .. 29
8.2 Efficiency (Recovery Switching Time) ........................ 29 8.2 Efficiency (Recovery Switching Time) ........................ 29
8.3 Robustness .................................................. 30 8.3 Robustness .................................................. 30
8.4 Resource Optimization ....................................... 31 8.4 Resource Optimization ....................................... 31
8.4.1 Recovery Resource Sharing ................................. 32 8.4.1 Recovery Resource Sharing ................................. 32
8.4.2 Recovery Resource Sharing and SRLG Recovery ............... 33 8.4.2 Recovery Resource Sharing and SRLG Recovery ............... 34
8.4.3 Recovery Resource Sharing, SRLG Disjointness and Admission. 34 8.4.3 Recovery Resource Sharing, SRLG Disjointness and Admission. 35
9. Summary and Conclusions ...................................... 35 9. Summary and Conclusions ...................................... 36
10. Security Considerations ..................................... 35 10. Security Considerations ..................................... 37
11. Acknowledgments ............................................. 36 11. Acknowledgments ............................................. 38
12. Intellectual Property Considerations ........................ 37 12. Intellectual Property Considerations ........................ 38
13. References .................................................. 38
13.1 Normative References ....................................... 38
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13.2 Informative References ..................................... 38 12.1 IPR Disclosure Acknowledgement ............................. 38
14 Author's Address ............................................. 40 13. References .................................................. 39
13.1 Normative References ....................................... 39
13.2 Informative References ..................................... 40
14 Editor's Address ............................................. 40
2. Contributors 1. Contributors
This document is the result of the CCAMP Working Group Protection This document is the result of the CCAMP Working Group Protection
and Restoration design team joint effort. Besides the editors, the and Restoration design team joint effort. Besides the editors, the
following are the authors that contributed to the present memo: following are the authors that contributed to the present memo:
Deborah Brungard (AT&T) Deborah Brungard (AT&T)
200 S. Laurel Ave. 200 S. Laurel Ave.
Middletown, NJ 07748, USA Middletown, NJ 07748, USA
E-mail: dbrungard@att.com E-mail: dbrungard@att.com
Sudheer Dharanikota (Consult) Sudheer Dharanikota
E-mail: sudheer@ieee.org EMail: sudheer@ieee.org
Jonathan P. Lang (Rincon Networks) Jonathan P. Lang (Rincon Networks)
E-mail: jplang@ieee.org EMail: jplang@ieee.org
Guangzhi Li (AT&T) Guangzhi Li (AT&T)
180 Park Avenue, 180 Park Avenue,
Florham Park, NJ 07932, USA Florham Park, NJ 07932, USA
E-mail: gli@research.att.com E-mail: gli@research.att.com
Eric Mannie (Consult) Eric Mannie
E-mail: eric_mannie@hotmail.com EMail: eric_mannie@hotmail.com
Dimitri Papadimitriou (Alcatel) Dimitri Papadimitriou (Alcatel)
Francis Wellesplein, 1 Francis Wellesplein, 1
B-2018 Antwerpen, Belgium B-2018 Antwerpen, Belgium
E-mail: dimitri.papadimitriou@alcatel.be EMail: dimitri.papadimitriou@alcatel.be
Bala Rajagopalan (Tellium) Bala Rajagopalan
2 Crescent Place - P.O. Box 901 EMail: braj@earthlink.net
Oceanport, NJ 07757-0901, USA
E-mail: braja@tellium.com
Yakov Rekhter (Juniper) Yakov Rekhter (Juniper)
1194 N. Mathilda Avenue 1194 N. Mathilda Avenue
Sunnyvale, CA 94089, USA Sunnyvale, CA 94089, USA
E-mail: yakov@juniper.net EMail: yakov@juniper.net
Conventions used in this document: 2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC-2119 [2]. this document are to be interpreted as described in [RFC2119].
Any other recovery-related terminology used in this document Any other recovery-related terminology used in this document
conforms to the one defined in [TERM]. The reader is also assumed to conforms to the one defined in [TERM]. The reader is also assumed to
be familiar with the terminology developed in [GMPLS-ARCH], [RFC-
3471], [RFC-3473], [GMPLS-RTG] and [LMP].
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be familiar with the terminology developed in [GMPLS-ARCH],
[RFC3471], [RFC3473], [GMPLS-RTG] and [LMP].
3. Introduction 3. Introduction
This document provides an analysis grid to evaluate, compare and This document provides an analysis grid to evaluate, compare and
contrast the Generalized MPLS (GMPLS) protocol suite capabilities contrast the Generalized MPLS (GMPLS) protocol suite capabilities
with respect to the recovery mechanisms currently proposed at the with respect to the recovery mechanisms currently proposed at the
IETF CCAMP Working Group. Here, the focus will only be on transport IETF CCAMP Working Group. Here, the focus will only be on transport
plane survivability and recovery issues and not on control plane plane survivability and recovery issues and not on control plane
resilience related aspects. Although the recovery mechanisms resilience related aspects. Although the recovery mechanisms
described in this document impose different requirements on GMPLS- described in this document impose different requirements on GMPLS-
based recovery protocols, the protocol(s) specifications will not be based recovery protocols, the protocol(s) specifications will not be
covered in this document. Though the concepts discussed here are covered in this document. Though the concepts discussed here are
technology independent, this document will implicitly focus on technology independent, this document will implicitly focus on
Sonet/SDH [T1.105]/[G.707], Optical Transport Networks (OTN) [G.709] Sonet/SDH [T1.105]/[G.707], Optical Transport Networks (OTN) [G.709]
and pre-OTN technologies except when specific details need to be and pre-OTN technologies except when specific details need to be
considered (for instance, in the case of failure detection). considered (for instance, in the case of failure detection).
In the present release, a detailed analysis is provided for each of A detailed analysis is provided for each of the recovery phases as
the recovery phases as identified in [TERM]. These phases define the identified in [TERM]. These phases define the sequence of generic
sequence of generic operations that need to be performed when a operations that need to be performed when a LSP/Span failure (or any
LSP/Span failure (or any other event generating such failures) other event generating such failures) occurs:
occurs:
- Phase 1: Failure detection - Phase 1: Failure detection
- Phase 2: Failure localization and isolation - Phase 2: Failure localization and isolation
- Phase 3: Failure notification - Phase 3: Failure notification
- Phase 4: Recovery (Protection/Restoration) - Phase 4: Recovery (Protection/Restoration)
- Phase 5: Reversion (normalization) - Phase 5: Reversion (normalization)
Failure detection, localization and notification phases together are Failure detection, localization and notification phases together are
referred to as fault management. Within a recovery domain, the referred to as fault management. Within a recovery domain, the
entities involved during the recovery operations are defined in entities involved during the recovery operations are defined in
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recovery mechanisms detailed in this document can be analyzed are recovery mechanisms detailed in this document can be analyzed are
introduced to assess the current GMPLS protocol capabilities and the introduced to assess the current GMPLS protocol capabilities and the
potential need for further extensions. This document concludes by potential need for further extensions. This document concludes by
detailing the applicability of the current GMPLS protocol building detailing the applicability of the current GMPLS protocol building
blocks for recovery purposes. blocks for recovery purposes.
4. Fault Management 4. Fault Management
4.1 Failure Detection 4.1 Failure Detection
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Transport failure detection is the only phase that can not be Transport failure detection is the only phase that can not be
achieved by the control plane alone since the latter needs a hook to achieved by the control plane alone since the latter needs a hook to
the transport plane to collect the related information. It has to be the transport plane to collect the related information. It has to be
emphasized that even if failure events themselves are detected by emphasized that even if failure events themselves are detected by
the transport plane, the latter, upon failure condition, MUST the transport plane, the latter, upon a failure condition, MUST
trigger the control plane for subsequent actions through the use of trigger the control plane for subsequent actions through the use of
GMPLS signalling capabilities (see [RFC-3471] and [RFC-3473]) or GMPLS signalling capabilities (see [RFC3471] and [RFC3473]) or Link
Link Management Protocol capabilities (see [LMP], Section 6). Management Protocol capabilities (see [LMP], Section 6).
Therefore, by definition, transport failure detection is transport Therefore, by definition, transport failure detection is transport
technology dependent (and so exceptionally, we keep here the technology dependent (and so exceptionally, we keep here the
"transport plane" terminology). In transport fault management, "transport plane" terminology). In transport fault management,
distinction is made between a defect and a failure. Here, the distinction is made between a defect and a failure. Here, the
discussion addresses failure detection (persistent fault cause). In discussion addresses failure detection (persistent fault cause). In
the technology-dependent descriptions, a more precise specification the technology-dependent descriptions, a more precise specification
will be provided. will be provided.
As an example, Sonet/SDH (see [G.707], [G.783] and [G.806]) provides As an example, Sonet/SDH (see [G.707], [G.783] and [G.806]) provides
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pointer. pointer.
- Payload type: checks that compatible adaptation functions are used - Payload type: checks that compatible adaptation functions are used
at the source and the sink. This is normally done by adding a at the source and the sink. This is normally done by adding a
signal type identifier at the source adaptation function and signal type identifier at the source adaptation function and
comparing it with the expected identifier at the sink. For comparing it with the expected identifier at the sink. For
instance, the payload signal label and the corresponding payload instance, the payload signal label and the corresponding payload
signal mismatch detection. signal mismatch detection.
- Signal Quality: monitors the performance of a signal. For - Signal Quality: monitors the performance of a signal. For
instance, if the performance falls below a certain threshold a
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defect excessive errors (EXC) or degraded signal (DEG) - is instance, if the performance falls below a certain threshold a
defect - excessive errors (EXC) or degraded signal (DEG) - is
detected. detected.
The most important point is that the supervision processes and the The most important point is that the supervision processes and the
corresponding failure detection (used to initiate the recovery corresponding failure detection (used to initiate the recovery
phase(s)) result in either: phase(s)) result in either:
- Signal Degrade (SD): A signal indicating that the associated data - Signal Degrade (SD): A signal indicating that the associated data
has degraded in the sense that a degraded defect condition is has degraded in the sense that a degraded defect condition is
active (for instance, a dDEG declared when the Bit Error Rate active (for instance, a dDEG declared when the Bit Error Rate
exceeds a preset threshold). exceeds a preset threshold).
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LMP communication channel, these failure conditions are reported to LMP communication channel, these failure conditions are reported to
the PXC and subsequent recovery actions performed as described in the PXC and subsequent recovery actions performed as described in
Section 5. As such from the control plane viewpoint, this mechanism Section 5. As such from the control plane viewpoint, this mechanism
turn the OLS-PXC composed system into a single logical entity turn the OLS-PXC composed system into a single logical entity
allowing the consideration of the same failure management mechanisms allowing the consideration of the same failure management mechanisms
for such entity as for any other O-E-O capable device. for such entity as for any other O-E-O capable device.
More generally, the following are typical failure conditions in More generally, the following are typical failure conditions in
Sonet/SDH and pre-OTN networks: Sonet/SDH and pre-OTN networks:
- Loss of Light (LOL)/Loss of Signal (LOS): Signal Failure (SF) - Loss of Light (LOL)/Loss of Signal (LOS): Signal Failure (SF)
condition where the optical signal is not detected any longer on
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condition where the optical signal is not detected any longer on
the receiver of a given interface. the receiver of a given interface.
- Signal Degrade (SD): detection of the signal degradation over - Signal Degrade (SD): detection of the signal degradation over
a specific period of time. a specific period of time.
- For Sonet/SDH payloads, all of the above-mentioned supervision - For Sonet/SDH payloads, all of the above-mentioned supervision
capabilities can be used, resulting in SD or SF condition. capabilities can be used, resulting in SD or SF condition.
In summary, the following cases apply when considering the In summary, the following cases apply when considering the
communication between the detecting and reporting entities: communication between the detecting and reporting entities:
- Co-located detecting and reporting entities: both the detecting - Co-located detecting and reporting entities: both the detecting
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Failure localization provides to the deciding entity information Failure localization provides to the deciding entity information
about the location (and so the identity) of the transport plane about the location (and so the identity) of the transport plane
entity that detects the LSP(s)/span(s) failure. The deciding entity entity that detects the LSP(s)/span(s) failure. The deciding entity
can then make an accurate decision to achieve finer grained recovery can then make an accurate decision to achieve finer grained recovery
switching action(s). Note that this information can also be included switching action(s). Note that this information can also be included
as part of the failure notification (see Section 4.3). as part of the failure notification (see Section 4.3).
In some cases, this accurate failure localization information may be In some cases, this accurate failure localization information may be
less urgent to determine if it requires performing more time less urgent to determine if it requires performing more time
consuming failure isolation (see also Section 4.5). This is consuming failure isolation (see also Section 4.4). This is
particularly the case when edge-to-edge LSP recovery (edge referring particularly the case when edge-to-edge LSP recovery (edge referring
to a sub-network end-node for instance) is performed based on a to a sub-network end-node for instance) is performed based on a
simple failure notification (including the identification of the simple failure notification (including the identification of the
working LSPs under failure condition). In this case, a more accurate working LSPs under failure condition). In this case, a more accurate
localization and isolation can be performed after recovery of these localization and isolation can be performed after recovery of these
LSPs. LSPs.
Failure localization should be triggered immediately after the fault Failure localization should be triggered immediately after the fault
detection phase. This operation can be performed at the transport detection phase. This operation can be performed at the transport
plane and/or, if unavailable (via the transport plane), the control plane and/or, if unavailable (via the transport plane), the control
plane level where dedicated signaling messages can be used. When plane level where dedicated signaling messages can be used. When
performed at the control plane level, a protocol such as LMP (see performed at the control plane level, a protocol such as LMP (see
[LMP], Section 6) can be used for failure localization purposes. [LMP], Section 6) can be used for failure localization purposes.
4.3 Failure Notification 4.3 Failure Notification
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Failure notification is used 1) to inform intermediate nodes that an Failure notification is used 1) to inform intermediate nodes that an
LSP/span failure has occurred and has been detected 2) to inform the LSP/span failure has occurred and has been detected 2) to inform the
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deciding entities (which can correspond to any intermediate or end- deciding entities (which can correspond to any intermediate or end-
point of the failed LSP/span) that the corresponding service is not point of the failed LSP/span) that the corresponding service is not
available. In general, these deciding entities will be the ones available. In general, these deciding entities will be the ones
taking the appropriate recovery decision. When co-located with the taking the appropriate recovery decision. When co-located with the
recovering entity, these entities will also perform the recovering entity, these entities will also perform the
corresponding recovery action(s). corresponding recovery action(s).
Failure notification can be either provided by the transport or by Failure notification can be either provided by the transport or by
the control plane. As an example, let us first briefly describe the the control plane. As an example, let us first briefly describe the
failure notification mechanism defined at the Sonet/SDH transport failure notification mechanism defined at the Sonet/SDH transport
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restoration actions via the management plane. restoration actions via the management plane.
On the other hand, using a failure notification mechanism through On the other hand, using a failure notification mechanism through
the control plane would provide the possibility to trigger either a the control plane would provide the possibility to trigger either a
protection or a restoration action via the control plane. This has protection or a restoration action via the control plane. This has
the advantage that a control plane recovery responsible entity does the advantage that a control plane recovery responsible entity does
not necessarily have to be co-located with a transport not necessarily have to be co-located with a transport
maintenance/recovery domain. A control plane recovery domain can be maintenance/recovery domain. A control plane recovery domain can be
defined at entities not supporting a transport plane recovery. defined at entities not supporting a transport plane recovery.
Moreover, as specified in [RFC-3473], notification message exchanges Moreover, as specified in [RFC3473], notification message exchanges
through a GMPLS control plane may not follow the same path as the through a GMPLS control plane may not follow the same path as the
LSP/spans for which these messages carry the status. In turn, this LSP/spans for which these messages carry the status. In turn, this
ensures a fast, reliable (through acknowledgement and the use of ensures a fast, reliable (through acknowledgement and the use of
either a dedicated control plane network or disjoint control either a dedicated control plane network or disjoint control
channels) and efficient (through the aggregation of several LSP/span channels) and efficient (through the aggregation of several LSP/span
status within the same message) failure notification mechanism. status within the same message) failure notification mechanism.
The other important properties to be met by the failure notification The other important properties to be met by the failure notification
mechanism are mainly the following: mechanism are mainly the following:
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- Notification messages must provide enough information such that - Notification messages must provide enough information such that
the most efficient subsequent recovery action will be taken (in the most efficient subsequent recovery action will be taken (in
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most of the recovery types and schemes this action is even most of the recovery types and schemes this action is even
deterministic) at the recovering entities. Remember here that deterministic) at the recovering entities. Remember here that
these entities can be either intermediate or end-points through these entities can be either intermediate or end-points through
which normal traffic flows. Based on local policy, intermediate which normal traffic flows. Based on local policy, intermediate
nodes may not use this information for subsequent recovery actions nodes may not use this information for subsequent recovery actions
(see for instance the APS protocol phases as described in [TERM]). (see for instance the APS protocol phases as described in [TERM]).
In addition, since fast notification is a mechanism running in In addition, since fast notification is a mechanism running in
collaboration with the existing GMPLS signalling (see [RFC-3473]) collaboration with the existing GMPLS signalling (see [RFC3473])
that also allows intermediate nodes to stay informed about the that also allows intermediate nodes to stay informed about the
status of the working LSP/spans under failure condition. status of the working LSP/spans under failure condition.
The trade-off here is to define what information the LSP/span end- The trade-off here is to define what information the LSP/span end-
points (more precisely, the deciding entity) needs in order for points (more precisely, the deciding entity) needs in order for
the recovering entity to take the best recovery action: if not the recovering entity to take the best recovery action: if not
enough information is provided, the decision can not be optimal enough information is provided, the decision can not be optimal
(note that in this eventuality, the important issue is to quantify (note that in this eventuality, the important issue is to quantify
the level of sub-optimality), if too much information is provided the level of sub-optimality), if too much information is provided
the control plane may be overloaded with unnecessary information the control plane may be overloaded with unnecessary information
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node) implies a consistent decision based on the conditions for node) implies a consistent decision based on the conditions for
which a trade-off between fast convergence (at detecting node) and which a trade-off between fast convergence (at detecting node) and
fast notification (implying that correlation and aggregation fast notification (implying that correlation and aggregation
occurs at receiving end-points) can be found. occurs at receiving end-points) can be found.
4.4 Failure Correlation 4.4 Failure Correlation
A single failure event (such as a span failure) can result into A single failure event (such as a span failure) can result into
reporting multiple failures (such as individual LSP failures) reporting multiple failures (such as individual LSP failures)
conditions. These can be grouped (i.e. correlated) to reduce the conditions. These can be grouped (i.e. correlated) to reduce the
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number of failure conditions communicated on the reporting channel, number of failure conditions communicated on the reporting channel,
for both in-band and out-of-band failure reporting. for both in-band and out-of-band failure reporting.
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In such a scenario, it can be important to wait for a certain period In such a scenario, it can be important to wait for a certain period
of time, typically called failure correlation time, and gather all of time, typically called failure correlation time, and gather all
the failures to report them as a group of failures (or simply group the failures to report them as a group of failures (or simply group
failure). For instance, this approach can be provided using LMP-WDM failure). For instance, this approach can be provided using LMP-WDM
for pre-OTN networks (see [LMP-WDM]) or when using Signal Failure/ for pre-OTN networks (see [LMP-WDM]) or when using Signal Failure/
Degrade Group in the Sonet/SDH context. Degrade Group in the Sonet/SDH context.
Note that a default average time interval during which failure Note that a default average time interval during which failure
correlation operation can be performed is difficult to provide since correlation operation can be performed is difficult to provide since
it is strongly dependent on the underlying network topology. it is strongly dependent on the underlying network topology.
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Note: in the context of LSP/span protection, control plane actions Note: in the context of LSP/span protection, control plane actions
can be performed either for operational purposes and/or can be performed either for operational purposes and/or
synchronization purposes (vertical synchronization between transport synchronization purposes (vertical synchronization between transport
and control plane) and/or notification purposes (horizontal and control plane) and/or notification purposes (horizontal
synchronization between end-nodes at control plane level). This synchronization between end-nodes at control plane level). This
suggests the selection of the responsible plane (in particular for suggests the selection of the responsible plane (in particular for
protection switching) during the provisioning phase of the protection switching) during the provisioning phase of the
protected/protection LSP. protected/protection LSP.
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2. LSP/span Restoration 2. LSP/span Restoration
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- Phase 1: Failure detection Transport plane - Phase 1: Failure detection Transport plane
- Phase 2: Failure localization/isolation Transport/Control plane - Phase 2: Failure localization/isolation Transport/Control plane
- Phase 3: Failure notification Control plane - Phase 3: Failure notification Control plane
- Phase 4: Recovery switching Control plane - Phase 4: Recovery switching Control plane
- Phase 5: Reversion (normalization) Control plane - Phase 5: Reversion (normalization) Control plane
Therefore, this document primarily focuses on provisioning of LSP Therefore, this document primarily focuses on provisioning of LSP
recovery resources, failure notification mechanisms, recovery recovery resources, failure notification mechanisms, recovery
switching, and reversion operations. Moreover some additional switching, and reversion operations. Moreover some additional
considerations can be dedicated to the mechanisms associated to the considerations can be dedicated to the mechanisms associated to the
skipping to change at line 591 skipping to change at line 589
squelching, implies that failures (such as LoL) will propagate to squelching, implies that failures (such as LoL) will propagate to
edge nodes giving the possibility to initiate recovery actions edge nodes giving the possibility to initiate recovery actions
driven by upper layers. driven by upper layers.
The main disadvantage comes from the lack of interworking due to the The main disadvantage comes from the lack of interworking due to the
large amount of failure management (in particular failure large amount of failure management (in particular failure
notification protocols) and recovery mechanisms currently available. notification protocols) and recovery mechanisms currently available.
Note also, that for all-optical networks, combination of recovery Note also, that for all-optical networks, combination of recovery
with optical physical impairments is left for a future release of with optical physical impairments is left for a future release of
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this document since corresponding detection technologies are under this document since corresponding detection technologies are under
specification. specification.
5.2.3 Sonet/SDH Recovery 5.2.3 Sonet/SDH Recovery
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Some of the advantages of Sonet/SDH [T1.105]/[G.707] and more Some of the advantages of Sonet/SDH [T1.105]/[G.707] and more
generically any TDM transport plane recovery are that they provide: generically any TDM transport plane recovery are that they provide:
- Protection types operating at the data plane level are - Protection types operating at the data plane level are
standardized (see [G.841]) and can operate across protected standardized (see [G.841]) and can operate across protected
domains and interwork (see [G.842]). domains and interwork (see [G.842]).
- Failure detection, notification and path/section Automatic - Failure detection, notification and path/section Automatic
Protection Switching (APS) mechanisms. Protection Switching (APS) mechanisms.
skipping to change at line 645 skipping to change at line 644
context, two classes of transport mechanisms can be considered here context, two classes of transport mechanisms can be considered here
i.e. in-fiber or out-of-fiber (through a dedicated physically i.e. in-fiber or out-of-fiber (through a dedicated physically
diverse control network referred to as the Data Communication diverse control network referred to as the Data Communication
Network or DCN). The potential impact of the usage of an in-fiber Network or DCN). The potential impact of the usage of an in-fiber
(signalling) transport mechanism is briefly considered here. (signalling) transport mechanism is briefly considered here.
In-fiber transport mechanism can be further subdivided into in-band In-fiber transport mechanism can be further subdivided into in-band
and out-of-band. As such, the distinction between in-fiber in-band and out-of-band. As such, the distinction between in-fiber in-band
and in-fiber out-of-band signalling reduces to the consideration of and in-fiber out-of-band signalling reduces to the consideration of
a logically versus physically embedded control plane topology with a logically versus physically embedded control plane topology with
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respect to the transport plane topology. In the scope of this respect to the transport plane topology. In the scope of this
document, it is assumed that at least one IP control channel between document, it is assumed that at least one IP control channel between
each pair of adjacent nodes is continuously available to enable the each pair of adjacent nodes is continuously available to enable the
exchange of recovery-related information and messages. Thus, in exchange of recovery-related information and messages. Thus, in
either case (i.e. in-band or out-of-band) at least one logical or either case (i.e. in-band or out-of-band) at least one logical or
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physical control channel between each pair of nodes is always physical control channel between each pair of nodes is always
expected to be available. expected to be available.
Therefore, the key issue when using in-fiber signalling is whether Therefore, the key issue when using in-fiber signalling is whether
one can assume independence between the fault-tolerance capabilities one can assume independence between the fault-tolerance capabilities
of control plane and the failures affecting the transport plane of control plane and the failures affecting the transport plane
(including the nodes). Note also that existing specifications like (including the nodes). Note also that existing specifications like
the OTN provide a limited form of independence for in-fiber the OTN provide a limited form of independence for in-fiber
signaling by dedicating a separate optical supervisory channel (OSC, signaling by dedicating a separate optical supervisory channel (OSC,
see [G.709] and [G.874]) to transport the overhead and other control see [G.709] and [G.874]) to transport the overhead and other control
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| |----...----| |---------| |----...----| | | |----...----| |---------| |----...----| |
------- ------- ------- ------- ------- ------- ------- -------
t0 >>>>>>> F t0 >>>>>>> F
t1 x <---------------x t1 x <---------------x
Notification Notification
t2 <--------...--------x x--------...--------> t2 <--------...--------x x--------...-------->
Up Notification Down Notification Up Notification Down Notification
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------- ------- ------- ------- ------- ------- ------- -------
| | | |Tx Rx| | | | | | | |Tx Rx| | | |
| NodeA |----...----| NodeB |xxxxxxxxx| NodeC |----...----| NodeD | | NodeA |----...----| NodeB |xxxxxxxxx| NodeC |----...----| NodeD |
| |----...----| |xxxxxxxxx| |----...----| | | |----...----| |xxxxxxxxx| |----...----| |
------- ------- ------- ------- ------- ------- ------- -------
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t0 F <<<<<<< >>>>>>> F t0 F <<<<<<< >>>>>>> F
t1 x <-------------> x t1 x <-------------> x
Notification Notification
t2 <--------...--------x x--------...--------> t2 <--------...--------x x--------...-------->
Up Notification Down Notification Up Notification Down Notification
After failure detection, the following failure management operations After failure detection, the following failure management operations
can be subsequently considered: can be subsequently considered:
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operation is negligible. In case of bi-directional failure, node B operation is negligible. In case of bi-directional failure, node B
(and node C) has to correlate the received notification message (and node C) has to correlate the received notification message
from node C (node B, respectively) with the corresponding locally from node C (node B, respectively) with the corresponding locally
detected information. detected information.
- After some (pre-determined) period of time, referred to as the - After some (pre-determined) period of time, referred to as the
hold-off time, after which the local recovery actions (see Section hold-off time, after which the local recovery actions (see Section
5.3.4) were not successful, the following occurs. In case of 5.3.4) were not successful, the following occurs. In case of
unidirectional failure and depending on the directionality of the unidirectional failure and depending on the directionality of the
LSP, node B should send an upstream notification message (see LSP, node B should send an upstream notification message (see
[RFC-3473]) to the ingress node A and node C may send a downstream [RFC3473]) to the ingress node A and node C may send a downstream
notification message (see [RFC-3473]) to the egress node D. notification message (see [RFC3473]) to the egress node D.
However, in such a case only node A referred to as the "master" However, in such a case only node A referred to as the "master"
(node D being then referred to as the "slave" per [TERM]), would (node D being then referred to as the "slave" per [TERM]), would
initiate an edge to edge recovery action. Note that the other LSP initiate an edge to edge recovery action. Note that the other LSP
end-node (i.e. node D in this case) may be optionally notified end-node (i.e. node D in this case) may be optionally notified
using a downstream notification message (see [RFC-3473]). using a downstream notification message (see [RFC3473]).
In case of bi-directional failure, node B should send an upstream In case of bi-directional failure, node B should send an upstream
notification message (see [RFC-3473]) to the ingress node A and notification message (see [RFC3473]) to the ingress node A and
node C may send a downstream notification message (see [RFC-3473]) node C may send a downstream notification message (see [RFC3473])
to the egress node D. However, due to the dependence on the LSP to the egress node D. However, due to the dependence on the LSP
directionality, only ingress node A would initiate an edge to edge directionality, only ingress node A would initiate an edge to edge
recovery action. Note that the other LSP end-node (i.e. node D in recovery action. Note that the other LSP end-node (i.e. node D in
this case) should also be notified of this event using a this case) should also be notified of this event using a
downstream notification message (see [RFC-3473]). For instance, if downstream notification message (see [RFC3473]). For instance, if
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an LSP directed from D to A is under failure condition, only the an LSP directed from D to A is under failure condition, only the
notification message sent from node C to D would initiate a notification message sent from node C to D would initiate a
recovery action and, in this case, per [TERM], the deciding and recovery action and, in this case, per [TERM], the deciding and
recovering node D is referred to as the "master" while node A is recovering node D is referred to as the "master" while node A is
referred to as the "slave" (i.e. recovering only entity). referred to as the "slave" (i.e. recovering only entity).
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Note: The determination of the master and the slave may be based Note: The determination of the master and the slave may be based
either on configured information or dedicated protocol capability. either on configured information or dedicated protocol capability.
In the above scenarios, the path followed by the upstream and In the above scenarios, the path followed by the upstream and
downstream notification messages does not have to be the same as the downstream notification messages does not have to be the same as the
one followed by the failed LSP (see [RFC-3473] for more details on one followed by the failed LSP (see [RFC3473] for more details on
the notification message exchange). The important point, concerning the notification message exchange). The important point, concerning
this mechanism, is that either the detecting/reporting entity (i.e. this mechanism, is that either the detecting/reporting entity (i.e.
the nodes B and C) is also the deciding/recovery entity or the the nodes B and C) is also the deciding/recovery entity or the
detecting/reporting entity is simply an intermediate node in the detecting/reporting entity is simply an intermediate node in the
subsequent recovery process. One refers to local recovery in the subsequent recovery process. One refers to local recovery in the
former case and to edge-to-edge recovery in the latter one (see also former case and to edge-to-edge recovery in the latter one (see also
Section 5.3.4). Section 5.3.4).
5.3.3 Partial versus Full Span Recovery 5.3.3 Partial versus Full Span Recovery
skipping to change at line 808 skipping to change at line 808
the failure). In order to facilitate the definition of the the failure). In order to facilitate the definition of the
corresponding recovery mechanisms (and their sequence), one assumes corresponding recovery mechanisms (and their sequence), one assumes
here as well, that per [TERM] the deciding (and recovering) entity, here as well, that per [TERM] the deciding (and recovering) entity,
referred to as the "master" is the only initiator of the recovery of referred to as the "master" is the only initiator of the recovery of
the whole LSP (sub-)group. the whole LSP (sub-)group.
5.3.4 Difference between LSP, LSP Segment and Span Recovery 5.3.4 Difference between LSP, LSP Segment and Span Recovery
The recovery definitions given in [TERM] are quite generic and apply The recovery definitions given in [TERM] are quite generic and apply
for link (or local span) and LSP recovery. The major difference for link (or local span) and LSP recovery. The major difference
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between LSP, LSP Segment and span recovery is related to the number between LSP, LSP Segment and span recovery is related to the number
of intermediate nodes that the signalling messages have to travel. of intermediate nodes that the signalling messages have to travel.
Since nodes are not necessarily adjacent in case of LSP (or LSP Since nodes are not necessarily adjacent in case of LSP (or LSP
Segment) recovery, signalling message exchanges from the reporting Segment) recovery, signalling message exchanges from the reporting
to the deciding/recovery entity may have to cross several to the deciding/recovery entity may have to cross several
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intermediate nodes. In particular, this applies for the notification intermediate nodes. In particular, this applies for the notification
messages due to the number of hops separating the location of a messages due to the number of hops separating the location of a
failure occurrence from its destination. This results in an failure occurrence from its destination. This results in an
additional propagation and forwarding delay. Note that the former additional propagation and forwarding delay. Note that the former
delay may in certain circumstances be non-negligible; e.g. in case delay may in certain circumstances be non-negligible; e.g. in case
of copper out-of-band network, approximately 1 ms per 200km. of copper out-of-band network, approximately 1 ms per 200km.
Moreover, the recovery mechanisms applicable to end-to-end LSPs and Moreover, the recovery mechanisms applicable to end-to-end LSPs and
to the segments that may compose an end-to-end LSP (i.e. edge-to- to the segments that may compose an end-to-end LSP (i.e. edge-to-
edge recovery) can be exactly the same. However, one expects in the edge recovery) can be exactly the same. However, one expects in the
skipping to change at line 864 skipping to change at line 864
[TERM] defines the basic LSP/span recovery types. This section [TERM] defines the basic LSP/span recovery types. This section
describes the recovery schemes that can be built using these describes the recovery schemes that can be built using these
recovery types. In brief, a recovery scheme is defined as the recovery types. In brief, a recovery scheme is defined as the
combination of several ingress-egress node pairs supporting a given combination of several ingress-egress node pairs supporting a given
recovery type (from the set of the recovery types they allow). recovery type (from the set of the recovery types they allow).
Several examples are provided here to illustrate the difference Several examples are provided here to illustrate the difference
between recovery types such as 1:1 or M:N and recovery schemes such between recovery types such as 1:1 or M:N and recovery schemes such
as (1:1)^n or (M:N)^n referred to as shared-mesh recovery. as (1:1)^n or (M:N)^n referred to as shared-mesh recovery.
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1. (1:1)^n with recovery resource sharing 1. (1:1)^n with recovery resource sharing
The exponent, n, indicates the number of times a 1:1 recovery type The exponent, n, indicates the number of times a 1:1 recovery type
is applied between at most n different ingress-egress node pairs. is applied between at most n different ingress-egress node pairs.
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Here, at most n pairs of disjoint working and recovery LSPs/spans Here, at most n pairs of disjoint working and recovery LSPs/spans
share at most n times a common resource. Since the working LSPs/ share at most n times a common resource. Since the working LSPs/
spans are mutually disjoint, simultaneous requests for use of the spans are mutually disjoint, simultaneous requests for use of the
shared (common) resource will only occur in case of simultaneous shared (common) resource will only occur in case of simultaneous
failures, which is less likely to happen. failures, which is less likely to happen.
For instance, in the common (1:1)^2 case, if the 2 recovery LSPs in For instance, in the common (1:1)^2 case, if the 2 recovery LSPs in
the group overlap the same common resource, then it can handle only the group overlap the same common resource, then it can handle only
single failures; any multiple working LSP failures will cause at single failures; any multiple working LSP failures will cause at
least one working LSP to be denied automatic recovery. Consider for least one working LSP to be denied automatic recovery. Consider for
skipping to change at line 903 skipping to change at line 902
The (M:N)^n scheme is documented here for the sake of completeness The (M:N)^n scheme is documented here for the sake of completeness
only (i.e. it is not mandated that GMPLS capabilities would support only (i.e. it is not mandated that GMPLS capabilities would support
this scheme). The exponent, n, indicates the number of times an M:N this scheme). The exponent, n, indicates the number of times an M:N
recovery type is applied between at most n different ingress-egress recovery type is applied between at most n different ingress-egress
node pairs. So the interpretation follows from the previous case, node pairs. So the interpretation follows from the previous case,
except that here disjointness applies to the N working LSPs/spans except that here disjointness applies to the N working LSPs/spans
and to the M recovery LSPs/spans while sharing at most n times M and to the M recovery LSPs/spans while sharing at most n times M
common resources. common resources.
In both schemes, it results a "group" of sum{n=1}^N N{n} working In both schemes, it results in a "group" of sum{n=1}^N N{n} working
LSPs and a pool of shared recovery resources, not all of which are LSPs and a pool of shared recovery resources, not all of which are
available to any given working LSP. In such conditions, defining a available to any given working LSP. In such conditions, defining a
metric that describes the amount of overlap among the recovery LSPs metric that describes the amount of overlap among the recovery LSPs
would give some indication of the group's ability to handle would give some indication of the group's ability to handle
simultaneous failures of multiple LSPs. simultaneous failures of multiple LSPs.
For instance, in the simple (1:1)^n case, if n recovery LSPs in a For instance, in the simple (1:1)^n case, if n recovery LSPs in a
(1:1)^n group overlap, then it can handle only single failures; any (1:1)^n group overlap, then it can handle only single failures; any
simultaneous failure of multiple working LSPs will cause at least simultaneous failure of multiple working LSPs will cause at least
one working LSP to be denied automatic recovery. But if one consider one working LSP to be denied automatic recovery. But if one
for instance, a (2:2)^2 group in which there are two pairs of considers for instance, a (2:2)^2 group in which there are two pairs
overlapping recovery LSPs, then two LSPs (belonging to the same of overlapping recovery LSPs, then two LSPs (belonging to the same
pair) can be simultaneously recovered. The latter case can be pair) can be simultaneously recovered. The latter case can be
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illustrated by the following topology with 2 pairs of working LSPs illustrated by the following topology with 2 pairs of working LSPs
A-B-C and F-G-H and their respective recovery LSPs A-D-E-C and F-D- A-B-C and F-G-H and their respective recovery LSPs A-D-E-C and F-D-
E-H that share two common D-E link resources. E-H that share two common D-E link resources.
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A========B========C A========B========C
\\ // \\ //
\\ // \\ //
D =========== E D =========== E
// \\ // \\
// \\ // \\
F========G========H F========G========H
Moreover, in all these schemes, (working) path disjointness can be Moreover, in all these schemes, (working) path disjointness can be
enforced by exchanging information related to working LSPs during enforced by exchanging information related to working LSPs during
the recovery LSP signaling. Specific issues related to the the recovery LSP signaling. Specific issues related to the
combination of shared (discrete) bandwidth and disjointness for combination of shared (discrete) bandwidth and disjointness for
recovery schemes are described in Section 8.4.2. recovery schemes are described in Section 8.4.2.
5.5 LSP Recovery Mechanisms 5.5 LSP Recovery Mechanisms
5.5.1 Classification 5.5.1 Classification
LSPs/spans recovery time and ratio depend on the proper recovery LSP The recovery time and ratio of LSPs/spans depend on proper recovery
provisioning (meaning pre-provisioning when performed before failure LSP provisioning (meaning pre-provisioning when performed before
occurrence) and the level of recovery resources overbooking (i.e. failure occurrence) and the level of overbooking of recovery
over-provisioning). A proper balance of these two operations will resources (i.e. over-provisioning). A proper balance of these two
result in the desired LSP/span recovery time and ratio when single operations will result in the desired LSP/span recovery time and
or multiple failure(s) occur(s). Note also that these operations are ratio when single or multiple failure(s) occur(s). Note also that
mostly performed during the network planning phases. these operations are mostly performed during the network planning
phases.
The different options for LSP (pre-)provisioning and overbooking are The different options for LSP (pre-)provisioning and overbooking are
classified here below to structure the analysis of the different classified below to structure the analysis of the different recovery
recovery mechanisms. mechanisms.
1. Pre-Provisioning 1. Pre-Provisioning
Proper recovery LSP pre-provisioning will help to alleviate the Proper recovery LSP pre-provisioning will help to alleviate the
failure of the working LSPs (due to the failure of the resources failure of the working LSPs (due to the failure of the resources
that carry these LSPs). As an example, one may compute and establish that carry these LSPs). As an example, one may compute and establish
the recovery LSP either end-to-end or segment-per-segment, to the recovery LSP either end-to-end or segment-per-segment, to
protect a working LSP from multiple failure events affecting protect a working LSP from multiple failure events affecting
link(s), node(s) and/or SRLG(s). The recovery LSP pre-provisioning link(s), node(s) and/or SRLG(s). The recovery LSP pre-provisioning
options can be classified (as shown in the below figure) as follows: options can be classified (in the below figure) as follows:
(1) the recovery path can be either pre-computed or computed (1) the recovery path can be either pre-computed or computed
on-demand. on-demand.
(2) when the recovery path is pre-computed, it can be either pre- (2) when the recovery path is pre-computed, it can be either pre-
signaled (implying recovery resource reservation) or signaled signaled (implying recovery resource reservation) or signaled
on-demand. on-demand.
(3) when the recovery resources are pre-reserved, they can be either D.Papadimitriou et al. - Expires October 2004 18
(3) when the recovery resources are pre-signaled, they can be either
pre-selected or selected on-demand. pre-selected or selected on-demand.
Recovery LSP provisioning phases: Recovery LSP provisioning phases:
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(1) Path Computation --> On-demand (1) Path Computation --> On-demand
| |
| |
--> Pre-Computed --> Pre-Computed
| |
| |
(2) Signalling --> On-demand (2) Signalling --> On-demand
| |
| |
--> Pre-Signaled --> Pre-Signaled
skipping to change at line 1020 skipping to change at line 1021
| |
| |
+----- Shared (for instance: 1:N, M:N, etc.) +----- Shared (for instance: 1:N, M:N, etc.)
| |
Level of | Level of |
Overbooking -----+----- Unprotected (for instance: 0:1, 0:N) Overbooking -----+----- Unprotected (for instance: 0:1, 0:N)
Also, when using shared recovery, one may support preemptible extra- Also, when using shared recovery, one may support preemptible extra-
traffic; the recovery mechanism is then expected to allow preemption traffic; the recovery mechanism is then expected to allow preemption
of this low priority traffic in case of recovery resource contention of this low priority traffic in case of recovery resource contention
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during recovery operations. The following sections will consider the during recovery operations. The following sections will consider the
above-mentioned overbooking options when analyzing the different above-mentioned overbooking options when analyzing the different
recovery mechanisms. recovery mechanisms.
5.5.2 LSP Restoration 5.5.2 LSP Restoration
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The following times are defined to provide a quantitative estimation The following times are defined to provide a quantitative estimation
about the time performance of the different LSP restoration about the time performance of the different LSP restoration
mechanisms (also referred to as LSP re-routing): mechanisms (also referred to as LSP re-routing):
- Path Computation Time: Tc - Path Computation Time: Tc
- Path Selection Time: Ts - Path Selection Time: Ts
- End-to-end LSP Resource Reservation Time: Tr (a delta for resource - End-to-end LSP Resource Reservation Time: Tr (a delta for resource
selection is also considered, the corresponding total time is then selection is also considered, the corresponding total time is then
referred to as Trs) referred to as Trs)
- End-to-end LSP Resource Activation Time: Ta (a delta for - End-to-end LSP Resource Activation Time: Ta (a delta for
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LSP. LSP.
2. Without Route Pre-computation (or Full LSP re-routing) 2. Without Route Pre-computation (or Full LSP re-routing)
An end-to-end restoration LSP is dynamically established after the An end-to-end restoration LSP is dynamically established after the
failure(s) occur(s). Here, after failure occurrence, one or more failure(s) occur(s). Here, after failure occurrence, one or more
(disjoint) paths for the restoration LSP are dynamically computed (disjoint) paths for the restoration LSP are dynamically computed
and one is selected. As such, one can define this as a complete "LSP and one is selected. As such, one can define this as a complete "LSP
re-routing" mechanism. re-routing" mechanism.
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No reservation or selection of resources is performed along the No reservation or selection of resources is performed along the
restoration path before failure occurrence. As a result, there is no restoration path before failure occurrence. As a result, there is no
guarantee that a restoration LSP is available when a failure occurs. guarantee that a restoration LSP is available when a failure occurs.
The expected total restoration time T is thus equal to Tc (+ Ts) + The expected total restoration time T is thus equal to Tc (+ Ts) +
Trs. Therefore, time performance between these two approaches Trs. Therefore, time performance between these two approaches
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differs by the time required for route computation Tc (and its differs by the time required for route computation Tc (and its
potential selection time, Ts). potential selection time, Ts).
5.5.3 Pre-planned LSP Restoration 5.5.3 Pre-planned LSP Restoration
Pre-planned LSP restoration (also referred to as pre-planned LSP re- Pre-planned LSP restoration (also referred to as pre-planned LSP re-
routing) implies that the restoration LSP is pre-signaled. This in routing) implies that the restoration LSP is pre-signaled. This in
turn implies the reservation of recovery resources along the turn implies the reservation of recovery resources along the
restoration path. Two cases can be defined based on whether the restoration path. Two cases can be defined based on whether the
recovery resources are pre-selected or not. recovery resources are pre-selected or not.
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failure activation) while operations performed before failure failure activation) while operations performed before failure
occurrence takes Tc + Ts + Tr. occurrence takes Tc + Ts + Tr.
2. With both resource reservation and resource pre-selection 2. With both resource reservation and resource pre-selection
Before failure occurrence, an end-to-end restoration path is pre- Before failure occurrence, an end-to-end restoration path is pre-
selected from a set of pre-computed (disjoint) paths. The selected from a set of pre-computed (disjoint) paths. The
restoration LSP is signaled along this pre-selected path to reserve restoration LSP is signaled along this pre-selected path to reserve
AND select resources at each node but these resources are not AND select resources at each node but these resources are not
committed at the data plane level. Such that the selection of the committed at the data plane level. Such that the selection of the
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recovery resources is committed at the control plane level only, no recovery resources is committed at the control plane level only, no
cross-connections are performed along the restoration path. cross-connections are performed along the restoration path.
In this case, the resources reserved and selected for each In this case, the resources reserved and selected for each
restoration LSP may be dedicated or even shared between multiple restoration LSP may be dedicated or even shared between multiple
restoration LSPs whose associated working LSPs are not expected to restoration LSPs whose associated working LSPs are not expected to
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fail simultaneously. Local node policies can be applied to define fail simultaneously. Local node policies can be applied to define
the degree to which these resources can be shared across independent the degree to which these resources can be shared across independent
failures. Also, since a restoration scheme is considered, resource failures. Also, since a restoration scheme is considered, resource
sharing should not be limited to restoration LSPs starting and sharing should not be limited to restoration LSPs starting and
ending at the same ingress and egress nodes. Therefore, each node ending at the same ingress and egress nodes. Therefore, each node
participating to this scheme is expected to receive some feedback participating to this scheme is expected to receive some feedback
information on the sharing degree of the recovery resource(s) that information on the sharing degree of the recovery resource(s) that
this scheme involves. this scheme involves.
Upon failure detection/notification message reception, signaling is Upon failure detection/notification message reception, signaling is
skipping to change at line 1174 skipping to change at line 1175
time) by allowing the recovery of the individual LSP segments time) by allowing the recovery of the individual LSP segments
constituting the end-to-end LSP. constituting the end-to-end LSP.
Also, by using the horizontal hierarchy approach described in Also, by using the horizontal hierarchy approach described in
Section 7.1, an end-to-end LSP can be recovered by multiple recovery Section 7.1, an end-to-end LSP can be recovered by multiple recovery
mechanisms applied on an LSP segment basis (e.g. 1:1 edge-to-edge mechanisms applied on an LSP segment basis (e.g. 1:1 edge-to-edge
LSP protection in a metro network and M:N edge-to-edge protection in LSP protection in a metro network and M:N edge-to-edge protection in
the core). These mechanisms are ideally independent and may even use the core). These mechanisms are ideally independent and may even use
different failure localization and notification mechanisms. different failure localization and notification mechanisms.
6. Normalization 6. Reversion
Normalization is defined as the mechanism allowing switching of Reversion (a.k.a. normalization) is defined as the mechanism
normal traffic from the recovery LSP/span to the working LSP/span allowing switching of normal traffic from the recovery LSP/span to
previously under failure condition. Use of normalization is at the the working LSP/span previously under failure condition. Use of
discretion of the recovery domain policy. Normalization (also normalization is at the discretion of the recovery domain policy.
referred to as reversion) may impact the normal traffic (a second Normalization (also referred to as reversion) may impact the normal
hit) depending on the normalization mechanism used. traffic (a second hit) depending on the normalization mechanism
used.
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If normalization is supported 1) the LSP/span must be returned to If normalization is supported 1) the LSP/span must be returned to
the working LSP/span when the failure condition clears 2) the the working LSP/span when the failure condition clears 2) the
capability to de-activate (turn-off) the use of reversion should be capability to de-activate (turn-off) the use of reversion should be
provided. De-activation of reversion should not impact the normal provided. De-activation of reversion should not impact the normal
traffic regardless of whether currently using the working or traffic regardless of whether currently using the working or
recovery LSP/span. recovery LSP/span.
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Note: during the failure, the reuse of any non-failed resources Note: during the failure, the reuse of any non-failed resources
(e.g. LSP and/or spans) belonging to the working LSP/span is under (e.g. LSP and/or spans) belonging to the working LSP/span is under
the discretion of recovery domain policy. the discretion of recovery domain policy.
6.1 Wait-To-Restore (WTR) 6.1 Wait-To-Restore (WTR)
A specific mechanism (Wait-To-Restore) is used to prevent frequent A specific mechanism (Wait-To-Restore) is used to prevent frequent
recovery switching operations due to an intermittent defect (e.g. recovery switching operations due to an intermittent defect (e.g.
BER fluctuating around the SD threshold). BER fluctuating around the SD threshold).
skipping to change at line 1237 skipping to change at line 1239
However, deactivation (cancellation) of the wait-to-restore timer However, deactivation (cancellation) of the wait-to-restore timer
may occur in case of higher priority request attempts. That is the may occur in case of higher priority request attempts. That is the
recovery LSP/span usage by the normal traffic may be preempted if a recovery LSP/span usage by the normal traffic may be preempted if a
higher priority request for this recovery LSP/span is attempted. higher priority request for this recovery LSP/span is attempted.
6.3 Orphans 6.3 Orphans
When a reversion operation is requested normal traffic must be When a reversion operation is requested normal traffic must be
switched from the recovery to the recovered working LSP/span. A switched from the recovery to the recovered working LSP/span. A
particular situation occurs when the previously working LSP/span particular situation occurs when the previously working LSP/span
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cannot be recovered such that normal traffic can not be switched cannot be recovered such that normal traffic can not be switched
back. In such a case, the LSP/span under failure condition (also back. In such a case, the LSP/span under failure condition (also
referred to as "orphan") must be cleared i.e. removed from the pool referred to as "orphan") must be cleared i.e. removed from the pool
of resources allocated for normal traffic. Otherwise, potential de- of resources allocated for normal traffic. Otherwise, potential de-
synchronization between the control and transport plane resource synchronization between the control and transport plane resource
usage can appear. Depending on the signalling protocol capabilities usage can appear. Depending on the signalling protocol capabilities
and behavior different mechanisms are expected here. and behavior different mechanisms are expected here.
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Therefore any reserved or allocated resources for the LSP/span under Therefore any reserved or allocated resources for the LSP/span under
failure condition must be unreserved/de-allocated. Several ways can failure condition must be unreserved/de-allocated. Several ways can
be used for that purpose: either wait for the elapsing of the clear- be used for that purpose: either wait for the elapsing of the clear-
out time interval, or initiate a deletion from the ingress or the out time interval, or initiate a deletion from the ingress or the
egress node, or trigger the initiation of deletion from an entity egress node, or trigger the initiation of deletion from an entity
(such as an EMS or NMS) capable to react on the reception of an (such as an EMS or NMS) capable to react on the reception of an
appropriate notification message. appropriate notification message.
7. Hierarchies 7. Hierarchies
skipping to change at line 1276 skipping to change at line 1279
survivability. In general, it is expected that the recovery action survivability. In general, it is expected that the recovery action
is taken by the recoverable LSP/span closest to the failure in order is taken by the recoverable LSP/span closest to the failure in order
to avoid the multiplication of recovery actions. Moreover, recovery to avoid the multiplication of recovery actions. Moreover, recovery
hierarchies can be also bound to control plane logical partitions hierarchies can be also bound to control plane logical partitions
(e.g. administrative or topological boundaries). Each of them may (e.g. administrative or topological boundaries). Each of them may
apply different recovery mechanisms. apply different recovery mechanisms.
In brief, the commonly accepted ideas are generally that the lower In brief, the commonly accepted ideas are generally that the lower
layers can provide coarse but faster recovery while the higher layers can provide coarse but faster recovery while the higher
layers can provide finer but slower recovery. Moreover, it is also layers can provide finer but slower recovery. Moreover, it is also
desirable to avoid that similar layers with functional overlaps to desirable to avoid similar layers with functional overlaps to
optimize network resource utilization and processing overhead. In optimize network resource utilization and processing overhead. In
this context, this section intends to analyze these hierarchical this context, this section intends to analyze these hierarchical
aspects including the physical (passive) layer(s). aspects including the physical (passive) layer(s).
7.1 Horizontal Hierarchy (Partitioning) 7.1 Horizontal Hierarchy (Partitioning)
A horizontal hierarchy is defined when partitioning a single-layer A horizontal hierarchy is defined when partitioning a single-layer
network (and its control plane) into several recovery domains. network (and its control plane) into several recovery domains.
Within a domain, the recovery scope may extend over a link (or Within a domain, the recovery scope may extend over a link (or
span), LSP segment or even an end-to-end LSP. Moreover, an span), LSP segment or even an end-to-end LSP. Moreover, an
administrative domain may consist of a single recovery domain or can administrative domain may consist of a single recovery domain or can
be partitioned into several smaller recovery domains. The operator be partitioned into several smaller recovery domains. The operator
can partition the network into recovery domains based on physical can partition the network into recovery domains based on physical
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network topology, control plane capabilities or various traffic network topology, control plane capabilities or various traffic
engineering constraints. engineering constraints.
An example often addressed in the literature is the metro-core-metro An example often addressed in the literature is the metro-core-metro
application (sometimes extended to a metro-metro/core-core) within a application (sometimes extended to a metro-metro/core-core) within a
single transport layer (see Section 7.2). For such a case, an end- single transport layer (see Section 7.2). For such a case, an end-
to-end LSP is defined between the ingress and egress metro nodes, to-end LSP is defined between the ingress and egress metro nodes,
while LSP segments may be defined within the metro or core sub- while LSP segments may be defined within the metro or core sub-
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networks. Each of these topological structures determines a so- networks. Each of these topological structures determines a so-
called "recovery domain" since each of the LSPs they carry can have called "recovery domain" since each of the LSPs they carry can have
its own recovery type (or even scheme). The support of multiple its own recovery type (or even scheme). The support of multiple
recovery types and schemes within a sub-network is referred to as a recovery types and schemes within a sub-network is referred to as a
multi-recovery capable domain or simply multi-recovery domain. multi-recovery capable domain or simply multi-recovery domain.
7.2 Vertical Hierarchy (Layers) 7.2 Vertical Hierarchy (Layers)
It is a very challenging task to combine in a coordinated manner the It is a very challenging task to combine in a coordinated manner the
different recovery capabilities available across the path (i.e. different recovery capabilities available across the path (i.e.
skipping to change at line 1325 skipping to change at line 1328
a vertical coordination of the recovery mechanisms: a vertical coordination of the recovery mechanisms:
- The lower the layer the faster the notification and switching - The lower the layer the faster the notification and switching
- The higher the layer the finer the granularity of the recoverable - The higher the layer the finer the granularity of the recoverable
entity and therefore the granularity of the recovery resource entity and therefore the granularity of the recovery resource
Moreover, in the context of this analysis, a vertical hierarchy Moreover, in the context of this analysis, a vertical hierarchy
consists of multiple layered transport planes providing different: consists of multiple layered transport planes providing different:
- Discrete bandwidth granularities for non-packet LSPs such as OCh, - Discrete bandwidth granularities for non-packet LSPs such as OCh,
ODUk, STS_SPE/HOVC and VT_SPE/LOVC LSPs and continuous bandwidth ODUk, STS_SPE/HOVC and VT_SPE/LOVC LSPs and continuous bandwidth
granularities for packet LSPs granularities for packet LSPs
- Potentially, recovery capabilities with different temporal - Potential recovery capabilities with different temporal
granularities: ranging from milliseconds to tens of seconds granularities: ranging from milliseconds to tens of seconds
Note: based on the bandwidth granularity we can determine four Note: based on the bandwidth granularity we can determine four
classes of vertical hierarchies (1) packet over packet (2) packet classes of vertical hierarchies (1) packet over packet (2) packet
over circuit (3) circuit over packet and (4) circuit over circuit. over circuit (3) circuit over packet and (4) circuit over circuit.
Here below we briefly extend on (4), (2) being covered in [RFC Below we briefly expand on (4) only. (2) is covered in [RFC3386].
3386]. On the other hand (1) is extensively covered at the MPLS (1) is extensively covered by the MPLS Working Group, and (3) by the
Working Group, and (3) at the PWE3 Working Group. PWE3 Working Group.
In SDH/Sonet environments, one typically considers the VT_SPE/LOVC In SDH/Sonet environments, one typically considers the VT_SPE/LOVC
and STS SPE/HOVC as independent layers, VT_SPE/LOVC LSP using the and STS SPE/HOVC as independent layers, VT_SPE/LOVC LSP using the
underlying STS_SPE/HOVC LSPs as links, for instance. In OTN, the underlying STS_SPE/HOVC LSPs as links, for instance. In OTN, the
ODUk path layers will lie on the OCh path layer i.e. the ODUk LSPs ODUk path layers will lie on the OCh path layer i.e. the ODUk LSPs
using the underlying OCh LSPs as OTUk links. Note here that lower using the underlying OCh LSPs as OTUk links. Note here that lower
layer LSPs may simply be provisioned and not necessarily dynamically layer LSPs may simply be provisioned and not necessarily dynamically
triggered or established (control driven approach). In this context, triggered or established (control driven approach). In this context,
an LSP at the path layer (i.e. established using GMPLS signalling), an LSP at the path layer (i.e. established using GMPLS signalling),
for instance an optical channel LSP, appears at the OTUk layer as a for instance an optical channel LSP, appears at the OTUk layer as a
link, controlled by a link management protocol such as LMP. link, controlled by a link management protocol such as LMP.
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The first key issue with multi-layer recovery is that achieving The first key issue with multi-layer recovery is that achieving
individual or bulk LSP recovery will be as efficient as the individual or bulk LSP recovery will be as efficient as the
underlying link (local span) recovery. In such a case, the span can underlying link (local span) recovery. In such a case, the span can
be either protected or unprotected, but the LSP it carries MUST be be either protected or unprotected, but the LSP it carries MUST be
(at least locally) recoverable. Therefore, the span recovery process (at least locally) recoverable. Therefore, the span recovery process
can be either independent when protected (or restorable), or can be either independent when protected (or restorable), or
triggered by the upper LSP recovery process. The former case triggered by the upper LSP recovery process. The former case
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requires coordination to achieve subsequent LSP recovery. Therefore, requires coordination to achieve subsequent LSP recovery. Therefore,
in order to achieve robustness and fast convergence, multi-layer in order to achieve robustness and fast convergence, multi-layer
recovery requires a fine-tuned coordination mechanism. recovery requires a fine-tuned coordination mechanism.
Moreover, in the absence of adequate recovery mechanism coordination Moreover, in the absence of adequate recovery mechanism coordination
(for instance, a pre-determined coordination when using a hold-off (for instance, a pre-determined coordination when using a hold-off
timer), a failure notification may propagate from one layer to the timer), a failure notification may propagate from one layer to the
next one within a recovery hierarchy. This can cause "collisions" next one within a recovery hierarchy. This can cause "collisions"
and trigger simultaneous recovery actions that may lead to race and trigger simultaneous recovery actions that may lead to race
conditions and in turn, reduce the optimization of the resource conditions and in turn, reduce the optimization of the resource
utilization and/or generate global instabilities in the network (see utilization and/or generate global instabilities in the network (see
[MANCHESTER]). Therefore, a consistent and efficient escalation [MANCHESTER]). Therefore, a consistent and efficient escalation
strategy is needed to coordinate recovery across several layers. strategy is needed to coordinate recovery across several layers.
Therefore, one can expect that the definition of the recovery Therefore, one can expect that the definition of the recovery
mechanisms and protocol(s) is technology-independent such that they mechanisms and protocol(s) is technology-independent such that they
can be consistently implemented at different layers; this would in can be consistently implemented at different layers; this would in
turn simplify their global coordination. Moreover, as mentioned in turn simplify their global coordination. Moreover, as mentioned in
[RFC-3386], some looser form of coordination and communication [RFC3386], some looser form of coordination and communication
between (vertical) layers such a consistent hold-off timer between (vertical) layers such a consistent hold-off timer
configuration (and setup through signalling during the working LSP configuration (and setup through signalling during the working LSP
establishment) can be considered, allowing the synchronization establishment) can be considered, allowing the synchronization
between recovery actions performed across these layers. between recovery actions performed across these layers.
Note: Recovery Granularity 7.2.1 Recovery Granularity
In most environments, the design of the network and the vertical In most environments, the design of the network and the vertical
distribution of the LSP bandwidth are such that the recovery distribution of the LSP bandwidth are such that the recovery
granularity is finer at higher layers. The OTN and Sonet/SDH layers granularity is finer at higher layers. The OTN and Sonet/SDH layers
can only recover the whole section or the individual connections it can only recover the whole section or the individual connections it
transports whereas the IP/MPLS control plane can recover individual transports whereas the IP/MPLS control plane can recover individual
packet LSPs or groups of packet LSPs and this independently of their packet LSPs or groups of packet LSPs and this independently of their
granularity. On the other side, the recovery granularity at the sub- granularity. On the other side, the recovery granularity at the sub-
wavelength level (i.e. Sonet/SDH) can be provided only when the wavelength level (i.e. Sonet/SDH) can be provided only when the
network includes devices switching at the same granularity (and thus network includes devices switching at the same granularity (and thus
not with optical channel level). Therefore, the network layer can not with optical channel level). Therefore, the network layer can
deliver control-plane driven recovery mechanisms on a per-LSP basis deliver control-plane driven recovery mechanisms on a per-LSP basis
if and only if these LSPs have their corresponding switching if and only if these LSPs have their corresponding switching
granularity supported at the transport plane level. granularity supported at the transport plane level.
7.3 Escalation Strategies 7.3 Escalation Strategies
There are two types of escalation strategies (see [DEMEESTER]): There are two types of escalation strategies (see [DEMEESTER]):
bottom-up and top-down. bottom-up and top-down.
D.Papadimitriou et al. - Expires October 2004 26
The bottom-up approach assumes that lower layer recovery types and The bottom-up approach assumes that lower layer recovery types and
schemes are more expedient and faster than the upper layer one. schemes are more expedient and faster than the upper layer one.
Therefore we can inhibit or hold-off higher layer recovery. However Therefore we can inhibit or hold-off higher layer recovery. However
this assumption is not entirely true. Consider for instance a this assumption is not entirely true. Consider for instance a
Sonet/SDH based protection mechanism (with a less than 50 ms Sonet/SDH based protection mechanism (with a less than 50 ms
protection switching time) lying on top of an OTN restoration protection switching time) lying on top of an OTN restoration
mechanism (with a less than 200 ms restoration time). Therefore, mechanism (with a less than 200 ms restoration time). Therefore,
this assumption should be (at least) clarified as: lower layer this assumption should be (at least) clarified as: lower layer
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recovery mechanism is expected to be faster than upper level one if recovery mechanism is expected to be faster than upper level one if
the same type of recovery mechanism is used at each layer. the same type of recovery mechanism is used at each layer.
Consequently, taking into account the recovery actions at the Consequently, taking into account the recovery actions at the
different layers in a bottom-up approach, if lower layer recovery different layers in a bottom-up approach, if lower layer recovery
mechanisms are provided and sequentially activated in conjunction mechanisms are provided and sequentially activated in conjunction
with higher layer ones, the lower layers MUST have an opportunity to with higher layer ones, the lower layers MUST have an opportunity to
recover normal traffic before the higher layers do. However, if recover normal traffic before the higher layers do. However, if
lower layer recovery is slower than higher layer recovery, the lower lower layer recovery is slower than higher layer recovery, the lower
layer MUST either communicate the failure related information to the layer MUST either communicate the failure related information to the
skipping to change at line 1455 skipping to change at line 1456
pre-assigned (on a per-link basis) to a certain layer, e.g. a given pre-assigned (on a per-link basis) to a certain layer, e.g. a given
link will be recovered at the packet layer while another will be link will be recovered at the packet layer while another will be
recovered at the optical layer. recovered at the optical layer.
7.4 Disjointness 7.4 Disjointness
Having link and node diverse working and recovery LSPs/spans does Having link and node diverse working and recovery LSPs/spans does
not guarantee their complete disjointness. Due to the common not guarantee their complete disjointness. Due to the common
physical layer topology (passive), additional hierarchical concepts physical layer topology (passive), additional hierarchical concepts
such as the Shared Risk Link Group (SRLG) and mechanisms such as such as the Shared Risk Link Group (SRLG) and mechanisms such as
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SRLG diverse path computation must be developed to provide complete SRLG diverse path computation must be developed to provide complete
working and recovery LSP/span disjointness (see [IPO-IMP], [GMPLS- working and recovery LSP/span disjointness (see [IPO-IMP] and
RTG] and [CCAMP-SRLG]). Otherwise, a failure affecting the working [GMPLS-RTG]). Otherwise, a failure affecting the working LSP/span
LSP/span would also potentially affect the recovery LSP/span; one would also potentially affect the recovery LSP/span; one refers to
refers to such an event as "common failure". such an event as "common failure".
7.4.1 SRLG Disjointness 7.4.1 SRLG Disjointness
D.Papadimitriou et al. - Internet Draft - Expires March 2004 27 A Shared Risk Link Group (SRLG) is defined as the set of links
A Shared Risk Link Group (SRLG) is defined as the set of optical sharing a common risk (for instance, a common physical resource such
spans (or links or optical lines) sharing a common physical resource as a fiber link or a fiber cable). For instance, a set of links L
(for instance, fiber links, fiber trunks or cables) i.e. sharing a belongs to the same SRLG s, if they are provisioned over the same
common risk. For instance, a set of links L belongs to the same SRLG fiber link f.
s, if they are provisioned over the same fiber link f.
The SRLG properties can be summarized as follows: The SRLG properties can be summarized as follows:
1) A link belongs to more than one SRLG if and only if it crosses 1) A link belongs to more than one SRLG if and only if it crosses
one of the resources covered by each of them. one of the resources covered by each of them.
2) Two links belonging to the same SRLG can belong individually to 2) Two links belonging to the same SRLG can belong individually to
(one or more) other SRLGs. (one or more) other SRLGs.
3) The SRLG set S of an LSP is defined as the union of the 3) The SRLG set S of an LSP is defined as the union of the
individual SRLG s of the individual links composing this LSP. individual SRLG s of the individual links composing this LSP.
SRLG disjointness for LSP: SRLG disjointness is also applicable to LSPs:
The LSP SRLG disjointness concept is based on the following The LSP SRLG disjointness concept is based on the following
postulate: an LSP (i.e. sequence of links and nodes) covers an postulate: an LSP (i.e. sequence of links and nodes) covers an
SRLG if and only if it crosses one of the links or nodes SRLG if and only if it crosses one of the links or nodes
belonging to that SRLG. belonging to that SRLG.
Therefore, the SRLG disjointness for LSPs can be defined as Therefore, the SRLG disjointness for LSPs can be defined as
follows: two LSPs are disjoint with respect to an SRLG s if and follows: two LSPs are disjoint with respect to an SRLG s if and
only if they do not cover simultaneously this SRLG s. only if they do not cover simultaneously this SRLG s.
Whilst the SRLG disjointness for LSPs with respect to a set S of Whilst the SRLG disjointness for LSPs with respect to a set S of
SRLGs is defined as follows: two LSPs are disjoint with respect SRLGs is defined as follows: two LSPs are disjoint with respect
to a set of SRLGs S if and only if the common SRLGs between the to a set of SRLGs S if and only if the common SRLGs between the
sets of SRLGs they individually cover is disjoint from set S. sets of SRLGs they individually cover is disjoint from set S.
The impact on recovery is obvious: SRLG disjointness is a necessary The impact on recovery is noticeable: SRLG disjointness is a
(but not a sufficient) condition to ensure optical network necessary (but not a sufficient) condition to ensure network
survivability. With respect to the physical network resources, a survivability. With respect to the physical network resources, a
working-recovery LSP/span pair must be SRLG disjoint in case of working-recovery LSP/span pair must be SRLG disjoint in case of
dedicated recovery type. On the other hand, in case of shared dedicated recovery type. On the other hand, in case of shared
recovery, a group of working LSP/span must be mutually SRLG-disjoint recovery, a group of working LSP/span must be mutually SRLG-disjoint
in order to allow for a (single and common) shared recovery LSP in order to allow for a (single and common) shared recovery LSP
itself SRLG-disjoint from each of the working LSPs/spans. itself SRLG-disjoint from each of the working LSPs/spans.
8. Recovery Mechanisms Analysis 8. Recovery Mechanisms Analysis
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In order to provide a structured analysis of the recovery mechanisms In order to provide a structured analysis of the recovery mechanisms
detailed in the previous sections, the following dimensions can be detailed in the previous sections, the following dimensions can be
considered: considered:
1. Fast convergence (performance): provide a mechanism that 1. Fast convergence (performance): provide a mechanism that
aggregates multiple failures (this implies fast failure aggregates multiple failures (this implies fast failure
detection and correlation mechanisms) and fast recovery decision detection and correlation mechanisms) and fast recovery decision
independently of the number of failures occurring in the optical independently of the number of failures occurring in the optical
network (implying also a fast failure notification). network (implying also a fast failure notification).
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2. Efficiency (scalability): minimize the switching time required 2. Efficiency (scalability): minimize the switching time required
for LSP/span recovery independently of the number of LSPs/spans for LSP/span recovery independently of the number of LSPs/spans
being recovered (this implies an efficient failure correlation, a being recovered (this implies an efficient failure correlation, a
fast failure notification and time-efficient recovery fast failure notification and time-efficient recovery
mechanism(s)). mechanism(s)).
3. Robustness (availability): minimize the LSP/span downtime 3. Robustness (availability): minimize the LSP/span downtime
independently of the underlying topology of the transport plane independently of the underlying topology of the transport plane
(this implies a highly responsive recovery mechanism). (this implies a highly responsive recovery mechanism).
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Fast convergence is related to the failure management operations. It Fast convergence is related to the failure management operations. It
refers to the elapsing time between the failure detection/ refers to the elapsing time between the failure detection/
correlation and hold-off time, point at which the recovery switching correlation and hold-off time, point at which the recovery switching
actions are initiated. This point has been detailed in Section 4. actions are initiated. This point has been detailed in Section 4.
8.2 Efficiency (Recovery Switching Time) 8.2 Efficiency (Recovery Switching Time)
In general, the more pre-assignment/pre-planning of the recovery In general, the more pre-assignment/pre-planning of the recovery
LSP/span, the more rapid the recovery is. Since protection implies LSP/span, the more rapid the recovery is. Since protection implies
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pre-assignment (and cross-connection) of the protection resources, pre-assignment (and cross-connection) of the protection resources,
in general, protection recover faster than restoration. in general, protection recover faster than restoration.
Span restoration is likely to be slower than most span protection Span restoration is likely to be slower than most span protection
types; however this greatly depends on the efficiency of the span types; however this greatly depends on the efficiency of the span
restoration signalling. LSP restoration with pre-signaled and pre- restoration signalling. LSP restoration with pre-signaled and pre-
selected recovery resources is likely to be faster than fully selected recovery resources is likely to be faster than fully
dynamic LSP restoration, especially because of the elimination of dynamic LSP restoration, especially because of the elimination of
any potential crankback during the recovery LSP establishment. any potential crankback during the recovery LSP establishment.
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If one excludes the crankback issue, the difference between dynamic If one excludes the crankback issue, the difference between dynamic
and pre-planned restoration depends on the restoration path and pre-planned restoration depends on the restoration path
computation and selection time. Since computational considerations computation and selection time. Since computational considerations
are outside the scope of this document, it is up to the vendor to are outside the scope of this document, it is up to the vendor to
determine the average and maximum path computation time in different determine the average and maximum path computation time in different
scenarios and to the operator to decide whether or not dynamic scenarios and to the operator to decide whether or not dynamic
restoration is advantageous over pre-planned schemes depending on restoration is advantageous over pre-planned schemes depending on
the network environment. This difference depends also on the the network environment. This difference depends also on the
flexibility provided by pre-planned restoration versus dynamic flexibility provided by pre-planned restoration versus dynamic
restoration: the former implies a somewhat limited number of failure restoration: the former implies a somewhat limited number of failure
skipping to change at line 1601 skipping to change at line 1604
LSP restoration. However, local LSP restoration assumes that each LSP restoration. However, local LSP restoration assumes that each
LSP segment end-point has enough computational capacity to perform LSP segment end-point has enough computational capacity to perform
this operation while end-to-end LSP restoration requires only that this operation while end-to-end LSP restoration requires only that
LSP end-points provides this path computation capability. LSP end-points provides this path computation capability.
Recovery time objectives for Sonet/SDH protection switching (not Recovery time objectives for Sonet/SDH protection switching (not
including time to detect failure) are specified in [G.841] at 50 ms, including time to detect failure) are specified in [G.841] at 50 ms,
taking into account constraints on distance, number of connections taking into account constraints on distance, number of connections
involved, and in the case of ring enhanced protection, number of involved, and in the case of ring enhanced protection, number of
nodes in the ring. Recovery time objectives for restoration nodes in the ring. Recovery time objectives for restoration
mechanisms have been proposed through a separate effort [RFC-3386]. mechanisms have been proposed through a separate effort [RFC3386].
8.3 Robustness 8.3 Robustness
In general, the less pre-assignment (protection)/pre-planning In general, the less pre-assignment (protection)/pre-planning
(restoration) of the recovery LSP/span, the more robust the recovery (restoration) of the recovery LSP/span, the more robust the recovery
type or scheme is to a variety of single failures, provided that type or scheme is to a variety of single failures, provided that
adequate resources are available. Moreover, the pre-selection of the adequate resources are available. Moreover, the pre-selection of the
recovery resources gives in the case of multiple failure scenarios recovery resources gives in the case of multiple failure scenarios
less flexibility than no recovery resource pre-selection. For less flexibility than no recovery resource pre-selection. For
instance, if failures occur that affect two LSPs sharing a common instance, if failures occur that affect two LSPs sharing a common
link along their restoration paths, then only one of these LSPs can link along their restoration paths, then only one of these LSPs can
be recovered. This occurs unless the restoration path of at least be recovered. This occurs unless the restoration path of at least
one of these LSPs is re-computed or the local resource assignment is one of these LSPs is re-computed or the local resource assignment is
modified on the fly. modified on the fly.
D.Papadimitriou et al. - Expires October 2004 30
In addition, recovery types and schemes with pre-planned recovery In addition, recovery types and schemes with pre-planned recovery
resources, in particular LSP/spans for protection and LSPs for resources, in particular LSP/spans for protection and LSPs for
restoration purposes, will not be able to recover from failures that restoration purposes, will not be able to recover from failures that
simultaneously affect both the working and recovery LSP/span. Thus, simultaneously affect both the working and recovery LSP/span. Thus,
the recovery resources should ideally be as disjoint as possible the recovery resources should ideally be as disjoint as possible
(with respect to link, node and SRLG) from the working ones, so that (with respect to link, node and SRLG) from the working ones, so that
any single failure event will not affect both working and recovery any single failure event will not affect both working and recovery
LSP/span. In brief, working and recovery resource must be fully LSP/span. In brief, working and recovery resource must be fully
D.Papadimitriou et al. - Internet Draft - Expires March 2004 30
diverse in order to guarantee that a given failure will not affect diverse in order to guarantee that a given failure will not affect
simultaneously the working and the recovery LSP/span. Also, the risk simultaneously the working and the recovery LSP/span. Also, the risk
of simultaneous failure of the working and the recovery LSP can be of simultaneous failure of the working and the recovery LSP can be
reduced. This, by computing a new recovery path whenever a failure reduced. This, by computing a new recovery path whenever a failure
occurs along one of the recovery LSPs or by computing a new recovery occurs along one of the recovery LSPs or by computing a new recovery
path and provision the corresponding LSP whenever a failure occurs path and provision the corresponding LSP whenever a failure occurs
along a working LSP/span. Both methods enable the network to along a working LSP/span. Both methods enable the network to
maintain the number of available recovery path constant. maintain the number of available recovery path constant.
The robustness of a recovery scheme is also determined by the amount The robustness of a recovery scheme is also determined by the amount
skipping to change at line 1670 skipping to change at line 1672
require 1 (M, respectively) recovery LSP/span (shared between the N require 1 (M, respectively) recovery LSP/span (shared between the N
working LSP/span) allowing for extra-traffic. Obviously, 1+1 working LSP/span) allowing for extra-traffic. Obviously, 1+1
protection precludes and 1:1 recovery does not allow for any protection precludes and 1:1 recovery does not allow for any
recovery LSP/span sharing whereas 1:N and M:N recovery do allow recovery LSP/span sharing whereas 1:N and M:N recovery do allow
sharing of 1 (M, respectively) recovery LSP/spans between N working sharing of 1 (M, respectively) recovery LSP/spans between N working
LSP/spans. However, despite the fact that 1:1 LSP recovery precludes LSP/spans. However, despite the fact that 1:1 LSP recovery precludes
the sharing of the recovery LSP, the recovery schemes (see Section the sharing of the recovery LSP, the recovery schemes (see Section
5.4) that can be built from it (e.g. (1:1)^n) do allow sharing of 5.4) that can be built from it (e.g. (1:1)^n) do allow sharing of
its recovery resources. In addition, the flexibility in the usage of its recovery resources. In addition, the flexibility in the usage of
shared recovery resources (in particular, shared links) may be shared recovery resources (in particular, shared links) may be
D.Papadimitriou et al. - Expires October 2004 31
limited because of network topology restrictions, e.g. fixed ring limited because of network topology restrictions, e.g. fixed ring
topology for traditional enhanced protection schemes. topology for traditional enhanced protection schemes.
On the other hand, when using LSP restoration with pre-signaled On the other hand, when using LSP restoration with pre-signaled
resource reservation, the amount of reserved restoration capacity is resource reservation, the amount of reserved restoration capacity is
determined by the local bandwidth reservation policies. In LSP determined by the local bandwidth reservation policies. In LSP
restoration schemes with re-provisioning, a pool of spare resources restoration schemes with re-provisioning, a pool of spare resources
can be defined from which all resources are selected after failure can be defined from which all resources are selected after failure
occurrence for the purpose of restoration path computation. The occurrence for the purpose of restoration path computation. The
degree to which restoration schemes allow sharing amongst multiple degree to which restoration schemes allow sharing amongst multiple
D.Papadimitriou et al. - Internet Draft - Expires March 2004 31
independent failures is then directly inferred from the size of the independent failures is then directly inferred from the size of the
resource pool. Moreover, in all restoration schemes, spare resources resource pool. Moreover, in all restoration schemes, spare resources
can be used to carry preemptible traffic (thus over preemptible can be used to carry preemptible traffic (thus over preemptible
LSP/span) when the corresponding resources have not been committed LSP/span) when the corresponding resources have not been committed
for LSP/span recovery purposes. for LSP/span recovery purposes.
From this, it clearly follows that less recovery resources (i.e. From this, it clearly follows that less recovery resources (i.e.
LSP/spans and switching capacity) have to be allocated to a shared LSP/spans and switching capacity) have to be allocated to a shared
recovery resource pool if a greater sharing degree is allowed. Thus, recovery resource pool if a greater sharing degree is allowed. Thus,
the network survivability level is determined by the policy that the network survivability level is determined by the policy that
skipping to change at line 1725 skipping to change at line 1727
the Maximum LSP Bandwidth and the Maximum Reservable Bandwidth, the the Maximum LSP Bandwidth and the Maximum Reservable Bandwidth, the
amount of (over-provisioned) resources that can be used for shared amount of (over-provisioned) resources that can be used for shared
recovery purposes is known from the IGP. recovery purposes is known from the IGP.
In order to analyze this behavior, we define the difference between In order to analyze this behavior, we define the difference between
the Maximum Reservable Bandwidth (in the present case, this value is the Maximum Reservable Bandwidth (in the present case, this value is
greater than the Maximum Link Bandwidth) and the Maximum LSP greater than the Maximum Link Bandwidth) and the Maximum LSP
Bandwidth per TE link i as the Maximum Shareable Bandwidth or Bandwidth per TE link i as the Maximum Shareable Bandwidth or
max_R[i]. Within this quantity, the amount of bandwidth currently max_R[i]. Within this quantity, the amount of bandwidth currently
allocated for shared recovery per TE link i is defined as R[i]. Both allocated for shared recovery per TE link i is defined as R[i]. Both
D.Papadimitriou et al. - Expires October 2004 32
quantities are expressed in terms of discrete bandwidth units (and quantities are expressed in terms of discrete bandwidth units (and
thus, the Minimum LSP Bandwidth is of one bandwidth unit). thus, the Minimum LSP Bandwidth is of one bandwidth unit).
The knowledge of this information available per TE link can be The knowledge of this information available per TE link can be
exploited in order to optimize the usage of the resources allocated exploited in order to optimize the usage of the resources allocated
per TE link for shared recovery. If one refers to r[i] as the actual per TE link for shared recovery. If one refers to r[i] as the actual
bandwidth per TE link i (in terms of discrete bandwidth units) bandwidth per TE link i (in terms of discrete bandwidth units)
committed for shared recovery, then the following quantity must be committed for shared recovery, then the following quantity must be
maximized over the potential TE link candidates: sum {i=1}^N [(R{i} maximized over the potential TE link candidates:
- r{i})/(t{i} b{i})] or equivalently: sum {i=1}^N [(R{i} -
D.Papadimitriou et al. - Internet Draft - Expires March 2004 32 sum {i=1}^N [(R{i} - r{i})/(t{i} - b{i})]
r{i})/r{i}] with R{i} >= 1 and r{i} >= 1 (in terms of per component
bandwidth unit). In this formula, N is the total number of links or equivalently: sum {i=1}^N [(R{i} - r{i})/r{i}]
traversed by a given LSP, t[i] the Maximum Link Bandwidth per TE
link i and b[i] the sum per TE link i of the bandwidth committed for with R{i} >= 1 and r{i} >= 1 (in terms of per component
working LSPs and other recovery LSPs (thus except "shared bandwidth" bandwidth unit)
LSPs). The quantity [(R{i} - r{i})/r{i}] is defined as the Shared
(Recovery) Bandwidth Ratio per TE link i. In addition, TE links for In this formula, N is the total number of links traversed by a given
which R[i] reaches max_R[i] or for which r[i] = 0 are pruned during LSP, t[i] the Maximum Link Bandwidth per TE link i and b[i] the sum
shared recovery path computation as well as TE links for which per TE link i of the bandwidth committed for working LSPs and other
max_R[i] = r[i] which can simply not be shared. recovery LSPs (thus except "shared bandwidth" LSPs). The quantity
[(R{i} - r{i})/r{i}] is defined as the Shared (Recovery) Bandwidth
Ratio per TE link i. In addition, TE links for which R[i] reaches
max_R[i] or for which r[i] = 0 are pruned during shared recovery
path computation as well as TE links for which max_R[i] = r[i] which
can simply not be shared.
More generally, one can draw the following mapping between the More generally, one can draw the following mapping between the
available bandwidth at the transport and control plane level: available bandwidth at the transport and control plane level:
- ---------- Max Reservable Bandwidth - ---------- Max Reservable Bandwidth
| ----- ^ | ----- ^
|R ----- | |R ----- |
| ----- | | ----- |
- ----- |max_R - ----- |max_R
----- | ----- |
skipping to change at line 1773 skipping to change at line 1781
----- ----- ----- -----
----- ----- <--- Minimum LSP Bandwidth ----- ----- <--- Minimum LSP Bandwidth
-------- 0 ---------- 0 -------- 0 ---------- 0
Note that the above approach does not require the flooding of any Note that the above approach does not require the flooding of any
per LSP information or any detailed distribution of the bandwidth per LSP information or any detailed distribution of the bandwidth
allocation per component link or individual ports or even any per- allocation per component link or individual ports or even any per-
priority shareable recovery bandwidth information (using a dedicated priority shareable recovery bandwidth information (using a dedicated
sub-TLV). The latter would provide the same capability than the sub-TLV). The latter would provide the same capability than the
already defined Maximum LSP bandwidth per-priority information. Such already defined Maximum LSP bandwidth per-priority information. Such
D.Papadimitriou et al. - Expires October 2004 33
approach is referred to as a Partial (or Aggregated) Information approach is referred to as a Partial (or Aggregated) Information
Routing as described for instance in [KODIALAM1] and [KODIALAM2]. Routing as described for instance in [KODIALAM1] and [KODIALAM2].
They show that the difference obtained with a Full (or Complete) They show that the difference obtained with a Full (or Complete)
Information Routing approach (where for the whole set of working and Information Routing approach (where for the whole set of working and
recovery LSPs, the amount of bandwidth units they use per-link is recovery LSPs, the amount of bandwidth units they use per-link is
known at each node and for each link) is clearly negligible. The known at each node and for each link) is clearly negligible. The
latter approach is detailed in [GLI], for instance. Note also that latter approach is detailed in [GLI], for instance. Note also that
both approaches rely on the deterministic knowledge (at different both approaches rely on the deterministic knowledge (at different
degrees) of the network topology and resource usage status. degrees) of the network topology and resource usage status.
Moreover, extending the GMPLS signalling capabilities can enhance Moreover, extending the GMPLS signalling capabilities can enhance
the Partial Information Routing approach. This, by allowing working the Partial Information Routing approach. This, by allowing working
LSP related information and in particular, its path (including link LSP related information and in particular, its path (including link
and node identifiers) to be exchanged with the recovery LSP request and node identifiers) to be exchanged with the recovery LSP request
to enable more efficient admission control at upstream nodes of to enable more efficient admission control at upstream nodes of
shared recovery resources, in particular links (see Section 8.4.3). shared recovery resources, in particular links (see Section 8.4.3).
D.Papadimitriou et al. - Internet Draft - Expires March 2004 33
8.4.2 Recovery Resource Sharing and SRLG Recovery 8.4.2 Recovery Resource Sharing and SRLG Recovery
Resource shareability can also be maximized with respect to the Resource shareability can also be maximized with respect to the
number of times each SRLG is protected by a recovery resource (in number of times each SRLG is protected by a recovery resource (in
particular, a shared TE link) and methods can be considered for particular, a shared TE link) and methods can be considered for
avoiding contention of the shared recovery resources in case of avoiding contention of the shared recovery resources in case of
single SRLG failure. These methods enable for the sharing of single SRLG failure. These methods enable for the sharing of
recovery resources between two (or more) recovery LSPs if their recovery resources between two (or more) recovery LSPs if their
respective working LSPs are mutually disjoint with respect to link, respective working LSPs are mutually disjoint with respect to link,
node and SRLGs. A single failure then does not simultaneously node and SRLGs. A single failure then does not simultaneously
skipping to change at line 1827 skipping to change at line 1835
the current number of recovery LSPs sharing the recovery resources the current number of recovery LSPs sharing the recovery resources
reserved on the TE link and the current number of SRLGs recoverable reserved on the TE link and the current number of SRLGs recoverable
by this amount of (shared) recovery resources reserved on the TE by this amount of (shared) recovery resources reserved on the TE
link. The latter is equivalent to the current number of SRLGs that link. The latter is equivalent to the current number of SRLGs that
the recovery LSPs sharing the recovery resource reserved on the TE the recovery LSPs sharing the recovery resource reserved on the TE
link shall recover. Then, if explicit SRLG recoverability is link shall recover. Then, if explicit SRLG recoverability is
considered an additional TE link attribute including the explicit considered an additional TE link attribute including the explicit
list of SRLGs recoverable by the shared recovery resource reserved list of SRLGs recoverable by the shared recovery resource reserved
on the TE link and their respective shareable recovery bandwidth. on the TE link and their respective shareable recovery bandwidth.
The latter information is equivalent to the shareable recovery The latter information is equivalent to the shareable recovery
D.Papadimitriou et al. - Expires October 2004 34
bandwidth per SRLG (or per group of SRLGs) which implies to consider bandwidth per SRLG (or per group of SRLGs) which implies to consider
a decreasing amount of shareable bandwidth and SRLG list over time. a decreasing amount of shareable bandwidth and SRLG list over time.
Compared to the case of recovery resource sharing only (regardless Compared to the case of recovery resource sharing only (regardless
of SRLG recoverability, as described in Section 8.4.1), this of SRLG recoverability, as described in Section 8.4.1), this
additional TE link attributes would potentially deliver better path additional TE link attributes would potentially deliver better path
computation and selection (at distinct ingress node) for shared mesh computation and selection (at distinct ingress node) for shared mesh
recovery purposes. However, due to the lack of results of evidence recovery purposes. However, due to the lack of results of evidence
for better efficiency and due to the complexity that such extensions for better efficiency and due to the complexity that such extensions
would generate, they are not further considered in the scope of the would generate, they are not further considered in the scope of the
present analysis. For instance, a per-SRLG group minimum/maximum present analysis. For instance, a per-SRLG group minimum/maximum
shareable recovery bandwidth is restricted by the length that the shareable recovery bandwidth is restricted by the length that the
corresponding (sub-)TLV may take and thus the number of SRLGs that corresponding (sub-)TLV may take and thus the number of SRLGs that
it can include. Therefore, the corresponding parameter SHOULD not be it can include. Therefore, the corresponding parameter SHOULD not be
translated into GMPLS routing (or even signalling) protocol translated into GMPLS routing (or even signalling) protocol
extensions in the form of TE link sub-TLV. extensions in the form of TE link sub-TLV.
D.Papadimitriou et al. - Internet Draft - Expires March 2004 34
8.4.3 Recovery Resource Sharing, SRLG Disjointness and Admission 8.4.3 Recovery Resource Sharing, SRLG Disjointness and Admission
Control Control
Admission control is a strict requirement to be fulfilled by nodes Admission control is a strict requirement to be fulfilled by nodes
giving access to shared links. This can be illustrated using the giving access to shared links. This can be illustrated using the
following network topology: following network topology:
A ------ C ====== D A ------ C ====== D
| | | | | |
| | | | | |
skipping to change at line 1883 skipping to change at line 1891
(implying for instance, that the path followed by the working LSP is (implying for instance, that the path followed by the working LSP is
carried with the corresponding recovery LSP request). If node E can carried with the corresponding recovery LSP request). If node E can
guarantee that the working LSPs (A-C-D and B-C-D) are SRLG disjoint guarantee that the working LSPs (A-C-D and B-C-D) are SRLG disjoint
over the C-D span, it may securely accept the incoming recovery LSP over the C-D span, it may securely accept the incoming recovery LSP
request and assign to the recovery LSPs (A-E-F-D and B-E-F-D) the request and assign to the recovery LSPs (A-E-F-D and B-E-F-D) the
same resources on the link E-F. This, if the link E-F has not yet same resources on the link E-F. This, if the link E-F has not yet
reached its maximum recovery bandwidth sharing ratio. In this reached its maximum recovery bandwidth sharing ratio. In this
example, one assumes that the node failure probability is negligible example, one assumes that the node failure probability is negligible
compared to the link failure probability. compared to the link failure probability.
D.Papadimitriou et al. - Expires October 2004 35
To achieve this, the path followed by the working LSP is transported To achieve this, the path followed by the working LSP is transported
with the recovery LSP request and examined at each upstream node of with the recovery LSP request and examined at each upstream node of
potentially shareable links. Admission control is performed using potentially shareable links. Admission control is performed using
the interface identifiers (included in the path) to retrieve in the the interface identifiers (included in the path) to retrieve in the
TE DataBase the list of SRLG Ids associated to each of the working TE DataBase the list of SRLG Ids associated to each of the working
LSP links. If the working LSPs (A-C-D and B-C-D) have one or more LSP links. If the working LSPs (A-C-D and B-C-D) have one or more
link or SRLG id in common (in this example, one or more SRLG id in link or SRLG id in common (in this example, one or more SRLG id in
common over the span C-D) node E should not assign the same resource common over the span C-D) node E should not assign the same resource
over link E-F to the recovery LSPs (A-E-F-D and B-E-F-D). Otherwise, over link E-F to the recovery LSPs (A-E-F-D and B-E-F-D). Otherwise,
one of these working LSPs would not be recoverable in case of C-D one of these working LSPs would not be recoverable in case of C-D
span failure. span failure.
There are some issues related to this method, the major one being There are some issues related to this method, the major one being
the number of SRLG Ids that a single link can cover (more than 100, the number of SRLG Ids that a single link can cover (more than 100,
in complex environments). Moreover, when using link bundles, this in complex environments). Moreover, when using link bundles, this
approach may generate the rejection of some recovery LSP requests. approach may generate the rejection of some recovery LSP requests.
D.Papadimitriou et al. - Internet Draft - Expires March 2004 35
This occurs when the SRLG sub-TLV corresponding to a link bundle This occurs when the SRLG sub-TLV corresponding to a link bundle
includes the union of the SRLG id list of all the component links includes the union of the SRLG id list of all the component links
belonging to this bundle (see [GMPLS-RTG] and [MPLS-BUNDLE]). belonging to this bundle (see [GMPLS-RTG] and [MPLS-BUNDLE]).
In order to overcome this specific issue, an additional mechanism In order to overcome this specific issue, an additional mechanism
may consist of querying the nodes where such an information would be may consist of querying the nodes where such an information would be
available (in this case, node E would query C). The main drawback of available (in this case, node E would query C). The main drawback of
this method is that, in addition to the dedicated mechanism(s) it this method is that, in addition to the dedicated mechanism(s) it
requires, it may become complex when several common nodes are requires, it may become complex when several common nodes are
traversed by the working LSPs. Therefore, when using link bundles, traversed by the working LSPs. Therefore, when using link bundles,
skipping to change at line 1937 skipping to change at line 1944
| | faster recovery | Does not apply | | faster recovery | Does not apply
| | less flexible | | | less flexible |
| 1 | less robust | | 1 | less robust |
| | most resource consuming | | | most resource consuming |
Path | | | Path | | |
Setup ------------------------------------------------------------ Setup ------------------------------------------------------------
| | relatively fast recovery | Does not apply | | relatively fast recovery | Does not apply
| | relatively flexible | | | relatively flexible |
| 2 | relatively robust | | 2 | relatively robust |
| | resource consumption | | | resource consumption |
D.Papadimitriou et al. - Expires October 2004 36
| | depends on sharing degree | | | depends on sharing degree |
------------------------------------------------------------ ------------------------------------------------------------
| | relatively fast recovery | less faster (computation) | | relatively fast recovery | less faster (computation)
| | more flexible | most flexible | | more flexible | most flexible
| 3 | relatively robust | most robust | 3 | relatively robust | most robust
| | less resource consuming | least resource consuming | | less resource consuming | least resource consuming
| | depends on sharing degree | | | depends on sharing degree |
-------------------------------------------------------------------- --------------------------------------------------------------------
1a. Recovery LSP setup (before failure occurrence) with resource 1a. Recovery LSP setup (before failure occurrence) with resource
reservation (i.e. signalling) and selection is referred to as reservation (i.e. signalling) and selection is referred to as
LSP protection. LSP protection.
2a. Recovery LSP setup (before failure occurrence) with resource 2a. Recovery LSP setup (before failure occurrence) with resource
reservation (i.e. signalling) and with resource pre-selection is reservation (i.e. signalling) and with resource pre-selection is
referred to as pre-planned LSP re-routing with resource pre- referred to as pre-planned LSP re-routing with resource pre-
selection. This implies only recovery LSP activation after selection. This implies only recovery LSP activation after
D.Papadimitriou et al. - Internet Draft - Expires March 2004 36
failure occurrence. failure occurrence.
3a. Recovery LSP setup (before failure occurrence) with resource 3a. Recovery LSP setup (before failure occurrence) with resource
reservation (i.e. signalling) and without resource selection is reservation (i.e. signalling) and without resource selection is
referred to as pre-planned LSP re-routing without resource pre- referred to as pre-planned LSP re-routing without resource pre-
selection. This implies recovery LSP activation and resource selection. This implies recovery LSP activation and resource
(i.e. label) selection after failure occurrence. (i.e. label) selection after failure occurrence.
3b. Recovery LSP setup after failure occurrence is referred to as 3b. Recovery LSP setup after failure occurrence is referred to as
to as LSP re-routing, which is full when recovery LSP path to as LSP re-routing, which is full when recovery LSP path
computation occurs after failure occurrence. computation occurs after failure occurrence.
The term pre-planned refers thus to recovery LSP path pre- The term pre-planned refers thus to recovery LSP path pre-
computation, signaling (reservation), and a priori resource computation, signaling (reservation), and a priori resource
selection (optional), but not cross-connection. Also, the shared- selection (optional), but not cross-connection. Also, the shared-
mesh recovery scheme can be viewed as a particular case of 2a) and mesh recovery scheme can be viewed as a particular case of 2a) and
3a) using the additional constraint described in Section 8.4.3. 3a) using the additional constraint described in Section 8.4.3.
The implementation of these recovery mechanisms requires only The implementation of these recovery mechanisms requires only
considering extensions to GMPLS signalling protocols (i.e. [RFC- considering extensions to GMPLS signalling protocols (i.e. [RFC3471]
3471] and [RFC-3473]). These GMPLS signalling extensions should and [RFC3473]). These GMPLS signalling extensions should mainly
mainly focus in delivering (1) recovery LSP pre-provisioning for the focus in delivering (1) recovery LSP pre-provisioning for the cases
cases 1a, 2a and 3a, (2) LSP failure notification, (3) recovery LSP 1a, 2a and 3a, (2) LSP failure notification, (3) recovery LSP
switching action(s), and (4) reversion mechanisms. switching action(s), and (4) reversion mechanisms.
Moreover, the present analysis (see Section 8) shows that no GMPLS Moreover, the present analysis (see Section 8) shows that no GMPLS
routing extensions are expected to efficiently implement any of routing extensions are expected to efficiently implement any of
these recovery types and schemes. these recovery types and schemes.
10. Security Considerations 10. Security Considerations
This document does not introduce any additional security issue or This document does not introduce any additional security issue or
imply any specific security consideration from [GMPLS-ARCH]. imply any specific security consideration from [GMPLS-ARCH] to the
current RSVP-TE GMPLS signaling, routing protocols (OSPF-TE, IS-IS-
TE) or network management protocols (SNMP).
D.Papadimitriou et al. - Expires October 2004 37
However, the authorization of requests for resources by GMPLS-
capable nodes SHOULD determining whether a given party, presumable
already authenticated, has a right to access the requested
resources. This determination is typically a matter of local policy
control, for example by setting limits on the total bandwidth made
available to some party in the presence of resource contention. Such
policies may become quite complex as the number of users, types of
resources and sophistication of authorization rules increases. This
is particularly the case for recovery schemes that assume pre-
planned sharing of recovery resources, or contention for resources
in case of dynamic re-routing.
Therefore, control elements should match them against the local
authorization policy. These control elements must be capable of
making decisions based on the identity of the requester, as verified
cryptographically and/or topologically.
11. Acknowledgments 11. Acknowledgments
The authors would like to thank Fabrice Poppe (Alcatel) and Bart The authors would like to thank Fabrice Poppe (Alcatel) and Bart
Rousseau (Alcatel) for their revision effort, Richard Rabbat Rousseau (Alcatel) for their revision effort, Richard Rabbat
(Fujitsu Labs), David Griffith (NIST) and Lyndon Ong (Ciena) for (Fujitsu Labs), David Griffith (NIST) and Lyndon Ong (Ciena) for
their useful comments. their useful comments.
12. Intellectual Property Considerations Thanks also to Adrian Farrel for the thorough review of the
document.
This section is taken from Section 10.4 of [RFC2026]. 12. Intellectual Property Considerations
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed
pertain to the implementation or use of the technology described in to pertain to the implementation or use of the technology
this document or the extent to which any license under such rights described in this document or the extent to which any license
might or might not be available; neither does it represent that it under such rights might or might not be available; nor does it
has made any effort to identify any such rights. Information on the represent that it has made any independent effort to identify any
IETF's procedures with respect to rights in standards-track and such rights. Information on the procedures with respect to rights
standards-related documentation can be found in BCP-11. Copies of in RFC documents can be found in BCP 78 and BCP 79.
D.Papadimitriou et al. - Internet Draft - Expires March 2004 37 Copies of IPR disclosures made to the IETF Secretariat and any
claims of rights made available for publication and any assurances assurances of licenses to be made available, or the result of an
of licenses to be made available, or the result of an attempt made attempt made to obtain a general license or permission for the use
to obtain a general license or permission for the use of such of such proprietary rights by implementers or users of this
proprietary rights by implementors or users of this specification specification can be obtained from the IETF on-line IPR repository
can be obtained from the IETF Secretariat. at http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention
copyrights, patents or patent applications, or other proprietary any copyrights, patents or patent applications, or other
rights which may cover technology that may be required to practice proprietary rights that may cover technology that may be required
this standard. Please address the information to the IETF Executive to implement this standard. Please address the information to the
Director. IETF at ietf-ipr@ietf.org.
12.1 IPR Disclosure Acknowledgement
D.Papadimitriou et al. - Expires October 2004 38
By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been disclosed,
and any of which I become aware will be disclosed, in accordance
with RFC 3668.
13. References 13. References
13.1 Normative References 13.1 Normative References
[GMPLS-ARCH] E.Mannie (Editor) et al., "Generalized MPLS [BUNDLE] K.Kompella et al., "Link Bundling in MPLS Traffic
Architecture," Work in progress, draft-ietf-ccamp- Engineering," Work in progress, draft-ietf-mpls-bundle-
gmpls-architecture-07.txt, May 2003. 04.txt, August 2002.
[GMPLS-ARCH] E.Mannie (Editor) et al., "Generalized Multi-Protocol
Label Switching Architecture," Work in progress, draft-
ietf-ccamp-gmpls-architecture-07.txt, May 2003.
[GMPLS-RTG] K.Kompella (Editor) et al., "Routing Extensions in [GMPLS-RTG] K.Kompella (Editor) et al., "Routing Extensions in
Support of Generalized MPLS," Work in Progress, draft- Support of Generalized Multi-Protocol Label Switching,"
ietf-ccamp-gmpls-routing-06.txt, June 2003. Work in Progress, draft-ietf-ccamp-gmpls-routing-
09.txt, October 2003.
[LMP] J.P.Lang (Editor) et al., "Link Management Protocol [LMP] J.P.Lang (Editor) et al., "Link Management Protocol
(LMP)," Work in progress, draft-ietf-ccamp-lmp-09, May (LMP)," Work in progress, draft-ietf-ccamp-lmp-10.txt,
2003. October 2003.
[LMP-WDM] A.Fredette and J.P.Lang (Editors), "Link Management [LMP-WDM] A.Fredette and J.P.Lang (Editors), "Link Management
Protocol (LMP) for DWDM Optical Line Systems," Work in Protocol (LMP) for Dense Wavelength Division
progress, draft-ietf-ccamp-lmp-wdm-02.txt, March 2003. Multiplexing (DWDM) Optical Line Systems," Work in
progress, draft-ietf-ccamp-lmp-wdm-03.txt, October
[MPLS-BUNDLE]K.Kompella et al., "Link Bundling in MPLS Traffic 2003.
Engineering," Work in progress, draft-ietf-mpls-bundle-
04.txt, August 2002.
[RFC-2026] S.Bradner, "The Internet Standards Process -- Revision [RFC2026] S.Bradner, "The Internet Standards Process -- Revision
3," BCP 9, IETF RFC 2026, October 1996. 3," BCP 9, IETF RFC 2026, October 1996.
[RFC-2119] S.Bradner, "Key words for use in RFCs to Indicate [RFC2119] S.Bradner, "Key words for use in RFCs to Indicate
Requirement Levels," BCP 14, IETF RFC 2119, March 1997. Requirement Levels," BCP 14, IETF RFC 2119, March 1997.
[RFC-3471] L.Berger (Editor) et al., "Generalized MPLS - Signaling [RFC3471] L.Berger (Editor) et al., "Generalized Multi-Protocol
Functional Description," IETF RFC 3471, January 2003. Label Switching (GMPLS) Signaling Functional
Description," IETF RFC 3471, January 2003.
[RFC-3473] L.Berger (Editor) et al., "Generalized MPLS Signaling - [RFC3473] L.Berger (Editor) et al., "Generalized Multi-Protocol
RSVP-TE Extensions," IETF RFC 3473, January 2003. Label Switching (GMPLS) Signaling Resource ReserVation
Protocol-Traffic Engineering (RSVP-TE) Extensions,"
IETF RFC 3473, January 2003.
[TERM] E.Mannie and D.Papadimitriou (Editors), "Recovery [TERM] E.Mannie and D.Papadimitriou (Editors), "Recovery
(Protection and Restoration) Terminology for GMPLS," (Protection and Restoration) Terminology for
Generalized Multi-Protocol Label Switching (GMPLS),"
Work in progress, draft-ietf-ccamp-gmpls-recovery- Work in progress, draft-ietf-ccamp-gmpls-recovery-
terminology-02.txt, May 2003. terminology-04.txt, April 2004.
D.Papadimitriou et al. - Internet Draft - Expires March 2004 38 D.Papadimitriou et al. - Expires October 2004 39
13.2 Informative References 13.2 Informative References
[BOUILLET] E.Bouillet et al., "Stochastic Approaches to Compute [BOUILLET] E.Bouillet et al., "Stochastic Approaches to Compute
Shared Meshed Restored Lightpaths in Optical Network Shared Meshed Restored Lightpaths in Optical Network
Architectures," IEEE Infocom 2002, New York City, June Architectures," IEEE Infocom 2002, New York City, June
2002. 2002.
[CCAMP-LI] G.Li et al. "RSVP-TE Extensions For Shared-Mesh
Restoration in Transport Networks," Work in progress,
draft-li-shared-mesh-restoration-01.txt, November 2001.
[CCAMP-SRLG] D.Papadimitriou et al., "Shared Risk Link Groups
Encoding and Processing," Internet Draft, draft-
papadimitriou-ccamp-srlg-processing-01.txt, November
2002.
[DEMEESTER] P.Demeester et al., "Resilience in Multilayer [DEMEESTER] P.Demeester et al., "Resilience in Multilayer
Networks," IEEE Communications Magazine, Vol. 37, No. Networks," IEEE Communications Magazine, Vol. 37, No.
8, pp. 70-76, August 1998. 8, pp. 70-76, August 1998.
[G.707] ITU-T, "Network Node Interface for the Synchronous [G.707] ITU-T, "Network Node Interface for the Synchronous
Digital Hierarchy (SDH)," Recommendation G.707, October Digital Hierarchy (SDH)," Recommendation G.707, October
2000. 2000.
[G.709] ITU-T, "Network Node Interface for the Optical [G.709] ITU-T, "Network Node Interface for the Optical
Transport Network (OTN)," Recommendation G.709, Transport Network (OTN)," Recommendation G.709,
skipping to change at line 2103 skipping to change at line 2137
[G.783] ITU-T, "Characteristics of Synchronous Digital [G.783] ITU-T, "Characteristics of Synchronous Digital
Hierarchy (SDH) Equipment Functional Blocks," Hierarchy (SDH) Equipment Functional Blocks,"
Recommendation G.783, October 2000. Recommendation G.783, October 2000.
[G.806] ITU-T, "Characteristics of Transport Equipment - [G.806] ITU-T, "Characteristics of Transport Equipment -
Description Methodology and Generic Functionality", Description Methodology and Generic Functionality",
Recommendation G.806, October 2000. Recommendation G.806, October 2000.
[G.808.1] ITU-T, "Generic Protection Switching - Linear trail and [G.808.1] ITU-T, "Generic Protection Switching - Linear trail and
Subnetwork Protection," Draft Recommendation (work in Subnetwork Protection," Recommendation G.808.1,
progress), Version 0.5, January 2003. December 2003.
[G.841] ITU-T, "Types and Characteristics of SDH Network [G.841] ITU-T, "Types and Characteristics of SDH Network
Protection Architectures," Recommendation G.841, Protection Architectures," Recommendation G.841,
October 1998. October 1998.
[G.842] ITU-T, "Interworking of SDH network protection [G.842] ITU-T, "Interworking of SDH network protection
architectures," Recommendation G.842, October 1998. architectures," Recommendation G.842, October 1998.
[GLI] G.Li et al., "Efficient Distributed Path Selection for [GLI] G.Li et al., "Efficient Distributed Path Selection for
Shared Restoration Connections," IEEE Infocom 2002, New Shared Restoration Connections," IEEE Infocom 2002, New
York City, June 2002. York City, June 2002.
[IPO-IMP] J.Strand and A.Chiu, "Impairments and Other Constraints [IPO-IMP] J.Strand and A.Chiu, "Impairments and Other Constraints
On Optical Layer Routing," Work in Progress, draft- On Optical Layer Routing," Work in Progress, draft-
D.Papadimitriou et al. - Internet Draft - Expires March 2004 39
ietf-ipo-impairments-05.txt, May 2003. ietf-ipo-impairments-05.txt, May 2003.
[KODIALAM1] M.Kodialam and T.V.Lakshman, "Restorable Dynamic [KODIALAM1] M.Kodialam and T.V.Lakshman, "Restorable Dynamic
Quality of Service Routing," IEEE Communications Quality of Service Routing," IEEE Communications
Magazine, pp. 72-81, June 2002. Magazine, pp. 72-81, June 2002.
[KODIALAM2] M.Kodialam and T.V.Lakshman, "Dynamic Routing of [KODIALAM2] M.Kodialam and T.V.Lakshman, "Dynamic Routing of
Restorable Bandwidth-Guaranteed Tunnels using Restorable Bandwidth-Guaranteed Tunnels using
D.Papadimitriou et al. - Expires October 2004 40
Aggregated Network Resource Usage Information," IEEE/ Aggregated Network Resource Usage Information," IEEE/
ACM Transactions on Networking, pp. 399-410, June 2003. ACM Transactions on Networking, pp. 399-410, June 2003.
[MANCHESTER] J.Manchester, P.Bonenfant and C.Newton, "The Evolution [MANCHESTER] J.Manchester, P.Bonenfant and C.Newton, "The Evolution
of Transport Network Survivability," IEEE of Transport Network Survivability," IEEE
Communications Magazine, August 1999. Communications Magazine, August 1999.
[MPLS-OSU] S.Seetharaman et al., "IP over Optical Networks: A [RFC3386] W.Lai, D.McDysan, J.Boyle, et al., "Network Hierarchy
Summary of Issues," Work in Progress, draft-osu-ipo-
mpls-issues-02.txt, April 2001.
[RFC-3386] W.Lai, D.McDysan, J.Boyle, et al., "Network Hierarchy
and Multi-layer Survivability," IETF RFC 3386, November and Multi-layer Survivability," IETF RFC 3386, November
2002. 2002.
[RFC-3469] V. Sharma and F. Hellstrand (Editors), "Framework for [RFC3469] V.Sharma and F.Hellstrand (Editors), "Framework for
Multi-Protocol Label Switching (MPLS)- based Recovery," Multi-Protocol Label Switching (MPLS)- based Recovery,"
IETF RFC 3469, February 2003. IETF RFC 3469, February 2003.
[T1.105] ANSI, "Synchronous Optical Network (SONET): Basic [T1.105] ANSI, "Synchronous Optical Network (SONET): Basic
Description Including Multiplex Structure, Rates, and Description Including Multiplex Structure, Rates, and
Formats," ANSI T1.105, January 2001. Formats," ANSI T1.105, January 2001.
[TE-NS] K.Owens et al., "Network Survivability Considerations
for Traffic Engineered IP Networks," Internet Draft,
Work in Progress, draft-owens-te-network-survivability-
01.txt, July 2001.
[WANG] J.Wang, L.Sahasrabuddhe, and B.Mukherjee, "Path vs. [WANG] J.Wang, L.Sahasrabuddhe, and B.Mukherjee, "Path vs.
Subpath vs. Link Restoration for Fault Management in Subpath vs. Link Restoration for Fault Management in
IP-over-WDM Networks: Performance Comparisons Using IP-over-WDM Networks: Performance Comparisons Using
GMPLS Control Signaling," IEEE Communications Magazine, GMPLS Control Signaling," IEEE Communications Magazine,
pp. 80-87, November 2002. pp. 80-87, November 2002.
14. Author's Addresses 14. Editor's Addresses
Eric Mannie (Consult) Eric Mannie
E-mail: eric_mannie@hotmail.com EMail: eric_mannie@hotmail.com
Dimitri Papadimitriou (Alcatel) Dimitri Papadimitriou (Alcatel)
Francis Wellesplein, 1 Francis Wellesplein, 1
B-2018 Antwerpen, Belgium B-2018 Antwerpen, Belgium
Phone: +32 3 240-8491 Phone: +32 3 240-8491
E-mail: dimitri.papadimitriou@alcatel.be EMail: dimitri.papadimitriou@alcatel.be
D.Papadimitriou et al. - Internet Draft - Expires March 2004 40 D.Papadimitriou et al. - Expires October 2004 41
Full Copyright Statement Full Copyright Statement
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D.Papadimitriou et al. - Internet Draft - Expires March 2004 41 D.Papadimitriou et al. - Expires October 2004 42
 End of changes. 

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