Internet DRAFT - draft-ietf-ccamp-gmpls-recovery-terminology

draft-ietf-ccamp-gmpls-recovery-terminology





CCAMP Working Group                         CCAMP GMPLS P&R Design Team 
Internet Draft                                                          
Category: Informational                            Eric Mannie (Editor) 
Expiration Date: October 2005            Dimitri Papadimitriou (Editor) 
                                                                        
                                                             April 2005 
                                      
                                      
                                      
             Recovery (Protection and Restoration) Terminology 
          for Generalized Multi-Protocol Label Switching (GMPLS) 
                                      
            draft-ietf-ccamp-gmpls-recovery-terminology-06.txt 
                                      
                                      
                                      
Status of this Memo 
    
   This document is an Internet-Draft and is subject to all provisions 
   of section 3 of RFC 3667.  By submitting this Internet-Draft, each 
   author represents that any applicable patent or other IPR claims of 
   which he or she is aware have been or will be disclosed, and any of 
   which he or she become aware will be disclosed, in accordance with 
   RFC 3668. 
    
   Internet-Drafts are working documents of the Internet Engineering 
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Copyright Notice 
    
   Copyright (C) The Internet Society (2005). All Rights Reserved. 
 
 
Abstract 
    
   This document defines a common terminology for Generalized Multi- 
   Protocol Label Switching (GMPLS) based recovery mechanisms (i.e. 
   protection and restoration). The terminology is independent of the 
   underlying transport technologies covered by GMPLS. 
 
 
  
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Table of Contents 
    
   Status of this Memo .............................................. 1 
   Abstract ......................................................... 1 
   Table of Contents ................................................ 2 
   1. Contributors .................................................. 3 
   2. Introduction .................................................. 3 
   3. Conventions used in this document ............................. 4 
   4. Recovery Terminology Common to Protection and Restoration ..... 4 
   4.1 Working and Recovery LSP/Span ................................ 5 
   4.2 Traffic Types ................................................ 5 
   4.3 LSP/Span Protection and Restoration .......................... 6 
   4.4 Recovery Scope ............................................... 7 
   4.5 Recovery Domain .............................................. 7 
   4.6 Recovery Types ............................................... 7 
   4.7 Bridge Types ................................................. 9 
   4.8 Selector Types ............................................... 9 
   4.9 Recovery GMPLS Nodes ........................................ 10 
   4.10 Switch-over Mechanism ...................................... 10 
   4.11 Reversion operations ....................................... 10 
   4.12 Failure Reporting .......................................... 11 
   4.13 External commands .......................................... 11 
   4.14 Unidirectional versus Bi-Directional Recovery Switching .... 12 
   4.15 Full versus Partial Span Recovery Switching ................ 12 
   4.16 Recovery Schemes Related Time and Durations ................ 13 
   4.17 Impairment ................................................. 14 
   4.18 Recovery Ratio ............................................. 14 
   4.19 Hitless Protection Switch-over ............................. 14 
   4.20 Network Survivability ...................................... 14 
   4.21 Survivable Network ......................................... 14 
   4.22 Escalation ................................................. 14 
   5. Recovery Phases .............................................. 14 
   5.1 Entities Involved During Recovery ........................... 15 
   6. Protection Schemes ........................................... 16 
   6.1 1+1 Protection .............................................. 16 
   6.2 1:N (N >= 1) Protection ..................................... 16 
   6.3 M:N (M, N > 1, N >= M) Protection ........................... 16 
   6.4 Notes on Protection Schemes ................................. 17 
   7. Restoration Schemes .......................................... 17 
   7.1 Pre-planned LSP Restoration ................................. 17 
   7.1.1 Shared-Mesh Restoration ................................... 18 
   7.2 LSP Restoration ............................................. 18 
   7.2.1 Hard LSP Restoration ...................................... 18 
   7.2.2 Soft LSP Restoration ...................................... 18 
   8. Security Considerations ...................................... 18 
   9. IANA Considerations .......................................... 18 
   10. References .................................................. 18 
   10.1 Normative References ....................................... 18 
   10.2 Informative References ..................................... 19 
   11. Acknowledgments ............................................. 20 
   12. Editor's Address ............................................ 20 
   Intellectual Property Statement ................................. 21 
 
  
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   Disclaimer of Validity .......................................... 21 
   Copyright Statement ............................................. 21 
 
1. Contributors 
    
   This document is the result of the CCAMP Working Group Protection 
   and Restoration design team joint effort. The following are the 
   authors that contributed to the present document: 
    
   Deborah Brungard (AT&T) 
   Rm. D1-3C22 - 200 S. Laurel Ave. 
   Middletown, NJ 07748, USA 
   EMail: dbrungard@att.com 
    
   Sudheer Dharanikota  
   EMail: sudheer@ieee.org 
    
   Jonathan P. Lang (Sonos)  
   506 Chapala Street                    
   Santa Barbara, CA 93101, USA               
   EMail: jplang@ieee.org 
    
   Guangzhi Li (AT&T) 
   180 Park Avenue, 
   Florham Park, NJ 07932, USA 
   EMail: gli@research.att.com 
    
   Eric Mannie  
   EMail: eric_mannie@hotmail.com 
    
   Dimitri Papadimitriou (Alcatel) 
   Francis Wellesplein, 1  
   B-2018 Antwerpen, Belgium 
   EMail: dimitri.papadimitriou@alcatel.be 
    
   Bala Rajagopalan (Intel Broadband Wireless Division) 
   2111 NE 25th Ave.   
   Hillsboro, OR 97124, USA 
   EMail: bala.rajagopalan@intel.com 
    
   Yakov Rekhter (Juniper) 
   1194 N. Mathilda Avenue                  
   Sunnyvale, CA 94089, USA 
   EMail: yakov@juniper.net 
 
2. Introduction 
    
   This document defines a common terminology for Generalized Multi-
   Protocol Label Switching (GMPLS) based recovery mechanisms (i.e. 
   protection and restoration). 
    

 
  
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   The terminology proposed in this document is independent of the 
   underlying transport technologies and borrows from the G.808.1 ITU-T 
   Recommendation [G.808.1] and from the G.841 ITU-T Recommendation 
   [G.841]. The restoration terminology and concepts have been gathered 
   from numerous sources including IETF drafts. 
    
   In the context of this document, the term "recovery" denotes both 
   protection and restoration. The specific terms "protection" and 
   "restoration" will only be used when differentiation is required. 
    
   This document focuses on the terminology for the recovery of Label 
   Switched Paths (LSPs) controlled by a GMPLS control plane. The 
   proposed terminology applies to end-to-end, segment, and span (i.e. 
   link) recovery. Note that the terminology for recovery of the 
   control plane itself is not in the scope of this document. 
    
   Protection and restoration of switched LSPs under tight time 
   constraints is a challenging problem. This is particularly relevant 
   to optical networks that consist of Time Division Multiplex (TDM) 
   and/or all-optical (photonic) cross-connects referred to as GMPLS 
   nodes (or simply nodes, or even sometimes "Label Switching Routers, 
   or LSRs") connected in a general topology [RFC3945]. 
    
   Recovery typically involves the activation of a recovery (or 
   alternate) LSP when a failure is encountered in the working LSP. 
    
   A working or recovery LSP is characterized by an ingress interface, 
   an egress interface, and a set of intermediate nodes and spans 
   through which the LSP is routed. The working and recovery LSPs are 
   typically resource disjoint (e.g. node and/or span disjoint). This 
   ensures that a single failure will not affect both the working and 
   recovery LSPs. 
    
   A bi-directional span between neighboring nodes is usually realized 
   as a pair of unidirectional spans. The end-to-end path for a bi-
   directional LSP therefore consists of a series of bi-directional 
   segments (i.e. Sub-Network Connections, or SNCs, in the ITU-T 
   terminology) between the source and destination nodes, traversing 
   intermediate nodes. 
    
3. Conventions used in this document: 
 
   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in 
   this document are to be interpreted as described in [RFC2119]. 
    
4. Recovery Terminology Common to Protection and Restoration 
    
   This section defines the following general terms common to both 
   protection and restoration (i.e. recovery). In addition, most of 
   these terms apply to end-to-end, segment and span LSP recovery. Note 

 
  
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   that span recovery does not protect the nodes at each end of the 
   span, otherwise end-to-end or segment LSP recovery should be used. 
    
   The terminology and the definitions have been originally taken from 
   [G.808.1]. However, for generalization, the following language that 
   is not directly related to recovery has been adapted to GMPLS and 
   the common IETF terminology: 
    
   An LSP is used as a generic term to designate either an SNC (Sub-
   Network Connection) or an NC (Network Connection) in ITU-T 
   terminology. The ITU-T uses the term transport entity to designate 
   either a link, an SNC or an NC. The term "Traffic" is used instead 
   of "Traffic Signal". The term protection or restoration "scheme" is 
   used instead of protection or restoration "architecture". 
    
   The reader is invited to read [G.841] and [G.808.1] for references 
   to SDH protection and Generic Protection Switching terminology, 
   respectively. Note that restoration is not in the scope of 
   [G.808.1]. 
    
4.1 Working and Recovery LSP/Span 
    
   A working LSP/span is an LSP/span transporting "normal" user 
   traffic. A recovery LSP/span is an LSP/span used to transport 
   "normal" user traffic when the working LSP/span fails. Additionally, 
   the recovery LSP/span may transport "extra" user traffic (i.e. pre-
   emptable traffic) when normal traffic is carried over the working 
   LSP/span. 
    
4.2 Traffic Types 
    
   The different types of traffic that can be transported over an 
   LSP/span in the context of this document are defined hereafter: 
    
   A. Normal traffic: 
    
   User traffic that may be protected by two alternative LSPs/spans 
   (the working and recovery LSPs/spans). 
    
   B. Extra traffic: 
    
   User traffic carried over recovery resources (e.g. a recovery 
   LSP/span) when these resources are not being used for the recovery 
   of normal traffic; i.e. when the recovery resources are in standby 
   mode. When the recovery resources are required to recover normal 
   traffic from the failed working LSP/span, the extra traffic is pre-
   empted. Extra traffic is not protected by definition, but may be 
   restored. Moreover, extra traffic does not need to commence or be 
   terminated at the ends of the LSPs/spans that it uses. 
    
   C. Null traffic: 
    
 
  
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   Traffic carried over the recovery LSP/span if it is not used to 
   carry normal or extra traffic. Null traffic can be any kind of 
   traffic that conforms to the signal structure of the specific layer, 
   and it is ignored (not selected) at the egress of the recovery 
   LSP/span. 
    
4.3 LSP/Span Protection and Restoration 
    
   The following subtle distinction is generally made between the terms 
   "protection" and "restoration", even though these terms are often 
   used interchangeably [RFC3386]. 
    
   The distinction between protection and restoration is made based on 
   the resource allocation done during the recovery LSP/span 
   establishment. The distinction between different types of 
   restoration is made based on the level of route computation, 
   signaling and resource allocation done during the restoration 
   LSP/span establishment. 
    
   A. LSP/Span Protection 
    
   LSP/span protection denotes the paradigm whereby one or more 
   dedicated protection LSP(s)/span(s) is/are fully established to 
   protect one or more working LSP(s)/span(s). 
    
   For a protection LSP, this implies that route computation took 
   place, that the LSP was fully signaled all the way and that its 
   resources were fully selected (i.e. allocated) and cross-connected 
   between the ingress and egress nodes. 
    
   For a protection span, this implies that the span has been selected 
   and reserved for protection. 
    
   Indeed, it means that no signaling takes place to establish the 
   protection LSP/span when a failure occurs. However, various other 
   kinds of signaling may take place between the ingress and egress 
   nodes for fault notification, to synchronize their use of the 
   protection LSP/span, for reversion, etc. 
 
   B. LSP/Span Restoration 
    
   LSP/span restoration denotes the paradigm whereby some restoration 
   resources may be pre-computed, signaled and selected a priori, but 
   not cross-connected to restore a working LSP/span. The complete 
   establishment of the restoration LSP/span occurs only after a 
   failure of the working LSP/span, and requires some additional 
   signaling. 
    
   Both protection and restoration require signaling. Signaling to 
   establish the recovery resources and signaling associated with the 
   use of the recovery LSP(s)/span(s) are needed.  
    
 
  
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4.4 Recovery Scope 
    
   Recovery can be applied at various levels throughout the network. An 
   LSP may be subject to local (span), segment, and/or end-to-end 
   recovery. 
    
   Local (span) recovery refers to the recovery of an LSP over a link 
   between two nodes.  
    
   End-to-end recovery refers to the recovery of an entire LSP from its 
   source (ingress node end-point) to its destination (egress node end-
   point).  
    
   Segment recovery refers to the recovery over a portion of the 
   network of a segment LSP (i.e. an SNC in the ITU-T terminology) of 
   an end-to-end LSP. Such recovery protects against span and/or node 
   failure over a particular portion of the network traversed by an 
   end-to-end LSP.  
 
4.5 Recovery Domain 
    
   A recovery domain is defined as a set of nodes and spans over which 
   one or more recovery schemes are provided. A recovery domain served 
   by one single recovery scheme is referred to as a "single recovery 
   domain", while a recovery domain served by multiple recovery schemes 
   is referred to as a "multi recovery domain".  
    
   The recovery operation is contained within the recovery domain. A 
   GMPLS recovery domain must be entirely contained within a GMPLS 
   domain. A GMPLS domain (defined as a set of nodes and spans 
   controlled by GMPLS) may contain multiple recovery domains. 
    
4.6 Recovery Types 
    
   The different recovery types can be classified depending on the 
   number of recovery LSPs/spans that are protecting a given number of 
   working LSPs/spans. The definitions given hereafter are from the 
   point of view of a working LSP/span that needs to be protected by a 
   recovery scheme. 
    
   A. 1+1 type: dedicated protection 
    
   One dedicated protection LSP/span protects exactly one working 
   LSP/span and the normal traffic is permanently duplicated at the 
   ingress node on both the working and protection LSPs/spans. No extra 
   traffic can be carried over the protection LSP/span. 
    
   This type is applicable to LSP/span protection, but not to LSP/span 
   restoration. 
    
   B. 0:1 type: unprotected 
    
 
  
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   No specific recovery LSP/span protects the working LSP/span. 
   However, the working LSP/span can potentially be restored through 
   any alternate available route/span, with or without any pre-computed 
   restoration route. Note that there are no resources pre-established 
   for this recovery type. 
    
   This type is applicable to LSP/span restoration, but not to LSP/span 
   protection. Span restoration can be for instance achieved by moving 
   all the LSPs transported over of a failed span to a dynamically 
   selected span. 
    
   C. 1:1 type: dedicated recovery with extra traffic 
    
   One specific recovery LSP/span protects exactly one specific working 
   LSP/span but the normal traffic is transmitted only over one LSP 
   (working or recovery) at a time. Extra traffic can be transported 
   using the recovery LSP/span resources. 
    
   This type is applicable to LSP/span protection and LSP restoration, 
   but not to span restoration. 
    
   D. 1:N (N > 1) type: shared recovery with extra traffic 
    
   A specific recovery LSP/span is dedicated to the protection of up to 
   N working LSPs/spans. The set of working LSPs/spans is explicitly 
   identified. Extra traffic can be transported over the recovery 
   LSP/span. All these LSPs/spans must start and end at the same nodes. 
    
   Sometimes, the working LSPs/spans are assumed to be resource 
   disjoint in the network so that they do not share any failure 
   probability, but this is not mandatory. Obviously, if more than one 
   working LSP/span in the set of N are affected by some failure(s) at 
   the same time, the traffic on only one of these failed LSPs/spans 
   may be recovered over the recovery LSP/span. Note that N can be 
   arbitrarily large (i.e. infinite). The choice of N is a policy 
   decision. 
    
   This type is applicable to LSP/span protection and LSP restoration, 
   but not to span restoration. 
    
   Note: a shared recovery where each recovery resource can be shared 
   by a maximum of X LSPs/spans is not defined as a recovery type but 
   as a recovery scheme. The choice of X is a network resource 
   management policy decision. 
    
   E. M:N (M, N > 1, N >= M) type: 
    
   A set of M specific recovery LSPs/spans protects a set of up to N 
   specific working LSPs/spans. The two sets are explicitly identified. 
   Extra traffic can be transported over the M recovery LSPs/spans when 
   available. All the LSPs/spans must start and end at the same nodes. 
    
 
  
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   Sometimes, the working LSPs/spans are assumed to be resource 
   disjoint in the network so that they do not share any failure 
   probability, but this is not mandatory. Obviously, if several 
   working LSPs/spans in the set of N are concurrently affected by some 
   failure(s), the traffic on only M of these failed LSPs/spans may be 
   recovered. Note that N can be arbitrarily large (i.e. infinite). The 
   choice of N and M is a policy decision. 
    
   This type is applicable to LSP/span protection and LSP restoration, 
   but not to span restoration. 
 
4.7 Bridge Types 
    
   A bridge is the function that connects the normal traffic and extra 
   traffic to the working and recovery LSP/span. 
    
   A. Permanent bridge  
    
   Under a 1+1 type, the bridge connects the normal traffic to both the 
   working and protection LSPs/spans. This type of bridge is not 
   applicable to restoration types. There is of course no extra traffic 
   connected to the recovery LSP/span. 
    
   B. Broadcast bridge  
    
   For 1:N and M:N types, the bridge permanently connects the normal 
   traffic to the working LSP/span. In the event of recovery switching, 
   the normal traffic is additionally connected to the recovery 
   LSP/span. Extra traffic is either not connected or connected to the 
   recovery LSP/span. 
    
   C. Selector bridge 
    
   For 1:N and M:N types, the bridge connects the normal traffic to 
   either the working or the recovery LSP/span. Extra traffic is either 
   not connected or connected to the recovery LSP/span. 
    
4.8 Selector Types 
    
   A selector is the function that extracts the normal traffic either 
   from the working or the recovery LSP/span. Extra traffic is either 
   extracted from the recovery LSP/span, or is not extracted. 
    
   A. Selective selector  
    
   Is a selector that extracts the normal traffic from either the 
   working LSP/span output or the recovery LSP/span output. 
    
   B. Merging selector  
    
   For 1:N and M:N protection types, the selector permanently extracts 
   the normal traffic from both the working and recovery LSP/span 
 
  
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   outputs. This alternative works only in combination with a selector 
   bridge. 
 
4.9 Recovery GMPLS Nodes 
    
   This section defines the GMPLS nodes involved during recovery.  
 
   A. Ingress GMPLS node of an end-to-end LSP/segment LSP/span 
    
   The ingress node of an end-to-end LSP/segment LSP/span is where the 
   normal traffic may be bridged to the recovery end-to-end LSP/segment 
   LSP/span. Also known as source node in the ITU-T terminology. 
    
   B. Egress GMPLS node of an end-to-end LSP/segment LSP/span 
 
   The egress node of an end-to-end LSP/segment LSP/span is where the 
   normal traffic may be selected from either the working or the 
   recovery end-to-end LSP/segment LSP/span. Also known as sink node in 
   the ITU-T terminology. 
    
   C. Intermediate GMPLS node of an end-to-end LSP/segment LSP 
    
   A node along either the working or recovery end-to-end LSP/segment 
   LSP route between the corresponding ingress and egress nodes. Also 
   known as intermediate node in the ITU-T terminology. 
 
4.10 Switch-over Mechanism 
    
   A switch-over is an action that can be performed at both the bridge 
   and the selector. This action is as follows: 
    
   A. For the selector: 
    
   The action of selecting normal traffic from the recovery LSP/span 
   rather than from the working LSP/span.  
    
   B. For the bridge: 
    
   In case of permanent connection to the working LSP/span, the action 
   of connecting or disconnecting the normal traffic to the recovery 
   LSP/span. In case of non-permanent connection to the working 
   LSP/span, the action of connecting the normal traffic to the 
   recovery LSP/span. 
    
4.11 Reversion operations 
    
   A revertive recovery operation refers to a recovery switching 
   operation, where the traffic returns to (or remains on) the working 
   LSP/span if the switch-over requests are terminated; i.e. when the 
   working LSP/span has recovered from the failure. 
    

 
  
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   Therefore a non-revertive recovery switching operation is when the 
   traffic does not return to the working LSP/span if the switch-over 
   requests are terminated. 
    
4.12 Failure Reporting 
    
   This section gives (for information) several signal types commonly 
   used in transport planes to report a failure condition. Note that 
   fault reporting may require additional signaling mechanisms. 
    
   A. Signal Degrade (SD): a signal indicating that the associated data 
   has degraded. 
    
   B. Signal Fail (SF): a signal indicating that the associated data 
   has failed. 
    
   C. Signal Degrade Group (SDG): a signal indicating that the 
   associated group data has degraded. 
    
   D. Signal Fail Group (SFG): a signal indicating that the associated 
   group has failed. 
    
   Note: SDG and SFG definitions are under discussion at the ITU-T. 
 
4.13 External commands 
    
   This section defines several external commands, typically issued by 
   an operator through the Network Management System (NMS)/Element 
   Management System (EMS), which can be used to influence or command 
   the recovery schemes. 
    
   A. Lockout of recovery LSP/span: 
    
   A configuration action initiated externally that results in the 
   recovery LSP/span being temporarily unavailable to transport traffic 
   (either normal or extra traffic). 
    
   B. Lockout of normal traffic: 
    
   A configuration action initiated externally that results in the 
   normal traffic being temporarily not allowed to be routed over its 
   recovery LSP/span. Note that in this case extra-traffic is still 
   allowed on the recovery LSP/span. 
    
   C. Freeze: 
    
   A configuration action initiated externally that prevents any 
   switch-over action to be taken, and as such freezes the current 
   state. 
 
   D. Forced switch-over for normal traffic: 
    
 
  
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   A switch-over action initiated externally that switches normal 
   traffic to the recovery LSP/span, unless an equal or higher priority 
   switch-over command is in effect. 
    
   E. Manual switch-over for normal traffic: 
    
   A switch-over action initiated externally that switches normal 
   traffic to the recovery LSP/span, unless a fault condition exists on 
   other LSPs/spans (including the recovery LSP/span) or an equal or 
   higher priority switch-over command is in effect. 
    
   F. Manual switch-over for recovery LSP/span: 
    
   A switch-over action initiated externally that switches normal 
   traffic to the working LSP/span, unless a fault condition exists on 
   the working LSP/span or an equal or higher priority switch-over 
   command is in effect. 
    
   G. Clear: 
    
   An action initiated externally that clears the active external 
   command. 
 
4.14 Unidirectional versus Bi-Directional Recovery Switching 
    
   A. Unidirectional recovery switching: 
    
   A recovery switching mode in which, for a unidirectional fault (i.e. 
   a fault affecting only one direction of transmission), only the 
   normal traffic transported in the affected direction (of the LSP or 
   span) is switched to the recovery LSP/span. 
    
   B. Bi-directional recovery switching: 
    
   A recovery switching mode in which, for a unidirectional fault, the 
   normal traffic in both directions (of the LSP or span), including 
   the affected direction and the unaffected direction, are switched to 
   the recovery LSP/span. 
    
4.15 Full versus Partial Span Recovery Switching 
    
   Bulk LSP recovery is initiated upon reception on either span failure 
   notification or bulk failure notification of the S LSPs carried by 
   this span. In either case, the corresponding recovery switching 
   actions are performed at the LSP level such that the ratio between 
   the number of recovery switching messages and the number of 
   recovered LSP (in one given direction) is minimized. If this ratio 
   equals 1, one refers to full span recovery, otherwise, if this ratio 
   is greater than 1 one refers to partial span recovery. 
    
   A. Full Span Recovery 
    
 
  
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   All the S LSP carried over a given span are recovered under span 
   failure condition. Full span recovery is also referred to as "bulk 
   recovery". 
    
   B. Partial Span Recovery 
    
   Only a subset s of the S LSP carried over a given span are recovered 
   under span failure condition. Both selection criteria of the 
   entities belonging to this subset and the decision concerning the 
   recovery of the remaining (S - s) LSP are based on local policy. 
    
4.16 Recovery Schemes Related Time and Durations 
    
   This section gives several typical timing definitions that are of 
   importance for recovery schemes. 
    
   A. Detection time: 
    
   The time between the occurrence of the fault or degradation and its 
   detection. Note that this is a rather theoretical time since in 
   practice this is difficult to measure. 
    
   B. Correlation time: 
    
   The time between the detection of the fault or degradation and the 
   reporting of the signal fail or degrade. This time is typically used 
   in correlating related failures or degradations. 
    
   C. Notification time:  
    
   The time between the reporting of the signal fail or degrade and the 
   reception of the indication of this event by the entities that 
   decide on the recovery switching operation(s).  
 
   D. Recovery Switching time: 
    
   The time between the initialization of the recovery switching 
   operation and the moment the normal traffic is selected from the 
   recovery LSP/span. 
 
   E. Total Recovery time: 
    
   The total recovery time is defined as the sum of the detection, the 
   correlation, the notification and the recovery switching time. 
    
   F. Wait To Restore time: 
    
   A period of time that must elapse from a recovered fault before an 
   LSP/span can be used again to transport the normal traffic and/or to 
   select the normal traffic from. 
 

 
  
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   Note: the hold-off time is defined as the time between the reporting 
   of signal fail or degrade, and the initialization of the recovery 
   switching operation. This is useful when multiple layers of recovery 
   are being used. 
 
4.17 Impairment 
    
   A defect or performance degradation, which may lead to SF or SD 
   trigger. 
    
4.18 Recovery Ratio 
    
   The quotient of the actually recovery bandwidth divided by the 
   traffic bandwidth which is intended to be protected. 
    
4.19 Hitless Protection Switch-over 
    
   Protection switch-over, which does not cause data loss, data 
   duplication, data disorder, or bit errors upon recovery switching 
   action. 
 
4.20 Network Survivability 
    
   The set of capabilities that allow a network to restore affected 
   traffic in the event of a failure. The degree of survivability is 
   determined by the network's capability to survive single and 
   multiple failures. 
    
4.21 Survivable Network 
    
   A network that is capable of restoring traffic in the event of a 
   failure. 
    
4.22 Escalation 
    
   A network survivability action caused by the impossibility of the 
   survivability function in lower layers. 
 
5. Recovery Phases 
 
   It is commonly accepted that recovery implies that the following 
   generic operations need to be performed when an LSP/span or a node 
   failure occurs: 
    
   - Phase 1: Failure Detection 
    
   The action of detecting the impairment (defect of performance 
   degradation) as a defect condition and consequential activation of 
   SF or SD trigger to the control plane (through internal interface 
   with the transport plane). Thus, failure detection (that should 
   occur at the transport layer closest to the failure) is the only 
   phase that can not be achieved by the control plane alone. 
 
  
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   - Phase 2: Failure Localization (and Isolation) 
    
   Failure localization provides to the deciding entity information 
   about the location (and so the identity) of the transport plane 
   entity that causes the LSP(s)/span(s) failure. The deciding entity 
   can then take accurate decision to achieve finer grained recovery 
   switching action(s).  
    
   - Phase 3: Failure Notification 
    
   Failure notification phase is used 1) to inform intermediate nodes 
   that LSP(s)/span(s) failure has occurred and has been detected 2) to 
   inform the recovery deciding entities (which can correspond to any 
   intermediate or end-point of the failed LSP/span) that the 
   corresponding LSP/span is not available. 
    
   - Phase 4: Recovery (Protection or Restoration) 
    
   See Section 4.3. 
    
   - Phase 5: Reversion (Normalization) 
    
   See Section 4.11. 
 
   The combination of Failure Detection and Failure Localization and 
   Notification is referred to as Fault Management. 
    
5.1 Entities Involved During Recovery 
    
   The entities involved during the recovery operations can be defined 
   as follows; these entities are parts of ingress, egress and 
   intermediate nodes as defined previously: 
    
   A. Detecting Entity (Failure Detection): 
    
   An entity that detects a failure or group of failures; providing 
   thus a non-correlated list of failures.                               
    
   B. Reporting Entity (Failure Correlation and Notification): 
    
   An entity that can make an intelligent decision on fault correlation 
   and report the failure to the deciding entity. Fault reporting can 
   be automatically performed by the deciding entity detecting the 
   failure. 
    
   C. Deciding Entity (part of the failure recovery decision process): 
    
   An entity that makes the recovery decision or selects the recovery 
   resources. This entity communicates the decision to the impacted 
   LSPs/spans with the recovery actions to be performed. 
    
 
  
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   D. Recovering Entity (part of the failure recovery activation 
   process): 
    
   An entity that participates in the recovery of the LSPs/spans. 
    
   The process of moving failed LSPs from a failed (working) span to a 
   protection span must be initiated by one of the nodes terminating 
   the span, e.g. A or B. The deciding (and recovering) entity is 
   referred to as the "master" while the other node is called the 
   "slave" and corresponds to a recovering only entity.  
    
   Note: The determination of the master and the slave may be based on 
   configured information or protocol specific requirements. 
 
6. Protection Schemes 
    
   This section clarifies the multiple possible protection schemes and 
   the specific terminology for the protection. 
    
6.1 1+1 Protection  
    
   1+1 protection has one working LSP/span, one protection LSP/span and 
   a permanent bridge. At the ingress node, the normal traffic is 
   permanently bridged to both the working and protection LSP/span. At 
   the egress node, the normal traffic is selected from the better of 
   the two LSPs/spans. 
    
   Due to the permanent bridging, the 1+1 protection does not allow an 
   unprotected extra traffic signal to be provided. 
    
6.2 1:N (N >= 1) Protection  
    
   1:N protection has N working LSPs/spans carrying normal traffic and 
   1 protection LSP/span that may carry extra-traffic. 
    
   At the ingress, the normal traffic is either permanently connected 
   to its working LSP/span and may be connected to the protection 
   LSP/span (case of broadcast bridge), or is connected to either its 
   working or the protection LSP/span (case of selector bridge). At the 
   egress node, the normal traffic is selected from either its working 
   or protection LSP/span. 
    
   Unprotected extra traffic can be transported over the protection 
   LSP/span whenever the protection LSP/span is not used to carry a 
   normal traffic. 
    
6.3 M:N (M, N > 1, N >= M) Protection 
    
   M:N protection has N working LSPs/spans carrying normal traffic and 
   M protection LSP/span that may carry extra-traffic. 
    

 
  
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   At the ingress, the normal traffic is either permanently connected 
   to its working LSP/span and may be connected to one of the 
   protection LSPs/spans (case of broadcast bridge), or is connected to 
   either its working or one of the protection LSPs/spans (case of 
   selector bridge). At the egress node, the normal traffic is selected 
   from either its working or one of the protection LSP/span. 
    
   Unprotected extra traffic can be transported over the M protection 
   LSP/span whenever the protection LSPs/spans is not used to carry a 
   normal traffic. 
    
6.4 Notes on Protection Schemes 
    
   All protection types are either uni- or bi-directional, obviously, 
   the latter applies only to bi-directional LSP/span and requires 
   coordination between the ingress and egress node during protection 
   switching. 
    
   All protection types except 1+1 unidirectional protection switching 
   require a communication channel between the ingress and the egress 
   node. 
    
   In the GMPLS context, span protection refers to the full or partial 
   span recovery of the LSPs carried over that span (see Section 4.15). 
 
7. Restoration Schemes 
    
   This section clarifies the multiple possible restoration schemes and 
   the specific terminology for the restoration. 
    
7.1 Pre-planned LSP Restoration   
    
   Also referred to as pre-planned LSP re-routing. Before failure 
   detection and/or notification, one or more restoration LSPs are 
   instantiated between the same ingress-egress node pair than the 
   working LSP. Note that the restoration resources must be pre-
   computed, must be signaled and may be selected a priori, but not 
   cross-connected. Thus, the restoration LSP is not able to carry any 
   extra-traffic.    
    
   The complete establishment of the restoration LSP (i.e. activation) 
   occurs only after failure detection and/or notification of the 
   working LSP and requires some additional restoration signaling. 
   Therefore, this mechanism protects against working LSP failure(s) 
   but requires activation of the restoration LSP after failure 
   occurrence. After the ingress node has activated the restoration 
   LSP, the latter can carry the normal traffic. 
    
   Note: when each working LSP is recoverable by exactly one 
   restoration LSP, one refers also to 1:1 (pre-planned) re-routing 
   without extra-traffic.  
    
 
  
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7.1.1 Shared-Mesh Restoration 
    
   "Shared-mesh" restoration is defined as a particular case of pre-
   planned LSP re-routing that reduces the restoration resource 
   requirements by allowing multiple restoration LSPs (initiated from 
   distinct ingress nodes) to share common resources (including links 
   and nodes.)  
 
7.2 LSP Restoration 
    
   Also referred to as LSP re-routing. The ingress node switches the 
   normal traffic to an alternate LSP signaled and fully established 
   (i.e. cross-connected) after failure detection and/or notification. 
   The alternate LSP path may be computed after failure detection 
   and/or notification. In this case, one also refers to "Full LSP Re-
   routing." 
    
   The alternate LSP is signaled from the ingress node and may reuse 
   intermediate node's resources of the working LSP under failure 
   condition (and may also include additional intermediate nodes.) 
    
7.2.1 Hard LSP Restoration 
    
   Also referred to as hard LSP re-routing. A re-routing operation 
   where the LSP is released before the full establishment of an 
   alternate LSP (i.e. break-before-make).  
    
7.2.2 Soft LSP Restoration 
    
   Also referred to as soft LSP re-routing. A re-routing operation 
   where the LSP is released after the full establishment of an 
   alternate LSP (i.e. make-before-break).  
    
8. Security Considerations 
 
   Security considerations are detailed in [ANAL] and [FUNCT]. 
    
9. IANA Considerations 
    
   This document defines no new code points and requires no action by 
   IANA. 
    
10. References 
    
10.1 Normative References 
    
   [ANAL]       D.Papadimitriou and E.Mannie (Editors), "Analysis of 
                Generalized Multi-Protocol Label Switching (GMPLS)-
                based Recovery Mechanisms (including Protection and 
                Restoration)", Internet Draft (Work in progress), April 
                2005. 
    
 
  
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   [FUNCT]      J.P.Lang, B.Rajagopalan and D.Papadimitriou (Editors), 
                "Generalized MPLS Recovery Functional Specification," 
                Internet Draft (Work in progress), April 2005. 
    
   [RFC2026]    S.Bradner, "The Internet Standards Process -- Revision 
                3", BCP 9, RFC 2026, October 1996. 
    
   [RFC2119]    S.Bradner, "Key words for use in RFCs to Indicate 
                Requirement Levels," BCP 14, RFC 2119, March 1997. 
    
   [RFC3667]    S.Bradner, "IETF Rights in Contributions", BCP 78, 
                RFC 3667, February 2004. 
                 
   [RFC3668]    S.Bradner, Ed., "Intellectual Property Rights in IETF 
                Technology", BCP 79, RFC 3668, February 2004.    
 
10.2 Informative References 
   
   [RFC3386]    W.S.Lai, et al., "Network Hierarchy and Multilayer 
                Survivability," RFC 3386, November 2002. 
   
   [RFC3945]    E.Mannie (Editor), "Generalized Multi-Protocol Label 
                Switching (GMPLS) Architecture," RFC 3945, October 
                2004.  
    
   [T1.105]     ANSI, "Synchronous Optical Network (SONET): Basic  
                Description Including Multiplex Structure, Rates, and 
                Formats," ANSI T1.105, January 2001. 
    
   For information on the availability of the following documents,  
   please see http://www.itu.int 
    
   [G.707]      ITU-T, "Network Node Interface for the Synchronous 
                Digital Hierarchy (SDH)," Recommendation G.707, October 
                2000. 
    
   [G.783]      ITU-T, "Characteristics of Synchronous Digital 
                Hierarchy (SDH) Equipment Functional Blocks," 
                Recommendation G.783, October 2000. 
    
   [G.806]      ITU-T, "Characteristics of Transport Equipment - 
                Description Methodology and Generic Functionality," 
                Recommendation G.806, October 2000. 
 
   [G.808.1]    ITU-T, "Generic Protection Switching - Linear trail and 
                subnetwork protection," Recommendation G.808.1, 
                December 2003. 
 
   [G.841]      ITU-T, "Types and Characteristics of SDH Network 
                Protection Architectures," Recommendation G.841, 
                October 1998. 
    
 
  
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   [G.842]      ITU-T, "Interworking of SDH network protection 
                architectures," Recommendation G.842, October 1998. 
 
11. Acknowledgments 
    
   Many thanks to Adrian Farrel for having thoroughly review this 
   document. 
 
12. Editor's Addresses 
    
   Eric Mannie  
   EMail: eric_mannie@hotmail.com 
 
   Dimitri Papadimitriou  
   Alcatel 
   Francis Wellesplein, 1  
   B-2018 Antwerpen, Belgium  
   Phone: +32 3 240-8491  
   EMail: dimitri.papadimitriou@alcatel.be 
 
































 
  
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