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CCAMP Working Group                         CCAMP GMPLS P&R Design Team
Internet Draft
Category: Standard Track                           Eric Mannie (Editor)
Expiration Date: June 2004               Dimitri Papadimitriou (Editor)

                                                           January 2004



       Recovery (Protection and Restoration) Terminology for GMPLS

           draft-ietf-ccamp-gmpls-recovery-terminology-03.txt




Status of this Memo

  This document is an Internet-Draft and is subject to all provisions
  of Section 10 of RFC2026.

  Internet-Drafts are working documents of the Internet Engineering
  Task Force (IETF), its areas, and its working groups. Note that other
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  For potential updates to the above required-text see:
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1. Abstract

   This document defines a common terminology for Generalized Multi-
   Protocol Label Switching (GMPLS) based recovery mechanisms (i.e.
   protection and restoration) that are under consideration by the
   CCAMP Working Group. The proposed terminology is intended to be
   independent of the underlying transport technologies covered by
   GMPLS.





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2. 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 memo:

   Deborah Brungard (AT&T)
   Rm. D1-3C22 - 200 S. Laurel Ave.
   Middletown, NJ 07748, USA
   E-mail: dbrungard@att.com

   Sudheer Dharanikota (Consult)
   E-mail: sudheer@ieee.org

   Jonathan P. Lang (Rincon Networks)
   E-mail: jplang@ieee.org

   Guangzhi Li (AT&T)
   180 Park Avenue,
   Florham Park, NJ 07932, USA
   E-mail: gli@research.att.com

   Eric Mannie (Consult)
   Email: eric_mannie@hotmail.com

   Dimitri Papadimitriou (Alcatel)
   Fr. Wellesplein, 1
   B-2018, Antwerpen, Belgium
   Email: dimitri.papadimitriou@alcatel.be

   Bala Rajagopalan (Tellium)
   2 Crescent Place - P.O. Box 901
   Oceanport, NJ 07757-0901, USA
   E-mail: braja@tellium.com

   Yakov Rekhter (Juniper)
   1194 N. Mathilda Avenue
   Sunnyvale, CA 94089, USA
   E-mail: yakov@juniper.net

3. Introduction

   This document defines a common terminology for Generalized MPLS
   (GMPLS) based recovery mechanisms (i.e. protection and restoration)
   that are under consideration by the CCAMP Working Group.

   The terminology proposed in this document is intended to be
   independent of the underlying transport technologies and borrows
   from an ITU-T ongoing effort, the Draft Recommendation [G.808.1]
   (ex. G.GPS - Generic Protection Switching) and from the G.841 ITU-T
   Recommendation. The restoration terminology and concepts have been
   gathered from numerous sources including IETF drafts.


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   In the context of this document we will use the term "recovery" to
   denote both protection and restoration. The specific terms
   "protection" and "restoration" will only be used when
   differentiation is required.

   Note that this document focuses on the terminology for the recovery
   of LSPs controlled by a GMPLS control plane. We focus on end-to-end,
   segment and span (i.e. link) LSP recovery. Terminology for control
   plane recovery 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 TDM and/or all-optical
   (photonic) cross-connects referred to as GMPLS nodes (or simply
   nodes, or even sometimes "LSRs") connected in a general topology
   [GMPLS-ARCH].

   Recovery typically involves the activation of a recovery (or
   alternate) LSP when a failure is encountered in the working (or
   primary) 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.

   Conventions used in this document:

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in
   this document are to be interpreted as described in RFC-2119 [1].

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
   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


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   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 ITU-T generic protection terminology. 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.

   C. Null traffic:

   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.




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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 [TEWG].

   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 ore 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
   protecting 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
   protecting 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.

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.



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   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 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

   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.




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   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; M =< N) 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.

   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



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   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
   outputs. This alternative works only in combination with a selector
   bridge.





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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 Switching Mechanism

   A switch 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 requests are terminated; i.e. when the
   working LSP/span has recovered from the failure.

   Therefore a non-revertive recovery switching operation is when the
   traffic does not return to the working LSP/span if the switch
   requests are terminated.



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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 NMS/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.

   C. Freeze:

   A configuration action initiated externally that prevents any switch
   action to be taken, and as such freezes the current state.

   D. Forced switch for normal traffic:

   A switch action initiated externally that switches normal traffic to
   the recovery LSP/span, unless an equal or higher priority switch
   command is in effect.

   E. Manual switch for normal traffic:




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   A switch 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 command is in effect.

   F. Manual switch for recovery LSP/span:

   A switch 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 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

   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


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   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 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. Hold-off time:

   The time between reporting of signal fail or degrade, and the
   initialization of the recovery switching algorithm. This is useful
   when multiple layers of recovery are being used.

   D. 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.

   E. Switching time:

   The time between the initialization of the recovery switching
   algorithm and the moment the traffic is selected from the recovery
   LSP/span.

   F. Recovery time:

   The recovery time is defined as the sum of the detection,
   correlation, hold-off and switching times.

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.


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4.19 Hitless Protection Switch

   Protection switch, 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 networkÆs 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.

   - 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



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   intermediate or end-point of the failed LSP/span) that the
   corresponding LSP/span is not available.

   - Phase 4: Recovery (Protection or Restoration)

   See above.

   - Phase 5: Reversion (Normalization)

   See above.

   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 select the recovery
   resources. This entity communicates the decision to the impacted
   LSPs/spans with the recovery actions to be performed.

   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.



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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 protecting LSP/span that may carry extra-traffic.

   At the ingress, 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, M =< N) Protection

   M:N protection has N working LSPs/spans carrying normal traffic and
   M protecting LSP/span that may carry extra-traffic.

   At the ingress, a 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.

   Note1: 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.


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   Note2: all protection types except 1+1 unidirectional protection
   switching require a communication channel between the ingress and
   the egress node.

   Note3: 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.

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."


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   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

   This document does not introduce or imply any specific security
   consideration.

9. Intellectual Property Considerations

   This section is taken from Section 10.4 of [RFC2026].

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11. Copies of
   claims of rights made available for publication and any assurances
   of licenses to be made available, or the result of an attempt made
   to obtain a general license or permission for the use of such
   proprietary rights by implementors or users of this specification
   can be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights, which may cover technology that may be required to practice
   this standard.  Please address the information to the IETF Executive
   Director.

10. References

10.1 Normative References





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   [G.707]      ITU-T, "Network Node Interface for the Synchronous
                Digital Hierarchy (SDH)," Recommendation G.707, October
                2000.

   [G.841]      ITU-T, "Types and Characteristics of SDH Network
                Protection Architectures," Recommendation G.841,
                October 1998.

   [G.842]      ITU-T, "Interworking of SDH network protection
                architectures," Recommendation G.842, October 1998.


   [RFC-2026]   S.Bradner, "The Internet Standards Process -- Revision
                3", BCP 9, RFC 2026, October 1996.

   [RFC-2119]   S.Bradner, "Key words for use in RFCs to Indicate
                Requirement Levels," BCP 14, RFC 2119, March 1997.

   [T1.105]     ANSI, "Synchronous Optical Network (SONET): Basic
                Description Including Multiplex Structure, Rates, and
                Formats," ANSI T1.105, January 2001.

10.2 Informative References

   [BALA]       B.Rajagopalan et al., "Signaling for Protection and
                Restoration in Optical Mesh Networks," Internet Draft,
                Work in progress, draft-bala-protection-restoration-
                signaling-00.txt.

   [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 û
                Description Methodology and Generic Functionality,"
                Recommendation G.806, October 2000.

   [G.808.1]    ITU-T, "Generic Protection Switching û Linear trail and
                subnetwork protection," Draft Recommendation (work in
                progress), Version 0.5, January 2003.

   [GMPLS-ARCH] E.Mannie (Editor), "Generalized MPLS Architecture,"
                Internet Draft, Work in progress, draft-ietf-ccamp-
                gmpls-architecture-06.txt, April 2003.

   [SUDHEER]    S.Dharanikota et al., "NNI Protection and restoration
                requirements," OIF Contribution 507, 2001.

   [TEWG]       W.S.Lai, et al., "Network Hierarchy and Multilayer
                Survivability," Internet Draft, Work in progress,
                draft-ietf-tewg-restore-hierarchy-01.txt, June 2002.



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11. Acknowledgments

   Valuable comments and input were received from many people.

12. Author's Addresses

   Eric Mannie (Consult)
   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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