EECS864: Optical Communications Networks … Alanqar-GMPLS restoration...Wesam Alanqar April 14,...

Wesam AlanqarWesam AlanqarApril 14, 2003

EECS864: Optical Communications NetworksEECS864: Optical Communications NetworksStudent Lecture:Student Lecture:

GMPLS RestorationGMPLS RestorationA Business & Technical PerspectiveA Business & Technical Perspective

Information & Telecommunications Technology Center (ITTC), EECS, University of Kansas


Outline● Terminology: Protection vs. Restoration● Recovery Objectives● Recovery Mechanisms

λ Recovery Mechanisms Classification● Recovery Phases (Protection vs. Restoration)● Recovery in GMPLS

λ Recovery Objectives Impact on GMPLS λ GMPLS Recovery Flow Diagram

➥ Constraint-based routing➥ Signaling: Recovery LSP setup

λ GMPLS Recovery Components➥ Link Management Protocol (LMP)➥ Routing➥ Signaling

● GMPLS Recovery Examples:λ Local Recovery: 3-APSλ End-to-end Recovery: 3-APSλ Shared-mesh Recovery

● Conclusion


● Protection is fasterλ 50 ms SONET/SDH

λ Dedicated protection resources (pre-provisioning)

λ Least efficient bandwidth utilization

● Restoration is slowerλ In average, one order of magnitude

λ Pools of shared resources (more efficient bandwidth utilization)

● Path level recoveryλ Recovery mechanisms including both protection & restoration

λ Upon failure, end or intermediate nodes initiate (GMPLS LSP) recovery

● Link level recoveryλ Upon failure, intermediate nodes initiate (GMPLS LSP) recovery

Terminology: Protection vs. Restoration

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● Fast notification mechanism aggregating multiple failures

λ Efficient notification (and detection) mechanism

● Recovery period independent of number of LSP and nodes covered (recovery diameter)

λ Scalable notification and signaling mechanism

● Minimum connection service downtime

λ Highly responsive recovery mechanism (fast convergence)

● Minimum spare resource (transmission and switching) capacity required for failure recovery

λ Cost-effective recovery mechanism

Recovery Objectives

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Recovery Mechanisms

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Recovery Mechanisms: Classification

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● Phase 1:Fault Detectionλ Handle at the data plane layer closest to failure

λ LOL, BER, etc. at Optical layer

λ LOS, BER, etc. at SONET/SDH layer

● Phase 2: Fault Correlation

● Phase 3: Fault Localization-Isolationλ Communication between nodes to “localize” failure(control plane

driven using LMP, e.g.)

● Phase 4: Fault Notificationλ Communication between detecting node and node that institutes

recovery (RSVP-TE Notify, e.g.)

● Phase 5: Fault Recovery

● Phase 6: Reversion (Normalization)

Recovery Phases

FaultFaultManagement Management

PhasesPhases

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Recovery Phases: Protection

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Recovery Phases: Restoration

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Generalized MPLS building blocks: Recovery Components1. Constraint-based routing

2. Fault detection and fast recovery

3. LSP hierarchy & Forward Adjacency (FA)

4. Link bundling

5. Un-numbered links “Local significant address space”

6. IGP extensions-including optical impairments.

7. Signaling extensions

➥ SONET/SDH extensions

➥ G.709 extensions for next-generation 40G and above

8. Link management protocol (LMP) & DWD-LMP

➥ Detector Controller Interface(DCI-ITU) & LMP-WDM(IETF)

9. Operational models & OIF optical UNI

GMPLSbuilding blocks

GMPLS Recovery

Components

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● Fast notification mechanism aggregating multiple failuresλ Efficient notification (and detection) mechanism

λ Impact on RSVP-TE signaling :Notify request object and Notify message

● Recovery period independent of number of LSP and LSRλ Scalable signaling mechanism

λ Impact on RSVP-TE signaling :Multi-session notification in a SINGLE Notify message

● Minimum connection service downtimeλ Highly responsive recovery mechanism (fast convergence)

λ Path Search (Computation + Selection) and Activation (or Setup) must provide high responsiveness

● Minimum spare resource capacity required for failure recoveryλ Cost-effective recovery mechanism

λ Path Search and Activation must be efficient (traffic-engineering for optimized “resources”utilization)

Recovery Objectives Impact on GMPLS

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(1) Store information from IGP flooding in the DB (Control Plane Topology)

(2) Store traffic engineering information in the TE- DB (Data Plane Topology)

(3) Examine failure notification

(4) Calculate the path for the LSP through the data plane (TE Link) topology

(5) Represent path as an Explicit Route

(6) Pass Explicit Route to RSVP- TE (or CR- LDP) for signaling

GMPLS Recovery Flow DiagramConstraint-based routing

Extended IGPExtended IGP

Routing TableRouting Table Constraint Shortest Path Constraint Shortest Path First (CSPF)First (CSPF)

Failure NotificationFailure Notification(External Event)(External Event)

Traffic Traffic Engineering DBEngineering DB

Explicit RouteExplicit Route

Extended SignalingExtended Signaling

1 24 3

5

6

Metrics: Unreserved Bandwidth, Reservable Bandwidth, TE Metric aMetrics: Unreserved Bandwidth, Reservable Bandwidth, TE Metric and Resource Classnd Resource Class

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GMPLS Recovery Flow DiagramSignaling: Recovery LSP Setup

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● Process initiated by downstream node detecting the failure:λ Node D sends a ChannelStatus message upstream to Node Cλ Upon reception C sends a ChannelStatusAck message downstream to Node D

● Upstream node C determines if incoming data link (connected to the failed outgoing data link) is also under fault condition for the corresponding channels:

λ Upstream node C sends a ChannelStatus message downstream to D and a ChannelStatus message upstream to B

λ otherwise, the fault is localized and C sends a ChannelStatus message to D● Same message exchange is initiated from Node A towards B and between Node C and B

GMPLS Recovery Components: LMP for “Fault Localization”

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● Link protection type

λ Protection capabilities of TE links are advertised in IGP (Link Protection Type sub-

TLV is optional)

λ Link Protection Type includes:

➥ Extra-traffic, unprotected, shared, dedicated, and enhanced (rings)

λ A minimum level of (link or LSP) protection is specified at path instantiation A path selection

technique is used to satisfy minimum level

GMPLS Recovery Components : Routing Support

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● An Shared Risk Link Group (SRLG) is a set of links that share a common physical resource,

e.g., a fiber or a duct

● All links in an SRLG share the same risk (failure type)

● A link can simultaneously belong to multiple SRLGs.

● Two links belonging to the same SRLG may individually belong to other SRLGs

● Diverse routing of LSPs: a working and recovery LSP pair is SRLG disjoint

● SRLG of an LSP = union of the individual link SRLGs

● SRLG of a bundle = union of the components link SRLGs

GMPLS Recovery Components : Routing SupportSRLG for “path computation”

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● A single failure affects all links in the SRLG

λ Ex: Fibers in a duct, OCh’s in a fiber

● A link may belong to multiple SRLGs

(covering multiple links)

● A set of links may be a SRLG

● SRLG of an LSP: union of the SRLGs of its

links

● SRLG of a bundle: union of SRLGs of its

components links

GMPLS Recovery Components: Routing SupportSRLG for “path computation”

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● Link and Node Disjointness only between LSP1 and LSP2

λ If fiber duct 1 fails both LSP fail

● Link and Node Disjointness between LSP1 and LSP3

λ If fiber duct 1 fails only LSP1 fails (not LSP3)

λ If fiber duct 3 fails only LSP3 fails (not LSP1)

GMPLS Recovery Components: Routing SupportSRLG and Properties

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● Protection object (optional) included in the Path message to indicate specific protection attributes of an LSP

λ S bit indicates a working (S=0) or a recovery LSP (S=1)λ Link (Protection) Flags indicates the requested protection(s) for the outgoing interface or tunnel:

enhance, dedicated 1+1, dedicated 1:1, shared M:N, unprotected and/or extra traffic● Let end or intermediate nodes compute and select the path (thus the explicit route) of

end-to- end or intermediate (local) recovery LSP segments● Reserve resources without selection or allocation (corresponding label request and

assignment techniques are under consideration)● Send (optionally) the explicit route of the working LSP in the recovery LSP● Set the destination IP address of a Notify message

λ Using a dedicated Notify Requestobject carried in thePath message (for upstream notification)and/or in the Resv message (for downstream notification)

λ The destination IP address of the Notify message can be non-adjacent to the failure (one or more hop away from the failure)

GMPLS Recovery Components : Signaling Capabilities

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● Notify request objectλ Can be carried in Path and Resv messagesλ Indicates the IP address of the node that SHOULD be notified upon LSP failure detection

● Notify message λ Informs non-adjacent node of LSP-related events λ Includes ERROR_SPEC detailing the error and the IP address of failed link or detecting node

(correlation at receiver)λ Includes MESSAGE_ID if refresh reduction is supported

GMPLS Recovery Components : Signaling Capabilities

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● APS mechanisms implemented exclusively using the GMPLS control plane capabilities including:

λ Notification (Notify message)λ Switchover request (Path message)λ Switchover response (Resv message)

APS Mechanisms Capability

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● This process can be summarized as follows:λ Notification: Notify message from downstream to upstreamλ Switching Request: Path message from upstream to downstreamλ Switching Response: Resv message from downstream to upstream

GMPLS Recovery Examples:Local Recovery: 3-Phase APS

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● Intermediate nodes propagate the Path message unaltered (i.e. they do not replace the address of the Notify Request object with their own Node ID) -intermediate nodes are in this case not required to calculate any recovery LSP segment

● Main difference from local recovery is the destination address of the Notify message (the address of the ingress node) and the path of the recovery segment (from the ingress to the egress)

GMPLS Recovery Examples:End-to-End Recovery: 3-Phase APS

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● Working LSP 1 (A-B-C-D) with Recovery LSP 1’ (A-E-F-D) flagged as “secondary”

allowing for extra-traffic (preemption in case of working LSP failure)

● In case of LSP 1 failure, LSP 2 is preempted since using “extra traffic” link A-E-F-D

GMPLS Recovery Examples:Shared Meshed Recovery (1)

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● Working LSP 1 (A-B-C-D) with Recovery LSP 1’ (A-E-F-D) flagged as “secondary” with resource reservation but without resource allocation (soft-reserved LSP)

λ No resource consumption

● Any of the links A-E, E-F and F-D may carry extra-traffic for separate LSPs:λ LSP2 (H-A-E-J) and LSP3 (K-F-D-G)

GMPLS Recovery Examples:Shared Meshed Recovery (2)

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● GMPLS routing and signaling provides the required mechanisms to deliver fast, robust and

resource efficient recovery (including shared meshed recovery)

● Even when considering a relatively long inter-arrival LSP request time, such mechanisms are

required to increase the network survivability in case of failure

● Choosing a recovery strategy is strongly dependent upon:

λ Data plane requirements Capabilities (protection)

λ Required customer SLA

Conclusion

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1. List the three GMPLS recovery protocols. How those protocols coordinate with each other in

providing a network recovery via GMPLS?

2. What factors would you use in deciding to enable protection vs. restoration when designing a

nationwide transport network?

3. Transport plane protection can be implemented via transport plane or control plane (like

GMPLS), what reasons would you use to support your decision to implement protection via

control or transport plane?

Homework Questions

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References

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● Generalized Multi-Protocol Label Switching Architecture http://www.ietf.org/internet-drafts/draft-ietf-ccamp-gmpls-architecture-05.txtGMPLS Signaling Functional Description http://www.ietf.org/rfc/rfc3471.txt● GMPLS Signaling- (RSVP-TE) Extensions http://www.ietf.org/rfc/rfc3473.txt● GMPLS signaling – (CR-LDP) Extensionshttp://www.ietf.org/rfc/rfc3472.txt● Generalized MPLS Recovery Functional Specification http://www.ietf.org/internet-drafts/draft-ietf-ccamp-gmpls-recovery-functional-00.txt● Analysis of Generalized MPLS-based Recovery Mechanisms (Protection and Restoration) http://www.ietf.org/internet-drafts/draft-ietf-ccamp-gmpls-recovery-analysis-00.txt● Recovery (Protection and Restoration) Terminology for GMPLS http://www.ietf.org/internet-drafts/draft-ietf-ccamp-gmpls-recovery-terminology-01.txt

EECS864: Optical Communications Networks … Alanqar-GMPLS restoration...Wesam Alanqar April 14,...

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