Wdm Protection

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Protection & Restoration of

Optical Networks


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Terminology

Protection Uses pre-assigned capacity to ensure

survivability Restoration

Reroutes the affected traffic after failureoccurrence by using available capacity

Survivability Property of a network to be resilient to failures


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Classification of Schemes


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Reactive / Proactive

Reactive When an existing lightpath fails, a search is initiated to

find a new lightpath which does not use the failedcomponents. (After the failure happens)

It cannot guarantee successful recovery,

Longer restoration time

Proactive Backup lightpaths are identified and resources are reserved along

the backup lightpaths at the time of establishing the primary

lightpath itself. 100% restoration guarantee

Faster recovery


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Link Based vs. Path Based

Link-based Shorter restoration time Less efficient. Can only fix link failures

Path-based longer restoration time More efficient.


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Dedicated vs. MultiplexedBackup

Dedicated backup More robust Less efficient.

Backup multiplexing Less robust More efficient.


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Primary Backup MUX

Wavelength channel to be shared by aprimary and one or more backuppaths


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Resilience in Optical Networks

Linear Systems

1+1 protection 1:1 protection 1:N protection

Ring-based UPSR: Uni-directional Path Switched Rings

BLSR: Bi-directional Line Switched Rings Mesh-based

Optical mesh networks connected by optical cross-connects (OXCs) or optical add/drop multiplexers(OADMs)

Link-based/path-based protection/restoration Hybrid Mesh Rings

Physical: mesh Logical: ring


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Unidirectional WDM Path

Protected Rings 1+1 wavelength path selection

Signal bridged on both protection and

working fiber. Receiver chooses the better signal.

Failure:

Destination switches to the operational link. Revertive /Non revertive switching

No signaling required.


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Bidirectional Line switched

Ring Shares protection capacity among all the

spans on the ring

Link failure Working traffic from 1 fiber looped back onto

opposite direction.

Signaling protocol required

Node failure Line switching performed at both sides of the

failed node.


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2-Fiber WDM Ring


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BLSR - 4 Fiber

Fibers 2 working

2 protection Protection fiber: no traffic unless

failure.

Link Failure. APS channel required to coordinate theswitching at both ends of a failure.


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4-Fiber WDM Ring.


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4-Fiber WDM Ring

After a Link Failure


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4-Fiber WDM Ring

After a Node Failure


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Path Layer Mesh Protection

Protect Mesh as a single unit Pre-computed routes 1+1 path protection Protection route per light path Protection route per failure.

On the fly route computation. Centralized route computation and coordination Route computation and coordination at end nodes. Distributed route computation at path ends.

Decompose into protection domains. Pure rings P cycles


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Mesh Topologies

Fibers organized in protection cycles. Computed offline

4 fibers of each link is terminated by 42X2 protection switches Before link failure, switches in normal

position.

After failure, switches moved toprotection state and traffic looped backinto the protection cycles.


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2X2 Switch


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Protection Cycles (contd)

Criterion for protection cycles. Recovery from a single link failure in any

optical network with arbitrary topologyand bi-directional fiber links All protection fibers are used exactly once.

In any directed cycle both protection fibersin a pair are not used unless they are in abridge


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Protection Cycles


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Protection Cycles (contd)


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Network With Default

Protection Switching


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Network After a Link Failure


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Pcycles

Ring like restoration needed for someclient signals.

Mesh topologies: bandwidth efficient. Pcycles:Ring like speeds, Mesh like

capacity.

Addresses the speed limitation ofmesh restoration.


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Pcycles (contd)

Cycle oriented pre configuration of sparecapacity.

Can offer up to 2 restoration paths for afailure scenario. Span Failure

On cycle: similar to BLSR

Off the cycle: 2 paths. Time needed for calculating and connecting

restoration path is needed in non-real time.

P l


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P- cycles


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WDM Recovery

Fiber based restoration Entire traffic carried by a fiber is backed by

another fiber.

Bi-directional connection - 4 fibers.

WDM based recovery Protection for each wavelength. Bi-directional connection - 2 fibers Allows flexibility in planning the configuration

of the network. Recovery procedure similar to BLSR.


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Resilience in Multilayer Networks

Why resilience in multilayernetworks?

Avoid contention between differentsingle-layer recovery schemes.

Promote cooperation and sharing of

spare capacity


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PANEL: Protection Across

Network Layers

PANEL Guidelines


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PANEL Guidelines

Recovery in the highest layer is recommended when:

Multiple reliability grades need to be provided with finegranularity

Recovery inter-working cannot be implemented

Survivability schemes in the highest layer are more maturethan in the lowest layer

Recovery in the lowest layer is recommended when: The number of entities to recover has to be limited/reduced

The lowest layer supports multiple client layers and it isappropriate to provide survivability to all services in ahomogeneous way

Survivability schemes in the lowest layer are more mature than

in the highest layer It is difficult to ensure the physical diversity of working and

backup paths in the higher layer

Wdm Protection

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