Download - 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