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Protection and Restoration in Optical Network

Ling Huang [email protected]

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Outline

      Introduction to Network Survivability Optics in Internet Protection and Restoration in Internet Optical Layer Survivability   Protection in Ring Network Protection in Mesh Network Multi-Layer Resilience Conclusion.

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Network Survivability

   A very important aspect of modern networks   The ever-increasing bit rate makes an unrecovered failure a significant loss for network operators.

Cable cuts (especially terrestrial) are very frequent.

 No network-operator is willing to accept unprotected networks anymore.

Restoration = function of rerouting failed connections Survivability = property of a network to be resilient to failure  Requires physical redundancy and restoration protocols.

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Optics in the Internet

Data Center SONET SONET DWD M DWD M SONET

Access Metro Long Haul

SONET

Metro Access

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Optical Network: a Layered vision

Layer 3 2 1 0 IP ATM SONET Optics IP

MPLS Thin SONET

Opti cs Layer Inter working Packet Optical Packet IP/MPLS Smart Optical 2/3 0/1 Multi-physical layers

• multi & legacy services • robustness, QOS

1999 2001 Fewer physical layers

• IP service dominance • lower cost

2002

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Protection and Restoration in Internet

  A well defined set of restoration techniques already exists in the upper electronic layers:  ATM/MPLS   IP TCP Restoration speeds in different layers:  BGP-4: 15 – 30 minutes    OSPF: 10 seconds to minutes SONET: 50 milliseconds Optical Mesh: currently hundred milliseconds to minutes

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Why Optical Layer Protection

   Restoration in the upper layers is slow and require intensive signaling  On contrary 50-ms range when automatic protection schemes are implement in the optical transport layer.

Purpose of performing restoration in the optical layer:  To decrease the outage time by exploiting fast rerouting of the failed connection.

Main problem in adding protection function in a new layer:   Instability due to duplication of functions.

Need the merging of DWDM and electronic transport layer control and management.

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Why Optical Layer Protection?

  Advantages.

  Speed.

Efficiency.

Limitation  Detection of all faults not possible.(3R).

  Protects traffic in units of light paths.

Race conditions when optical and client layer both try to protect against same failure.

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Protection Technique Classification

   Restoration techniques can protect the network against:  Link failures   Fiber-cables cuts and line devices failures (amplifers) Equipment failures  OXCs, OADMs, eclectro-optical interface.

Protection can be implemented  In the optical channel sublayer (path protection)  In the optical multiplex sublayer (line protection) Different protection techniques are used for   Ring networks Mesh networks

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Protection in Ring Network

1+1 Path Protection Used in access rings for traffic aggregation into central office 1:1 Span and Line Protection Used in metropolitan or long haul rings 1:1 Line Protection Used for interoffice rings

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Protection in Mesh Networks

 Network planning and survivability design   Disjoint path idea: service working route and its backup route are topologically diverse.

Lightpaths of a logical topology can withstand physical link failures.

Working Path Backup Path

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Reactive / Proactive

Taxonomy

  Reactive    A search is initiated to find a new lightpath which does not use the failed components

after the failure happens

.

It can not guarantee successful recovery, Longer restoration time Proactive    Backup lightpaths are identified and resources are reserved

at the time of establishing the primary lightpath itself

.

100 percent restoration Faster recovery

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Path Protection / Line Protection

Normal Operation Path Switching: restoration is handled by the source and the destination.

fiber is available.

Line Protection.

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1+1 Protection

    Traffic is sent over two parallel paths, and the destination selects a better one.

In case of failure, the destination switch onto the other path.

Pros: simple for implementation and fast restoration Cons: waste of bandwidth

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1:1 Protection

    During normal operation, no traffic or low priority traffic is sent across the backup path.

In case failure both the source and destination switch onto the protection path.

Pros: better network utilization.

Cons: required signaling overhead, slower restoration.

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Shared Protection

Normal Operation    1:N Protection In Case of Failure Backup fibers are used for protection of multiple links Assume independent failure and handle single failure.

The capacity reserved for protection is greatly reduced.

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Multiplexing Techniques

 Primary Backup Multiplexing    Used in a dynamic traffic scenario, to further improve resource utilization.

Allows a wavelength channel to be shared by

one or more backup

paths.

a primary and

By doing so, the blocking probability of demands decreases at the expense of reduced restoration guarantee. (An increased number of lightpaths can be established) • A lightpath loses its recoverability when a channel on its backup lightpath is used by some other primary lightpath.

• It regains its recoverability when the other primary lightpath terminates.

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Survivability Design: Joint Optimization Problem    Problem Description  Given a network in terms of nodes (WXCs) and links, and a set of point-to-point demands, find both the primary lightpath and the backup lightpath for each demand so that the total required network capacity is minimized.

Notation      N: the set of nodes; L: the set of links; D: the set of demands C ij : the capacity weight for link (ij) W ij : the capacity requirement on link (ij)

in terms of # of wavelength

Objective  Minimize

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Integer Programming Formulation

1) Objective function 2) and 3) the flow conservation constraints for demand d primary path and backup path, respectively.

’ s 4) Logical relationship: the backup path consumes link capacity

iff

the primary path is affected by the fault.

5): Restoration route independent of the failure.

6): Link capacity requirement

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Multi-Layer Resilience

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Multi-Layer Resilience

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Multi-Layer Counter-Productive Behavior

Routing table Revision (no link) Routing table Revision (with link) Link Rediscovered Link in Traffic ALARM Link recovered through optical protection Link Down 10s ms 10s seconds 10s seconds

 Instant response to Level 1 alarms in high layer causes unnecessary routing activity, routing instability, and traffic congestion

Source: RHK

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Multi-Layer Interaction

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Multi-Layer Interaction

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Conclusion

    Different resilience schemes applicable in optical network have been discussed.

Network planning and topology design for survivability is computationally intractable and faster heuristic solutions are needed.

Multi-layer restoration is a hot point in current optical survivability research.

Joint IP/optical restoration mechanism is the trend in next generation optical network.

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Unidirectional Path Switched Ring (UPSR)

Signal sent on both working and protected path Sending Traffic N1 Best quality signal selected Receiving Traffic N2 Outside Ring = Working Inside Ring = Protection N3 N4 N1 send data to N2

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Unidirectional Path Switched Ring (UPSR)

Best quality signal selected Signal sent on both working and protected path Reply Traffic Receiving Traffic N1 N2 Outside Ring = Working Inside Ring = Protection N3 N4 N2 replies back to N1

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Bidirectional Line Switched Ring (2-Fiber BLSRs)

Sending/Receiving Traffic N1 N2 Sending/Receiving Traffic Both Rings = Working & Protection N4 N1 send data to N2 & N2 replies to N1 N3

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Bidirectional Line Switched Ring (4-Fiber BLSRs)

Sending/Receiving Traffic N1 OC-48 N4 N1 send data to N2 & N2 replies to N1 N3 N2 Sending/Receiving Traffic 2 Outside Rings = Working 2 Inside Rings = Protection