Protection and Restoration in Optical NetworkLing HuangHling@cs.berkeley.edu

OutlineIntroduction to Network SurvivabilityOptics in InternetProtection and Restoration in InternetOptical Layer SurvivabilityProtection in Ring NetworkProtection in Mesh NetworkMulti-Layer ResilienceConclusion.

Network SurvivabilityA very important aspect of modern networksThe 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 connectionsSurvivability = property of a network to be resilient to failureRequires physical redundancy and restoration protocols.

Optics in the Internet

Optical Network: a Layered vision199920022001

Protection and Restoration in InternetA well defined set of restoration techniques already exists in the upper electronic layers:ATM/MPLSIPTCPRestoration speeds in different layers:BGP-4: 15 30 minutesOSPF: 10 seconds to minutesSONET: 50 millisecondsOptical Mesh: currently hundred milliseconds to minutes

Why Optical Layer ProtectionRestoration in the upper layers is slow and require intensive signalingOn 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.

Why Optical Layer Protection?Advantages.Speed.Efficiency.LimitationDetection 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.

Protection Technique ClassificationRestoration techniques can protect the network against:Link failuresFiber-cables cuts and line devices failures (amplifers)Equipment failuresOXCs, OADMs, eclectro-optical interface.Protection can be implementedIn the optical channel sublayer (path protection)In the optical multiplex sublayer (line protection)Different protection techniques are used forRing networksMesh networks

Protection in Ring Network1+1 Path ProtectionUsed in access rings for traffic aggregation into central office 1:1 Line ProtectionUsed for interoffice rings1:1 Span and Line ProtectionUsed in metropolitan or long- haul rings

Protection in Mesh NetworksNetwork 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 PathBackup Path

Reactive / ProactiveReactiveA 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 timeProactiveBackup lightpaths are identified and resources are reserved at the time of establishing the primary lightpath itself.100 percent restorationFaster recoveryTaxonomy

Path Protection / Line Protection

1+1 ProtectionTraffic 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 restorationCons: waste of bandwidth

1:1 ProtectionDuring 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.

Shared ProtectionBackup fibers are used for protection of multiple linksAssume independent failure and handle single failure.The capacity reserved for protection is greatly reduced.

1:N ProtectionNormal OperationIn Case of Failure

Multiplexing TechniquesPrimary Backup Multiplexing Used in a dynamic traffic scenario, to further improve resource utilization.Allows a wavelength channel to be shared by a primary and one or more backup paths. 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.

Survivability Design: Joint Optimization ProblemProblem DescriptionGiven 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.NotationN: the set of nodes; L: the set of links; D: the set of demandsCij: the capacity weight for link (ij)Wij: the capacity requirement on link (ij) in terms of # of wavelengthObjective Minimize

1) Objective function

2) and 3) the flow conservation constraints for demand ds primary path and backup path, respectively.

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 requirementInteger Programming Formulation

Multi-Layer Resilience

Multi-Layer Resilience

Multi-Layer Counter-Productive Behavior Instant response to Level 1 alarms in high layer causes unnecessary routing activity, routing instability, and traffic congestionLink DownLink recovered through optical protectionRouting tableRevision (no link) Routing tableRevision (with link)Link Rediscovered10s ms10s seconds10s secondsALARMLink inTrafficSource: RHK

Multi-Layer Interaction

Multi-Layer Interaction

ConclusionDifferent 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.

Unidirectional Path Switched Ring (UPSR)Signal sent on both working and protected pathBest quality signal selectedReceiving TrafficN1 send data to N2N1N2Outside Ring = WorkingInside Ring = ProtectionSending TrafficN4N3

Unidirectional Path Switched Ring (UPSR)Reply TrafficN2 replies back to N1Receiving TrafficN1N2Outside Ring = WorkingInside Ring = ProtectionN4N3Signal sent on both working and protected pathBest quality signal selected

Bidirectional Line Switched Ring (2-Fiber BLSRs)Sending/ReceivingTrafficSending/ReceivingTrafficN1 send data to N2 & N2 replies to N1Both Rings = Working & ProtectionN1N2N4N3

Bidirectional Line Switched Ring (4-Fiber BLSRs)Sending/ReceivingTrafficSending/ReceivingTrafficOC-48N1 send data to N2 & N2 replies to N12 Outside Rings = Working2 Inside Rings = ProtectionN1N2N4N3

BPS2000, Baystack 450 & Passport 8600 (edge ethernet distribution & aggregation)OPTera Packet Edge on OPTera Metro 3000 series & OPTera OC-48 (ethernet over metro optical/Sonet)OPTera Metro 5000 series (ethernet over DWDM)

Preside (provisioning & management software)Juniper & Shasta (collateral IP services & routing platforms)Contivity (VPN/secure, encrypted tunnel services)

Migration to IP on Optics simpler, lower cost network robustness & QOS needed for some services