Protection of SDH

Optical Networks (3-4)-Network SurvivabilityInstructor: Xiaohong Jiang

School of Information Science

Lecture 3: Network Survivability

SurvivabilityProtectionOptical Networks EvolutionProtection for Point-to-Point LinksProtection for Ring NetworksProtection for Mesh Networks

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Survivability

DefinitionWhy Survivable Optical Networks

Survivability DefinitionSurvivability of a network can be defined as its ability to continue providing service in the presence of failure(s). A network is survivable if it has a certain degree of survivability.

A survivable network A non-survivable network

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Why Survivable Optical Networks

Potential bandwidth of one optical fiber exceeds several tens Tbps (note that the bandwidth of copper cable is only a few Mbps). A single failure can disrupt millions of users and result in millions of dollars of lost revenue to users and operators of a network.Note: The most likely failure event is fiber cut (link failure) and the protection is the key technique used to ensure survivability.

Link failure(fiber cut)Switch failure

Outline


ProtectionProtection DefinitionWorking and Protection PathsDedicated and Shared ProtectionRevertive and Nonrevertive ProtectionUnidirectional and Bidirectional Protection SwitchingPath Switching, Span Switching, and Ring Switching

Protection DefinitionProtection is to provide some redundant capacity within a network and automatically reroute traffic around the failure using this redundant capacity.

Working and Protection PathsWorking paths carry traffic under normal operation;Protection paths provide alternate paths to carry the traffic in case of failure.

Working and protection paths are usually diversely routed (link-disjoint) so that both path are not lost in the case of a single failure.

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Dedicated and Shared ProtectionDedicated protection provides each working path its own dedicated protection path;Shared protection allows bandwidth sharing among the protection paths of connections if the working paths of these connections will not fail simultaneously (usually link-disjoint).

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Dedicated protection Shared protection

Revertive and NonrevertiveProtection

Revertive protection automatically switch the traffic back from protection path onto the working path once the working path is repaired.Nonrevertive protection allows the traffic remains on the the protection path after the working path is repaired.

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Dedicated protection(revertive or non revertive)

Shared protection(revertive )

Unidirectional and Bidirectional Protection Switching

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Protection switching can be unidirectional or bidirectional.Unidirectional protection switching: In the event of a single fiber cut, only one direction of traffic is switched over to the protection fiber and the other direction remains on the original working fiber. (Suitable for dedicated protection schemes)Bidirectional protection switching: In the event of a single fiber cut, both directions are switched over to the protection fibers(Suitable for shared protection schemes)

(a) Normal operation (b) Unidirectional protectionswitching

(c) Bidirectional protectionswitching

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Path Switching, Span Switching, and Ring Switching

Path Switching, Span Switching, and Ring Switching involve how and where the traffic is rerouted in the event of a failure.Path switching: connection is rerouted end to end from its source to its destination along an alternate path.Span switching: connection is rerouted on a spare link between the nodes adjacent to the failure.Ring switching: connection is rerouted on a ring between the nodes adjacent to the failure.

Working path(a) Normal operation (b) Path switching (c) Span switching (d) Ring switching

Outline


Optical Networks Evolution

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Point-to-point WDM transmission

OADM-based WDM Ring Network

OXC-based WDM Mesh Network

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Network Autonomously Controlled by IndividualPhotonic MPLS Routers

MPLS: Multi-Protocol Label SwitchingOADM:Optical Add/Drop Multiplexer OXC: Optical Cross-connect

Photonic MPLS Routers

Fast Optical Burst Data Switching Network

Outline


Protection for Point-to-Point Links (Automatic Protection Switching )

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

1+1 Protection

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Source Destination

In 1+1 protection, traffic is transmitted simultaneously on two separate fibers (usually over disjoint routes) from source to the destination, and the destination simply selects one of the two fibers for reception. If that fiber is cut, the destination simply switches over to the other fiber and continues to receive data.1+1 protection is fast but requires high bandwidth redundancy.

1:1 Protection In 1:1 protection, there are still two fibers from source to the destination. However, traffic is transmitted over only one fiber at a time (working fiber). If that fiber is cut, the source and the destination both switch over to the other protection fiber.1:1 protection is not as quick as 1+1 protection in restoring traffic, but results in a better bandwidth utilization.

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1:N Protection 1:N protection is a generalization of 1:1 protection, in which N working fibers share s single protection fiber. This scheme can handle the failure of any single working fiber. 1:N protection is very efficient in terms of bandwidth utilization.

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Protection for Ring Networks (Self-Healing Rings)

Ring networksUnidirectional Path-Switched RingBidirectional Line-Switched Ring (BLSR)BLSR-Span SwitchingBLSR-Ring SwitchingRing Interconnection-a simple wayRing Interconnection-dual homing

Ring Networks

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A ring is the simplest topology that is 2-connected, that is, provide two separate paths between any pair of nodes. Ring networks are popular for carrier as well as enterprise networks.


Protection for Ring Networks

Unidirectional Path-Switched Ring (UPSR)In a UPSR, one fiber (a path) is used as working fiber and the other as the protection fiber. Traffic is transmitted simultaneously on the working fiber in the clockwise directionand on the protection fiber in the counterclockwise direction. A UPSR is essentially 1+1 protection.

Bidirectional Line-Switched Rings (BLSR)In a four-fiber BLSR, two fibers (a line) are used as working fibers and, two are used for protection. Unlike a UPSR, working traffic in a BLSR can be carried on both directionsalong the ring (usually along shortest path between two nodes). A BLSR is essentially 1:1 protection. The BLSR employs two protection mechanisms: span switching and ring Switching.

BLSR-Span SwitchingIn span switching, if a transmitter or receiver on a working fiber fails, the traffic is routed onto the protection fiber in the same span (Span switching can also be used to restore traffic in the event of fiber cut,provided the protection fibers on thatspan are routed separately from the working fibers. However, this is usually not the case. So ring switching is usually used to restore traffic in case of fiber or cable cut.)

Span switching

BLSR-Ring SwitchingIn the ring switching, the traffic on the failed link is rerouted around the ring on the protection fibers between the nodes adjacent to the failure.Note: BLSRs (1:1 protection) are more efficient than UPSRs(1+1 protection), because BLSRs provide spatial reuse capabilities by allowing protection bandwidth to be shared between spatially separated connections.

Ring switching

Ring Interconnection-a simple wayThe entire network typically consists of multiple rings interconnected with each other, and a connection may have to be routed through multiple rings to get t its destination.

The simplest way for rings interconnection is to connect the drop sides of two AMDs on different rings back to back. Note this interconnection is broken if one of the AMDs fails or there is a problem with the cabling between the two ADMs.

Ring Interconnection-Dual homingDual homing makes use of two hub nodes to perform the interconnection.

In dual homing, each end node is connected to two hub nodes so as to be able to recover from the failure of a hub node or the failure of any interconnection between the hub nodes.

Outline


Protection for Mesh NetworksThere are two main pre-designed protection techniques against single-link failure in WDM Mesh networks:Link-based protectionPath-based protection

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Link-based protection

Path-based protection

Link-based Protection for Mesh Networks

In link-based protection, a protection path is reserved for each link based on ring switching.

Dedicated link protection:A protection lightpath is dedicated to a particular link. If the protection paths of two links are overlapped, then different wavelengths must be used in the overlapped links.

Shared link protection : It allows different backup paths to share a wavelength on the overlapping links, if the corresponding working channels are on different links. It utilizes capacity more efficient than dedicated link protection

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Path-based Protection for Mesh Networks

In path-based protection, a protection path is reserved for each working path.

Dedicated path protection: It provides each working path its own dedicated protection path;

Shared path protection: Itallows bandwidth sharing among the protection paths of connections if the working paths of these connections will not fail simultaneously (usually link-disjoint).

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Documents

Protection of SDH