Multicast lightpaths

Multicast applications may include multimedia, medical imaging, digital audio, HDTV, video conferencing, interactive distance learning, and distributed games.

In order to support multi-casting, the WDM network requires multicast-capable wavelength-routing switches at the network node. These switches are capable of replicating data streams from one input port to multiple output ports. There are two types of switch architectures that are usually used:N. Singhal and B. Mukherjee, "Protecting multicast sessions in WDM optical mesh networks," J. Lightwave Technol., vol. 21, Apr. 2003

• The first type of switch architecture is an opaque switch architecture which utilizes electronic cross-connects with optical-electrical-optical (OEO) conversion.
• The other is transparent switch architecture which utilizes all optical cross-connects (OXCs).

Multicast lightpaths protection refers to the network's prompt response to reroute traffic onto an alternative path in the event of a failure.

In a dedicated backup path, resources are exclusively allocated to a single connection and not shared with other connections along the backup path.

In a shared backup path, resources may be shared between multiple backup paths for different connections.

File:Multicast L1.png

Several protection schemes have been proposed in the literature to protect the multicast connections. The simplest idea to protect the multicast tree from single fiber failure is to compute a link disjoint backup tree. In a link disjoint backup tree, a multicast session from source node F to destination nodes A, B, C, D and E forms a light tree. F is the root and the remaining nodes are the leaves. The primary light tree is shown in solid lines and (directed-link-disjoint) the back up light tree is shown in dotted lines carrying traffic from source node to destinations.

The ring based approach is also proposed to protect multicast session.C. Boworntummarat, L. Wuttisittikulkij, and S. Segkhoonthod, "Lighttree based Protection Strategies for Multicast Traffic in Transport WDM Mesh Networks with Multi-fiber Systems", in Proc. IEEE ICC'04, June 2004, vol. 3, pp.1791–1795

The segment protection scheme is another way to protect multicast connections.N. Singhal, L. sahasrabuddhe, and B. Mukherjee, "Provisioning of Survivable Multicast Sessions Against Single Link Failures in Optical WDM Mesh Networks", IEEE/OSA Journal of Lightwave Technology, vol. 21, no. 11, pp. 2587–2594, Nov. 2003. A segment in a multicast tree is defined as the sequence of edges from the source or any splitting node (on a tree) to a leaf node or to a downstream splitting node. A destination node is always considered as a segment end node because it is either a leaf node in a tree or a splitting node.

A multicast protection scheme through spanning paths is also one of the key approaches to protecting multicast sessions.N. Singhal, C. Ou, and B. Mukherjee, "Shared Protection for Multicast Sessions in Mesh Networks", in Proc. IEEE OFC'05, pp. 823-825, 2005N. Singhal, C. Ou, B. Mukherjee, "Cross-sharing vs. Self-sharing Trees for Protecting Multicast Sessions in Mesh Networks", Journal of Computer Networks, vol 50, no. 2, pp. 200-106, Feb. 2006.H. Luo, H. Yu, L. Li, and S. Wang, "On Protecting Dynamic Multicast Sessions in Survivable Mesh WDM Networks", in Proc. OFC'2006H. Luo, L. Li, and H. Yu, "Algorithm for Protecting Light-trees in Survivable Mesh Wavelength-division-multiplexing Networks", Journal of Optical Networking, vol. 5, no. 12, pp. 1071–1083, 2006. A spanning path in a multicast tree is defined as a path from a leaf node to any other leaf node in the light tree. The scheme derives backup paths for every spanning path in the multicast tree.

Dedicated backup path protection (DBPP) for multicast connections:

Depending on the network topology, a dedicated backup path concept can be applied for multicast traffic. A dedicated backup path protection is a multicast session from source node F to destination nodes A, B, C, D, and E which form the light tree. A dedicated backup path protection scheme can be applied to protect multicast traffic from link failure. This is easy to achieve with one-to-one protection where the dedicated backup path is already provisioned and traffic is simply switched to it on failure.

File:Mesh Dedicated Backup Path Protection.png

File:Mesh Shared Backup Path Protection Before Failure.png

File:Mesh Shared Backup Path Protection After Failure.png

Shared backup path protection (SBPP) for multicast connections:

The SBPP technique can be used for multicast connections at the optical layer because of its resource efficiency, due to the fact that the backup paths can share wavelength channels on links while their corresponding primary paths are link disjoint. Paths can share links with working paths and protection paths of other leaves.

In a shared backup path protection before failure FE and FA are primary paths. The optical line is reserved for shared protection of both FE and FA.

Path protection technique for multicast connections (multiple unicast connections):

Protection schemes for multicast connections are important for the following reasons:

1. Loss of connectivity: network failures such as fiber cuts in a communication network occur often enough to cause service disruption, and lead to significant information loss in the absence of adequate backup mechanisms.
2. SLA: it is important for providers to follow SLAs and guaranteed service. It is important to protect multicast connections to maintain the SLA.
3. Business reputation: network availability is one of the key aspects of multicasting connections. A company loses money and reputation when its network fails.

• Availability
• IP multicast
• Optical add-drop multiplexer
• Optical mesh network
• Optical transport network
• Unicast

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Category:Fiber-optic communications