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Saturday, 21 August 2010

Light tree seminar

The concept of a light-tree is introduced
in a wavelength-routed optical network. A light-tree is a
point-to-multipoint generalization of a lightpath. A lightpath is a
point-to-point all-optical wavelength channel connecting a transmitter
at a source node to a receiver at a destination node. Lightpath
communication can significantly reduce the number of hops (or
lightpaths) a packet has to traverse; and this reduction can, in turn,
significantly improve the network’s throughput. We extend the
lightpath concept by incorporating an optical multicasting capability
at the routing nodes in order to increase the logical connectivity of
the network and further decrease its hop distance. We refer to such a
point-to-multipoint extension as a light-tree. Light-trees cannot only
provide improved performance for unicast traffic, but they naturally
can better support multicast traffic and broadcast traffic. In this
study, we shall concentrate on the application and advantages of
light-trees to unicast and broadcast traffic. We formulate the
light-tree-based virtual topology design problem as an optimization
problem with one of two possible objective functions: for a given
traffic matrix,


(i) Minimize the network-wide average packet hop distance, or,

(ii) Minimize the total number of transceivers in the network. We
demonstrate that an optimum light-tree-based virtual topology has clear
advantages over an optimum light path-based virtual topology with
respect to the above two objectives.

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