10-05-2012, 04:42 PM
Design of Light-Tree Based Logical Topologies for Multicast Streams in Wavelength Routed Optical Networks
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INTRODUCTION
Optical networks based on Wavelength Division
Multiplexing (WDM) are the most promising candidates for the
next generation backbone networks. In a wavelength-routed
network, data are transported in all-optical WDM channels
referred to as lightpaths. The set of lightpaths forms the logical
topology of a WDM network. Data are processed electronically
only at each node of a logical topology (i.e., at the endpoints of
the lightpath), and switched optically at intermediate nodes of
the underlying physical network. Design of logical topologies
has been studied in recent years [1-4], and the goal is to
minimize the congestion (i.e., the load on each channel), or the
resources used in physical networks.
PROBLEM FORMULATION
The problem to be studied is comprised of two parts:
routing and wavelength assignment of light-trees, and logical
topology design. We assume the physical topology, the number
of power splitters and wavelength converters in the network,
and the number of optical transmitters and receivers at each
node are given as parameters. We assume that the power loss
of power splitting can be neglected because optical amplifiers
are used. We also assume that each wavelength converter is a
full range wavelength converter [16], i.e., each wavelength on
a channel can be converted to any other wavelength.
Design of Light-Tree Based Logical Topologies
In this section, we extend the formulation described above
to solve the logical topology design problem. A logical
topology is a hypergraph, in which each node represents a
switch capable of electronic processing. Each hyperedge
represents a light-tree in the physical network. A node
incapable of electronic processing can’t be the root of a lighttree.
We use the formulation of light-trees described in the last
section to find the hyperedges for the logical topology. The
traffic over the logical topology is composed of multiple
multicast streams to which an end-to-end delay bound is
guaranteed. Each multicast stream has a sender and several
receivers.