| Wavelength division multiplexing (WDM) in optical fiber networks is widely viewed as the technology with the potential to satisfy the ever-increasing bandwidth needs of network users effectively and on a sustained basis. In WDM networks, nodes are equipped with optical cross-connects (OXCs), devices which can optically switch a signal on any given wavelength from any input port to any output port. This makes it possible to establish lightpaths between any pair of network nodes. A lightpath is a clear channel in which the signal remains in optical form throughout the physical path between the two end nodes. The set of lightpaths established over the fiber links defines a virtual topology. Consequently, the problem arises of designing virtual topologies to optimize a performance measure of interest for a set of traffic demands.; With the deployment of commercial WDM systems, it has become apparent that the cost of network components, especially line terminating equipment (LTE) is the dominant cost in building optical networks, and is a more meaningful metric to optimize than, say, the number of wavelengths. Furthermore, since the data rates at which each individual wavelength operates continue to increase (to OC-192 and beyond), it becomes clear that a number of independent traffic components must be multiplexed in order to efficiently utilize the wavelength capacity. These observations give rise to the concept of traffic grooming , which refers to the techniques used to combine lower speed components onto available wavelengths in order to meet network design goals such as cost minimization. Traffic: grooming is a hard problem in general which remains computationally intractable even for simple networks.; We consider the problem of traffic grooming in ring, star and tree topologies. We provide theoretical results regarding achievability bounds for these networks as well as practical frameworks to obtain increasingly better feasible solutions with the expenditure of more computational power. |
