Grooming multicast traffic in unidirectional SONET/WDM rings

In this paper we study the problem of efficient grooming of given non-uniform multicast traffic demands on a unidirectional SONET/WDM ring. The goal is to try to minimize the network cost as given by (i) the number of wavelengths required per fiber and (ii) the number of electronic add-drop multiplexers (ADMs) required on the ring. The problem is NP hard for both the cost functions. We observe that the problem with cost function (i) can be reduced to a corresponding traffic grooming problem for unicast traffic which can then be modelled as a standard circular-arc graph coloring problem. For cost function (ii), we construct a graph based heuristic and compare it against the multicast extension of the best known unicast traffic grooming heuristic (Zhang, 2000). We observe that our heuristic requires fewer ADMs than required by the multicast extension of the unicast heuristic given in (Zhang, 2000). We also develop a lower bound and compare it against some upper bounds to study the maximum penalty of not employing intelligent wavelength assignment and/or traffic grooming under the unidirectional SONET/WDM ring scenario.