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 [1]. We observe that our heuristic requires fewer ADMs than required by the multicast extension of the unicast heuristic given in [1]. 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