Grooming of multicast sessions in metropolitan WDM ring networks

With the introduction of WDM into the metro environment, the need to cost-effectively handle finer “sub-wavelength” capacities has become paramount. In this paper, we address the problem of routing and wavelength assignment of multicast sessions with sub-wavelength traffic demands, in the scenario of metropolitan WDM ring networks. In order to support multicasting, individual nodes need to have the capability to duplicate traffic. We consider two different node architectures which perform the duplication in optical and electronic domain, respectively. As traffic duplication at the electronic level is much more expensive than the optical alternative [X.-H. Jia, D.-Z. Du, X.-D. Hu, M.-K. Lee, J. Gu, Optimization of wavelength assignment for QoS multicast in WDM networks, IEEE Trans. Commun. 49 (2) (2001) 341-350], we study the problem of assigning routes and wavelengths to the multicast sessions so as to minimize electronic copying. We present an ILP formulation of this problem. The solution to this problem can be divided into three phases-1. routing of multicast sessions, 2. construction of circles by grouping non-overlapping arcs and 3. grouping these circles onto wavelengths. We propose a heuristic algorithm which implements the routing as well as circle construction phases simultaneously and then groups the circles. We present extensive simulation results to show that our approach leads to much lower equipment cost than that obtained by routing each multicast session along its minimum spanning tree and then using the best known heuristic for circle construction [X. Zhang, C. Qiao, An effective and comprehensive approach to traffic grooming and wavelength assignment in SONET/WDM rings, IEEE/ACM Trans. Networking 8 (5) (2000) 608-617].