Wavelength and Offset Window Assignment Schemes to Avoid Contention in OBS Rings

This paper proposes a simple procedure to ensure burst transmission without losses in Optical Burst Switching ring networks. The contention problem is solved by providing a scheme that pre-assigns, to each communication, a given wavelength and an offset window. This approach does not need any additional control information and, since burst contention is avoided, the network capacity and the wavelength utilization are maximized under dynamic traffic assumptions. The study is done by using techniques from graph theory. In particular, the so-called (acyclic) restriction digraphs provide a sharp lower bound for the number of required wavelengths, and support a greedy algorithm for assigning a suitable offset window to each communication. An alternative formulation of the obtained schemes, in terms of matrices, is also discussed. Simulation results of different feasible solutions are provided, showing low transmission delays and quite balanced wavelength utilization.