Contention and congestion minimization in OBS networks

Abstract

All-optical networks (AON) based optical burst switching (OBS) promise to be the ultimate backbone network technology solution for next generation( NG) as well as fu­ ture generation (FG)networks because of their relatively higher resources utilization, great flexibility at lower cost and potential massive bandwidth capacities both at trans­ mission and switching levels. By design, buffering is not provisioned in interior nodes. End users exchange data with one another through end-to-end light channels, called lightpaths in which wavelength continuity is maintained. In practice, their establish­ ing, in a cost effective manner remains an inescapable challenge. The routing and wave­ length assignment (RWA) problem entices successful establishment of a physical route for each lightpath connection request, assigning a wavelength to each route and at the same time ensm·ing end to end continuity, subject to the limited number of wave­ lengths. The wavelengths must be assigned such that no lightpaths can share the same wavelength simultaneously on a given fibre, or else contentions may occur. Some data bursts may be discarded whenever contention occurs among multiple bursts that arrive simultaneously at any interior node using the same wavelength and are intended for the same output port. Because of the buffer-less nature of OBS networks, conten­ tion/congestion in the core network can quickly lead to degradation in overall network performance at moderate to high traffic levels due to heavy burst loses. In this disser­ tation we propose and evaluate a congestion management approach we refer to as '"en­ hanced congestion management" which gears towards rendering and guaranteeing a consistent QoS as well as rational and fair use of available network links. Simulation results show that the scheme can effectively minimize both contention and congestion and at the same time improving both throughput and effective utilization under mod­ erate to high network traffic loads