Providing absolute QoS through virtual channel reservation in optical burst switching networks

This paper proposes a new absolute QoS differentiation scheme call Virtual Channel Reservation (VCR) scheme for Optical Burst Switching (OBS) networks. The scheme provides worst case guarantee on the drop probability of higher priority classes. In existing literature, there are very few contributions that support efficient absolute QoS guarantee in OBS networks, which is critical for burst drop sensitive applications. The service differentiation among each priority class in VCR is achieved by applying the concepts of virtual channel reservation and pre-emption, rather than by implementing optical buffer or extra offset time. Pre-emption in OBS literature often means the discard of a scheduled burst or a burst in service. One potential side effect of pre-emption, however, is bandwidth under utilization in multi-node scenarios. To address this problem, we also contribute a new informing header (i-header) mechanism. Simulations are conducted to evaluate the performance of VCR, both with and without i-headers. Results show that VCR without i-headers is able to meet the absolute QoS requirements in both single-node and multi-node scenarios. In addition, the introduction of i-header effectively reduces downstream bandwidth wastage caused by pre-emption in the multi-node scenario. The contribution of VCR and i-header are significant for the following practical reasons. First, VCR does not use optical buffers or extra offset time to achieve service differentiation; hence long end-to-end delay problems will not arise. Second, VCR conforms theoretically to the Conservation Law; hence as far as overall drop probability is concerned, VCR will outperform other QoS techniques like Guard Channel (GC) and JET QoS schemes. The last statement will be verified both theoretically and by the many simulation scenarios presented in the paper.