Exploring node light-splitting capability for burst grooming in optical burst switched networks

Abstract

Optical burst switching (OBS) is a switching concept which lies between optical circuit switching and optical packet switching. Both node switching time and burst size can impact the resource efficiency of an OBS network. To increase resource utilization, burst grooming has been proposed where numerous data bursts are coalesced to form a larger burst that will be switched as one unit in order to reduce the resource waste and switching penalty. In this article, assuming burst grooming can only be realized at edge nodes, we study the burst grooming problem where sub-bursts originating from the same source may be groomed together regardless of their destinations under certain conditions. We explore the capability that core nodes can split incoming light signals to support multicast to achieve more efficient burst grooming. Specifically, core nodes can transmit the groomed burst to multiple downstream nodes if the sub-bursts in the groomed burst have different destinations. The groomed burst will traverse a tree which spans the source and all the destinations of the sub-bursts in the groomed burst. The destination egress nodes recognize, de-burstify, and drop the sub-bursts destined to these nodes, i.e., the sub-bursts destined to these egress nodes are removed from the groomed burst. At the same time, the remaining sub-bursts may be groomed with sub-bursts at these egress nodes subject to burst grooming criteria. We propose two effective burst grooming algorithms, (1) a no over-routing waste approach (NoORW); and (2) a minimum relative total resource ratio approach (MinRTRR). Our simulation results have shown that the proposed algorithms are effective in terms of the burst blocking probability, the average burst end-to-end delay, the number of sub-bursts per groomed burst, as well as the resource waste.