A posteriori versus a priori access strategies in slotted all-optical WDM rings

Abstract

The paper presents the concept of “a posteriori” access strategy, as opposed to the previously studied concept of “a priori” strategy, to provide a fair and efficient access technique in slotted wavelength division multiplexing (WDM) rings under a large variety of traffic patterns. Using a posteriori strategies, the source node selects the packet for transmission based on the state of the WDM channels in the arriving slot, thus adapting the access decision to the instantaneous traffic in the various channels. The packet selection process of a posteriori strategies, when contrasted with a priori strategies, yields fair and efficient utilization of the ring bandwidth without requiring the equalization of the ring latency, nor imposing restrictions on the traffic patterns allowed in the system. Since the same features cannot be provided by a priori access strategies, a posteriori strategies offers a more versatile access control that justifies the higher implementation complexity due to the multi-channel sensing and on-line packet selection.