Ingress Traffic Conditioning in Slotted Optical Packet Switched Networks

Optical Packet Switched (OPS) networks are known to suffer from high packet losses due to contentions. Techniques such as fiber delay line (FDL) buffering and wavelength conversion help to relieve contentions to an extent, but are expensive and are therefore used sparingly. This paper explores how electronic edge nodes can condition the traffic entering the OPS network with the objective of utilising the few available FDLs (or wavelength converters) more effectively to reduce contention losses further within the all-optical core. The benefits of ingress traffic conditioning in electronic networks are well known, but we believe its advantages for OPS networks with sparse contention resolution resources have not been fully evaluated. This paper considers a time-slotted OPS network comprising core nodes with limited FDL buffering. The edge-nodes are allowed to condition the ingress traffic by controlling the release of packets into the optical network in accordance with a particular scheme. In this context, our contributions are two-fold. First, we show analytically that for an optical switch with given FDL buffering capacity, contention losses on its output link can be minimised by evenly spacing packets on that link. This motivates edge traffic conditioning as an effective means of reducing contention losses in the OPS core. However, ingress traffic conditioning incurs a penalty, namely an increased queueing delay at the edge node. As our second contribution, we quantify via simulation the reduction in packet losses and the accompanying increase in end-to-end delay as the traffic conditioning varies. Our simulated OPS network topology is based on an actual trans-continental Australian network called CeNTIE (a research network in the same vein as Internet2 and Canarie), modeled with realistic traffic flows carrying long-range dependent traffic. We believe our proposal can assist a network operator to trade-off delay for loss when choosing an operating point for the OPS network.