Resilient Packet Ring Low Priority Traffic Latency

Resilient Packet Ring (RPR IEEE 802.17) is an insertion buffer, dual ring technology, utilizing a back pressure based fairness algorithm to distribute bandwidth when congestion occurs. The fairness algorithm may oscillate and under some conditions the oscillations continue indefinitely even under stable load conditions. In this paper, we evaluate the latency experienced by packets sent during such oscillations. We analyze transient behavior and how the oscillations of the fairness algorithm influence the jitter caused by unfair access to the ring, as well as jitter caused by the insertion buffers around the ring. We conclude that, in most cases, latency and jitter are within acceptable bounds. A modification to the RPR fairness algorithm has previously been proposed by the authors, but its implications on latency has never before been demonstrated. We compare the improved fairness algorithm to the original, and find that the modified algorithm, for all evaluated scenarios, perform at least as well as the original with respect to latency and jitter. In some problem scenarios, we find that the modified algorithm performs significantly better than the original.