An accurate model for fair rate calculation in resilient packet rings

Resilient packet ring (RPR), which is being standardized as IEEE 802.17, is a new medium access control (MAC) protocol for high-speed metro-area ring networks. RPR supports spatial reuse and therefore requires to ensure fairness among different nodes competing for the ring bandwidth. In order to achieve fairness among nodes, a fairness algorithm is employed at each RPR node. In case of congestion, the fairness algorithm calculates and advertises a fair rate to all upstream nodes contributing to the congestion point. Consequently, the congested node will be able to insert its local traffic into the ring. In this paper, we develop an accurate model for fair rate calculation in the standard RPR fairness algorithm. We first ignore the link propagation delay and model the system using a non-linear discrete-time low-pass filter. We then consider link propagation delay and develop a more realistic model. We verify our model by simulation results and analyze the effect of system parameters on the calculated fair rate. This model can be used to evaluate performance of the RPR standard fairness algorithm in terms of stability and convergence time