This paper presents the results of a simulation study of blocking and non-blocking switching for hierarchical ring networks. The switching techniques include wormhole, virtual cut-through, and slotted ring. We conclude that slotted ring network performs better than the more popular wormhole and virtual cut-through networks. We also show that the size of the node buffers is an important parameter and that choosing them too large can hurt performance in some cases. Slotted rings have the advantage that the choice of buffer size is easier in that larger than necessary buffers do not hurt performance and hence a single choice of buffer size performs well for all system configurations. In contrast, the optimal buffer size for virtual cut-through and wormhole switching nodes varies depending on the system configuration and the level in the hierarchy in which the switching node lies.

In this paper, we present an analysis of a high-speed slotted ring with a single packet buffer at each station. Assuming that distances between stations affect the network performance only through the sum of themselves (this will be called the "lumpability assumption"), we introduce a model system called the lumped model in which stations are aggregated at a single point on the ring with their relative positions preserved. At the instant when each slot visits the aggregated point of the lumped model, we build a Markov chain by recording the system state of buffers and slots. From the steady state probabilities of the Markov chain, we obtain the mean waiting time and the blocking probability of each station. It will be shown analytically and by simulation that the analysis based on the lumped model yields accurate results for various network conditions.