Packet loss analysis of nonblocking ATM switches with nonuniform traffic and performance improvement by output buffer sharing

We present new results derived from the packet loss analysis of a generic Nx/N nonblocking ATM switches with speedup factor m and finite input/output buffers under nonuniform traffic. We adopt a queue loss scheme which allows packet loss at output buffers if the finite output buffers at each output port cannot accommodate all arriving packets. Exact packet loss probabilities of the switch at inputs and outputs are derived by using the matrix geometric solution technique. Our discrete time Markov chain analysis is more accurate than continuous time analysis, considering file fixed ATM cell size. It is shown that the optimal packet loss performance is obtained at the speed-up factor 2, not at larger values, with moderate input and output buffer sizes less than 30, for the practical range of uniform traffic load up to 0.8, to meet the given packet loss requirement, say 10^-9. This result suggests that we do not need to design with large speed-up factor for the practical range of packet loss and track load requirements, knowing that the large speed-up factor often means excessive cost and complexity involved in implementing the switch design. We also study how the different sizes of input and output buffers affect the switch performance. In particular, for nonuniform traffic study, we investigate the effect of each nonuniform parameters, such as nonuniformity at the input/output and output port addressing, on the switch performance. Finally, we introduce a concept of output traffic pressure, which is defined as output traffic intensity felt at unit buffer. Based on this idea, we propose an output buffer sharing scheme, to improve the packet loss performance degraded by nonuniform traffic. With this scheme we can significantly improve packet loss performance of nonuniform traffic. Furthermore, with a small increase in buffer budget we may achieve the performance very close to that of uniform traffic