A TDM-based multibus packet switch

A new packet switch architecture using two sets of time-division multiplexed buses is proposed. The horizontal buses collect packets from the input links, while the vertical buses distribute the packets to the output links. The two sets of buses are connected by a set of switching elements which coordinate the connections between the horizontal buses and the vertical buses so that each vertical bus is connected to only one horizontal bus at a time. The switch has the advantages of: 1) adding input and output links without increasing the bus and I/O adaptor speed; 2) being internally unbuffered; 3) having a very simple control circuit; and 4) having 100% throughput under uniform traffic. A combined analytical-simulation method is used to obtain the packet delay and packet loss probability. Numerical results show that for satisfactory performance, the buses need to run about 30% faster than the input line rate. With this speedup, even at a utilization factor of 0.9, each input adaptor requires only 31 buffers for a packet loss rate of 10^-6. The output queue behaves essentially as an M/D/1 queue.