Broadband Communications Congestion Control in a Broadband Multisource Packet Switch.

A new algorithm for congestion control in a Fast Packet Switch (FPS) is investigated, called the Dynamic Assignment Time Slot (DATS) algorithm. DATS is an algorithm for packet flow control from the input to their destination for a class of interconnected fabrics. For a frame of n time slots, the switch fabric for the framed broadband packet switch delivers n or less packets to each output port from the input ports which request packet delivery to that output port. The denied requests are left over for the next frame with higher priority. The sophisticated mechanism is based on scheduling packet arrival times at the input stage to resolve the output port conflict (two or more inputs, on some time slot, requesting the same output). The key element of the analysis of this algorithm is a time slot rearrangement of r service packets in a frame of n time slots at the Head Of Matrix (HOM); the input frames with their time slots are considered as a matrix. The switch performance is studied, analyzing the throughput-delay characteristic for poisson arrival traffic, modeled by random output port requests. The steady state throughput and delay equations are derived. The effect of the frame length n and the average message length m on the throughput and delay are examined. The validity of the results obtained using DATS algorithm is checked by a simulation model. Mathematical and simulation results are close to each other. The DATS algorithm improves the switch performance. In a comparison with (HUI87) FPS with maximum throughput of 58%, DATS algorithm with n = 2 gives the switch throughput equals to 67%. As n increases the throughput increases too. For n = 100, throughput is increased to 78.8%. The switch performance is greatly affected by the average message length m. As the average number of packet per message is decreased, the throughput will increase. For frame length n = 100 time slot and m = n/2, n/4, and n/10, the throughput will be 78%, 88% and 94% respectively.