The limits of input-queued switch performance with future packet arrival information

This paper investigates the benefit of a hypothetical oracle that gives future packet arrival information in a fixed-size-packet switch. While future information has no effect on output-queued (OQ) switch performance, this paper shows in simulation, the input-queued (IQ) switch with no switch fabric speed up has wait-time and buffer-size performance close to that of the OQ switch even with only a few time slots of future information. This finding suggests that the performance difference between input and OQ switches may be smaller than previous studies suggest. This paper investigates the theoretical aspects of using future information and shows the following. IQ switches are proved equivalent (in number of packets sent) to OQ switches for 2 inputs and 2 outputs. A linear-time algorithm is presented for achieving this equivalence. Larger switches are strictly not equivalent, and optimally using future information is in the worst case NP-hard. A heuristic that simplifies using the future information is investigated and found to be sub-optimal in rare instances for larger switches while optimal for 2 × 2 switches.