Cell-sorting device for creating synchronous variable-length optical packet switches

We consider the design of a synchronous variable-length optical packet switch. Fixed-length packet switches may be used to switch variable-length packets if the packets are first divided into multiple fixed-length cells. However, for many fixed-length switch architectures, cells from multiple packets will become interspersed, and packet integrity will not be preserved. We describe the design of a fiber-delay-line-based cell sorter that when appended to the output of a fixed-length packet switch converts the switch into a variable-length packet switch by enabling variable-length packets to exit contiguously. We describe two implementations of the cell sorter. The first is simply a bank of delay lines. The second uses two stages of time-slot interchange and reduces the number of delay line elements to be a logarithmic function of the maximum packet length. We also estimate the packet-blocking probabilities of the resulting variable-length packet switch and verify our results via simulation.