A Time Slotted Model for All-Optical Variable-Length Packet Switching without Packet Alignment

This paper studies an all-optical slot-switching model that is able to accommodate variable-length optical packets without the necessity for packet alignment. This is called the variable-length-packet fixed-length-slot (VPFS) switching scheme. In a VPFS network, all switches adopt the same slot size but slot boundaries are not synchronized from one switch to another. When a packet of any length arrives at a switch, a slot or multiple consecutive slots must be assigned to carry that packet from the input to the destined output, with the condition that the chain of slots carrying the packet cannot be broken up and routed separately in the switch. Given a selected slot size, s, and the average length of packet, x, we show that the expected arrival overhead of a packet due to asynchronous slot boundary is equal to s, thus the maximum throughput of the VPFS scheme is limited to x/(x +s). Although a small slot size is preferable in order to maximize the throughput, the challenge of switching is a compromise. The proposed model can be used for evaluating the performances of different variable-length optical packet switching scenarios.