PTES: A new packet transmission technique in bufferless slotted OPS networks

Optical packet contention is the major problem in optical packet switching (OPS) networks. In this paper, a software-based contention reduction scheme is proposed for all-optical multi-fiber slotted OPS networks, called packet transmission based on the scheduling of empty time-slots (PTES), suitable for overlaid star topology used in a metropolitan area with heterogeneous distances. In the scheduling procedure (performed in a distributed manner by each edge node of a star network) within a frame interval, some time-slots are scheduled as empty time-slots and the remaining time-slots are scheduled as non-empty. Then, an edge node must avoid sending its traffic in empty time-slots. Instead, non-empty time-slots can be used for traffic transmission. With respect to this scheduling, the variance of the number of non-empty time-slots that carry traffic from all edge nodes is minimized in the core node at each time-slot, thus reducing the traffic loss. Mathematical formulas are also provided to compute the traffic loss and delay under PTES. Performance evaluation results illustrate that PTES can reduce the number of collision events and traffic loss, especially at light and moderate traffic loads.