Unslotted deflection routing in all-optical networks

When nodes of a communication network have identical input- and output-link capacities, it is possible to use as few as one packet buffer per link, if one is willing to deflect-or misroute-a subset of simultaneously arriving fixed-length packets from preferred to alternate output links. This scheme, known as deflection routing, can achieve very fast packet switching in regular networks and has been proposed as the basic routing and switching protocol of several all-optical networks. The performance models of deflection-routing networks that have appeared in the literature have assumed that time is slotted and packets arrive at nodes on time-slot boundaries. In practice, however, slotted operation is difficult to implement in all-optical networks. The present authors evaluate by simulation the performance of deflection routing in unslotted networks. The evaluations show a surprising degradation of throughput in unslotted deflection routing networks, compared to slotted networks, and reveal situations where severe congestion occurs. To overcome these limitations they propose the use of specific control mechanisms in unslotted networks that allow one to eliminate congestion and to improve substantially the network throughput