A demand driven access protocol for high speed networks

A demand driven access (DDA) protocol for fiber-optic slotted rings is presented. The proposed protocol is simple and distributed. Under light load conditions, the protocol allows for efficient use of the available bandwidth since no overhead is incurred. In effect, the protocol is demand driven since access arbitration is only activated as the load increases in order to guarantee all nodes a maximum access delay. The protocol is designed for a counter-rotating dual-ring topology. Counter-rotating rings are required to carry backpressure control information in the opposite direction of the data flow. Furthermore, slots are freed at the destination node (as opposed to the source node). This considerably increases the potential throughput of the network. Simulation results demonstrate that for a ring a N nodes, given a uniform destination distribution, a maximum throughput of close to N/4 packets per slot time is achieved under heavy load conditions. Under these load conditions, the average access delay per packet is also on the order of N/4 slot times. The DDA protocol is shown to outperform FDDI both in terms of throughput and access delay