Bimodal throughput, nonmonotonic delay, optimal bandwidth dimensioning, and analysis of receiver collisions in a single-hop WDM local lightwave network

A wavelength division multiplexing (WDM)-based local lightwave network employing a passive-star topology is considered. Users access the control channel according to the slotted-ALOHA random access protocol and the data channels according to a delayed-ALOHA protocol. It is shown that this system can have a bimodal throughput characteristic if its control channel is over-dimensional (which means that the control channel is allocated a larger share of the total system bandwidth than is needed). A recommendation for proper network-bandwidth dimensioning is made. A finite user population model that enables one to analyze the degradation of the system throughput because of receiver collisions, which could be ignored in infinite population models, is developed. The system´s delay characteristic is also analyzed, and, for the case of an overdimensioned control channel and small values of backoff delay (which is required to resolve packet collisions in a random access system), the mean packet delay is found to be nonmonotic, i.e., the delay can decrease even when the offered load is increased