The pi-persistent protocol for unidirectional broadcast bus networks

A protocol for multiaccess communication over unidirectional bus networks is proposed, and its performance capabilities are determined. Under this protocol, time is slotted with a slot equaling a packet´s transmission time. A station with a packet to send persists in transmitting its packet in an empty slot with probability p_i until it is successful. Three criteria for fairness in selection of the p_i are modeled using Markov chains, which are solved to obtain the proper p_i that satisfy each fairness criterion. Unlike previous studies of unidirectional bus networks, stations are allowed to buffer more than one packet. The average packet delay for this protocol is bounded, and the maximum achievable throughput approaches unity with increasing buffer size. Further, the protocol provides better delay versus throughput behavior for fixed packet lengths than previous round-robin schemes, its performance is insensitive to bus characteristics, and it appears to be particularly well suited for fiber-optic network applications requiring long distances and high bandwidths. Simulation results that confirm the predicted performance are included