Transient performance analysis of nonpersistent CSMA and CSMA-CD protocols

Abstract

A framework for the analysis of the performance of nonpersistent CSMA (carrier sense multiple access) and CSMA-CD (CSMA with collision detection) protocols in a fixed-length time segment is proposed. Closed-form and numerical results that shed new light on the short-term behavior of these protocols and that can be applied to the analysis of integrated protocols are provided. The key parameter ( phi (l)) that influences the protocol behavior is defined, as well as the transient throughput and average packet delay. Curves of phi (l) versus l, of the throughput, and of the average delay as a function of the segment length show interesting characteristics of the protocol behavior. Periodic components can be observed in phi (l), the throughput, and the average delay, particularly in the case of higher traffic. Two periodic components exist in the case of CSMA-CD protocols, with periods equal to the packet length plus one slot and to the jamming time plus one slot. The periodic components are more evident in the CSMA than in the CSMA-CD case. The effect of these periodicities is such that, in some conditions, an increase in the segment length results in a throughput reduction and an increment in the delay. >