Queueing analysis of CSMA protocols

It is known that random multiple access protocols, such as CSMA, CSMA/CD, etc, present instability problems. Several mechanisms may be used to overcome this difficulty. For example, in Ethernet, the most well-known implementation of the CSMA/CD protocol, a control scheme is imposed on the retransmission mechanism (exponential backoff). In this paper we consider ap approach that provides for stability and is of an adaptive nature. The basic idea is to alternate CSMA(/CD) and Reservation TDMA periods. The operation of the CSMA(/CD) protocol is interrupted once in a while so that a Reservation TDMA epoch will start. Several criteria which may be used in order to define switching rules from CSMA(/CD) periods to Reservation TDMA periods can be proposed. In this paper analytical models for the description of the Restricted Backlog Protocols in which the size of busy user population is the switching criterion are developed. Their performance is compared with that of the pure CSMA(/CD), the Reservation TDMA and other similar adaptive protocols (Hybrid and Restricted Collision Protocols) and it is shown that the Restricted Backlog Protocols exhibit the best throughput-delay characteristics for both low and high channel utilization.