Delay distributions of slotted ALOHA and CSMA

In this paper, we derive the closed-form delay distributions of slotted ALOHA and nonpersistent carrier sense multiple access (CSMA) protocols under steady state. Three retransmission policies are analyzed. We find that under a binary exponential backoff retransmission policy, finite average delay and finite delay variance can be guaranteed for 2 and 4 3, respectively, where is the channel traffic and is the channel throughput. As an example, in slotted ALOHA, ln 2 2 and 3(ln 4 ln 3) 4 are the operating ranges for finite first and second delay moments. In addition, the blocking probability and delay performance as a function of max (maximum number of retransmissions allowed) is also derived.