UC Santa Cruz

All channel-access protocols designed to date based on carrier sensing (namely CSMA, CSMA/CD, CSMA/CA) and the standards based on them (e.g., IEEE 802.11 DCF) have used transmission strategies that are independent of the state of the protocol. In particular, most protocols assume a non-persistent transmission strategy in which a node with a packet to send that detects a busy channel simply backs off. We introduce the first state-aware persistence strategy for carrier-sense multiple access (CSMA) protocols. A node with a packet to send that detects a busy channel decides to transmit once the channel is free depending on whether the ongoing busy period is successful and how early its local packet is ready relative to the start of the ongoing busy period. We provide a simple unifying analysis for CSMA operating in a wireless network with non-persistence and state-aware persistence. Our analysis considers the use of acknowledgments (ACK) and takes into account the effect that receive-to-transmit turnaround times have on performance. The results show that state-based persistence can provide better throughput values relative to a non-persistent strategy, and that new persistence strategies are needed that tailor the amount of persistence to the channel traffic load.