Reversing the collision-avoidance handshake in wireless networks

Many medium-access control (MAC) protocols for wireless networks proposed or implemented to date are based on collisionavoidance handshakes between sender and receiver. In the vast majority of these protocols, including the IEEE 802.11 standard, the handshake is sender initiated, in that the sender asks the receiver for permission to transmit using a short control packet, and transmits only after the receiver sends a short clear-to-send notification. We analyze the effect of reversing the collision-avoidance handshake, making it receiver initiated and compare the performance of a number of these receiver-initiated protocols with the performance of protocols based on sender-initiated collision avoidance. The receiver-initiated protocols we present make use of carrier sensing, and are therefore applicable to either baseband or slow frequencyhopping radios in which an entire packet can be sent within the same frequency hop (which is the case of FHSS commercial radios that support IEEE 802.11). It is shown that the best-performing MAC protocol based on receiver-initiated or sender-initiated collision avoidance is one in which a node with data to send transmits a dual-purpose small control packet inviting a given neighbor to transmit and asking the same neighbor for permission to transmit.