Hardware and MAC Assumptions

We assume that all nodes are using IEEE 802.11a - SSCH could also be used with other MACs in the IEEE 802.11 family, but this evaluation is beyond the scope of our paper. IEEE 802.11a supports 13 orthogonal channels, and we assume no co-channel interference, a reasonable assumption for physically separated nodes [9]. We expect wireless cards to be capable of switching across channels. As we discuss in more detail at the beginning of Section 4, recent work has reduced this switching delay to approximately 80 $\mu$s ([3,17]). We assume that each wireless card contains only a single half-duplex single-channel transceiver.

We require that NICs with a buffered packet wait after switching for the maximum length of a packet transmission before attempting to reserve the medium. This prevents hidden terminal problems from occurring just after switching. This requirement about the hardware is not necessary if the NIC packet buffer can be cleared whenever the channel is switched.