We implemented TBR in the HostAP [15] driver running on a Linux PC as a proof of concept. The HostAP driver implements access point functionality so that PCs equipped with popular Prism chipset based 802.11 cards can act as APs. We use unique 6-byte MAC addresses as node identifiers.
We note that TBR requires APs to set up per-node output queue. However,
the total buffer space requirement is comparable between a normal AP and
an AP with TBR. For instance, if an existing AP has the total queue size
of x packets than a TBR-equipped AP can setup n queues each with
packets, where n is the number of competing nodes. For
ease of implementation, our TBR implementation uses FIFO queues. As
explained before, TBR can work with any buffering scheme.
Finally, we note that the current implementation of TBR does not use the retransmission information in computing the packet transfer time but we plan to do so in the future. Thus, TBR in some cases can cause slight biases in granting channel occupancy time to competing nodes. Nonetheless, as we show in Section 5, it does well in achieving its goal.