A-DCF: Design and implementation of delay and queue length based wireless MAC

Abstract

Optimal CSMA, which is fully distributed wireless MAC theory, has provided a rule of dynamically adapting CSMA parameters according to some theoretically developed principles, and has reported to offer nice analytical guarantees on throughput and fairness. Despite a couple of research efforts that transfer Optimal CSMA to practical protocols, e.g., O-DCF, our evaluation results show that they are still far from being deployable in practice mainly due to bad performance with TCP. In this paper, we first investigate how Optimal CSMA based MAC conflicts with TCP and degrades end-to-end performance, if poorly transferred to practice. Then, we propose a new wireless MAC protocol, called A-DCF, that inherits the basic framework and rationale of Optimal CSMA and O-DCF, but are largely redesigned to make A-DCF work well with TCP. The key idea of A-DCF lies in smartly exploiting both queue length and delay which widens our design space for compatibility with TCP. Our extensive simulation and experimental results demonstrate that A-DCF outperforms the traditional 802.11 and O-DCF. Particularly, we report our implementation code of A-DCF as a device driver module. To our knowledge, it is the first driver-level implementation of an Optimal CSMA based MAC protocol, being of broad interest to the community.