Empirical study on a session layer resource control over 802.11 DCF wireless LAN

Achievement of the QoS guarantee has come to be expected even in the wireless LAN communications. Because it is difficult to realize remodeling the MAC method of layer 2, we focus on the realization of per-flow QoS (throughput) using TCP control in layer 4. In the concrete, TCP-AV which has bandwidth reservation mechanism is used. A lot of paper has already been published about fairness of throughput in terms of the interaction between IEEE802.11 wireless LAN protocol and TCP, evaluated with simulation. However, many problems are remained caused by implementation. In particular, it is difficult only by simulation to evaluate influence that the implementation of the wireless LAN give to a fairness control matter and the influence due by non-equal control of TCP-AV. Thus it is important to evaluate it in the environment where the system is actually used. In this paper, we have investigated the degree of the fairness of per-flow throughput caused by the difference of implementation forms of wireless LAN interfaces, and evaluated per-flow throughput when TCP-AV is employed on wireless LAN on real machines. First, we have examined about the size of buffer of the wireless LAN access point, whether numerical value used by conventional simulation was proper. In addition, we have investigated the reason of the throughput unfairness caused by the difference of implementation forms of wireless LAN interfaces. Furthermore, as a result of evaluation using TCP-AV on a wireless environment, we have confirmed that TCP-AV can guarantee the bandwidth reservation up to 10% more of the fair-share value, which is represented as the maximum bandwidth divided by the number of flows.