Evaluating Fairness In Heterogeneous Wireless Ad Hoc Networks

When both TCP Vegas and TCP Reno share the same wired network, TCP Reno dominates and obtains most of the bandwidth due to its more aggressive mechanisms. In this paper, a simulation study of the compatibility of TCP Reno and TCP Vegas in wireless IEEE 802.11 ad hoc networks using both static and mobile network configurations, is presented. It is shown that when both coexist in the same static ad hoc network, TCP Vegas generally dominates and gets most of the wireless bandwidth. The main reason is that the static wireless ad hoc network environment does not favor the aggressive nature of TCP Reno. However, using a mobile network model, it is shown that TCP Reno is slightly more dominant than TCP Vegas. This is because TCP Vegas is more sensitive to node mobility and the resulting high variability of RTT caused by re-routing. This causes TCP Vegas to lose some of its advantages in mobile environments. In all scenarios examined, it is shown that better fairness can be achieved, while not sacrificing goodput performance, via the use of a small TCP maximum window size.