The dynamics of responsiveness and smoothness in heterogeneous networks

Additive increase/multiplicative decrease-based protocols, including transmission control protocol (TCP), TCP-friendly, and a new generation of rate-based protocols, attempt to control the tradeoff of responsiveness and smoothness. Traditionally, smoothness has not been a main concern since it does not impact the performance of regular Internet applications such as the Web, FTP, or e-mail. However, multimedia-driven protocols attempt to favor smoothness at the cost of responsiveness. In general, smoothness and responsiveness constitute a tradeoff; however, we uncover undesirable dynamics of the protocols in the context of wireless/mobile networks with high-error rate or frequent handoffs: low responsiveness is not counterbalanced by gains in smoothness, but instead, produces a conservative behavior that degrades protocol performance with both delay-tolerant and -sensitive applications. Based on our observations, as well as on further analysis of the impact of the bottleneck queue on channel utilization, we seek an alternative strategy for smooth window adjustments. We introduce a new parameter γ, which implements a congestion avoidance tactic and reaches better smoothness without damaging responsiveness.