Understanding the impact of TFRC feedbacks frequency over long delay links

TFRC is a transport protocol specifically designed to carry multimedia streams. TFRC does not enable a reliable and in order data delivery services. However TFRC implements a congestion control algorithm which is friendly with TCP. This congestion control relies in a feedback mechanism allowing receivers to communicate to the senders an experienced drop rate. Although the current TFRC RFC states that there is little gain from sending a large number of feedback messages per RTT, recent studies have shown that in long-delay contexts, such as satellite-based networks, the performance of TFRC can be improved by increasing the feedback frequency. Nevertheless, currently it is not clear how and why this increase may improve the performance of TFRC. Therefore, in this paper, we aim at understanding the impact that multiple feedback per RTT may have (i) on the key parameters of TFRC (RTT and error rate) and (ii) on the network parameters (reactiveness, fairness and link utilization). We also provide a detailed description of the micromechanisms at the origin of the improvements of the TFRC behavior when multiple feedback per RTT are delivered, and determine the context where such feedback frequencies should be applied.