On TCP performance over asymmetric satellite links with real-time constraints

Real-time transmission over asymmetric satellite IP links is challenging, since satellite systems commonly exhibit long propagation delays, while bandwidth asymmetry often enforces a variable and infrequent rate of acknowledgment packets (ACKs) across the upstream channel with several undesirable implications. In this context, we formulate an analytical model in order to quantify the impact of satellite systems and link asymmetry on TCP performance and real-time delivery. We emphasize on the effects of asymmetric links, and especially on the implications that cause interruptions in the sending rate, and eventually disturb smooth delivery. Since TCP performance is in part throttled by the rate of arriving ACKs, we additionally investigate the impact of delayed ACKs. Although delayed ACKs occasionally diminish the transmission rate, we uncover notable gains in terms of smoothness and real-time delivery. Furthermore, we demonstrate conclusive performance studies tackling the supportive role of selective acknowledgments (SACK) and the effect of varying bit error rates. Our simulation results illustrate that most existing end-to-end solutions do not comply with the stringent Quality of Service (QoS) provisions of time-sensitive applications, resulting in ineffective bandwidth utilization and varying delays in data delivery. Finally, with the absence of a satellite-optimized TCP implementation for real-time transmission, we identify the most prominent end-to-end solutions that manage to alleviate most of the impairments induced by asymmetric satellite links, sustaining a relatively smooth transmission rate. (c) 2007 Elsevier B.V. All rights reserved.