On the performance of additive increase multiplicative decrease (AIMD) protocols in hybrid space-terrestrial networks

It is well known that TCP does not perform well in networks with large propagation delay and high link loss probability, which are typical in hybrid space-terrestrial networks. Implementing Automatic-Repeat-Request (ARQ) retransmission over satellite links in hybrid networks has been proposed to enhance TCP performance by hiding the link losses from TCP. This paper analyzes the impact of implementing ARQ over satellite links on TCP performance. In particular, this paper focuses on the window flow control mechanism of TCP, and provides an exact model for a hybrid space-terrestrial system with transport layer Additive-Increase-Multiplicative-Decrease (AIMD) protocols and satellite link layer ARQ. Both Go-Back-N (GBN) and Selective-Repeat (SRP) are considered, and the delay of acknowledgements (ACKs) of ARQ are taken into account. The numerical solutions for the throughput as a function of different protocol and packet loss parameters are presented. Both the analysis and numerical results show that in most cases, implementing ARQ over satellite links can significantly improve TCP performance, and that proper choices of the protocol parameters can significantly improve the system performance as well. Although the paper focuses on hybrid space-terrestrial networks, the analysis and results are also applicable to other networks with large bandwidth-delay product and one error-prone bottleneck link.