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Enhancing the performance of TCP over satellite links

Understanding the interaction between TCP and MAC layer protocols in satellite networks is critical to providing high levels of service to users. We separate our study of TCP and MAC layer protocols into two parts. We consider the problem of scheduling at bottleneck links and propose two new queue management algorithms. They are capable of offering higher levels of fairness as well as lower latencies in a variety of scenarios. We also consider the problem of random access in satellite networks and its effect on the functionality of TCP. We propose two queue management schemes: the Shortest Window First (SWF) and the Smallest Sequence Number First (SSF) with Approximate Longest Queue Drop. Our schedulers transmit short messages with minimal delay. The SWF scheduler transmits short messages with low delay without increasing the delay experienced by long messages, provided that short messages do not make up the majority of the load. Our schedulers show increased fairness over other commonly used schedulers when traffic is not homogeneous. They provide higher levels of throughput to isolated misbehaving (high propagation delays or error rates) sessions. We consider the performance of TCP over random access channels. Researchers have extensively studied TCP and random access protocols, specifically ALOHA, individually. However, little progress has been made in understanding their combined performance. Through simulation, we explore the relationship between TCP and ALOHA parameters. We show that TCP can stabilize the performance of ALOHA. In addition, we relate the behavior of ALOHA's backoff policy to that of TCP and optimize parameters for maximum goodput. Thesis Supervisor: Eytan Modiano Title: Assistant Professor