TCP is competitive against a limited adversary
Jeff A. Edmonds, Suprakash Datta, Patrick W. Dymond · 2003
The well-known Transport Control Protocol (TCP) is a crucial component of the TCP/IP architecture on which the Internet is built, and is a de facto standard for reliable communication on the Internet. At the heart of the TCP protocol is its congestion control algorithm. While most practitioners believe that TCP congestion control algorithm performs very well, a complete analysis of the congestion control algorithm is yet to be done. A lot of effort has, therefore, gone into the evaluation of different performance metrics like throughput and average latency under TCP. In this paper, we approach the problem from a different perspective and use the the competitive analysis framework to provide some answers to the question “how good is the TCP/IP congestion control algorithm? ” First, we prove that for networks with a single bottleneck (or point of congestion), TCP is competitive to the optimal centralized (global) algorithm in minimizing the user-perceived latency or flow time of the sessions, provided we limit the adversary by giving it strictly less resources than TCP. Specifically, we show that with O(1) times as much bandwidth and O(1) extra time per job, TCP is O(1)-competitive against an optimal global algorithm. We motivate the need for allowing TCP to have extra resources by observing that existing lower bounds for nonclairvoyant scheduling algorithms imply that no online, distributed, non-clairvoyant algorithm can be competitive with an optimal offline algorithm if both algorithms were given the same resources. Second, we show that TCP is fair by proving that it converges quickly to allocations where every session gets its fair share of network bandwidth. 1