TCP-Vegas Slow Start Performance in Large Bandwidth Delay Network

With the rapid expansion of the Internet, it has become possible for end hosts that are separated long apart to be connected through high bandwidth links. This environment, called a Large Bandwidth Delay Network, poses a major challenge to the performance of the Internet. A long-delay connection usually suffers from being treated unfairly when competing with short-delay connections. A link, to avoid being under-utilized, has to be equipped with an a buffer as large as the bandwidth delay product of the longest connection. TCP-Vegas is known as a potential solution to these problems. According to a number of previous studies, it is said to fairly treat connections with different propagation delays and avoid under-utilization even with a buffer that is independent of the bandwidth delay product. In this paper we show, from simulation and analysis, that the current TCP-Vegas does NOT achieve high utilization in such a large bandwidth delay network, because of its slowstart phase. Moreover, to avoid loss, TCP-Vegas slow-start requires a buffer that is proportional to the square root of the bandwidth delay product. We propose a solution to these problems and analyze its performance. Keywords— TCP, congestion control, TCP-Vegas, slowstart, Large Bandwidth Delay, LBD, utilization, convergence delay, burstiness.