How to Identify the Speed Limiting Factor of a TCP Flow

Despite the end of the Internet bubble, operators continue to increase the capacity of their networks. The question now rises whether these improvements still result in faster communications, or whether most flows are limited by other aspects. In order to answer this question, actual network traffic needs to be analyzed. Therefore, in this paper methods are proposed to identify the factors that limit the speed of TCP flows. Three main categories will be distinguished: the network, the TCP buffers and the application layer. Our proposed methods have been tested on real traces; in many cases it turned out that the network was not the limiting factor.