Effect of TCP on Self-Similarity of Network Traffic

It is now well known that Internet traffic exhibits self-similarity, which cannot be described by traditional Markovian models such as the Poisson process. In this work, we simulate a simple network with a full implementation of TCP-Reno. We also assume Poisson arrivals at the application layer specifically to determine whether TCP can cause self-similarity even when input traffic does not exhibit long-range dependence. Our study shows that, at some loads TCP can induce the appearance of self-similarity. In particular, when load is low and loss is rare, traffic looks Poisson. When load is high and the network is overloaded, TCP congestion control can smooth out the burstiness of the aggregate stream so that traffic at the bottleneck tends to Poisson. However, when load is intermediate and the network is prone to occasional bouts of congestion, as is typical of many networks, traffic can become self-similar. Moreover, factors such as round trip time and number of streams passing through the bottleneck can cause the network to become congested at different loads, and consequently affect the range of load over which self-similarity can be observed. The impact of one self-similar TCP stream has also been observed. In particular, our study show that if one or more streams passing through the bottleneck is self-similar and the aggregate flow does not exceed the capacity, traffic observed at the bottleneck will also be self-similar.