MODELLING TCP TRAFFIC: A STATE-BASED APPROACH

Abstract

In this paper, a state-based modelling of TCP traffic is presented. During a connection, TCP stays in either of the following states: Slow Start, Congestion Avoidance, Loss Recovery (Fast Recovery and/or Fast Retransmit) and Time Out. We propose the use of discrete-time batch Markov process (D-BMAP) to model the traffic generated by a TCP connection. The main contributions of the paper are the followings. Firstly, we provide a simple unified model for all well-known versions of TCP-based on the D-BMAP process. Secondly, we introduce a new concept, namely the TCP characterization matrix for a TCP connection that characterizes the transition probabilities between the states of TCP. This matrix is crucial in our state-based analysis. Thirdly, we present a technique to detect the states of TCP. We have developed our technique into a tool called TCP-ASD that automates state detection of a TCP connection. Our tool can automatically detect the beginning and the end of the states of TCP and thus the sojourn time distributions as well as other statistics that we use in our analysis. We also discuss the trade-offs between simplicity and accuracy in the state-based approach. Finally, we use simulation and numerical analysis to validate our proposed model.