Discrete-time modeling of TCP Reno under background traffic interference with extension to RED-based routers

Abstract

This paper introduces a discrete-time model which captures the essential protocol features of the congestion control mechanism used by the TCP Reno protocol, subject to interference from other sources. Under this model, a single target session is modeled according to the TCP Reno mechanism, including slow start, congestion avoidance, fast retransmit and fast recovery. At the same time, other sources are modeled as a background process using a discrete batch Markov arrival process (D-BMAP). The D-BMAP process has been modified such that the transitions between the phases are dependent on the number of lost packets from the background process. This introduces a feedback process, which can be used to model an aggregation of TCP sources. In order to capture all the TCP Reno protocol features, two levels of Markov process modeling are used: a microscopic level, at the packet transmission time boundaries, and a macroscopic one, at the start of the new transmission windows. In addition, it is shown how the model can be extended to model networks with RED-based routers.Several performance measures are derived, and numerical examples which demonstrate the protocol features are presented.