Analytic models for highspeed TCP fairness analysis

Abstract

Highspeed TCP (HSTCP) has been proposed to make better use of large congestion window flows. Due to the nature of HSTCPs congestion avoidance increase rate, mathematical analysis of HSTCP fairness is rarely found in the literature. We develop analytic models for HSTCP congestion avoidance. Based on the work for standard TCP fairness analysis in E. Altman et al. (2000), we construct a model to predict the throughput share of two long lived HSTCP flows sharing an adaptive RED buffer, with increasingly disproportionate RTTs. We show that HSTCP inherits standard TCPs problem of fairness of flows with different RTT, even in the ideal case of non-synchronised loss. We also show that in the presence of some degree of loss synchronisation, HSTCPs fairness can degrade rapidly as the ratio of RTT increases. However, we also show that, as the shared buffer's bandwidth increases, adaptive RED is better capable of preventing loss synchronisation.