This paper deals with optimizing end-to-end window control algorithms that achieve proportional fairness in the long run, and also investigating their steady state and transient or short-term fairness. An abstracted stochastic model of a bottlenecked connection is employed and the window control is designed to minimize the buffer queue variance while keeping the mean queue level at a target value, taking the round-trip delay into account. An optimal minimum variance window control algorithm and its generalized version are derived with the major aim of reducing the window size fluctuations. A relation between the generalized version and the (p, 1) proportionally fair algorithm is investigated. Also we derive the stability limits of the generalized minimum variance window control algorithm which can be useful during network design. The effects of both the target queue length and a weighting parameter on the steady state and short-term fairness, as measured by Jain's fairness and short-term fairness indices, calculated over short time intervals, are investigated by simulation. The generalized algorithm has better fairness properties as compared to existing algorithms such as that employed in TCP Vegas.

The emerging, ATM network will support permanent, semi-permanent and switched virtual channel connections (SVCC). A number of simulation studies have been carried out to study the performance of SVCCs using empirical data. The absence of an analytical model has prevented the study of SVCCs under known traffic distributions. In this paper, we develop a new delayed vacation model to facilitate the performance study of SVCCs with configurable inactivity timer in the ATM network interface card (NIC). Comparison with simulation results indicates that the proposed model is very accurate and can be effectively used to optimise the performance of SVCCs by selecting an appropriate inactivity timer.