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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.comnet.2005.08.005 Byline: Mingwei Gong, Carey Williamson Keywords: Web server performance; Scheduling; Fairness; Simulation; Performance analysis Abstract: This paper uses trace-driven simulation to study the unfairness properties of Web server scheduling strategies, such as Processor Sharing (PS) and Shortest Remaining Processing Time (SRPT). We use a general-purpose probe-based sampling approach to estimate the mean and variance of the job response time for different job sizes, for arbitrary arrival processes and service time distributions. The results illustrate two different aspects of unfairness called endogenous unfairness and exogenous unfairness. We quantify each, focusing on the mean and variance of slowdown conditioned on job size, for a range of system loads. Our work confirms recent theoretical results regarding the asymptotic convergence of scheduling policies with respect to slowdown, and illustrates typical performance results for a practical range of job sizes in an empirical workload. Finally, we show the sensitivities of SRPT and PS scheduling to selected characteristics of the arrival process and job size distribution. Author Affiliation: Department of Computer Science, University of Calgary, 2500 University Drive NW, Calgary, AB, Canada T2N 1N4 Article History: Received 25 January 2005; Revised 24 June 2005; Accepted 19 August 2005 Article Note: (miscellaneous) Responsible Editor: C.B. Westphall

Abstract: TCP (Transmission Control Protocol) is one of the protocols which are widely used in Internet environments. This paper presents an analytical model developed using the stochastic reward net (SRN) modeling technique for the TCP flow behavior in WLANs. The purpose of developing an analytical model is the evaluation of stationary TCP flow behavior. In this paper, we focus the attention on the TCP variant called TCP Reno which is implemented by most operating systems. The performance of TCP Reno is investigated through the SRN model. The model captures aspects such as congestion window (cwd) evolution, slow start and congestion avoidance phases, TCP packet transmissions, management of packet losses due to time-out, and due to generation of triple duplicate acknowledgements. The performance metrics such as throughput and delay of the TCP traffic are obtained using the SRN model. On the basis of these performance measures, the existing unfairness between the downstream and upstream flow at the AP in WLANs is also shown. The proposed analytical model is validated via simulation. [ABSTRACT FROM AUTHOR]