We develop a general methodology for characterizing Web server access patterns based on a spectral analysis of finite collections of observed data from real systems. Our approach is used together with the access logs from the IBM Web site for the 1996 Olympic Games to demonstrate some of its advantages over previous methods and to analyze certain aspects of large-scale Web server performance.

Queueing networks are a powerful abstraction for modeling systems involving contention for resources, e.g., manufacturing lines and computer systems. Queueing networks are especially effective in modeling computer communication systems. Most papers concerning queueing models of communication describe analytic solution of queueing models. This paper describes simulation models based on "extended" queueing networks. The primary advantage of using a queueing network representation for simulation of a computer communication system is the high level of description, in comparison with conventional simulation programming languages. For queueing network models to be used effectively for simulation of contention systems, appropriate software is needed. The research queueing package (RESQ) is a general purpose tool for modeling contention for resources and associated system characteristics. RESQ facilitates i) appropriate abstraction of system characteristics through its definitions of extended queueing networks, ii) efficient and convenient definition and revision of models through its integrated interactive and batch model definition interface, and iii) effective experimentation with simulation models through facilities for parameterized sets of experiments, interactive running of simulations and statistical analysis of simulation results. With a tool such as RESQ, an analyst can produce results in days instead of weeks, and so an analyst can answer questions which otherwise would be left unanswered.

Abstract Several requirements are placed on queueing models of computer systems. These include credibility, accuracy, timeliness and cost. Modelling software can have critical impact on all of these requirements. We survey the characteristics of major pieces of queueing software. Based on this survey we synthesize a set of design objectives for queueing software. Finally, we discuss our own queueing network software, the Research Queueing Package (RESQ), in light of these objectives.