Admission control for Web server systems - design and experimental evaluation

evaluatio

adaptive control

xvi.574 : 24 c

Dynamic Pictures and Interactive Learning

The paper presents interactive learning tools used in courses in automatic control at Lund Institute of Technology. The learning tools are aimed at improving the understanding of and intuition for the abstract parts of the control courses. The paper presents dynamic interactive modules for a course in sampled-data systems. The tools are implemented in Matlab and used over Internet. 1. Introduction Most engineering courses contains abstract concepts that are important for the understanding of the material. Examples in control courses are controllability, observability, and the connection between di#erent representations #time domain and frequency domain#. Often it is di#cult to convey the intuition to the students through conventional lectures and problem solving sessions. To learn a subject the students need to be active. The old rule #learning by doing" is still very relevant. Laboratory experiments are good for the understanding. However, the laboratory experiments must, in general..

Minimum variance prediction of linear time-varying systems

In this paper we study the problem of minimum variance prediction for linear time-varying systems. We consider the standard time-varying autoregression moving average (ARMA) model and develop a predictor which guarantees minimum variance prediction for a large class of linear time-varying systems. The predictor is developed based on a pseudocommutation technique for dealing with noncommutativity of linear time-varying operators in a transfer operator framework. We also show connections between this input-output predictor and the Kalman predictor via an example

Design and Evaluation of Load Control in Web Server Systems

Nonlinear discrete-time modeling of a web server system is investigated. Server systems typically contain nonlinearities such as saturations and bounded queue lengths. The incoming traffic and service rates are best modeled by stochastic processes, well described and analyzed by queuing theory. Here, we develop and validate a control theoretic model of a general single server queue, a so-called G/G/1-system. Based on the nonlinear system model, design of admission controllers are presented and the closed loop stability is analyzed. The behavior of the server model is verified with respect to queue theoretic models

Admission Control of the Apache Web Server

Web sites are exposed to high rates of incoming requests. The servers may become overloaded during temporary traffic peaks when more requests arrive than the server is designed for. An admission control mechanism rejects some requests whenever the arriving traffic is too high and thereby maintains an acceptable load in the system. This paper presents how admission control mechanisms can be designed with a combination of queueing theory and control theory. In this paper we model an Apache web server as a G/G/1-system and then design a PI-controller, commonly used in automatic control, for the server. The controller has been implemented as a module inside the Apache source code. Measurements from the laboratory setup show how robust the implemented controller is, and how it correspond to the results from the theoretical analysis. I