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Analysis of buffer delay in web-server control

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2 Author(s)
Kjaer, M.A. ; Dept. of Autom. Control, Lund Univ., Lund, Sweden ; Robertsson, A.

This paper addresses a problem related to control of web servers. Due to architectual issues, relevant measurements can only be taken over a limited part of the server system, which leaves the controller unaware of what happens in buffers proceeding the actual web-server (for instance, in the TCP/IP layers). In earlier presented work we modeled such a system and proved that the unmeasured buffering turned a measurement of an input disturbance into a state-dependent variable. In this paper we investigate how these new properties effect a traditional control design consisting of feedback in combination with a feed-forward mechanism. The stability analysis suggests that under certain circumstances, the system enters limit cycles due to the feedback mechanism introduced by the designed feed-forward controller. We verify the analysis by both simulations and experiments.

Published in:

American Control Conference (ACC), 2010

Date of Conference:

June 30 2010-July 2 2010