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Effects of Neglecting Buffers in Feed-Forward Design for Web Servers

Kjaer, Martin Ansbjerg LU and Robertsson, Anders LU (2009) Fourth International Workshop on Feedback Control Implementation and Design in Computing Systems and Networks
Abstract
This paper addresses a problem related to control of web servers. Due to implementation issues, relevant measurements are only taken over the a limit 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). We model this and reveals that the unmeasured buffering introduces an extra zero in the relationship between the process control-signal and output. Furthermore, it is shown that a measurement of a disturbance-input actually is state dependent. We also investigate how these new properties affects a traditional feed--forward design. The stability analysis suggests that under certain circumstances, the system becomes unstable due to the... (More)
This paper addresses a problem related to control of web servers. Due to implementation issues, relevant measurements are only taken over the a limit 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). We model this and reveals that the unmeasured buffering introduces an extra zero in the relationship between the process control-signal and output. Furthermore, it is shown that a measurement of a disturbance-input actually is state dependent. We also investigate how these new properties affects a traditional feed--forward design. The stability analysis suggests that under certain circumstances, the system becomes unstable due to the feedback mechanism introduced by the designed feed-forward. We verify the analysis by both simulations and experiments. (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to conference
publication status
published
subject
keywords
Feed-forward, queuing theory, modeling
conference name
Fourth International Workshop on Feedback Control Implementation and Design in Computing Systems and Networks
language
English
LU publication?
yes
id
6b705f6f-f862-4058-93ba-9d4d3bf906b3 (old id 1453985)
date added to LUP
2009-08-05 09:11:59
date last changed
2016-04-16 10:54:10
@misc{6b705f6f-f862-4058-93ba-9d4d3bf906b3,
  abstract     = {This paper addresses a problem related to control of web servers. Due to implementation issues, relevant measurements are only taken over the a limit 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). We model this and reveals that the unmeasured buffering introduces an extra zero in the relationship between the process control-signal and output. Furthermore, it is shown that a measurement of a disturbance-input actually is state dependent. We also investigate how these new properties affects a traditional feed--forward design. The stability analysis suggests that under certain circumstances, the system becomes unstable due to the feedback mechanism introduced by the designed feed-forward. We verify the analysis by both simulations and experiments.},
  author       = {Kjaer, Martin Ansbjerg and Robertsson, Anders},
  keyword      = {Feed-forward,queuing theory,modeling},
  language     = {eng},
  title        = {Effects of Neglecting Buffers in Feed-Forward Design for Web Servers},
  year         = {2009},
}