| 1. |
- Kihl, Maria, et al.
(författare)
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Control-theoretic Analysis of Admission Control Mechanisms for Web Server Systems
- 2008
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Ingår i: World Wide Web. - : Springer Science and Business Media LLC. - 1386-145X .- 1573-1413. ; 11:1, s. 93-116
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Tidskriftsartikel (refereegranskat)abstract
- 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 GI/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 corresponds to the results from the theoretical analysis.
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| 2. |
- Andersson, Mikael, et al.
(författare)
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Admission control of the Apache web server
- 2004
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Ingår i: Seventeenth Nordic Teletraffic Seminar, NTS 17, Fornebu, Norway, 25-27 August 2004. - 8242305951
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 3. |
- Kihl, Maria, et al.
(författare)
-
Analysis of admission control mechanisms using non-linear control theory
- 2003
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Ingår i: Proceedings of the 8th IEEE International Symposium on Computers and Communication. Vol. 2. - 076951961X ; , s. 1306-1311
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Konferensbidrag (refereegranskat)abstract
- All service control nodes can be modelled as a server system with one or more servers processing incoming requests. In this paper we show how non-linear control theory may be used when analyzing admission control mechanisms for server systems. Two models are developed, one linear and one non-linear. We show that, due to the non-linearities appearing in a real server system, linear control theory is sufficient when designing controllers for these systems. With non-linear analysis, however, the dynamics of a server system may be analysed and taken care of by choosing the controller parameters appropriately.
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| 4. |
- Kihl, Maria, et al.
(författare)
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Control theoretic modelling and design of admission control mechanisms for server systems
- 2004
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Ingår i: NETWORKING 2004, Networking Technologies, Services, and Protocols; Performance of Computer and Communication Networks; Mobile and Wireless Communications / Lecture Notes in Computer Science. - 1611-3349 .- 0302-9743. - 9783540219590 ; 3042, s. 1366-1371
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Konferensbidrag (refereegranskat)abstract
- The admission control mechanism is an important part of many communication systems. In this paper we investigate load control mechanisms for server systems, that is systems that may be modelled as queueing systems. We show how control theory can be used when designing controllers for a G/G/1-system. We design a PI-controller for the system and compare the steady-state and transient behavior of this controller with the behavior of a static controller.
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| 5. |
- Kihl, Maria, et al.
(författare)
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Performance Modelling and Control of Server Systems using Non-linear Control Theory
- 2003
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Ingår i: Providing quality of service in heterogeneous environments : proceedings of the 18th International Teletraffic Congress, ITC-18, Berlin, Germany, 31 August - 5 September 2003 (Teletraffic science and engineering ; vol. 5). - 0444514554 ; 5A-B, s. 1151-1160
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Konferensbidrag (refereegranskat)abstract
- All service control nodes, for example SCPs, HLRs, and MSCs, are constructed as a server system with one or more servers that process incoming requests. Since service control nodes are sensitive to overload, admission control mechanisms are often implemented. In this paper, we model and analyse admission control mechanisms for server systems with control theoretic methods. We develop a nonlinear stochastic control theoretic model of a GI/G/1-system. Further, we show that this model can be used to design admission control mechanisms that behave well in the “real” system, that is the queuing system. We develop two types of controllers for the system, one PI-controller and one RST-controller, both commonly used in automatic control. Also, we discuss some of the limitations of previous work in this area, in which only deterministic and linear models have been used.
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| 6. |
- Robertsson, Anders, et al.
(författare)
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Admission control for Web server systems - design and experimental evaluation
- 2004
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Ingår i: 43rd IEEE Conference on Decision and Control : Nassau, Bahamas, 14 - 17 December 2004. - 0780386825 ; , s. 531-536
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Konferensbidrag (refereegranskat)abstract
- In communication systems, all service control nodes, such as for example Web sites or mobile switching centers, can be modeled as a server system with one or more servers processing the incoming requests. To avoid overload at the service node some type of admission control mechanism is usually implemented to guarantee good performance also during high traffic loads. In this paper we investigate, from a control point of view, the nonlinear discrete-time modeling of a server system, and the analysis and design of load control mechanisms based upon this model. Verification of the server model behavior with respect to queue theoretic models are made and the load control mechanisms are implemented on an Apache Web server and experimentally evaluated.
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| 7. |
- Robertsson, Anders, et al.
(författare)
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Analysis and design of admission control systems in web-server systems
- 2003
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Ingår i: Proceedings of the 2003 American Control Conference. Vol. 1. - 0743-1619. - 0780378962 ; , s. 254-259
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Konferensbidrag (refereegranskat)abstract
- All service control nodes, for example Web sites or Mobile Switching Centers, can be modeled as server systems with one or more servers processing the incoming requests. To avoid overload at the service control node different types of admission control mechanisms are usually implemented. In this paper we discuss, from a control point of view, the modeling of a service control-node. The queue is assumed to be an M/G/1-system and is modeled by a nonlinear flow model and a simplified discrete-time model is used in the analysis and design of the system. An admission control system based on a PI-controller combined with an anti-reset windup feature is developed. The stability of the admission control system is analyzed and the stability of the closed loop system is proved. The results from the simplified queue model are verified through discrete-event simulations of the system.
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| 8. |
- Robertsson, Anders, et al.
(författare)
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Design and evaluation of load control in web-server systems
- 2004
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Ingår i: Proceedings of the 2004 American Control Conference, ACC : June 30 - July 2, 2004, Boston Sheraton Hotel, Boston, Massachusetts. - 0743-1619. - 0780383354 ; , s. 1980-1985
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Konferensbidrag (refereegranskat)abstract
- 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. Finally, experimental evaluation is performed on an Apache Web server in a laboratory network. A traffic generator is used to represent client requests. The control of the Apache server has been re-written to implement our algorithms. We show that the control theoretic model aligns well with the experiments on the Web-server. Measurements in the laboratory setup show the robustness of the implemented controller, and how it corresponds to the results from the theoretical analysis and the simulations.
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