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A robust active queue management scheme for network congestion control
Zhou C., He J., Chen Q. Computers and Electrical Engineering39 (2):285-294,2013.Type:Article
Date Reviewed: Jul 31 2014

Transmission control protocols (TCP) at the senders and queue management schemes at the intermediate routers have been made to cooperate in order to improve the efficiency of computer networks. In this paper, the authors propose “a novel robust active queue management (AQM) scheme based on H-infinity feedback control theory.” The AQM scheme utilizes a feedback controller that maintains queue length stability and robustness against various external disturbances and against perturbations that are induced in typical TCP models. The authors set controller parameters according to the linear matrix inequality techniques.

This topic has been studied for quite some time. Many AQM schemes have been proposed to address queue stability and robustness issues, such as random early detection (RED), RED-based variants (such as gentle random early detection (GRED)), controlled delay (CoDel), approximated fair and controlled delay (AFCD), and others. However, the authors argue that some issues still remain open. The first is the aforementioned issue of robustness against disturbances. The second is that “the modeling uncertainties or the model perturbations for the TCP/AQM network are not considered simultaneously with link capacity disturbance.” Therefore, the most significant contribution of this paper is the development of a robust AQM algorithm for the TCP flow model that accounts for such disturbances and modeling perturbations. Previous AQM schemes, such as RED, CoDel, and AFCD, do not focus much on modeling the TCP/AQM networks under disturbances and uncertain circumstances.

The authors start with a fluid model of TCP dynamics, which is pretty typical in previous works. They formulate their own H-infinity control design for an AQM system with a sufficient condition for asymptotic stability. The parameters of the feedback controller are set based on linear matrix inequality techniques. The novel H-infinity control design provides robust state feedback for the TCP/AQM system; therefore, the formula may be a good guideline for determining the robust state of the TCP/AQM system in the future.

The evaluation part of the paper is weak. The authors evaluate the performance of the proposed RC scheme in NS2 simulation. Compared to other peer AQM schemes such as PI, REM, and RED, the RC scheme seems to have a lower queue length and a more stable queue. To demonstrate robustness, the authors show the packet loss rate under time-varying flows. They show that the RC scheme is robust against traffic flows that vary with time. However, some other scenarios are overlooked, such as different networking topologies, larger link capacity, and longer round-trip time (RTT). Moreover, recently published AQM schemes, which are more focused on queue stability and robustness issues, such as CoDel and AFCD, are not considered in the evaluation part.

Reviewer:  Lin Xue Review #: CR142573 (1411-0957)
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Network Management (C.2.3 ... )
 
 
Network Protocols (C.2.2 )
 
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