An Adaptive Virtual Queue (AVQ) Algorithm for Active Queue Management

Virtual queue-based marking schemes have been recently proposed for Active Queue Management (AQM) in Internet routers. We consider a particular scheme, which we call the Adaptive Virtual Queue (AVQ), and study its following properties: its stability in the presence of feedback delays, its ability to maintain small queue lengths, and its robustness in the presence of extremely short flows (the so-called web mice). Using a linearized model of the system dynamics, we present a simple rule to design the parameters of the AVQ algorithm. We then compare its performance through simulation with several well-known AQM schemes such as RED, REM, Proportional Integral (PI) controller, and a nonadaptive virtual queue algorithm. With a view toward implementation, we show that AVQ can be implemented as a simple token bucket using only a few lines of code

Design and performance evaluation of a state-space based AQM

Recent research has shown the link between congestion control in communication networks and feedback control system. In this paper, the design of an active queue management (AQM) which can be viewed as a controller, is considered. Based on a state space representation of a linearized fluid flow model of TCP, the AQM design is converted to a state feedback synthesis problem for time delay systems. Finally, an example extracted from the literature and simulations via a network simulator NS (under cross traffic conditions) support our study

Cost of AQM in stabilizing TCP

In this paper, we propose a unified mathematical framework based on receding horizon control for analyzing and designing AQM (Active Queue Management) algorithms in stabilizing TCP (Transfer Control Protocol). The proposed framework is based on a dynamical system of the given TCP and a linear quadratic cost on transients in queue length and flow rates. We derive the optimal receding horizon AQMs (RHAs) that stabilizes the linearized dynamical system with the minimum cost. Conversely, we show that any AQM with an appropriate structure solves the same optimal control problem with appropriate weighting matrix. We interpret existing AQM's such as RED, REM, PI and AVQ as different approximations of the optimal AQM, and discuss the impact of these approximations on performance

Design of Feedback Controls Supporting TCP Based on the State–Space Approach

This paper investigates how to design feedback controls supporting transmission control protocol (TCP) based on the state-space approach for the linearized system of the well-known additive increase multiplicative decrease (AIMD) dynamic model. We formulate the feedback control design problem as state-space models without assuming its structure in advance. Thereby, we get three results that have not been observed by previous studies on the congestion control problem. 1) In order to fully support TCP, we need a proportional-derivative (PD)-type state-feedback control structure in terms of queue length (or RTT: round trip time). This backs up the conjecture in the networking literature that the AQM RED is not enough to control TCP dynamic behavior, where RED can be classified as a P-type AQM (or as an output feedback control for the linearized AIMD model). 2) In order to fully support TCP in the presence of delays, we derive delay-dependent feedback control structures to compensate for delays explicitly under the assumption that RTT, capacity and number of sources are known, where all existing AQMs including RED, REM/PI and AVQ are delay-independent controls. 3) In an attempt to interpret different AQM structures in a unified manner rather than to compare them via simulations, we propose a PID-type mathematical framework using integral control action. As a performance index to measure the deviation of the closed-loop system from an equilibrium point, we use a linear quadratic (LQ) cost of the transients of state and control variables such as queue length, aggregate rate, jitter in the aggregate rate, and congestion measure. Stabilizing gains of the feedback control structures are obtained minimizing the LQ cost. Then, we discuss the impact of the control structure on performance using the PID-type mathematical framework. All results are extended to the case of multiple links and heterogeneous delays

A Fairness Investigation on Active Queue Management Schemes in Wireless Local Area Network

Active Queue Management (AQM) is scheme to handle network congestion before it happened by deciding which packet has to be dropped, when to drop it, and through which port have to drop when it has become or is becoming congested. Furthermore, AQM schemes such as Random Early Detection (RED), Random Early Marking (REM), Adaptive Virtual Queue (AVQ), and Controlled Delay (CoDel) have been proposed to maintain fairness when unresponsive constant bit rate UDP flows share a bottleneck link with responsive TCP traffic. However, the performance of these fair AQM schemes need more investigation especially evaluation in WLANs environment. This paper provides an experimental evaluation of different AQM schemes in WLAN environment with presence of two different types of flows (TCP flows and UDP flows) to study the behavior of these AQM schemes which might punish some flows unfairly. The simulation method has conducted in this paper by using Network Simulation 2 (ns-2) with the topology of bottleneck scenario. The result has shown that REM and AVQ both obtain higher fairness value than RED and Codel. However, CoDel has given the lowest fairness comparing with RED scheme which have given a moderated value in terms of fairness in WLANs environment. Besides, AQM schemes must be chosen not only based on its performance or capability to indicate the congestion and recovering overflow situation but also considering fairness with different types of flows and the environment as well, such as WLANs environment

Network level performance of differentiated services (diffserv) networks

The Differentiated Services (DiffServ) architecture is a promising means of providing Quality of Service (QoS) in Internet. In DiffServ networks, three service classes, or Per-hop Behaviors (PHBs), have been defined: Expedited Forwarding (EF), Assured Forwarding (AF) and Best Effort (BE). In this dissertation, the performance of DiffServ networks at the network level, such as end-to-end QoS, network stability, and fairness of bandwidth allocation over the entire network have been extensively investigated. It has been shown in literature that the end-to-end delay of EF traffic can go to infinity even in an over-provisioned network. In this dissertation, a simple scalable aggregate scheduling scheme, called Youngest Serve First (YSF) algorithm is proposed. YSF is not only able to guarantee finite end-to-end delay, but also to keep a low scheduling complexity. With respect to the Best Effort traffic, Random Exponential Marking (REM), an existing AQM scheme is studied under a new continuous time model, and its local stable condition is presented. Next, a novel virtual queue and rate based AQM scheme (VQR) is proposed, and its local stability condition has been presented. Then, a new AQM framework, Edge-based AQM (EAQM) is proposed. EAQM is easier to implement, and it achieves similar or better performance than traditional AQM schemes. With respect to the Assured Forwarding, a network-assist packet marking (NPM) scheme has been proposed. It has been demonstrated that NPM can fairly distribute bandwidth among AF aggregates based on their Committed Information Rates (CIRs) in both single and multiple bottleneck link networks