A Review of Router based Congestion Control Algorithms <s> B. Relative Comparison of various router based approach <s> Selective packet dropping policies have been used to reduce congestion and transmission of traffic that would inevitably be retransmitted. For data applications using best-effort services, packet dropping policies (PDPs) are congestion management mechanisms implemented at each intermediate node that decide, reactively or proactively, to drop packets to reduce congestion and free up precious buffer space. While the primary goal of PDPs is to avoid or combat congestion, the individual PDP designs can significantly affect application throughput, network utilization, performance fairness, and synchronization problems with multiple transmission control protocol (TCP) connections. Scalability and simplicity are also important design issues. This article surveys the most important selective packet dropping policies that have been designed for best-effort traffic in ATM and IP networks, providing a comprehensive comparison between the different mechanisms. <s> BIB001 </s> A Review of Router based Congestion Control Algorithms <s> B. Relative Comparison of various router based approach <s> With the rapid proliferation of the WWW, the Internet has seen enormous growth in both the demand for access from its users and in the demand for new services from its applications. This dissertation focuses on these two important challenges to today's Internet: supporting an explosion in the number of users and supporting a myriad of new applications which require more out of the network than the best-effort service that the Internet currently provides. ::: The first half of this dissertation focuses on the problem of maximizing network efficiency in times of extremely heavy congestion. Over the last decade, TCP congestion control has been instrumental in allowing the network to deliver service in times of high demand. Through analysis, simulation, and experimentation, this dissertation uncovers a number of significant weaknesses in TCP's congestion control algorithm and in current active queue management mechanisms such as RED. With additional growth in demand, these weaknesses are shown to severely degrade network efficiency by driving up packet loss rates in the network. To address these shortcomings, several new queue management (Adaptive RED, BLUE) and congestion control algorithms (SUBTCP) are proposed and evaluated. These algorithms are shown to eliminate packet loss and maximize link utilization much more effectively than TCP and current active queue management algorithms can. ::: In addition to packet loss, another problem with today's congestion control and queue management algorithms is that they only deliver applications a single service, best-effort. As the need for new services has grown, the inability to provide service differentiation across flows beyond best-effort service has become problematic. The second half addresses the problem of supporting additional services across the Internet. In particular, these chapters focus on building scalable, deployable mechanisms for supporting bandwidth guarantees across the Internet based on simple priority mechanisms as outlined by the Differentiated Services working group of the IETF. Using minor extensions to the queue management (Enhanced RED) and congestion control algorithms in place today, these mechanisms provide applications more predictable behavior out of the network and enable the deployment of a large number of bandwidth-sensitive applications. <s> BIB002 </s> A Review of Router based Congestion Control Algorithms <s> B. Relative Comparison of various router based approach <s> In active queue management (AQM), core routers signal transmission control protocol (TCP) sources with the objective of managing queue utilization and delay. It is essentially a feedback control problem. Based on a recently developed dynamic model of TCP congestion-avoidance mode, this paper does three things: 1) it relates key network parameters such as the number of TCP sessions, link capacity and round-trip time to the underlying feedback control problem; 2) it analyzes the present de facto AQM standard: random early detection (RED) and determines that REDs queue-averaging is not beneficial; and 3) it recommends alternative AQM schemes which amount to classical proportional and proportional-integral control. We illustrate our results using ns simulations and demonstrate the practical impact of proportional-integral control on managing queue utilization and delay. <s> BIB003 </s> A Review of Router based Congestion Control Algorithms <s> B. Relative Comparison of various router based approach <s> We propose a new active queue management (AQM) scheme to improve the performance of the well-known random early detection (RED) AQM. The new AQM is based on the proportional derivative (PD) control principle, and we call it PD-RED. In PD-RED we introduce minimal changes to RED. We demonstrate the improvement in performance of PD-RED over adaptive RED AQM by simulations. <s> BIB004 </s> A Review of Router based Congestion Control Algorithms <s> B. Relative Comparison of various router based approach <s> Active Queue Management (AQM) can maintain smaller queuing delay and higher throughput by purposefully dropping the packets at intermediate nodes. Almost all the existing AQM schemes neglect the impact of large delay on their performance. In this study, we first show an unexpected fact through simulation experiments, which is the dramatic oscillations appear in the queues controlled by several popular AQM schemes, including RED, PI controller and REM, in large delay networks. With appropriate model approximation, we design a robust AQM controller to compensate for the delay using the principle of internal mode compensation in control theory. Our novel algorithm restrains the negative effect on queue stability caused by large delay. Simulation results show that the integrated performance of the proposed algorithm outperforms that of several well-known schemes when the connections have large delay, while keeping buffer queue short. <s> BIB005 </s> A Review of Router based Congestion Control Algorithms <s> B. Relative Comparison of various router based approach <s> Among various active queue management schemes (AQM), random early detection (RED) is probably the most extensively studied. Unlike the existing RED enhancement schemes, we replace the linear packet dropping function in RED by a judicially designed nonlinear quadratic function. The rest of the original RED remains unchanged. We call this new scheme Nonlinear RED, or NLRED. The underlying idea is that, with the proposed nonlinear packet dropping function, packet dropping becomes gentler than RED at light traffic load but more aggressive at heavy load. As a result, at light traffic load, NLRED encourages the router to operate in a range of average queue sizes rather than a fixed one. When the load is heavy and the average queue size approaches the pre-determined maximum threshold (i.e. the queue size may soon get out of control), NLRED allows more aggressive packet dropping to back off from it. Simulations demonstrate that NLRED achieves a higher and more stable throughput than RED and REM, another efficient variant of RED. Since NLRED is fully compatible with RED, we can easily upgrade/replace the existing RED implementations by NLRED. <s> BIB006 </s> A Review of Router based Congestion Control Algorithms <s> B. Relative Comparison of various router based approach <s> Active Queue Management (AQM) is an effective mechanism to improve the performance of end-to-end congestion control. However, existing AQM schemes are sensitive to network traffic changes. In this paper, we propose a novel AQM algorithm based, for the first time, on the optimized second-order system model, called Adaptive Optimized Proportional Controller (AOPC). AOPC measures the latest packet loss ratio, and uses it as a complement to queue length in order to dynamically adjust packet drop probability. Through using TCP throughput model, AOPC is capable of detaching from the number of TCP sessions N and insensitive to various network conditions. The parameter tuning rule is in compliance with the optimized second-order system model which has a small overshoot and fast convergence speed. We comprehensively evaluate the performances of AOPC through extensive simulations using NS2 simulator, and contrast it with previous approaches such as REM, PI, PID, PIP, and LRED. Simulation results demonstrate that AOPC is more responsive to time-varying network conditions than other algorithms, and obtains the best tradeoff between utilization and delay. <s> BIB007 </s> A Review of Router based Congestion Control Algorithms <s> B. Relative Comparison of various router based approach <s> Several variants of the Transmission Control Protocol (TCP) have been proposed for overcoming the inefficiency of the TCP Reno when operating in high-speed networks. However, these variants by themselves cannot prevent network congestion. Congestion avoidance also relies on other mechanisms, such as Active Queue Management (AQM). This paper introduces a novel optimal AQM policy to operate in networks that adopt the High Speed TCP (HSTCP) variant as their transport protocol. The effectiveness of various optimal controllers is evaluated and the performance of the new policy is compared to that of Random Early Detection (RED) policy. Results, derived via simulation, reveal the advantages of adopting HSTCP-H2 in large bandwidth-delay product networks. <s> BIB008
Sun et al BIB004 have emphasized that heuristic based approach like RED is the most prominent and widely studied AQM. However, it is very difficult to parameterize RED in order to obtain good performance under different congestion scenarios. Ren et al BIB005 commented that the algorithm design based on theoretical analysis and evaluation should be more reliable than one  found that Control theoretic approaches have been widely used to analyze and design mechanisms to improve the performance of various software systems BIB001 . The main reason is that this kind of approach enables the analysis and design for meeting desired steady-state and transient performance goals BIB003 . RED follows heuristic approach. The disadvantage of designing in an ad hoc way is that very little is known about why these AQMs work and very little explanation is given when they fail. Wang et al BIB007 commented that a control theoretic approach gives a framework for network researchers to design an AQM controller to regulate the system. Pi, PID, LRED controllers indeed enhances the performance in wide network scenarios; however, the connatural demerit of these controllers is that the control parameters are configured in particular network scenarios so that they lack of flexibility. The strong correlation between the control parameters and network parameters makes these controllers be prone to be unstable. Santi et al BIB008 pointed that while using heuristic approach, efficient parameter setting is a major challenge. When threshold values are not correctly defined, the performance of RED can be even worse than that of the traditional tail drop policy mechanism. To overcome this difficulty, numerous studies based on heuristics have been conducted  BIB002 . Nonetheless, these studies neither assure that an equilibrium point can be reached nor guarantee stability of queue length. Various studies have been conducted in an attempt to derive an adequate configuration of RED parameters in a systematic way BIB003 BIB006 . One of these approaches is the use of Control Theory to design AQM policies that ensure stability about an equilibrium point. Santi et al BIB008 emphasized that the advantage of the use of control theoretic policies is that they consider the intrinsic nature of feedback in network congestion. In these policies, controllers are responsible for determining the appropriate values of the drop/mark probability so that the queue length will stabilize independent of network conditions.Active Queue Management controllers based on Control Theory are defined to overcome the difficulties in tuning AQM parameters. The design of the controller takes into consideration a detailed description of the system, assuring system stability under various network conditions. From the above discussion it is clear that control theoretic approach of designing router based congestion control algorithms prove its importance as compare to other approaches and is accepted as a major dimension of research by the academicians and practitioners because of its relative advantages.