A Review of Router based Congestion Control Algorithms <s> A. Available methods for Router based Congestion Control <s> Abstract This paper describes the Dynamic-RED (DRED) algorithm, an active queue management algorithm for TCP/IP networks. In random early detection (RED), one of the goals is to stabilize the queue lengths in routers. However, the current version of RED does not succeed in this goal because the equilibrium queue length strongly depends on the number of active TCP connections. Using a simple control-theoretic approach, DRED randomly discards packets with a load-dependent probability when a buffer in a router gets congested. Over a wide range of load levels, DRED is able to stabilize a router queue occupancy at a level independent of the number of active TCP connections. The algorithm achieves this without estimating the number of active TCP connections or flows and without collecting or analyzing state information on individual flows. The benefits of stabilized queues in a network are high resources utilization, bounded delays, more certain buffer provisioning, and traffic-load-independent network performance in terms of traffic intensity and number of connections. <s> BIB001 </s> A Review of Router based Congestion Control Algorithms <s> A. Available methods for Router based Congestion Control <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> BIB002 </s> A Review of Router based Congestion Control Algorithms <s> A. Available methods for Router based Congestion Control <s> Active queue management disciplines such as RED and its extensions have been widely studied as mechanisms for providing congestion avoidance, differentiated services and fairness between different traffic classes. With the emergence of new applications with diverse Quality-of-Service requirements over the Internet, the need for mechanisms that provide differentiated services has become increasingly important. We propose fair adaptive bandwidth allocation (FABA), a buffer management discipline that ensures a fair bandwidth allocation amongst competing flows even in the presence of non-adaptive traffic. FABA is a rate control based AQM discipline that provides explicit fairness and can be used to partition bandwidth in proportion to pre-assigned weights. FABA is well-suited for allocation of bandwidth to aggregate flows as required in the differentiated services framework. Since FABA can be extended to scenarios such as aggregate, hierarchical and weighted flows, it can serve as a useful method for enforcing service level agreements at the edge of the network. We study and compare FABA with other well known queue management disciplines and show that FABA ensures fair allocation of bandwidth across a much wider range of buffer sizes at a bottleneck router. Further, FABA is shown to give high values of fairness coefficient for diverse applications such as FTP, Telnet and HTTP. FABA uses randomization and has an O(1) average time complexity, and, is therefore scalable. The space complexity of the proposed algorithm is O(B) where B is the buffer size at the bottleneck router. We argue that though FABA maintains per active-flow state, through O(1) computation, reasonably scalable implementations can be deployed which is sufficient for network edges. <s> BIB003 </s> A Review of Router based Congestion Control Algorithms <s> A. Available methods for Router based Congestion Control <s> In this paper, we propose a new AQM algorithm that considers both the average queue length and the estimated packet arrival rate together in order to detect and control incipient congestion. It predicts the average queue length and controls it to maintain a certain reference value to achieve high link utilization and low queueing delay. Simulation results confirm the stability of our proposed algorithm under various network environments and show its performance advantages over other competitive AQM algorithms <s> BIB004 </s> A Review of Router based Congestion Control Algorithms <s> A. Available methods for Router based Congestion Control <s> A new rate-based active queue management (AQM) algorithm, called Yellow, is proposed in the paper. Yellow uses the load factor (link utilization) as a main merit to manage congestion. To improve congestion control performance, a queue control function (QCF) is introduced as a secondary merit. The sufficient condition for globally asymptotic stability is presented based on Lyapunov theory. Furthermore, the principle for parameter settings is given based on the bounded stable conditions. We then illustrate that Yellow outperforms the recently proposed AQM algorithms in terms of link utilization, packet loss and robust performance through extensive simulations. <s> BIB005 </s> A Review of Router based Congestion Control Algorithms <s> A. Available methods for Router based Congestion Control <s> This paper proposes a rate-based active queue management algorithm or RAQM. It uses the aggregated traffic input rate to calculate packet drop probability according to an exponential rule. The proposed RAQM algorithm works in two modes: queue-independent and queue-dependent. In the queue-independent mode, it only relies on the aggregate traffic input rate to regulate the input rate to the expected value, i.e. expected link utility. In the queue-dependent mode, it also uses the instantaneous queue length to further adjust the packet drop probability and to regulate the queue length to the expected value. We analyze the stability and investigate practical implementation issues of the RAQM. Simulations are carried out to study RAQM performance and to compare with other AQM algorithms, in particular PI and REM schemes. The results demonstrate that RAQM achieves better stability and faster response as it can quickly regulate the queue length to the expected value with small overshoot. RAQM also obtains better tradeoff between link utilization and queuing delay, and obtains higher goodput with the same buffer size as in PI and REM schemes. Finally RAQM has O(1) complexity, thus independent of the number of flows. <s> BIB006 </s> A Review of Router based Congestion Control Algorithms <s> A. Available methods for Router based Congestion Control <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> BIB007 </s> A Review of Router based Congestion Control Algorithms <s> A. Available methods for Router based Congestion Control <s> Active queue management (AQM) is an effective means to enhance congestion control, and to achieve trade-off between link utilization and delay. The de facto standard, random early detection (RED), and many of its variants employ queue length as a congestion indicator to trigger packet dropping. Despite their simplicity, these approaches often suffer from unstable behaviors in a dynamic network. Adaptive parameter settings, though might solve the problem, remain difficult in such a complex system. Recent proposals based on analytical TCP control and AQM models suggest the use of both queue length and traffic input rate as congestion indicators, which effectively enhances stability. Their response time generally increases however, leading to frequent buffer overflow and emptiness. In this paper, we propose a novel AQM algorithm that achieves fast response time and yet good robustness. The algorithm, called Loss Ratio-based RED (LRED), measures the latest packet loss ratio, and uses it as a complement to queue length for adaptively adjusting the packet drop probability. We develop an analytical model for LRED, which demonstrates that LRED is responsive even if the number of TCP flows and their persisting times vary significantly. It also provides a general guideline for the parameter settings in LRED. The performance of LRED is further examined under various simulated network environments, and compared to existing AQM algorithms. Our simulation results show that, with comparable complexities, LRED achieves shorter response time and higher robustness. More importantly, it trades off the goodput with queue length better than existing algorithms, enabling flexible system configurations <s> BIB008 </s> A Review of Router based Congestion Control Algorithms <s> A. Available methods for Router based Congestion Control <s> We focus on the problem of the stability of congestion control for networks with large round-trip communication delays. Nearly all the existing AQM schemes neglect the impact large communication delay has on system behavior, such as stability, robustness and convergence. The drastic queue oscillations in large delay networks of PI, REM and DC-AQM decrease link utilization and introduce avoidable delay jitter. To address this problem, we propose a robust IMC-PID congestion controller based on the internal model control principle to restrict the negative impact of the stability caused by large delay. Simulation results demonstrate that the integrated performance of our proposed scheme outperforms others as communication delay increases, and achieves high link utilization and small delay jitter. <s> BIB009 </s> A Review of Router based Congestion Control Algorithms <s> A. Available methods for Router based Congestion Control <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> BIB010 </s> A Review of Router based Congestion Control Algorithms <s> A. Available methods for Router based Congestion Control <s> Random early detection (RED) is an effective congestion control mechanism acting on the intermediate gateways. We describe a new active queue management scheme, Effective RED (ERED) that aims to reduce packet loss rates in a simple and scalable manner. We made a few change to packet drop function of existing RED scheme. The rest of the original RED remains unchanged. We achieve this by making several refinements and by controlling packet dropping function both with average queue size and instantaneous queue size. Simulations demonstrate that ERED achieves a highest throughput and lowest packet drops than RED, Blue, REM, FRED, LDC and SRED. Since ERED is fully compatible with RED, we can easily upgrade/replace the existing RED implementations by ERED. <s> BIB011 </s> A Review of Router based Congestion Control Algorithms <s> A. Available methods for Router based Congestion Control <s> Two major goals of queue management are flow fairness and queue-length stability However, most prior works dealt with these goals independently. In this paper, we show that both goals can be effectively achieved at the same time. We propose a novel scheme that realizes flow fairness and queue-length stability. In the proposed scheme, high-bandwidth flows are identified via a multilevel caching technique. Then, we calculate the base drop probability for resolving congestion with a stable queue, and apply it to individual flows differently depending on their sending rates. Via extensive simulations, we show that the proposed scheme effectively realizes flow fairness between unresponsive and TCP flows, and among heterogeneous TCP flows, while maintaining a stable queue. <s> BIB012 </s> A Review of Router based Congestion Control Algorithms <s> A. Available methods for Router based Congestion Control <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> BIB013 </s> A Review of Router based Congestion Control Algorithms <s> A. Available methods for Router based Congestion Control <s> Active queue management has been proved to be an effective mechanism at the intermediate nodes to alleviate network congestion. A novel robust active queue management scheme based on H-infinity feedback control theory is proposed in this paper. A TCP model with link capacity disturbances, modeling uncertainties and time-varying delay is investigated, and the objective is to design a feedback controller which guarantee the queue length stability and robustness against the external disturbances and model perturbations. Meanwhile a simple on-line estimation of TCP window size is adopted instead of state observer which reduces computation burden significantly. The controller parameters are obtained through the standard linear matrix inequality techniques. Finally NS-2 simulation results demonstrate effectiveness of the proposed method. <s> BIB014
Kamara et al BIB003 (2004) stated that with the emergence of new applications with diverse Quality-ofService requirements over the Internet, the need for mechanisms that provide differentiated services has become increasingly important and they proposed FABA a rate control based AQM discipline that is well suited to network edges or gateways (e.g., the ISPs). Long et al BIB005 (2005) demonstrated the inherent weakness of current rate-based active queue management algorithms and proposed a new AQM method 'Yellow' with key design goals to predict incipient congestion timely and accurately with controlled queuing delays, stability, and robustness to variation in traffic load. Liu et al  (2005) introduced and analyzed a decentralized network congestion control algorithm which has dynamic adaptations at both user ends and link ends, a so-called general primal-dual algorithm and introduced an AQM scheme Exponential-RED (E-RED) which outperforms RED with larger throughput and lower queuing delay and is inherently stable when combined with TCP-Reno or its variants for high-speed networks. Wang et al BIB006 (2005) proposed rate-based algorithm 'RAQM' which uses the aggregated traffic input rate to iteratively compute the packet drop probability according to an exponential rule, in order to regulate the input rate to an expected value. RAQM obtains good stability and fast response under diverse network environment and can regulate the queue length to an expected value and achieve a better tradeoff between goodput and queuing delay. Hong et al BIB004 Copyright © 2014 MECS I.J.Computer Network and Information Security, 2014, 1, 1-10 (2007) proposed a new AQM algorithm 'PAQM' that considers both the average queue length and the estimated packet arrival rate together in order to detect incipient congestion. The proposed algorithm predicts the average queue length and controls it to maintain a certain reference value to achieve high link utilization and low queuing delay and has low complexity and easy configuration. Abbasov et al BIB011 (2009) proposed effective-RED a refinement to classic RED scheme with aims to reduce packet loss rates in a simple and scalable manner. Kim et al BIB012 (2011) stated that flow fairness and queue-length stability are the two major goals of queue management however; most prior works dealt with these goals independently. They proposed a new scheme 'P-AQM' which consists of a multilevel caching technique to detect high-bandwidth flows accurately with minimal overhead; and a drop policy for achieving both flow fairness and queue-length stability at the same time. 2) Optimization Approach Lapsley et al  (1999) first proposed an optimization approach to congestion control method REM which was derived from earlier work on the Optimization Flow Control (OFC). REM uses Proportional Marking and Online measurement techniques for congestion control which results in fairer bandwidth sharing and allows for the provision of differentiated services between users. 3) Control Theoretic Approach Aweya et al BIB001 (2001) stated that it is difficult to parameterize RED queues to perform well under different congestion scenarios and further considered router queue length stabilization as one of the goal of queue management methods. They commented that traditional RED does not succeed in this goal because the equilibrium queue length strongly depends on the number of active TCP connections and first proposed a simple Control Theoretic Approach, DRED randomly discard packets with a load-dependent probability when a buffer in router gets congested and is able to stabilize a router queue occupancy at a level independent of the number of active TCP connections which results in high resource utilization, bounded delays, more certain buffer provisioning and traffic-load-independent network performance. Hollot et al BIB002 (2002) analyzed a combined TCP and AQM model from a control engineering standpoint and uncovered limitations of the averaging algorithm in RED. Further they proposed and designed two alternative AQM controllers, first one was 'proportional controller' which showed good transient response but suffered steady-state errors in queue regulation, second one was 'PI controller' which exhibited better performance under all cases considered. Ren et al BIB007 (2005) found that almost all the existing AQMs schemes neglected the impact of large delay on their performance and they first showed an unexpected dramatic oscillation appear in the queues controlled by several popular AQM schemes, including RED, PI controller and REM, in large delay networks. With appropriate model approximation, they design a robust AQM controller 'DC-AQM' to compensate for the delay using the principle of 'internal mode compensation' in control theory and found that DC-AQM algorithm is superior to other algorithms for large delay and small reference queue length. Chang et al  (2006) proposed a queue-based adaptive PI controller 'Q-SAPI' for AQM with a aim to improve the transient performance of the fixed-gain PI controller while maintaining its steady-state performance over a wide range of uncertainties and showed its versatile ability in addressing the tradeoff between responsiveness and small steady-state error under the dynamic network and traffic conditions. Wang et al BIB008 (2007) proposed a novel AQM method 'LRED" which first incorporated packet loss ratio as a complement to queue length for congestion estimation and further they found that the use of packet loss ratio enables LRED to catch network dynamics in time, thus achieving fast control response and better performance in terms of goodput, average queue length, and packet loss ratio. Wang et al BIB009 (2008) have focused on the problem of the stability of congestion control for networks with large round-trip communication delays and commented that nearly all the existing AQM schemes neglected the impact large communication delay has on system behavior, such as stability, robustness and convergence which results in low link utilizations and/or high delay jitters. To address the congestion control stability issue they proposed a congestion controller, called 'IMC-PID' which was able to restrict the negative impact on queue stability caused by large delay. Wang et al BIB010 (2008) further proposed a novel AQM based on the 'optimizedsecond-order-system' model, called Adaptive Optimized Proportional Controller(AOPC) which is more responsive to time varying network conditions than other algorithms and achieve the best tradeoff between utilization and delay. Kim et al BIB012 (2011) have proposed a novel scheme which consists of a multilevel caching approach which detect high-bandwidth flows accurately with minimal overhead; and a drop policy for achieving both flow fairness and queue-length stability simultaneously. Santi et al BIB013 (2011) first introduced a novel optimal AQM approach to operate in large bandwidth-delay product networks which uses HSTCP as its transport protocol. Zhou et al BIB014 (2013) have given a novel robust active queue management scheme based on H-infinity feedback control theory for the Internet TCP flow model. For the purpose of our study and based on the above discussion, we propose here a revised taxonomy of Router based Congestion control approaches as in Fig.1 .