OBS中TCP业务的分段指示拥塞控制策略

传统的TCP拥塞控制算法主要是针对电通信网络中包交换机制提出的,当这种拥塞控制算法应用到光突发交换（OBS）中会出现很多问题,甚至会使网络性能急剧恶化。为了改善传统的TCP拥塞控制算法在OBS网络中的性能,提出了一种分段指示拥塞控制技术,它能根据光网络链路的占用情况,在OBS边缘节点随机地标记不同TCP流的数据包以阻止网络拥塞。该方法不仅能对网络拥塞迅速地做出反应,而且还能应对OBS的假超时现象（FTO）,进一步改善OBS网络的性能。     

TCP-Cherry for satellite IP networks: Analytical model and performance evaluation

TCP-Cherry is a novel TCP congestion control scheme that we devised for ensuring high performance over satellite IP networks and the alikes which are characterized by long propagation delays and high link errors. In TCP-Cherry, two new algorithms, Fast-Forward Start and First-Aid Recovery, have been proposed for congestion control. Our algorithms use supplement segments, i.e., low-priority segments to probe the available bandwidth in the network for the TCP connections along with carrying new data blocks. In this paper, we present our new congestion control scheme, TCP-Cherry and devise an analytical model for it. Our major contributions in this paper include the analytical model and equations for performance evaluation, validation of the analytical model through comparison between analytical and simulation results and devising a guideline to tune the buffer related parameters both at the sender as well as the receiver ends for optimum throughput performance. Experiments show that simulation results and the calculated throughput from our analytical model match quite closely, thereby verifying the appropriateness of the model. In addition, from analysis of simulation results, we discover that a buffer size at the receiver, rwnd, that is around four times maxcwnd, or the maximum congestion window at the sender side, is likely to maintain high throughput over a wide range of operating conditions.     

TCP-aware network coding with opportunistic scheduling in wireless mobile ad hoc networks

This paper presents a scheme that employs TCP-aware network coding with opportunistic scheduling to enhance TCP throughput in wireless mobile ad hoc networks. Specifically, it considers a TCP parameter, congestion window size, and wireless channel conditions simultaneously to improve TCP throughput performance. Evaluation of this scheme is carried out by using ns2 simulations in different scenarios. The results show that the proposed scheme gives approximately 35% throughput improvement in a high mobility environment and about 33% throughput increase in no or low mobility environment as compared to traditional network coding with opportunistic scheduling. This paper also proposes a new adaptive-W (i.e., adaptive Waiting time) scheme whose objective is to adaptively control waiting time of overheard packets that are stored in a buffer to achieve tradeoff between throughput and overhead.     

一种Ad Hoc网络端到端的TCP拥塞控制改进方案

传统的TCP协议是为有线网络而设计的,它假定数据包的丢失是由网络拥塞引起的,然而在Ad Hoc网络中,除拥塞丢包外,其它非拥塞因素也会引起数据包的丢失。分析Ad Hoc网络影响TCP性能的主要因素,在原有拥塞控制方案MMJI的基础上,提出了一种端到端的TCP拥塞控制改进方案（Imp MMJI）。该方案能根据前向路径跳数自适应调整拥塞窗口的大小,防止拥塞窗口过快增长,当发生路由改变或链路中断时,重新计算拥塞窗口cwnd和ssthresh的值,以确保路由重建前后TCP连接负载率的一致性;并在ACK应答包的TCP首部增加了状态标志位,结合多个度量参数联合判断网络状态,提高网络状态识别的准确性,使发送端实时采取相应的措施。仿真结果表明,该方案能使网络吞吐量得到明显的提高,改善了TCP的性能。     

An integrated congestion control mechanism for optimized performance using two-step rate controller in optical burst switching networks

Optical burst switching (OBS) is a promising solution to implement the optical internet backbone. However, the lack of adequate congestion-control mechanisms may result in high burst loss. Schemes such as fiber delay line (FDL), wavelength conversion, and deflection routing to reduce burst collision are unable to prevent the network congestion effectively. To address this problem, we propose and investigate a global solution, called Integrated Congestion-Control Mechanism (ICCM), for OBS networks. ICCM, which combines congestion avoidance with recovery mechanism, restricts the amount of burst flows entering the network according to the feedback information from core routers to edge routers to prevent network congestion. Also, a flow-policing scheme is proposed to intentionally drop the overloaded traffic with a certain probability at a core router to support fairness among flows. Moreover, the transmission rate of each flow is controlled to achieve optimized performance such as maximizing throughput or minimizing loss probability using two-step rate controller at the edge router. Simulation results show that ICCM effectively eliminates congestion within the network and that, when combined with a flow-policing mechanism, the fairness for competing flows can be supported while maintaining effective network performance.     

一种改进的无线网络TCP拥塞控制算法

传统基于有线环境的传输控制协议(TCP)技术无法适应链路质量相对较差的无线环境。为此,提出一种改进的对数增加自适应减少(NewLIAD)算法。在慢启动阶段根据带宽确定最优拥塞窗口,在网络拥塞阶段动态减少拥塞窗口,以保证系统的整体吞吐量。仿真结果表明,该算法有较好的发送速率平滑性,能减少数据抖动,提升无线网络的TCP性能。     

LIAD: Adaptive bandwidth prediction based Logarithmic Increase Adaptive Decrease for TCP congestion control in heterogeneous wireless networks

For accessing plentiful resources in the Internet through wireless mobile hosts, diverse wireless network standards and technologies have been developed and progressed significantly. The most successful examples include IEEE 802.11 WiFi for wireless networks and 3G/HSDPA/HSUPA for cellular communications. All IP-based applications are the primary motivations to make these networks successful. In TCP/IP transmissions, the TCP congestion control operates well in the wired network, but it is difficult to determine an accurate congestion window in a heterogeneous wireless network that consists of the wired Internet and various types of wireless networks. The primary reason is that TCP connections are impacted by not only networks congestion but also error wireless links. This paper thus proposes a novel adaptive window congestion control (namely Logarithmic Increase Adaptive Decrease, LIAD) for TCP connections in heterogeneous wireless networks. The proposed RTT-based LIAD has the capability to increase throughput while achieving competitive fairness among connections with the same TCP congestion mechanism and supporting friendliness among connections with different TCP congestion control mechanisms. In the Congestion Avoidance (CA) phase, an optimal shrink factor is first proposed for Adaptive Decreasing cwnd rather than a static decreasing mechanism used by most approaches. Second, we adopt a Logarithmic Increase algorithm to increase cwnd while receiving each ACK after causing three duplicate ACKs. The analyses of congestion window and throughput under different packet loss rate are analyzed. Furthermore, the state transition diagram of LIAD is detailed. Numerical results demonstrate that the proposed LIAD outperforms other approaches in goodput, fairness, and friendliness under diverse heterogeneous wireless topologies. Especially, in the case of 10% packet loss rate in wireless links, the proposed approach increases goodput up to 156% and 1136% as compared with LogWestwood+ and NewReno, respectively.     

TCP is Competitive with Resource Augmentation

The well-known Transport Control Protocol (TCP) is a crucial component of the TCP/IP architecture on which the Internet is built, and is a de facto standard for reliable communication on the Internet. At the heart of the TCP protocol is its congestion control algorithm. While most practitioners believe that the TCP congestion control algorithm performs very well, a complete analysis of the congestion control algorithm is yet to be done. A lot of effort has, therefore, gone into the evaluation of different performance metrics like throughput and average latency under TCP. In this paper, we approach the problem from a different perspective and use the competitive analysis framework to provide some answers to the question “how good is the TCP/IP congestion control algorithm?” We describe how the TCP congestion control algorithm can be viewed as an online, distributed scheduling algorithm. We observe that existing lower bounds for non-clairvoyant scheduling algorithms imply that no online, distributed, non-clairvoyant algorithm can be competitive with an optimal offline algorithm if both algorithms were given the same resources. Therefore, in order to evaluate TCP using competitive analysis, we must limit the power of the adversary, or equivalently, allow TCP to have extra resources compared to an optimal, offline algorithm for the same problem. In this paper, we show that TCP is competitive to an optimal, offline algorithm provided the former is given more resources. Specifically, we prove first that for networks with a single bottleneck (or point of congestion), TCP is ${\mathcal{O}}(1)The well-known Transport Control Protocol (TCP) is a crucial component of the TCP/IP architecture on which the Internet is built, and is a de facto standard for reliable communication on the Internet. At the heart of the TCP protocol is its congestion control algorithm. While most practitioners believe that the TCP congestion control algorithm performs very well, a complete analysis of the congestion control algorithm is yet to be done. A lot of effort has, therefore, gone into the evaluation of different performance metrics like throughput and average latency under TCP. In this paper, we approach the problem from a different perspective and use the competitive analysis framework to provide some answers to the question “how good is the TCP/IP congestion control algorithm?” We describe how the TCP congestion control algorithm can be viewed as an online, distributed scheduling algorithm. We observe that existing lower bounds for non-clairvoyant scheduling algorithms imply that no online, distributed, non-clairvoyant algorithm can be competitive with an optimal offline algorithm if both algorithms were given the same resources. Therefore, in order to evaluate TCP using competitive analysis, we must limit the power of the adversary, or equivalently, allow TCP to have extra resources compared to an optimal, offline algorithm for the same problem. In this paper, we show that TCP is competitive to an optimal, offline algorithm provided the former is given more resources. Specifically, we prove first that for networks with a single bottleneck (or point of congestion), TCP is O(1){\mathcal{O}}(1)-competitive to an optimal centralized (global) algorithm in minimizing the user-perceived latency or flow time of the sessions, provided we allow TCP O(1){\mathcal{O}}(1) times as much bandwidth and O(1){\mathcal{O}}(1) extra time per session. Second, we show that TCP is fair by proving that the bandwidths allocated to sessions quickly converge to fair sharing of network bandwidth.     

Improving TCP fairness and performance with bulk transmission control over lossy wireless channel

The traditional windows-based TCP congestion control mechanism produces throughput bias against flows with longer packet roundtrip times; the flow with a short packet roundtrip time preoccupies the shared network bandwidth to a greater extent than others. Moreover, the blind window reduction that occurs whenever packets are lost decreases the network utilization severely, especially in networks with high packet losses. This paper proposes a sender-based TCP congestion control, called TCP-BT. The scheme estimates the network bandwidth depending on the transmission behavior of applications, and adjusts the congestion window by considering both the estimated network bandwidth and the packet roundtrip time to improve fairness as well as transmission performance. The scheme has been implemented in the Linux platform and compared with various TCP variants in real environments. The experimental results show that the proposed scheme improves transmission performance, especially in networks with congestion and/or high packet loss rates. Experiments in real commercial wireless networks have also been conducted to support the practical use of the proposed mechanism.     

不确定TCP网络中的滑模拥塞控制策略

针对TCP（Transmission Control Protocol,传输控制协议）网络中的拥塞控制问题,提出了一种滑模拥塞控制策略。基于TCP网络拥塞控制模型,利用线性矩阵不等式设计了一个渐近稳定的滑模面,该滑模面能够补偿TCP网络中的不确定性因素的影响。另外,为了减小路由器中队列长度的振荡,提出了一种改进的到达条件。多种情况下的仿真实验表明,所提出的控制策略与普通的滑模拥塞控制策略相比具有更好的稳定性和鲁棒性。     

A network rate management protocol with TCP congestion control and fairness for all

Our study is motivated by the need to enable quality of service (QoS), congestion control and fair rate allocation for all end applications. We propose a new approach to address these needs which is different from the current practice whereby end applications pursue their own rate control using TCP. Our approach comprises a network rate management protocol (RMP) that controls the rate of all flows (at an aggregate level based on routes) subject to QoS requirements. The RMP control also facilitates a new TCP sliding-window congestion control based on the fair target rates computed by the RMP. Each non-TCP aggregate flow is policed by its respective edge router and each TCP flow adapts its window size as to achieve the RMP suggested fair target rate. The stability analysis of the new TCP congestion control is performed in a linearly scalable framework, which is less restrictive than a fluid model. We show that our proposed control is linearly scalable and establish its global asymptotic stability under arbitrary and variable information time lags, aka totally asynchronous conditions. The stability and the vitality of our control is verified by two means. One is a simulation of a network comprising 74 core links and up to 768 flows, each using its own access link. The simulation is also used to compare our control with the congestion control algorithms used in Fast, Vegas and Reno TCPs. The second verification means is an actual implementation of the control in the Linux kernel and its experimentation in a WAN testbed network comprising six routers and long haul links running UDP flows as well as CUBIC, N-RENO and C-TCP flows. Our experiments demonstrate that our approach can guarantee fair rates for all flows and QoS to premium flows.     

基于DupAck的Ad Hoc网络TCP性能改进

为改进传输控制协议(TCP)在无线网络环境下的性能,分析Ad Hoc网络数据丢失的原因,提出一种区分无线丢包和拥塞丢包的算法。该算法通过在发送端检测返回的重复Ack的相对单向传输时延,探测到网络真实的拥塞状况,以便采取合理的拥塞控制措施。仿真结果表明,该算法能够正确区分无线丢包和拥塞丢包,改善Ad Hoc网络的TCP性能。     

Anti-windup compensator for active queue management in TCP networks

In this paper, we apply a dynamic anti-windup scheme for improving the performance of a conventional proportional–integral (PI) controller for active queue management (AQM) supporting TCP flows. When a PI controller is used for AQM, the windup phenomenon of the integral action can cause performance degradation because the packet drop probability is limited between 0 and 1. Therefore we suggest a TCP/AQM model with a saturating actuator and apply a dynamic anti-windup method for improving the performance of the conventional PI AQM scheme. The proposed scheme not only provides graceful performance degradation, but also guarantees the stability of the overall system with the linearized TCP model. We verify the performance of the proposed scheme through ns-2 simulations. The simulation results show that our scheme outperforms the conventional PI controller when the traffic load is not stationary, which is always the case in real network environment.     

一种基于TCP控制报文的MAC层自适应算法

由于无线信道的特殊性,在WLAN应用中,TCP的传输性能会下降。提出依据TCP报文控制段采用不同的MAC传输参数的调整方案。该方案考虑到了802.11MAC参数的可调整性和TCP控制报文在传输流程的重要性,可有效提高控制报文在无线信道上传输能力,避免了由于信道访问冲突和拥塞而造成TCP性能下降的问题,从而提高TCP的传输效率。通过仿真验证了该方案的可行性。     

Delay-based TCP congestion avoidance: A network calculus interpretation and performance improvements

In delay-based TCP congestion avoidance mechanisms, a source adjusts its window size to adapt to changes in network conditions as measured through changing queueing delays. Although network calculus (NC) has been used to study window flow control and determine performance bounds, there is a lack of a bridge between NC theory and the practical issues of delay-based TCP congestion avoidance. In this paper, we use an NC-based approach to derive ideal congestion controllers for representative delay-based window flow control models with time-variant feedback delays. We show that the basic delay-based TCP congestion avoidance mechanisms in TCP Vegas, Enhanced TCP Vegas, and FAST TCP can be viewed as different approaches to approximating a certain NC controller. Moreover, we derive another NC controller that is explicitly constructed to address the throughput degradation of the current delay-based methods due to delayed acknowledgement (ACK) packets caused by network traffic in the reverse path (ACK packet) direction. The approximation of this F-model NC-based controller is shown to provide better throughput and fairness over the existing delay-based methods for a variety of network topologies in ns-2 simulations.     

基于强度控制的并行TCP拥塞控制策略研究

随着网络带宽的不断提升,基于并行TCP的应用方式得到广泛使用。当节点为同一个应用打开多个TCP连接时,对于使用单一TCP连接的网络用户存在严重的不公平。提出一种基于强度控制的并行TCP拥塞控制方案TCP C,使这些TCP流共享拥塞信息,同时限制并行TCP流的有效连接数量,以控制并行流的侵略性。实验结果显示该方案能够较好地保证公平性,同时有效地利用网络带宽。     

一种新的流媒体拥塞控制机制及其性能模拟

分析了Padhye‘s TCP吞吐量模型存在的缺陷,提出一种新的基于动态TCP吞吐量模型的流媒体拥塞控制机制,它能够保证动态环境下的TCP友好性,并对网络状态的变化有很好的响应性。详细阐述了该拥塞机制的原理并给出了动态TCP模型的吞吐量公式。最后,通过NS模拟,验证了该拥塞机制的优越性。     

无线传感器网络TCP性能的改善机制

在无线传感器网络中,节点分布过于密集或大量数据流的突发将造成拥塞,导致报文丢失,引起吞吐量下降和能量浪费。该文提出一种新的拥塞控制机制PTCP,通过分段调整慢启动阶段的TCP窗口增长速度控制拥塞。仿真结果证明,该机制有效解决了传感器网络中的拥塞控制问题,提高了无线传感器网络的TCP性能。     

Extending TCP congestion control to multicast

This paper proposes a new single-rate multicast congestion control scheme named PGMTCC, which has been implemented and investigated in PGM. The primary idea of PGMTCC is to extend Sack TCP congestion control mechanism to multicast in order to make multicast perform almost the same as Sack TCP under all kinds of network conditions. To achieve this goal, first of all, the sender should accurately select a receiver with the worst throughput as a representative (acker) by a simplified equation of TCP throughput. Then the Sack TCP congestion control mechanism, with some modifications to be adapted to multicast, is deployed to take charge of congestion control between the sender and the acker. Moreover, in our scheme, the problem of the feedback suppression is considered and solved by a selective suppression mechanism of feedback. NS2 is used to test and investigate the performance of our scheme. As expected, PGMTCC performs almost like Sack TCP under all kinds of conditions. We believe that it is TCP-friendly, robust and scalable.     

嵌入式Linux 3G无线路由器TCP/IP性能优化

分析了嵌入式Linux小型3G无线路由器的网络传输性能,以数据吞吐量和端到端往返时间为性能指标,通过仿真软件NS2分析比较5种TCP拥塞控制算法在UMTSHSDPA网络中的性能,调整TCP参数以改善网络数据传输性能.性能测试结果表明,基于仿真环境和实际物理环境,所提出的TCP拥塞控制算法及网络参数优化均可靠有效,在CPU主频80 MHz时,TCP/IP传输平均数据吞吐量可达750.4 kbit/s,较优化前提升了38.1％.