一种基于带宽估计的无线网拥塞控制机制

针对无线网提出了一种基于带宽估计的拥塞控制机制。该机制利用TCP确认帧携带的数据包到达时间来估算包到达速率，从而得到带宽的估计值。在此基础上用带宽的估计值更新拥塞窗口，避免在发生链路错误时启动拥塞控制机制，由此提高了TCP在无线网上的性能。实验结果表明，算法能减少链路差错对TCP性能带来的影响，提高了TcP在无线网上的吞吐率。     

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。     

基于CTCP的动态调整拥塞控制算法

空间网络具有传播延时长、信道丢包率高等特点,使得传统的地面路由协议TCP协议难以适应于空间网络。CTCP是一种结合网络编码技术的新型传输协议,实验表明在高丢包率的空间网络环境中的性能要优于传统的TCP协议。但由于CTCP的拥塞控制方式类似于TCP-Reno,拥塞窗口的调整是静态设定的,使得CTCP的拥塞控制机制在多变复杂的空间网络环境效果并不理想。本文提出一种基于CTCP的动态调整拥塞控制算法H-CTCP,通过对空间网络中的可用带宽进行实时估算,动态设定拥塞窗口。实验证明,改进后的拥塞控制算法更能适应高丢包率的空间网络环境,大大提高CTCP的传输性能。     

一种改进的TCP拥塞控制算法及仿真

TCP协议提供面向连接、可靠的服务,但应用于时延敏感的实时网络时,并不能保证实时性。当网络负载过大时,会出现拥塞、传输延迟和丢包等问题。为了降低网络拥塞概率,提出了一种改进的TCP拥塞控制算法TCP-EB。该算法根据确认数据包的速率估计网络可用带宽,调整拥塞窗口的大小,提高带宽利用率。出现拥塞时,对窗口衰减速度进行限制,保证传输的优先级高于其他数据流。最后将TCP-EB与传统拥塞控制算法TCP Reno、TCP Vegas进行比较,结果表明,提高了网络吞吐量和网络传输的平滑性。     

TCP传输中往返时延偏移智能响应机制研究

为了提高高丢包率环境下的TCP传输性能,提出一种往返时延偏移智能响应机制。对往返时延偏移值进行标准化处理得到标准延迟因子,用这个因子对拥塞窗口增长和减小量进行修正,实现拥塞窗口增长速度随往返时延偏移自适应调整,能够区分随机丢包和网络拥塞。开发Linux内核模块实现了往返时延偏移智能响应机制,可快速部署到所有基于AIMD策略的拥塞控制机制。仿真结果表明,使用往返时延偏移智能响应机制,平均吞吐量超过cubic算法57%,能够有效提升高丢包率环境的带宽利用率。     

面向噪声丢包感知的无线网络拥塞算法

针对无线网络链路干扰大、误码率高等特点，以及TCP Westwood算法（TCPW）存在估算带宽时过度依赖包的反馈，缺乏区分传输过程中丢包类型的缺点等问题，提出一种TCPW拥塞控制优化算法--TCPW-F。该算法利用发送速率等构建拥塞因子[F]作为判断丢包类型的依据，同时对判定发生噪声丢包时的拥塞窗口进一步调整，避免噪声丢包引起的窗口下降，提高该情况下窗口的发送效率。仿真结果表明，TCPW-F算法在时延性能方面表现更优，单位时间抖动趋于稳定的速度更快。在同一信道带宽下增大包生成速率，改进算法的实时吞吐量明显高于原算法，具备一定的噪声丢包感知能力，无线网络的TCP传输质量获得较大改善。     

一种新型的端到端TCP拥塞控制机制

拥塞控制机制是决定TCP协议性能的重要因素。传统拥塞控制机制在卫星网络中运用时会导致TCP性能的大幅下降。本文提出了一种新的适应于卫星网络大延时特点的端到端拥塞控制机制,通过观察连续的不同长度的数据包的RTT的变化来确定网络带宽和适宜的拥塞窗口。实验结果证明,这种新机制在吞吐量、公平性、友好性方面均好于当前主流的端到端拥塞控制机制。     

一种新的流媒体拥塞控制算法

提出一种新的拥塞控制算法(TCP MS).该算法更适用于流媒体应用,有更高的带宽利用率、公平性,传输速率也更平滑.不同于传统的利用丢包率和排队延迟来探测拥塞的TCP拥塞控制算法,该算法通过确认数据包的速率来探测拥塞,并在每一轮往返时间内及时调整窗口.该算法提供的拥塞窗口变化更准确,传输速率抖动更小.因此,提高了网络带宽的利用率以及传输速率的平滑性.最后,文章将TCP MS与典型的基于丢包率的TCP Reno算法和基于排队延迟的TCP Vegas算法在带宽利用率、速率抖动以及公平性等方面分别做了比较,仿真结果表明TCP MS是一种理想的流媒体拥塞控制算法.     

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。     

TCP Yuelu:一种基于有线/无线混合网络端到端的拥塞控制机制

无线链路传输数据的比特率出错导致TCP协议在有线／无线混合网络环境下性能低下,在改进算法TCPReno的基础上,文章提出了一种适用于有线／无线混合网络的拥塞控制机制,该机制包括一种分阶段平滑慢启动机制,改善了突发流量对网络性能的损害,引入网络测量技术获得了往返时间（RTT）、网络带宽、瓶颈链路队列长度等网络状态参数,区分网络拥塞和无线链路比特差错,避免了终端节点对网络状态不了解产生的盲目行为,有效改进了TCP的加性增加乘性减少（AIMD）窗口调节机制,提高了网络性能．同时,在仿真软件NS2中实现了该算法,进行了大量的仿真实验,实验结果表明TCP Yuelu有效降低了网络抖动,提高了网络传输性能,并保持了良好的公平性和对其它TCP流的友好性．     

V2G网络中基于带宽自适应的拥塞控制协议优化

V2G网络下PLC链路带宽受限、高误码率等特点导致现有的TCP NewReno拥塞控制机制缺乏对丢包类型的有效判断,将链路上由噪声干扰的随机错误丢包与网络拥塞丢包统一当做拥塞事件处理,从而造成不必要的拥塞避免,导致了低吞吐量问题.根据此问题,提出了一种基于带宽自适应的拥塞控制算法.该算法通过分组预测拥塞等级感知网络状态,由此估计可用带宽来判断丢包类型,实现了拥塞窗口自适应调节.仿真结果表明该算法在拥塞窗口的增长、吞吐量、公平性、收敛性和友好性等方面都优于现有算法,V2 G网络的吞吐量得到明显提升.     

MANET中TCP改进研究综述

传统TCP(transmission control protocol)本是为有线网络设计,它假设包丢失全是由网络拥塞引起,这个假设不能适应于MANET (mobile ad hoc network),因为MANET中除了拥塞丢包以外,还存在由于较高比特误码率、路由故障等因素引起的丢包现象.当出现非拥塞因素丢包时,传统TCP将错误地触发拥塞控制,从而引起TCP性能低下.任何改进机制都可以分为发现问题和解决问题两个阶段.首先概括了MANET中影响TCP性能的若干问题;然后针对发现问题和解决问题两个阶段,详细地对每一阶段中存在的各种可行方法进行了分类、分析和比较;最后指出了MANET中TCP性能优化的研究方向.     

Improving Throughput of Transmission Control Protocol Using Cross Layer Approach

Most of the internet users connect through wireless networks. Major part of internet traffic is carried by Transmission Control Protocol (TCP). It has some design constraints while operated across wireless networks. TCP is the traditional predominant protocol designed for wired networks. To control congestion in the network, TCP used acknowledgment to delivery of packets by the end host. In wired network, packet loss signals congestion in the network. But rather in wireless networks, loss is mainly because of the wireless characteristics such as fading, signal strength etc. When a packet travels across wired and wireless networks, TCP congestion control theory faces problem during handshake between them. This paper focuses on finding this misinterpretation of the losses using cross layer approach. This paper focuses on increasing bandwidth usage by improving TCP throughput in wireless environments using cross layer approach and hence named the proposed system as CRLTCP. TCP misinterprets wireless loss as congestion loss and unnecessarily reduces congestion window size. Using the signal strength and frame error rate, the type of loss is identified and accordingly the response of TCP is modified. The results show that there is a significant improvement in the throughput of proposed TCP upon which bandwidth usage is increased.     

Improving fairness among TCP flows by stateless buffer control with early drop maximum

Transmission control protocol (TCP) has been recognized as the most important transport-layer protocol for the Internet. It is distinguished by its reliable transmission, flow control, and congestion control. However, the issue of fair bandwidth-sharing among competing flows was not properly addressed in TCP. As web-based applications and interactive applications grow more popular, the number of short-lived flows conveyed on the Internet continues to rise. With conventional TCP, short-lived flows will be unable to obtain a fair share of available bandwidth. As a result, short-lived flows will suffer from longer delays and a lower service rate. It is essential for the Internet to come up with an effective solution to this problem in order to accommodate the new traffic patterns.With a more equitable sharing of bottleneck bandwidth as its goal, a stateless queue management scheme featuring early drop maximum (EDM) is developed and presented in this article. The fundamental idea is to drop packets from those flows having more than an equal share of bandwidth. The congestion window size of a TCP sender is carried in the options field on each packet. The proposed scheme will be exercised on routers and make its decision on packet dropping according to the congestion windows. In case of link congestion, the queued packet with the largest congestion window will be dropped from the queue. This will lower the sending rate of its sender and release part of the occupied bandwidth for the use of other competing flows. By so doing, the entire system will approach an equilibrium point with a rapid and fair distribution of bandwidth. As a stateless approach, the proposed scheme inherits numerous advantages in implementation and scalability.Extensive simulations were conducted to verify the feasibility and the effectiveness of the proposed approach. As revealed in the simulation results, the proposed scheme outperforms existing stateless techniques, including Drop-Tail and Random Early Drop, in many respects, such as a fairer sharing of available bandwidth and a shorter response time for short-lived flows.     

面向数据中心租户带宽特征的虚拟拥塞控制方法性能分析

数据中心租户使用的遗留设备中仍存在没有实现显式拥塞通知ECN的情况,导致数据中心网络中存在ECN流抢占非ECN流带宽资源的不公平现象。虚拟拥塞控制方法通过修改数据包接收窗口字段进行拥塞控制,改善了上述不公平现象。从租户主机数目、带宽需求、网络拥塞程度、拥塞控制算法等四个角度出发,建立对应的符合数据中心租户带宽特征的仿真场景,通过仿真实验分析虚拟拥塞控制方法在上述场景中的性能。结果表明：（1)虚拟拥塞控制方法的性能良好,不受租户主机个数、租户带宽差异以及网络拥塞程度的影响;（2）虚拟拥塞控制算法的性能在拥塞控制算法不同环境下的表现存在差异,当使用YeAH TCP时解决ECN不公平性效果较差。     

Learning-TCP: A stochastic approach for efficient update in TCP congestion window in ad hoc wireless networks

In this work, we attempt to improve the performance of TCP over ad hoc wireless networks (AWNs) by using a learning technique from the theory of learning automata. It is well-known that the use of TCP in its present form, for reliable transport over AWNs leads to unnecessary packet losses, thus limiting the achievable throughput. This is mainly due to the aggressive, reactive, and deterministic nature in updating its congestion window. As the AWNs are highly bandwidth constrained, the behavior of TCP leads to high contentions among the packets of the flow, thus causing a high amount of packet loss. This further leads to high power consumption at mobile nodes as the lost packets are recovered via several retransmissions at both TCP and MAC layers. Hence, our proposal, here after called as Learning-TCP, focuses on updating the congestion window in an efficient manner (conservative, proactive, and finer and flexible update in the congestion window) in order to reduce the contentions and congestion, thus improving the performance of TCP in AWNs. The key advantage of Learning-TCP is that, without relying on any network feedback such as explicit congestion and link-failure notifications, it adapts to the changing network conditions and appropriately updates the congestion window by observing the inter-arrival times of TCP acknowledgments. We implemented Learning-TCP in ns-2.28 and Linux kernel 2.6 as well, and evaluated its performance for a wide range of network conditions. In all the studies, we observed that Learning-TCP outperforms TCP-Newreno by showing significant improvement in the goodput and reduction in the packet loss while maintaining higher fairness to the competing flows.     

APS-FeW: Improving TCP throughput over multihop adhoc networks

TCP is a reliable transport protocol tuned to perform well over traditional wired networks. Although it performs well for wired networks, TCP’s implicit assumption that any packet loss is due to congestion is not valid any longer in mobile ad hoc networks. It is observed that TCP induces the over-action of routing protocol and reduces the performance of the connection. Fraction window increment (FeW) scheme for TCP improves the connection performance by limiting TCP’s aggressiveness. But to some extent, this limitation is too strict in that it eliminates the possibility to deliver more bytes under the same congestion window. To solve this problem, we propose an adaptive packet size (APS) scheme to work on top of FeW for TCP. The proposed scheme utilizes the advantages of both legacy TCP and FeW to achieve high performance over multihop 802.11 networks. Extensive simulation results demonstrate that APS over FeW outperforms FeW alone by 10–25% according to different scenarios, e.g., chain-topology, grid-topology, and random-topology with mobility.     

基于延迟抖动分析的TCP友好拥塞控制算法

基于因特网的以UDP为传输协议的实时多媒体数据传输需要在保证实时性和可靠性的基础上,能够与因特网其他服务所使用的TCP协议公平共享有限的带宽。本文采用基于实时传输协议（RTP）和实时传输控制协议（RTCP）的反馈拥塞控制算法,提出一种简单的拥塞控制机制,使UDP数据流能与TCP数据流和平共处;研究了基于速率控制的TCP友好拥塞控制策略-TFRC,分析了其基本机制和关键问题;提出利用延迟抖动作为潜在拥塞信号来改进TFRC的速率控制机制,以适应实时业务低抖动的要求,并通过NS仿真验证了改进的TFRC算法对实时业务的良好性能。     

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.     

门户环境中基于语义数据协作应用集成方法

目前,门户的功能定位已经从传统的信息集成转向应用集成.门户环境中应用间的进一步集成实际上表现为Portlet互操作问题. 现有Portlet互操作方法在共享范围、标准兼容方面存在不足且难于集成已有应用系统.提出了一种基于语义数据协作的Portlet互操作方法,其基本思想是:将参与互操作的Portlet抽象为ShadowComponent组件,然后基于本体建立ShadowComponent之间的语义数据关联,并使用ECA(event-condition- action)规则实现Portlet互操作.实验证明,该方法无须对已有应用作任何修改即可完成门户中的应用集成.