确认平滑:一种改善无线链路上的TCP性能的实现

许多研究者已经发现，在无线链路上使用链路层自动请求重传(ARQ)来恢复无线链路差错，会在无线链路上和TCP源端产生大量的突发性流，从而使路由器拥塞，导致分组丢失和吞吐量下降．本文提出了一种解决方案，在ARQ的接收端，利用漏桶对接收确认分组进行平滑，使分组的发送能保持一定的间隔．仿真结果表明，平滑能提供更好的吞吐量性能和更低的丢失率。     

基于Vegas协议的包错误检测机制

为解决无线或异质网络中TCP拥塞控制性能不稳定的问题,提出一种基于Vegas协议的包错误检测机制。该机制扩展了TCP Vegas头部选项并允许接收端返回一个发生包错误的特殊ACK给TCP发送端,保留TCP Vegas机制端对端的语义,无须修改基站或中间节点。NS2模拟实验表明,该机制可区分包丢失的原因,能较好避免由包错误产生的超时重传,提高传输性能。     

VPN网络中的TCP性能改进方案

随着网络规模的增大,数据的传输延迟和丢失概率也随之增大,进而对TCP传输造成了较大影响.针对此现象,本文提出基于VPN网关的快速重传机制,通过在VPN网络中引入隧道重传协议,降低点到点传输中TCP数据的丢失概率,并为TCP协议提供一条可靠的传输链路.实际的测试表明,网关上的快速重传机制可以有效减小数据的丢失概率,并由此提升TCP协议的传输性能.     

TCP消息传递及其重传可靠性

IP协议（网际协议）解决了不同网络的主机之间的通信问题。但IP协议存在一个问题就是不能检测数据报的丢失,而这种情况是会经常发生的。任何一分组交换网,如Internet中,如果有许多数据在同一时刻经过某Internet的处理路由器或某条线路,这些问题需要在传输层解决。在Internet中,主要依靠TCP协议。TCP协议（传输控制协议）位于传输层,是面向连接的,提供了双向的即全双工的连接,TCP协议保证在数据信息丢失后进行重发,能够去掉重复的数据信息,还能保证精确地按原发送顺序重新组装数据。     

一种改善TCP在无线网络上性能的方法

介绍了几种改善TCP在无线移动网络上性能的技术，并提出了一种改善的方法：将ICMP控制报文内嵌到TCP报文，形成显式丢失通知（ELN）应答报文，通知TCP发送端包丢失的原因。     

一种CDMA2000链路层自适应重传算法

TCP协议应用在3G无线网络中时，其传输性能受到了无线网络物理层帧差错率的严重影响。链路层重传技术可以大大改善TCP数据传输性能因无线信道误码率大而下降的情况。主要研究了CDMA2000中链路层重传技术对无线TCP数据传输的影响，并结合TCP层重传超时机制，提出了一种新的自适应链路层重传算法，提高了TCP在无线链路的数据传输性能。最后对该算法进行仿真，验证了此算法可以显著提高TCP吞吐率。     

一种改善Ad Hoc网络中TCP性能的跨层方法

大量研究表明AdHoc网络中TCP的性能非常差,这主要是由于TCP的拥塞控制机制不能有效地解决由共享信道竞争造成的分组丢失问题。文中提出了一种根据TCP发射端MAC层的RTS重发次数,来自适应地调整TCP的最大窗口大小的跨层方法,以控制网络中分组的数量,减小信道竞争。仿真结果表明,该方法能够显著地提高TCP的吞吐量,并改善其稳定性。     

移动网络中重传超时问题的研究

作为广泛使用的网络传输控制协议,TCP(Transmission Control Protocol)在高速移动网络中遇到了新的性能瓶颈。首先由于移动网络中存在随机位错误导致的丢包,而TCP协议不能有效区分这类丢包与拥塞丢包,导致TCP频繁的降低拥塞窗口无法有效利用移动网络的带宽资源。其次,高速移动网络的发展使得带宽时延积BDP(Bandwidth-Delay Product)进一步增大,在发生丢包时TCP协议中的流量控制将导致性能瓶颈和易引起重传超时。通过Wireshark工具抓取大量的tracing进行分析,发现重传超时的主要原因是重传数据包再次被丢,而TCP又不能发现丢失原因,因此无法进行再次重传最终导致重传超时。针对这一问题,本文提出的方法 DTOR(Detect Timeout and Retransmission)可以帮助TCP检测到重传数据包再次丢失并触发再次重传,DTOR使网络带宽利用率提升了20%左右。     

MANET中基于邻居节点的重传控制算法

针对移动Ad hoc网络传统重传机制存在的局限性,提出了一种新的重传控制算法(EX-TCGM),利用传输路径上的邻居节点传输丢失的数据包,使得路由上的任何节点都能够重传;并从理论上对该算法的有效性进行了分析。通过仿真,与按需距离矢量路由协议(AODV)、机会路由协议(ExOR)和基于分组移动的传输控制方法(TCGM)进行了性能对比和分析,EX-TCGM相对原协议在端到端平均时延和吞吐量上有所提高,数据包平均成功传输率相对其他协议显著增加。     

基于误码丢包率监测的无线TCP改进

针对无线环境下TCP错误调用拥塞控制算法致使性能下降的情况,提出一种基于误码丢包率监测的无线TCP改进方法。利用显式拥塞通知的路由器配合区分分组丢失性质,在数据发送端采用实时误码丢包率监测,并根据监测结果调整TCP段尺寸。仿真结果表明,改进后的TCP吞吐量在误码率为1E-4时超过TCP_SACK和TCP_Reno近1倍。     

Improving TCP performance over wired–wireless networks

Today there is a growing demand for Internet services over WLAN hotspots. Majority of the Internet services today are based on TCP. However, TCP is not well-suited for heterogeneous networks consisting of wired and wireless networks. Losses in wireless network, which are quite frequent, are often misinterpreted by the TCP sender as loss due to congestion, which leads to poor performance of TCP. Hence, it is important to shield the TCP sender from wireless error. In this paper, we propose an improved method for identifying cases of wireless losses and tackling the loss at the local link level through MAC layer retransmissions. We then evaluate the effect of MAC layer retransmissions on the performance of TCP both analytically and empirically. Our empirical results show that significant improvement in TCP performance is possible through MAC layer retransmission.     

无线网络下TCP重传定时器研究

鉴于无线网络的固有特性,传统TCP重传定时器在无线网络下易出现过早超时,致使TCP启用拥塞控制机制,降低了TCP吞吐量。该文改进了传统TCP重传定时器RTO设置算法,使之自适应于网络状况的变化。仿真结果表明,在链路误码率较高时,此方案较好地避免了过早超时,有效改善了无线环境下TCP性能。     

Engineering TCP transmission and retransmission mechanisms for wireless networks

Transmission Control Protocol (TCP) provides mechanisms for reliable data communications. Although it works well in wired networks, it fails to offer satisfactory performance in lossy and wireless environments. And in the multi-hop wireless infrastructure, packet delivery suffers high cumulative loss rate if traveling over multiple wireless hops. The Selective acknowledgment (SACK) is one header option that might be used to combat segment corruptions in air channels. In this paper, an alternative set of flow control mechanisms is proposed to handle high packet loss rate in a wireless medium. Using a measurement-based mechanism, sustainable segment delivery is achievable through a novel size-reduction method. Multiple segment retransmission mechanisms are introduced to reduce successive timeout events. One single byte loss is sufficient to waste all other bytes in a file received at a destination. That is, a good TCP flow control mechanism should provide a high successful file transmission completion rate, and this is set as our design goal. Through thorough simulations, our proposed multi-segment retransmission designs perform with higher successful file transfer rate and fewer timeout events than NewReno and SACK under a wide range of packet loss probabilities.     

基于前向纠错的自适应网络传输机制

针对无线网络中的传输控制协议（TCP）因为丢包触发丢包重传机制而导致传输性能大幅下降的问题,提出了一种基于前向纠错的自适应传输机制（AdaptiveFEC）。该机制通过前向纠错来减少数据段的丢失,以避免触发TCP的丢包重传机制,从而达到提升TCP传输性能的目的。首先,根据当前的网络状况以及当前连接的数据传输特征确定当前时间段中的最优冗余段比例;然后,利用TCP数据段中的数据段序号信息实时进行网络状况的估计,从而根据网络波动来动态更新冗余段比例。大量实验结果说明,在20 ms的往返时延以及5%丢包率的传输环境中,相较于静态的前向纠错机制,AdaptiveFEC能够使得TCP连接的传输速率平均提升42%,当运用在文件下载的应用中时,所提机制能够使得下载速度提升至原来的两倍。     

基于往返延迟抖动区分丢包的TCPW改进

针对TCP Westwood(TCPW)在高误码率无线网络环境下不能区分无线丢包和拥塞丢包的问题,提出了一种基于往返延迟抖动区分丢包的TCPW改进协议,称之为TCPWBJ。它根据测得的往返延迟抖动划分拥塞等级,区分无线丢包和拥塞丢包,并根据拥塞等级进行相应的拥塞控制。仿真结果表明,TCPW BJ算法在高误码率无线网络中,显著提高了带宽利用率和吞吐量,并保持良好的公平性与友好性。     

Buffer Coding for Reliable Transmissions over Wireless Networks

In-network caching is a useful technique for reducing latency and retransmission overhead of lost packets for reliable data delivery in wireless networks. However, in-network caching is challenging to implement in memory constrained devices such as RFIDs and sensors, and also in Wireless LAN (WLAN) gateways for large-scale deployments. In this paper we propose a novel technique for management of in-network caches using XOR coding for optimizing the use of limited buffer space in presence of random and burst packet losses. We identify two critical parameters, coding degree and coding distance for the coding scheme. As a case-study we implement our approach over Snoop and evaluate its performance for WLANs. We further propose a self-adaptive algorithm that tunes coding degree on the fly based on the measured coding behavior and packet loss probability. Using simulations in ns-2, we observe that in our simulation settings, when the size of the retransmission buffer in the gateway is less than 16 packets per TCP flow, the throughput can be enhanced by up to 30% for random losses and up to 20% for burst losses.     

Achieving high throughput and TCP Reno fairness in delay-based TCP over large networks

The transport control protocol (TCP) has been widely used in wired and wireless Internet applications such as FTP, email and http. Numerous congestion avoidance algorithms have been proposed to improve the performance of TCP in various scenarios, especially for high speed and wireless networks. Although different algorithms may achieve different performance improvements under different network conditions, designing a congestion algorithm that can perform well across a wide spectrum of network conditions remains a great challenge. Delay-based TCP has a potential to overcome above challenges. However, the unfairness problem of delay-based TCP with TCP Reno blocks widely the deployment of delay-based TCP over wide area networks. In this paper, we proposed a novel delay-based congestion control algorithm, named FAST-FIT, which could perform gracefully in both ultra high speed networks and wide area networks, as well as keep graceful fairness with widely deployed TCP Reno hosts. FAST-FIT uses queuing delay as a primary input for controlling TCP congestion window. Packet loss is used as a secondary signal to adaptively adjust parameters of primary control process. Theoretical analysis and experimental results show that the performance of the algorithm is significantly improved as compared to other state-of-the-art algorithms, while maintaining good fairness.     

无线移动网络中增强TCP性能的技术综述

TCP是因特网上的主要传输协议，在数据包丢失主要是由拥塞引起的传统网络上，TCP可以充分发挥其性能，但是在无线移动网络中，TCP将无线信道比特差错和移动切换引起的数据包丢失误归于网络发生拥塞而采取拥塞控制措施，不必要地降低了端到的吞吐率，导致自身性能的下降，首先阐述了当前无线移动网络的发展状况和TCP面临的问题，在此基础上，综述和评价了各种增强TCP性能的技术方案，最后，结合无线移动通信系统的最新进展，分析和探讨了当前存在的问题和进一步的研究方向。     

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.