TCP在无线通信中存在的问题及解决方案

TCP和IP协议非常简单且可靠,它们的组合决定了目前的大多数通信方式(从有线骨干网到混合网)。TCP协议最初是为有线网络而设计的,目前已成为大多数应用事实上的标准。在有线网络中随机比特差错率可以忽略,拥塞主要由包丢失造成。很多研究都表明未修改的TCP协议在无线环境中的性能很差,因为它无法区分数据包的丢失是由于拥塞还是传输差错造成的。文章分析了TCP在无线IP通信中存在的问题,详细给出了相应的解决方案。     

TCP在无线通信中的问题及解决方案

TCP协议最初是为有线网络而设计的。在有线网络中随机比特差锗率是可以忽略的。拥塞主要是由包丢失造成的。很多研究都表明未修改的标准TCP协议在无线环境中的性能是很差的,因为它无法区分出数据包的丢失是由于拥塞还是传输差错。本文分析TCP在无线IP通信环境中存在的问题,并详细给出相应的解决方案。     

无线网络中传输控制协议的研究

传统TCP(传输控制协议)拥塞控制协议本是为有线网络设计,它假设包丢失完全是由网络拥塞引起。在无线网络环境下除了拥塞丢包外,还存在较高的比特误码率、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。文章在分析传统TCP在无线网络中存在问题的基础上,对目前无线TCP发展和技术进行归纳和比较,进一步给出无线传输协议的研究和发展方向。     

TCP丢包检测技术分析

在有线网络环境中,分组丢失往往是由于网络拥塞造成的,因此传输控制协议(TCP)能够良好运行;然而当TCP运行在无线环境中,由于误码率高,信号衰落以及频繁的移动等特性造成丢包时,TCP拥塞窗口依旧盲目减半,导致其性能大幅度下降。本文首先阐述了无线环境中出现的拥塞丢包、随机丢包、突发丢包以及发生包的重新排序的原因,在此基础上,总结了处理这些问题的方法并对他们进行了评价,最后,分析了进一步的研究方向。     

全IP蜂窝通信系统TCP性能的改进

在无线网络中,造成丢包的主要原因是无线链路的高误码率(BER)及主机在区域间移动。如果TCP的丢包处理简单采用启动拥塞控制机制,势必导致网络传输性能恶化。本文以全IP蜂窝通信系统为例,概述TCP/IP协议组用于无线链路的性能问题,提出解决这些问题的方案,分析该方案的优点和局限性。     

核心网深度优化之TCP加速解决方案研究

随着4G网络的全面覆盖,移动应用伴随着4G大宽带高速率特点不断地在演变,移动网络上4G流量中75%以上使用的是TCP协议,而TCP协议最初是在有线网络环境下设计的,无线网络环境下非拥塞导致的丢包可能性要大得多,加上无线网络环境的小带宽,大时延,可移动性等特点,TCP协议在无线网络环境上的工作效率远不如有线网络,TCP协议对于无线网络的高延时和中/低带宽的情况存在优化的空间。     

一种基于带宽估计的战术互联网TCP改进机制

无线的战术互联网通常面临复杂的电磁环境,高误码率、终端的频繁移动等恶劣的通信环境使得针对有线网络设计的TCP协议传榆性能急剧下降.针对战术互联网提出了一种基于带宽估计的TCP改进机制,该机制利用TCP确认帧携带的数据包到达时间来估算带宽,并用动态的低通滤波器来平滑带宽的估计值.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TCP在战术互联网中的性能.实验结果表明,该算法能减少链路差错对TCP性能带来的影响,提高TCP在战术互联网上的传输性能.     

城域网中的网络地址

目前,国内众多有线电视台利用冗余光纤网络建立了城域网,从事网络信息服务,为广大企事业单位提供宽带、高速数据传输业务。在所建设的网络中,采用的网络传输协议多是TCP/IP(Transmission Control Protocol传输控制协议/Internet Protocol因特网协议)协议。Internet之所以能将广阔范围内各种各样网络系统的计算机互联起来,主要是因为应用了“一统天下”的TCP/IP协议。在应用TCP/IP协议的网络环境中,为了唯一地确定一台主机的位置,必须为TCP/IP     

对TCP/IP计算机网络拥塞控制的研究

为提升计算机的网络性能,更好地避免拥塞现象的发生,需要对其进行必要的技术控制。鉴于此,对基于TCP/IP协议的网络拥塞控制方法进行分析。在TCP拥塞控制中主要采用TCP Tahoe,TCP Reno,TCP New Reno以及TCP Sack四种方法,其中TCP New Reno对快速恢复算法进行了改进,通过对TCP协议中的Reno进行可视化处理,实行对网络拥塞的有效管理。而IP拥塞控制方法则分为FIFO,FQ和WFQ,RED以及ECN四种类型,通过队列调度管理方式实现了对网络拥塞的有效管理。     

流量/拥塞控制技术研究

流量/拥塞控制的基本目的是以分布处理的方式有效地控制结点间的数据流,从而避免网络中出现拥塞。拥塞控制相应的控制策略称为拥塞控制算法(协议)。简述了Internet上基于TCP/IP的拥塞控制机制,分析和比较了TCP/IP上具体实现算法的稳定性,讨论了TCP/IP拥塞控制所面临的问题。     

Enhancement of TCP over wired/wireless networks with packet loss classifiers inferred by supervised learning

TCP is suboptimal in heterogeneous wired/wireless networks because it reacts in the same way to losses due to congestion and losses due to link errors. In this paper, we propose to improve TCP performance in wired/wireless networks by endowing it with a classifier that can distinguish packet loss causes. In contrast to other proposals we do not change TCP’s congestion control nor TCP’s error recovery. A packet loss whose cause is classified as link error will simply be ignored by TCP’s congestion control and recovered as usual, while a packet loss classified as congestion loss will trigger both mechanisms as usual. To build our classification algorithm, a database of pre-classified losses is gathered by simulating a large set of random network conditions, and classification models are automatically built from this database by using supervised learning methods. Several learning algorithms are compared for this task. Our simulations of different scenarios show that adding such a classifier to TCP can improve the throughput of TCP substantially in wired/wireless networks without compromizing TCP-friendliness in both wired and wireless environments.     

JTCP: jitter-based TCP for heterogeneous wireless networks

Transmission control protocol (TCP), a widely used transport protocol performs well over the traditional network which is constructed by purely wired links. As wireless access networks are growing rapidly, the wired/wireless mixed internetwork, a heterogeneous environment will get wide deployment in the next-generation ALL-IP wireless networks. TCP which detects the losses as congestion events could not suit the heterogeneous network in which the losses will be introduced by higher bit-error rates or handoffs. There exist some unsolved challenges for applying TCP over wireless links. End-to-end congestion control and fairness issues are two significant factors. To satisfy these two criteria, we propose a jitter-based scheme to adapt sending rates to the packet losses and jitter ratios. The experiment results show that our jitter-based TCP (JTCP) conducts good performance over the heterogeneous network.     

TCP-friendly flow control of wireless multimedia using ECN marking

In a wireless network packet losses can be caused not only by network congestion but also by unreliable error-prone wireless links. Therefore, flow control schemes which use packet loss as a congestion measure cannot be directly applicable to a wireless network because there is no way to distinguish congestion losses from wireless losses. In this paper, we extend the so-called TCP-friendly flow control scheme, which was originally developed for the flow control of multimedia flows in a wired IP network environment, to a wireless environment. The main idea behind our scheme is that by using explicit congestion notification (ECN) marking in conjunction with random early detection (RED) queue management scheme intelligently, it is possible that not only the degree of network congestion is notified to multimedia sources explicitly in the form of ECN-marked packet probability but also wireless losses are hidden from multimedia sources. We calculate TCP-friendly rate based on ECN-marked packet probability instead of packet loss probability, thereby effectively eliminating the effect of wireless losses in flow control and thus preventing throughput degradation of multimedia flows travelling through wireless links. In addition, we refine the well-known TCP throughput model which establishes TCP-friendliness of multimedia flows in a way that the refined model provides more accurate throughput estimate of a TCP flow particularly when the number of TCP flows sharing a bottleneck link increases. Through extensive simulations, we show that the proposed scheme indeed improves the quality of the delivered video significantly while maintaining TCP-friendliness in a wireless environment for the case of wireless MPEG-4 video.     

TCP Veno: TCP enhancement for transmission over wireless access networks

Wireless access networks in the form of wireless local area networks, home networks, and cellular networks are becoming an integral part of the Internet. Unlike wired networks, random packet loss due to bit errors is not negligible in wireless networks, and this causes significant performance degradation of transmission control protocol (TCP). We propose and study a novel end-to-end congestion control mechanism called TCP Veno that is simple and effective for dealing with random packet loss. A key ingredient of Veno is that it monitors the network congestion level and uses that information to decide whether packet losses are likely to be due to congestion or random bit errors. Specifically: (1) it refines the multiplicative decrease algorithm of TCP Reno-the most widely deployed TCP version in practice-by adjusting the slow-start threshold according to the perceived network congestion level rather than a fixed drop factor and (2) it refines the linear increase algorithm so that the connection can stay longer in an operating region in which the network bandwidth is fully utilized. Based on extensive network testbed experiments and live Internet measurements, we show that Veno can achieve significant throughput improvements without adversely affecting other concurrent TCP connections, including other concurrent Reno connections. In typical wireless access networks with 1% random packet loss rate, throughput improvement of up to 80% can be demonstrated. A salient feature of Veno is that it modifies only the sender-side protocol of Reno without changing the receiver-side protocol stack.     

A Novel Wireless TCP and its Steady State Throughput Model

1　Introduction　WiththegrowthofwirelessnetworksandtheInter net,thedatatransmissionserviceoverwirelessnet worksbecomesmoreattractive .InthecurrentInternet,TCPiswidelyusedinpopularapplicationslikeTelnet,FTP ,andHTTP .　TCPisareliableconnection oriented protocolthatimplementscongestioncontrolbymeansofaslidingwindowalgorithm .TCPTahoeandReno[1～ 2 ] ,whichmakeuseoftheSlowStart (SS)andCongestionAvoid ance (CA)algorithmstoadjustthewindowsize ,havegotmuchsuccessintheInternet.Inparticular…     

TCP-Jersey for wireless IP communications

Improving the performance of the transmission control protocol (TCP) in wireless Internet protocol (IP) communications has been an active research area. The performance degradation of TCP in wireless and wired-wireless hybrid networks is mainly due to its lack of the ability to differentiate the packet losses caused by network congestions from the losses caused by wireless link errors. In this paper, we propose a new TCP scheme, called TCP-Jersey, which is capable of distinguishing the wireless packet losses from the congestion packet losses, and reacting accordingly. TCP-Jersey consists of two key components, the available bandwidth estimation (ABE) algorithm and the congestion warning (CW) router configuration. ABE is a TCP sender side addition that continuously estimates the bandwidth available to the connection and guides the sender to adjust its transmission rate when the network becomes congested. CW is a configuration of network routers such that routers alert end stations by marking all packets when there is a sign of an incipient congestion. The marking of packets by the CW configured routers helps the sender of the TCP connection to effectively differentiate packet losses caused by network congestion from those caused by wireless link errors. This paper describes the design of TCP-Jersey, and presents results from experiments using the NS-2 network simulator. Results from simulations show that in a congestion free network with 1% of random wireless packet loss rate, TCP-Jersey achieves 17% and 85% improvements in goodput over TCP-Westwood and TCP-Reno, respectively; in a congested network where TCP flow competes with VoIP flows, with 1% of random wireless packet loss rate, TCP-Jersey achieves 9% and 76% improvements in goodput over TCP-Westwood and TCP-Reno, respectively. Our experiments of multiple TCP flows show that TCP-Jersey maintains the fair and friendly behavior with respect to other TCP flows.     

Corruption‐aware adaptive increase and adaptive decrease algorithm for TCP error and congestion controls in wireless networks

The conventional TCP tends to suffer from performance degradation due to packet corruptions in the wireless lossy channels, since any corruption event is regarded as an indication of network congestion. This paper proposes a TCP error and congestion control scheme using corruption‐aware adaptive increase and adaptive decrease algorithm to improve TCP performance over wireless networks. In the proposed scheme, the available network bandwidth is estimated based on the amount of the received integral data as well as the received corrupted data. The slow start threshold is updated only when a lost but not corrupted segment is detected by sender, since the corrupted packets still arrive at the TCP receiver. In the proposed scheme, the duplicated ACKs are processed differently by sender depending on whether there are any lost but not corrupted segments at present. Simulation results show that the proposed scheme could significantly improve TCP throughput over the heterogeneous wired and wireless networks with a high bit error rate, compared with the existing TCP and its variants. Copyright © 2008 John Wiley & Sons, Ltd.     

Enhancing Fairness and Throughput of TCP in Heterogeneous Wireless Access Networks

Most of the recent research on TCP over heterogeneous wireless networks has concentrated on differentiating between packet drops caused by congestion and link errors, to avoid significant throughput degradations due to the TCP sending window being frequently shut down, in response to packet losses caused not by congestion but by transmission errors over wireless links. However, TCP also exhibits inherent unfairness toward connections with long round-trip times or traversing multiple congested routers. This problem is aggravated by the difference of bit-error rates between wired and wireless links in heterogeneous wireless networks. In this paper, we apply the TCP Bandwidth Allocation (TBA) algorithm, which we have proposed previously, to improve TCP fairness over heterogeneous wireless networks with combined wireless and wireline links. To inform the sender when congestion occurs, we propose to apply Wireless Explicit Congestion Notification (WECN). By controlling the TCP window behavior with TBA and WECN, congestion control and error-loss recovery are effectively separated. Further enhancement is also incorporated to smooth traffic bursts. Simulation results show that not only can the combined TBA and WECN mechanism improve TCP fairness, but it can maintain good throughput performance in the presence of wireless losses as well. A salient feature of TBA is that its main functions are implemented in the access node, thus simplifying the sender-side implementation.     

基于专家控制的无线网络拥塞控制机制的研究

由于无线网络中存在高误码、信号衰落、切换等原因，使得传统TCP的应用受到了挑战。本文提出了将专家控制用于无线网络的拥塞控制方案，它通过推理判断，确定当前的TCP连接状况，进而区分网络拥塞和无线链路差错，然后再针对不同的原因，选取正确的控制策略实施拥塞控制。仿真结果表明，该方法增强了网络对拥塞以及随机差错的实时处理能力，提高了网络的吞吐量，算法本身具有较强的顽健性。