TCP友好速率控制协议的分析及应用

传统的TCP由于采用速率减半的拥塞退避机制而使其在数据传输时易产生过大的速率波动,而UDP不具备拥塞退避机制,在拥塞的网络环境中,UDP流将大量抢占TCP流的网络带宽,同时自身的丢包也迅速增加,并可能带来系统拥塞崩溃的潜在危险,因此TCP和UDP都不能很好地满足实时流媒体业务的需要。文中研究了一个具有拥塞退避机制、网络吞吐量波动小,且能够与TCP协议公平分享带宽的传输协议———TCP友好速率控制协议(TFRC),并将其应用于实时多媒体流传输应用程序。研究测试结果表明采用TFRC后多媒体的实时播放较TCP平滑了许多。     

流媒体自适应传输控制的研究

流媒体是指多媒体数据流在网络上一边传输一边播放的一种多媒体通信服务.提供尽力而为服务的Internet不能为流媒体保证网络带宽、传输延迟、分组丢失以及分组错误等,而自适应传输控制机制能够提高流媒体服务的传输服务质量和传输服务的公平性.本文探讨流媒体自适应传输控制技术所涉及的各个方面,包括拥塞控制、质量自适应和错误控制.     

基于自适应加权平均的TCP友好拥塞控制机制

TCP友好拥塞控制是保证实时媒体流和组播业务在Internet广泛应用的关键技术.基于收端TCP模拟方案TEAR(TCP emulation at receivers),提出了一个根据丢包类型和当前拥塞周期的持续时间动态调整加权平均参数的拥塞控制机制,称为自适应TCP友好拥塞控制方案ATFCC(adaptive TCP-Friendly congestion control).仿真结果表明,ATFCC方案在速率平滑程度和TCP友好性方面的性能优于TCP友好速率控制协议TFRC(TCP-Friendly rate control).     

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。     

端到端的流媒体传输控制技术研究综述

随着多媒体应用的发展,因特网上的流媒体传输技术已成为研究热点。在因特网上传输音频或视频流需要有带宽、延迟、丢包率等诸多的QoS要求,但当前的因特网并不提供任何QoS保证,这对流媒体在因特网上的传输提出巨大挑战。该文从端到端的传输控制技术角度入手,给出了一个因特网上流媒体传输的总体框架,然后依此框架为线索,对流媒体传输所必需的协议栈、拥塞控制、自适应速率编码、速率整形、差错控制等技术的研究进展进行了概括总结并进行了对比,同时提出了进一步的研究建议。     

拥塞／速率控制算法及其在多媒体数据传输中的应用

基于Internet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基础上,能够与Internet其他服务所使用的TCP协议合理共享有限的带宽,在研究多种拥塞控制算法的基础上,提出了一种简单实用的TCP友好拥塞／速率控制算法,并将该算法应用在一个实用的IP电话软件中,取得了预期的效果。     

Stochastic TCP friendliness: Expanding the design space of TCP-friendly traffic control protocols

While the current definition of TCP friendliness has enabled a wide variety of traffic control protocols other than TCP, it still considerably restricts the design space of TCP-friendly traffic control protocols. For example, some multimedia streaming applications prefer a smooth sending rate on a time scale of tens of seconds, however, a UDP flow maintaining such a long smoothness time scale is naturally not TCP friendly by the current definition. In this paper, we propose an innovative method to relatively compare the degrees of TCP friendliness of different traffic control protocols, and use it to define a new class of TCP friendliness definitions, called stochastic TCP friendliness (STF). STF greatly expands the design space of TCP-friendly traffic control protocols, while still effectively maintaining the desired fairness of the Internet. To demonstrate the expanded design space, we also develop a new congestion control protocol, called TCP-friendly CBR-Like Rate Control (TFCBR), for multimedia streaming applications which do not require a high sending rate but prefer a smooth sending rate on a time scale of tens of seconds. TFCBR is stochastically TCP friendly, however, it is not TCP friendly by the current definition.     

A real-time protocol for the Internet based on the least mean square algorithm

Generally, real-time applications based on the User Datagram Protocol (UDP) generate large volumes of data and are not sensitive to network congestion. In contrast, Transmission Control Protocol (TCP) traffic is considered "well-behaved" because it prevents the network becoming congested by means of closed-loop control of packet-loss and round-trip-time. The integration of both sorts of traffic is a complex problem, and depends on solutions such as admission control that have not yet been deployed on the Internet. Moreover, the problem of quality-of-service (QoS) and resource allocation is extremely relevant from the point of view of convergence of streaming media and data transmission on the Internet. In this paper an adaptive real-time protocol based on the least mean square (LMS) algorithm is proposed to estimate the application UDP bandwidth in order to reduce the quadratic error between the packet loss and a target. Moreover, the LMS algorithm is also applied to make sure that the reduction in the average bandwidth allocated to each TCP process will not be higher than a given percentage of the average bandwidth allocated before the beginning of the UDP application.     

Internet上基于两端的流媒体QoS控制

在Internet这类无法可靠保证服务质量QoS的网络环境中,拥塞和带宽的不足成为流媒体应用的主要瓶颈,所以,流媒体应用的关键是QoS控制机制.QoS控制大致分为两大类:基于路由和基于两端.基于两端的QoS控制技术的基本思想是:网络状况好的时候多传些数据增强播放质量,网络状况不好的时候则只传输能够达到基本播放效果的数据.即QoS技术能够动态地调节传输数据量的多少.主要分析和介绍了相关的流媒体编码技术、基于客户端的QoS控制和基于服务器端的QoS控制技术.     

Media- and TCP-friendly congestion control for scalable video streams

This paper presents a media- and TCP-friendly rate-based congestion control algorithm (MTFRCC) for scalable video streaming in the Internet. The algorithm integrates two new techniques: i) a utility-based model using the rate-distortion function as the application utility measure for optimizing the overall video quality; and ii) a two-timescale approach of rate averages (long-term and short-term) to satisfy both media and TCP-friendliness. We evaluate our algorithm through simulation and compare the results against the TCP-friendly rate control (TFRC) algorithm. For assessment, we consider five criteria: TCP fairness, responsiveness, aggressiveness, overall video quality, and smoothness of the resulting bit rate. Our simulation results manifest that MTFRCC performs better than TFRC for various congestion levels, including an improvement of the overall video quality.     

Extending equation-based congestion control to high-speed and long-distance networks

TCP-friendly rate control (TFRC), an equation-based congestion control protocol, has been a promising alternative to TCP for multimedia streaming applications. However, TFRC using the TCP response function, has the same poor performance as TCP in high-speed and long-distance networks. In this paper, we propose high-speed equation-based rate control (HERC), as an extension of TFRC by replacing the TCP response function with a high-speed response function. HERC could be used for applications, such as high-definition video streaming, and remote collaboration involving high-resolution visualization, which prefer a high-speed and relatively smooth sending rate. The impact of a general high-speed response function on the throughput and smoothness of HERC is studied analytically and verified by using simulation. Our result indicates that by using the response function of a high-speed TCP variant and tuning HERC parameters accordingly, HERC can compete fairly with high-speed TCP flows in the same network, while maintaining the desired smoothness of TFRC.     

TCP及TCP-friendly拥塞控制策略讨论

自从20世纪80年代报道了第一次拥塞崩溃以来，TCP拥塞控制策略在不断地进行完善和改进，通过快速重传和快速恢复等机制使它能很好地对网络拥塞做出及时的响应。但是随着网络技术的发展，音频和视频等多媒体业务(如IP Phone、视频会议)在网上的应用越来越多，而这些应用采用的一般都是不提供拥塞控制的协议(如UDP)，因此如何对这些业务流进行拥塞控制，使它们能与TCP流一起公平地共享网络带宽，满足TCP-friendly要求变得越来越重要。该文先对TCP拥塞控制进行讨论，然后对TCP-friendly拥塞控制策略和以后的研究方向进行了讨论。     

一种基于模型的实时媒体流拥塞控制机制

随着因特网上实时媒体流应用的不断增多，采用AIMD算法的TCP拥塞控制已显出其不足，研究一种适合于实时媒体传输且具有有效拥塞控制机制的TCP友好的传输协议，已成为因特网传输领域的一个重要课题。本文在分析了已有实时媒体流拥塞控制算法的基础上，提出了一种基于模型的实时媒体流拥塞控制机制MBCC。该机制采用TCP吞吐量模型，根据丢包事件率和对未来往返时间RTT的预测值较为平滑地调节发送速率。实验证明，该机制不仅能准确跟踪可用带宽，具有平滑的发送速率，而且是TCP友好的。     

基于带宽充分利用的TCP友好拥塞控制机制

当基于TCP的应用和基于UDP的应用共享网络时，由于UDP协议没有拥塞控制机制，为了防止基于UDP的应用占尽所有的带宽，UDP应该具有TCP友好性(TCP_friendly)。提出一种机制以解决该问题。在保证UDP数据流的发送速率不大于TCP数据流的发送速率的基础上，利用剩余可用的带宽发送best_efort数据流，在网关采用改进的支持包标记处理的RED(随机早期检测)队列管理机制对不同流量进行相应的处理。     

Research into two source-based control algorithms for Internet traffic flows

TCP and UDP are the major applications over the Internet, the characteristics of them lead to different network transmission behaviors. Two source-based mechanisms are proposed in this paper to regulate TCP and UDP flows. One is the congestion control mechanism, which uses TCP flows’ congestion signal to regulate the flows at the source node. The other is the time slot mechanism, which is a time-sharing application to control their flow transmission. Based on the priorities of flows, different bandwidth proportions are allocated and differential services are provided for flows. Several scenarios are simulated to observe the transmission operations of these two mechanisms. Simulation results show some insights into two mechanisms. Moreover, the several simulation parameters that may impact the performance of these two mechanisms are summarized.     

基于ECN的实时多媒体的实时多媒体流TCP友好控制

随着Internet上多媒体应用的日益增加,实时多媒体流的TCP友好控制成为当前的研究热点。该机制基于RTP/RTCP协议,以ECN的方式将拥塞状况通知发送端,在路由器中采用RED队列管理策略,在端主机采用TCP友好的速率调节机制。ECNBCC机制具有TCP友好的特性并且可以对网络早期拥塞作出反应,从而降低丢包率和网络延时,该机制也可用于无线网络多媒体流的拥塞控制。     

Adaptive efficient video transmission over the Internet based on congestion control and RS coding

An approach based on adaptive congestion control and adaptive error recovery with RS (Reed-Solomon) coding method is presented for efficient video transmission over the Internet. Featured by weighted moving average rate control and TCP-friendliness, AVSP, a novel adaptive video streaming protocol, is designed with adjustable rate control parameters so as to respond quickly to the QoS status fluctuation during video transmission over the Internet. Combined with congestion control policy, an adaptive RS coding error recovery scheme with variable parameters is presented to enhance the robustness of MPEG video transmission over the Internet with restriction to the total system bandwidth .     

TCP友好拥塞／速率控制算法及其在多媒体数据传输中的应用

基于Intenret的以UDP为传输协议的实时多媒体数据传输,需要在保证 实时性和可靠性基础上,能够与Internet其它服务所使用的TCP协议共享有限的带宽,基于这种需要,该文在研究了多种拥塞控制算法的基础上,提出了一种简单实用的TCP友好拥塞／速率控制算法,并将该算法应用在一个实用的Internet IP电话软FreePhone中,通过试验证明,该方法实用有效,并取得了预期的效果。     

Resource allocation for multimedia streaming over the Internet

This paper addresses the resource allocation problem for multiple media streaming over the Internet. First, we present an end-to-end transport architecture for multimedia streaming over the Internet. Second, we propose a new multimedia streaming TCP-friendly protocol (MSTFP), which combines forward estimation of network conditions with information feedback control to optimally track the network conditions. Third, we propose a novel resource allocation scheme to adapt media rate to the estimated network bandwidth using each media's rate-distortion function under various network conditions. By dynamically allocating resources according to network status and media characteristics, we improve the end-to-end quality of services (QoS). Simulation results demonstrate the effectiveness of our proposed schemes     

面向TCP友好性的IP网络实时流媒体流预测控制

为了解决IP网络实时流媒体流控中既要避免网络拥塞又要将接收端缓冲区长度控制在合理范围的难题, 本文提出了一种面向TCP友好性的IP网络实时流媒体流预测控制算法. 该算法将IP网络实时流媒体流控转化为具有TFRC约束时变不确定条件的预测控制问题, 使用改进的动态矩阵控制算法(DMC)进行优化求解. 仿真实验结果表明该方法能够适应IP网络的复杂环境, 满足了TCP友好性要求, 有效地消除了网络传输抖动对播放带来的不利影响, 具有良好的实用性.