TCP友好的速率控制

TCP友好的速率控制(TFRC)主要适用于实时数据传输的一种拥塞控制机制,具有突出的TCP友好性即在相同的环回时间(RTT)下可以和TCP流享有近乎相同的带宽,从而避免了由于UDP等传输层协议缺乏拥塞控制而带来的网络拥塞甚至崩溃.本文简要介绍了它的协议机制并通过一些仿真和试验的结果初步讨论了其性能.     

一种拥塞感知的TFRC协议慢启动算法

 本文分析了TFRC(TCP-Friendly Rate Control)协议在慢启动阶段采用类似TCP协议的倍增发送速率机制存在的问题,提出了一种利用回路响应时间(Round Trip Time,RTT)来自适应调节慢启动阶段速率的算法.通过分析实际RTT值和EWMA(Exponentially Weighted Moving Average)处理后的平均RTT值来感知网络当前的拥塞状况,以调节发送速率的激进程度.仿真实验表明,该方法对TFRC协议具有明显的改进作用,减少了慢启动阶段结束时的报文丢失率,提高了协议的传输平稳度和吞吐量,从而能更有效地适应多媒体流的传输要求.     

TFRC协议改进

为了对非TCP流进行拥塞控制,使它们与TCP流公平地分享带宽,人们设计了多种对TCP友好(TCP-Friendly)的协议。而TFRC(TCPFriendlyRateControl)协议是其中最重要的一种,它是IETF的提议标准。发送端根据接收端的反馈信息计算合理的发送速率。但如果贪婪接收端提供虚假反馈信息,会使发送端以不合理的高速率发送数据。本文对TFRC协议进行改进,使发送端能检测出虚假反馈信息,并对贪婪接收端进行惩罚。     

无线网络中TCP友好流媒体传输改进机制

为保持无线网络中多媒体业务对TCP的友好性，提出了一种适用于无线网络的动态自适应的流媒体传输速率调节机制。该机制通过在接收端区分网络拥塞丢包和链路错误随机丢包，准确判断网络的拥塞状况结合接收端缓存区占用程度，自适应实施多级速率调节，实现了TCP流友好性和流媒体服务质量（QoS）的折中。由于准确区分出无线链路误码丢包和动态调整流媒体QoS要求，该机制能维持较高的网络利用率。仿真实验结果显示在连接数为2和32，链路误码率从0到0．1变化时TCP,TFRC和吞吐量幅度下降幅度较大，WTFCC幅度下降相对较慢，最大相差达2M；在网络负载重时，尽管链路误码率较低，WTFCC区分链路错误与拥塞丢包，因此，端到端丢包率高于TCP和TFRC，但整体传输吞吐量也高于两者。归一化吞吐量显示WTFCC对TCP流友好。     

异构网络中基于移动IP切换的TFRC改进

TCP-Friendly Rate Control（TFRC）是一种专门针对实时多媒体流在Internet中传输的拥塞控制方案,但在有线无线异构网络频繁的越区切换中,传统的TFRC存在数据流变化异常的问题。针对此问题,提出了基于移动IP切换的TFRC拥塞控制方案,并利用ns进行仿真分析。结果表明,在网络发生移动IP的切换后,该方案能够准确判断出网络切换状态,并快速增加发送速率,充分利用网络带宽,减小用于增加发送速率的时长,从而减小传输时延。     

一种基于多路复用的多媒体流TCP友好拥塞控制机制

本文重点研究在多路复用的链路环境中,TCP友好与多媒体流最低速率阈值限定之间的权衡关系,提出了一种基于多路复用的TCP友好速率控制算法-MTCRC(Multiplexing and threshold-constrained rate control).MTCRC引入基于概率的随机试验技术,以保证多媒体流在多路复用时,当友好速率低于限定的最低速率时,通过在适当的时间对部分流的挂起操作,使多媒体流的平均吞吐量仍保持TCP友好.MTCRC是对TFRC(TCP-friendly rate control)的改进,它在保持TFRC良好的速率平滑性的同时,增加了对多媒体流最低速率阈值限定特性及多路复用链路环境的考虑,使其既能尽量保持多媒体流应用的有效性,又能与竞争的TCP流公平地分享带宽.模拟结果显示:MTCRC的性能明显优于TFRC.     

基于显式速率的TCP友好的UDP拥塞控制策略

本文提出了一种基于显式速率的UDP拥塞控制策略：通过源端和网络中的路由器相互配合，使得实时UDP应用能够根据网络的反馈以瓶颈链路的公平带宽为速率发送数据。此种控制策略对TCP应用是友好的，并且提高了网络的吞吐量和利用率。仿真结果表明：基于显式速率的UDP拥塞控制策略与采用TFRC(TCP—Friendly Rate Control)的UDP拥塞控制策略相比，在吞吐量、TCP友好性等方面性能有较大提高。     

传输实时多媒体流的新协议TFRC

当前实际网络中传输实时多媒体流使用UDP协议；但UDP与TCP间不公平。基于此近几年提出了TCP友好的概念，TFRC是其中发展较好的一个协议，是当前的一个研究热点。由于国内对其研究较少，对TFRC很有介绍的必要。     

联合无线网络编码与TCP Vegas的多播协议优化研究

为解决移动自组网中网络编码多播路由协议因业务传输负载增大,而产生的网络拥塞现象,本文提出了一种可靠的基于TCP Vegas窗口拥塞控制的网络编码多播路由协议。该协议的核心思想是发送节点采用发送窗口自调整和反馈消息触发发送窗口调整的机制,综合的调节数据包的发送速率,来改善网络拥塞现象,从而可以降低丢包率。仿真结果表明,当传输负载增大时,基于窗口拥塞控制的网络编码多播路由协议可使得系统的总开销大大降低,分组投递率获得了相对的提升。     

无线ad hoc网络中基于帧传输效率的拥塞控制方法

提出以一种基于帧传输效率的MAC层拥塞通告机制,当中间节点检测到帧传输效率小于某一阈值时,通过ECN通告使发送方主动降低发送速率.该机制只需在链路层完成,不需改变现有的传输层协议.仿真结果表明该方法能较大地提高网络的效率,尤其在多流情况下比原有的TCP协议的吞吐量提高了50%左右,同时能够保证多流之间的公平性.     

VIRAL: coupling congestion control with fair video quality metric

Video streaming is often carried out by congestion controlled transport protocols to preserve network sustainability. However, the success of the growth of such non-live video flows is linked to the user quality of experience. Thus, one possible solution is to deploy complex quality of service systems inside the core network. Another possibility would be to keep the end-to-end principle while making aware transport protocols of video quality rather than throughput. The objective of this article is to investigate the latter by proposing a novel transport mechanism which targets video quality fairness among video flows. Our proposal, called VIRAL for virtual rate-quality curve, allows congestion controlled transport protocols to provide fairness in terms of both throughput and video quality. VIRAL is compliant with any rate-based congestion control mechanisms that enable a smooth sending rate for multimedia applications. Implemented inside TFRC a TCP-friendly protocol, we show that VIRAL enables both intra-fairness between video flows in terms of video quality and inter-fairness in terms of throughput between TCP and video flows.     

Equation-based end-to-end single-rate multicast congestion control

Among the recently proposed single-rate multicast congestion control protocols is transmission control protocol-friendly multicast congestion control (TFMCC; Widmer and Handley 2001; Floyd et al. 2000; Widmer et al. IEEE Netw 15:28–37, 2001), which is an equation-based single-rate protocol that extends the mechanisms of the unicast TCP-friendly rate control (TFRC) protocol into the multicast domain. In TFMCC, each receiver estimates its throughput using an equation that estimates the steady-state throughput of a TCP source. The source then adjusts its sending rate according to the slowest receiver within the session (a.k.a., current-limiting receiver, CLR). TFMCC is a relatively simple, scalable, and TCP-friendly multicast congestion control protocol. However, TFMCC is hindering its throughput performance by adopting an equation derived from the unicast TFRC protocol. Further, TFMCC is slow to react to congestion conditions that usually result in a change of the CLR. This paper is motivated by these two observations and proposes an improved version of TFMCC, which we refer to as hybrid-TFMCC (or H-TFMCC for short). First, each receiver estimates its throughput using an equation that models the steady-state throughput of a multicast source controlled according to the additive increase multiplicative decrease (AIMD) approach. The second modification consists of adopting a hybrid sender/receiver-based rate control strategy, where the sending rate can be adjusted by the source or initiated by the current or a new CLR. The source monitors RTT variations on the CLR path, in order to rapidly adjust the sending rate to network conditions. Simulation results show that these modifications result in remarkable performance improvement with respect to throughput, time to react, and magnitude of oscillations. We also show that H-TFMCC remains TCP-friendly and achieves a higher fairness index than that achieved by TFMCC.     

Limitations of Equation-Based Congestion Control

We study limitations of an equation-based congestion control protocol, called TCP-friendly rate control (TFRC). It examines how the three main factors that determine TFRC throughput, namely, the TCP-friendly equation, loss event rate estimation, and delay estimation, can influence the long-term throughput imbalance between TFRC and TCP. Especially, we show that different sending rates of competing flows cause these flows to experience different loss event rates. There are several fundamental reasons why TFRC and TCP flows have different average sending rates, from the first place. Earlier work shows that the convexity of the TCP-friendly equation used in TFRC causes the sending rate difference. We report two additional reasons in this paper: 1) the convexity of where is a loss event period and 2) different retransmission timeout period (RTO) estimations of TCP and TFRC. These factors can be the reasons for TCP and TFRC to experience initially different sending rates. But we find that the loss event rate difference due to the differing sending rates greatly amplifies the initial throughput difference; in some extreme cases, TFRC uses around 20 times more, or sometimes 10 times less, bandwidth than TCP. Despite these factors influencing the throughput difference, we also find that simple heuristics can greatly mitigate the problem.     

TFRC friendliness and the case of ECN

The TFRC protocol has been proposed as a TCP‐friendly protocol to transport streaming media over the Internet. However, its deployment is still questionable because it has not been compared to other important protocols, analysed in the presence of important mechanisms, such as the explicit congestion notification (ECN), and studied under more realistic network conditions. In this paper, we address these three aspects, including other congestion control protocols not considered before in the same investigation, such as TCP Tahoe, Reno, Newreno, Vegas, Sack, GAIMD, and the Binomial algorithms, the effect of using ECN in the friendliness of the protocols, and the fairness of the protocols under static and dynamic network conditions. We found that TFRC can be safely deployed in the Internet if competing with TCP Tahoe, New Reno and SACK since fairness is achieved under all scenarios considered. We also found that ECN actually helps in achieving better fairness. However, fairness problems arise when TFRC competes with TCP Reno, GAIMD, SQRT or IIAD in static or dynamic conditions, or both. We used normalized throughput, fairness index, and convergence time as the main performance metrics for comparison. Copyright © 2004 John Wiley & Sons, Ltd.     

Measurement-based TFRC: improving TFRC in heterogeneous mobile networks

As a well-known multimedia stream transport protocol, TFRC provides smooth transfer rate under stable network conditions, and achieves good fairness to TCP. However, it is not flexible in heterogeneous mobile networks because the available bandwidth varies rapidly. This paper proposes a measurement based TFRC (MBTFRC) protocol, which uses passive bandwidth measurements at the receiver to improve the flexibility of TFRC. In addition, a window-based EWMA filter with two weights is used to achieve stability and fairness simultaneously. Simulation results verify the flexibility, stability and fairness of MBTFRC.     

A study of a simple preventive transport protocol

The main qualities of a protocol for multimedia flows transportation are related to the way congestions are handled. This paper addresses the problem of end-to-end congestion control performed in the Internet transport layer. We present a simple protocol called Primo, which determines the appropriate sending rate in order to maximize network resources usage and minimize packets loss. Comparison with existing transport protocols (Tcp Reno, Sack, Vegas andTfrc) are considered, regarding various efficiency criteria such as sending and reception rates stability, loss rate, resources occupancy rate and fairness.     

一种在接收端实现的TCP-Friendly拥塞控制机制

本文提出了一种基于速率的单播TCP-Friendly拥塞控制算法——RAAR(Rate Adaptation at Receivers)控制机制.RAAR是一种接收端的速率自适应算法,它抛弃了每包反馈机制,采用GAIMD(General Additive Increase Multiplicative Decrease)策略进行拥塞控制,其主要控制操作由接收方完成.本文建立了简化的数学模型对其进行吞吐量的分析,得到在RAAR中用于TCP-Friendly 的GAIMD拥塞控制中α与 β的关系.通过与TFRC及TEAR这两种重要的TCP-Friendly协议进行对比研究发现,RAAR协议在对TCP协议的友好性,协议内的公平性以及速率的平滑性等方面具有更好的综合性能.由于RAAR不需进行每包反馈,且主要功能在接收方实现,因此可方便地将该机制引入多媒体组播传输系统中.     

Improving Transport Layer Performance in Multihop Ad Hoc Networks by Exploiting MAC Layer Information

The traditional TCP congestion control mechanism encounters a number of new problems and suffers a poor performance when the IEEE 802.11 MAC protocol is used in multihop ad hoc networks. Many of the problems result from medium contention at the MAC layer. In this paper, we first illustrate that severe medium contention and congestion are intimately coupled, and TCP's congestion control algorithm becomes too coarse in its granularity, causing throughput instability and excessively long delay. Further, we illustrate TCP's severe unfairness problem due to the medium contention and the tradeoff between aggregate throughput and fairness. Then, based on the novel use of channel busyness ratio, a more accurate metric to characterize the network utilization and congestion status, we propose a new wireless congestion control protocol (WCCP) to efficiently and fairly support the transport service in multihop ad hoc networks. In this protocol, each forwarding node along a traffic flow exercises the inter-node and intra-node fair resource allocation and determines the MAC layer feedback accordingly. The end-to-end feedback, which is ultimately determined by the bottleneck node along the flow, is carried back to the source to control its sending rate. Extensive simulations show that WCCP significantly outperforms traditional TCP in terms of channel utilization, delay, and fairness, and eliminates the starvation problem     

一种无线传感器网络公平数据收集方案(英文)

To solve the slow congestion detection and rate convergence problems in the existing rate control based fair data collection schemes, a new fair data collection scheme is proposed, which is named the improved scheme with fairness or ISWF for short. In ISWF, a quick congestion detection method, which combines the queue length with traffic changes of a node, is used to solve the slow congestion detection problem, and a new solution, which adjusts the rate of sending data of a node by monitoring the channel utilization rate, is used to solve the slow convergence problem. At the same time, the probability selection method is used in ISWF to achieve the fairness of channel bandwidth utilization. Experiment and simulation results show that ISWF can effectively reduce the reaction time in detecting congestion and shorten the rate convergence process. Compared with the existing tree-based fair data collection schemes, ISWF can achieve better fairness in data collection and reduce the transmission delay effectively, and at the same time, it can increase the average network throughput by 9.1% or more.