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Burst assembly is one of the key factors affecting the TCP performance in optical burst switching (OBS) networks. When the
TCP congestion window is small, the fixed-delay burst assembler waits unnecessarily long, which increases the end-to-end delay
and thus decreases the TCP goodput. On the other hand, when the TCP congestion window becomes larger, the fixed-delay burst
assembler may unnecessarily generate a large number of small-sized bursts, which increases the overhead and decreases the
correlation gain, resulting in a reduction in the TCP goodput. In this paper, we propose adaptive burst assembly algorithms
that use the congestion window sizes of TCP flows. Using simulations, we show that the usage of the congestion window size
in the burst assembly algorithm significantly improves the TCP goodput (by up to 38.4% on the average and by up to 173.89%
for individual flows) compared with the timer-based assembly, even when the timer-based assembler uses the optimum assembly
period. It is shown through simulations that even when estimated values of the congestion window size, that are obtained via
passive measurements, are used, TCP goodput improvements are still close to the results obtained by using exact values of
the congestion window. 相似文献
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为了计算无线自组织网络中准确的TCP容量,并利用其进行有效的窗口控制,以避免拥塞窗口增长过速的问题,提出一种适用于无线自组织网络TCP容量的优化计算。此方法基于时延和空间复用率,考虑网络中竞争干扰,解决了以往的计算方法对拓扑不能广泛适用的问题。模拟结果显示,基于文章的TCP容量进行拥塞窗口调节,能有效地提高网络的吞吐量。 相似文献
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In this letter, a new transport layer mechanism is proposed to improve the performance of transport control protocol (TCP) in mobile networks. The proposed mechanism is comprised of two parts: a loss classifier (LC) and a congestion window extrapolator (CWE). Based on LC, the cause of packet loss during roaming is determined. If the loss is considered to be caused by congestion in the wireline, the congestion window is halved; otherwise, the packet is considered to be lost in the last hop, the wireless portion, and the sender adjusts the size of the congestion window based on CWE. We conduct simulations to evaluate the performance of the proposed mechanism. The results show that our mechanism significantly improves TCP performance as compared with existing solutions for mobile networks. 相似文献
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TCP Smart Framing, or TCP-SF for short, enables the Fast Retransmit/Recovery algorithms even when the congestion window is small. Without modifying the TCP congestion control based on the additive-increase/multiplicative-decrease paradigm, TCP-SF adopts a novel segmentation algorithm: while Classic TCP always tries to send full-sized segments, a TCP-SF source adopts a more flexible segmentation algorithm to try and always have a number of in-flight segments larger than 3 so as to enable Fast Recovery. We motivate this choice by real traffic measurements, which indicate that today's traffic is populated by short-lived flows, whose only means to recover from a packet loss is by triggering a Retransmission Timeout. The key idea of TCP-SF can be implemented on top of any TCP flavor, from Tahoe to SACK, and requires modifications to the server TCP stack only, and can be easily coupled with recent TCP enhancements. The performance of the proposed TCP modification were studied by means of simulations, live measurements and an analytical model. In addition, the analytical model we have devised has a general scope, making it a valid tool for TCP performance evaluation in the small window region. Improvements are remarkable under several buffer management schemes, and maximized by byte-oriented schemes. 相似文献
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TCP Westwood: End-to-End Congestion Control for Wired/Wireless Networks 总被引:11,自引:0,他引:11
Casetti Claudio Gerla Mario Mascolo Saverio Sanadidi M.Y. Wang Ren 《Wireless Networks》2002,8(5):467-479
TCP Westwood (TCPW) is a sender-side modification of the TCP congestion window algorithm that improves upon the performance of TCP Reno in wired as well as wireless networks. The improvement is most significant in wireless networks with lossy links. In fact, TCPW performance is not very sensitive to random errors, while TCP Reno is equally sensitive to random loss and congestion loss and cannot discriminate between them. Hence, the tendency of TCP Reno to overreact to errors. An important distinguishing feature of TCP Westwood with respect to previous wireless TCP extensions is that it does not require inspection and/or interception of TCP packets at intermediate (proxy) nodes. Rather, TCPW fully complies with the end-to-end TCP design principle. The key innovative idea is to continuously measure at the TCP sender side the bandwidth used by the connection via monitoring the rate of returning ACKs. The estimate is then used to compute congestion window and slow start threshold after a congestion episode, that is, after three duplicate acknowledgments or after a timeout. The rationale of this strategy is simple: in contrast with TCP Reno which blindly halves the congestion window after three duplicate ACKs, TCP Westwood attempts to select a slow start threshold and a congestion window which are consistent with the effective bandwidth used at the time congestion is experienced. We call this mechanism faster recovery. The proposed mechanism is particularly effective over wireless links where sporadic losses due to radio channel problems are often misinterpreted as a symptom of congestion by current TCP schemes and thus lead to an unnecessary window reduction. Experimental studies reveal improvements in throughput performance, as well as in fairness. In addition, friendliness with TCP Reno was observed in a set of experiments showing that TCP Reno connections are not starved by TCPW connections. Most importantly, TCPW is extremely effective in mixed wired and wireless networks where throughput improvements of up to 550% are observed. Finally, TCPW performs almost as well as localized link layer approaches such as the popular Snoop scheme, without incurring the overhead of a specialized link layer protocol. 相似文献
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Hiroyuki Hisamatsu Hiroyuki Ohsaki Masayuki Murata 《International Journal of Communication Systems》2005,18(7):639-656
The Internet uses a window‐based congestion control mechanism in transmission control protocol (TCP). In the literature, there have been a great number of analytical studies on TCP. Most of those studies have focused on the statistical behaviour of TCP by assuming a constant packet loss probability in the network. However, the packet loss probability, in reality, changes according to the packet transmission rates from TCP connections. Conversely, the window size of a TCP connection is dependent on the packet loss probability in the network. In this paper, we explicitly model the interaction between the congestion control mechanism of TCP and the network as a feedback system. By using this model, we analyse the steady state and the transient state behaviours of TCP. We derive the throughput and the packet loss probability of TCP, and the number of packets queued in the bottleneck router. We then analyse the transient state behaviour using a control theoretic approach, showing the influence of the number of TCP connections and the propagation delay on the transient state behaviour of TCP. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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针对目前Internet中TCP拥塞控制和式增加、积式减小和窗口变化机制,分析了TCP流量控制带宽分配的公平性问题。 相似文献
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Fei Peng Victor C. M. Leung 《International Journal of Wireless Information Networks》2007,14(3):225-236
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. 相似文献
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Various version of Transmission Control Protocol (TCP) congestion window model are available in the literature. TCP congestion control is handled in two phases: (a) slow start and (b) congestion avoidance. This paper deals with congestion avoidance phase that is based on additive increase multiplicative decrease (AIMD) mechanism in which window size either increase by one or cuts to half of the previous window size. For distribution of window sizes, a model developed by Yan et al has been presented for two loss indications: (a) triple duplicate (TD) and (b) time‐outs (TOs) only while it does not deal with the window size limitation. It does not allow to cap over the TCP congestion window size if the buffer size is restricted to a fixed value though window size could not move beyond that. The unconstrained window size moves on in the presence of low loss probability. In this paper, we propose a model for the case where the window size is bounded by a maximum value that makes applicable to window size limitation as well. Further, the work has been extended to develop a new model that obtains a cumulative distribution function for TD periods (TDPs). The proposed model is validated on ns‐2, and we conclude that observed results for distribution function are very closed to our proposed model. 相似文献
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卫星ATM是近年来卫星通信领域的一个研究热点,TCP业务在卫星ATM中的传输是其中一个重要的研究课题.由于在TCP协议中主要是通过对窗口的控制来实现拥塞控制,而卫星信道传输的长延时特性大大降低了TCP层拥塞控制的效率.本文提出一种基于UBR传输的明确窗口指示拥塞控制策略,仿真结果表明在效率、公平性、VBR背景传输下的性能等各方面,取得了比目前广泛使用的Reno TCP更好的结果.并且该算法实现简单,交换机实现零信元丢失的缓冲区很小并且与TCP源连接的数目无关. 相似文献
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基于TCP/IP的卫星通信传输链路的改进 总被引:2,自引:0,他引:2
卫星网络固有的一些特性影响了TCP/IP的性能。针对延迟、拥塞率、比特差错率、网络不对称性等问题,提出了支持较大的流量控制窗口及改进拥塞控制算法的方法,对现有的TCP/IP进行了改进。 相似文献
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We consider a modification of TCP congestion control in which the congestion window is adapted to explicit bottleneck rate feedback; we call this RATCP (Rate Adaptive TCP). Our goal in this paper is to study and compare the performance of RATCP and TCP in various network scenarios with a view to understanding the possibilities and limits of providing better feedback to TCP than just implicit feedback via packet loss. To understand the dynamics of rate feedback and window control, we develop and analyze a model for a long-lived RATCP (and TCP) session that gets a time-varying rate on a bottleneck link. We also conduct experiments on a Linux based test-bed to study issues such as fairness, random losses, and randomly arriving short file transfers. We find that the analysis matches well with the results from the test-bed. For large file transfers, under low background load, ideal fair rate feedback improves the performance of TCP by 15%-20%. For small randomly arriving file transfers, though RATCP performs only slightly better than TCP it reduces losses and variability of throughputs across sessions. RATCP distinguishes between congestion and corruption losses, and ensures fairness for sessions with different round trip times sharing the bottleneck link. We believe that rate feedback mechanisms can be implemented using distributed flow control and recently proposed REM in which case, ECN bit itself can be used to provide the rate feedback. 相似文献
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LIU Gang ZHANG De-yun LIU Jing DING Hui-ning School of Electronics Information Engineering Xi'an Jiaotong University Xi'an P.R. China School of Computer Science Engineering Xi'an University of Technology Xi'an P.R. China Northwest Regional Network of CERNET Xi'an Jiaotong University Xi'an P.R. China. 《中国邮电高校学报(英文版)》2004,11(2)
1 Introduction TransmissionControlProtocol(TCP) [1 ] iswidelyusedinthecurrentInternet,andmanyofpopularInternetservices,includingHyperTextTransferProtocol (HTTP) [2~3] andFileTransferProtocol(FTP) [4] ,useitasthede factostandardtransport layer protocol.TCPVegas[5~6] wasproposedin1 994,whichovercameseveraldrawbacksofTCPReno[7] ,andcanachievebetween 40and 70 percentbetterthroughputascomparedtotheimplementa tionofTCPintheRenodistributionofBSDU NIX[8] andotherTCPversion[9~1 1 ]… 相似文献
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《Lightwave Technology, Journal of》2009,27(4):386-395
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This work proposes a stochastic model to characterize the transmission control protocol (TCP) over optical burst switching
(OBS) networks which helps to understand the interaction between the congestion control mechanism of TCP and the characteristic
bursty losses in the OBS network. We derive the steady-state throughput of a TCP NewReno source by modeling it as a Markov
chain and the OBS network as an open queueing network with rejection blocking. We model all the phases in the evolution of
TCP congestion window and evaluate the number of packets sent and time spent in different states of TCP. We model the mixed
assembly process, burst assembler and disassembler modules, and the core network using queueing theory and compute the burst
loss probability and end-to-end delay in the network. We derive expression for the throughput of a TCP source by solving the
models developed for the source and the network with a set of fixed-point equations. To evaluate the impact of a burst loss
on each TCP flow accurately, we define the burst as a composition of per-flow-bursts (which is a burst of packets from a single
source). Analytical and simulation results validate the model and highlight the importance of accounting for individual phases
in the evolution of TCP congestion window. 相似文献