Comments on "Modeling TCP reno performance: a simple model and its empirical Validation"

In this Comments, several errors in Padhye , 2000, are pointed out. The more serious of these errors result in an over prediction of the send rate. The expression obtained for send rate in this Comments leads to greater accuracy when compared with the measurement data than the originals end rate expression in Padhye et al.     

Analysis of TCP Vegas and TCP Reno

In this paper we use an analytic fluid approach in order to analyze the different features of both Vegas and Reno TCP versions. We then use simulations to confirm our analytic results. When the available bandwidth is high, indeed Vegas can retransmit less than one‐fifth as much data as Reno does, so that the higher the available bandwidth is, the more efficient Vegas is. However, under heavy congestion Vegas behaves like Reno and does not manage to make efficient use of its new mechanism for congestion detection. The analytic results that we obtain are the evolution of the window size, round trip times and their averages, and the average throughput. This revised version was published online in June 2006 with corrections to the Cover Date.     

一种改进的TCP稳态流吞吐量模型及其性能分析

根据对Internet上TCP稳态数据流的实测分析,在Padhye模型的基础上,本文提出了一种改进的TCP稳态数据流模型。该模型不仅考虑了三次重复应答和超时事件对TCU稳态流吞吐量的影响,而且还充分考虑了超时后慢启动过程的影响。文中给出了改进模型与实测结果的分析比较,表明改进的模型能更好地预测实际TCP数据流的吞吐量性能。最后,本文还分析了模型的几个主要参数对TCP吞吐量性能的影响。     

Equilibrium and Fairness of Networks Shared by TCP Reno and Vegas/FAST

It has been proved theoretically that a network with heterogeneous congestion control algorithms that react to different congestion signals can have multiple equilibrium points. In this paper, we demonstrate this experimentally using TCP Reno and Vegas/FAST. We also show that any desired inter-protocol fairness is in principle achievable by an appropriate choice of Vegas/FAST parameter, and that intra-protocol fairness among flows within each protocol is unaffected by the presence of the other protocol except for a reduction in effective link capacities. Dummynet experiments and ns-2 simulations are presented to verify these results.     

On TCP performance in a heterogeneous network: a survey

Transmission media carrying Internet traffic present a wide range of characteristics, some of which, such as transmission errors, long end-to-end delay, and bandwidth asymmetry, may cause a degradation of the TCP performance. Many works have studied the performance of TCP over these media, most of which focus on a particular network type. In this work we study TCP performance independent of the type of network by considering the different possible characteristics of the connection path. We present the problems and the different proposed solutions. This study permits us to understand the limitations of the actual solutions and the required modifications to let TCP cope with a heterogeneous Internet on an end-to-end basis     

Analytic models for the latency and steady-state throughput of TCP Tahoe, Reno, and SACK

Continuing the process of improvements made to TCP through the addition of new algorithms in Tahoe and Reno, TCP SACK aims to provide robustness to TCP in the presence of multiple losses from the same window. In this paper we present analytic models to estimate the latency and steady-state throughput of TCP Tahoe, Reno, and SACK and validate our models using both simulations and TCP traces collected from the Internet. In addition to being the first models for the latency of finite Tahoe and SACK flows, our model for the latency of TCP Reno gives a more accurate estimation of the transfer times than existing models. The improved accuracy is partly due to a more accurate modeling of the timeouts, evolution of cwnd during slow start and the delayed ACK timer. Our models also show that, under the losses introduced by the droptail queues which dominate most routers in the Internet, current implementations of SACK can fail to provide adequate protection against timeouts and a loss of roughly more than half the packets in a round will lead to timeouts. We also show that with independent losses SACK performs better than Tahoe and Reno and, as losses become correlated, Tahoe can outperform both Reno and SACK.     

Modeling TCP SACK performance over wireless channels with semi-reliable ARQ/FEC

Providing reliable data communications over wireless channels is a challenging task because time-varying wireless channel characteristics often lead to bit errors. These errors result in loss of IP packets and, consequently, TCP segments encapsulated into these packets. Since TCP cannot distinguish packet losses due to bit corruption from those due to network congestion, any packet loss caused by wireless channel impairments leads to unnecessary execution of the TCP congestion control algorithms and, hence, sub-optimal performance. Automatic Repeat reQuest (ARQ) and Forward Error Correction (FEC) try to improve communication reliability and reduce packet losses by detecting and recovering corrupted bits. Most analytical models that studied the effect of ARQ and FEC on TCP performance assumed that the ARQ scheme is perfectly persistent (i.e., completely reliable), thus a frame is always successfully transmitted irrespective of the number of transmission attempts it takes. In this paper, we develop an analytical cross-layer model for a TCP connection running over a wireless channel with a semi-reliable ARQ scheme, where the amount of transmission attempts is limited by some number. The model allows to evaluate the joint effect of stochastic properties of the wireless channel characteristics and various implementation-specific parameters on TCP performance, which makes it suitable for performance optimization studies. The input parameters include the bit error rate, the value of the normalized autocorrelation function of bit error observations at lag 1, the strength of the FEC code, the persistency of ARQ, the size of protocol data units at different layers, the raw data rate of the wireless channel, and the bottleneck link buffer size.     

Modeling TCP behavior in a differentiated services network

The differentiated services architecture has been proposed for providing different levels of services and has received wide attention. A packet in a diff-serv domain is classified into a class of service according to its contract profile and treated differently by its class. While many studies have addressed issues on the diff-serv architecture (e.g., dropper, marker, classifier and shaper), there have been few attempts to analytically understand a flow's behavior in a diff-serv network. We propose simple models of TCP behavior in a diff-serv network. Our models quantitatively characterize TCP throughput as functions of the contract rate, the packet-drop rate and the round-trip time in either two-drop precedence or three-drop precedence network. We also extend our models to aggregated flows. The models are validated through a number of simulations     

Explicit window adaptation: a method to enhance TCP performance

We study the performance of TCP in an internetwork consisting of both rate-controlled and nonrate-controlled segments. A common example of such an environment occurs when the end systems are part of IP datagram networks interconnected by a rate-controlled segment, such as an ATM network using the available bit rate (ABR) service. In the absence of congestive losses in either segment, TCP keeps increasing its window to its maximum size. Mismatch between the TCP window and the bandwidth-delay product of the network results in accumulation of large queues and possibly buffer overflows in the devices at the edges of the rate-controlled segment, causing degraded throughput and unfairness. We develop an explicit feedback scheme, called explicit window adaptation, based on modifying the receiver's advertised window in TCP acknowledgments returning to the source. The window size indicated to TCP is a function of the free buffer in the edge device. Results from simulations with a wide range of traffic scenarios show that this explicit window adaptation scheme can control the buffer occupancy efficiently at the edge device, and results in significant improvements in packet loss rate, fairness, and throughput over a packet discard policy such as random early detection (RED)     

Modeling TCP SACK performance over wireless channels with completely reliable ARQ/FEC

In this paper, we propose an analytical cross‐layer model for a Transmission Control Protocol (TCP) connection running over a covariance‐stationary wireless channel with a completely reliable Automatic Repeat reQuest scheme combined with Forward Error Correction (FEC) coding. Since backbone networks today are highly overprovisioned, we assume that the wireless channel is the only one bottleneck in the system which causes packets to be buffered at the wired/wireless interface and dropped as a result of buffer overflow. We develop the model in two steps. At the first step, we consider the service process of the wireless channel and derive the probability distribution of the time required to successfully transmit an IP packet over the wireless channel. This distribution is used at the next step of the modeling, where we derive expressions for the TCP long‐term steady‐state throughput, the mean round‐trip time, and the spurious timeout probability. The developed model allows to quantify the joint effect of many implementation‐specific parameters on the TCP performance over both correlated and non‐correlated wireless channels. We also demonstrate that TCP spurious timeouts, reported in some empirical studies, do not occur when wireless channel conditions are covariance‐stationary and their presence in those measurements should be attributed to non‐stationary behavior of the wireless channel characteristics. Copyright © 2011 John Wiley & Sons, Ltd.     

TCP performance over mobile ad hoc networks: a quantitative study

In this paper, we study the performance of the transmission control protocol (TCP) over mobile ad‐hoc networks. We present a comprehensive set of simulation results and identify the key factors that impact TCP's performance over ad‐hoc networks. We use a variety of parameters including link failure detection latency, route computation latency, packet level route unavailability index, and flow level route unavailability index to capture the impact of mobility. We relate the impact of mobility on the different parameters to TCP's performance by studying the throughput, loss‐rate and retransmission timeout values at the TCP layer. We conclude from our results that existing approaches to improve TCP performance over mobile ad‐hoc networks have identified and hence focused only on a subset of the affecting factors. In the process, we identify a comprehensive set of factors influencing TCP performance. Finally, using the insights gained through the performance evaluations, we propose a framework called Atra consisting of three simple and easily implementable mechanisms at the MAC and routing layers to improve TCP's performance over ad‐hoc networks. We demonstrate that Atra improves on the throughput performance of a default protocol stack by 50%–100%. Copyright © 2004 John Wiley & Sons, Ltd.     

编码TCP的建模与性能分析

研究了无线网络端到端分组丢失和编码纠错对TCP协议工作过程的影响机制,基于三维Markov链建模描述TCP拥塞窗口和可用窗口的变迁过程,在忽略慢启动阶段的条件下,以最大窗口尺寸、端到端分组丢失率和编码冗余系数为输入参数,通过数值计算求解编码TCP的吞吐率,据此定量分析影响编码TCP性能的因素。基于NS2的模拟实验结果表明基于Markov链的数值计算结果具有较高的准确度。     

Enhancing TCP performance with a load-adaptive RED mechanism

This paper describes a technique for enhancing the effectiveness of RED by dynamically changing the threshold settings as the number of connections (and system load) changes. Using this technique, routers and switches can effectively control packet losses and TCP timeouts while maintaining high link utilization. Copyright © 2001 John Wiley & Sons, Ltd.     

A simple model of EMI-induced timing jitter in digital circuits, its statistical distribution and its effect on circuit performance

A simple model has been developed to characterize electromagnetic interference induced timing variations (jitter) in digital circuits. The model is based on measurable switching parameters of logic gates, and requires no knowledge of the internal workings of a device. It correctly predicts not only the dependence of jitter on the amplitude, modulation depth and frequency of the interfering signal, but also its statistical distribution. The model has been used to calculate the immunity level and bit error rate of a synchronous digital circuit subjected to radio frequency interference, and to compare the electromagnetic compatibility performance of fast and slow logic devices in such a circuit.     

On TCP performance enhancing proxies in a wireless environment

TCP performance enhancement in wireless access networks is an important ongoing area of research. It is known that the hostile nature of the wireless channel and the mobile nature of wireless users interact adversely with standard TCP congestion control mechanisms [1], causing a drastic reduction in throughput. This article surveys a selection of different approaches to managing TCP performance over wireless links, and presents the results of simulation and field trial results of a novel TCP performance enhancing proxy over diverse cellular radio access technologies based on the GSM, cdma2000, and UMTS standards. The proposed TRL TCP performance enhancing proxy has the advantages of being completely transparent to both TCP endpoints and tunable to different access technologies, and frequently achieves the maximum throughput available from any of the studied radio access technologies.     

FAST TCP over optical burst switched networks: Modeling and stability analysis

FAST TCP is important for promoting data-intensive applications since it can cleverly react to both packet loss and delay for detecting network congestion. This paper provides a continuous time model and extensive stability analysis of FAST TCP congestion-control mechanism in bufferless Optical Burst Switched Networks (OBS). The paper first shows that random burst contentions are essential to stabilize the network, but cause throughput degradation in FAST TCP flows when a burst with all the packets from a single round is dropped. Second, it shows that FAST TCP is vulnerable to burst delay and fails to detect network congestion due to the little variation of round-trip time, thus unstable. Finally it shows that introducing extra delays by implementing burst retransmission stabilizes FAST TCP over OBS. The paper proves that FAST TCP is not stable over barebone OBS. However, it is locally, exponentially, and asymptotically stable over OBS with burst retransmission.     

n-scroll chaos generators: a simple circuit model

n-scroll attractors which are generated from a generalised and simple circuit model are presented. The nonlinear characteristics can be systematically designed by adding comparators. A 5-scroll attractor circuit realisation is shown, which has been experimentally verified using current feedback opamps     

Throughput and energy performance of TCP on a wideband CDMA air interface

In this paper, we present a study on the performance of TCP, in terms of both throughput and energy consumption, in the presence of a wideband CDMA radio interface typical of third generation wireless systems. The results show that the relationship between throughput and average error rate is largely independent of the network load, making it possible to introduce a universal throughput curve, empirically characterized, which gives throughput predictions for each value of the user error probability. Furthermore, the study of the energy efficiency shows the possibility to select an optimal power control threshold to maximize the trade‐off between throughput and energy, thereby potentially achieving very significant energy gains. Copyright © 2001 John Wiley & Sons, Ltd.     

TCP smart framing: a segmentation algorithm to reduce TCP latency

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.     

WLAN中TCP性能改进的跨层方案仿真

随着无线网络的迅速发展,如何改进TCP在无线网络中的传输性能这一课题,已经成为国内外研究的热点.文章分析了现有的几种典型的TCP改进方案,并在此基础上介绍一种新的跨层方案.通过在传输层和链路层之间引入ARQ Snoop代理,在链路层检测并重传ARQ分组的同时,协调WLAN MAC子层的ARQ机制与TCP的ARQ策略.