TCP稳态流中慢启动序列对吞吐量性能的影响

在计算TCP稳态数据流吞吐量时一般都忽略了由于分组丢失而形成的各个慢启动阶段。在考虑TCP稳态数据流中慢启动序列的情况下,对Padhye的经典TCP稳态数据流模型进行了扩展。通过将Padhye的模型与扩展后的模型作比较,证明了在使用Padhye的模型作为多媒体流量控制模型时忽略超时后慢启动阶段的可行性和正确性。     

光突发交换网络中的传输控制协议性能

光突发交换(OBS)是IP over WDM核心网络采用的交换技术。在OBS网络中,送往同一边缘节点的IP分组汇聚成传输和交换的基本单元———数据突发(DB),DB丢弃会导致大量IP分组丢失,显著影响传输层的性能。文中分析OBS网络的参数对传输控制协议(TCP)吞吐量和时延的影响。仿真结果表明,DB丢包率越高,TCP性能越差。在低丢包率情况下,随着DB长度的增加,TCP吞吐量和端到端时延明显增加,高丢包率情况下则不明显;随着汇聚周期的增加,TCP吞吐量逐渐下降,端到端时延逐渐增加。     

基于Gilbert丢包机制的TCP吞吐量模型

 丢包机制是推导TCP吞吐量模型的关键,直接影响模型的准确性.本文利用四状态Gilbert丢包机制来描述端到端路径上的丢包行为,对TCP的拥塞控制过程进行建模,在此基础上提出了一种更精确的TCP吞吐量模型.实验表明,改进的模型能较好的与实际值相拟合,可以更精确地预测实际TCP数据流的吞吐量性能.     

数据包大小对TCP流性能的影响

在互联网时代,如何提高网络通信质量一直是研究热点,当前网络通信大部分数据流都采用TCP流。对于TCP流性能的影响因素如丢包、时延已有大量研究,但是数据包大小对其的影响却罕有涉及。另一方面,网络通信的质量很大程度上取决于路由器的性能,而路由器的性能又很大程度上取决于路由器的缓存设置。因此本文从数据包大小这一新的切入点入手,研究在不同的路由器缓存下,其对TCP流性能的影响。论文介绍了TCP协议、路由器缓存、数据包等相关概念,提出了实验方案的网络拓扑模型,选择了NS2平台进行网络仿真。在实验中,我们通过改变数据包大小和路由器缓存容量,得到了对应的实验数据并进行了分析整理,总结出了TCP流吞吐量和丢包率在数据包大小改变时的变化规律,即丢包率随数据包大小的增加呈线性增长,路由器缓存越小丢包率越大;TCP流的吞吐量随数据包大小的增加缓慢变大,路由器缓存达到一定值后不再成为瓶颈因素。     

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。     

混合网络环境下的TCPW改进算法

针对TCP Westwood(简称TCPW)拥塞避免算法在高误码率无线网络环境下不能区分丢包原因和性能仍显不足的问题,分析RTT的变化,提出了一种简单有效的改进算法,称为TCP VT,能有效地区分拥塞丢包和无线丢包,仿真实验表明,改进后的算法在高误码率情况下提高了网络利用率和吞吐量,同时仍具有良好的公平性和友好性.     

传输层网络编码性能分析

底层网络随机丢包导致的传输控制协议(TCP)传输性能恶化的问题由来已久.为了保障TCP的吞吐量在无线网络环境下依然能够保持在较好的性能,通过分析传输层网络编码(TCP/NC)协议的基本原理,分别利用NS-2搭建了软件仿真平台和Wi-Fi开发板搭建了硬件仿真平台.在2种平台上分别测试了传输层网络编码的性能并且分析了TCP的拥塞窗口和吞吐量性能.实验结果表明:传输层网络编码能够有效克服底层的随机丢包带来的影响,提升TCP吞吐量.     

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。     

无线Mesh网中基于网络编码的多路径TCP研究

在无线多跳网络中,本地重传和网络编码已经被成功地应用到多路径技术上以增加吞吐量并减少丢包。然而,在提高UDP传输性能的同时,也产生了数据包重排序和延迟等副作用,严重影响了TCP性能。针对此问题,主要提出一种基于网络编码的多路径传输方案NC-MPTCP,即在无线mesh网络的多条路径中引入网络编码、执行拥塞控制以及使用一个基于信用的方法控制节点的传输速率,提高网络的吞吐量以及增加网络传输的可靠性。该方案使用一个简单的算法,评估丢包率以及发送线性组合数据包的速率,用来降低目的节点的数据包解码延迟和防止TCP的超时重传。仿真结果表明设计的NC-MPTCP有效。     

丢包感知的线性编码在无线Mesh网络中的应用

采用网络编码提高无线Mesh网络的吞吐量己成为目前研究的热点.文献[1]中,作者提出了一种在无线Mesh网络中采用网络编码的MAC层先验式混合协议,它采用异或编码的算法,这种算法在低丢包环境下性能较好,但不适合高丢包率环境.文章提出了一种适用于无线Mesh网络的线性网络编码方法,并采用复合解码策略,能确保在高丢包的环境...     

一种基于链路带宽估计的无线TCP改进算法

本文提出了一种能够通过带宽估计来判断无线链路报文段丢失原因,并采取相应拥塞控制机制的无线TCP算法-TCP_LD(TCP Loss Detection).文章采用Padhye模型的建模方法,推导了TCP_LD的稳态流量模型.理论分析和仿真结果说明,TCP_LD能够有效的区分出发生报文段丢失的原因,即拥塞丢失或者链路突发差错,从而提高系统的流量.     

Performance analysis of the IEEE 802.11e wireless networks with TCP ACK prioritization

With the advent of multimedia over wireless local area networks, the IEEE 802.11e standard was proposed to incorporate Quality of Service (QoS). It has been found that the throughput of Transmission Control Protocol (TCP) is less than that of User Datagram Protocol (UDP) in the IEEE 802.11e. This is because the TCP acknowledgment packets are queued up at the access points. In this paper, two types of TCP acknowledgment prioritizing schemes are proposed. The proposed schemes improve the overall throughput of TCP while maintaining the QoS requirements. We also analyze the problem of starvation of lower priority traffic and its effects on the performance of lower priority TCP traffic. The proposed dynamic scheme of TCP acknowledgment prioritization aims at improving the throughput of the lower priority TCP traffic under heavy network load while maintaining the QoS requirements of the higher priority traffic. The schemes have been verified through extensive simulation.     

Performance Comparison and Analysis of IP and MPLS Networks

1　ＩｎｔｒｏｄｕｃｔｉｏｎＡｎａｎａｌｙｓｉｓｏｆｐｅｒｆｏｒｍａｎｃｅｕｓｉｎｇＭＰＬＳ ＴＥｉｓｐｒｅｓｅｎｔｅｄｉｎｔｈｅｐａｐｅｒ.ＷｈｅｎＭｕｌｔｉＰｒｏｔｏｃｏｌＬａｂｅｌＳｗｉｔｃｈｉｎｇ(ＭＰＬＳ)ｉｓｆｉｒｓｔｉｎｔｒｏｄｕｃｅｄｉｎＮｅｔｗｏｒｋＳｏｃｉｅｔｙ[2～ 3] ,ｔｈｅｏｒｉｇｉｎａｌｉｄｅａａｂｏｕｔＭＰＬＳｉｓｔｈａｔｉｔｍａｐｓＬ3ｒｏｕｔｉｎｇ (ｔｈｅｔｒａｄｉｔｉｏｎａｌｌｏｎｇｅｓｔａｄｄｒｅｓｓｍａｔｃｈ)ｔｏＬ2ｓｗｉｔｃｈｉｎｇ(ｔｈｅｆｉｘｅｄｓｈｏｒｔｌａ…     

The impact of multihop wireless channel on TCP performance

This paper studies TCP performance in a stationary multihop wireless network using IEEE 802.11 for channel access control. We first show that, given a specific network topology and flow patterns, there exists an optimal window size W* at which TCP achieves the highest throughput via maximum spatial reuse of the shared wireless channel. However, TCP grows its window size much larger than W* leading to throughput reduction. We then explain the TCP throughput decrease using our observations and analysis of the packet loss in an overloaded multihop wireless network. We find out that the network overload is typically first signified by packet drops due to wireless link-layer contention, rather than buffer overflow-induced losses observed in the wired Internet. As the offered load increases, the probability of packet drops due to link contention also increases, and eventually saturates. Unfortunately the link-layer drop probability is insufficient to keep the TCP window size around W'*. We model and analyze the link contention behavior, based on which we propose link RED that fine-tunes the link-layer packet dropping probability to stabilize the TCP window size around W*. We further devise adaptive pacing to better coordinate channel access along the packet forwarding path. Our simulations demonstrate 5 to 30 percent improvement of TCP throughput using the proposed two techniques.     

Multi-layer loss recovery in TCP over optical burst-switched networks

It is well-known that the bufferless nature of optical burst-switching (OBS) networks cause random burst loss even at low traffic loads. When TCP is used over OBS, these random losses make the TCP sender decrease its congestion window even though the network may not be congested. This results in significant TCP throughput degradation. In this paper, we propose a multi-layer loss-recovery approach with automatic retransmission request (ARQ) and Snoop for OBS networks given that TCP is used at the transport layer. We evaluate the performance of Snoop and ARQ at the lower layer over a hybrid IP-OBS network. Based on the simulation results, the proposed multi-layer hybrid ARQ + Snoop approach outperforms all other approaches even at high loss probability. We developed an analytical model for end-to-end TCP throughput and verified the model with simulation results.     

基于模糊逻辑的无线网络流量自适应控制

文章在分析现有提高无线TCP性能方案的基础上，提出一种新的流量控制方法，即基于显式窗口反馈的无线网络流量控制方案。在Snoop中引入有线网络的显示窗口自适应（EWA）算法，通过对BS共享缓存的实时监测，应用模糊控制算法预测当前拥塞窗口（cwnd）的大小，并显式反馈给发送端，使TCP的发送窗口能快速响应网络负荷状况的变化．避免分组的丢失。仿真结果表明．该方法增强了网络对拥塞的自适应性以及对无线信道差错的实时处理能力．提高了网络的吞吐量。     

DATCP: deadline-aware TCP for the commoditized data centers

Many flows in data centers have deadlines and missing deadlines would hurt application performance such as affecting response quality in Web applications or delaying computing jobs in MapReduce-like systems.However,transmission control protocol(TCP) which is widely used in data centers now cannot provide deadline-aware transmission service.Service differentiation only distinguishes flows with different priority but is unable to guarantee completion time.In this paper,we propose a new protocol named deadline-aware TCP(DATCP) to provide deadline-aware transmission service for the commoditized data centers,which can be used as a flexible method for flow scheduling.DATCP combines flow urgency and importance to calculate precedence.Flow urgency is dynamically adjusted according to the gap between desired rate and actual throughput.Setting importance can avoid starving the important but no-urgent flows.Furthermore,a flow quenching method is presented which allows as many high precedence flows as possible to meet deadlines under heavy network load.By extensive simulations,the performance of DATCP was evaluated.Simulation results show that DATCP can make flows meet deadlines effectively.     

A stochastic model for the behavior of multiple TCP NewReno sources over optical burst switching network

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.