无线网络TCP协议纯端到端解决方案研究

针对无线环境中误码率偏高的特点,着重讨论改善TCP协议性能的方案,并重点研究了纯端到端解决方案中的两种典型TCP协议：TCPW和TCP-Real协议。纯端到端解决方案保持了TCP协议端到端的语义。通过不同误码率下传输性能的仿真,表明两种协议在无线环境下性能均明显优于其他TCP协议。     

TCP/IP拥塞控制方法在Linux系统环境中的应用

目前广泛应用在Internet上的拥塞控制大都采用的是TCP/IP中的基于滑动窗口技术的端到端(end-to-end)控制方法。首先对TCP R eno和TCP V egas协议的原理进行了分析,然后探讨了这些拥塞控制协议在L inux中的应用,最后在通用拥塞控制协议的基础上提出了一种算法模型。对比分析表明该算法能使网络对拥塞作出快速响应,从而有效地克服了端到端拥塞控制方法的缺陷。     

Evaluating transport protocol performance over a wireless mesh backbone

IEEE 802.11n wireless physical layer technology increases the deployment of high throughput wireless indoor mesh backbones for ubiquitous Internet connectivity at the urban and metropolitan areas. Most of the network traffic flows in today’s Internet use ‘Transmission Control Protocol’ (TCP) as the transport layer protocol. There has been extensive works that deal with TCP issues over wireless mesh networks as well as noisy wireless channels. Further, IEEE 802.11n is well known for its susceptibility to increased channel losses during high data rate communication. This paper investigates the dynamics of an end-to-end transport layer protocol like TCP in the presence of burst and correlated losses during IEEE 802.11n high data rate communication, while maintaining fairness among all the end-to-end flows. For this purpose, we evaluate four TCP variants-Loss Tolerant TCP (LT-TCP), Network Coded TCP (TCP/NC), TCP-Horizon and Wireless Control Protocol (WCP), where the first two protocols are known to perform very well in extreme lossy networks, and the last two are specifically designed for mesh networks. Our evaluation shows that WCP performs better in a IEEE 802.11n supported mesh networks compared to other three variants. However, WCP also results in negative impact at high data rates, where end-to-end goodput drops with the increase in physical data rate. The analysis of the results reveals that explicit loss notifications and flow balancing are not sufficient to improve transport protocol performance in an IEEE 802.11n supported mesh backbone, rather a specific mechanism is required to synchronize the transport queue management with lower layer scheduling that depends on IEEE 802.11n features, like channel bonding and frame aggregation. The findings of this paper give the direction to design a new transport protocol that can utilize the full capacity of IEEE 802.11n mesh backbone.     

无线自组织网络中动态源路由协议的移动性分析

针对移动性对无线网的影响,相关研究工作都需要定性、定量地对路由协议进行分析。由于动态源路由(DSR)协议在Ad hoc网络中应用广泛,对其进行实验分析就显得非常有意义。在实验的数据结果上,给出了无线网络吞吐量、平均端到端时延以及丢包率的性能对比,并且对协议改进进行了展望。     

TCP Performance and Behaviors with Local Retransmissions

TCP has been the dominant transport protocol over the global Internet, and its performance over a hybrid wireless/wireline network has attracted much attention in recent years. This paper investigates the end-to-end TCP performance, in terms of normalized throughput, effective goodput, and packet delay, over wireless lossy links with local retransmissions. The results reveal that local retransmissions can increase the normalized TCP throughput in different wireless bandwidth, delay, and error settings, at the cost of a decrease in effective goodput and an increased packet delay. The performance observation is explained by the explored TCP endpoint behaviors, including the spurious timeout and duplicated acknowledgment. Analysis shows that spurious timeouts with local retransmissions are rare due to the conservative TCP timeout algorithm. However, spurious duplicated acknowledgments have negative impact and a further improvement with the D-SACK proposal is evaluated.     

An Accurate and Scalable Clock Synchronization Protocol for IEEE 802.11-Based Multihop Ad Hoc Networks

This paper studies the fundamental problem of clock synchronization in IEEE 802.11-based multihop ad hoc networks. Clock synchronization is important for power saving, network throughput, and efficiency of many protocols in an IEEE 802.11-based mobile ad hoc network. The scalability problem of 802.11 timing synchronization has been studied extensively in single hop ad hoc networks, and good solutions are available. These solutions, however, do not perform well in a multihop environment. A few multihop solutions for clock synchronization have been proposed recently, but the performances are still not very good. The maximum clock offset is still more than 200 mus for these protocols. This paper proposes an adaptive protocol through beacon transmission prioritization, frequency adjustment, and construction of dominating set. The frequency adjustment is proved to be bounded. Simulation studies show that the proposed protocol is able to limit the maximum clock offset to under 50 mus after protocol stabilization. The improvement is more than 400 percent over the current solutions. The proposed protocol also shows great long-term stability, and it handles mobility very well.     

Investigating the performance of TCP in mobile ad hoc networks

Mobile ad hoc networks have several inherent characteristics (e.g. dynamic topology, time-varying and bandwidth constrained wireless channels, multi-hop routing, and distributed control and management). The goal of this work is to investigate the impact of these characteristics on the performance of TCP. First, we investigate throughput performance of TCP as a function of path length (i.e. multiple wireless hops), node mobility, and traffic intensity. Next, we examine the ‘fairness’ of the ad hoc network with regard to equal sharing of network bandwidth among multiple TCP flows. Third, we evaluate the impact of two on-demand routing protocols (i.e. AODV and DSR) on the throughput of TCP. Finally, a factorial design experiment is conducted to quantify the effects and interactions of three factors, which influence the throughput of TCP. These factors include routing, node speed, and node pause time. Two key results were observed. Results show that traffic intensity (e.g. number of concurrent flows) is significantly affects TCP throughput, suggesting the need for congestion control, scheduling and traffic management schemes. Second, source routing achieves higher throughputs while also generating significantly less routing overhead than AODV. Results also show that in some instances, the fairness of the network is very uneven among concurrent TCP flows, resulting in several sending stations achieving very little or no throughput.     

An IMS-based integration architecture for WiMax/LTE handover

To enable seamless handovers for broadband networks, many researchers have addressed the integration of heterogeneous access technologies to provide users with always-on connectivity. Currently, there are several researches reported in the literature that discuss the integration of beyond 3G networks such as 3GPP Long Term Evolution LTE and mobile WiMax networks. They mainly focused on providing mobile users with seamless mobility when switching between heterogeneous access networks. In this context, many solutions for integration architecture have been proposed with mobility management considerations such as loose and tight coupling, IP Multimedia Subsystem IMS-based architecture and Evolved Packet Core EPC-based solutions for the purpose of providing mobile users with seamless handovers. In this paper, we present the different integration solutions and propose an integration architecture for WiMax and LTE access technologies with EPC as core network and IMS for service provisioning. A vertical handover VHO scheme is presented based on cross-layer approach that enables vertical handover with less handover latency and signaling cost.     

Performance evaluation of user applications in the ITS scenario: An analytical assessment of the NeMHIP

Internet connectivity in the ITS context is a flourishing demand that has to be covered by efficient information and communication technologies. Thanks to the provision of this connectivity, not only end users will profit from communication services, but also services for controlling the operation of the vehicle will benefit from the Internet connectivity. Services related to the operation and control of the vehicles exchange sensitive data, so strong security properties have to be ensured for this type of services. In addition, because of the privacy concerns related to the end users, it is desired to provide this kind of services with an adequate security level. From the communication point of view, a vehicle can be regarded as a mobile network where nodes onboard obtain continuous and optimal Internet connectivity, so, its mobility has to be managed. In the same way, network mobility management protocols should not only avoid security leaks, but also they have to ensure an adequate security level. It is needless to say that the introduction of security properties cannot render not fulfilling service performance requirements. In fact, the trade-off between security and application performance is a must. ITS standardisation bodies have adopted the NEtwork MObility Basic Support (NEMO BS) protocol to manage the mobility of networks. However, it still presents shortcomings like lack of security support and routing problems, which leads to a bad performance. One of the most promising design approaches is to consider a base mobility management protocol that provides out of the box security and route optimisation support like the Host Identity Protocol (HIP). Different solutions based on HIP can be found to solve network mobility in the literature, but none of these solutions aim at solving securely and efficiently network mobility management. That is, the provision of security properties to the network mobility management itself and to the end-to-end data communications while not increasing the signalling overhead and the manageability level remains unsolved. In this paper, we present the NeMHIP. NeMHIP is a secure and efficient network mobility management protocol which is based on HIP. In order to demonstrate its feasibility, we have carried out a study by means of analytical modelling to assess the performance of user applications with stringent QoS requirements like VoIP. Results demonstrate that the introduction of the NeMHIP in the ITS context is feasible because security properties are ensured while application performance requirements are satisfied. Therefore, we successfully achieve the trade-off between security and performance.     

容迟容断网络路由协议研究

容迟容断网络近年来得到了广泛的研究和应用.容迟容断网络中源节点和目的节点之间不存在持续稳定的端到端路径,因而传统网络的路由协议无法适用于容迟容断网络.为了完成容迟容断网络消息传输,采用基于存储-转发的路由机制.容迟容断网络路由协议性能受链路生存时间、节点缓存大小以及网络中节点移动模型等影响.对容迟容断网络路由协议的研究和进展进行了较为深入的探讨,对主要路由协议的性能进行了比较,并总结了未来的研究方向.     

Phoebus: A system for high throughput data movement

Phoebus is an infrastructure for improving end-to-end throughput in high-bandwidth, long-distance networks by using a “session layer” protocol and “gateways” in the network. Phoebus has the ability to dynamically allocate network resources and to use segment-specific transport protocols between gateways, as well as to apply other performance-improving techniques on behalf of the user. We have developed interfaces to Phoebus to allow its use in various real applications and data movement services. This paper extends our earlier work with tests of Phoebus-enabled applications on both real-world networks as well as over configurable network testbeds that allow us to modify latency and loss rates. We demonstrate that Phoebus improves the performance of bulk data transfer in a variety of network configurations and conditions.     

A Dynamic Performance-Based Flow Control Method for High-Speed Data Transfer

New types of specialized network applications are being created that need to be able to transmit large amounts of data across dedicated network links. TCP fails to be a suitable method of bulk data transfer in many of these applications, giving rise to new classes of protocols designed to circumvent TCP's shortcomings. It is typical in these high-performance applications, however, that the system hardware is simply incapable of saturating the bandwidths supported by the network infrastructure. When the bottleneck for data transfer occurs in the system itself and not in the network, it is critical that the protocol scales gracefully to prevent buffer overflow and packet loss. It is therefore necessary to build a high-speed protocol adaptive to the performance of each system by including a dynamic performance-based flow control. This paper develops such a protocol, Performance Adaptive UDP (henceforth PA-UDP), which aims to dynamically and autonomously maximize performance under different systems. A mathematical model and related algorithms are proposed to describe the theoretical basis behind effective buffer and CPU management. A novel delay-based rate-throttling model is also demonstrated to be very accurate under diverse system latencies. Based on these models, we implemented a prototype under Linux, and the experimental results demonstrate that PA-UDP outperforms other existing high-speed protocols on commodity hardware in terms of throughput, packet loss, and CPU utilization. PA-UDP is efficient not only for high-speed research networks, but also for reliable high-performance bulk data transfer over dedicated local area networks where congestion and fairness are typically not a concern.     

数据中心网络中基于传输速率分配算法的TCP协议

传输控制协议(Transmission Control Protocol,TCP)是数据中心网络中常用的传输协议。然而,同一个网络环境下,由于TCP协议的公平共享原则,TCP无法保障不同优先级业务的服务质量。针对该问题,提出了基于传输速率分配算法的TCP(Transmit Rate Allocation based TCP,TRA-TCP)。汇聚节点实时监测记录不同优先级业务的数据传输速率,并为不同优先级的业务流分配不同的传输速率,以保障高优先级业务的QoS。实验表明,与已有协议相比,TRA-TCP协议最高能够将高优先级业务的吞吐量提升50%,并且将高优先级业务的时延保持在0.1秒以下。     

Design,implementation and experimental evaluation of an end-to-end vertical handover scheme on NCTUns simulator

This paper presents the simulation study of “Host based autonomous Mobile Address Translation” using NCTUns simulator. It is a network layer, end-to-end vertical handover solution, based upon modification of “Mobile IP with address Translation”. Vertical handover approaches generally require new network elements, a new layer in TCP/IP stack, or fixing a protocol at a particular layer. To enhance handover experience, recent approaches focus on reducing signalling, localizing the registration, creating hierarchies, using proxy, preparing handover in advance, predicting target network, or exploiting multicasting and path extension techniques. These approaches, however, demand change in the network infrastructure to support mobility and limit the scope of mobility. Despite end-to-end signalling, the Host based autonomous Mobile Address Translation scheme ensures minimum service disruption and distinctly allows global mobility of the mobile node without requiring any modification in the network. We have simulated the mobility of a multi-interface mobile node in a heterogeneous network environment composed of WiFi (IEEE802.11a, IEEE802.11b) and WiMAX (IEEE802.16e) access networks. Performance of the scheme is evaluated taking into account wide range of end-to-end delays between mobile node and the correspondent node, various speeds of the mobile node and different packet loss rates of the network. Based on our detailed simulation study, it has been observed that this scheme offers reduced service disruption time, packet loss and packet latency. The service disruption time is found to be significantly low (typically in the range of 10 ms) compared to that of Mobile IP (which is in the order of 100 ms); this makes this new scheme perfectly suitable for real time applications. Low service disruption time consequently reduces the packet loss by manyfold and the packet latency remains unaffected during and after handover due to translation of address at the source. The results suggest that this protocol is a viable vertical handover solution due to its simplicity, scalability, low overhead and ready deployability.     

基于GloMoSim的AdHoc网络路由协议仿真研究

针对24台移动终端在无线自组织网络中的联网通信需求,需要选择一种能够适应AdHoc网络拓扑结构不断变化的路由协议。文章对AdHoc网络的路由协议进行了分类和比较,并通过GloMoSim仿真平台,结合具体的网络仿真场景,着重对AdHoc网络中的AODV和DSR两种按需路由协议进行性能仿真测试,比较不同移动速度下两种协议的平均端到端时延、分组投递率和吞吐量性能优劣。实验表明,节点在GloMoSim平台中成功实现了通信互联,无论节点在静止状态还是高速移动情况下,AODV的性能都要优于DSR协议。     

异构无线网络中TCP Vegas算法的研究与改进

异构无线网络是将不同接入技术、不同性能的网络融合到一起构成的单个逻辑网络。异构无线网络中,TCP端到端的拥塞控制机制对网络的健壮性和稳定性具有非常重要的作用,因此是网络研究的一个热点问题。针对异构无线网络中移动节点发生垂直切换时传输层性能下降的特点,提出了一种基于TCP Vegas的传输层拥塞控制算法B-Evegas。给出了垂直切换发生时的传输控制方法,垂直切换后拥塞窗口的恢复采用带宽估计与分段增加策略,并引入了快速恢复机制,在拥塞窗口过大时根据链路的时延指数性地减小拥塞窗口。仿真结果表明,该算法是合理的,可以有效提高垂直切换发生后TCP连接的吞吐量或者减小数据包的传输时延。     

基于负载均衡的战场自组织网络多径路由研究

移动Ad hoc网络中的多路径路由协议能够减小路由发现延迟,提高网络生存时间,受到了人们的广泛关注.详细分析了AOMDV多路径路由协议的机制和特点,针对多径路由协议在负载均衡时采用的随机转发策略,提出了一种改进的基于AOMDV协议的负载均衡传输方案,该方案能够避免TCP在多径传输时的乱序.仿真结果表明,在不影响UDP性能的情况下,该方法能显著改善TCP的传输性能.     

Ad Hoc路由协议在不同移动环境中的性能仿真

影响Ad Hoc网络路由性能的因素很多,如节点的移动、网络的负载、节点数目的变化等;而其中节点的移动是其中最关键的因素之一.该文对四种典型的路由协议进行了理论分析,并提出了一个仿真模型,使得节点在网络所在区域内以不同的速度移动.利用GlomoSim仿真工具对四种路由协议进行了仿真,对路由协议主要的几种参数：平均报文接收率、平均端到端的延时与路由控制报文的总负载进行了统计分析.仿真结果与理论分析一致,并对仿真结果进行了详细的分析比较,得出了AODV路由协议最适合移动要求较高的网络的结论.     

Transparent TCP acceleration

Transparent transmission control protocol (TCP) acceleration is a technique to increase TCP throughput without requiring any changes in end-system TCP implementations. By intercepting and relaying TCP connections inside the network, long end-to-end feedback control loops can be broken into several smaller control loops. This decrease in feedback delay allows accelerated TCP flows to react more quickly to packet loss and thus achieve higher throughput performance. Such TCP acceleration can be implemented on network processors, which are increasingly deployed in modern router systems. In our paper, we describe the functionality of transparent TCP acceleration in detail. Through simulation experiments, we quantify the benefits of TCP acceleration in a broad range of scenarios including flow-control bound and congestion-control bound connections. We study accelerator performance issues on an implementation based on the Intel IXP2350 network processor. Finally, we discuss a number of practical deployment issues and show that TCP acceleration can lead to higher system-wide utilization of link bandwidth.     

嵌入式Linux 3G无线路由器TCP/IP性能优化

分析了嵌入式Linux小型3G无线路由器的网络传输性能,以数据吞吐量和端到端往返时间为性能指标,通过仿真软件NS2分析比较5种TCP拥塞控制算法在UMTSHSDPA网络中的性能,调整TCP参数以改善网络数据传输性能.性能测试结果表明,基于仿真环境和实际物理环境,所提出的TCP拥塞控制算法及网络参数优化均可靠有效,在CPU主频80 MHz时,TCP/IP传输平均数据吞吐量可达750.4 kbit/s,较优化前提升了38.1％.