使用EHN＋机制提高移动网络中TCP性能

TCP协议是一种在因特网上广泛使用的端到端可靠传输协议，移动网络中无线链路的高误码率(BER)和越区切换导致了TCP性能严重降低。在本文中，我们分析了切换过程中TCP遇到的问题，着重考察了TCP从高可用带宽链路切换至低可用带宽链路时遇到的问题，并根据EHN机制提出了EHN 机制，解决了TCP从高可用帝宽链路切换至低可用常宽链路时出现的超时重传导致TCP在切换过程中性能下降的问题，提高了TCP在切换时的可靠性和性能，并给出了模拟结果。     

基于MIPv6的TCP性能增强方法

TCP协议假定链路上的数据丢失率极小，所以当数据传输中出现丢包情况时，它认为是由于网络拥塞而导致的，并且相应地采取拥塞避免机制。然而在无线网络中，由于信道比特差错率高，移动主机切换等原因，经常会导致数据的丢失。如果把这种情况下的数据报丢失错误归因于网络拥塞而采取拥塞控制机制，则不必要地降低了吞吐量，导致自身性能下降。文章首先介绍了针对无线移动网络所常用的TCP性能增强方法，然后提出了一种基于MIPv6的移动主机切换情况下TCP性能增强的方法并进行了分析。     

MPSSF:一种低失序的缓存转发移动切换方案

全IP无线移动网络的微移动协议在无线接入网采用快速切换技术降低移动切换时延，同时采用了数据包缓存转发技术来解决切换过程中的丢包。多流转发方案存在较多的失序，使上层的TCP协议不适当地启动拥塞控制机制而降低吞吐量。单流转发方案虽然没有失序，但是会占用较多的网络资源并增加数据包的时延。提出一种多径单流转发方案MPSSF，较好地解决了移动切换过程中数据包的丢失与失序问题，同时网络资源消耗以及数据包时延也比单流转发方案显著减小。网络模拟实验表明，MPSSF在移动切换时避免了数据包失序，保持了TCP的拥塞窗口，对TCP性能的改善效果优于多流转发方案及单流转发方案。     

移动支持协议切换性能研究

切换是移动支持协议研究的重要内容,其性能好坏对移动网络的性能和服务质量提供具有至关重要的影响.在合适的网络模型和切换模型的基础上,通过理论分析和数值仿真的方法对各类移动支持协议(包括移动IP与微观移动协议以及不同的微观移动协议)的切换性能进行了深入的研究和比较.结果表明,切换性能受无线网络参数和移动支持协议的路径更新算法两个因素影响;采用微观移动协议时的切换性能好于只使用移动IP时的情形;在所有微观移动协议中,MIP-RR和MMP协议中的路径更新算法切换性能最佳.     

提高移动计算环境下平滑切换机制的数据传输性能

在移动IP协议中，为了减少切换过程中的丢包率引入了平滑切换机制，但该机制只能恢复部分丢失的分组。当切换过程中有连续的3个以上分组被丢失，并且有2个以上通过平滑切换机制得以恢复时就会因触发TCP层的错误快速重传导致网络吞吐率下降。本文对该问题进行分析并提出了解决的方法。     

LEO卫星网络中TCP协议性能研究

在低地球轨道卫星网络中,星地切换会造成数据包丢失,导致应用于地面有线网络中的TCP协议产生盲目快速重传,从而削弱TCP协议性能。针对该问题,在异构网络边界处加入性能增强代理模型,通过阈值调节发送速率,屏蔽切换对源端的影响。理论分析和仿真实验表明,在不同误码率情况下,该方法的平均吞吐量优于常规TCP,可避免短时间内由连续切换和误码造成的TCP性能下降。     

无线异构网络环境下的MIPv6集成切换框架*

针对多接口移动节点在无线异构网络环境下的切换问题,将移动IPv6水平切换与垂直切换相结合,提出了一个无线异构网络环境下的移动IPv6集成切换框架,使移动节点在网络侧实体的支持下能够自主选择切换目标网络并进行水平或垂直切换。为改进移动IPv6的切换性能,为该框架设计了水平及垂直切换协议,并进行了实验验证。     

无线移动网络中增强TCP性能的技术综述

TCP是因特网上的主要传输协议，在数据包丢失主要是由拥塞引起的传统网络上，TCP可以充分发挥其性能，但是在无线移动网络中，TCP将无线信道比特差错和移动切换引起的数据包丢失误归于网络发生拥塞而采取拥塞控制措施，不必要地降低了端到的吞吐率，导致自身性能的下降，首先阐述了当前无线移动网络的发展状况和TCP面临的问题，在此基础上，综述和评价了各种增强TCP性能的技术方案，最后，结合无线移动通信系统的最新进展，分析和探讨了当前存在的问题和进一步的研究方向。     

无线网络中TCP性能改进技术研究

因特网和移动通信的结合是未来通信发展的趋势，作为因特网传输层协议标准的TCP协议在未来无线网络中仍将发挥着重要作用。但是由于TCP是专为有线网络而设计的，在无线网络中的性能并不理想，因此需要对传统的TCP协议进行改进以增强其性能。文章对无线网络中TCP性能的改进技术进行了阐述，并着重对ELN协议进行了分析。     

基于移动代理的普适计算模型研究与设计

针对普适环境下移动IP协议的局限性,将集智能性、移动性,安全性等诸多特性于一身的移动代理引入普适计算,详细地阐述了实现过程并进行性能分析与仿真实验.结果表明,普适移动设备在引入移动代理后,能够快速平滑地实现切换,从而大大减少了切换延迟和传输过程中的状态信息量,降低了移动设备在切换期间的丢包率,有效地改善了网络的性能.     

A per-application mobility management platform for application-specific handover decision in overlay networks

With the advance of various wireless access technologies, the demand for a mobile user equipped with multiple air interfaces simultaneously executing diverse applications emerged. In such network environments, per-application mobility management is a key to allow each application of an end user device to dynamically and fully take advantage of the most suitable access technology. In this paper, we devised a comprehensive architectural platform with cross-layer techniques to realize this disruptive technology, i.e., per-application mobility management. The proposed platform enables the triggering of vertical handover decisions based on the dynamic measurements from the entire protocol stack. For per-application, the handover decision as well as the mobility management and the transport/application protocol control adaptation for handover performance optimization are made with cross-layer techniques. Through the simulation results, it is shown that multi-layer handover triggering of the proposed platform enhances the QoS of the application services by making handover decisions when the QoS requirements of an application is not satisfied as well as when a mobile user moves out of the current access network in overlay network environments. It is also presented that per-application handover based on the proposed platform enhances the QoS of the application services compared to the handover approaches which make every on-going service flows handover together to the same access network.     

MIPv6切换性能测量和瓶颈分析

MIPv6(mobile IPv6)是IETF(Internet Engineering Task Force)工作组提出的IP层移动解决方案.切换是影响MIPv6性能的关键因素.从网络层、传输层和应用层3个层次测量分析MIPv6切换性能,确定协议层次性能相互影响与切换性能瓶颈.根据网络层切换过程,改进其测量移动检测时延的方法,测量MIPv6各个阶段的切换时延并提出减少各阶段时延的建议,分析发现切换性能瓶颈.进一步完成传输层性能测量,分析移动切换对TCP滑动窗口的影响,发现TCP的特性将影响切换过程中上层应用的性能;以FTP应用为例,测量并分析了移动切换对上层应用的影响.相关结论对设计高效的移动切换协议提供了研究基础.     

一种无线切换认证协议的性能改进*

切换认证协议是确保移动节点在无线网络中多个接入点之间进行快速安全切换的关键。在设计切换认证协议时,必须充分考虑移动节点计算、存储能力低以及电池容量小等特点。针对无线局域网的切换认证协议HashHand双线性对运算消耗资源大的缺陷,提出了一种新的快速切换认证协议。该协议不使用对运算,仅使用加法群的点乘运算替代,提高了协议的效率。并且具有用户匿名性与不可追踪性,有条件的隐私保护性。用户与认证服务器满足互认证性,能够安全地协商会话密钥并且周期性地更新。该协议能有效地抵制重放攻击和拒绝服务攻击。     

无线环境下基于SCTP的并行多路径传输

随着网络接入技术的多样和接入设备的廉价,越来越多的移动终端具备多家乡的特性,而现有TCP/IP协议栈只能使用单一接口传输数据,无法充分利用多家乡的优势。在流控制传输协议(SCTP)基础上,设计了路径选择模块和快速路径切换模块,实现了一种无线并行多路径传输（Wireless CMT）解决方案,使得多家乡终端能够同时使用多个接口并行传输数据。在实际无线网络环境对Wireless CMT带宽聚合效果和快速路径切换效果分别进行测试验证。测试结果表明,Wireless CMT使无线网络传输效率和可靠性都得到了明显提升。     

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.     

On UDP continuity over vertical handovers

Today’s mobile devices such as smart phones are equipped with multiple wireless access technologies, so multi-radio operation is becoming the norm. These devices frequently face vertical handover scenarios such as exiting Wi-Fi hotspot towards cellular network coverage. Unfortunately, the vertical handover execution is still done in a very primitive way even with middleware support, and the reality is that any active service at the time of handover is aborted or at least severely disrupted when it happens. In this paper, we explore how the transport layer can independently overcome the disruption caused by the vertical handover and obtain service continuity with or without underlying vertical mobility support infrastructures such as Media Independent Handover (MIH) or Access Network Discovery and Selection Function (ANDSF). In particular, we focus on the case of User Datagram Protocol (UDP), and explore how to evolve it for vertical handover. In particular, we show that UDP can be enriched with options while keeping application transparency and enabling incremental deployment as is the case for Transmission Control Protocol (TCP). We implement the proof-of-concept prototype and demonstrate that it performs well under dynamic Cellular-WiFi vertical handover settings with off-the-shelf smart phones operating across commercial 3G cellular carriers and Internet Service Provider (ISP) networks. We also consider the ways to utilize the evolved UDP for other applications, as the addition of carrying options or in-band signaling capability opens a whole new horizon for the usability of UDP.     

多跳快速切换代理移动IPv6预认证协议的安全分析

第三代移动通信系统的长期演进标准中,使用代理移动IPv6协议来实现异构无线接入网络互联及移动性管理。LTE-Advaned网络支持协同无线通信,通过在网络中引入中继节点来扩大蜂窝的覆盖范围和信道容量并减少网络的传输延迟。文章对LTE—Advanced网络结构进行了扩展,加入了能支持中继功能的服务网关,该网关采用快速切换PMIPv6协议来完成预先切换。文章对此协议进行了扩展,使其支持多跳和中继功能。文章主要研究多跳快速切换PMIPv6协议的安全性,采用认证选项实现了预认证协议。并给出了详细的流程。文章采用Kerberos的Ticket概念,通过在协议中加入Ticket来实现安全上下文的传输。该认证协议是在移动节点切换到目的端之前完成的,大大减少认证协议所产生的延迟。最后文章对认证测试的形式化方法进行扩展,加入了消息认证码,证明了此预认证协议的认诅陡。     

Performance comparison of end-to-end mobility management protocols for TCP

Mobility management for TCP connections has been discussed in literature since last several years. Many mobility management solutions have been proposed including end-to-end solutions and infrastructure dependent solutions. These solutions operate at different layers of TCP/IP protocol stack. End-to-end mobility management solutions have the advantage of not requiring the deployment of additional entities in network infrastructure to handle mobility management as compared to the infrastructure dependant solutions. Performance analysis of these end-to-end mobility management protocols seems missing in literature. In this paper, we analyze the performance of different end-to-end mobility management protocols using mathematical modeling. Evaluation has been carried out for evaluating the handover delay, throughput degradation time and protocol overhead. Some security and implementation issues pertaining to these protocols have also been discussed. Results show that protocols that allow simultaneous communication through multiple network interfaces provide throughput stability during vertical handovers, thus facilitating smooth handovers.