【作者】 TRAORE SOUNGALO；

【导师】 李仁发；

【作者基本信息】 湖南大学 ， 计算机应用技术， 2013， 博士

【摘要】 蜂窝网有着较低的带宽但辐射范围很广,相比较而言无线局域网(WLAN)则有着较高的带宽和较窄的辐射范围。最新的发展趋势表明基于3G标准和无线局域网的蜂窝网络为用户提供了多种多样的服务。事实上,当用户访问不同层次架构的网络时可以自动从一种网络标准迁移到另一种标准,比如从802.11网到3G网络、4G网络,这仅仅取决于可利用的资源和Qos要求,不需要任何人为的干涉。目前,即使是从WLAN到通用移动通信系统(UMTS)或从UMTS到WLAN的转换在信息技术中也得到了广泛的应用,但数据质量传输服务的下降以及通信阻塞的发生不可避免。本篇论文的重点就在于解决这些在网络通信中的关键问题。在介绍我的工作之前,文章首先对WLAN和蜂窝网做了简单介绍,既对LAN的优势进行了总结也详细阐述了WLAN标准,这里我们保留了轻量级架构模型,因为它允许单个设备上的无线应用协议这样使得问题很简单。随着各种标准的不断应用,我们知道IEEE802.11b标准是通用的WLAN标准,最先在WiFi(无线保真)中得到应用,后来推广到应用802.11,802.11a,802.11b网络。我们认为不管WLAN的方便性能及成本如何,在无线网络中的无线电波可能引起网络阻塞并且UMTS或蜂窝网为广大手机用户通信提供的便利好于GSM技术。另外,本文也对其他相关的工作展开了探讨,如早前用于WLAN性能估计的技术方法,用于WLAN/UMTS整合技术和性能分析的一些方法等等,本文都做了相关的介绍。论文主要做了如下四个方面的贡献：1.提出了一种新的方法来评价和改善WLAN性能首先,我们提出了一些方法通过OPNET Modeler9.1工具(数据率,分段阈值、缓冲区大小三个参数影响的方法以及基于吞吐量,访问延迟,重传机制,流量负载,队列大小等物理特征的一些机制)来改善WLAN通信的性能。也就是我们提出了用数据率、物理特征、分段阈值三种方法来改善及评估WLAN,性能分析则是通过参数分析如吞吐量,访问延迟,重传次数以及丢失的数据包来评价的。通过OPNET仿真结果显示,增加传输的数据率,提高吞吐量,优化访问延迟,减少重传次数都是很好的优化无线局域网的方法,另外优化物理层特性也能很好的提高WLAN的性能。事实上,在物理层进行红外编码在提高吞吐量,优化访问延迟,减少重传次数等参数问题上远远好于进行跳频编码。仿真结果还表明,分段阈值可以大大方便无线局域网中的数据转换。2.采用三种方法对WLAN和3G网络交互应用进行了相关的性能分析在这里,我们利用三种方法(Mobile IP,网关和仿真器)整合了WLAN和3G网络,并且基于UMTS-WLAN交互策略中的垂直切换延迟对三种方法的性能进行了分析,从OPNET Modeler11.5仿真结果来分析得到一种最合适的整合WLAN和3G网络的方法。另外,我们描述了基于这三种方法评估UMTS-WLAN交互性能所面临的最主要的问题。Mobile IP方法是其中最简单应用于多个分层架构网络的方法,仿真结果显示使用这种方法得到的结果有着最大的延迟,不能提供实时服务及应用；而采用网关的方法则需要较短的延迟,使得两种网络能各自独立的工作且实现它们之间的自由切换,这种方法目前大量运用于当前的网络之中；仿真器的方法用最小的时延得到了最佳的性能,但这种方法缺乏灵活性,使得两种网络之间的连接过于紧凑。仿真结果显示使用仿真器的方法使得两种网络是紧耦合还是松耦合的方式主要取决于用户是否通过UMTS的核心网络进行通信。事实上,紧耦合一个最主要的缺陷在于当WLAN中的数据通过UMTS网络时,这些数据可能引起UMTS网络中出现一个瓶颈。另外紧耦合的方法很难处理不同无线网络中的协议栈,需要适应不同网络类型之间的整合等问题,这就使得松耦合的方式占据了优势,使其在网络整合中得到了广泛的应用。尽管如此,松耦合的方式也存在一些局限性,它最大的不便在于通过因特网来整合两种不同的网络。因为在这种情况下,信号需要传输很长的距离这样会引起较大的时延,因此,松耦合的方式不能提供实时性能。另外,切换在WLAN-UMTS整合中的Qos评价指标中非常关键,松耦合在两种不同网络间切换时需要较长的延迟且具有较高的丢包率,因此我们将研究重点集中于WLAN和UMTS网络之间的切换上。采用松耦合的方式是一种最简单的应用在分层网络上交互的方法,但需要较长的时延,同时我们注意到时延在WLAN-UMTS整合的Qos要求中有着很重要的意义。3.提出一种新的方法(IQCS)对WLAN和3G/4G网络进行垂直分析。这里我们提出了一种新的方法(执行Qos控制机制),我们介绍了执行Qos控制机制(IQCS)的每一个步骤且通过OPNET Modeler11.5仿真器在IQCS之下分析从WLAN到UMTS的切换输出。由于我们的方法基于Qos管理机制,我们也通过ETSI设计网络架构对整合WLAN和UMTS网络中的Qos问题及整合802.11和蜂窝网进行了分析。采用松耦合和紧耦合两种不同的方法对WLAN和蜂窝网进行了整合。松耦合就像其名字所述,它在这两种不同网络间有着较少的整合。在这种方案下,WLAN和蜂窝网络是两种分开的接口网络,WLAN接口网络依附于因特网,蜂窝网络则是核心网络,通常情况下接口网络没有任何意义,但核心网络则是相互连接在一起,不需要修改UMTS核心网络,一种WLAN和3G/4G网络之间的松耦合可以利用已知的机制来满足用户的需求。例如采用认证、授权、计费(AAA)服务来满足用户对这些网络的订阅,时延Mobile IP来方便用户在不同的接口网络之间进行切换。这种方案的好处在于使得核心网络有最小的改变以达到减少成本的目的。当我们认识到松耦合是一种最简单的在不同层次网络中执行策略和标准之后,我们的时延和仿真都将使用基于松耦合的架构。我们提出的协议模型支持用户间的实时传输,它既具有WLAN高速率的特征也有3G网络覆盖面广的特征。仿真结果显示,在具有较低垂直切换丢弃概率和阻塞概率的前提下,实现多框架的方法比没有实现多框架的方法在对最终用户保证Qos的前提下能提供更好的性能。在整合网络时既然提到了Qos问题,与同类的无线网络不同,整合WLAN和UMTS网络时的Qos有一些基本的瓶颈：首先,WLAN和UMTS在无线电接口上有着不同的传输速率,WLAN能提供11Mb/s到54Mb/S的速率,而UMTS的速率在车上时为144kb/s,行人的速率在384kb/s,最快室内的速度也只有2mb/s,所以在切换这两种网络时很难保持Qos的一致。如果我们仅仅维持在UMTS上的Qos而不管WLAN,则WLAN高速率的特性我们就完全没有应用了。另一方面,如果我们在UMTS网络中使用WLAN的参数,那么这个连接根本就不成立。因此,保持一个合理的Qos,我们需要考虑两种不同网络之间不同的传输速率特别是在有切换动作产生的时候。第二个限制在于WLAN是在自由的ISM带宽上传输,尽管有一些技术如采用传播频谱的方式来减少干涉但WLAN网络仍然有着很多不可控制的干涉因素。这些超出能量控制和难以保证Qos等问题在一定条件下是很难解决的。在包交换网络中为了保证Qos,必须采用某种机制控制网速在一定的阈值之下以保证系统提供满意的性能。第三个瓶颈在于3G/4G网络是在合理且小心的计划下设计完成在其之上有着成熟的控制算法,有着很好的Qos水平,而WLAN网络则需面临各种不同的复杂的外部环境,很难达到前者的Qos水平,为了解决这一问题我们提出了一种新的控制Qos的方法。我们所提出的Qos架构假设有一个包在UMTS网络和核心网络间交换,使其扮演GPRS网络与其它核心网络进行包交换时一样的角色。众所周知,因特网在管理个人流量和资源保留时有一些基本的可扩展的限制,它的衍生体,在较粗糙的服务保障前提下提供可扩展性问题的优化方法。为了有效的使用蜂窝网中广泛的资源同时维持较好的服务质量,我们采用基于保留的系统。在WLAN中保留是通过HCF到WLAN来实现的,而UMTS则通过基站的功能来实现,文章对以上两种组件做出了分析。我们提出的新的方法包括：Qos策略供给,降解文档,Qos连接接纳控制(CAC), Qos移动管理模块和Qos检测。对于Qos策略供给,带Qos要求的用户上下文首先被送入策略供给模块(PPM)处理,它同时包含了用户信息和传输的类信息；接着带降解文本的Qos信号生成并同时发送给用户和连接接纳控制模块(CAC)。当数据流已传输完毕,流量仪表计算其时间属性是否满足Qos的要求。假设所建立的最终用户Qos文本不满足要求,检测部分将状态信息传给CAC或其他组件来触发特殊的处理。这种回馈机制使得Qos能实现在不同网络间的自动变换。用户的检测对CAC上的Qos有着重大的影响,这就需要调用检测管理模块(MMM)。在蜂窝和WLAN整合网络中,当移动节点进入热点区域或离开热点区域时可能发生切换动作,这是因为热点区域通常覆盖的是蜂窝网,实际的切换是不需要发生的,这就取决于用户的最终决定,这就分为触发切换和可取的切换(DH)两种。节点会因切换而变得不同,这是因为移动节点可以同时连接在WLAN和蜂窝网上,因此系统并不是实时关键的,当移动节点进入WLAN时,一个可取的切换就发生了,这就意味着数据的路径可以改变,在此之前的数据流所建立的Qos都将改变。一种较简单的解决此类问题的方法是在一定节点进入WLAN之前生成一个新的WLAN保留区,由于DH的时间容忍特性而使得这种方法可行。另外意识到无线连接带宽将自动提高,新的提交的Qos文件可以考虑用户的订阅状态并给出合适的要求。一种普通的切换发生在有移动节点从WLAN进入蜂窝网的时候,必须产生一个新的预留区。实际切换时间需保持连续以提供无缝服务,在WLAN中用户订阅的网络资源超出了UMTS的范围,那么发生的丢弃切换将频繁发生。这就需要采用一种合理的机制嵌入到CAC和检测管理模块之间用来通过降解文档的定义降低用户的Qos要求。因此系统性能在可接受的Qos范围内得到有效的提高。4.将我们IQCS方法与另外两种不同的方法进行对比这个部分将我们所提出的方法与基于SCTP的VHO机制以及基于策略的Qos方法进行对比。基于SCTP的VHO机制,基于策略的Qos方法以及我们所提出的方法有着共同的目标,那就是最小化服务质量的衰退。在这里将我们所提出的算法与其他方法主要是在WLAN和UMTS交互切换过程中(也就是在不同网络间的切换尽量做到无缝和有效)的服务质量衰退问题进行对比。因此,我们选择之前的基于SCTP的VHO机制和基于策略的Qos方法用于UMTS-WLAN系统。以上提到的三种方法都是为了解决当前交互网络中存在的一些问题,如UMTS核心网络中的阻塞问题,最小化服务质量衰减问题等等。另一方面,也是如何在分层环境下(WLAN和UMTS)保证Qos的重要解决方案。尽管这些方法都有着最小化服务质量衰减的共同目标,但他们有着不同的性能指标。从我们的分析结果看来,我们所提出的方法扩大了通信负载条件下的可利用率减少了丢包率和访问阻塞率,是在实时环境下最简单可行的方法也是最可靠的。整篇论文,为了引出本研究所做出的贡献,我们描述了从WLAN的发展历史到第一台电话机发明以来对蜂窝网通信的评价标准直到现在应用的4G蜂窝网络,也对现在出现的一些新型技术做了简单介绍,另外也简单阐述了垂直切换这个重要概念。在第一章,我们重点介绍了WLAN技术和蜂窝网络这两个重要概念,首先我们描述了WLAN架构,无线LAN组件,操作模式,拓扑结构,介绍了无线LAN的优势和WLAN标准。随着各种不同标准的引出我们强调IEEE802.11b是当前应用最广的WLAN标准,且最先使用此标准的是WiFi,紧接着将802.11a和802.11b合并成802.11标准。不管WLAN所提供的便利性和成本如何,在无线网络中无线电波将造成网络传输的阻塞。UMTS系统使用与GPRS类似的核心网络并且使用新的无线接口,与无线网络不同,无线蜂窝网络由于其公开性有着更多的限制和安全问题,使得3G/4G安全架构提供了诸如身份验证、保密性、完整性等安全机制。WAP协议使用网络安全层如TLS/WTLS/SSL来为HTTP通信提供安全通道。尽管UMTS提供了安全性能,但也面临着新的亟需研究者来解决的问题。文章还就一些如评价和提高WLAN性能、如何整合WLAN/UMTS网络及其性能分析、分层架构网络中的垂直切换分析研究等相关工作进行了讨论。我们通过OPNET9.1仿真给出的结果显示可以通过提高数据传输率的方式来改善WLAN的性能。假设数据传输率从1mbps提高到11Mbps,相应的吞吐量将提高27%到30%。同时根据理论公式的证明,我们提高数据传输率,所接收的数据也会增加。文中方案1与方案2相比较其平均访问时延也会相应的减少。在600s的仿真时间内,方案2开始时访问时延与方案1相当,接着出现线性增长,但最后其访问时延比方案一要长90%-95%。这是由于在高速率传输过程中,数据在缓冲区停留的时间较短因而得到了非常好的结果。同样在方案一中由于数据准确的传输,相比较方案2而言减少了69%的重传数据。事实上,增加数据传输速率是一种很好的优化无线局域网性能的方法,数据传输率提高了,相应的吞吐量也就增加了,而访问延迟减小了,也大大减少了重传的次数。对于吞吐量、重传次数和访问延迟三个物理特性,仿真结果显示采用红外编码的方式是一种最好的技术,跳频的方法是这三种中最差的,而直接序列编码的方式则介于两者之间。跳频方法与直接序列编码的方式在吞吐量和延迟方面差别并不大,这是由他们的编码差异仅仅为15%-17%而决定的,但在重传率方面,直接编码的方式比跳频方法要好了40%-43%。另外,对于这三个参数红外编码是最好的选择变量的方法。对于吞吐量,红外编码的方式优于跳频方法和直接编码30-33%。在仿真的最后,红外编码的方式存在70%-75%的吞吐量的变化,其性能要比直接编码的方式好60-62%,其减少率相当于跳频编码的78%-80%。在600秒的仿真时间内,对于WLAN中的整体延迟,红外编码的方式要优于跳频及直接序列编码方法的85%-90%,但红外编码的延迟存在着波动。由以上可知,调整物理层的特征可以很大程度上的提高WLAN的性能,采用分段阈值的方法则可以方便在无线局域网中的数据转换。如果缓存大小加大,则重传次数将会降低,在仿真的初期,文中方案7重传次数比方案6少了30%-35%,但到最后其重传次数达到与其相等的次数。队列的大小随着缓存的增加也会相应的减小,这是因为较大的缓存发送包所用的时间较短,所以队列在较大缓存区内可以持续不断的建立。我们的仿真结果与真实情况仅仅相差1-1.5%。以上情况说明采用分段的机制可以方便无线局域网数据之间的转换。最后因本文的第一条贡献,采用数据率、物理特征和分段阈值这三种方法来提高WLAN性能是非常重要的,它可以用于无线局域网的评估及改善。通过第一个贡献,我们知道可以通过吞吐量、访问延迟、重传的次数、丢失的数据包来分析WLAN的性能。OPNET仿真结果显示,增加数据率是一种优化无线局域网性能的方法,同样也可以优化吞吐量、访问延迟以及重传次数来达到相同的目的。优化物理层特征,可以很大程度上改善WLAN的性能,事实上,若评价WLAN的关键点在吞吐量、访问延迟、重传次数之上,则在物理层采用红外编码的方式是最好的方法,跳频的方式却并不适用。仿真结果显示在无线局域网中采用分段阈值的方法可以很好的方便数据之间的转换。通过上述描述可以得知有三种整合WLAN和UMTS网络的方式：Mobile IP,网关和仿真器的方法。OPNET仿真结果显示Mobile IP的方法是最简单的实现分层网络的整合的方法,仿真结果同时也指出这种方法有着较长的切换延迟不能提供达到预期目标的Qos。我们描述了评估UMTS-WLAN网络性能的方法有三种,Mobile IP是最简单的处理分层网络的方式。仿真结果显示它有着较长的切换时延,不能满足实时要求及相关方面的应用。比较而言,采用网关的方法有着较短的时延,使得两种不同网络之间相互独立且能实现他们之间的相互切换,是目前应用到真实网络环境中的普遍的方法。仿真器的方法在切换延迟上是具有最佳性能的方法,但这种方法由于实现两种网络间的紧耦合而缺乏灵活性。从仿真结果得知,松耦合和紧耦合最大的区别在于用户的通信是否穿过UMTS核心网络。其中松耦合是最简单的实现分层网络间整合的方式和标准,但它有着较长的时延。另外我们知道切换在WLAN-UMTS整合网络中Qos的要求上发挥着重要的作用。实际上我们通过仿真得到了多种分析和评价UMTS-WLAN整合网络的方法：采用Mobile IP分析,采用网关分析和采用仿真器的方法,这里我们将简单的将其进行了对比。UMTS/WLAN整合网络中垂直切换时延的数据在文中表中给出以比较他们之间的不同,该表格非常清晰的给出了结果,从中可以看出,Mobile IP的方法由于传输数据需要经过因特网(内部代理,外部代理)而得到了最差的性能,网关和仿真器方法则仅仅通过内部网交换信息,采用网关的方法的延迟仅仅比仿真器方法长一点点。但用户数量超过2000的时候我们知道Mobile IP的方法需要200ms的网络配置时间,这就使得该方法对某些实时要求的系统是不可接受的。当整合WLAN和UMTS网络时,认证、授权、计费(AAA)是必须考虑的因子,AAA管理机制在WLAN-UTMS整合网络中有着非常重要的地位。认证是从一个相互命名空间中预先存在的标签声明身份的行为,使其作为消息的发送者或通道的终点。授权是决定用户是否有着特殊的证书而具有特定的权利。这种特殊权利可以是,比如到资源的接口。计费则是用于收集资源消耗数据以用于趋势分析,能力规划,计费审计和成本分配,这三个原则适用于所有不同类型的网络,特别适用于作为公共网络的3G网络和采用IEEE802.11标准的局域网。但UMTS和WLAN网络有着不同的数据库和AAA程式。为了应用AAA策略,WLAN-UMTS整合的方法使用了通用用户使用模块(USIM)。整合UMTS和WLAN的一个好处在于通用计费,也就是用户将收到一个各种混杂网络使用情况的收费单。事实上,整合了3G和WLAN网络之后,我们必须提供相应的计费机制,这种计费机制能提供不可抵赖服务,这是非常重要的一点,特别是3G网络和WLAN网络被不同的运营商登陆的时候,若不能提出这样的机制,那不同的运营商之间可以相互欺骗,密谋计费支出,这就会造成一定程度上的混乱。这样就有两种不同的计费策略可供选择：事先支付和事后支付。在前一种计费策略下,用户必须预先支付一些钱,当这些用户使用网络服务时,主运营商将根据用户的诚信检测收费信息,当用户在诚信接口网络之外,这项网络服务也随之终止。在后一种策略下,用户与国内服务提供商签订计费协议,定期支付其使用费用。基于垂直切换分析的Qos分析与增强在WLAN和3G/4G网络中得到了广泛应用,我们在OPNET Modeler11.5工具平台下提出了新的方法(IQCS),结果显示在保证最终用户需求的Qos的前提下,采用执行多媒体架构的方法在保持可接受Qos与较低的垂直切换丢失概率和访问阻塞概率前提下性能优于非执行的方法。这就是说我们提出的方法(执行Qos控制机制：IQCS)在整合WLAN和UMTS的垂直切换输出上大大的提高了服务质量。通过这一部分仿真实验用来调查所提出的方法是怎样在整合3G/4G与WLAN网络时提高整体Qos的,我们设计的实验其访问到达时间服从独立的柏松分布,而每一个连接的会话时间服从指数分布。众所周知,丢失一个已连接的通信的开销大于拒绝一个新的连接,因此蜂窝网保留了一定的带宽用于切换访问以减少垂直切换丢失的概率。这一保留的所谓的守卫带宽既可以是动态的也可以是静态的,动态的方法通常在控制开销上优于静态的方法,而静态的方法往往由于其设计简单而受到更多的青睐。仿真实验在不同的通信负载情况下进行,我们将自己提出的方法与不执行多媒体服务的方法进行了对比。实验中,我们在同等条件下进入WLAN和UMTS,计算整个系统的性能优劣,在整合网络中提出的执行控制机制支持下比较带宽利用率,这里非执行控制机制是在不同通信负载条件下实验的。很明显,采用执行多媒体连接的方式优于非执行多媒体方式,且随着通信负载的增大,其优势更明显。执行多媒体方式能更好的利用带宽的原因在于我们所提出的机制允许网络通过降解文本自动调节Qos,为新的切换访问提供了适量的资源。理所当然,通过执行多媒体机制所产生的垂直切换丢失概率明显低于非执行多媒体的方式,当通信负载越大,其优势更加明显。这就说明我们所提出的方法在整合WLAN和蜂窝系统时降低了垂直切换丢失包的数量。除此之外,我们还给出了在采用多媒体连接和非多媒体连接时访问阻塞概率的情况。仿真结果显示,随着通信负载的增加其访问阻塞概率也相应的增加,相对而言,采用执行多媒体的方法明显的减少了访问阻塞的概率。最后,本研究提出了一种新的方法(执行Qos控制机制IQCS)在分层架构网络如UMTS和WLAN发生垂直切换时用来控制和增强Qos以最小化服务质量的降解。本论文我们基于ETSI所设计的网络架构提出了蜂窝网和WLAN网络的整合模型,这有效的整合了802.11和蜂窝网(松耦合方法)两种标准,我们将新方法作为IQCS中的一个组件对每一个步骤都进行了分析,通过仿真实验说明我们提出的系统是可靠的。我们所提出的方法支持实时属性,既可以利用WLAN系统中高速率的特点又可以利用3G/4G网络所具有的覆盖区域广等优点,仿真实验结果表明,执行多媒体架构的方式在具有较低垂直切换丢失率和访问阻塞概率的同时维持最终用户所要求的Qos前提下比非执行多媒体的方式具有更好的性能。这就是说IQCS在有垂直切换在分层网络中发生时,可以很好的提高服务质量。文章的最后,将基于SCTP的VHO机制和基于策略的Qos机制与我们提出的新的方法进行了对比。基于SCTP的VHO机制,基于策略的Qos机制以及我们提出的方法都有着最小化服务质量降解的目的,但却有着不同的性能。我们的目的是当有切换发生在WLAN和UMTS交互网络中时,与其他的能最小化服务质量降解也就是尽可能有效且无缝的实现切换的方法进行对比。因此,我们选择了基于SCTP的VHO机制和基于策略的Qos机制用于整合UMTS-WLAN系统。这里最主要的目的是设计一种UMTS/WLAN VHO机制来使得在两种网络间的切换尽可能的无缝且有效。使用SCTP的方式来支持UMTS/WLAN VHO其理论基础在于SCTP的多巢穴特征。从视图关联点来看,结点网络接口是否是同一种并不重要,接口都可以通过它的IP地址增加到当前的连接之中。M-SCTP在移动管理策略中提高了端到端的软件切换方案。对于在UMTS和WLAN交互环境中基于策略的Qos管理方式,用户可以在不同的环境例如公司、住宅、公共场所下使用UMTS网络,类似的WLAN网也可以在不同的诸如以上环境下使用,不同的环境可能牵涉到不同的管理域和不同的网络集成。例如在WLAN中不同的环境如公共场所、企业、住宅可能有着不同的安全机制和策略。基于策略的Qos管理架构在UMTS和WLAN交互网络中支持端到端Qos服务。以上提到了三种方法都是为了解决当前交互网络中存在的各种问题,如UMTS的阻塞问题,最小化服务质量降解问题等等。另一方面,如何保证在分层网络环境下的Qos也是我们面临的一个难题,尽管所有方法都为了最小化服务质量降解,但他们有着不同的性能,从这些方法的对比结果中可以看出,我们提出的IQCS方法与基于SCTP的VHO机制和基于策略的Qos机制相比,我们所提出来的方法允许较大的负载利用率,降低了丢失概率和访问阻塞概率,在实时环境中是最简单可行的,在最小化Qos降解问题上也是最可靠的。更多还原

【Abstract】 Wireless LAN connections generally provide higher bandwidth but smaller coverage area as compared cellular networks which have lower bandwidth and wide coverage. Recent trends indicate that cellular networks based on3G standards and wireless Local Area Networks (WLANs) coexist to offer multimedia services to end users. However, while users roam throughout this heterogeneous network, they should be automatically and transparently switched from one access technology to another such as from802.11networks to3G or4G ones, depending upon the availability of resources and QoS requirements, without any user intervention. Nowadays, even if switched from WLAN to UMTS or vice versa is a successful application in information technology, the quality of service of data transmission linked to vertical handoff dropping and call blocking probability remains to be desired. In order to contribute to the resolution of this important issue we conducted researches which constitute our doctoral thesis.Before presenting our majors contributions, an overview of WLAN and Cellular technologies are given. Indeed through this section of our thesis we firstly address WLAN architectures. We withhold that in Lightweight architecture model, the management of operation is easy because it gives the permission to WAP from single device. We present the benefits of wireless LAN and also expose WLAN standards. As far as this variety of standard is concerned we underline that IEEE802.11b is the most popular WLAN standards and the term WiFi (Wireless Fidelity) was first introduce in this standard however later this term was changed to mean any type802.11network together with802.11a,802.11b dual band. We show that despite the productivity convenience and cost advantage that WLAN offers, the radio waves used in wireless networks create a risk where the network can be hacked. We underline that UMTS or Cellular Networks technologies offer greats advantages with mobiles phone communication than GSM technology. Also, we present some related work to our topics discussed in this thesis. Some previous techniques used to evaluate and improve WLAN performance and also several methods about WLAN/UMTS integrated issues and performance analysis, are quotedThis thesis makes four major contributions:Firstly, we address some methods (the effect of parameters as methods:Data rate, Fragmentation threshold and Buffer size and also Physical Characteristics are analyzed based on throughput, media access delay, retransmission attempts, traffic load and queue size) to improve the performance of WLAN connection via OPNET Modeler9.1. In fact we implemented three methods for improving WLAN performance such as data rate, physical characteristics and fragmentation threshold in order to evaluate and improve our wireless Local Area Network. The performance has been analyzed with the help of the parameters like throughput, media access delay, the number of retransmission attempts, dropped data packets. OPNET simulation result show that increasing the data rate is a method to optimize the performance of wireless local area networks such as increasing the data rate, the performance can be optimized in terms of throughput; media access delay and the number of Retransmission attempts. Tuning the physical layer characteristic, can greatly improve the WLAN performance. In fact the infrared coding at the physical layer proves to be the best if performance criteria are defined in terms of throughput, the media access delay and the number of retransmission attempts while the frequency hopping is not preferred coding method at the physical layer for the above performance parameters. The simulation results also shown that Fragmentation Threshold, can greatly facilitate data transition in Wireless LANs.Secondly, we propose an integrated architecture of WLAN and3G networks based in three approaches (Mobil IP, Gateway and Emulator). From OPNETTM Modeler11.5simulations we determined the most appropriate method to integrate WLAN and3G networks. We analyze the performance evaluation of each method based on Vertical handoff latency according to UMTS-WLAN interworking strategies (methods). Here we described the main issues of evaluating UMTS-WLAN interworking performance based on3approaches. Mobile IP approach is the easiest deployment strategy and the standards to implement the interworking of the heterogeneous network. The simulation results show that it suffers from long handover latency and might not be able to offer real-time services and applications. The gateway approach obtains a much lower latency than mobile IP approach. It helps the two networks to operate independently and also provides the capability of the intersystem roaming. This approach is applicable to the current network environment. The emulator approach achieves the best performance in terms of handover latency. Moreover, this approach lacks the flexibility since the two networks are tightly coupled. From the simulation results, it also appears that the main difference between tight coupling and loose coupling is whether the user’s traffic is delivered through the network core of UMTS or not. In fact the disadvantage of the tight coupling approach is that, as the data traffic of WLAN traverse via the UMTS network, they potentially create a bottle neck in the UMTS network. Moreover, this technique is considered more complicated than the loose coupling technique because protocol stacks of different wireless networks need to be compatible for such type of integration so only the loose coupling method is used to integrate the two networks. However the loose coupling has some limits. In fact, the main disadvantage of using the loose coupling is that two networks are integrated via the internet. Therefore, signal traffic needs to traverse long paths which cause high handoff latency. Therefore, real-time services are highly affected. Handoff is an important criterion in WLAN-UMTS integrated QoS measurements and loose-coupled network cannot support service continuity to other access network during handover, thus loose-coupled sheme has long handover latency and packet loss hence our interested on presenting Vertical handover between WLAN and UMTS. The loose coupling is the easiest deployment strategy and the standards to implement the interworking of the heterogeneous network and it suffers from long handover latency and we also know that Handoff plays an important role in WLAN-UMTS integrated QoS.Thirdly, we propose a new method (an Implemented QoS Control Scheme). We introduce each step as component of the Implemented QoS Control Scheme (IQCS) and also focus on vertical handover analysis outcomes from WLAN and UMTS (3G/4G) interworking under the implemented QoS Control Scheme approach via OPNET Modeler11.5simulations. Since our new method is based on QoS management we also address QoS issues for integrating WLAN and UMTS networks according to the ETSI (European Telecommunication standard institute) designed network architecture that efficiently integrates802.11and cellular. Two different fundamental methods have been proposed for merging WLAN and cellular networks namely loose coupling and tight coupling. Loose coupling has less integration between the two types of networks, as its name implies. In this scenario, the WLAN and cellular networks are two separate access networks. The WLAN access network is attached to the Internet backbone, and the cellular networks into the cellular core network. The access networks do not have anything in common, but the core networks are connected together. Without necessarily modifying the UMTS core network, a loosely coupled WLAN and3G or4G network can use existing mechanisms to accommodate its user’sneeds, for instance, using an authentication, authorization and accounting (AAA) server to handle the user subscription to these networks and using mobile IP (MIP) to facilitate users roaming among different access networks. The motivation is to try and minimize the changes to the cellular core networks, therefore reducing cost of this solution. Our simulation and experiments will use the interworking architecture based on loose coupling since we have seen in that loose coupling is the easiest deployment strategy and the standards to implement the interworking of the heterogeneous network. Our proposed model supports the delivery of adaptive real-time flows for end users taking the advantage of high data rate WLAN systems as well as the wide coverage area of3G networks. The simulation results show that the implemented multimedia framework performance is better than the non-implemented approach in terms of lower vertical handoff dropping probability and call blocking probability while still maintain acceptable QoS to the end users. As far as QoS Issues for Integrated Network are concerned, unlike in the homogeneous wired networks, providing QoS for integrated WLAN and UMTS networks has some fundamental bottlenecks: Firstly, WLAN and UMTS have different transmission-rate capacity over the radio interfaces; therefore the handoff between the two systems makes the maintenance of QoS connection very hard. WLAN can provide a transmission speed from11Mb/s up to54Mb/s theoretically, while UMTS has only144kb/s at vehicular speed,384kb/s at pedestrian speed and2Mb/s when used indoor. If we keep the QoS resource assigned by UMTS to a connection which is actually in a WLAN hotspot, the advantage of the high speed of WLAN is not fully taken. On the other hand, if we use a WLAN parameter for a station in the UMTS network, the connection may not be admitted at all. Therefore, to maintain a sensible QoS framework, one has to consider the significant difference transmission capacity between two systems especially when user handover takes place. The second constraint is that WLAN operates on a free ISM band and has a lot of uncontrollable interference (i.e. microwave), although some techniques are used to reduce the interference like spreading spectrum. Such kinds of problems are beyond engineering control and hard QoS guarantee is very difficult to achieve in certain conditions. To support QoS in packet switching networks, there has to be some mechanisms to control network loads under a threshold so that the system can provide a satisfied performance. The third bottleneck is that3G or4G cellular networks are very well designed with careful network planning and mature admission control algorithms. The achievable QoS level is relatively high, while WLAN works under a more robust environment and is difficult to achieve. To solve these issues a new Method for QoS Controlling has been proposed. Our proposed QoS framework assumes a packet switching core network based on the UMTS network architecture. However, this holds the same relationship with some GPRS networks or other packet switching cellular systems. It is well known that Internet has some fundamental scalability limitations when it comes to manage individual traffic flows with the approach of resource reservation. Its successor, the prioritization approach addresses the scalability problem at the cost of coarser service granularity. To enable efficient use of scarce resources provided by the cellular networks while also maintaining strong service guarantees, we adopt the reservation based systems. In WLAN the reservation is achieved by using the HCF of the WLAN and in UMTS is achieved by the functionality of Base Station. We analyze each of the proposed components below. The new method contains:QoS Policy Provisioning, Degradation Profile, QoS Connection Admission Control (CAC), QoS Mobility Management Module (MMM) and QoS Monitoring. For QoS Policy provisioning, Users’context with QoS requirement is first issued to policy provisioning module (PPM), where the users’subscribed information together with traffic classes. Then a QoS signal with suggested degradation profile is made and sent to both the end user and connection admission control (CAC) module. Once the streaming data has been transmitted, traffic meters measure its temporal properties against the QoS contract. If the established end users’QoS profile is not satisfied, this monitor may pass the state information to CAC or other components to trigger specific actions. This feedback approach enables the QoS merits to adapt with the dynamic changes in the networks. About QoS Mobility Management Module (MMM), users’mobility has a significant impact on the QoS of CAC and it plays an important role in the model. Within an integrated cellular and WLAN network, a handover can occur when a mobile node enters a Hot-Spot area or when it decides to leave the Hot-Spot area. Because Hot-Spots are usually within the coverage of cellular networks, the actual handover is not necessary to happen and a decision should be made on the users’desire. This is user triggered handover (Handover Triggering) or Desirable Handover (DH). Note it is different from the general term of handover, because it is not time critical as the mobile nodes can be connected to WLAN and cellular networks simultaneously. A DH may occur when a mobile node roams into a WLAN. This implies that the route taken by data will change. Any QoS established for that flow before will be disrupted. A simple solution is to establish a new WLAN reservation before handing the mobile node over the WLAN, because DH’s time tolerance makes this approach realistic. Also notice that the wireless link bandwidth will have risen dramatically, so the new submitted QoS profile should consider users’subscription status and give an appropriate request. A normal handover occurs when a mobile node roams from WLAN into a cellular network. A new reservation has to be made again. Moreover the actual handover time needs to be kept tightly in order to provide seamless service. Since the network resources that the user booked in WLAN is normally over the capacity of the UMTS, the actual probability of dropping handoff could be very high. An adaptation mechanism is needed to be embedded in CAC and this module, which can reduce the user’s QoS request by the definition of degradation profile. Therefore, the system performance can be improved without losing acceptable QoS level.Fourthly, two methods such as SCTP-based VHO Scheme and policy-based QoS have been compared with our proposed method. SCTP-based VHO Scheme and policy-based QoS and our proposed new method (IQCS) have the same aim that is to minimize the service quality degradations. Our aim here is to compare our method with other methods which can minimize the service quality degradations during handover between WLAN and UMTS interworking or in other words make the handover between the two networks as seamless and efficient as possible. Thus, we choose the SCTP-based VHO Scheme presented in some previous work and policy-based QoS architecture for WLAN as a prelude to an integrated QoS architecture for the integrated UMTS-WLAN system. All these proposed three methods architecture aim to solve the problems existing in present interworking solutions, such as congestion in the UMTS core network or minimize the service quality degradations. On the other hand, it’s a significant issue of how to guarantee the quality of service (QoS) in the heterogeneous environment (WLAN and UMTS). Although these methods have the same aim that is minimize the service quality degradations, they have different performances. From our analysis it appears that our new method is the easiest feasible method in real time among the three and is the most reliable in term of minimize the QoS degradation since it allow a large utilization over traffic load and reduce dropping probability over traffic load and call blocking probability.Through this thesis, in order to show up the contribution of this research we firstly retrace the history of WLAN than present the evolution of cellular communication since the invention of the first phone until the last technology used to communicate via cellular networks which is4G Some emerging technologies have been addressed also and we introduce the vertical handover by given the concept of this important component of our thesis. We present in one chapter WLAN technology and Cellular Networks (UMTS), two important components of our research. We firstly address WLAN architectures and then we describe Wireless LAN different components and operating modes or topologies. We present the benefits of wireless LAN and also expose WLAN standards. As far as this variety of standard is concerned we underline that IEEE802.11b is the most popular WLAN standards and the term WiFi (Wireless Fidelity) was first introduce for this standard however later this term was changed to mean any type of802.11network together with802.11a,802.11b dual band. Despite the productivity convenience and cost advantage that WLAN offers, the radio waves used in wireless networks create a risk where the network can be hacked. However, UMTS system uses the same core network as the GPRS and uses entirely new radio interface. Compared to Wired Networks, Wireless Cellular Networks have a lot of limitations and security issues in UMTS remain a serious task because Cellular Networks are open to attacks. The3G and4G security architectures provide features such as authentication, confidentiality, integrity etc. Also, the WAP protocol makes use of network security layers such as TLS/WTLS/SSL to provide a secure path for HTTP communication. Although UMTS provides good security features, there are always new security issues that come up and researchers are actively pursuing new and improved solutions for these issues. Some related works to our topics discussed in this thesis are briefly presented such as previous techniques used to evaluate and improve WLAN performance and also several methods about WLAN/UMTS integrated issues and performance analysis. Some researcher’s works on vertical handover analysis within heterogeneous networks are also underlined.Our simulations results via OPNET9.1show that evaluating and improving WLAN performance can be done by increasing the data rate. It has been observed that as we increase the data rate from1Mbps to11Mbps, the throughput increases by about27-30%.This is also predictable from the theoretical viewpoint that as we increase the data rate, the number of bits received increases. Also the average media access delay reduces from scenario1to scenario2. Initially it was near to the value of media access delay of scenario1and after that it increases linearly and then it will end up at the difference about90-95%to scenario1at the end of simulation period of600simulation seconds. This is very encouraging result and it is understandable because the data will stay for less time in media (buffer) for higher data rate scenarios. The retransmission attempts also decreases by about69%from scenario1to scenario2that is because we increase the data rate the packets are delivered accurately and there is less requirement of retransmissions in scenario1and after that it increases linearly. The data transfer rate (DTR) is the amount of digital data that is moved from one place to another in a given time. It can be viewed as the speed of travel of a given amount of data from one mobile to another. In general, the greater the bandwidth of a given path, the higher the data transfer rate. In the two scenarios one is with data rate of1Mbps and another scenario is created with data rate of11Mbps and the data rate is the parameter signifies the speed of the nodes connected in our designed Wireless Local Area Network. In fact increasing the data rate is a method to optimize the performance of wireless local area networks such as increasing the data rate, the performance can be optimized in terms of throughput; media access delay and the number of Retransmission attempts. About Physical characteristics, the simulation results show that the infrared coding proves to be the best technique, while the frequency hopping method proves to be the worst among the three and the direct sequence coding proves to be lying between the infrared and frequency hopping techniques for the three parameters that are the throughput, number of retransmission attempts and the Delay. The difference in (FH) and (DS) coding is very less for throughput and for the delay the difference in these coding techniques is not very high which is about15-17%, but for retransmission attempts the DS is performing much better than the FH coding by about40-43%. Moreover, for all the three parameters the infrared coding is the best among three available options. For throughput, the performance of infrared is better by about30-33%as compare to the DS and FH coding, also at the end of simulation there is a transition in the throughput of infrared coding by about70-75%. For retransmission attempts, the performance of infrared coding is performing well by about60-62%as compare to DS coding while this reduction is about78-80%for the FH coding. For the overall delay in WLAN, the infrared performs better than DS and FH by about85-90%, for entire simulation duration of600simulation seconds. However, at the end there is a transition in the delay of infrared coding. It appears clearly that tuning the physical layer characteristic, can greatly improve the WLAN performance and also Fragmentation Threshold can greatly facilitate data transition in Wireless LANs. If the buffer size is increased, then the number of Retransmission attempts would be reduced, at the starting time of simulation period it is about30-35%lesser than scenario6, but till the end of simulation the retransmission attempts become approximately equal to the retransmission attempts of scenario7. Also the size of the queue will be decreased for larger buffer due to the fact that the larger buffer will take less time to send the packets, so the queue size will not build up continuously for larger buffer. This reduction difference is about1-1.5%throughout the simulation. The above reason allows us to affirm that fragmentation mechanism can greatly facilitate data transition in Wireless LAN. Finally for this first contribution it is important to indicate that we implemented three methods for improving WLAN performance such as data rate, physical characteristics and fragmentation threshold in order to evaluate and improve our wireless Local Area Network. Finally we can retain that for the first contribution, the performance has been analyzed with the help of the parameters like throughput, media access delay, the number of retransmission attempts, dropped data packets. OPNET simulation result show that increasing the data rate is a method to optimize the performance of wireless local area networks such as increasing the data rate, the performance can be optimized in terms of throughput; media access delay and the number of Retransmission attempts. Tuning the physical layer characteristic, can greatly improve the WLAN performance. In fact the infrared coding at the physical layer proves to be the best if performance criteria are defined in terms of throughput, the media access delay and the number of retransmission attempts while the frequency hopping is not preferred coding method at the physical layer for the above performance parameters. The simulation results also shown that Fragmentation Threshold, can greatly facilitate data transition in Wireless LANs.As far as the main issues of integrating WLAN and UMTS networks based on three approaches, such as:Mobile IP, Gateway and Emulator approaches are concerned, the OPNET simulation results also show that Mobile IP approach is the easiest deployment strategy to implement the interworking of the heterogeneous network, however, the simulation results also show that this approach suffers from long handover latency and might not be able to offer good Quality of Service even it remains practicable. We described the main issues of evaluating UMTS-WLAN interworking performance based on3approaches. Mobile IP approach is the easiest deployment strategy and the standards to implement the interworking of the heterogeneous network. The simulation results show that it suffers from long handover latency and might not be able to offer real-time services and applications. The gateway approach obtains a much lower latency than mobile IP approach. It helps the two networks to operate independently and also provides the capability of the intersystem roaming. This approach is applicable to the current network environment. The emulator approach achieves the best performance in terms of handover latency. Moreover, this approach lacks the flexibility since the two networks are tightly coupled. From the simulation results, it also appears that the main difference between tight coupling and loose coupling is whether the user’s traffic is delivered through the network core of UMTS or not. Since loose coupling is the easiest deployment strategy and the standards to implement the interworking of the heterogeneous network and it suffers from long handover latency and we also know that Handoff plays an important role in WLAN-UMTS integrated QoS. In fact we present some performance and evaluation for the UMTS-WLAN interworking according to different approaches based on simulation. The three different approaches are compared here, mobile IP, gateway and emulator approaches. The vertical handover latency of different strategies of UMTS/WLAN interworking are presented in a table in order to compare them. Eexperiments results have been illustrated clearly. From which, it is clear that mobile IP obtains the poorest performance since the signaling packets have to go to Internet (home agent and foreign agents). Gateway and emulator approaches only involve the message exchange within intra-network. The latency of gateway approach is a little bit higher than the emulator approach. We also learn that mobile IP approach will introduce more than200ms latency under this network configuration while the users are more than2000. The latency might not be acceptable for real-time applications. When integrating WLAN and UMTS, Authentication Authorization and Accounting and Billing are important factors to analyze. AAA management is a key element in an integrated WLAN-UMTS network. Authentication is the act of verifying a claimed identity, in the form of a pre-existing label from a mutually known namespace, as the originator of the message (message authentication) or as the channel end point. Authorization is the act of determining whether a particular right can be granted to the presenter of a particular credential. This particular right can be, for example, an access to a resource. Accounting is the act of collecting resource consumption data for the purposes of performing trend analysis, capacity planning, billing, auditing, and cost allocation. These principles are applicable to all kinds of networks, in particular to3G Wireless infrastructures targeted to public networks such as UMTS as well as local area networks like IEEE802.11, but UMTS and WLAN networks have different databases and AAA procedures. The method of WLAN-UMTS interworking described is based on the use of Universal Subscriber Identity Module (USIM) functionality for AAA purposes. One of the advantages for interworking of UMTS and WLAN is common billing which means that a subscriber will receive a single combine bill for using services offered by different network operators. In fact, while3G and WLANs are integrated, billing agreements or billing mechanisms must be provided. The billing mechanisms should support non-repudiation service. This is a very important issue especially when the3G network and the WLAN network are administrated by different operators. If there’s not such a mechanism provided, operators may deceive each other. Moreover, the two operators can collude with each other for common billing. Furthermore two billing Options are possible; pre-paid and post-paid billing. In prepaid billing, a subscriber has paid some money in advance. When the subscriber uses network services, the home network operator checks the charging information and deduct corresponding amount of money from the subscriber’s credit. When the subscriber is out of credit access network services is denied. In post-paid billing, a subscriber has a billing agreement with the home service provider to pay at intervals and is charged regularly for the usage within this period.As far as the QoS analysis and enhancement are concerned based on Vertical Handoff Analysis between WLAN and3G/4G Networks under our proposed new method (IQCS) via OPNET Modeler11.5, results reveal that the implemented multimedia framework performance is better than the non-implemented approach in terms of lower vertical handoff dropping probability and call blocking probability while still maintain acceptable QoS to the end users. This means that our proposed new method (Implemented QoS Control Scheme: IQCS) greatly improve the quality of service during Vertical handover outcome from the integrated network WLAN and UMTS. Through this section, simulation experiments are used to investigate how the proposed approach can improve the overall QoS for the integrated3G/4G networks and WLAN networks, the call arrivals in our simulation follow an independent Poisson process and the session time of each connection is exponentially distributed. It is well known that dropping an established communication is worse than rejecting a new call. Therefore cellular systems reserve a guard bandwidth for the handoff calls in order to reduce the vertical handoff dropping probability. The reserved guard bandwidth can be either static or dynamic. The dynamic approach often outperforms the static one at the expense of generating more control overheads. However, the static approach is often attractive in practice owing to its design simplicity. The simulation is carried out under various traffic loads. We compare the proposed approach with non-implemented multimedia services. In the experiments, we set the load to WLAN and UMTS identical in each single experiment and calculate the overall system performance merits. Comparative bandwidth utilization supported by the proposed implemented control scheme in the integrated network to that without the implemented control scheme under various traffic loads. Clearly, the utilization for implemented multimedia connection is better than that for non-implemented multimedia. When the traffic load becomes higher, the advantage is more evident. The reason why implemented multimedia can better utilize the system bandwidth is that the proposed scheme allows the network intelligently adjust each admitted QoS connection by its degradation profile and give sufficient amount of resources for the new or handoff calls. The vertical handoff dropping probability for implemented multimedia connection is less than that for non-implemented multimedia. When the traffic load becomes higher, the trend is more evident. It reveals that the proposed approach reduces a great number of vertical handoff dropping calls for the integrated WLAN and cellular system. The call blocking probability over the traffic load for implemented multimedia connections and non-implemented multimedia connections is shown. From simulation results, it is clear that with the increment of the traffic load the call blocking probability is increased. The implemented approach reduced the call blocking probability compared with non-implemented approach. Finally it is important to address that specifically, this research has proposed a new method (Implemented QoS Control Scheme IQCS) to control and enhance the QoS during vertical handoff between heterogeneous networks such as UMTS and WLAN can minimize the service quality degradations. Through this thesis we address the integrated model of cellular and WLAN networks according to the ETSI (European Telecommunication standard Institute) designed network architecture that efficiently integrates802.11and cellular (loosely coupled method). We analyze each step of our new method as a component of IQCS. The system performance reliability is confirmed via simulations. Our proposed model supports the delivery of adaptive real-time flows for end users taking the advantage of high data rate WLAN systems as well as the wide coverage area of3G or4G networks. The simulation results show that the implemented multimedia framework performance is better than the non-implemented approach in terms of lower vertical handoff dropping probability and call blocking probability while still maintain acceptable QoS to the end us更多还原