一种基于无线局域网的移动IP快速切换方案

为了使移动节点在无线局域网环境中进行快速有效的切换，我们提出了一种基于管理域的快速切换方案。该方案将多个相邻的无线局域网组成一个单独的域，采用层次管理方式，使域内各个子网通过专用的Mac桥连接，减少了移动节点域内切换过程中产生的注册时延和数据包的丢失。     

基于双阀门值的自适应无缝切换

WLAN和GPRS网络是两种使用最广泛的无线网络技术，两者具有很强的互补性。WLAN能提供较高的数据速率．但只适合热点地区应用。GPRS能提供随时在线的连接，但数据速率较低。假如用户能在两者之间无缝切换，无线数据服务的性能和灵活性将得到极大提高。WLAN／GPRS融合网络可以提供随时随地的无缝接入和移动计算。论文主要基于WLAN网络的可用性、尽可能使用WLAN以达到既高速又廉价的无线接入服务，研究WLAN和GPRS的无缝切换，提出基于双阀门值的自适应无缝切换算法，仿真实验证明这种算法在切换次数和尽可能使用WLAN之间取得较好的平衡。     

Design novel weighted rating of multiple attributes scheme to enhance handoff efficiency in heterogeneous wireless networks

With the availability of multiple access interfaces, mobile device users can move between heterogeneous wireless networks. Service providers now must try harder to satisfy their users by ensuring connection service quality. The vertical handoff scheme plays an important role in this endeavor. We propose a novel handoff scheme that features two operating processes: attributes rating and network ranking. A self-developed WRMA (Weighted Rating of Multiple Attributes) method is used to rate attributes. TOPSIS is employed to rank networks. The WRMA-based handoff scheme, as we shall call it hereafter, select an AHP-SAW handoff model to compare with. The WRMA, which rates attributes directly, is relatively simple to use. Further, TOPSIS was found to be more precise than SAW in ranking networks. We also compared our handoff scheme with the traditional NIST signal handoff model. Four Key Performance Indicators of packet drop ratio, delay, jitter and throughput were applied in our experiments. Results demonstrate our handoff scheme outperformed the NIST model in lowering packet drop ratio for all four traffic types. Higher average throughput is achieved. Experiments also show improvements on packet delay and jitter. Such improvements can significantly enhance link service quality, making it more suitable for voice and video traffic applications.     

End-to-End Security Across Wired-Wireless Networks for Mobile Users

ABSTRACT

Recent advances in mobile computing and wireless communication technologies are enabling high mobility and flexibility of anytime, anywhere service access for mobile users. As a result, network connections of such users often span over heterogeneous networking environments consisting of wired and wireless networking technologies. Both network heterogeneity and user mobility make the securing of data transmission over heterogeneous networks challenging and complex. In this paper, we focus on the challenge of providing secure end-to-end network transmissions to wireless mobile users. To minimize service interruption during ongoing secure sessions of mobile users, we present the design and implementation of an approach based on the well-known Internet Protocol Security (IPSec) standard. We conducted a performance evaluation of our implementation using a Voice over IP (VoIP) application over an actual network testbed. Our empirical performance results demonstrate a packet loss improvement of 17% to 34% (for various VoIP packet sizes) and a handoff delay improvement of almost 24% validating the high efficiency of our proposed approach.     

Performance of GSM networks with general packet radio services

Recently, most of the mobile network providers start to introduce general packet radio service (GPRS) in their existing GSM networks. GPRS is the technology that will enable more efficient Internet applications to run on mobile networks even before the installation of 3G systems. However, it is not yet clearly understood, how the new data services will affect the overall network performance. This paper provides a framework for analytical performance evaluation of a single GSM/GPRS cell based on a multidimensional Markov chain model. Important performance measures like new call and handover blocking probabilities, moments of the blocking period distributions, achievable average data rates and resource utilization are determined. Introducing a new connection admission control (CAC) algorithm, different partitioning strategies between GSM and GPRS resources are investigated. Finally, the influence of typical GPRS applications like Internet browsing on traditional GSM services has been studied.     

基于运动趋势的自适应垂直切换算法及其性能评价

采用不同的无线接入技术的多种网络的融合可以提高无线传输性能,为移动用户提供随时随地的网络连接.垂直切换是异构无线网络相互融合的基础.在垂直切换过程中,切换判定是一个非常重要的环节,直接决定切换性能.文中给出了常用的迟滞电平算法和驻留定时器算法中切换判定条件的形式化表达,并对其进行了性能分析.在此基础上,提出了一种自适应的垂直切换算法,通过分析节点的运动趋势,自适应地调节切换触发条件,有效提高垂直切换性能.所涉及的运算均为初等计算,算法简单,适用于低能量、低运算能力的移动设备.仿真实验表明,该算法的综合性能优于迟滞电平算法和驻留定时器算法.     

IPv6 based relay gateway protocol in hybrid networks

During the past few years, WMAN (Wireless Metropolitan Area Network) and WLAN (Wireless Local Area Network) provided fast, convenient and reliable solution for all kinds of users. With the development of the communication technology, the future wireless networks will allow mobile users access Internet anywhere, anytime. Therefore, it is a natural trend to combine different wireless networks to provide a seamless roaming for users. It is feasible for mobile terminal which have multiple modes to handoff between different networks. A relay gateway protocol for the WLAN-mode nodes (mono-mode WLAN nodes and dual-mode nodes) in the hybrid network of IEEE 802.16 WMANs and IEEE 802.11 WLANs is proposed to provide wider mobility. Dual-mode mobile nodes with good service can provide WLAN links to nearby WLAN-mode nodes with bad service or out of the WLAN coverage. Simulation results show that the relay gateway scheme can improve network performance of the hybrid networks. Moreover, the relay gateway method can bring additional service coverage and increase the capacity of WMANs and WLANs.     

Handoff performance analysis of PMIPv6-based distributed mobility management protocol-urban scenario

Mobility management allows the networks to track down a mobile user's location for sending datagrams and to retain the connection when the user changes its location points repeatedly. Whenever a node switches between one base station and another, the connectivity is maintained through a process called handoff management. For real-time traffic implementations in wireless network communications, handover performance is essential. A mobile node is blocked from transmitting and receiving a datagram for a longer time as the handover delay increases. Unacceptable handover delays are common in real-time communication services. To guarantee smooth connectivity and continuous provision of services, effective handoff methods are required. The handoff efficiency of network-based distributed mobility management (DMM) is studied extensively in this article, along with a comparison to PMIPv6. We specifically investigate how handover delay, session recovery, and packet loss are influenced by cell radius. From the analytical and simulation findings this paper concludes that network-based DMM performs better than PMIPv6.     

Scanless fast handoff technique based on global Path-Cache for WLANs

Wireless LANs (WLANs) have been widely adopted and are more convenient as they are interconnected as wireless campus networks and wireless mesh networks. However, time-sensitive multimedia applications, which have become more popular, could suffer from long end-to-end latency in WLANs. This is due mainly to handoff delay, which in turn is caused by channel scanning. This paper proposes a technique called Global Path-Cache (GPC) that provides fast handoffs in WLANs. GPC properly captures the dynamic behavior of the network and mobile stations (MSs), and provides accurate next-AP (access point) predictions to minimize the handoff latency. Moreover, the handoff frequencies are treated as time-series data, thus GPC calibrates the prediction models based on short-term and periodic behaviors of mobile users. Our simulation study shows that GPC virtually eliminates the need to scan for APs during handoffs and results in much better overall handoff delay compared to existing methods.     

Context-aware handoff middleware for transparent service continuity in wireless networks

Advances in wireless networking and content delivery are enabling new challenging provisioning scenarios where a growing number of users access continuous services, e.g., audio/video streaming, while moving among different points of attachment to the Internet, possibly with different connectivity technologies, e.g., Wi-Fi, Bluetooth, and cellular 3G. That calls for novel middlewares capable of dynamically personalizing service provisioning to the characteristics of client environments, in particular to discontinuities in wireless resource availability due to handoffs. The paper proposes a novel middleware solution, called Mobile agent-based Ubiquitous multimedia Middleware (MUM), that performs effective and context-aware handoff management to transparently avoid service interruptions during both horizontal and vertical handoffs. MUM exploits the full visibility of wireless connections available and their handoff implementations (handoff awareness), of service quality requirements and handoff-related quality degradations (QoS awareness), and of network topology and local resource availability (location awareness); that visibility enables MUM to provide original solutions for handoff prediction, multimedia continuity via adaptive data buffering/pre-fetching, and proactive re-addressing/rebinding.     

基于移动用户位置预测的垂直切换算法

针对异构无线网络环境中现有垂直切换算法存在难以实现移动用户接入网络的无缝切换,无法向用户提供稳定通信服务的问题,提出一种基于移动用户位置预测的垂直切换算法。首先利用用户移动轨迹的相似性,使用用户轨迹数据离线训练LSTM模型以学习各用户普遍具有的移动规律;然后在线加载LSTM模型进行用户位置预测,从而使用模糊逻辑分析计算下一时刻用户对应候选网络的回报值,并选取回报值最高的网络进行切换。实验结果表明,该算法与已有垂直切换算法相比,在不同的用户移动速度和用户规模条件下的切换次数、切换失败次数和切换时延均有明显下降,内存消耗较低,能够实现无缝切换。     

An Efficient Handoff Decision Algorithm for Vertical Handoff Between WWAN and WLAN

Vertical handoff is one significant challenge for mobility management in heterogeneous wireless networks. Compared with horizontal handoff, vertical handoff involves different wireless network technologies varying widely in terms of bandwidth, delay, coverage area, power consumption, etc. In this paper, we analyze the signal strength model of mobile node and present a new vertical handoff decision algorithm. This algorithm can adapt to the change of mobile node＇s velocity and improve the handoff efficiency significantly. We analyze the algorithm＇s performance and the effect of different parameters on handoff triggering. In addition, we propose three performance evaluation models and verify the algorithm＇s feasibility and effectiveness in simulations.     

基于移动Ad Hoc路由技术的无线局域网

无线网关的覆盖范围受到衰减和干扰等因素的限制，因此部署无线网关的代价是比较高的。为了减少所需的网关数，同时又能保持相同的覆盖范围，可以将Adhoc路由协议集成到无线局域网的网络协议中，从而使不在网关直接传输范围内的结点也能够间接地获取Internet连接。详细讨论了这种无线局域网的地址配置和路由问题。仿真结果验证了该方法的有效性。     

基于移动网络的IPv6网络模型

通过移动无线网络接入Internet的主机可能会经常变换接入点,本文在构建一个完整IPv6网络模型,同时通过引入软切换,有效解决了移动主机在切换过程中可能出现的数据丢失。     

Malicious actions against the GPRS technology

This paper presents the malicious actions (attacks), which threaten the general packet radio services (GPRS) network, the GPRS mobile users, and the data that either reside at the network or are transferred through it. These attacks may be performed by malicious third parties, mobile users, network operators or network operator personnel, which exploit the security weaknesses of the GPRS security architecture. Moreover, the attackers take advantage of the lack of adequate security measures that should protect certain parts of the GPRS architecture. The possible attacks against GPRS targets the equipment of mobile users, the radio access network, the GPRS backbone network, and the interfaces that connect the latter to other GPRS networks or the public Internet. The results of these attacks might be the compromise of end-users security, the users over billing, the disclosure or alteration of critical information, the services unavailability, the network breakdown, etc. The analyzed attacks and their consequences increase the risks associated with the usage of GPRS, and, thus, influence its deployment that realizes the concept mobile Internet. In order to defeat certain attacks and enhance the level of security provided by GPRS, specific security measures are proposed.     

Mobility management for m-commerce requests in wireless cellular networks

Increasing number of sophisticated services provided by the current wireless communication systems have caused a significant transition from E-commerce to M-commerce. Enterprises have provided considerable new opportunities to promote their businesses accessible from small mobile devices such as personal digital assistant (PDA) or mobiles phones. These facilities are envisioned as the most convenient way of using M-commerce. Using such services from mobile phones or PDAs equipped with GSM/GPRS involve effective mobility management mechanisms in cellular networks—a popular architecture for wireless networks. Success of such systems will largely depend on the reliable connection for the roaming users. Consequently, Quality of Service (QoS) provision is one of the most challenging issues in the heterogeneous wireless network-based m-commerce systems. Such m-commerce systems enable users to roam between different wireless networks operators and geographical areas while providing interactive broadband services and seamless connectivity. This paper presents an analytical framework to model scarce channels in any cell for maximizing channel utilization and efficient handling of handover requests. Typical numerical experiments are presented to validate the analytical solution against simulation to study the effect of bursty traffic upon the performance of the cell in any cellular networks.     

WLAN与蜂窝混合网络有效的信道切换策略

针对无线局域网WLAN(Wireless Local Area Network)与蜂窝混合网络,提出一种具有抢占蜂窝网络信道的切换策略。当使用蜂窝信道的终端移入WLAN覆盖区域时,只有在该终端所使用的信道被抢占时,该机制才进行垂直切换以减少因切换造成的时延与丢包;建立了该切换策略的三维马尔可夫模型,分析了WLAN网络的终端数、蜂窝信道的利用率、信道接入请求阻塞率、信道抢占率与信道被抢占率的性能。详细的仿真结果证明了提出的模型的有效性,当WLAN覆盖面积比例为0.2时,信道抢占概率最大;当终端移动速度达到100km/h时,信道被抢占的概率是移动速度为20km/h的3倍;提出的信道切换策略与随机切换策略相比,显著地降低了业务的丢包率与传输时延。     

Case study on handoff strategies for wireless overlay networks

One of the most challenging topics for next‐generation wireless networks is the process of vertical handoff since many of wireless technologies overlap each other and build a heterogeneous topology. Several parameters, pertaining to user/application requirements and network conditions, such as data rate, service cost, network latency, speed of mobile, and etc. must be considered in the handoff process of heterogeneous networks along with RSSI information. In this paper, adaptive fuzzy logic‐based vertical handoff decision‐making algorithms are presented for wireless overlay networks which consist of GSM/GPRS/Wi-Fi/UMTS/WiMAX technologies. The parameters data rate, monetary cost, speed of mobile and RSSI information are processed as inputs of the proposed fuzzy‐based systems. According to these parameters, an output value, which varies between 1 and 10, is produced. This output value is utilized to determine whether a handoff process is necessary or not and to select the best candidate access point in the vicinity. The results show that, compared to the traditional RSSI‐based algorithm significantly enhanced outcomes can be achieved for both user and network as a consequence of the proposed fuzzy‐based handoff systems. The simulation results are also compared with those of classical MADM (Multiple Attribute Decision Making) method, i.e. SAW (Simple Additive Weighting). According to the results obtained, the proposed vertical handoff decision algorithms are able to determine whether a handoff is necessary or not, properly, and select the best candidate access network considering the aforementioned parameters. Moreover, fuzzy‐based algorithm noticeably reduces the number of handoffs compared to SAW‐based algorithm.     

一种无线异构网络的自适应垂直切换算法

针对移动节点在异构网络间切换性能不理想的问题,提出了一种自适应主动预测的垂直切换算法。采用一种面向当前应用程序的代价函数对可接入网络进行评估与选择;根据稳定周期、移动节点的运动速度及所处位置来自动调整切换执行时间,使移动节点能自适应地进行切换判决。仿真结果表明,该算法可以有效地减少切换延迟、分组丢失及切换次数,提高系统的切换性能,改善业务的QoS。     

IP-over-satellite: Internet connectivity blasts off

Many emerging broadband network technologies are dependent upon terrestrial based physical wiring to support megabit- and gigabit-per-second transmission rates. But the thirst for Internet connectivity and high performance remains unquenched. It cannot, and should not, be constrained by the physical wire. Wireless radio frequency (RF) mechanisms (such as general packet radio service, or GPRS) are becoming more popular for connecting mobile and fixed end users to the Internet, but they include performance and configuration limitations posed by technical, environmental, and geographic factors. An ideal solution would be a broadband wireless technology offering performance comparable to that of terrestrial links while supporting residential, corporate, and ISP network configurations and reaching just about anybody in the world, i.e., satellite communications