利用上下文转移实现移动IPv6上的IMS无缝切换

Mobility support for the next generation IPv6 networks has been one of the recent research issues due to the growing demand for wireless services over internet. In the other hand, 3GPP has introduced IP Multimedia Subsystem as the next generation IP based infrastructure for wireless and wired multimedia services. In this paper we present two context transfer mechanisms based on predictive and reactive schemes, to support seamless handover in IMS over Mobile IPv6. Those schemes reduce handover latency by transferring appropriate session ＇information between the old and the new access networks. Moreover, we present two methods for QoS parameters negotiations to preserve service quality along the mobile user movement path. The performances of the proposed mechanisms are evaluated by simulations.     

GSM与WCDMA互操作策略及应用分析

GSM与WCDMA网络之间的互操作是3G网络基于2G网络渐进发展的主要特征之一,是运营商投资效益最大化的必要保证,积极开展双网互操作策略研究及应用实践成为现阶段中国联通网络优化的重点所在,文章结合现网实际应用情况对互操作策略进行了探讨。     

异构无线网络环境下的切换触发时间选择算法

对移动用户在异构网络环境下的切换触发时间选择问题进行了研究。首先对移动终端触发切换的时间选择问题进行了理论分析,找到了最佳切换触发时间所应满足的条件。然后在切换耗时估计和接收信号强度预测的基础上,提出了一种预测最佳切换触发时间的算法。仿真结果表明,本算法能够有效降低用户的分组丢失概率和切换失败概率。     

Fast Duplicate Address Detection for Seamless Inter-Domain Handoff in All-IPv6 Mobile Networks

In All-IP networks, each computer or communication equipment needs an IP address. To supply enough IP addresses, the new Internet protocol IPv6 will be used in next generation mobile communication. Although IPv6 improves the existing Internet protocol (IPv4), Duplicate Address Detection (DAD) mechanism may consume resources and suffer from long delay. DAD is used to make sure whether the IP address is unique or not. When a mobile node performs an inter-domain handoff, it will first generate a new IP and perform a DAD procedure. The DAD procedure not only wastes time but also increases the signaling load on Internet. In this paper, we propose a new DAD mechanism to speed up the DAD procedure. We create a DAD table in access or mobility routers in All-IP networks and record all IP addresses of the area. When a new IP address needs to perform DAD, it can just search in the DAD table to confirm the uniqueness of the address. Furthermore, we propose a new method, Fast Duplicate Address Detection (Fast DAD), to reduce data search time. Simulation results show that our method outperforms the existing DAD methods.     

基于负载均衡的MEH静态切换机制

对欧洲电信标准化协会（ETSI）提出的针对移动边缘主机（MEH）服务器的切换机制进行了补充和完善,提出了基于负载均衡的MEH静态切换机制。该机制通过将用户设备对应应用实例迁移到与其所属本地高负载服务器相邻的某个低负载服务器,实现了缓解原控制服务器处瓶颈效应、均衡网络节点间负载、优化信令平均等待时延的目的。分析和仿真结果表明,提出的静态切换机制能够在均衡网络负载和提升用户满意度方面对ETSI规范提供有效的补充和完善。     

多控制器集群流媒体缓存代理的研究

为满足用户分散的大规模视频流媒体应用需求,该文提出了一种基于多控制器集群缓存代理结构(Multi- controller based Cluster Streaming Cache Proxy, MCSCP),该体系由一组控制器构成控制子系统,由多个内容存储器构成分布式存储子系统。对控制子系统的关键问题进行了深入研究：采用图论思想给出控制器组的选取算法,设计了一种基于优先级的主控制器选举和在线切换协议(Priority based Master-controller Election and Handover, PMEH)。建立数学模型分析了多控制器体系对系统可靠性的改善程度,讨论了控制器选取算法的性能,研究了协议中报文发送间隔变量与系统开销的关系,并使用仿真实验给出了该参数的最佳取值范围。     

移动IPv6在无线局域网中的实现

介绍了移动IPv6的工作机制,提出一个移动IPv6和无线局域网(WLAN)集成的设计方案,以实现移动终端在无线局域网之间无缝切换,并建立实际的实验环境对移动IPv6进行测试.     

利用卫星遥感技术绘制大区域光缆线路图

讲述如何免费共享全球卫星地图资源,介绍利用下载的高清卫星地图绘制大区域光缆线路图的方法。     

Performance evaluation of an optimized intersegment handover procedure for hybrid constellation satellite systems

Satellite system architectures based on geostationary or Low Earth Orbit (LEO)/Medium Earth Orbit (MEO) constellation suffer from their intrinsic limitations in terms of coverage or flexibility. Traffic requirements concerning broadband services are expected to be very uneven both in time and space. To match this requirement and to improve coverage an innovative satellite system architecture, composed of a LEO/MEO segment to complement a Geostationary Earth Orbit (GEO) segment, has been proposed. In this scenario, to achieve interworking and to make it possible to hold the call while switching between the two segments, efficient intersegment handover (ISHO) procedures must be identified. The paper, after introducing the classical ISHO schemes, aims at defining and analysing an ISHO procedure developed to perform handover in case of hybrid constellations based on the use of both GEO and LEO/MEO orbits. Performance evaluation will be carried out for different system configurations utilizing a dynamic satellite constellation simulator in the time domain. The execution delay and its complementary cumulative distribution have been evaluated for different constellation geometry at different distances from the gateway. Copyright © 2002 John Wiley & Sons, Ltd.     

PCB激光投影成像扫描技术分析

通过对印制电路板激光投影成像技术使用的步进重复扫描和六边形无接缝扫描方法进行比较,揭示了六边形无接缝扫描技术的优越性能,对六边形无接缝扫描技术的均匀曝光过程及其实现的原理进行了阐述,并对影响扫描成像的曝光量和曝光速度等因素进行了分析.