An IMS-based network architecture for WiMAX-UMTS and WiMAX-WLAN interworking

The IP Multimedia Subsystem (IMS) seems to be the technology that will prevail in Next Generation Networks (NGNs), since the interworking environment and the service flexibility that this technology offers to the currently deployed wireless broadband technologies makes it appealing to users, service developers and network operators. In this paper we propose a heterogeneous network model based on the IMS that integrates the Worldwide Interoperability for Microwave Access (WiMAX), Universal Mobile Telecommunications System (UMTS) and Wireless Local Area Network (WLAN) technologies and provides guaranteed QoS. We present the complete signalling flow concerning the authorization, registration, session set up and vertical handoff processes, as well as, an analytic model for cost analysis of the proposed architecture.     

OmniCon: a Mobile IP‐based vertical handoff system for wireless LAN and GPRS links

Wi‐Fi based hotspots offer mobile users broadband wireless Internet connectivity in public work spaces and corporate/university campuses. Despite the aggressive deployment of these hotspots in recent years, high‐speed wireless Internet access remains restricted to small geographical areas due to the limited physical coverage of wireless LANs. On the other hand, despite their lower throughput, cellular networks have a significantly wider coverage and are thus much more available. Recognizing that 2.5G or 3G cellular networks can effectively complement wireless LANs, we set out to develop a vertical handoff system that allows mobile users to seamlessly fall back to such cellular networks as the general packet radio service (GPRS) or 3G whenever wireless LAN connectivity is not available. The resulting handoff mechanism allows a network connection of a mobile node to operate over multiple wireless access networks in a way that is transparent to end user applications. In this paper, we present the design, implementation, and evaluation of a fully operational vertical handoff system, called OmniCon, which enables mobile nodes to automatically switch between wireless LAN and GPRS, based on wireless LAN availability, by introducing a simple extension to the existing Mobile IP implementation. We discuss the design issues in the proposed vertical handoff system for heterogeneous networks, including connection setup problems due to network address translation, and the disparity in link characteristics between wireless LANs and GPRS. A detailed performance evaluation study of the OmniCon prototype demonstrates its ability to migrate active network connections between these two wireless technologies with low handoff latency and close to zero packet loss. Copyright © 2006 John Wiley & Sons, Ltd.     

On the design of mobility management scheme for 802.16-based network environment

In this paper, we investigate the characteristics of IEEE 802.16 and conclude that it is better to equip BS (base station) and SS (subscriber station) with Layer 3 functionality. Therefore, an 802.16 network can act as the backbone network of different subnets for better deployment. Based on the two IEEE Specifications, 802.16-2004 and 802.16e, we propose two kinds of paradigms of the 802.16 network technology for mobile networking. In the first paradigm, a novel concept called middle-domain mobility management in between macro- and micro-domain for 802.16-2004 is proposed. The management scheme of middle-domain is designed to accommodate different micro-mobility protocols in an 802.16-2004 network environment. Moreover, a mathematical analysis and simulation study are presented for performance evaluation. In the second paradigm, by comparing with traditional overlay networks (e.g. GPRS/WLAN), we have found that the characteristics for the 802.16e/802.11 overlay network are actually different from traditional overlay networks. To provide more efficient vertical handoff, a novel protocol called speed-based vertical handoff scheme (SVH) is proposed. A Simulation study has demonstrated that SVH can achieve a better performance than its WLAN-first counterpart in terms of less signaling and fewer packet losses.     

基于Mobile IP的异构网络系统切换方法的研究

针对当前3G网络的发展和无线局域网（Wlan）的兴起,研究了Wlan和3G网络的集成架构和混合异构网络的垂直切换管理。引入Mobile IP技术来达到无缝漫游,同时提出了多接入网络环境下检测Wlan信号强度的异构网间切换方法,并根据延时和中断时间来分析切换方法的性能。试验结果表明该切换方法能够及时有效地改进异构网络的切换效率。     

基于CAPWAP协议的WLAN集中管理系统的研究与实现

针对大规模部署无线局域网（WLAN）存在的维护困难,成本高等问题,就应用于接入控制器(AC)和无线终端（WTP）间通信交互的CAPWAP协议进行了研究与实现。在Linux系统下实现了CAPWAP协议主要功能,如状态机管理、WTP集中配置等;搭建了本地转发架构下的WLAN集中管理系统的实现平台,并采用了Wireshark抓包工具,Chariot和Iperf软件进行测试。抓包结果验证了该架构的可行性,吞吐量和用户数据协议(UDP)测试结果表明网络性能高效稳定。     

自适应门限的异构无线网络预切换机制

以无线局域网（WLAN）和WiMAX网络融合构成的异构网络为研究对象,研究了多模移动终端基于FMIPv6机制完成异构无线网络之间垂直切换的操作流程。针对垂直切换过程中使用固定门限值预切换机制存在的不足,提出了一种自适应门限预切换机制,并详细分析了垂直切换过程中目标网络接入时延,从而为所提出的自适应门限值预切换机制提供了理论依据。在仿真部分,扩充了NS2仿真平台上已有的功能模块,从而验证了所提出的自适应门限预切换机制的性能。     

网络与终端协同选择及切换机制的研究

提出了一种智能切换机制,用于实现在异构网络中网络与终端的协同选择及切换功能。随着各种业务和应用的发展,异构网络融合是信息和通信技术的必然趋势。根据多接入、多终端等应用环境的要求,采用AHP与URA等多属性决策理论,为用户选择最佳的目标网络和目标终端,并提出相应的智能切换信令流程,包括网络切换、终端切换、网络与终端联合切换方式,最终构建以用户为中心的多终端智能空间,实现个人移动性管理。仿真表明,该智能切换机制可以有效地实现网络和终端的协同选择,并可以保证在异构网络切换QoS性能,为现代服务业的业务及应用的发展提供可靠的理论依据。     

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.     

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.     

异构网络中信令压缩的应用*

作为标准的信令协议,会话发起协议(session initiation protocol,SIP)可以很好地支持异构网络中的移动性。但是,SIP消息传输过程中带来的高时延会影响VoIP等实时性应用的服务质量。针对这种情况,提出了一个基于信令压缩的异构网络框架,用户在使用SIP消息注册、鉴权时产生的信令消息均被压缩后再进行传输。仿真结果显示,在该框架下信令压缩可以缩短20%的传输时延和节省30%的网络开销。