A call admission control framework for voice over WLANs

In this article a call admission control framework is presented for voice over wireless local area networks (WLANs). The framework, called WLAN voice manager, manages admission control for voice over IP (VoIP) calls with WLANs as the access networks. WLAN voice manager interacts with WLAN medium access control (MAC) layer protocols, soft-switches (VoIP call agents), routers, and other network devices to perform end-to-end (ETE) quality of service (QoS) provisioning and control for VoIP calls originated from WLANs. By implementing the proposed WLAN voice manager in the WLAN access network, a two-level ETE VoIP QoS control mechanism can be achieved: level 1 QoS for voice traffic over WLAN medium access and level 2 QoS for ETE VoIP services in the networks with WLANs as the local access. The implementation challenges of this framework are discussed for both level 1 and level 2. Possible solutions to the implementation issues are proposed and other remaining open issues are also addressed.     

Smart WLAN Discovery for Power Saving of Dual‐Mode Terminals

Dual‐mode terminals (DMTs) equipped with cellular and WLAN interfaces have become popular in recent years. Users of DMTs can enjoy high‐speed WLAN Internet access and wide area Internet access to cellular networks. However, a DMT may consume power inefficiently when discovering a WLAN with inherently limited service coverage. In this letter, we propose to use smart WLAN discovery (SWD) to minimize the power consumption required for WLAN discovery. To minimize the power consumption of a DMT, an SWD DMT activates its WLAN interface only when the DMT transfers data within the WLAN coverage area. The simulation results of SWD show an improved power‐saving performance compared to previous WLAN discovery schemes.     

无线局域网的安全性分析和研究

无线局域网因其易移动、低成本和高可靠性的优点,得到了广泛的应用.但其接入的不可控制性正是其安全性问题的症结所在.文中从扩频通信、访问控制、数据加密3方面讨论了IEEE802.11系列无线局域网的网络接入和数据传输的安全性机制,介绍了新一代无线局域网中使用的安全技术及新的安全标准的IEEE 802.11i.重点研究了无线局域网的访问控制技术和数据加密技术.     

3GPP与WLAN互连的技术

主要介绍第三代移动通信合作计划(3GPP———3GPartnershipProject)与无线局域网(WLAN)互连的结构,3GPP用户可通过WLAN开展WLAN接入业务。在WLAN中,通过3GPP预约,使用客户识别模块(SIM)/用户服务识别模块(USIM)接入通用IC卡(UICC),使3GPP与WLAN终端互连。文中还介绍基于3GPP的WLAN接入认证授权、IEEE802.11i中的认证和密钥协定、3G-WLAN互连中的认证和授权、复用3GPP的归属位置注册器等,描述了用户数据如何选路和接入业务,最后介绍WLAN中基于3GPP的计费方法(预付费和后付费),以及如何对这些用户计费和对归属网络中基于IP的计费。     

Enabling location‐based services in wireless LAN hotspots

The wide deployment of IEEE 802.11 Wireless LAN (WLAN) makes possible application services developed in WLAN hotspots. Owing to the small cell size in WLAN hotspots, it is practical to develop location‐based services with the awareness of the WLAN access points (APs) that mobile devices currently access. In this paper, we propose an effective location determination technique using the inherent SNMP support in WLAN APs. It is shown that the current location of a mobile device can be determined from the SNMP traps sent by APs. Since the SNMP‐based approach doesn't need any particular software or hardware in mobile devices, location‐based services can be widely deployed, especially in public WLAN hotspots. To further enable location‐based services through the WWW, this paper also considers the location determination of a mobile device from its IP address, retrieved in a WWW environment. In addition, we propose a web service framework for location‐based services in WLAN hotspots. Thus, location‐based services can be developed in a standard way. Copyright © 2005 John Wiley & Sons, Ltd.     

WLAN分流技术在智能管道中的应用

文章认为由于智能终端和移动互联网的发展给移动网络带来巨大压力,因此为移动用户提供无线局域网(WLAN)接入成为移动网络数据业务分流的重要手段。基于WLAN分流技术,文章分析了用于解决WLAN和移动网络业务连续性问题的新技术,如全球移动通信系统增强数据传输速率技术无线接入网络/陆地无线接入网/通用移动通信系统陆地无线接入网/陆地无线接入网/增强通用移动通信系统陆地无线接入网(GERAN/UTRAN/E-UTRAN)与WLAN网络之间的业务连续性技术、接入网络发现和选择功能和非无缝的WLAN分流技术。     

WLAN：进入无线互联时代的新机遇

无线局域网(WLAN)应用主要是服务运营商在人群密集或流动性大的热点地区为公众提供无线接入因特网或企业内部网的服务。全球WLAN业务用户大多集中在美国,欧洲的运营商日渐看好WLAN业务,自2001年起,中国的电信运营商以及厂商在WLAN方面也开始有所动作。     

无线局域网技术与应用

作为宽带有线接入网的延伸和补充，无线局域网（WLAN）以其灵活性和可移动性，越来越受到业界的广泛关注，显示出极大的应用前景。本介绍了WLAN的主要标准情况以及技术的特点和优势，并结合中国电信的实际情况阐述了其应用。     

An energy‐efficient transmission mechanism for VoIP over IEEE 802.11 WLAN

Voice over IP (VoIP) over WLAN (VoWLAN) is an important application for public and private WLANs. However, VoWLAN systems suffer from several technical challenges such as power consumption of a WLAN station (STA) and service capacity of an access point (AP), making the commercial deployment of a large‐scale VoWLAN service problematic. This study presents a cross‐layer and energy‐efficient mechanism for transmitting VoIP packets over IEEE 802.11 WLAN. The proposed mechanism considers the characteristics of voice packets that can tolerate certain loss, and dynamically disables the medium access control (MAC) layer acknowledgement for voice packets. In doing so, the time and energy consumed to transmit and receive voice packets for an STA can be reduced. Simulation results demonstrate that the mechanism improves the energy efficiency of a VoWLAN STA and WLAN utilization without sacrificing voice qualities. Copyright © 2009 John Wiley & Sons, Ltd.     

On the support of voice call continuity across UMTS and wireless LANs

In this paper, we address the architecture and the procedures that can enable voice call handover from UMTS to WLAN and we also study how efficiently the WLAN can support the voice calls transferred from UMTS. Our study is based on a practical simulation model that lets us quantify the maximum number of voice calls that can be handed over from UMTS to WLAN, subject to maintaining the same level of UMTS QoS and respecting some WLAN policies. In addition, several other voice call performance metrics are derived. Our results indicate that an IEEE 802.11e access point can support a limited number of voice calls handed over from UMTS, which depends primarily on the applied WLAN bandwidth sharing policy (i.e., how the bandwidth is shared between WLAN voice and data users) and the QoS requirements. The performance of the WLAN scheduling algorithm is also of paramount importance and in our study we consider the so‐called ARROW scheduler. Although the simulation results are derived for a specific bandwidth sharing policy, they can readily be scaled and provide practical upper bounds for the number of UMTS voice calls that can be seamlessly admitted to a WLAN access point. Copyright © 2007 John Wiley & Sons, Ltd.     

四网协同组网中核心网演进分析

本文主要探讨了无线接入多样化情况下,核心网在四网协同组网演进中的阶段性分析,可分为三大阶段:GSM/TD-SCDMA核心网融合组网,完成GSM/TD-SCDMA的共接入;PS域完成GSM/TD-SCDMA/WLAN的融合组网,并积极向SAE演进,实现GSM/TD-SCDMA/WLAN/LTE的共接入;IMS网络真正成为接入无关的融合核心网控制网络。     

An adaptive p-persistent MAC scheme for multimedia WLAN

The letter proposes an adaptive p-persistent-based (APP) medium access control (MAC) scheme for the IEEE 802.11e distributed WLAN supporting multimedia services. The APP MAC scheme adaptively gives differentiated permission probabilities to transmission stations which are in different access category and with various waiting delay. Simulation results show that the APP MAC scheme can improve the performance of multimedia WLAN, such as small voice packet dropping probability, low delay variation, and high system throughput, compared to conventional MAC algorithms     

无线局域网MAC协议分析和仿真研究

随着笔记本电脑、掌上电脑、智能手机等移动终端的普及,无线局域网（WLAN）以其接入灵活、架构和扩展方便等优点得到了迅速发展,WLAN的网络性能（吞吐量、时延等）取决于MAC子层的接入协议。该文从原理上对WLANMAC的实现方式和差异进行了分析,并利用广泛使用的网络仿真软件OPNETITGuru针对差异进行了仿真分析,有助于深入理解MAC接入控制原理和不断演进的相关标准。     

无线局域网QoS机制解析

无线局域网（WLAN）技术的发展带来的多媒体业务流量的剧增,使无线网络的资源管理、服务质量（QoS）保障等问题日益突出,传统的媒体访问控制（MAC）协议需要重新设计才能有效地解决无线网络的QoS问题。本文介绍了无限局域网QoS技术的发展,包括针对IEEE802．11 MAC层协议进行的各种QoS增强技术。通过与传统的802．11标准的MAC层进行对比分析．讨论了IEEE802．11e的2个新策略：增强的分布式协调功能和混合协调功能。通过对受控竞争机制的分析,指出了IEEE802．11e仍存在的不足及未来的发展方向。     

Toward a generic "always best connected" capability in integrated WLAN/UMTS cellular mobile networks (and beyond)

The next generation of mobile communications, broadly referred to as 4G, is based on a heterogeneous infrastructure comprising different wireless (and wired) access systems in a complementary manner. 4G mobile users enjoys seamless mobility and ubiquitous access to applications in an always best connected (ABC) mode that employs the most efficient combination of available access systems. The ongoing commercialization of 3G cellular mobile networks and their upcoming enhancement with WLAN radio access provides a wireless platform suitable for the introduction of "ABC" capabilities. We analyze the implications of the "ABC" vision in a UMTS/WLAN network context, and reveal important issues that arise. Further on, we identify major requirements, point out the limitations of current UTMS/WLAN standards from an ABC viewpoint, and discuss key enabling technologies and research efforts. We formulate a generic application model for an ABC capability in the interworked UMTS/WLAN architecture and analyze its complexity proving that, in principle, being always best connected translates to a family of NP-hard problems. To complement our analysis, we present an object-oriented design of a real-time UML model for an ABC mobile system. Finally, we summarize the advantages of our ABC model and provide directions for future work.     

一种WLAN与LTE网络融合方案

3GPP23.234规范中提出研究WLAN等非3GPP接入EPC的互通架构。用户终端(UE)可以通过WLAN,以S2a、S2b或S2c等接口接入EPC。文章针对安全性低和改造复杂的问题,提出WGW-S2a融合网络架构——部署WGW网元支持EAP-AKA认证报文转发并具有MAG功能,采用EAP-SIM/AKAover802.1x实现安全的统一认证,WLAN用户接入EPC时IP地址分配由PDNGW分配。在WGW-S2a融合网络架构中,WLAN网络与EPC之间的接口仍然符合3GPP标准的S2a接口。     

WLAN技术在软交换系统中的应用

文章主要讨论无线局域网（WLAN）如何接入软交换系统,通过对WLAN技术标准、网络架构及承载能力的探讨,揭示了软交换系统无线应用面临的挑战,在此基础上给出了一些有前景的应用,如VoWLAN、远程无线监控、无线即时消息和定位服务等的解决方案。文章认为宽带无线接入标准WiMAX有望成为WLAN的升级版,一旦成熟,并与软交换等NGN技术相结合,将会实现人们追求的。网络无所不在,信息随手可得”的美好愿望。     

同播ROF型分布式天线系统中无线局域网MAC层协议性能分析(英文)

The performance of three wireless local-area network(WLAN) media access control(MAC) protocols is investigated and compared in the context of simulcast radioover-fiber-based distributed antenna systems(RoF-DASs) where multiple remote antenna units(RAUs) are connected to one access point(AP) with different-length fiber links.The three WLAN MAC protocols under investigation are distributed coordination function(DCF) in basic access mode,DCF in request/clear to send(RTS/CTS) exchange mode,and point coordination function(PCF).In the analysis,the inter-RAU hidden nodes problems and fiber-length difference effect are both taken into account.Results show that adaptive PCF mechanism has better throughput performances than the other two DCF modes,especially when the inserted fiber length is short.     

IMS及其与WLAN的互通模型研究

3GPP IMS与WLAN之间的互通可以将IMS核心网络业务扩展到WLAN接入环境中,同时使WLAN成为3GPP系统的一种补充接入技术。介绍了3GPPIMS的网络结构,分析了IMS中SIP协议及其扩展,重点讨论了IMS与WLAN的互通模型,以及如何支持3GPP目前定义的几种业务互通等级。