WLAN的增值应用--VoWLAN

随着无线通信技术和移动终端的迅猛发展,以IEEE 802.11为基础的无线局域网(WLAN)的应用越来越广泛。2001年,中国的电信运营商以及国内外众多厂商在WLAN方面开始动作,WLAN的应用推广活动凸现了这一市场的竞争势态。中国电信大力扩展“天翼通”业务,利用其广泛覆盖的宽带接入网络,打造独有的“有线+无     

基于WLAN的语音和数据应用

1前言随着WLAN技术的问世和推广,运营商能够通过令人兴奋的全新方式为最终客户提供NGN业务。同时,VoIP技术也取得了最新进展,SIP、软交换机、软/硬客户端、3G标准得到了完善,这些因素使NGN业务具备了极强的吸引力。NGN/WLAN集成的主要推动因素是:为连接WLAN的用户提供全面的Succes鄄sion语音和多媒体业务;使WLAN成为有线和无线公用网络的自然扩展;利用WLAN技术,将有线和无线集成到一种无缝的服务中。北电网络的解决方案充分考虑了上述因素,它能够独立地以安全、可扩展的无线接入方式将无线/有线广域网连接到无线局域网。部署…     

WLAN在电信及企业的应用尝试

1概述 目前人们所谈及的无线接入大多数是指固定无线接入,最近两年被看好的固定无线接入的热门体制有三种:即频段为3.5GHz的固定无线接入系统、频段为26GHz的本地多点分配业务系统和频段在2.4GHz的无线局域网、无线接入系统及蓝牙技术.由于2.4GHz频段的无线电台站,按照信息产业部发布的<微功率(短距离)无线电设备暂行规定>(信部[1998]178号)进行管理,即只要设备性能指标满足规定并取型号核准证,设台无需办理电台执照,这无疑给2.4GHz使用的普及奠定了良好的基础.     

运营商级WLAN安全应用的探讨

无线局域网（WLAN）技术的发展使人们摆脱了线缆的束缚，更方便、灵活、快捷地访问网络资源，也给运营商提供了寻找新的增值点的机会。IDC（国际数据集团）的报告显示，运营商对WLAN的需求体现在三个方面：一是传统运营商利用WLAN补充固网的覆盖；二是移动运营商将WLAN与3G互补     

WLAN数据安全技术攻防

随着Internet和WLAN(无线局域网)技术、WLAN市场、服务和应用的快速发展,人们在扩展了获取和发布能力的同时,也带来信息被污染和被破坏的危险。通过对WLAN安全技术的介绍,让使用者对WLAN的安全性有一个了解。     

诊脉WLAN市场

无线局域网（WLAN），通常也被称为Wi-Fi．现在正成为电信业发展的一大亮点。分析了WLAN与3G的特点及区别，认为它们各有特点．不可互相替代。介绍WLAN的4个主要发展阶段，指出WLAN存在的8个问题。若要促进WLAN快速发展，应加大宣传力度，必须满足市场需求，并加强与运营商的合作。最后指出WLAN将大有作为。     

德州仪器宣布支持中国WLAN标准6月推出芯片

德州仪器 (TI) 2月 6日在北京宣布 ,德州仪器将全力支持中国推出的无线局域网 (WLAN)安全标准 WAPI,并且将在今年 6月中国正式实施这个标准之前推出支持这个标准的芯片产品。德州仪器亚洲区总裁程天纵在接受媒体采访时表示 ,WTO有相关规定 ,成员国家在五个领域内可以制定自己的     

无线局域网WLAN在高校校园网中的应用

无线局域网WLAN作为高校校园网的扩展和补充,在组网、覆盖、密度、移动、扩展和管理等方面具有显著优势,应用需求广泛。合理规划、组建和应用校园无线网络,对于促进数字化校园建设、推动高等教育信息化起到重要作用     

WLAN在中国的发展状况和标准进展

无线局域网(WLAN)最近成了继3G之后通信行业最关注的一个话题。实际上，WLAN在中国并不是一个新生的事物，近几年随着宽带接入的不断发展，具有无线宽带上网功能的WLAN再次被运营商和一些设备制造商看好，重新提到新的建设日程上来。近日，Wi—Fi主席亲自造访中国，其目的就是大力推广其802、11系列标准，说服中国的设备制造商加入其中，并不断壮大Wi-Fi联盟，进而推动WLAN在全球的发展和应用。目前，中国WLAN市场逐步显现出强烈发展的势头，各运营商也开始大力铺设WLAN网络，并极力推广其应用，然而，作为一种无线接入方式，WLAN最大的缺陷——安全性成了大家关注的问题，再有其不同标准设备的兼容性以及应用模式也是制约WLAN发展的主要问题。前不久，中国宽带无线IP标准组颁布了两项WLAN国家标准，在中国市场上，到底采用何种标准才能安全有效地发展WLAN，这也是所有运营商和制造商不得不关心的问题。     

在NGN网络中实现WLAN话音和数据应用

随着WLAN技术的问世和推广,运营商能够通过令人兴奋的全新方式为最终客户提供NGN业务。同时,VoIP技术也取得了一些最新进展,包括SIP、软交换机、软/硬客户端、GSM和CDMA网络3G标准的完善,这些因素使NGN业务具备了极强的吸引力,我们提供NGN的方式将不受媒介和位置的限制。近期,NGN如何向WLAN延伸,成为一个新的课题,本文将介绍北电网络在该领域的技术方案,期望给其他设备提供商以及相关运营商提供参考。     

无线局域网上的VoIP

VoiceoverIPonWLAN(无线局域网上的VoiceoverIP)是一种新兴技术,它能使IP语音在802.11无线局域网中传送。通过所设计的一个网络体系,对VoWIP技术进行了较详细的分析,并对VoWIP技术所面临的一些挑战进行了介绍。     

无线局域网技术和应用

简述了无线局域网（WLAN）的组成，网络拓扑结构和安全性，并分析了WLAN的关键技术，WLAN技术的优劣和WLAN的实际应用，以及中国移动开展WLAN业务的市场前景和盈利模式。     

Improving Voice and Data Services in Cellular/WLAN Integrated Networks by Admission Control

In this paper, we study voice and data service provisioning in an integrated system of cellular and wireless local area networks (WLANs). With the ubiquitous coverage of the cellular network and the disjoint deployment of WLANs in hot-spot areas, the integrated system has a two-tier overlaying structure. As an essential resource allocation aspect, admission control can be used to properly admit voice and data calls to the overlaying cells and WLANs. A simple admission scheme is proposed in this study to analyze the dependence of resource utilization and the impact of user mobility and traffic characteristics on admission parameters. Both admission control and rate control are considered to limit the input traffic to the WLAN, so that the WLAN operates in its most efficient states and effectively complements the cellular network. The call blocking/dropping probabilities and data call throughput are evaluated for effective and accurate derivation of the admission parameters. It is observed that the utilization varies with the configuration of admission parameters, which properly distributes the voice and data traffic load to the cells and WLANs. Mobility and traffic variability have a significant impact on the selection of the admission parameters.     

Modified Wideband Bowtie Antenna for WLAN and High Speed Data Communication Applications

A simple method is proposed for enhancement in bandwidth and gain of the self complementary Bowtie antenna. This method overcomes the use of complicated fractal structures to increase the bandwidth and gain of the Bowtie antenna. Using this simple method, by making variation of the single dimension of the antenna structure, the bandwidth is improved by 21% and return loss S₁₁ is also improved of whole of the band of interest. The major importance of this simple technique is that it can be applied to any rectangular microstrip antenna. The resonance frequencies and bandwidths can also be steered within the limited ranges also.

     

A Channel Access Protocol for Integrated Voice/Data Applications

A new multiaccess protocol is proposed for an integrated voice/data application. The protocol, which is a variation of virtual time CSMA (VT-CSMA), takes advantage of the periodicity of voice packets and possesses a number of important features. With this protocol, voice stations appear to have a dedicated time-division multiplexed (TDM) slot, and the delay of a voice packet is bounded by the length of a frame (defined to be the period between two consecutive voice packets from a voice station). Also, the amount of data added to the channel has little effect on the voice traffic. When silence detection is used, many more voice conversations can be supported without losing the dedicated-slot characteristic. This is in contrast to a movingboundary TDM system where the excessive bandwidth saved by silence detection can only be used for data. The protocol requires no global synchronization and is easy to implement. Simulation results are presented to evaluate its performance.     

IEEE 802.11 WLAN支持语音与数据业务的自适应传输方案研究

IEEE 802.11标准中的MAC协议当采用DCF和PCF时是一种随机竞争接入与轮询相结合的协议。该文通过仿真在分析研究此MAC协议对语音、数据业务综合传输性能的基础上,提出了一种支持语音与数据业务的自适应传输方案。仿真结果表明,在满足语音业务最大允许时延的前提下,自适应传输方案通过动态、合理地调整协议参数,可以提高数据业务的传输性能,从而增加网络容量。特别地,本方案不需要改动协议本身,易于实现。     

Voice capacity analysis of WLAN with unbalanced traffic

An analytical model to study the performance of wireless local area networks (WLANs) supporting asymmetric nonpersistent traffic using the IEEE 802.11 distributed coordination function mode for medium access control (MAC) is developed. Given the parameters of the MAC protocol and voice codecs, the voice capacity of an infrastructure-based WLAN, in terms of the maximum number of voice connections that can be supported with satisfactory user-perceived quality, is obtained. In addition, voice capacity analysis reveals how the overheads from different layers, codec rate, and voice packetization interval affect voice traffic performance in WLANs, which provides an important guideline for network planning and management. The analytical results can be used for effective call admission control to guarantee the quality of voice connections. Extensive simulations have been performed to validate the analytical results.     

A Cross-Layer Approach for WLAN Voice Capacity Planning

This paper presents an analytical approach to determining the maximum number of on/off voice flows that can be supported over a wireless local area network (WLAN), under a quality of service (QoS) constraint the authors consider multiclass distributed coordination function (DCF) based medium access control (MAC) that can provision service differentiation via contention window (CW) differentiation. Each on/off voice flow specifies a stochastic delay bound at the network layer as the QoS requirement. The downlink voice flows are multiplexed at the access point (AP) to alleviate the MAC congestion, where the AP is assigned a smaller CW compared to that of the mobile nodes to guarantee the aggregate downlink throughput. There are six-fold contributions in this paper: 1) a nonsaturated multiclass DCF model is developed; 2) a cross-layer framework is proposed, which integrates the network-layer queueing analysis with the multiclass DCF MAC modeling; 3) the channel busyness ratio control is included in the framework to guarantee the analysis accuracy; 4) the framework is exploited for statistical multiplexing gain analysis, network capacity planning, contention window optimization, and voice traffic rate design; 5) a head-of-line outage dropping (HOD) scheme is integrated with the AP traffic multiplexing to further improve the MAC channel utilization; 6) performance of the proposed cross-layer analysis and the associated applications are validated by extensive computer simulations.