VoWLAN技术中若干问题探讨

VoWLAN(VoIP over WLAN)技术是一种利用无线局域网(WLAN)来传输VoIP帧的技术。由于WLAN和VoIP的固有缺陷,使VoWLAN技术中仍有许多问题尚待解决。文章对VoWLAN技术中的语音质量、安全、功耗和移动性管理4个主要问题及其解决方案进行探讨,最后展望了VoWLAN技术的发展前景。     

VoWLAN在无线宽带网络上的实现

VoWLAN(voice over wireless local area network)是对有线的VoIP(voice over Internet protocol)系统的扩展。VoWLAN的技术优势在于综合了VoIP和移动电话的优势,既有VoIP的价廉和强大的增值功能,又有移动电话的漫游便利性。阐述了实现VoWLAN组网的网络结构以及接入点和终端配置,并针对城市区域内不同规模无线网络VoWLAN的实现提出了相应的解决方案。     

VoWLAN技术研究与测试

目前的IT产业领域中，WLAN和VoIP是人们关注的热点，因此使用WLAN提供语音服务（VoWLAN）的终端设备也就应运而生。VoWLAN终端设备利用现有的WLAN网络实现无线的VoIP语音通话，用户可以通过VoWLAN终端设备在WLAN网络的覆盖范围内随时进行语音通话。这既发挥了IP网络成本低的特点，又使得用户获得WLAN带来的方便性。     

蓄势待发的IP手机市场

VoWLAN(Voice Over WLAN) 移动终端设备——IP手机,能够基于 IP方式提供语音、数据和视频业务 (Triple Play),正日益受到用户的关注。作为VoWLAN移动终端的一种, GSM／Wi-Fi双模IP手机具有显著的优势,通过双模IP手机,用户可以在 Wi-Fi覆盖区域内拨打便宜或免费的 VoIP电话,此外,Wi-Fi提供的高速接入能力使用户尽享丰富多彩的宽带应用成为可能。随着Wi-Fi网络在国内的快速部署和改善。整合了移动性     

VOWLAN技术：现状及挑战

本文就VoWLAN的市场驱动力、技术挑战以及商用化现状进行分析和研究，并对未来VoWLAN的市场发展趋势进行探讨。 一、VoWLAN概念 WLAN技术的逐渐普及与VoIP的迅速发展，使得将两者结合起来的VoWLAN应用逐渐受到电信行业的关注，很多设备商非常看好这个市场，尤其是将VoWLAN概念引入到手机中，并与蜂窝网络结合为用户提供无缝的移动VoIP，更是受到业界普遍的关注。     

VoWLAN企业级应用模式及解决方案

VoWLAN是指通过WLAN提供VoIP业务,它的技术优势在于综合了VoIP和移动电话的优势,既有VoIP的低价格和强大的增值功能,又有移动电话的漫游便利性。VoWLAN应用有运营商的企业级VoWLAN和企业自建VoWLAN两种方案,为所有运营商都带了新的机遇和挑战,是在新一轮竞争中抢占先机的一个重要应用。VoWLAN为企业带来通信便利和通信费用的节约,使电信设备商可以同时切入运营商市场和企业通信市场,成为综合服务商的一个应用方向。     

VoWLAN技术研究与测试

目前的IT产业领域中,WLAN和V o I P是人们关注的热点,因此使用W L A N提供语音服务(V o W L A N)的终端设备也就应运而生。VoWLAN终端设备利用现有的W L A N网络实现无线的V o I P语音通话,用户可以通过V o W L A N终端设备在W L A N网络的覆盖范围内随时进行语音通话。这既发挥了IP网络成本低的特点,又使得用户获得W L A N带来的方便性。一、VoWLAN应用方式VoWLAN系统有两种应用方式,一种针对有线办公和住宅电话,也就是基于传统终端的解决方案,如图1所示。对于传统的语音终端,为了实现VoIP,需要添加VoIP网关设备…     

降低通信成本：VoWLAN一跃成为杀手应用

VoWLAN(Voice over WLAN)是WLAN与VoIP结合的新兴应用技术,简而言之,就是要在WLAN的环境中实现VoIP通话.     

VoWLAN的挑战与发展

VoWLAN是Voice over WLAN的简称,就是无线局域网语音通信。本文首先介绍了VoIP和VoWLAN,重点论述了VoWLAN面临的挑战及相应的解决方法,最后介绍了VoWLAN的发展现状和前景。     

基于分布式AC的VoWLAN系统的研究简

VoWLAN是VolP与WLAN的有机结合,是一种前景广泛的新兴应用。传统的WLAN网络对终端移动性支持不佳,不能满足VoWLAN的实时性要求。本文结合新兴的集中式WLAN网络架构,提出基于分布式AC的WLAN网络架构,并分析该架构对于VoWLAN业务的支持。     

Variable bit rate VOiP in IEEE 802.11e wireless LANs [medium access control protocols for wireless LANs]

WLANs have become a ubiquitous networking technology deployed everywhere. Meanwhile. VoIP is one popular application and a viable alternative to traditional telephony systems due to its cost efficiency. VoIP over WLAN (VoWLAN) has been emerging as an infrastructure to provide low-cost wireless voice services. However, VoWLAN poses significant challenges due to the characteristics of contention-based protocols and wireless networks. In this article we propose two mechanisms to provide quality of service for variable bit rate VoIP in IEEE 802.11e contention-based channel access WLANs: access time-based admission control and access point dynamic access. Simulation results are conducted to study these schemes.     

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.     

Quality assurance of voice over WLANs (VoWLANs) with differentiated services

Several technical issues make commercial and large voice over wireless local area network (VoWLAN) services difficult to provide. The most challenging issue when voice over Internet Protocol (VoIP) services are ran over IEEE 802.11-based WLANs is the bandwidth inefficiency due to the considerable overhead associated with WLAN packet transmission. In this work, we propose a session-based quality-of-service management architecture (SQoSMA) to overcome the low number of VoIP calls in IEEE 802.11 Wireless LANs and the negative effect of new call addition when the WLAN reaches its capacity. The SQoSMA combines data and control planes to detect VoWLAN QoS degradations and performs either an adaptive audio codec switching or a call stopping to fix VoWLAN issues in a differentiated services manner. In addition, our solution deals with user sessions information, by considering user priority (from its agreement) to guarantee a certain level of its multimedia applications. Performance evaluation using a real test-bed shows that call codec change and call stopping techniques can easily assure high-priority calls with acceptable call blocking probability.     

VoWLAN通信平台的设计与实现

VoWLAN也叫VoWiFi或者WiFi VoIP。它是基于无线网络技术和VoIP网络,是两者的有机结合。即是通过WLAN提供VoIP业务,使得终端用户通过WLAN拨打IP电话成为现实。本文提出了在基于Linux操作系统的SIP应用服务器及VoIP网关中,如何通过SIP信令和传统的PSTN数据通信线路与无线网络无缝连接方案,从而实现IP网络与传统电话间的实时语音通信、电话会议、语音信箱、视频通信、短消息、数据传输等业务。本设计已成功应用于某企业的实时语音通信平台,获得良好的效果。     

VoWLAN监听系统的设计与实现

将WLAN与VoIP两项技术结合起来的VoWLAN业务目前发展迅速,随之而来的VoWLAN监听问题也为人们所重视。现有的VoWLAN监听装置大都架设不便,容易被目标发现且精准度不高。论文提出了一种VoWLAN监听系统的实现方法,使用方便灵活,可对无线局域网内的语音通话进行安全有效的监听。本系统采用分布式架构,系统按功能分开物理模块,重点介绍了语音还原技术,并对系统的实现进行了详细说明。测试表明,该系统能够有效地实现VoWLAN监听。     

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。     

Mobility management for VoIP service: Mobile IP vs. SIP

Wireless Internet access has gained significant attention as wireless/mobile communications and networking become widespread. The voice over IP service is likely to play a key role in the convergence of IP-based Internet and mobile cellular networks. We explore different mobility management schemes from the perspective of VoIP services, with a focus on Mobile IP and session initiation protocol. After illustrating the signaling message flows in these two protocols for diverse cases of mobility management, we propose a shadow registration concept to reduce the interdomain handoff (macro-mobility) delay in the VoIP service in mobile environments. We also analytically compute and compare the delay and disruption time for exchanging signaling messages associated with the Mobile IP and SIP-based solutions.     

VoIP体系协议的分析与研究

VoIP是一种在Internet网络上进行语音通信的新业务。H.323、MGCP、Skype、H.248、SIP是VoIP的重要协议。论文在分析这些协议结构的基础上,研究和对比了各种VoIP协议的使用特点,为架构不同的VoIP网络提出了协议选择建议。     

一种新的VoIP组网解决方案

随着NGN语音网规模增大,设备管理、网络安全等问题成为网络运行维护的难点和重点.该文在分析当前NGN语音网建设中面临的诸多问题基础上,分析介绍一种新的VoIP组网解决方案以及相关协议,并进一步阐述边界网关和接入网关对这种方案所需做的功能特性支持以及基于其上的扩展网管特性.