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：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。     

VoWLAN挑战与发展

VoWLAN是Voice over FWLAN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。     

NGN+IP PBX多业务网络方案

随着IP技术及其应用的广泛普及,目前众多企业都开始迈向VoIP,力求通过采用新的业务和应用达到提高生产效率和降低通信成本的目的,近几年出现的IP PBX技术,就是企业专网VoIP市场的代表.在企业VoIP市场日益兴旺的同时,运营商的NGN VoIP技术也在近几年内在全国各地应用.     

NGN+IP PBX多业务网络方案探讨

一、引言随着IP技术及其应用的广泛普及,目前众多企业都开始迈向VoIP,通过采用新的业务和应用,以达到提高生产效率和降低通信成本的目的,近几年出现的IP PBX技术,就是企业专网VoIP市场的代表。在企业VoIP市场日益兴旺的同时,运营商的NGN VoIP技术也在短短的几年时间在全国开展起来。由于其先进的开放理念,以软交换为核心的NGN技术一出现,就受到了全球运营商、设备供应商和软件开发商的高度重视,一些新的业务不断出现。该网     

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。     

颠覆蜂窝式架构：Extricom突破企业级WLAN布局瓶颈

业内观察人士认为,WLAN的企业级应用方兴未艾。目前,在企业级VoIP的推波助澜下,欧美一些基于VoIP与Wi-Fi技术相结合的企业无线电话（VoWLAN）应用发展迅速。根据Infonetics Research的报告,到2007年,全球31%的企业将会使用VoWLAN;到2009年,这一比例将上升到62%。     

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。     

Extricom突破企业级WLAN布局瓶颈

业内观察人士认为,WLAN的企业级应用方兴未艾.目前,在企业级VoIP的推波助澜下,欧美一些基于VoIP与Wi-Fi技术相结合的企业无线电话(VoWLAN)应用发展迅速.根据Infonetics Research的报告,到2007年,全球31%的企业将会使用VoWLAN;到2009年,这一比例将上升到62%.     

PIANO: A power saving strategy for cellular/VoWLAN dual-mode mobiles

The integration of cellular and VoIP over WLAN (VoWLAN) systems recently has attracted considerable interest from both academia and industry. A cellular/VoWLAN dual-mode system enables users to access a low-cost VoIP service in a WLAN hotspot and switch to a wide-area cellular system without WLANs. Unfortunately, cellular/VoWLAN dual-mode mobiles suffer the power consumption problem that becomes one of the major concerns for commercial deployment of the dual-mode service. In this study, we present a novel power saving mechanism, called PIANO (paging via another radio), for the integration of heterogeneous wireless networks, and further apply the proposed methods to implement a cellular/VoWLAN dual-mode system. Based on the proposed mechanisms, a dual-mode mobile can completely switch off its WLAN interface, only leaving the cellular interface awake to listen to paging messages. When a mobile receives a paging message from its cellular interface, it wakes up the WLAN interface and responds to connection requests via WLAN networks. Therefore, a dual-mode mobile reduces the power consumption by turning off the WLAN interface during idle, and can also receive VoWLAN services. Measurement results based on the prototype system demonstrate that the proposed methods significantly extend the standby hours of a dual-mode mobile.     

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.     

基于WLAN的VoIP终端移动性管理研究

目前,随着WLAN的发展,VoIP(Voice over Internet Protocol)技术在其中的应用也越来越广泛。但VoWLAN仍然面临着移动终端切换时延过长、话音容量低、安全隐患以及QoS保证等技术上的挑战。文章简要介绍了VoIP技术,重点研究了VoWLAN终端的移动性管理,在现有支持移动性管理协议的基础上,融合各层协议提出了一种改进的移动性管理新方案。     

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.     

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.     

3G手机VoIP话音的QoS实现技术研究

在对3G手机VoIP话音QoS的主要实现技术进行分析的基础上,提出了3G手机VoIP话音QoS新的实现技术。文中通过对实时传输控制协议（RTCP协议）的详细研究,同时根据3G系统无线信道的具体特点,说明了实时传输控制协议运用于3G手机VoIP话音的QoS控制中的缺陷,并阐述了相应的控制解决方法。在基于Android的3G智能手机的VoIP客户端软件中,综合运用VoIP话音QoS的主要成熟实现技术,同时结合文中提出的VoIP话音QoS的解决思路,实现了对VoIP话音的QoS的控制。基于Android的3G智能手机的VolP客户端软件通过在不同的网络环境条件下的测试,VoIP话音质量良好,说明文中提出的3G手机VoIP话音QoS新的实现技术具有一定的实用价值。     

Network‐initiated simultaneous mobility in voice over 3GPP‐WLAN

VoIP over WLAN (VoWLAN) gradually has become a popular application with the fast maturing of both WLAN and Voice over IP (VoIP) technology. However there exists one problem that heavily affects the satisfaction of the users which is that the mobility of the mobile host (MH) can disrupt or even intermittently disconnect an ongoing real‐time session. Therefore the issue of how to reduce the handover delay gets more and more important. This paper proposes a Network‐Initiated SimUltaneouS mobility (NISUS) mechanism to facilitate terminal mobility with the session initiation protocol (SIP) in Voice over 3GPP‐WLAN. We design the E2E tunnel state model running on the packet data gateway (PDG) referring to the CAMEL concept. The NISUS is triggered at the PDG by detecting the state transition of the E2E tunnel state model that represents the occurrence of a handover. Then the PDG sends the handover request to notify the Mobility Server (MS) to perform a third party call control (3PCC) and a third party registration on behalf of the MH in parallel for session re‐establishment. With the help of the MS we ensure the lost signaling messages could be correctly re‐sent to moving hosts. Moreover the Master‐Slave Determination procedures derived from H.245 are proposed for the MS in order to handle the racing conditions fairly when two MSs involved in a simultaneous mobility issue 3PCC calls respectively at about the same time. We demonstrate the NISUS works well in the simultaneous and non‐simultaneous movement cases. Analytical results show that the handover delay can be improved significantly by using the NISUS compared with the mobile‐initiated simultaneous/non‐simultaneous mobility. Copyright © 2010 John Wiley & Sons, Ltd.     

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。     

Effective VoIP call routing in WLAN and cellular integration

In cellular-WLAN integration, a dual-mode mobile station (MS) typically disables the WLAN module for power saving. A major problem is that for an incoming VoIP call (or data session), the MS will not be able to receive this call from the WLAN. It turns out that the call is directed to the cellular network. This letter proposes a simple push solution where an MS can accurately detect a VoIP call from paging signaling of the cellular network. Then the WLAN module of the MS is turned on and the VoIP call is connected to the MS through the relatively inexpensive WLAN.