VoIP技术与Wi-Fi结合的未来探讨

随着宽带通信和Wi～Fi接入点的日益增多，以及VoIP的日益普及．两种技术的融合已成趋势。IP语音传输（VoIP）提供了以低成本在网上打电话的方案，而Wi-Fi（一种无线传输的规范）扔掉了连线。如果两者相结合（现在这对组合已被称为VoFi），就可以通过任何能够访问的Wi—Fi连接，以低成本拨打无线电话。文中通过介绍VoFi相关工作原理以及VoFi目前还面临着音质的问题进行了深入地分析，对未来的发展提出了展望。     

VoIP渐行渐近——ZDNet美国语音市场调查新发现

IP 语音(VoIP) 允许在分组数据网络上实现语音、传真信息与传统的数据包同时传输,可为各个层次的应用。 VoIP 的实现优势在于获得更低成本的传统语音与传真服务,同时用户还将受益于基于 VoIP 的,具有突破性的新型服务,如基于 web 的呼叫中心、协作式白板 (collaborative white boarding)、远程通信交换以及可提高个人效率的产品(如”跟踪”服务与统一消息处理) 等新型应用都是 VoIP 巨变的组成部分。     

图片新闻

分析人士表示,同时具备Wi-Fi 和蜂窝移动通信功能的手机一旦问 世,其功能将超越目前只具备Wi-Fi功 能的VoIP手机。消费者可以通过家庭 无线网关、公共热点以及VoIP服务使 用这种混合功能手机。而企业级产品 则可通过公司的PBX互联,实现更大 范围内的漫游。     

VoIP通信若干安全问题探讨

VoIP是利用互联网实现语音传输的一种新型通讯技术和业务模式。VoIP网络可以在IP网内为用户提供廉价的语音服务,相对于传统的公共电话网(PSTN)通信,VoIP具有明显的价格优势,但随着VoIP的普及,其安全问题已经日益凸显。VoIP安全问题常给用户、运营商带来难以预料的风险,提出安全问题的应对策略具有实际经济意义。     

基于Wi-Fi和3G的无线双模VoIP网关的研究与设计

提出采用IP2202 MCU、基于88W8686 SoC芯片的Wi-Fi模块和H9918 EVDO 3G模块的组合,构建无线双模VoIP语音网关,实现语音通信的低成本、低功耗和机动灵活性。     

VoIP智能终端设计

通信技术的成熟和发展,使VoIP智能终端高效率、低成本、多业务的优势日益明显.介绍一种基于SIP/RTP协议的VoIP终端的设计和实现方案.硬件以由DSP和MIPS核构成的双核处理器芯片Infineon PSB21553E为平台;软件基于MIPSLinux内核,采用RADVISION协议栈构建终端系统,对VoIP实现方案做了具体设计,并对服务质量做了分析.     

一种基于RSSI的无线网络接口低功耗方法

通过对Wi-Fi无线网络接口卡(Wi-Fi NIC,Wi-Fi network interface card)功耗特性的研究与分析发现,Wi-Fi接口活动功耗与上行/下行传输速率成线性关系.接收信号强度指示器(RSSI,received signalstrength indicator)是影响数据传输率的重要因素.智能移动终端在高信号强度环境下具有更高的数据传输速率、更低的丢包率与错误率,为节省Wi-Fi数据传输功耗并减小数据延时,提出一种基于RSSI的Wi-Fi NIC低功耗管理方法,通过检查RSSI值,选择性发送或推迟发送延时容忍(delay tolerant)的非实时数据,保证数据在高信号强度下传输,使得数据传输总时间缩短的同时获得功耗节省.     

你的网络需要无线接入的VoIP吗?

通信技术的日新月异,使得Wi-Fi与VoIP的技术应用开始与人们的生活工作密切相关。目前,新一代互联网电话(VoIP)与无线局域网络(WLAN)这两个在过去纪念中具有标志性意义的网络事物正开始相互融合,新生的无线局域网电话(V o W L A N)也开始清晰地出现在人们的视野当中。种新技术上     

WLAN上跑语音——谈VoIP基于无线局域网的应用

虽然 WLAN(无线局域网)由于安全标准的不确定性,严重阻碍了其发展的步伐,但利用基于 WLAN 的 VoIP 来代替或补充目前现有的电话系统,如通过笔记本电脑、PDA 或者新型的 Wi-Fi 电话与 WLAN 语音服务器连接,将成为了促使 WLAN 广泛应用的亮点之一, 换占之,无线网络上跑语音即将成为现实。作为一种成熟的网络通信技术,VoIP 在有线网络已逐渐开始广泛应用,而基于 WLAN 的 VoIP 技术以与之相补充显示了其市场潜力。虽然目前在无线网络上实现 VoIP 还面临着无线吞吐量的波动、热点间漫游、Wi- Fi 电话终端缺乏等问题的困扰,但基于 WLAN 的 VoIP 应用代表了市场发展的趋势。可软硬件实现基于 WLAN 的 VoIP 实现可通过软硬来实现,其工作方式分为两个部分。一是基于 SpectraLink、Symbol Technologies Inc．Cisco 等公司的     

高校VoIP平台搭建案例研究

本文介绍了语音在校园网上传输VoIP的技术特点、国际标准以及VoIP在校园网上的应用和发展状况,并对VoIP的技术体系结构进行了详细阐述,重点以某大学VoIP系统与传统网络的融合为实例进行研究。     

On the performance of secure user-centric VoIP communication

Motivated by the increased Wi-Fi coverage in metropolitan areas and the emergence of user-centric wireless access schemes, we focus on the provision of secure, user-centric voice services and explore their potential performance-wise, by designing a VoIP communications scheme tailored to open-access wireless environments, but also with wider applicability, and experimenting with it to estimate its upper bounds on VoIP capacity, under constraints posed by user-centrism; operation at low-cost and on user-controlled equipment, minimal dependence on centralized entities, and tackling specific security challenges. We identify quality degradation factors and quantify their importance by simple analysis and experimentation, showing that typical user Wi-Fi equipment can sustain a satisfactory number of concurrent secure VoIP sessions with acceptable Quality of Experience and, at the same time, protection from malicious user activity can be offered to access providers, while a level of roaming privacy can be guaranteed.     

基于Qtopia Phone Edition和嵌入式Linux的VoFi Phone模块的设计与实现

介绍了VoFi(VoiceoverIPoverWiFi)Phone模块在嵌入式Linux系统MontaVistaLinuxConsumerElectronicsEdition和QtopiaPhoneEdition软件平台上的设计与实现。在分析了QtopiaPhoneLibrary结构的基础上,给出了在保持其原有架构不变的前提下扩展VoFiPhone模块的设计方案,并按照自顶向下的顺序,介绍了模块各部分的实现。对QtopiaPhoneLibrary架构的分析以及使用低耦合的方式在其上扩展VoFiPhone模块的方法对开发其他基于QtopiaPhoneLibrary的应用也有参考意义。     

The changing usage of a mature campus-wide wireless network

Wireless Local Area Networks (WLANs) are now commonplace on many academic and corporate campuses. As “Wi-Fi” technology becomes ubiquitous, it is increasingly important to understand trends in the usage of these networks. This paper analyzes an extensive network trace from a mature 802.11 WLAN, including more than 550 access points and 7000 users over seventeen weeks. We employ several measurement techniques, including syslog messages, telephone records, SNMP polling and tcpdump packet captures. This is the largest WLAN study to date, and the first to look at a mature WLAN. We compare this trace to a trace taken after the network’s initial deployment two years prior.We found that the applications used on the WLAN changed dramatically, with significant increases in peer-to-peer and streaming multimedia traffic. Despite the introduction of a Voice over IP (VoIP) system that includes wireless handsets, our study indicates that VoIP has been used little on the wireless network thus far, and most VoIP calls are made on the wired network.We saw greater heterogeneity in the types of clients used, with more embedded wireless devices such as PDAs and mobile VoIP clients. We define a new metric for mobility, the “session diameter”. We use this metric to show that embedded devices have different mobility characteristics than laptops, and travel further and roam to more access points. Overall, users were surprisingly non-mobile, with half remaining close to home about 98% of the time.     

基于VxWorks的嵌入式网管代理在IP电话网关适配器中的实现

IP电话网关适配器是IPGW和PBX结合的产品,跨接在IP网和电路交换网之间。它作为协议格式转换器和数据格式转换器,是IP电话网中比较复杂的部件。SNMPAgent在IP电话网关适配器中的实现程度决定着整个IP电话网络的可管性。该文结合IP电话网关适配器设计的实际要求,给出了一个基于VxWorks操作系统的SNMPAgent的实现实例,并从实用角度出发,对Agent的模块性、安全性、独立性给予了必要的改进和完善。     

基于K-Means和FCM的增强型Wi-Fi指纹定位策略

研究了通过数据处理算法以提高Wi-Fi指纹库室内定位性能的问题.首先采集Wi-Fi指纹样本,将其放入MySQL数据库中和R工程;其次将Wi-Fi指纹库分成若干个簇,使用K-均值聚类（K-Means）和模糊C-均值聚类（FCM）对待定位的Wi-Fi指纹进行聚类分析;最后,提出增强型的聚类策略（ECS）应用于Wi-Fi指纹匹配定位中.实验结果表明,ECS较仅使用FCM算法,其定位耗时缩短约50%-80%,且定位精度上有所改善;ECS较仅使用K-Means算法,其定位精度提高约20%-40%,且定位稳定性较强并自动更新Wi-Fi指纹库.     

Wi—Fi宽带无线的应用研究

Wi—Fi迅速席卷了笔记本电脑市场，目前己经向手机、游戏机等嵌入式领域发展，成为构建数字家庭和数字企业的主要无线技术。文中专门研究了Wi—Fi的应用情况，包括Wi—Fi的应用场景以及Wi—Fi的行业应用，旨在通过对Wi—Fi的市场和应用场景的研究，为中国乃至全球的宽带无线发展提供一些思路。     

A VoIP Traffic Identification Scheme Based on Host and Flow Behavior Analysis

With the development of network and multimedia coding techniques, more and more Voice over Internet Protocol (VoIP) applications have emerged. The traffic identification on VoIP applications becomes an important issue in network management and traffic analysis. In this paper, a new traffic identification scheme, which combines traffic flow statistic analysis with host behavior estimation, is proposed to identify the VoIP traffic at the transport layer of the Internet. The host IP addresses and the port numbers are examined as the host behavior to distinguish the VoIP traffic from traditional traffic flows. The packet size has been modeled by a function of entropy while the inter-packet time has been modeled by the self-adaptive estimation. The experiment results show that our scheme could obtain a stable performance. At the same time, the proposed scheme could maintain its validity when existing VoIP applications are updated or the new ones admitted. Both accuracy and flexibility can be improved.     

Automated construction of Wi-Fi-based indoor logical location predictor using crowd-sourced photos with Wi-Fi signals

Owing to the recent proliferation of smartphones and the SNS, a large number of images taken by smartphones at various places have been uploaded to SNSs. In addition, smartphones are equipped with various sensors such as Wi-Fi modules that enable us to generate an image associated with the sensory information that represents the context in which the image was captured. This study demonstrates the benefits of images associated with Wi-Fi signals in the automated construction of a Wi-Fi-based indoor logical location classifier that predicts a semantic location label of a user’s position for shopping complexes. In this study, a logical location class refers to the store class label in a shopping complex, such as Starbucks and H&M. Given a collection of images associated with Wi-Fi signals taken at a shopping complex and the complex’s floor plan, the proposed method first estimates the store label at which an image was taken by analyzing the image and crawled online images of branch stores. Then, the 2D coordinates of the images taken at branch stores on the floor coordinate system can be estimated using the floor plan. Subsequently, by using the Wi-Fi signals of the branch store images and their estimated 2D coordinates, we construct a transformation function that maps Wi-Fi signals onto the 2D coordinates, and we adopt this function to predict an indoor location class of an observed Wi-Fi scan from a smartphone possessed by an end user. The proposed transformation function comprises an ensemble of sub-functions designed based on CVAEs. Finally, we demonstrate the effectiveness of the proposed method for three actual shopping complexes.     

Assessing the risk of intercepting VoIP calls

Voice over-IP (VoIP) solutions and services for corporate telephony are usually marketed as ‘cost-free’ and ‘secure’: this paper shows that both statements are false in general. Though being no doubt about the economical benefits resulting from the adoption of VoIP products instead of the standard telephony, hidden costs related to VoIP services security arise whenever a company intends to assure the privacy of its phone conversations. This conclusion is extensively justified in the literature and this article aims at reasserting it by analysing the risk that a VoIP phone call may be intercepted when travelling across the Internet. The purpose of deriving a well-known conclusion consists in proving that a general and formal risk assessment method can be used in place of ad-hoc methods not only without losing the strength in the results but also adding up a sound mathematical and engineering foundation.     

Design and realization of ad-hoc VoIP with embedded p-SIP server

In this paper we design and implement the pseudo session initiation protocol (p-SIP) server embedded in each mobile node to provide the ad-hoc voice over Internet protocol (VoIP) services. The implemented p-SIP server, being compatible with common VoIP user agents, integrates the standard SIP protocol with SIP presence to handle SIP signaling and discovery mechanism in the ad-hoc VoIP networks. The ad-hoc VoIP signaling and voice traffic performances are analyzed using E-model R rating value for up to six hops in the implemented test-bed. We also conduct the interference experiments to imitate the practical ad-hoc VoIP environment. The analyzed results demonstrate the realization of ad-hoc VoIP services by using p-SIP server.