VoIP技术及其应用（上）

VoIP又称IP电话或IP网络电话,是Voice over IP的缩写,这种技术通过对语音信号进行编码数字化、压缩处理成压缩帧,然后转换为IP数据包在IP网络上进行传输,从而达到了在IP网络上进行语音通信的目的。     

一种基于SIP协议的VoIP服务质量保证

针对下一代网络中IP电话VoIP服务质量QoS的需求,对目前国内外各种QoS技术进行了分析研究,介绍了基于SIP协议的VoIP网络协议栈结构,提出了一种基于Q-SIP的VoIP网络服务器架构模型,并对其主要的功能模块进行了详细的阐述。     

基于USB接口的VoIP手柄设计

引言 VoIP是指将语音信号进行编码、压缩和分包等处理, 通过IP网络进行传输, 实现计算机-计算机、普通电话-普通电话、计算机与普通电话之间进行话音通信的技术.     

互联网实时语音通信技术的研究

1.引言Interne在t全世界范围内的快速发展和语音信号处理技术的进步,促进了VoIP(IP网络下的语音技术)业务的兴起。由于VoIP业务以传统的Internet为基本平台,具有不可比拟的价格优势,因此发展前景十分广阔。我们通过设计的两台计算机间的语音通信软件,实现了全双工语音通信。PC-PC的语音传输,需要麦克风、音响、声卡等设备就可以通过IP网实现这种应用。这种VoIP方案的显著优点就是可以支持多媒体通信,主要适用于计算机用户。其原理是利用电话软件把送入话筒的声音进行编码压缩、分组,变成IP数据报,经Interne网t络传送;接收端利用软…     

IP电话:网络、技术和协议

IP语音传输,或称为VoIP(Voiceover IP)是指将语音信号进行编码、压缩和分包等处理,通过IP网络进行传输,然后在接收端还原出话音的一种语音传输方式。而网络电话或IP电话则是通俗的说法,意思是通过 Internet网打电话。无论哪一种说法,关键都在于利用了IP网络进行语音的传输。     

破解Skype之谜,冰之眼打造VoIP安全

VoIP又称IP电话,是Voice over IP的缩写,这种技术通过对语音信号进行编码数字化、压缩处理成压缩帧,然后转换为IP数据包在IP网络上进行传输,从而达到了在IP网络上进行语音通信的目的。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。目前,越来越多的企业开始采纳VoIP技术,并从中获益。     

引领VoIP通信市场发展新趋势

数字通信已经发展到电话与计算机同化,即应用互联网语音协议(VoIP,VoiceoverInternetProtocol)技术实现在一个网络上同时传输语音、数据和视频。VoIP是一种以IP电话为主,并推出相应增值业务的技术。VoIP最大的优势是能广泛地采用Internet和全球IP互连的环境,提供比传统业务更多     

语音视频加速融合——VoIP拓宽网络应用

VoIP是一种以IP电话为主,并推出相应的增值业务的技术。其优势是能广泛地采用Internet和全球IP互连的环境,提供比传统业务更多、更好的服务。同时,由于宽带用户的快速增长和传统语音业务的价格下降,单纯利用IP为用户提供语音已经越来越不能满足市场的需求。因此利用IP提供视频通信是一个重要的业务,也是网络发展的大势所趋。而作为互为补充的两种基于I P的网络应用,I P语音与视频会议应用系统的融合加速。过去,VoIP技术被认为是在未来的电信网络中承载语音业务的基本技术。随着基于H.323协议的IP电话长途网络建设逐步平稳,逐渐意识…     

VoIP的应用及配置实例

Internet不断地在变换着自己的角色,网络中流动的“比特”所代表的内容已从原来单纯的“数据”逐渐向“多媒体”演变.基于Internet的各种业务的发展更是层出不穷.IP电话(Voice over IP,简写为VoIP)就是其中之一.在技术推动和市场驱动的双重促进下,近年来IP电话得到了很大的发展.VoIP技术有两种典型应用:模拟电话与模拟电话相连的VoIP通信、IP电话/软件的VoIP通信技术.通过分析VoIP技术,针对IP电话/软件的VoIP典型应用进行配置和测试,实现了在IP网络上免费传送语音数据的需求.     

支持QoS的SIP代理服务器方案的设计与实现

从如何提高基于SIP协议的VoIP系统的语音质量出发,分析了该系统与MPLS技术结合处的难点,并提出了一种支持QoS的SIP代理服务器模型的解决方案。该方案的设计结构清晰、可扩展性强,解决了SIP代理服务器在IP网络中没有会话服务质量控制能力的问题,是一种好的融合VoIP及MPLS两大技术的应用模型。该方案目前已运用于基于嵌入式Linux平台的VoIP系统中,完全能够满足高质量语音的需求。     

VoIP基本安全对策的研究

VoIP又称IP电话或IP网络电话,是一种利用Internet或者其他基于IP网络作为传输载体实现语音通讯的技术。本文针对IP电话发展与普及过程中出现的安全问题进行了研究,并在分析现有网络业已存在的安全威胁的基础上,讨论了部署VoIP时的安全对策。最后,针对一些机构在实施VoIP过程中可能出现的安全问题,给出了相应的防护建议。     

VoIP development in China

Several factors have spurred the explosive growth of VoIP phone use in China, including customer incentives such as improved voice quality and lower cost per call, and provider incentives such as higher profits and upgrade paths to next-generation technologies. The voice over Internet protocol, also called IP telephony, offers a new type of service that uses the Internet protocol, intranets, and extranets to deliver voice information. In contrast to traditional telephone services, which operate through a circuit-switched network, VoIP uses a packet-switched network. This distinction results in differences in implementation, quality of service (QoS), and operating costs. Since the service was introduced to the public in China in April 1999, VoIP toll telephone traffic has increased with astonishing speed. By the end of 2002, VoIP toll telephone traffic had surpassed traditional toll telephone traffic in China in both domestic longdistance and international call areas, including phone calls to and from Hong Kong, Macao, and Taiwan.     

QoS-aware path switching for VoIP traffic using SCTP

Voice over Internet protocol (VoIP) has been a prevalent multimedia service nowadays. It allows us to transmit voice data over IP networks. However, quality of service (QoS) is a major challenge to VoIP services. It must provide similar quality to traditional public switched telephone network or cellular phone services. Therefore, QoS related protocols have become important for real-time applications. Multi-protocol label switch (MPLS) is one of the important techniques to improve the network performance from QoS point of view. It employs label swapping to speed up packet forwarding. However, when a large number of users utilize VoIP services, the network congestion issue still exists. It causes delay, jitter and packet loss that affect VoIP QoS. In this paper, we propose a QoS-aware path switching strategy by using stream control transmission protocol (SCTP) in MPLS network to improve the VoIP traffic. This was done by employing SCTP selective acknowledgment mechanism to report the transmission parameters of primary path and to determine the criteria to switch to backup path. Simulation results show significant improvement in VoIP QoS.     

Voice quality prediction models and their application in VoIP networks

The primary aim of this paper is to present new models for objective, nonintrusive, prediction of voice quality for IP networks and to illustrate their application to voice quality monitoring and playout buffer control in VoIP networks. The contributions of the paper are threefold. First, we present a new methodology for developing perceptually accurate models for nonintrusive prediction of voice quality which avoids time-consuming subjective tests. The methodology is generic and as such it has wide applicability in multimedia applications. Second, based on the new methodology, we present efficient regression models for predicting conversational voice quality nonintrusively for four modern codecs (G.729, G.723.1, AMR and iLBC). Third, we illustrate the usefulness of the models in two main applications - voice quality prediction for real Internet VoIP traces and perceived quality-driven playout buffer optimization. For voice quality prediction, the results show that the models have accuracy close to the combined ITU PESQ/E-model method using real Internet traces (correlation coefficient over 0.98). For playout buffer optimization, the proposed buffer algorithm provides an optimum voice quality when compared to five other buffer algorithms for all the traces considered.     

An Overlay Architecture for High-Quality VoIP Streams

The cost savings and novel features associated with voice over IP (VoIP) are driving its adoption by service providers. Unfortunately, the Internet's best effort service model provides no quality of service guarantees. Because low latency and jitter are the key requirements for supporting high-quality interactive conversations, VoIP applications use UDP to transfer data, thereby subjecting themselves to quality degradations caused by packet loss and network failures. In this paper, we describe an architecture to improve the performance of such VoIP applications. Two protocols are used for localized packet loss recovery and rapid rerouting in the event of network failures. The protocols are deployed on the nodes of an application-level overlay network and require no changes to the underlying infrastructure. Experimental results indicate that the architecture and protocols can be combined to yield voice quality on par with the public switched telephone network     

支持PC终端的数字化语音交换系统的设计

VoIP技术是指通过TCP／IP网络传输分组语音和传真，本文设计一个基于VoIP的实时语音交换系统．该系统在企业内部网络中利用现有计算机和网络等硬件条件，实现了一套电话分机系统的功能，基于本系统能够方便地实现电话会议、呼叫转移和录音电话等功能．     

Design and implementation of QoS-provisioning system for voice over IP

In this paper, we address issues in implementing voice over IP (VoIP) services in packet switching networks. VoIP has been identified as a critical real-time application in the network QoS research community and has been implemented in commercial products. To provide competent quality of service for VoIP systems comparable to traditional PSTN systems, a call admission control (CAC) mechanism has to be introduced to prevent packet loss and over-queuing. Several well-designed CAC mechanisms, such as the site-utilization-based CAC-and the link-utilization-based CAC mechanisms have been in place. However, the existing commercial VoIP systems have not been able to adequately apply and support these CAC mechanisms and, hence, have been unable to provide QoS guarantees to voice over IP networks. We have designed and implemented a QoS-provisioning system that can be seamlessly integrated with the existing VoIP systems to overcome their weakness in offering QoS guarantees. A practical implementation of our QoS-provisioning system has been realized.     

Admission control by implicit signaling in support of voice over IP over ADSL

Voice over DSL (VoDSL) is a technology that enables the transport of data and multiple voice calls over a single copper-pair. Voice over ATM (VoATM) and Voice over IP (VoIP) are the two main alternatives for carrying voice over DSL. ATM is currently the preferred technology, since it offers the advantage of ATM’s built-in Quality of Service (QoS) mechanisms. IP QoS mechanisms have been maturing only in recent years. However, if VoIP can achieve comparable performance to that of VoATM in the access networks, it would facilitate end-to-end IP telephony and could result in major cost savings. In this paper, we propose a VoIP-based VoDSL architecture that provides QoS guarantees comparable to those offered by ATM in the DSL access network. Our QoS architecture supports Premium and Regular service categories for voice traffic and the Best-Effort service category for data traffic. The Weighted Fair Queuing algorithm is used to schedule voice and data packets for transmission over the bottleneck link. Fragmentation of large data packets reduces the waiting time for voice packets in the link. We also propose a new admission control mechanism called Admission Control by Implicit Signaling. This mechanism takes advantage of application layer signaling by mapping it to the IP header. We evaluate the performance of our QoS architecture by means of a simulation study. Our results show that our VoIP architecture can provide QoS comparable to that provided by the VoATM architecture.     

基于网络性能的VoIP语音质量评价模型

在VoIP应用中,为了实现服务质量的监测和路径切换,通常需要测量路径的网络性能,并将网络性能映射到语音质量评价.本文提出一种基于网络性能的VoIP语音质量评价模型,该模型在E-Model的基础上进行了改进,只考虑网络性能的动态变化对语音质量的影响.新的模型考虑更少的影响因素,比E-Model更容易计算,因此更适用于VoIP系统的语音质量评价.通过实验比较了新的模型和简单的网络参数评价模型,结果显示该模型具有更好的语音质量描述能力.     

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。