H.323网守在呼叫路由中的应用研究

以H．323网守在VoIP体系结构中的作用和地位为基础,重点阐述了H．323网守在呼叫路由中的应用;通过实际的项目开发经验和理论研究成果,提出了一种分布式网守拓扑结构中域内和域间呼叫路由的解决方案,使用这种网守拓扑结构作为对分级网守结构中网络拓展的一种补充,从而加速了H．323网守在VoIP体系中进行注册节点地址解析和呼叫路由的进程。目前,这种方法在VANLINK公司H．323网守中已经得到证实。     

Emerging alternatives to today's advanced service architectures for Internet telephony: IN and beyond

Two principal sets of standards are emerging for Internet telephony: H.323 from the ITU-T, and session initiation protocol (SIP) from the IETF. The advanced service architecture that comes with H.323 is rather archaic, and reminiscent of the old days of circuit–switched telephony. The one that comes with SIP is more modern, but has its share of deficiencies. While improvements are being made, alternatives are being sought. Two trends are noticeable in the search for alternatives: the return to the old and well-known intelligent network (IN) architectural framework, and the exploration of more recent approaches, such as mobile agent technology, that go beyond IN. This paper scrutinizes the trends in the search for alternatives to today's ITU-T and IETF advanced service architectures for Internet telephony. We successively review the IN-based architectures that are emerging, and the mobile agent-based architectures that are being explored. Many circuit–switched networks that adhere to the IN architectural framework have been deployed worldwide. The emerging IN-based advanced service architectures may facilitate the reuse of this installed base. They will however fall short when it comes to supporting the wide range of advanced services expected from Internet telephony. Mobile-agent-based advanced services architectures are much more promising, although the technology is not yet mature. Their inherent flexibility can easily help in exploiting to the fullest extent the host of opportunities Internet telephony brings. The return to the IN architectural framework may be economically viable in the short and medium terms. There is however no doubt that it will be imperative to go further in the long term. Mobile agent technology is certainly among the venues worth being explored for going beyond IN.     

基于嵌入式系统的H.323协议网守的研究

基于IP网络的多媒体通信业务是当今电信事业发展的热点之一。作为相关的重要标准，ITU-T的H.323标准获得了广泛的应用。文章对H.323系统中的网守单元的实现进行了探索，并设计出基于嵌入式系统的网守程序模块。     

ITU-T standardization activities for interactive multimedia communications on packet-based networks: H.323 and related recommendations

The Telecommunication Sector of the International Telecommunication Union (ITU-T) has developed a series of recommendations together comprising the H.323 system that provides for multimedia communications in packet-based (inter)networks. This series of recommendations describe the types and functions of H.323 terminals and other H.323 devices as well as their interactions. The H.323 series of recommendations includes audio, video and data streams, but an H.323 system minimally requires only an audio stream to be supported. Motivated by straightforward interoperability with the ISDN and PSTN networks and a variety of other protocols, the recommendation H.323 has been accepted as being the standard for IP telephony, developed by the ITU-T and broadly backed by the industry—which is also adopted by both the Voice over IP (VoIP) forum and the European Telecommunication Standards Institute (ETSI). This paper presents an overview of the H.323 system architecture with all its functional components and protocols and points out all the related specifications.     

An architecture for residential Internet telephony service

Network gateways are used to set up calls between the public switched telephone network (PSTN) and the Internet, but existing gateways support a relatively small number of lines. To meet the scalability and availability requirements of mass-market deployment of carrier-grade telephony services, the authors propose an architecture based on the decomposition of Internet gateway functionality. The media transformation function of today's H.323 gateways is separated from the gateway control function, and intelligence is centralized in a call agent. The Media Gateway Control Protocol is introduced; MGCP is an Internet draft currently under discussion by the IETF for standardizing the interface between a call agent and the media transformation gateway     

Policy support for H.323 call handling

The need for policies to control calls is justified by the changing face of communications. An overview is given of a general architecture and language for policies. It is then shown how these are adapted for control of calls using the H.323 multimedia communications standard. Policy support for H.323 was created by extending an open source gatekeeper. The core policy language has been specialised to deal with call control in general, and for H.323 in particular. Examples are given of policies for H.323, illustrating how traditional features can be made to work more flexibly through use of policies. Examples are also provided of policies specific to H.323, and policies that can take advantage of other information such as the context of a call.     

The design and simulated performance of a mobile video telephonyapplication for satellite third-generation wireless systems

The design and performance of a low bit-rate video telephony service for mobile third-generation (3G) systems is presented. The ITU-T G.723.1 speech coding and the ITU-T H.263 video coding recommendations are used, as proposed by the ITU-T H.324 low bit-rate multimedia communications recommendation. The target bit-rate for the H.324 service is 64 kb/s. The design is performed in conjunction with that of a wideband-code division multiple access (W-CDMA) radio transmission technology (RTT) system, proposed by the European Space Agency (ESA) for the satellite component of the ITU IMT-2000 standard. Most of the results could also be applied to the 3G terrestrial systems. The use of concatenated channel coding with convolutional inner coding and Reed-Solomon (RS) outer coding is investigated. Service designs based on equal error protection (EEP) and unequal error protection (UEP) schemes for the audio and video sources are compared. The simulation of the proposed video telephony services shows that significantly more graceful video and audio degradation is obtained with the proposed UEP scheme than with a more straightforward EEP method. The UEP scheme reduces significantly the occurrence of highly annoying audio and video artefacts, allowing satellite-based video telephony services that are compatible with the current Internet-based applications     

基于线索树的IP电话系统寻址

针对电信运营中分组实时语音网络存在的时延问题,基于H．323建议的IP电话网络体系,提出一种动态的系统寻址方案,系统原型建立在线索树上,结点之间的互访通过线索直接提交到最近共同祖先结点,在其子树树内部完成最终定位。该方案可以减少整个系统寻址时间,极大地减轻域间网络负担。     

H.323标准及其在Internet上的应用

Ｈ．３２３ 系列标准是基于信包交换网络的多媒体会议标准,它使用ＴＣＰ／ＩＰ协议,在Ｉｎｔｅｒｎｅｔ／Ｉｎｔｒａｎｅｔ中具有广阔的应用前景。本文对Ｈ．３２３标准的实体及其体系结构进行了概要性的介绍,之后给出了基于Ｉｎｔｅｒｎｅｔ的多媒体会议系统和ＩＰ电话系统的组成及原理     

VOIP系统实现协议的分析和比较

随着Internet的发展，语音越来越成为Internet的一个重要组成部分。本文介绍四种主要的VOIP实现技术；H．323，SIP，MGCP和H．248，然后分析和比较它们的优缺点。H．323由于协议本身的局限性，它的主导地位正在逐渐为MGCP技术所替代。MGCP技术是当前VOIP市场上的热点，而MEGACO／H．248则是将来OVIP网广泛接受的标准协议。     

基于H.323的Intranet集成服务实现的探讨

本文以在Intranet上实现提供基于H.323标准的集成服务为目标,首先介绍了集成服务的内容,随后重点讨论了如何在遵从H.323标准的前提下,利用网守的控制功能区分实时通信和存储转发的服务要求,并进行H.323终端的呼叫管理。     

H.323视频会议网守的研究与实现

在对 H.32 3系统及其相关 H.32 3协议进行研究和分析的基础上 ,研究了网守各功能的具体实现。并设计实现了基于多线程的网守程序 ,使其不仅可以完成网守的基本功能 ,同时又可以实时监控网守的状态信息 ,提高了网守软件实用化程度     

H.323体系结构的一个改进模型

介绍IP电话标准H.323的体系结构，指出了其体系结构中存在的一些缺陷。随后作者借用ESTI TIPHON所提出的H.323网关分解模型，加入新的实体域定制服务器，提出了一个改进模型，并对新的地址解析机制及服务定制机制进行分析，最后给出了一个应用实例。     

基于SIP协议的IP电话技术

现在的IP电话系统大部分还是基于H.323协议族,而H.323沿袭了传统电信网的运行和管理模式,本身较复杂,在应用于IP电话时存在着不可避免的缺陷。会议初始化协议(SIP)是由IETF制订的用于在两个或多个用户之间建立、修改和终止多媒体会话的信令协议。文中主要介绍了基于SIP的IP电话系统协议栈结构、SIP协议的基本内容以及其在IP电话中的具体应用。最后在与H.323协议进行了比较之后,提出了一些现存的问题并且做出了相应的前景展望。     

A voice over IP service architecture for integrated communications

The rapid evolution of Internet telephony has introduced new service implementation paradigms. The authors propose a service architecture that integrates circuit based telecommunications with the Internet through the control elements of traditional and emerging networks, specifically the gatekeepers of VoIP and the SCPs of PSTN     

基于Internet的视频会议系统的设计与实现

桌面视频会议是近年来网络应用的重点,国际电信联盟(ITU)也为基于分组交换网络(PBN)的多媒体会议系统制定了H.323建议。论文介绍了一个依据ITU-TH.323建议开发的、适用于TCP/IP网络的多点视频会议系统。在该系统中,用软件实现了MCU,大大降低了系统成本。该系统使用C/S结构和集中式的控制方式,适合在Internet上使用。测试结果表明,该系统具有较高的实用价值。     

QoS可控的网络可视电话设计与实现

设计并实现了基于USB接口的低成本网络可视电话系统，描述了其内嵌的QoS控制机制。基于区分服务体系，对IP数据包的ToS字段进行不同的编码设置，以区别服务的优先级；采用双向链表结构的抖动缓冲区进行时延抖动的平滑，链表的节点位数据帧或空闲帧，二者可动态切换，输入线程和输出线程互斥地对其进行读写操作。实验证明，在多数应用场合下，系统的通信时延小于30ms，丢包率低于10%。     

Integrating Internet telephony services

Cost savings and the ease of developing and adding new services have motivated great interest in Internet telephony, which integrates services provided by the Internet with the public switched telephone network (PSTN). Internet telephony relies on several protocols, including the real-time transport protocol (RTP) for multimedia data transport and the session initiation protocol (SIP) or H.323 for establishing and controlling sessions. SIP can integrate with other Internet services, such as email, the Web, voice mail, instant messaging, conference calling, and multimedia collaboration. We have implemented a SIP-based software suite called the Columbia Internet extensible multimedia architecture (Cinema), which we installed and integrated with the existing private branch exchange (PBX) infrastructure in the computer science department at Columbia University. The Cinema environment provides interoperability with the PSTN, programmable Internet telephony services, and IP-based voice mail. It also integrates Web access and e-mail for unified messaging and supports multiparty multimedia conferencing. The setup lets us extend our PBX capacity and will eventually let us replace it while keeping our existing phone numbers. It also provides an environment in which we can easily add new services and features, including interoperation with existing multimedia tools, e-mail access from standard. telephones, network appliance control, and instant messaging support     

基于H．323协议的VoIP在电话银行中的解决方案

本文介绍了与VoIP技术相关的H．323协议和SIP规范，阐述了一个成功的基于H．323协议的VoIP电话银行远程接入方案。     

一种IP电话体系结构的设计与实现*

在H-323协议规定的多媒体通信系统的基础上,提出了具有三层结构的新一代电话网络体系。同时开发出IP电话通信协议——IPTCP协议,架构出承载于宽带IP网络的新一代电话系统。