摘要
铁道部于96年引进的符合H.320框架标准的电视会议系统近年来在铁路的生产和运输工作中发挥了巨大作用,满足了铁路电视会议对于高质量视频、音频的要求。然而,随着我国铁路的不断提速,高速铁路建设步伐的加快,电视电话会议系统也增加了对远程协助、抢险救灾、远程工作指导等多方面的需求,仅有音频和视频已经越来越不能满足会议需要,还需增加数据通信的功能。
电视会议系统在中国已经走过了10多个年头,从最早的昂贵的H320系统到现在的便宜的H323系统,技术和性价比发生了翻天覆地的变化。目前,大部分中小企业和政府部门都在积极的筹建自己的网络视频会议系统,可以大胆地预测,今后几年中,视频会议系统的发展和普及将会突飞猛进,尤其是基于IP的H.323会议电视系统。
考虑到铁路对网络视频会议系统的特殊需要及铁路系统的特点,本文基于成熟的H.323国际视频会议标准,讨论了一种适应铁路行业需求应用的多媒体网络会议系统架构,并着重研究了在此架构下的数据应用之一——视频白板的原理及实现。
为了搭建能够进行多方通信的网络平台,该网络会议架构参考了多个协议标准模型,包括H.323、T120、RTP/RTCP、SIP等,这些协议分别为会议平台提供音视频数据通道、数据通信及应用、多媒体支持和会议管理的功能。在此平台基础上,设计了具有在正在播放的视频的动态画面上进行标记功能的网络会议电子白板。此白板程序,运用了作为T.120终端标准的NetMeeting COM组件作为多方数据通信通道,在Microsoft公司的VisualStudio.NET 2003开发平台用C++语言编写。实现了连接会议、指定窗口绑定、多人同时标记、透明等诸多功能。
The video conference system according with H.320 protocol which was introduced by Ministry of Railways has made great effect on railway production and transportation.It satisfied the requirements of railway video conference with high quality of video and audio.However,along with speeding up of railways and high-speed railway development in our country,the video and telephone conference system need many new requirements,such as remote assistance,rush to deal with emergencies,remote guidance in field works and so on.The conferences only have video and audio couldn't meet our requirements already, we need to increase the function of data communication.
Video conference system has developed for more than 10 years in China. From the costly system of H.320 in early stage to the low cost system of H323, the technology and cost performance have greatly changed.At present,most small company and government ministries are building their own video conference systems.So we can forecast that after few years,the development and usage of video conference system will make quite great progress,especially the video conference system which is based on IP and H.323.
Considering the special requirements of video conference system in railways,here discussed a multimedia network conference system architecture based on the mature H.323 international video conference standard,and emphasized to research one of the data applications upon this architecture--the design and realization of video white board.
In order to build the multi-communication network platform which supports the multi-communication conference,this network conference architecture referenced many protocol standard models,including H.323,T120, RTP/RTCP,SIP.These protocols respectively provide channels for audio and video data,function of data communication,application as well as the function of multimedia support and conference management for the conference platform. Based on this platform,a network conference media white board is designed, you can mark on dynamic movies by using it.This white board program uses the components of NetMeeting for multi-communication channel.It was developed on Microsoft Company's Visual Studio.NET 2003 IDE and programmed by VC++ and C++ language.It has achieved the functions below:connecting conferences,binding the window which has been choiced,marking by more than one person at the same time,transparence and so on.
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