Internet is nowadays widely used in the world, it provides numerous services, such as
on-line booking, BtoB (business to business) services, databases accesses to the companies. But
all these services are asynchronous, which means that there is a delay between an action from the
user and the response from the service (it's a client/server architecture; a computer provides a
service which is used by one or several clients). The new generation of network communication
tools tries to reach the real time level, which means that there is no delay between the action of
the user and the response.
Real time chats, or for instance video on demand, are the new services provided by the
Internet today. These applications appeared recently and are still in development. One really
interesting applications for these technologies is video conference.
Video conference is a technology which allows people to communicate through computer
networks using an audio stream and a video stream. In a few words, people using video
conference can hear and see their correspondents.
Video conference has been very popular only over ISDN (dedicated digital phone lines).
These days, packet-switched networks, such as IP networks, have opened the door to newer
protocols including H.323. The computing power of the desktop systems, the kind of computers
that can be found in the companies or at home, allows the use of video conference applications.
Moreover, webcams, these little low resolution cameras that can be plugged on a regular
computer, are becoming cheaper and cheaper, and almost every computer has now audio
capabilities.
H.323 is the standard for video conference. It can be used over IP (Internet Protocol), and
possibly over all kinds of switched-packet networks (LAN/Local Area Network, MAN/
Metropolitan Area Network, and WAN/Wide Area Network, including the Internet). It was
defined by the ITU (it is the leading publisher of telecommunication technology, regulatory and
standards information ) in 1996. It is updated almost every year, to fit the new progresses in
network capabilities and computing power. The latest version is H.323.5. It was defined in 2003.
The scope of H.323 covers real-time voice, video and data communication over packet-switched
networks. It has multipoint capabilities (several people can communicate with several other people at
the same time) voice and video conferencing capabilities.
The H.323 protocol can be defined as an "umbrella" specification, which means that the protocol
includes several other protocols. In the H.323, the H.225.0, the H.245, the H.450.x, the T.120
protocols are also defined. In addition to these protocols H.323 uses audio codecs (H.261 and H.263),
video codecs (G.711, G.722, G.723.1, G.728 and G.729), and a real-time transport layer called
RTP/RTCP (Real-time Protocol and Real-time Control Protocol). All these protocols cover a different
aspect of the video conference system.
Video conference is one of the most exciting communication media, and will certainly take

a bigger and bigger place in our future. H.323 is a mature protocol that can be safely used for this
purpose. It is widely used by telecom companies, and offers interesting alternatives to the regular
telephone. With the growing power of Internet and the need of world wide communications,
there is no doubt that video conference will be tomorrow for our society what telephone is
nowadays.

1, regulatory  ['regjulətəri]
a. 取缔的,统制的,调整的
2, codecs  
n. 多媒体数字信号编解码器（codec的复数形式）