| Today, the multimedia computer technology and data communication technology has made rapid development, so only a simple voice and text communications can no longer meet the growing demand, it is urgent for the wish to see an integrated voice, multimedia images and text communication tools. In the extensive use of the telegraph, telephone, fax and E-Mail after the video conference system has emerged a new means of communication that can be said that the emergence of video conferencing systems to meet the people's demand for new communications tools. Video conferencing systems can be point to point communication, you can multi-multipoint communication. In the same transmission line can have video, audio, data and other information on a variety of media to meet the real-time multi-point interactive communications needs. At the same time, in each sub-venue visual information available through the venue to see the other participants of the activities, meetings and documents and other information content. In short, the video conferencing system is a rapid and efficient means of communication, it is widely used off-site meeting was held, the release of important information, important decision making and other fields.Video conferencing terminal, the channel is the network, multi-point controller and control management software together form a video conferencing system. Among them, the role of video conferencing terminal is that it completed the video signal acquisition, editing and display output, audio signal acquisition, editing and output, video and audio data compression encoding and decoding signals and other functions. Therefore, the final step of information processing in two cases, or through the channel via a standard compressed stream line interface to the terminal, or is processed through the terminal in line with international standards of compressed stream through the line interface to the channel. In addition to the aforementioned features, a variety of communication control information is formed by the terminal, including: synchronous control and indication signals, the frame structure, call the call rules and rules of multiple terminals, encryption standard, transmission density Key management standards and remote camera control protocols.With this video conferencing system will meet the people are concentrated in a conference room has a special configuration, this meeting room can be similar to meeting rooms and remote communicate with each other, send and receive the equivalent of a video conferencing center, and ultimately the video conferencing between two points. Because the number of people attending the meeting more, so I hope there is a higher voice and video effects, a system should generally have the following components: one or more monitors with large screens, audio equipment, a little more complicated with high resolution dedicated graphics camera, with high quality cameras, control equipment and other equipment to meet the requirements of different users.At the technical level, it can be said videoconferencing related technology is relatively mature, and it is also internationally recognized technical standards have emerged, and this is by the International Telecommunication Union (ITU) H.320 and H. proposed 323 protocol suite. Currently based on H. 320 agreement is in the TV conference system a period of transition, from a network point of view, is the line from the circuit switched network and ISDN networks to IP packet switching transition; and from the market point of view, moving from large companies to small working group Desktop personal work even single-family changes. Therefore, based on H. 323 video communications are gradually being of concern to everyone. Following is a brief description of what H. 320 and H. 323 characteristics of these two technologies.Traditional video conferencing systems and technology system to some extent limit the H. 320, it is not flexible enough to lead to very poor, and function, it is another disadvantage is H. H. 320 terminals and 320 MCU line required the use of user fees and user costs are more expensive stand-alone.For H. 323, because it uses more advanced TCP / IP technology, to make it not only provides more features, but also significantly reduce the need for the use of subscriber line charges and the cost of user terminals. Therefore, it is cost-effective.Into a variety of networking, the more common is the DDN, IP, ISDN and leased line, relatively speaking, satellite, PSTN, etc., though not of the technology as used above, but there are certain applications. By DDN, green, etc. for networking, so that transmission bandwidth 2Mbit / s, the advantages of doing so is a good quality of network transmission, but the disadvantage is the cost more expensive. In contrast, the use of the bandwidth required for PSTN only 64Kbit / s, we can see its hard to meet the needs of image transmission, in view of ISDN cheaper, really on the specific circumstances, by using three lines of strategy, so that it increased to 384Kbit / s of bandwidth. Meanwhile, IP is a more effective strategy, if the need to establish with the bandwidth-rich IP network, you can use IP, so as to achieve cost-saving purposes.In the transmission process, will encounter some of the more intractable data, such as: a wide range of coverage, how fast mass transfer file data while maintaining its stability. Given the current terrestrial networks are still many shortcomings, resulting in a "satellite video conference system", in this system, video conferencing transmission channel is a satellite communication channel, and for more sharing of the conference system implementation is dependent on the advanced satellite communications technology. In the video conference system, its wide range of associated encryption algorithm, of course, the standard recommendations, their algorithm can not find instructions, but the instructions for the encryption algorithm, or the need for some way to give The. The note should include the following details: the initial vector length and the session key; in the initialization vector generated on the basis of initial variables.If you want to conduct IP video conference to promote a greater degree, to the public of the purpose of operation, be sure to address a number of operational issues, such as user management, business management, accounting management, and video switching. In view of the non-Internet connectivity, support and reliable hosting for business - trying to send (best effort) service. In other words, the network still can not ensure the availability of application data streams to the bandwidth it requires, and it can not ensure the transmission of data streams, such as delay, loss rate of these quality indicators. For some non-real time services such as data services and so on, best-effort way to meet the requirements as much as possible, but if the audio or video into a way for real-time communications applications, the network will need to find a way to achieve a certain QoS support end to end bearer service. Can be seen in what way to improve real-time performance, to ensure that communications QoS, IP video system has become the key technology of a specific request at the same time, this is a difficult technical problems must be overcome. |
