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Currently, the transmission networks for video conferencing are all using existing electrical intelligence networks (such as digital communication channels like digital microwave, digital fiber or satellite) or computer networks. For example, videoconferencing signals may be transmitted at an E1 rate (2.048 Mbit/s) or lower (e.g., 384 Kbit/s) in a PCM digital channel or a DDN network may be transmitted at a rate of 64 Kbit/s, 128 Kbit/s, or PX 64 Kbit/s on an N-ISDN network may be transmitted in a packetized manner on a computer local area network.
Video conferencing system mainly consists of terminal equipment, transmission channel (communication network) and multi-point control unit (MCU: Multipoint Control Unit) three parts.?
Wherein, the user terminal equipment and MCU is a video conferencing system is unique to the part, while the communication network is not unique to the video conferencing system, it is already in existence all kinds of communication networks, video conferencing equipment in the communication network operation, the need for the following equipment and the environment:
1, the user terminal equipment
Video conferencing terminal equipment video, audio, data, signaling and other digital signals, respectively, the video, audio, data and other digital signals.
Video conferencing terminal equipment will video, audio, data, signaling and other digital signals were processed into a composite digital code stream, and then it will be transformed into a network interface compatible with the user, in line with the transmission network of the channel frame structure of the signal format in the channel transmission. One of the user? Network interface is a video conference terminal equipment (or MCU) to meet the requirements of the transmission channel interface with the digital circuit interface.
2, communication line network
Video conferencing transmission medium can be used fiber optic cable, cable, microwave, and satellite and other digital channels, or other types of transmission channels. Within the scope of the user access network, HDSL, ADSL and other equipment can be used for transmission. Videoconferencing services can be carried out in a variety of existing communication networks, such as SHD digital communication networks, DDN, ISDIV. ATM or frame relay networks, as well as in a variety of computer networks, such as LAN, WAN, Internet and so on. Whether it is a telecommunication network or a computer network, video conferencing systems mainly use them to transmit dynamic or static image signals, voice signals, data signals and system control signals.
3, multi-point control unit (MCU)
In the current communication and control mechanism of the various networks themselves, but also can not fully meet the conference television system required by the multi-point to multi-point communication and control functions. Therefore, in addition to terminal equipment, communication lines, video conferencing system to carry out multi-point audio-visual information transmission and switching, but also must be added to the multi-point control unit equipment.MCU according to certain guidelines to deal with the audio-visual signals, and they will be assigned to the channel should be connected. In a sense, the role of the MCU is like the telephone network switch, but its functions and requirements than the telephone switch complex, must be required by the user to transmit the information transmitted to the other side of the equipment.
4, transmission and interface technology
Video conferencing with the help of communication networks, communication lines for information transmission, and the reality of a variety of communication networks, public **** telephone network (PSTN), integrated services digital network (IS-DN), digital data network (DDN), a variety of private networks, LAN (including Ethernet, token ring network, FDDI), and a variety of wireless channels. various wireless channels. Therefore, the videoconferencing system must be based on the transmission characteristics of different channels and networks to carry out a variety of media data transmission. The videoconferencing terminal or MCU must convert its own composite code stream into the data frame format, signal format and inter-control protocol that the transmission network can accept, and then send it to the transmission network through the network interface. Or you can look specifically ? Web Link