Conference Television Technology and Its Development Beijing Posts and Telecommunications University Image Treatment and Transmission Labs All Children Yang Chengjun began in the 1960s, and the world developed countries began researching the simulation conference TV system and gradually commercialization. In the end of the 1960s, under the push of compression coding technology, the simulation system turned to the digital system. In the early 1980s, 2 Mbit / s colored digital conference television systems, Japan and the United States formed non-standard domestic conference TV networks were developed. In the mid-1980s, the rapid development of large-scale integrated circuit technology, the image codec technology made breakthroughs, and the cost of network communication is reduced, providing a good development conditions for conference TV. At the end of the 1980s, multimedia technology, computer technology, and communication network technologies were rapidly developed. CCITT (ITU-T) forms H. 200 Series recommendations, the unified video input and output standards, algorithm standards, error check criteria, and a series of interoperable mode conversion criteria, solve different manufacturers' interworking problems, which greatly promotes the development of conference TV. In recent years, the conference TV business has begun to promote the use of my country, and the national conference TV backbone has been built, and it has gradually developed to remote medical, distance teaching. The development of the conference television system products also maintains synchronization with international synchronization. On the basis of developing a private network-based conference television system, N-ISDN-based multimedia microcomputer terminal and multi-point conference control unit (MCU) has also entered the practical phase last year. Based on predictions, information retrieval and IP telephony account for only a small part of all data services and multimedia traffic, most of the traffic is occupied by images such as images, video and conference television, and require high quality assurance. According to market investigations and forecasts, Tektronix has drawn the following conclusions that its business growth in 2002 will reach $ 734.5 billion, so they decided to go into the video field. Table 1 WebTV (IP / TV) family ownership survey and predicts are an example, you can see the use and growth of video services. Conference television system and terminal constitute 1. The basic topology of the conference television system consists of terminal equipment, network equipment. Network devices include multipoint control units (MCUs) and transmission networks. If it is a point-to-point conference television system, it does not require MCU, which is a visual telephone system. Multi-point conferencing systems based on circuit switching networks must be implemented through MCUs, and the package switching network implements multi-conference servers. Different communication networks, the terminal and multi-point control unit MCU of the conference television system are not the same. The terminal device can be a dedicated multimedia conference terminal, which can be a normal computer installed with the necessary audio, video hardware, and software, or a telephone, etc.
Multi-point conference television systems mainly include audiovisual multimedia conference terminals T1 to TN, multi-point control units (or multi-point conferencing servers) MCU1 ~ MCUM and communication networks. 2. The main components of the conference television system (1) Gatekeeper, Gatekeeper for H. The communication function is not completed in the 323 network. The main role is: address translation, access control, bandwidth management, bandwidth control, regional management, call control management, call control. (2) Gateway, mainly responsible for the conversion encoding of communication between terminals of different networks, including calls, control protocols, reputation, and reciprocating code stream structures, video speech conversions. (3) The purpose of the MCU is to connect three or more terminal systems in the same conference. The MCU is exchanged as a conference control center, and audio streams can also be used as a bridge of a shaped network conference system terminal. (4) Terminal, users participate in meetings by means of terminals, the terminal mainly completes the view, audio codec, and the reputation of data information. 3. The relevant standards of the conference TV are the standardization process of the conference TV system. CCITT has established an audiovisual conference research team in the early 1980s, which includes corresponding to different network environments, including (N-ISDN, PSTN, B-ISDN, LAN). Multimedia communication terminal standard.
Mainly: ITU-T H. 320, narrowband video telephone system and terminal (N-ISDN); ITU-T 324, low bit rate multimedia communication terminal (PSTN); ITU-THH. 323, multimedia communication system based on package exchange; ITU-T h. 322, providing a local area multimedia communication system and terminal that guarantees business quality; ITU-T 321, B-ISDN environment H. 320 adaptation; ITU-T H. 310, Broadband Multimedia Communication System and Terminal (ATM / B-ISDN). H. The 300 series standard includes its corresponding video, audio, communication protocol, multiplexing / synchronous H. 200 Series standard, its data communication protocol uses T. ITU-T No. 8 set. 120 Series standard. Video Code: ITU-T H. 261, h. 263 and H263 series low bit rate communication video codec; speech codec: ITU-T G. 711, g. 722, g. 728, g. 723.1 Message decoding standards.
System Control: ITU-T H. 221 frame structure of 64K to 1920K channels in audiovisual services; ITU-T 243 three or more audio-visual terminals are used until 2Mbit / s digital channel establishment of communication; ITU-T 230 audiovisual system frame synchronization control and instruction signal; ITU-T 242 Use a system that establishes a communication between the audio-visual terminal of the 2 Mbit / s digital channel. 4. Conference TV Related Key Technologies (1) Video Coding Technology. The compression of the source is one of the core technologies in the communications field. For video services, compression techniques are particularly important because the video signal has a large amount of data, and the rate of the standard PAL signal is 216Mbit / s. If it is not compressed basically impossible to transmit, it can only be transmitted on communication trunk when compressed to 2 mbit / s, and it is impossible to scale to end users. Therefore, it is necessary to improve the compression efficiency, and on the one hand, it is achieved by the dodge of image quality, but is mainly increasing coding efficiency. MPEG2 is mainly used for video coding for higher rates. For video encoding of extremely low rates, the corresponding compression criteria should be used, and the main compression criteria are MPEG4 standards for ITU-T H263 and ISO. However, MPEG4 has a large amount of calculation, and it is still difficult to practice. It is mainly used to H263 and H. 263 . H. 263 can adapt to communication networks with high-error rate. H. 263 standards, in H. 263 Based on the encoding method a lot of improvements, and exists in the form of options. In the improved option, it takes into account the improvement of coding efficiency, and the enhancement of channel fault-tolerant ability is also taken into account.
When H263 and H263 are in the case of the same video quality, the transmission rate is only 50%. H. 263 has gradually become one of new technologies. (2) Beginning in the 1960s, the world developed countries began researching the simulation conference television system and gradually commercialization. In the end of the 1960s, under the push of compression coding technology, the simulation system turned to the digital system. In the early 1980s, 2 Mbit / s colored digital conference television systems, Japan and the United States formed non-standard domestic conference TV networks were developed. In the mid-1980s, the rapid development of large-scale integrated circuit technology, the image codec technology made breakthroughs, and the cost of network communication is reduced, providing a good development conditions for conference TV. At the end of the 1980s, multimedia technology, computer technology, and communication network technologies were rapidly developed. CCITT (ITU-T) forms H. 200 Series recommendations, the unified video input and output standards, algorithm standards, error check criteria, and a series of interoperable mode conversion criteria, solve different manufacturers' interworking problems, which greatly promotes the development of conference TV. In recent years, the conference TV business has begun to promote the use of my country, and the national conference TV backbone has been built, and it has gradually developed to remote medical, distance teaching. The development of the conference television system products also maintains synchronization with international synchronization. On the basis of developing a private network-based conference television system, N-ISDN-based multimedia microcomputer terminal and multi-point conference control unit (MCU) has also entered the practical phase last year. Based on predictions, information retrieval and IP telephony account for only a small part of all data services and multimedia traffic, most of the traffic is occupied by images such as images, video and conference television, and require high quality assurance. According to market investigations and forecasts, Tektronix has drawn the following conclusions that its business growth in 2002 will reach $ 734.5 billion, so they decided to go into the video field. Conference television system and terminal constitute 1. The basic topology of the conference television system consists of terminal equipment, network equipment. Network devices include multipoint control units (MCUs) and transmission networks. If it is a point-to-point conference television system, it does not require MCU, which is a visual telephone system. Multi-point conferencing systems based on circuit switching networks must be implemented through MCUs, and the package switching network implements multi-conference servers. Different communication networks, the terminal and multi-point control unit MCU of the conference television system are not the same. The terminal device can be a dedicated multimedia conference terminal, which can be a normal computer installed with the necessary audio, video hardware, and software, or a telephone, etc.
Multi-point conference television systems mainly include audiovisual multimedia conference terminals T1 to TN, multi-point control units (or multi-point conferencing servers) MCU1 ~ MCUM and communication networks. 2. The main components of the conference television system (1) Gatekeeper, Gatekeeper for H. The communication function is not completed in the 323 network. The main role is: address translation, access control, bandwidth management, bandwidth control, regional management, call control management, call control. (2) Gateway, mainly responsible for the conversion encoding of communication between terminals of different networks, including calls, control protocols, reputation, and reciprocating code stream structures, video speech conversions. (3) The purpose of the MCU is to connect three or more terminal systems in the same conference. The MCU is exchanged as a conference control center, and audio streams can also be used as a bridge of a shaped network conference system terminal. (4) Terminal, users participate in meetings by means of terminals, the terminal mainly completes the view, audio codec, and the reputation of data information. 3. The relevant standards of the conference TV are the standardization process of the conference TV system. CCITT has established an audiovisual conference research team in the early 1980s, which includes corresponding to different network environments, including (N-ISDN, PSTN, B-ISDN, LAN). Multimedia communication terminal standard.
Mainly: ITU-T H. 320, narrowband video telephone system and terminal (N-ISDN); ITU-T 324, low bit rate multimedia communication terminal (PSTN); ITU-THH. 323, multimedia communication system based on package exchange; ITU-T h. 322, providing a local area multimedia communication system and terminal that guarantees business quality; ITU-T 321, B-ISDN environment H. 320 adaptation; ITU-T H. 310, Broadband Multimedia Communication System and Terminal (ATM / B-ISDN). H. The 300 series standard includes its corresponding video, audio, communication protocol, multiplexing / synchronous H. 200 Series standard, its data communication protocol uses T. ITU-T No. 8 set. 120 Series standard. Video Code: ITU-T H. 261, h. 263 and H263 series low bit rate communication video codec; speech codec: ITU-T G. 711, g. 722, g. 728, g. 723.1 Message decoding standards.
System Control: ITU-T H. 221 frame structure of 64K to 1920K channels in audiovisual services; ITU-T 243 three or more audio-visual terminals are used until 2Mbit / s digital channel establishment of communication; ITU-T 230 audiovisual system frame synchronization control and instruction signal; ITU-T 242 Use a system that establishes a communication between the audio-visual terminal of the 2 Mbit / s digital channel. 4. Conference TV Related Key Technologies (1) Video Coding Technology. The compression of the source is one of the core technologies in the communications field. For video services, compression techniques are particularly important because the video signal has a large amount of data, and the rate of the standard PAL signal is 216Mbit / s. If it is not compressed basically impossible to transmit, it can only be transmitted on communication trunk when compressed to 2 mbit / s, and it is impossible to scale to end users. Therefore, it is necessary to improve the compression efficiency, and on the one hand, it is achieved by the dodge of image quality, but is mainly increasing coding efficiency. MPEG2 is mainly used for video coding for higher rates. For video encoding of extremely low rates, the corresponding compression criteria should be used, and the main compression criteria are MPEG4 standards for ITU-T H263 and ISO. However, MPEG4 has a large amount of calculation, and it is still difficult to practice. It is mainly used to H263 and H. 263 . H. 263 can adapt to communication networks with high-error rate. H. 263 standards, in H. 263 Based on the encoding method a lot of improvements, and exists in the form of options. In the improved option, it takes into account the improvement of coding efficiency, and the enhancement of channel fault-tolerant ability is also taken into account.
