| Foreword: In the 21st century, where information technology is rapidly developing, the research and application of computer technology and communication technology has always been a hot field. "Video Conferencing" provides us with the best means of transmitting images, sounds and data in two directions. This paper combines the construction and application of the video conference of the Beijing court system, and discusses how to construct a video conferencing system with stable performance and complete functions. |
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First, the positioning should be accurate
Each unit must carefully consider its use before deciding to build a video conferencing system. Choose the appropriate transmission quality according to different value orientations. Generally speaking, the quality of video conference service can be divided into three levels: high quality: the circuit is based on DDN, E1 leased line, conforms to the International Telecommunications Union (ITU) H.320 network protocol standard, the channel rate should be 2M, the device is Full hardware codec (multimedia digital signal codec), 30fps FCIF format video, rich circuit interface and intelligent voice and other functions. Applicable to large-scale backbone video TV systems built by state agencies, government departments and telecom operators. Medium quality: The circuit is generally based on a dedicated IP network, conforming to the (ITU) H.323 network protocol standard, and the channel rate should be above 768k. The device is also full hardware Codec, 20~30fps FCIF format video. Suitable for a range of office meetings or distance learning. Low quality: Provides pure software Codec, 10fpsFCIF format video, based on IP circuits. Compliant with (ITU) H.323 desktop video conferencing requirements, channel rates below 384k. Meet the general simple use requirements.
The video conferencing system of the Beijing Court covers the city's three intermediate courts, 18 district and county courts, and 54 people's courts, mainly for the purpose of holding conference television and transmitting high-quality trial images of the city's courts. The choice of which network transmission method should be decided according to different value orientations, the primary consideration of the Beijing court building video conference network is the problem of clear images and stable network. Therefore, we chose the H.320 protocol and high-quality E1 leased line transmission scheme.
Second, the circuit is guaranteed
In 2001, the video conferencing system was built. The optical cable circuit was laid by the local telecommunications bureau to the courts. The 2M transmission circuit was leased by PDH transmission, and the telecom exchanges were connected by SDH transmission. Finally, all the circuits were connected to the main venue of the high court. 155M optical transceiver, the network is a star structure. The whole circuit is transmitted by optical cable, which lays the foundation for reliable, confidential and safe operation of video conferencing system. Video conferencing enjoys 2M bandwidth exclusively. To ensure stable transmission, the circuit interface uses E1 mode to avoid conversion equipment due to G.703-V.35. Loss and fault hazard, the circuit between the main venue Codec-MCU-optical transceiver-optical modem-substation Codec is very simple. The network protocol follows the H.320 protocol standard of the International Telecommunications Union (ITU), so that the image information is strictly transmitted separately from other network information, which avoids the possibility of data interference between the H.323 protocol and ensures stable and reliable transmission of the image signal.
Third, equipment is the key
"If you want to do something good, you must first sharpen your tools." To build a stable and reliable video conferencing network, not only requires good data transmission channels for security, but also must have high-performance video conferencing equipment. Through actual testing and repeated screening, we selected 24 fourth-generation Galaxy Series 755 Codec video conferencing terminal equipment from VITA. The device adopts an open PC interface and modular design, supports H.320 and H.323 dual protocol modes, and is easy to operate, easy to upgrade, and has powerful multimedia and data transmission functions; it can be used without affecting image transmission quality. The dual-stream function of data transmission; under the support of the local network management software of VTEL, the administrator can monitor the operation of the whole network in the central console; the system fault can be detected and diagnosed at the remote end, and the device can be started and performed. Parameter configuration can replace the remote administrator to operate the device, which realizes the intelligent operation and management of the device. In practice, we use this management function to play a significant role in ensuring the smooth progress of the entire network conference.
Fourth, stability is a requirement
The image multipoint controller (MCU) in the video conference network is a key device in the network. Its main functions are: node selection, conference establishment, real-time control, resource allocation, data forwarding, protocol parsing, and so on. Whether the performance of the MCU device is stable and reliable will directly affect the quality of the video conference. We have selected an imported brand product that has been widely used in China's H.320 network. It should be said that the transmission circuits, video terminals and MCU devices that guarantee the three main factors of stable operation of video conferences have been carefully selected and have the conditions for holding high-quality video conferences.
However, the practice proves that this is not the case. The key to stable and reliable operation of the network depends on the quality of the device itself, and also on the quality of the circuit, that is, whether the error rate of the circuit exceeds the specified range and whether the network clock is uniform. The former can be solved by end-to-end test adjustment of the circuit through the BER tester, but it is not easy to ensure the unified clock of the whole network. In practice, it is found that when the clock drifts within a certain range, the video signal can still be transmitted. When the drift exceeds the allowable range, the image will inevitably appear mosaic phenomenon. When the clock is seriously out of synchronization, the data will be re-negotiated between Codec and MCU. The internal resources of the MCU are intensified, and the MCU may be disordered. As a result, some remote Codec suddenly lose contact with the MCU, causing some conferences to be interrupted. Analysis of the cause of the failure: PDH is a transparent transmission circuit, unlike the DDN circuit, there is no clock source in the PDH network. The remote Codec device and the central MCU device are connected to several SDH networks in the city through a PDH circuit to form a video conference network. The MCU device only extracts one SDH clock as a clock for the video conference network, and uses the inter-network clock. Drift to a certain extent, Codec can not keep the clock synchronization with the MCU, which may cause the MCU to work disorder and cause video conference interruption failure. This kind of failure hazard is accompanied by the network which is really worrying.
V. Reliability is the purpose
We removed the main venue MCU equipment using Codec point-to-point connection, which fundamentally solved the problem of network clock troubles. VTEL's hypermedia terminal Vista VX has advanced network management functions and a variety of connection ports. The VITE's hypermedia terminal Vista VX device has been added to the main venue, and the sub-site equipment has not changed. After the upgrade, the E1 circuit is directly connected to each Vista VX device, and the VTEL central multipoint conference control unit replaces the MCU device to achieve clear, highly stable and reliable video conferencing requirements.
Each unit must carefully consider its use before deciding to build a video conferencing system. Choose the appropriate transmission quality according to different value orientations. Generally speaking, the quality of video conference service can be divided into three levels: high quality: the circuit is based on DDN, E1 leased line, conforms to the International Telecommunications Union (ITU) H.320 network protocol standard, the channel rate should be 2M, the device is Full hardware codec (multimedia digital signal codec), 30fps FCIF format video, rich circuit interface and intelligent voice and other functions. Applicable to large-scale backbone video TV systems built by state agencies, government departments and telecom operators. Medium quality: The circuit is generally based on a dedicated IP network, conforming to the (ITU) H.323 network protocol standard, and the channel rate should be above 768k. The device is also full hardware Codec, 20~30fps FCIF format video. Suitable for a range of office meetings or distance learning. Low quality: Provides pure software Codec, 10fpsFCIF format video, based on IP circuits. Compliant with (ITU) H.323 desktop video conferencing requirements, channel rates below 384k. Meet the general simple use requirements.
The video conferencing system of the Beijing Court covers the city's three intermediate courts, 18 district and county courts, and 54 people's courts, mainly for the purpose of holding conference television and transmitting high-quality trial images of the city's courts. The choice of which network transmission method should be decided according to different value orientations, the primary consideration of the Beijing court building video conference network is the problem of clear images and stable network. Therefore, we chose the H.320 protocol and high-quality E1 leased line transmission scheme.
Second, the circuit is guaranteed
In 2001, the video conferencing system was built. The optical cable circuit was laid by the local telecommunications bureau to the courts. The 2M transmission circuit was leased by PDH transmission, and the telecom exchanges were connected by SDH transmission. Finally, all the circuits were connected to the main venue of the high court. 155M optical transceiver, the network is a star structure. The whole circuit is transmitted by optical cable, which lays the foundation for reliable, confidential and safe operation of video conferencing system. Video conferencing enjoys 2M bandwidth exclusively. To ensure stable transmission, the circuit interface uses E1 mode to avoid conversion equipment due to G.703-V.35. Loss and fault hazard, the circuit between the main venue Codec-MCU-optical transceiver-optical modem-substation Codec is very simple. The network protocol follows the H.320 protocol standard of the International Telecommunications Union (ITU), so that the image information is strictly transmitted separately from other network information, which avoids the possibility of data interference between the H.323 protocol and ensures stable and reliable transmission of the image signal.
Third, equipment is the key
"If you want to do something good, you must first sharpen your tools." To build a stable and reliable video conferencing network, not only requires good data transmission channels for security, but also must have high-performance video conferencing equipment. Through actual testing and repeated screening, we selected 24 fourth-generation Galaxy Series 755 Codec video conferencing terminal equipment from VITA. The device adopts an open PC interface and modular design, supports H.320 and H.323 dual protocol modes, and is easy to operate, easy to upgrade, and has powerful multimedia and data transmission functions; it can be used without affecting image transmission quality. The dual-stream function of data transmission; under the support of the local network management software of VTEL, the administrator can monitor the operation of the whole network in the central console; the system fault can be detected and diagnosed at the remote end, and the device can be started and performed. Parameter configuration can replace the remote administrator to operate the device, which realizes the intelligent operation and management of the device. In practice, we use this management function to play a significant role in ensuring the smooth progress of the entire network conference.
Fourth, stability is a requirement
The image multipoint controller (MCU) in the video conference network is a key device in the network. Its main functions are: node selection, conference establishment, real-time control, resource allocation, data forwarding, protocol parsing, and so on. Whether the performance of the MCU device is stable and reliable will directly affect the quality of the video conference. We have selected an imported brand product that has been widely used in China's H.320 network. It should be said that the transmission circuits, video terminals and MCU devices that guarantee the three main factors of stable operation of video conferences have been carefully selected and have the conditions for holding high-quality video conferences.
However, the practice proves that this is not the case. The key to stable and reliable operation of the network depends on the quality of the device itself, and also on the quality of the circuit, that is, whether the error rate of the circuit exceeds the specified range and whether the network clock is uniform. The former can be solved by end-to-end test adjustment of the circuit through the BER tester, but it is not easy to ensure the unified clock of the whole network. In practice, it is found that when the clock drifts within a certain range, the video signal can still be transmitted. When the drift exceeds the allowable range, the image will inevitably appear mosaic phenomenon. When the clock is seriously out of synchronization, the data will be re-negotiated between Codec and MCU. The internal resources of the MCU are intensified, and the MCU may be disordered. As a result, some remote Codec suddenly lose contact with the MCU, causing some conferences to be interrupted. Analysis of the cause of the failure: PDH is a transparent transmission circuit, unlike the DDN circuit, there is no clock source in the PDH network. The remote Codec device and the central MCU device are connected to several SDH networks in the city through a PDH circuit to form a video conference network. The MCU device only extracts one SDH clock as a clock for the video conference network, and uses the inter-network clock. Drift to a certain extent, Codec can not keep the clock synchronization with the MCU, which may cause the MCU to work disorder and cause video conference interruption failure. This kind of failure hazard is accompanied by the network which is really worrying.
V. Reliability is the purpose
We removed the main venue MCU equipment using Codec point-to-point connection, which fundamentally solved the problem of network clock troubles. VTEL's hypermedia terminal Vista VX has advanced network management functions and a variety of connection ports. The VITE's hypermedia terminal Vista VX device has been added to the main venue, and the sub-site equipment has not changed. After the upgrade, the E1 circuit is directly connected to each Vista VX device, and the VTEL central multipoint conference control unit replaces the MCU device to achieve clear, highly stable and reliable video conferencing requirements.
Each unit must carefully consider its use before deciding to build a video conferencing system. Choose the appropriate transmission quality according to different value orientations. Generally speaking, the quality of video conference service can be divided into three levels: high quality: the circuit is based on DDN, E1 leased line, conforms to the International Telecommunications Union (ITU) H.320 network protocol standard, the channel rate should be 2M, the device is Full hardware codec (multimedia digital signal codec), 30fps FCIF format video, rich circuit interface and intelligent voice and other functions. Applicable to large-scale backbone video TV systems built by state agencies, government departments and telecom operators. Medium quality: The circuit is generally based on a dedicated IP network, conforming to the (ITU) H.323 network protocol standard, and the channel rate should be above 768k. The device is also full hardware Codec, 20~30fps FCIF format video. Suitable for a range of office meetings or distance learning. Low quality: Provides pure software Codec, 10fpsFCIF format video, based on IP circuits. Compliant with (ITU) H.323 desktop video conferencing requirements, channel rates below 384k. Meet the general simple use requirements.
The video conferencing system of the Beijing Court covers the city's three intermediate courts, 18 district and county courts, and 54 people's courts, mainly for the purpose of holding conference television and transmitting high-quality trial images of the city's courts. The choice of which network transmission method should be decided according to different value orientations, the primary consideration of the Beijing court building video conference network is the problem of clear images and stable network. Therefore, we chose the H.320 protocol and high-quality E1 leased line transmission scheme.
Second, the circuit is guaranteed
In 2001, the video conferencing system was built. The optical cable circuit was laid by the local telecommunications bureau to the courts. The 2M transmission circuit was leased by PDH transmission, and the telecom exchanges were connected by SDH transmission. Finally, all the circuits were connected to the main venue of the high court. 155M optical transceiver, the network is a star structure. The whole circuit is transmitted by optical cable, which lays the foundation for reliable, confidential and safe operation of video conferencing system. Video conferencing enjoys 2M bandwidth exclusively. To ensure stable transmission, the circuit interface uses E1 mode to avoid conversion equipment due to G.703-V.35. Loss and fault hazard, the circuit between the main venue Codec-MCU-optical transceiver-optical modem-substation Codec is very simple. The network protocol follows the H.320 protocol standard of the International Telecommunications Union (ITU), so that the image information is strictly transmitted separately from other network information, which avoids the possibility of data interference between the H.323 protocol and ensures stable and reliable transmission of the image signal.
Third, equipment is the key
"If you want to do something good, you must first sharpen your tools." To build a stable and reliable video conferencing network, not only requires good data transmission channels for security, but also must have high-performance video conferencing equipment. Through actual testing and repeated screening, we selected 24 fourth-generation Galaxy Series 755 Codec video conferencing terminal equipment from VITA. The device adopts an open PC interface and modular design, supports H.320 and H.323 dual protocol modes, and is easy to operate, easy to upgrade, and has powerful multimedia and data transmission functions; it can be used without affecting image transmission quality. The dual-stream function of data transmission; under the support of the local network management software of VTEL, the administrator can monitor the operation of the whole network in the central console; the system fault can be detected and diagnosed at the remote end, and the device can be started and performed. Parameter configuration can replace the remote administrator to operate the device, which realizes the intelligent operation and management of the device. In practice, we use this management function to play a significant role in ensuring the smooth progress of the entire network conference.
Fourth, stability is a requirement
The image multipoint controller (MCU) in the video conference network is a key device in the network. Its main functions are: node selection, conference establishment, real-time control, resource allocation, data forwarding, protocol parsing, and so on. Whether the performance of the MCU device is stable and reliable will directly affect the quality of the video conference. We have selected an imported brand product that has been widely used in China's H.320 network. It should be said that the transmission circuits, video terminals and MCU devices that guarantee the three main factors of stable operation of video conferences have been carefully selected and have the conditions for holding high-quality video conferences.
However, the practice proves that this is not the case. The key to stable and reliable operation of the network depends on the quality of the device itself, and also on the quality of the circuit, that is, whether the error rate of the circuit exceeds the specified range and whether the network clock is uniform. The former can be solved by end-to-end test adjustment of the circuit through the BER tester, but it is not easy to ensure the unified clock of the whole network. In practice, it is found that when the clock drifts within a certain range, the video signal can still be transmitted. When the drift exceeds the allowable range, the image will inevitably appear mosaic phenomenon. When the clock is seriously out of synchronization, the data will be re-negotiated between Codec and MCU. The internal resources of the MCU are intensified, and the MCU may be disordered. As a result, some remote Codec suddenly lose contact with the MCU, causing some conferences to be interrupted. Analysis of the cause of the failure: PDH is a transparent transmission circuit, unlike the DDN circuit, there is no clock source in the PDH network. The remote Codec device and the central MCU device are connected to several SDH networks in the city through a PDH circuit to form a video conference network. The MCU device only extracts one SDH clock as a clock for the video conference network, and uses the inter-network clock. Drift to a certain extent, Codec can not keep the clock synchronization with the MCU, which may cause the MCU to work disorder and cause video conference interruption failure. This kind of failure hazard is accompanied by the network which is really worrying.
V. Reliability is the purpose
We removed the main venue MCU equipment using Codec point-to-point connection, which fundamentally solved the problem of network clock troubles. VTEL's hypermedia terminal Vista VX has advanced network management functions and a variety of connection ports. The VITE's hypermedia terminal Vista VX device has been added to the main venue, and the sub-site equipment has not changed. After the upgrade, the E1 circuit is directly connected to each Vista VX device, and the VTEL central multipoint conference control unit replaces the MCU device to achieve clear, highly stable and reliable video conferencing requirements.
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