[ Huaqiang Security Network News ] For most users, the most important factors for video conferencing systems are the following: audio and video quality, system price, system security and scalability. There are two main situations in the current ubiquitous network environment. One is based on circuit-switched networks, such as ISDN, DDN, and PSTN. The other is a packet-switched network such as ATM, IP, Frame Relay, and so on. 
Utilizing ISDN Lines <br> For most individual users and small business users, accessing ISDN lines is a more economical option. ISDN utilizes a public telephone network to provide end-to-end digital channel connections to users for carrying various telecommunication services, including voice and non-voice. Conference television is transmitted over the ISDN channel using ISDN lines at rates ranging from 384 kb/s to 2 Mb/s. Since ISDN performs communication charging according to the B channel (64 kb/s) used, the domestic communication rate of the 1B channel is equivalent to the ordinary telephone communication rate (the most widely used circuit switching method).
For users with less communication and shorter communication time, the cost of using ISDN is much lower than the cost of renting DDN line or frame relay circuit, and it has the characteristics of high speed, low investment, convenient networking, etc. System application requirements. However, the national ISDN network is still in the process of continuous upgrading, and the reliability and stability are still insufficient compared to the dedicated line.
Renting DDN Lines <br> Large enterprises and institutions often have high requirements for video effects. At this time, you can choose the access method of DDN line. The DDN dedicated line has high transmission quality, small network delay, high circuit reliability, high network security, and convenient networking. Although DDN has the above advantages, the digital circuit provided by DDN is a semi-permanent connection, that is, the connection is maintained regardless of whether the user transmits data, so the cost is relatively high, which is not suitable for users with short communication time, but only for long Time-to-point and multi-point-to-point communication connections because the DDN line charges for the number of peer-to-peer. If some subordinate departments of the group users are connected to the company headquarters, they can use the multi-point-to-point DDN line networking. However, if subordinate departments need to communicate frequently, if they take a point-to-point connection, the company's subordinate departments will form a mesh. Net, so the cost of the user is too high.
System using PSTN <br> For ordinary individual users, if you want to try video conferencing, you can try PSTN access. The PSTN public telephone network is currently the most widely used network system, and its advantages are wide coverage, easy to use, low price, and easy networking. However, the network speed can only reach 56 kbps, the line quality is poor, and the transmission rate is low, which is far from enough for video conference audio and image transmission. The software-based video conferencing system can achieve an image transmission rate of 4f/s. The biggest disadvantage is that the image quality is too poor, which will greatly affect the quality of the conference, and is generally used rarely.
Using an ATM network <br> If you want good video effects and access to an ATM network, ATM network access is also an option. ATM is an asynchronous transfer mode that combines the advantages of circuit switching and packet switching to deliver wideband signals at any rate that can carry voice, data, image and video signals. The biggest feature of this technology is QoS guarantee. This scheme is recommended for units with line conditions and high quality requirements. It is characterized by good image quality and convenient networking (no need to connect all video conference terminal lines to MCU), high reliability. However, the equipment costs are high and an ATM network is required for access.
IP-based systems <br> The most convenient way to access is the IP network. IP-based networks use packet switching technology because packet switching does not guarantee order and fixed delays, so there is no guarantee of fixed latency and bandwidth. In order to better solve the service quality of real-time communication, protocols such as UDP/IP, RTP, RTCP, and RSVP are adopted. The video conferencing system applied to broadband IP networks such as ADSL and FTTB+LAN has achieved good results. Today, IP networks are ubiquitous, and this method is convenient and inexpensive. However, since packet switching-based IP networks follow the principle of best effort delivery, the video conferencing effect of this access method is worse than that of ISDN and DDN. However, its good cost performance has been favored by more and more users, especially for small and medium-sized enterprises and individuals with sufficient network bandwidth.
Using satellite access <br> Satellite networks have the performance advantages unmatched by terrestrial networks in video conferencing at medium and long distances. They can cover remote areas such as sea and mountains, with high transmission rate and good security, and flexible construction and relocation of the venue. Convenience is a good choice for multinational companies. The satellite broadband video conferencing system supports the integrated transmission of multi-session video, files and data. The disadvantage of this scheme is that it is expensive. In addition to the channel fee for renting satellites, the construction cost of each satellite ground station is about 200,000 yuan. At the same time, satellite communication has a large delay and is not suitable for video conferencing systems with high real-time requirements.
Frame Relay Mode <br> Frame Relay access mode is also a professional conference access method. The frame relay technology is mainly used to transmit data services. The frame relay frame is suitable for encapsulating data units of a local area network and transmitting burst services. It is a way of wide area network communication. The network has high efficiency, large network throughput, low communication delay, and the access rate of frame relay users ranges from 64 kbit/s to 2 Mbit/s, and even reaches 34 Mbit/s. Frame-based network costs are high, but the video is good.
For users with less communication and shorter communication time, the cost of using ISDN is much lower than the cost of renting DDN line or frame relay circuit, and it has the characteristics of high speed, low investment, convenient networking, etc. System application requirements. However, the national ISDN network is still in the process of continuous upgrading, and the reliability and stability are still insufficient compared to the dedicated line.
Renting DDN Lines <br> Large enterprises and institutions often have high requirements for video effects. At this time, you can choose the access method of DDN line. The DDN dedicated line has high transmission quality, small network delay, high circuit reliability, high network security, and convenient networking. Although DDN has the above advantages, the digital circuit provided by DDN is a semi-permanent connection, that is, the connection is maintained regardless of whether the user transmits data, so the cost is relatively high, which is not suitable for users with short communication time, but only for long Time-to-point and multi-point-to-point communication connections because the DDN line charges for the number of peer-to-peer. If some subordinate departments of the group users are connected to the company headquarters, they can use the multi-point-to-point DDN line networking. However, if subordinate departments need to communicate frequently, if they take a point-to-point connection, the company's subordinate departments will form a mesh. Net, so the cost of the user is too high.
System using PSTN <br> For ordinary individual users, if you want to try video conferencing, you can try PSTN access. The PSTN public telephone network is currently the most widely used network system, and its advantages are wide coverage, easy to use, low price, and easy networking. However, the network speed can only reach 56 kbps, the line quality is poor, and the transmission rate is low, which is far from enough for video conference audio and image transmission. The software-based video conferencing system can achieve an image transmission rate of 4f/s. The biggest disadvantage is that the image quality is too poor, which will greatly affect the quality of the conference, and is generally used rarely.
Using an ATM network <br> If you want good video effects and access to an ATM network, ATM network access is also an option. ATM is an asynchronous transfer mode that combines the advantages of circuit switching and packet switching to deliver wideband signals at any rate that can carry voice, data, image and video signals. The biggest feature of this technology is QoS guarantee. This scheme is recommended for units with line conditions and high quality requirements. It is characterized by good image quality and convenient networking (no need to connect all video conference terminal lines to MCU), high reliability. However, the equipment costs are high and an ATM network is required for access.
IP-based systems <br> The most convenient way to access is the IP network. IP-based networks use packet switching technology because packet switching does not guarantee order and fixed delays, so there is no guarantee of fixed latency and bandwidth. In order to better solve the service quality of real-time communication, protocols such as UDP/IP, RTP, RTCP, and RSVP are adopted. The video conferencing system applied to broadband IP networks such as ADSL and FTTB+LAN has achieved good results. Today, IP networks are ubiquitous, and this method is convenient and inexpensive. However, since packet switching-based IP networks follow the principle of best effort delivery, the video conferencing effect of this access method is worse than that of ISDN and DDN. However, its good cost performance has been favored by more and more users, especially for small and medium-sized enterprises and individuals with sufficient network bandwidth.
Using satellite access <br> Satellite networks have the performance advantages unmatched by terrestrial networks in video conferencing at medium and long distances. They can cover remote areas such as sea and mountains, with high transmission rate and good security, and flexible construction and relocation of the venue. Convenience is a good choice for multinational companies. The satellite broadband video conferencing system supports the integrated transmission of multi-session video, files and data. The disadvantage of this scheme is that it is expensive. In addition to the channel fee for renting satellites, the construction cost of each satellite ground station is about 200,000 yuan. At the same time, satellite communication has a large delay and is not suitable for video conferencing systems with high real-time requirements.
Frame Relay Mode <br> Frame Relay access mode is also a professional conference access method. The frame relay technology is mainly used to transmit data services. The frame relay frame is suitable for encapsulating data units of a local area network and transmitting burst services. It is a way of wide area network communication. The network has high efficiency, large network throughput, low communication delay, and the access rate of frame relay users ranges from 64 kbit/s to 2 Mbit/s, and even reaches 34 Mbit/s. Frame-based network costs are high, but the video is good.
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