The network video conference system should actually be called the network multimedia communication system, and the video conference is only a kind of basic application which the network multimedia communication system is very typical. The basic function of the network multimedia communication system is to meet the people across the space boundaries, to achieve off-site “interview” needs.
Network video conferencing system is the most important factors for users to focus on the following aspects: audio and video quality, system prices, system security and scalability. There are two main situations in the current network environment, one is based on circuit-switched networks such as ISDN, DDN, PSTN and so on. The other is based on packet switching networks, such as ATM, IP, frame relay and so on.
Using ISDN lines
For most of the individual users and small business users, the use of ISDN line access is a more economical and practical choice. ISDN uses the public telephone network to provide end-to-end digital channel connections to users, including voice and non-voice, including a variety of telecommunications services. With ISDN lines, conference TV is delivered over ISDN channels at a rate of 384kb / s to 2Mb / s. Since ISDN uses the B channel (64kb / s) for communication and billing, the domestic communication rate of the 1B channel is equivalent to the ordinary telephone communication rate (according to the most widely used circuit switching mode).
For users with less communication and shorter communication time, the cost of using ISDN is much lower than that of leasing DDN leased line or frame relay circuit, and it has the characteristics of high speed, less investment and convenient networking. It can meet the basic conference television System application requirements. But the national ISDN network is still in the escalating stage, reliability and stability relative to the line there are deficiencies.
Rent a DDN line
Large enterprises and institutions often require a higher impact on the video, then you can choose DDN line access. Using DDN line transmission quality is higher, the network delay is small, the circuit reliability is high, the network security is high, the networking is convenient. Although the DDN has the above advantages, but because the DDN provides a digital circuit for the semi-permanent connection, that is, regardless of whether the user data transmission, the connection has been maintained, so the cost is relatively high, not suitable for shorter communication time users, Time-to-point and multi-point-to-point communication connections, since DDN leases are charged at the number of point-to-point. If some of the group subordinate departments connected with the company headquarters, you can use multi-point-to-point DDN line network, but if the subordinate departments also need to communicate frequently, if then take point-to-point connection, the company subordinate departments between the networkNetwork, so the user’s cost is too high.
Use PSTN system
For ordinary personal users, if you want to try video conferencing can try PSTN access. PSTN public telephone network is currently the most widely used network system, its advantages are wide coverage area, easy to use, the price is low, easy to network. But the network speed can only reach 56kbps, line quality is poor, the transmission rate is low, for video conferencing sound, image transmission is far enough. Software-based network video conferencing system can achieve 4f / s image transfer rate, its biggest drawback is the poor image quality, will greatly affect the quality of the meeting, generally used very little.
Use ATM network
If you want a good video effect, and access to the ATM network is very convenient, ATM network access is also an option. ATM is an asynchronous transfer mode, which combines the advantages of circuit switching and packet switching, can transmit any rate of broadband signals, can transmit voice, data, images and video signals. The biggest feature of the technology is a QoS guarantee, for the line conditions, the quality of the high demand of the unit recommended by the program, which is characterized by good image quality, networking video conferencing classic quotations network video conferencing system classic joke video conferencing Software funny video videoconferencing solutions entertainment gossip convenience (no need to put all the video conferencing terminal lines are connected to the MCU), high reliability. But the equipment costs are high, and the need for ATM network access.
IP – based systems
Access the most simple way than the IP network. IP-based networks use packet switching technology because packet switching does not guarantee orderly and fixed latency, and therefore can not guarantee a fixed delay and bandwidth. In order to better solve the real-time communication quality of service, using UDP / IP, RTP, RTCP and RSVP and other protocols. Application of ADSL, FTTB + LAN and other broadband IP network network video conferencing system has achieved very good results. In the IP network everywhere today, this way networking convenience, cheap. However, because the packet-based IP network is to follow the principle of the best effort to deliver, so this access to the video conference effect compared to ISDN, DDN and other special lines worse. But its good price has been more and more users of all ages, especially for the network bandwidth is sufficient for small and medium enterprises and individuals to use. The use of satellite access satellite network in the long-distance video conferencing with terrestrial network can not match the performance advantages, can cover the sea, mountains and other remote areas, high transmission rate, good security, and the venue construction and relocation of flexible and convenient Multinational companies a good choice, satellite broadband network video conferencing system to support multi-channel video, documents and data integrated transmission broadcast. The shortcomings of this program is expensive, in addition to renting satellite channel fees, the construction cost of each satellite ground station is about 200,000 yuan. At the same time, satellite communication delay is large, not suitable for real-time requirements of high network video conferencing systems.