For most users, the most important factors of video conferencing system are the following aspects: Audio and video quality, system price, security and scalability of the system. At present, there are two main types of network environment, one is based on circuit switching network, such as ISDN, DDN, PSTN and so on. The other is a packet-switched network, such as ATM, IP, Frame Relay, and so on.
Leveraging ISDN lines
For most individual users and small business users, using ISDN line access is a relatively economical and practical option. ISDN uses the public telephone network to provide end-to-end digital channel connectivity to the user to host a wide range of telecommunications services, including voice and non voice. ISDN lines are used to transmit conference televisions on an ISDN channel at a rate of 384kb/s to 2mb/s. Because ISDN communicates with the B-channel (64KB/S) used, the domestic communication rate for the 1B channel is equivalent to the ordinary telephone rate (in the most widely used circuit-switching mode).
For users with less traffic and shorter communication time, the cost of using ISDN is much lower than the cost of renting DDN or Frame relay circuit, and it has the characteristics of high speed, less investment and convenient networking, and can meet the application requirements of basic conference TV system. However, the national ISDN network is still in the upgrading phase, reliability and stability relative to the way of the special line is still inadequate.
Leased DDN Line
Large enterprises and institutions often require higher video effects, then you can choose the DDN line access mode. The use of DDN special line transmission quality is high, network delay is small, circuit reliability is high, network security is high, networking is convenient.
Although DDN has the above advantages, however, because the digital circuit provided by DDN is a semi-permanent connection, that is, regardless of whether the user transmits data, this connection has been maintained, so the cost is relatively high, not suitable for short communication time users, but only for a long time point-to-point and point-to-point communication connections, Because the DDN line according to the number of point-to-point to charge.
If some of the group's users are affiliated with the company's headquarters, can be used in a DDN-point way of the network, but if the subordinate departments also need to communicate frequently, if the point-to-point connection, the company under the various departments to form a mesh network, so that the user's cost is too high.
Systems using the PSTN
For ordinary individual users, if you want to try a video conferencing can try the PSTN access. PSTN public telephone network is currently the most widely used network system, its advantages are wide coverage, easy to use, low price, easy networking. But the network speed can reach only 56kbps, the line quality is poor, the transmission rate is low, for video conference voice, image transmission is not enough. The software based video conferencing system can achieve the 4F/S image transmission rate, its biggest disadvantage is that the image quality is too poor, will greatly affect the quality of the meeting, generally used very little.
Using ATM Networks
If you want good video effects, and access to ATM network is very convenient, ATM network access mode is also a choice. ATM is the asynchronous transfer mode, which combines the advantages of circuit switching and packet switching, and can transmit the wideband signal at any rate, which can transmit voice, data, image and video signal.
The biggest feature of the technology is the QoS guarantee, for the line conditions, high quality requirements of the unit recommended the use of this scheme, its characteristics are good image quality, networking convenience (without all the TV conferencing terminal lines are linked to the MCU), high reliability. But the equipment cost is high, and needs to have the ATM network to be available for access.
The system based on IP network
The easiest way to access is the IP network. The IP based network adopts packet switching technology, because packet switching does not guarantee the order and fixed delay, so it can not guarantee the fixed delay and bandwidth. In order to solve the business quality of real-time communication, the UDP/IP, RTP, RTCP and RSVP protocols are adopted. The video conferencing system used in ADSL, Fttb+lan and other broadband IP networks has achieved good results.
In the IP network ubiquitous today, this way networking convenience, cheap. However, because the packet-switched IP network follows the principle of making the best effort to deliver, the video conferencing effect of this access mode is inferior to that of ISDN, DDN and so on. But its good price-performance has been more and more users of the favor, especially suitable for network bandwidth enough for small and medium-sized enterprises and individuals to use.
Using satellite access
The satellite network has the incomparable performance advantage in the remote video conference, can cover to the sea, mountains and other remote areas, high transmission rate, good security, and the venue construction and relocation of flexible, convenient, is a good choice for multinational companies, satellite broadband video conferencing system to support multi-channel video conferencing, The comprehensive transmission of documents and data broadcasts. The disadvantage of this scheme is that it is expensive and the construction cost of each satellite Earth station is about $200,000, in addition to the channel fee for the leased satellite. At the same time, the satellite communication delay is not suitable for the video conferencing system with high real-time requirement.
Frame Relay Mode
The Frame Relay access mode is also a kind of professional conference access mode. Frame Relay technology is mainly used to transfer data service, Frame Relay frame is suitable for encapsulating data unit of LAN, transmitting burst service, it is a way of WAN communication. This kind of network efficiency is high, network throughput is big, communication delay is low, the access rate of Frame Relay user is 64kbit/s to 2mbit/s, even can reach 34mbit/s. The network cost based on frame relay is high, but the video effect is good.