【 Weak current College 】 construction based on IP network video conferencing system technology---Power By 【 China power house network 】

1 preface with the multimedia computer technology and communication technology for development, a new technology--multimedia communications technology, it is a multimedia, communications, computers, and networks of mutual penetration and development of products, integrated computer interactivity, multimedia communication of complex, distributed, and the authenticity of the TV, etc., with obvious advantages. Currently, how in the IP network better and faster delivery of video, audio, has become one of today's hot topics. 2 construction based on IP network video conferencing system technical requirements as IP network rate increasingly higher, from narrowband to broadband, hosting business from non-real-time to live, IP technology has become an implementation of video, audio, data, and so the best choice for comprehensive business. The establishment of the IP network video conferencing system requires a variety of technical support, is more complex, full of multimedia applications. 2.1 adequate high-bandwidth
You want to transfer the video, you must have sufficient network bandwidth, just like the cart to have wide enough to pass of the road, otherwise, the video data through the network. To frame 1024 × 768 pixels, for example, if you use 12bit represent each pixel, the total need 9.4Mb, according to 25 frames/sec transfer rate is 1 sec requires the amount of data transferred is 235Mb. In the existing network, transfer such data is unacceptable. 2.2 good compression technology
Only the high compression ratio of compression algorithms, effectively reduce the amount of data, in order to make video and audio data in the IP network transmission possible. For example: in H.323 conferencing systems, image encoding mainly uses the H.261 and H.263 standards, support for CIF, QCIF resolution, which was perfected in H.263 and H.264 is better than MPEG-IV compression ratio higher standards, saving 50% of the encoding rate, but the network has better support for HDTV and DVD image quality. 2.3 to have multicast IP network technology
Multicast is an address broadcast, send and receive a one-to-many relationship. During the transfer process, sender-side only need to send a packet that is located in the multicast group within the users can share this packet. In the video conference system application, adds a node signal transmission to each node, whether it be repeated using point-to-point communication, or broadcast, is a serious waste of network bandwidth, and multicast data transmission technology will be spread to the network node, reduces the amount of data in the network. 2.4 must have compatible transport protocol
TCP, UDP protocols are not well supported video conference system, this requires corresponding protocols such as RTP, RTCP, RSVP, etc. RTP is running on top of UDP, audio, video, data is encapsulated in the RTP packets, each RTP packet is encapsulated in the UDP packet, and then encapsulated in IP packets for transmission. In the underlying network support multicast, RTP can also use multicast to multiple destination endpoint to send data. RTCP is RTP Control Protocol for feedback control, detection of QoS and delivery-related information, on RTP data transceiver made adjustments to maximize the use of network resources. 2.5 QA to provide services
Network quality of service between the network and users, as well as a network to communicate with users on information transmission and sharing of quality conventions. First, in any network, time delay always exist. Video conference system with high reliability requirements of real-time and, in order to access the site's real presence, audio, video of delay must be less than 0.25s, maximum delay variation should be less than 10ms. Secondly, in the video conference system, also called lip sync, only reached the time synchronization, to natural and effective expression for complete information on the venue. Third, to allow a certain degree of packet loss rate. Because of the limited capacity of perception, in a video conference system, individual packet loss, the human eye is not, so you can allow certain ber, packet loss rate should be controlled in the acceptable range. 3 based on the IP network video conferencing system protocol is based on the IP network video conferencing system standards are: H.323 and SIP.
H.323 follows the traditional telephone signaling mode, more mature, has appeared in many products, forming a more mature application system and market system. SIP protocol to audio and video transmission as an application on the Internet, increases the signalling and QoS requirements, draws on other Internet standards and protocols for design ideas, follow the simple, open and compatible and scalable principle, relatively simple, but it has not been long since its launch, the Protocol is not very mature, the application is not very much. 4 closing with the network, multimedia, communications technology and the rapid development and performance improvement, based on the IP network video conferencing system technology will continue to be developed and perfected, is bound to its unique advantages are widely applied to the Internet, Extranet, Intranet, to government agencies, trade groups, research institutes, medical institutions and individuals, providing convenient offsite AC, a working, learning, life, an indispensable tool.