Based On IP Network Video Frequency Multicast System Realization

A lot of department, company and school have their own LAN because of the fast development of computer network. It offered nice communication network and terminal unit that are used in studying videoconference at LAN or Internet. Moreover using videoconference can reduce the payout especially videoconference at LAN dispense with added communication expense. This is predominance of videoconference at LAN. This paper just studies how to realize the videoconference at LAN.This article studies how to realize the videoconference at LAN by referencing from the corresponding standard called H.323, which based on IP network. The software is the emphasis of study, and the hardware part is simpler than the software part. It is mostly made up of multimedia capture, which can capture the video, and 100BaseT shared Ethernet, and terminal unit etc.The first problem to be solved is what control mode of conference to choose. According to the actual hardware condition, not adopting the GK (Gatekeeper) and MCU (multipoint control unit), a conference control mode named not centralizing control mode that combines the broadcasting conference and distributing multipoint conference is designed. Through this mode we can directly encapsulate the function of GK and MCU in the terminal unit. It means that we should adopt IP multicasting to send video to the appointed group and dispense with copying and sending video to sink many times. So efficiency of transmission is improved and the occupancy ratio of net bandwidth is reduced.IP single-cast is one mode of IP communication. The host computer can send information packet to the appointed computer. The other mode of IP communication is IP broadcast. The host computer can send information packet to all computers that are at the same network segment. IP multicast is a net transmission mode between the IP single-cast and IP broadcast. The host computer can send IP information packet to one group of computers that are at IP network. So we can say that IP multicast is a one-point to two-point corresponding mode, namely more than one sink can receive same information in same time from the source sender. An emphasis of this article is to realize the video IP multicast, which mainly comprise socket initialization, video sending and video receiving. Of cause, realization of the last two parts must be based on the finish of the first one.Videoconference system should have function of sharing whiteboard in order that person who attending the videoconference can handle real-time. Sharing whiteboard is a typical sharing-application tool, in which a interface window is shared by many long-distance attendees, every attendee can paint on the canvas with some simple painting tools. A simple sharing whiteboard is designed in this paper. It can finish simple painting, including automatically paint regular geometry figure and drawing artificially. It extends the function of videoconference. Sharing whiteboard is realized by information driving, it means every perform of painting can drive an one of information in the queue, which drive the long-distance computer to finish one perform of painting.Using computer as terminal unit of videoconference,we can make the best of the software of the computer to extend the function of videoconference. In this system, we also realize the function of file transmission one point to another. File is transmitted in the manner of data stream. First, it transforms the file into data stream and then sends it in packet. Any two points can use file transmission, so it is more convenient to attendee to communion and cooperate.At the end of the paper the result of experiment and the judge of system performance are given. First we use several standard video images to do the experiment. Then we use the video image captured by USB to do the experiment. The test datasheet shows, on a 10Mbps Ethernet, the effect of video transmission id good, and the frame velocity of video receiving is over 15 fps under general conditions, and the mos value of video is generally over 4.5. As to the occupation of CPU,the ratio is about 6%. The occupation ratio of net bandwidth is about 91%, which is more than that of CPU because the video is not compressed. The data above is all gained on the base of sending video in 30 fps, and it is according with the academic result. The occupation ratio of CPU and net bandwidth of sharing whiteboard is less than that of video multicast because sharing whiteboard is droved by painting information. While the occupation ration of net bandwidth of file transmission is related with the length of file.I haven't finished the compression of video image because time is not much enough. If video encoding and decoding is added to the system, the occupation ratio of net bandwidth must be reduced and the system will be more useful. C++ Builder development platform is used in the software design. It supplies good software circumstance for programming for server and workstation that run Windows OS on the LAN supporting TCP/IP protocols.Along with the advancement of processing ability of computer, the development of digital information processing and network communication technology, videoconference system based on IP network surely can reach the request of special meeting room, and become a major power in the field of videoconference.