| The current information age is built on IP network technologies. The IP networks based on TCP/IP protocol are progressing rapidly, IP over anything has indubitably become a fact. As the world stepping into the information age, the traditional way of simple voice and text communication can't satisfy the public needs any longer, so they need a new communication way which put audio, video, text and other data all together. To meet the needs for communications, multimedia computer technology and communication technology combine together, developing a new multimedia communication technology gradually. With the development of modern network & multimedia communication technology, the intercommunions between enterprises are more and more frequent. So Videoconference System based on IP network is becoming a hotspot of the communication research field at present.Now Videoconference system, an application of multimedia communication, applies network and multimedia technologies to implement conference. Through Videoconference, people who are not in the same place can communicate freely and effectively with each other. The price of hardware Videoconference system is expensive, so it can't be used widely by ordinary users. Software Videoconference System is under increasing popularity in low-price market because of its distinct advantage in low price,convenient operation and agile function. But most software Videoconference Systems (especially multiple point systems) transmit video via server, efficiency and quality can't turn up trumps at present. This kind of system depends too much on server, which makes server become a choke point in internet. Videoconference system has characters of real-time, high speed,wide bandwidth, so network bandwidth can't satisfy its requirements generally. The conflict between limited bandwidth and progressive application of Videoconference system is becoming increasingly serious. So it is an exigent subject to economize the bandwidth to make sure the application of Videoconference systems.To resolve the problems discussed above, this paper establishes and implements a new set of Videoconference system based on IP Multicast. This system adopts IP Multicast to transmit video stream, DirectShow technology to manage video stream, and designs the communication mechanisms among every terminals referring to H.332 protocol. Finally, this paper tests the performance of entire system in detail. A good result has been got, and it approves that IP Multicast can economize a great deal of bandwidth.Firstly, this paper discusses the national and overseas recent researches on Videoconference system; Secondly, the related technologies of the system are given a deep research, mainly including DirectShow, Recommendation H.323 and H.332, the theory of IP Multicast communication and the problems existing, and so on; Then the paper designs and implements this Videoconference system depending on analysis of the functions and requirements of server and client in this system. These systems includes control messages communication, send and receive Filter for the video stream, the interaction of the video between every client; And the application of Videoconference system over Internet is researched and designed, then the paper presents the blueprint of throughout NAT firewall; Finally, the performance of entire system gains tests and analyses in detail.This video communication platform is referred to ITU-T Recommendation H.332, which implements multicast video communication function among multiple session terminals over the networks that support IP Multicast. As the Network and Transport Layer, it is responsible for control messages interaction based on H.332, transmission and management of real-time multicast video stream. And high Application level is responsible for providing simple interface for users, and dealing with user's control operations.There are two types of communication processing. One is control messages communication between terminals and server, mainly consisting of management and interaction of login, logout, speak and user information, which are transmitted through reliable TCP protocol; The other is video data transmission among terminals, mainly including video capture, video codec, video transmission, videoplayer and so on, which are transmitted through unreliable UDP protocol. This Videoconference system is in a distributed mode. Based on the Multicast network, the system can make the remote and motive members to join a conference.In detailed design and implement process, this system uses Windows Socket criterion for control messages communication, and deployed DirectShow module in Microsoft DirectX SDK and filters for transmitting video stream. First, compile the code of filters for video multicast transmission; Then add the video capture filter, video codec/decoder filter and video player filter to the system, which accomplishes entire Videoconference system.Considering the safety of the inner network, most enterprises install network firewall to protect the inner resource from unexpected destroying by the outside. Therefore, it needs to resolve the problem about throughout firewalls when writing programs about network data transmission. NAT (network address translator) is a kind of network firewall, and many companies use it as a meshwork device for safety due to its function of masking the inner IP address. It is difficult to attack a computer if the hacker does not know the inner IP address.With the fast development of Internet and the urgent limitation of the IPv4 address, it makes abroad use of NAT devices, which aims at making the IP address reuse.When using the NAT, you can only apply one legal IP address to connect your LAN to Internet. After in-depth research on the NAT technologies, this paper gives the blue print of throughout NAT firewall; it can resolve the problem existing in the Videoconference system.In conclusion, this paper deeply researches on the related technologies in video communication field, and realizes a software Videoconference system based on IP multicast, and then analysis the difficulty related to this system. The idea that uses IP multicast to transmit video without MCU and the filter which is implemented for video transmission have great reference and practicality for developing similar software in the future. For the sake of the time, this system is not perfect, and the author will improve it during afterward works. |
PDF Full Text Request