Implement Of Real-time Transport Protocol Based On DM642 And PC Platform

Computer communications and network technology have achieved rapid development in the past 10 years, especially in the 1990s. However, the communications systems and networks are designed for conventional data applications, such as FTP file transfer, e-mail; and do not take into account the large amount and high real-time demand of real-time data transfer, therefore, the traditional IP network seriously affects the applications of real-time multimedia over Internet. To make up for the shortcomings of the Internet in real-time data transmission, IETF's A/V TWG (Audio/Video Transmission Working Group) developed a real-time data transmission protocol--RTP (Real-time Transport Protocol, RFC 1889) in 1996, and the improved version of the RTP (RFC 3550) is developed in July 2003. RTP provides support for the end-to-end real-time data service (such as interactive Audio / Video).At first, the paper studies the development of video communications, and analyses that traditional IP network is not suitable for the real-time data transmission. Second, RTP is more suitable for real-time data transmission, and the research on implement of RTP is necessary. RTP is implemented respectively according to DM642 platform and PC platform's own characteristics. Ensure that the real-time video data can be transmitted reliablely through Internet. Based on this, a kind of RTP-based QoS (Quallity of Service) adaptive mechanism is proposed and implemented. The experiments proved that the mechanism is effective. The full text is divided into six chapters. Main tasks as follows: The first chapter analyzes the development of video communication. Traditional IP network is not suitable for transmission of real-time data. To make up for the shortcomings of the Internet, RTP is proposed by IETF. The research on implement of RTP is necessary. The first chaper also introduces the content of the paper.The second chapter describes the basic design of RTP, including RTP and RTCP (Real-time Transport Control Protocol). This chapter introduces terms anddefinitions about RTP (such as RTP session, RTP port), the structure of RTP packet and RTCP packet, and main function of RTCP.Chapter 3 shows the characteristics of the DM642 development platform and PC platform, and describes the key technologies used in the system. Including DM642 chip, the BIOS system, NDK network development kits, the windows socket programming, and multithreaded programming methods.Chapter 4 is the core of this paper. This chapter describes the design of video communication system using RTP and the realization of every module. RTP is implemented by programming on the DM642 platform and PC platform, and a video communications system using RTP is established. The entire system is based on client/server model, including the following three parts:1. DM642 Video Server: It consists of analog camera and DM642 multi-channel real-time image processing platform. The server software running on DM642 platform completes real-time video capture, video compression, video compression stream segmentation and RTP packet encapsulation and transmission. Besides, the system analyses the status of network according to RTCP receiver reports, then changes transmission rate accordingly by changing video format. The server software on DM642 platform is running on DSP/BIOS, and it is designed refer to the RF5 (Reference Framework Level 5), including video data capture task, video encoding task, data transmiting task and feedback information processing task. Every task is an infinite loop. Task waits for and processes data in the loop, and sends data to other task. To achieve synchronization, SCOM mechanism is used for communication between tasks. So the video data capture task, video encoding task, data transmiting task and feedback information processing task can work concordantly.2. Network communications equipment: The transmission channel and related equipment.3. PC client: Computer connecting to the network.The client software runs on PC platform. PC receives the RTP packets from DM642 video server, assemblesRTP packets to a frame, decodes and displays the image; meanwhile it sends feedback information in the form of RTCP receiver report to DM642 video server. So DM642 server can make judgments of network status based on feedback information, and change rate of transmission.PC's program uses multithreading, including receiving thread, video decoding and displaying thread and session maintaining thread. Receiving thread is developed using SOCKET technology, and it deals with receiveing of RTP packet and RTCP packet from DM642 video server. When receiving RTP packet, the receiving thread will unpacktize it and transfer the video data to video decoing thread. Video decoding and displaying thread will decode and display the image to user. When receiving RTCP packet, the receiving thread will unpacktize it and transfer the report to RTP session maintaining thread. RTP session maintaining thread maintains statistical information during a RTP session.In chapter 5, a RTP-based QoS adaptive mechanism is proposed and embedded in the video communication system which described in chapter 4. The mechanism does't need to change the existing RTP, and achieves end-end feedback information by RTCP receiver report. The sender can know the receiver's status by the feedback information timely and compute the network throughput by formula, so as to adjust video format timely to change the transmission rate then better adapt to network conditions.Chapter 6 makes a summary of the paper, and points out the direction in the future.In summary, this paper presents the implementation and application of RTP in video communication system. A video communication using RTP is implemented on TI DM642 platform and PC platform. Based on this, a RTP-based QoS adaptive mechanism is desingned and embedded in the system. Experiments prove the mechanism is effective. At present, there are many inadequacies in the system, and in the follow-up work will be further improved.