摘要
可视电话使人们在通话时能够看到对方影像，是一种发展前景看好的多媒体通信设备，它不仅适用于家庭生活，而且还可以广泛应用于各项商务活动、远程教学、安防监控、医院护理、医疗诊断、科学考察等不同行业的多种领域。随着科学技术的进步和人民生活水平的提高，打破了原先的技术条件和经济状况的限制，大规模发展可视电话成为可能。尤其是面对突如其来的“非典”疫情，各大通讯公司以最快的速度为省城各大医院开通了可视电话，协助全社会战胜“非典”病魔起着很大的作用。
为此，我们进行了基于H.323和Trimedia TM1300处理器芯片的IP可视电话系统的设计和实现。H.323是ITU—T推出的用于IP分组网络的多媒体通信终端协议，Trimedia TM1300处理器芯片是Philips公司推出的一种基于多媒体应用的具有VLIW指令，含有128个通用寄存器，32位的高性能处理器，它能够通过编程实现通信协议，完成高质量的音频、视频处理和网络接口。我们设计的IP可视电话系统主要集中在音视频编解码的实时实现、H.323协议栈的实现、一些必要的网络通信协议如PPPoE、SMTP、POP3、IMAP、DHCP等实现，在保证压缩音视频的QoS质量的同时，尽可能地发展各种增值业务服务如邮件系统、浏览网页和组成家庭智能系统等。
本文主要针对作者在实现IP可视电话系统中所从事的研究工作而展开的，将重点放在IP可视电话系统中TCP／IP协议栈在pSOS+上的移植、网络通信协议如PPPoE、PPP、SMTP、IMAP、POP3、DNS、DHCP等协议的实现、H.263视频编码及其码率控制算法研究、视频编码中基于程序结构和7M1300 DSP专用指令的优化方法，同时初步介绍H.323、SIP、H.264及嵌入式系统中的实时操作系统(RTOS)pSOS+。在第一章中先简介IP可视电话系统的发展历程、前景和软硬件框架结构，然后简要说明作者的研究工作。在第二章中阐述了ITU-T的H.323、IETF的SIP多媒体框架协议以及它们之间的比较。在第三章中阐述了基于IP的网络通信协议的实现，主要是OpenBSD中的TCP／IP协议栈在pSOS+上的移植和PPPoE、PPP、SMTP、IMAP、POP3、DNS、DHCP协议、嵌入式Web服务器的实现，然后介绍如何利用RTP／RTCP来检测网络有效带宽，其中的网络有效带宽就是在第六章提出的码率控制算法中确定目标帧率的依据之一。在第四章中主要阐述了H.261、H.263、H.263+标准的内容及其比较、H.264标准及其与H.263编码性能的比较。在第五章中阐述了H.263视频编码中基于程序结构和TM1300 DSP专用指令的优化方法。在第六章中详细阐述了视频编码中的关键技术之一的码率控制算法，其中提出了一种简单、有效、适合网络带宽抖动的自适应可变帧率的码率控制算法。
IP video phone provides face to face communication service and is a hopeful product. It is not only fit for the family life, but also widely applied in various business affairs, long-distance teaching, secret monitor, hospital nurse, medical treatment , science research and other fields. Now with the developing of modern science and technology and the improvement of living level, the technology and the finance status limits are overcomed and the time of developing video phone is coming. It was well known that various communication companys presented lots of hospitals video phones in time when sars arised suddenly, which played an important role in contributing to the overcoming of the disaster.
So we design a video phone system based on H.323 and Trimedia TM1300 DSP. H.323 is the standard about multimedia communication released by ITU-T. TM1300 including a very powerful, general-purpose VLIW processor core (the DSPCPU) that coordinates all on-chip activities is a media processor for high-performance multimedia applications that deal with high-quality video and audio. The DSPCPU implements a 32-bit linear address space and 128, fully general-purpose 32-bit registers. The video phone system designed by us is mainly the real-time implement of A-V codec the implement of H.323 protocol stack and the implement of the network communication protocol for example PPPoE SMTP and POP3 etc. So we not only ensure that the QoS of the A-V codec's datum, but also develop the increment services for example E-mail system and browser etc.
The paper will emphasis on the graft and realization of the internet protocols H.263 video codec rate control algorithms for video encoder and optimization methods of the codec based on TM1300. H.323 SIP, H.264 and pSOS+ are also simply introduced. In the first chapter, the developping history and foreground of IP video phone and the system framework of the video phone including hardware and software framework are introduced. Then the research work is also introduced in this chapter. In the next chapter, H.323 SIP the difference of H.323 and SIP are introduced. In the third chapter, the graft of TCP/IP in OpenBSD on pSOS+ and the realization of the internet protocols including PPPoE PPP SMTP POP3 IMAP DNS DHCP, embedded WEB server and how to estimate network state used by RTP/RTCP are introduced. In the fourth chapter, firstly H.261 , H.263 H.263+ standards and their differences are introduced. Secondly the improved H.264 standard and the performance comparison of the H.263 and H.264 are introduced. In the fifth chapter, some optimization methods about program structure and optimization methods based on TM1300 are introduced. In the sixth chapter, the research of rate control methods which is the most difficult in my study is introduced.
引文
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