| VoIP (i.e. Voice over IP) is the mostly direct achievement of the fusion of Telecommunication Network and Computer Network. Due to the features of saving bandwidth, low price, open and flexible structure, VoIP technology has been greatly developed and widely applied. Meanwhile, the service support requirement to VoIP terminal is also increased, such as Wireless Access, Video Communicaiton, Multi-protocol Support and other add-value services. However, the most development method of VoIP terminal is based on SOC solution which integrated protocol and codeing interface or low-level DSP chip currently. Although this method is easily to use, the function of it is limited and hard to be upgraded. If you need some new service support, you often need a brand-new solution.The target of design that presented in this paper is to realize an IP terminal platform in which general embedded prosessor is used as the core. The basic voice-call function based on IP platform is realized; at same time, the resource and interface are enoughly prepared for realization of IP Multi-service Terminal (voice, data, and video) based on the strong computing capability and abundant interface of general embedded prosessor as well as embedded software platform. The most new service requirement can be achieved by only interface extension and software development.The key technologies involved in VoIP was firstly analysed and summarized, including Voice Process, Signal Protocol and QoS insurance technology. SIP protocol was choosed as the signal protocol applied in our design based on the comparing of the maindream VoIP signal protocols. The network structure, protocol format, call process of SIP was detailedly researched. Based on these researches, the design and realization of a powerful VoIP terminal platform was achieved by using embedded technology. The terminal hardware was designed by using ARM9 embeded microprocesser as the core, embedded Linux was adopted as the software platform. The actual work I have done including the porting of SIP protocol stack, the development of Linux audio driver program according to Linux 2.4 driver specification and datasheet of audio chip, the development of UA software by using API of SIP protocol stack. The specification of chips in terminal, circuit design and development of software were all detailedly introduced in this paper. The test is performed according to design target, including voice-call test, protocol operation test and power consumption test.Finally, the advantage and features of this design is analysed by comparing to traditional solutions. The influence and benefit to development work of using ARM9+Linux architecture was also discussed. The shortage of current work is analyzed based on the testing result and the improving plan is submitted. The future work plans were provided, including GUI development, WLAN support, video communication and multi-protocol support. |
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