Design And Implementation Of SIP Client Based On Mobile Terminals

In recent year, As the rapid development of network technology, mobile VoIP has showed up with a strong potential. The marketing research and investigation institute ON World has predicted that by the year 2011 the number of the world mobile VoIP users will be more than one hundred million. Through mobile VoIP, users can pay much less toll fee for calling as well as enjoy the feelings of this mobile communication. The functions of mobile VoIP are embodied by the SIP client programs running on the mobile terminals, however, the implementation of that is quite difficult, for one reason, the hardware resources are rather limited, that is, the low calculating ability of CPU, the precious memory. For another, there are dozens of operation systems, and the huge difference.Besides, the volume of the mobile terminals restricts the resolution and the operating manners which are mostly touchscreens and keys.The SIP client was designed to contain five modules: PAL(Platform Abstraction Layer), SIP stack, media stack, function wrapper and UI. The PAL is the base of Cross-platform, it implements the abstraction of the operating system APIs and data types, otherwise, it provides an independent memory management mechanism which will help the effective use of memory and avoid memory leaks. The SIP stack makes some improvement based on pjsip so that user can do the register without manully input the realm parameter. The media stack adds optimised G.729A to pjmedia and do some other improvement. Furthermore, it adjust some parameters of the media stack to improve voice quality. The function wrapper wraps the sip stack and the media stack. Furthermore, it implemet some other functions like playing file, generating digit tone, playing ringback tone, reading and writing ini-file, etc. User interface is developed using C++ and is closely related to the operating system. The UI design as much as possible to follow the style of the original operating system at the same time pursuit the high ease of use.Based on all the design work, this paper implements the SIP client program running on the Windows Mobile. This program has great portability, it only needs some interface programming before transplanting to Symbian,Linux,etc. Besides, it has strong scalability for increasing new functions like instant messaging.