| Recently, the Internet technology has been rapidly developed, and the applications based on the Internet have also been emerging endlessly, thereinto, the VoIP technology emerged and has been developed extensively. Similar to traditional phone, VoIP also requires the support of the signaling system. Currently, SIP and H.323 are the most widly used, and most influential signaling protocols in the world. Because the SIP protocol is flexibile, simple and easy to implement, it has great potential to be widly utilized, and has been considered as the core of the next generation network control protocols. Research and development of SIP have attracted significant attention in our country and aborad, and its development prospect is immeasurable.This dissertation is supported by a research project funded by an enterprise, and according to the requirements, the VoIP terminal software is designed and implemented, and the software has been used in the industry filed. Firstly, the hierarchical structure, network entities, SIP meaagaes and SIP transactions of the SIP protocol are introduced. Then the hardware of the embedded VoIP telephony is described. The hardware is based on the phone terminal produced by the word's leading chip supplier Infineon phone company, and the core part of the terminal is the second-generation IP phone chip INCA-IP2 of the Infineon company. INCA-IP2 includes two innovative MIPS CPU architecture, one of them provides a working platform for the operating system, the other is responsible for voice processing. INCA-IP2 integrates two Ethernet ports and AFE (analog front end), and it integrates the main functions of IP phone, and also provides keyboard, LED and display interface for users'control functions.Embedded operating system linux is used as the software platform, and TAPI and HAPI are used to control voice and keyboard, respectively. Due to the fact that developing a complete SIP protocol stack software is a very complex project, the open source osip2/eXosip2 are used as the SIP protocol stack module for the software developing of the terminal equipment. SDP protocol is adopted to negotiate transmission parameters for multimedia communication, and ortp protocol stack is used for voice transmission. In the design and implementation of UA, multithreading mechanism and modular programming technique are used, and a calling state machine is constructed to manage the interaction of control signaling and state transition. The realized terminal software has the functions of registering, dial-up, receiving a call and refusing a call, volume control, and the quality of voice communication is good. |
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