Research And Implemnetation Of Embedded VoIP Terminal Based On PXA255

VoIP technology that transmit speech over internet is the core technology of new value-added services over current network. At present, the research on VoIP focus on two fields. One is developing new ways of VoIP implementation combined with embedded system and expanding the area of application, such as intranet, wireless terminal, new structure, IPBX and so on. The other is about how to improve the quality of current VoIP communication, include using high performance DSP, good control signal, real-time technology of speech, low-rote coding technology, security and so on.Considering the development direction of VoIP and the hot point of embedded system technology, this project tries to design and implement a VolP terminal. At first, the hardware of embedded terminal was designed which consist of a micro processor-PXA255, network controller, speech codec, LCD and touch screen. Then the embedded Linux system environment was build to support application software. Base on the above hardware and soft environment, the software of VoIP client was designed and implemented. Taking the protocol stack H.323 as reference, the signal that including login, registration, call, communication controller, system controller was designed and implemented. R also supports short message communication and user management. A kind of low-bit rate codec was embedded in system to economize network resource. To insure the quality of communication, a kind of adaptive signal-wobble elimination buffer was designed and implemented basing on speech signal transmitted by JRTP. At last, with the Qt/e kit, a friendly and pretty GUI was developed, which could supply perfect management of system to users.Because of the high performance of micro processor and linux, combining with optimized software, the embedded terminal owns predominance of high reliability, expansibility, transportability and low cost with high performance. It is advanced and useful in many fields.