| In the article, knowledge and technology of voice CODEC and transmission over IP network is studied. Key applications about voice communication over IP network are described. The main protocols about voice transmit over IP network are introduced, such as TCP/IP,RTP. Basic index about voice CODEC and CODEC kinds are presented. Also, G.729, one of the voice coding protocols, is introduced.Based on the knowledge above, the author has designed an intelligent phone redial-control device and the software about voice real-time communication on IP network, according to the demands of certain enterprises and requirement for the subjectThe intelligent phone redial-control device provide not only the functions of outside phone redial inside phone, phone time recording and displaying but also the new function of outside phone redial outside phone. These make it had certain practicability. For the design of device, we use LE78D11+LE77D11, the chipset leading the field in voice CODEC, and CPC5621, the chip interfacing to PSIN network, to do the work about voice signal input, digital process and CODECAlso, we use AT89C55WD as MCU of device and control program of device is written by hardware program language C51.The software base on computer and internet as the physical platform, providing the main functions such as collection of voice data, CODEC and playing of voice, real-time communication of voice data between two computers over the Internet and file storage of voice data. The software development environment is object-oriented VC++6.0. The function of voice data collection and playing are realized by using audio service APIs providing by Microsoft to communicates with audio card. The function of communication over IP network is performed by class CSOCKET and WAVE format file is used for storing the voice datas. The software provide two CODEC ways, one is WAVE_FORMAT_DSPGROUP_TRUESPEECH, another is G.729. |
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