| With the rapid development of Internet technology, voice interaction over Internet is becoming increasingly popular. VoIP (Voice over IP) technology has become one of the fastest growing technologies in Internet field. However, as the VoIP transmission medium, IP network currently exists a variety of security risks. It is that IP data packets on the network is very likely being stolen by hackers, resulting in a serious consequence that part of voice is lost or tapped. Therefore, the secure transmission of VoIP is a very important issue and becomes a hot spot of research and application. In order to protect the security of VoIP transmission, it is necessary to encrypt the voice data and voice compression at low bit rate is chosen for decreasing the large computation of encryption. AMBE is a kind of voice compression coding algorithm based on MBE with high voice quality, low coding rate, background noise resistance and stronger anti-interference ability. The algorithm is embedded into the microchip AMBE-1000 manufactured by DVSI company, which is a kind of voice codec chip with 2.4kb/s at the lowest rate.The system in this paper is based on the hardware platform which consists of a low-bit-rate voice compression chip AMBE-1000 and an ARM-core-based embedded microprocessor. The system works on Linux platform, depending on cross-compile development environment. For the intercommunication with other SIP equipments, application programs are developed on the oSIP protocol stack which is transplanted to the Linux platform. It has accomplished the key management of VoIP encrypted transmission through SIP extended functions. A simple encryption algorithm is applied over ARM. Testing and performance analysis show that the actual compression rate is less than 4.8kb/s and the system realizes high voice quality. |
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