Research And Implementation Of VoIP Voice Gateway Base On A Low-Cost DSP

The rapid development of computer networks has witnessed an increasing appearance of real-time multimedia services based on the IP package network in recent years. Owning to the abundance of service platforms as well as the low price advantage, VoIP technologies are able to provide strong and valid guarantees for voice communications over a long distance, thus becoming a hotspot in nowaday's technique researches.The core equiment in the VoIP system is IP Gateway, in which digital signal processors (DSP) are widely used in order to guarantee voice communications. The signaling technique also plays a crucial part in the development of VoIP and among them two most widely used are H.323 and SIP. The SIP protocol is designed to meet with the evolving direction of VoIP and future networks and is believed to have a good market propect due to its embodiments of Internet system structure and the simplicity, extensibility and realizability of its text-based signals.The paper outlines a plan in which a VoIP voice gateway is developed based on a low-cost DSP chip-AR1688. AR1688, provided by Palm Micro Co., Ltd for VoIP solutions, is a SOC that highly integrates a Micro Control Unit (MCU) and a high performance Digital Sigal Processor (DSP) with the advantages of small size, low power consuming and low cost. The AR1688-based VoIP Ethernet voice gateway designed in this paper will enable small enterprises and home users to make their IP calls with plain old telephone service (POTS) by means of LAN accessing rather than PSTN.The paper illustrates VoIP theory basis that has things to do with product design and analyzes voice coding and decoding technologies, communication protocols, VoIP system formation and what a VoIP gateway demands. Then priorities are given to the AR1688-based VoIP Ethernet voice gateway developing process which includes hardware and software design. Circuit schematic plotting and Printed Circuit Board (PCB) plotting are described in the hardware design part while the software design part includes the status definition of AR1688 main control flow, the design of DSP-drived real-time voice processing module, the pick and transplantation of the SIP protocol stack and the design of Soft Gateway. Finally results are given showing that such designed VoIP gateway is able to work steady, successfully achieving what was expected after circuit tests, module function tests and integrated tests.