Design And Implementation Of An Agent Device Based On VoIP/IM And Mobile Technology

With the development of mobile internet technology, more and more people choose to use instant messaging (IM) applications on smart phone. However, for the great mass of the second-generation (2G) networks users, the quality of Voice over Internet Protocol (VoIP) has fallen sharply due to lack of network bandwidth, thus affecting the user experience. In order to solve the above problem, this paper proposes a method to design and implement a communication agent device.The agent device includes two main blocks, namely, a host and a mobile client. The mobile client is a TCP client and is implemented by Qt language on the Android platform. The host including a PC and a3G module can be divided into four function modules which respectively are a telephone module, a control module, an IM client and a TCP server. Each function module on the host is developed on PC under Linux operation system. The telephone module fulfils the function of delivering voice data between the IM client and the device user’s smart phone through developing the3G module. The IM client is implemented based on open source PJSIP stack and is used in the process of IM to accomplish basic functions as login, VoIP and so on. The TCP server communicates with the TCP client on a user’s smart phone and forwards IM requests from the TCP client to the control module. In addition, buddies list and their presence status as well as incoming instant messages on the IM client are sent synchronously to the TCP client through the TCP server. The control module receives requests sent from the TCP client and fulfils the corresponding functions by controlling the operations of the telephone module and the IM client.By implementing the above agent device, users can enjoy a fluent VoIP communication under the2G networks with a TCP client installed on their smart phones. In addition, other IM functions, e.g. instant message communication, can also be realized. In the process of IM, low bandwidth occupied information such as IM requests and instant messages are transmitted via GPRS network on device user’s smart phone. Instant voice which requires relatively high bandwidth is delivered to the user’s smart phone via the telephone module in the form of circuit-switched (CS) voice, thus achieving the goal of excellent voice communication.After testing, the device runs stably and all functions reach the design requirements. The result shows that the device can meet the needs of2G mobile users and provide fluent IM service.