Design And Implementation Of A VoIP/IM Technique Based Communication System And Its Roaming Method

With the improvement of living standards and consumption levels, the number of mainland China citizens going abroad is becoming increasingly enormous. However, when abroad and contacting with domestic friends, people have to undertake expensive charge of international roaming communication. This thesis proposes a communication system based on Voice over IP/Instant Message (VoIP/IM) technique to solve this issue. Communicating through the proposed system can largely decrease communication expense and at the same time reserve the communication habit of domestic friends.The proposed communication system is made up of two parts, namely, a local part and a user’s smart phone part. Specifically, the hardware of the local part is composed of a development board of a 3G development board and a PC with Linux operation system. The 3G development board and the PC are connected using a USB line. The local part can be functionally split into a telephone module, a local SIP client module, and a control module. The telephone module is developed based on a SIM 5215 chip and its evaluation board. The purpose of the telephone module is to communicate with domestic friends, and relay voice data and short messages between the phones of domestic friends and the local SIP client.Developed based on the PJSIP protocol stack, the local SIP client is used to interact with the user’s smart phone part in terms of IM messages, subscription for the Presence message of friends and VoIP calls, and to interact with the telephone module in terms of voice data and messages. The control module controls coordinated operations of the local SIP client and the telephone module, and realizes the call and short message functions of entire system. Likewise, the user’s smart phone part is composed of a roaming SIP client and a phone module. Here the former is a software installed in the user’s smart phone at abroad and the latter is just the user’s smart phone. The roaming SIP client is achieved by re-developing the CSipSimple client and its purpose is to show the caller’s real information when the user answers the VoIP call in a roaming area.With the above system, users at abroad can enjoy a whole range of communication services. They can not only initiate and receive calls, but also send and receive short messages. In addition, the problem of high international roaming fees can be addressed by transmitting voice data and short messages mainly through IP network. At last, it is the local SIM card that directly communicates with the domestic friends, and this can ward off storing the user’s new number to comply with the domestic friends’ habit.Through testing, the system runs stably, and all functions reach their design requirements. Phone calls and SMS can be well controlled and the system can do corresponding operations according to different states. In summary, the anticipate target is achieved.