Ip Telephony Based On Sip Protocol And Implementation Of On The Phone

VoIP is one of the most important applications in the Next Generation Network. SIP(Session Initiation Protocol) is one of the signaling protocols to develop the VoIP system. SIP is simple, flexible,distributed controled and easy to be extended. As 3GPP has adopted SIP as the controlling protocol for the IP Multimedia Subsystem, the research of SIP is becoming a spotlight in the field of IP telephony.With the development of high bandwidth wireless communications, the bandwidth and QoS issue are no longer the obstacle for deploying networking and multimedia applications on mobile devices over wireless network.To develop and deploy a high performance IP telephony over mobile devices is feasible and can provide seamless connectivity to the VoIP end user.However, the current SIP based VoIP applications use C/S archetecture, which is hard to be deployed in a small group meeting situation with ease.The contribution and feature of this paper includes:1) Analysed the SIP protocol, which is one of the key technologies in VoIP. Worked out extensions for the current SIP archetecture to adapt to the peer to peer network archetecture.2) Discussed key technical issues in designing a SIP based IP telephony under windows mobile devices, designed a software archetecture with high portability.3) Designed a SIP transaction model based on gnu osip protocol stack. Enhanced the existing osip stack with an applicatin-state-machine to harmonize the signalling and media transactions. Designed the SIP transport layer which is not mentioned in the osip stack.4) Designed a realtime audio gathering and playback subsystem, with enhanced realtime audio playback quality.5) Designed a high performance session timer mechanism to support multiple session timers in the SIP statemachine.The SIP based telephony is a promising technology in the embedded and mobile environment, thus is worthwhile for future research and discussion. In the end of this paper, the prospect of SIP extension was described to provide a guideline for the futurework.