Design And Implementation Of Calling Functions For Digital Trunking Terminal Based On Public Network

Digital trunking system is a professional dispatching communication system,mainly used in government,public safety,electricity,transportation,logistics,civil aviation,petrochemical and military and other departments.Public network digital trunking system has the advantages of low network cost,wide signal coverage and rich spectrum resources,which is a supplement to private network digital trunking system.Calling functions include individual call,group call,priority call,call holding and resuming,emergency call and so on,which implement the command and dispatch of trunking system.Therefore,the research on calling functions of digital trunking terminal based on public network is of great practical value.Based on the review of research status of digital trunking system at home and abroad,calling functions of digital trunking terminal based on public network are researched and realized,the main works are as follows:1.The composition of digital trunking system based on public network and the calling functions of terminal are described.The effects of encoding and network jitter on voice quality and the effect of signaling delay on the call state machine are analyzed.The fault tolerance of the terminal is expounded.2.The software architecture of terminal is proposed.The interface between terminal and access server,the interface between terminal and media gateway,and the user interface are defined.The signaling processes of individual call,group call,priority call,call holding and resuming,and emergency call are designed.The working processes of terminal signaling processing module,PTT module,call state machine,voice module and message notification center are elaborated.The key technologies such as the fault tolerance mechanism of the call state machine and the caching mechanism are put forward.3.Based on Android operating system,signaling processing module,PTT module,call state machine,voice module and message notification center of terminal are developed by using Java language in the Android Studio development environment to realize the calling functions such as individual call,group call,priority call,call holding and resuming,and emergency call.The voice packet rearrangement mechanism and anti-network jitter mechanism are proposed to ensure the voice quality.4.The call flows of individual call,group call,priority call,call holding and resuming,and emergency call,voice packet rearrangement and anti-network jitter are tested.The test results show that the terminal software realizes the calling functions and meets the design requirements.