| With the simple and flexible advantages,SIP protocol has been gradually taking the place of the original H.323 protocol and becomes the core protocol in VoIP,thus,the research on voice gateway based on SIP becomes a hot issue.However,most recent research is put on soft terminals,and embedded terminals also have the complexity problems on the signaling control and extensive use,so this thesis designs and implements a kind of embedded voice gateway that simplifies the signaling control for the extensive use of the sip terminal.The terminal this thesis research on can make users from different locations communicate with others in voice over IP.It uses sip signal technology to set up the voice session and complete the signal control,with the SDP and RTP transport technology,the voice gateway achieves the real-time voice communication from end to end.This thesis firstly research on the voice communication technique based on SIP,which include SIP and sip signal call, real time transport protocol and media negotiation SDP as well as its packet format and application described in detail.It introduces the architecture of voice gateway.Hardware implementation,the main chip function,the process of voice signal are outlined in the hardware;System software simpley introduce embedded operating systemμclinux and emphasize on the transplanting ofμclinux's bootloader and core.The voice gateway application software design thinking and concrete realization are discussed on detail,which include its application location,running state design,task partitioning and function. The module's interface design,task process design,data structure definition are emphasized on.The transaction state machine based on message mapping is designed to solve the complexity problem on the signaling control;in the part of media session,the interface and work flow about voice processing is mainly introduced.The voice gateway SIP signal process conforms to RFC3261,and its voice quality is clear by system test.The study of subject promote to the integration of voice and data at the network edge,and realizing the existing network to the next generation network evolution is of great practical significance. |
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