Research Of Embedded Audio Transmission System Based On SIP Protocol

With the development of communication and network technology, SIP has been concerned more and more for its simplicity and flexibility, which gradually replaces H.323 protocol and becomes the core VoIP signaling protocol. Meanwhile, applications of embedded system have extended from industry control system to consumer electronics with the development of embedded technology. The combination of embedded technology, communication technology and network has been paid more and more attentions. Embedded VoIP terminal will be an important application of embedded system. Therefore, we design and implement an embedded SIP terminal based ARM9 in this paper.Firstly, an embedded SIP terminal is designed, which is based on the detailed analysis of SIP architecture, message mechanism, SDP, RTP, the secure problems faced by SIP, and combination of embedded technology. We adopt S3C2410X ARM9 chip as core controller and Linux operating system as development platform. Terminal software includes three modules, i.e., SIP stack, media processing module and SIP UA module. SIP stack MySipStack suitable for embedded environment is introduced to SIP protocol. Media processing module is achieved by RTP transmission module and speech processing. We also design SIP UA based on API specification of SIP protocol stack. Finally, the consistency, interoperability and performance of the terminal are evaluated according to the design objective. Experimental results show that our approach is feasible in function, interoperability, and implementation process.Secondly, STUN, a NAT traverse method for client, is studied. The major items involved include STUN workflow traverse the NAT, SIP signaling and media flow traverse NAT. A solution for NAT traversal based on combination of STUN and TURN method is proposed, because STUN scheme can not traverse the Symmetric NAT. In the end, the test environment is designed to evaluate the method. The experimental results verify the method and can implement SIP traverse to all types of NAT, while achieving better performance.