| Most VoIP systems are based on SIP or H.323 comunication controlprotocols. The Session Initiation Protocol (SIP) advanced by IETF has itsdistinct advantages: it is very concise in the structure, easy to be extended andmore suitable to access the Internet. It can control the media gate way and thuscontrol the PC call streaming in a multi-domain network effectively. Under thecircumstance that Softswitch is to become the next generation technology ofnetwork switch, SIP is considered as the kernel protocol in access layer of theSoft switch technology, and it has been successfully applied to severalrepresentative communication systems due to the interest of lots of famoustelecommunication companies.For safety or some other reasons, net are made into subnet. At theborderline it places NAT/FW, which is a challenge to SIP call. How SIP UAtraverse NAT or Firewall, and successfully connect another UA in other sonnet is a problem.The problem, along with some main ideas of its solution is introducedhere. This article focuses on the resolution of this problem for SIP.First, after the article research for several modes of the sign traversingNAT/FW, we found the same problem in the modes that it is indispensable toupdate the existent equipment and software for holding on requirement. This isthe most difficult in practice.The article putted forward the proxy mode based on deeply research forwork mechanism and network structure of SIP. After comparison, the proxymode don't need to change any network equipments and software, it is veryapplicable and effective and may connect different types users.Second, SIP R-proxy was designed and realized based on the proxy mode.The R-proxy has the functions of proxy server, registrar server and relayingSIP information and media stream.Three, SIP video terminal was realized. The R-proxy was examined totraverse NAT/FW by SIP video terminal. |
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