Many research activities have been provided to allow Session Initiation Protocol (SIP) based communication in Peer-to-Peer (P2P). We have contributed to these activities by proposing a scalable proxy topology building and routing in P2P SIP network where SIP location service is integrated in proxies that run over peer entities. Therefore as SIP cannot work efficiently through a NAT (Network Address Translation) device without using a specific NAT traversal mechanism, our proposed architecture needs an efficient NAT traversal technique which can work easily and make end-to-end communication effective in our framework by meeting our previously defining requirements. This paper provides a suitable technique to our P2P SIP framework for SIP signaling and media flow. Our NAT traversal solution proposes an implementation of a smart SIP registrar server which stores the client end device's public contact information (IP address and port) instead of its private address and maintains this public address in the NAT device table. This approach allows the proxy node to always send the SIP signaling message to the correct address by checking the Registrar server before each transmission. To enable media flow to be exchanged between the two SIP clients, we use a media relay located in the public network. The proxy server of the originator of the signaling message is allowed to replace suitably the private addresses in the message body by the public addresses of the media relay. We provide some relevant experimental results to show that the approach is feasible.
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