Research of NAT traversal based on RTP relay server under mobile internet environment

NAT (Network Address Translation) traversal is one of the main obstacles to restrict the development of SIP (Session Initiation Protocol). This paper analyzes problems about SIP/NAT traversal and proposes a scheme for SIP operating through NAT with the cooperation of SIP server and RTP relay server and designs the architecture of the relay server according to the characteristics of the mobile Internet environment. This paper presents the principle and the architecture of the scheme, and describes the implementation how SIP traverse all kinds of NAT.