Using 2N VoiceBlue Lite VoIP GSM Gateway Behind NAT Firewall with Dynamic IP Address
09 May 2006 16:42
Using VoIP gateways behind a NAT firewall with a dynamic IP address (typical of ADSL connection) usually means checking the NAT firewall IP address whenever the connection is reopened. The VoIP gateway behind a NAT firewall uses the public IP address of the NAT firewall as a so-called 'fake' IP address. The VoIP gateway sends this 'fake' IP address to a registrar server while registering or to a SIP proxy when it sends an INVITE packet. If the NAT firewall IP address is changed, the VoIP gateway sends the 'fake' IP address in the INVITE packet with a faulty IP address and the registrar / SIP proxy replies to the faulty IP address, which means that communication is not established.
Therefore, the VoiceBlue Lite VoIP GSM gateway is capable of using the STUN service for checking its 'fake' IP address. The STUN server responds to the request generated by VoiceBlue Lite and its response contains the NAT firewall IP address ('fake' IP address). It is necessary to provide the STUN server IP address and the time of the next STUN request. VoiceBlue automatically requests for its 'fake' IP address in regular intervals as defined. The STUN service uses port 3478 and so the NAT firewall should open this port.
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