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Unread 08-26-2009, 04:48 AM   #5
boatman
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Quote:
Originally Posted by hongkongpom View Post
Am I correct that you only need this if your ATA is plugged into a router?
Yes, SIP and RTP ports can change when the packet goes through the router. STUN is one way for your ATA to know it's external IP address and external SIP and RTP ports. The ATA puts these details into some SIP packets, most importantly the SDP packet from which the other party's SIP device reads your public IP address and RTP port number (the connection information), so you can get a more direct voice (RTP) connection.

If you don't want to use STUN you can forward the SIP and RTP ports instead. That preserves the port numbers through NAT traversal. As for the external IP address, your ATA can get that during the registration process.

People who have not configured their ATAs to send the correct connection information can still use Voxalot but must use Voxalot's 'symmetric NAT handling' option. These are the same people who report problems when 'symmetric NAT handling' fails, as happened a couple times earlier this year (on one proxy only).
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