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VoIP NAT

221 bytes added, 21 January
Mention configuring the public address, or using a STUN server to obtain it
*The Technicolor broadband routers we used to supply with Home::1 provide a full SIP/NAT ALG which means they work such that neither the phone nor our call server know NAT is in use. This appears to be a well implemented ALG and just works.
*Using a FireBrick FB2700 providing NAT has no ALG and does simple dynamic port forwarding of outgoing UDP connections with a default timeout of over 2 minutes. This also just works as the call server recognises the NAT and sends one minute keep-alive packets to hold the NAT session open, as well as sending symmetric RTP response packets.
*Some phones allow the public IP address to be entered in the configuration (e.g. Grandstream products have a "Use NAT IP" option).
*A STUN server enables a phone to be told its public IP address (e.g. ''stun.aa.net.uk).
*Other cases where testing has been done have usually required one or other approach, and in some cases required "NAT assist" to be disabled on phones or routers to allow the correct operation.
*SIP and NAT requires the call server, NAT device and phone to all play nicely and can still mean problems. There are a few specific cases we have tested and found reliable, but we cannot guarantee it will work in all cases or without some specific configuration settings
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