VoIP NAT

NAT on our Voiceless platform does work in many cases. However, due to the nature of NAT, and the numerous implementation and 'fixes' and 'bodges' in routers, it can be tricky to get working. Lots of the phones that we've tested do just work without the need for an ALG, Stun, Port Forwarding etc., but other network equipment (i.e. the router) may get in the way.

We'd always suggest using public IP addresses for VoIP devices.

If you do want to use NAT, then here are some tips if you are struggling:

Disable UPnP on routers
Disable SIP ALG on the router (or try enabling)
Disable Stun settings on the VoIP phone (or try enabling it - stun.aa.net.uk can be used)

If NAT works, then well done, but if not we cannot guarantee to be able to make it work. We can provide broadband lines with constant quality monitoring and public IPs that can be used for VoIP - even multiple lines through different back-haul suppliers for extra resilience. Do speak to us.

NAT is not officially supported, but generally can be made to work.

The technicolor broadband routers we 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.

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.

Further information: http://aa.net.uk/kb-telecoms-sipnat.html