[asterisk-users] asterisk 1.4.X, T.38 and NAT

[Antoine Megalla]

Hi,

I have been trying to get T.38 to work with clients behind NAT for the past week but with no success.

I have an asterisk server on the public internet and several Grandstream (I tried Linksys too) HT502 ATAs behind NAT in different locations.
I tried every possible combination of NAT, canreinvite, t38pt_usertpsource entries, I even tried asterisk 1.4.19, 1.4.24.1, 1.4.25 all with the same result; Failure.

I can see the t38 negotiations, and I think the problem is in the reinvite message after T.38 detection.

Only one case is working:
Both ATAs are on the same NATed network, 
Asterisk server is on the public internet in another locations
canreinvite = yes for both ATAs
NAT = yes
t38pt_usertpsource = no

The reason I think this case is working is that the reInvite is sent with the private IPs of the ATAs, and since they are on the same network, they can find each other and continue the call successfully.

This case leads me to think that the problem is NAT related and has something to do the the reInvite after fax detection, something is being sent incorrectly on the reinvite, either the IPs or the ports.

does anyone have an idea about how to solve this problem.

your help is much appreciated.

Antoine Megalla.