[asterisk-users] UDPTL T38 via NAT

[Martin]

>>>>> I've got the following setup :
>>>>> [FAX-ATA]--[PBX LAN]--[Firewall]--[PBX WAN]-----[upstream SIP]
I don't see where your NAT is in this scenario....

>>>>> Got UDPTL packet from 62.180.xx.xx:36170 (type 0, seq 0, len 32)
>>>>> Sent UDPTL packet to 172.16.0.156:4460 (type 0, seq 186, len 32)
>>>>> Got UDPTL packet from 62.180.xx.xx:36170 (type 0, seq 0, len 29)
>>>>>
>>>>> This means my outgoing udptl traffic is correctly translated, but
>>>>> somehow i'm sending 172.16.0.156 instead of my public IP address on the
>>>>> firewall.
What about externip=62.180.xxx.xxx?

>>>> Did you try t38pt_usertpsource=yes ?
AFAIK this is about a port used for rtp, not ip address...

I'm currently trying this over 2 NATs against eachother (yes, the worst 
case....) with some ports forwarded but with rare success. One of those NAT's 
rewrites a port numbers for some reason (i see the ATA registered on port 50xxx 
or so, the same for rtp. I think t38pt_usertpsource is meant for such a case...?
[asterisk 1.6]-LAN-[NAT gateway]----inet-----[NAT gateway]-LAN-[ATA]-[FAX]
Has anybody some positive experience with this?
Any idea why NAT messes up the port numbers?
Martin L