We have a customer with a SPA112 on the latest firmware (1.3.3-015). We are experiencing an issue with T38 RE-INVITES with the SDP, whereby, the SPA is not inserting the public IP address on the c=IN line - it is using the private address. This ONLY happens on a RE-INVITE when fax is detected. Normal Voice calls are working fine. SIP ALG on the firewall is disabled, so the SPA is handling NAT itself with RPORT.
Call flow is as follows:
IP: 220.127.116.11 is the address of the service provider
I cannot say for sure as I don't have a Cisco T.38 ATA yet (it's in shipping).
However, I can tell you from LOTS of experience with CISCO SPA504Gs that are behind NAT, we experienced very similar problems establishing audio streams until we set the NAT SETTINGS for all of the to YES:
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