Any help appreciated - 1. Firewall checker shows OK, however does not seem to address anything to do with port 10000. Port 10000 for both TCP & UDP, both inbound and outbound, are forwarded to internal 3CX server (seems to be indicated below per reinvite request). 2. FaxDIRECTSDP variable set to "1" 3. 3CX Fax Server Provisioning templates (both) modified according to 12.1.2009 FAX over VOIP document in blog (tested both in original and modified formats) 4, Fax extension "888" shows registered during testing. System stopped and restarted after any change to ensure correct attributes loaded. 5. Voip provider - "NexVortex" , cited as tested/approved t38 carrier. 6. STUN is "Off" 7. Voice calls (internal and external) all work just fine. Have been unble to get fax machines to connect. Can hear tones from each, but connection never established. Nexvortex advised - "Your T.38 codec reinvite contained a private IP address in the SDP data: c=IN IP4 192.168.0.250..t=0 0..m=image 10000 udptl t38..a=T38FaxVersion :0..a=T38MaxBitRate:14400..a=T38FaxRateManagement:transferredTCF..a=T38FaxM axBuffer:10500..a=T38FaxMaxDatagram:1500..a=T38FaxUdpEC:t38UDPRedundancy.. The NAT translation in your 3CX configuration needs to be corrected. The c= string must ALWAYS contain the public IP address of your network." I had assumed that a change of this type would be covered in the provisioning template changes covering NAT. I have stated both the local and public IP addresses as indicated in the blog document. I can include logs if needed, but Nexvortex seemingly has identified the issue, and it is now a question of how to get the reinvite to point to the public Ip rather then the local. Anyone using NexVortex with fax and having success? Can you share what you ended up doing? Thanks in advance.