I have a fax server connected to my UCM 6.1.4 cluster via a sip trunk. It is using T.38 protocol. Most things are working OK but I have one customer's fax number that I am unable to connect when sending. I can send a fax to this machine from an external fax machine, but not from the fax server. If I call the machine from a regular phone, it answers but I get nothing but dead air. This leads me to believe that the customer is using a line sharing device of some kind, and it is looking for a CNG tone before sending the call to the fax machine. To test this, I placed a call from a regular phone and then hit the 1 button a couple of times. I got a message stating "1 is not a valid option."
What is strange though, is that I can send faxes to this customer from my lab call manager / faxcom solution. It goes through every time. This would imply that the CNG tone is being sent from the lab solution.
Who generates this CNG tone? Would the fax server do it, or does the gateway do it once it realizes that this is a T.38 call? The gateway in the lab is a 2811 with a PRI connection. The gateway in production is a 3845 with several PRI connections.
Any help will be greatly appreciated.