I’ve been deploying a lot of CUBE environments of late with faxing working from the T.38 protocol. I did want to jot something down regarding faxing to the PSTN via ISDN using an ATA190 registered to CUCM (doesn’t really matter what version) and connected the Voice gateway via a SIP Trunk.

I’m based in Australia and the fax settings I’ve found to be most successful as follows.

ATA190 Device Configuration page in CUCM

•  Ring Voltage = 70V

• Ring Frequency = 25Hz

• Fax Mode = NSE Fax Pass-through g711alaw

 Voice Gateway (Cisco IOS)

Under the Voice Service Voip Menu.

• modem passthrough nse codec g711alaw

CUCM SIP Trunk configured as per normal, no special configuration. I have aLaw configured, I found  uLaw (which is also acceptable in Australia) was working for outbound faxing but not for inbound faxing, however I have had some case where the opposite is true.

Just a matter of making logical/strategic changes to the faxing configuration to ensure both directions are operating correctly.