Changing Transfer Capability

I am currently experimenting with trying to get a modem to dial out through our system.

The analog line is provided by a Vega 50 analog to IP gateway and is all set up for Data transfer however when the call is initiated it comes up with the following in Asterisk:

– Requested transfer capability: 0x00 - SPEECH

The modem handshake therefore fails, sometimes it connects but not for long. Sometimes Asterisk detects a CED tone and disables the echo canceller however not every time.

Looking at the below link suggests there are different settings specifically for fax and data calls but I have no idea on where to start with this. I don’t want to change anything that could impact our SPEECH calls as that side of things is working beautifully.

Is there context that I can create that either every call from a particular extension or to a particular number changes the transfer capability?

exten => 123,1,Set(CHANNEL(transfercapability)=SPEECH) … B-361.html

Any guidance appreciated