Analog Fax Modem

I switched to freepbx.
I have a ISDN Pri.I need some help with my Analog Fax modem.
I am very confused reading all the posts.What i need is when a call comes in ,the agent picks it up.If its a fax call he transfers the call to an extension were my modem is.(connected to a fax server).
Do i need a fxs/fxo gateway to connect my modem ?
Is this going to work that way ?

TIA for any help.

version 4.211.64-7
someone please share his knowledge.