What factors do I need to consider when integrating an analog fax on the cisco pbx

unknown

I have fxs ports to give dial tone to the fax. But will I need a dedicated line over a sip trunk for the fax depending if the provider accepts fax over the trunk. What do I need to take into consideration when adding a analog fax to the cisco pbx to send and recieve faxes?

shodown

Most of my designs that involve sip trunking I use a FXO port for a line for the faxing. I've been burned to many times with provideres saying it will work, but then it never comes through sometimes its the customer(calling the provider getting all there calls G729 and forgetting they have faxing) or the provider where the conversions in the network just aren't reliable enough for SIP.

to sum this up

Get a FXO line for faxing
with a FXS its pretty stright foward most of the time the tweaks take place on the fax itself.

Also is this a CME system or a full blown cucm. I have some follow ups to ask.