Fax and Analogue phone on a single phone number

Question

How does this work? If I have a single phone line, say 0207223333 and on the line I have a BT splitter with an analogue phone and a fax connected. If I was then to dial that number, how would it distinguish to dial the phone or fax? Or is this not possible, what would happen?

Answer 1

IIRC, the originating FAX is supposed to emit it's carrier tone as soon as the connection is made (whereas an originating data modem waits for the answering side to emit a carrier tone first).

So an answering device can listen very briefly to the line and determine if it's FAX or voice.

Answer 2

as i understand it (which may well be badly!), in the same way that a call can continue to an answerphone, if the incoming call goes unanswered it can begin to initiate a fax.

I think that's why you can buy combined fax/phones which ring the phone section as a call comes in before the fax itself begins.

The bit i'm unsure of is if that were true then why on a sending side do they have to hit a button to start the fax. Perhaps that's picked up by the other end listening out for it.