Re: flexfax: Receiving fax only

[Toralf Lund <toralf@praha.kscanners.no>]

David Woolley wrote:
> 
> > of things. - When trying to call the fax number using a regular
> > telephone one can hear a lot of noise before the normal fax interaction
> > appears to start. In other words, the modem starts sounding like a fax
> > only after tried to send some other kind of data for a while.
> 
> This is not a valid test.  You need to generate fax calling tone from
> the calling end for a fax modem to autodetect fax mode; in fact, I'm
I think you missed my point. I don't want the modem to autodetect fax
mode, I want the modem to stay in fax mode at all times.

> pretty sure that that is the only difference between a fax call and a
> 300 bps data call.  If you don't send calling tone followed by V.21
> originate carrier, the modem will probably go into a V.34 initialisation
> sequence, and when that fails, eventually fall back to V.21 data mode.
> 
> Roughly the protocol is something like:
> 
> caller sends fax calling tone
> callee send 2100Hz echo suppressor/answer tone, followed by V.21 (300bps)
> carrier
> conversation at 300 bps
> caller sends high speed training sequence (e.g. V.29, 9600 bps half duplex)
> somehow callee confirms successful train (may be by secondary channel)
> caller sends fax data using V.29 etc.
> caller and callee switch back to V.21 for end of page
> cycle repeats
> 
> The first V.21 session is the infamous Phase B and the second is Phase D.
> The V.29 portion is Phase C.
> 
> As a result, you will get rather a lot of different tone types in a valid
> fax call.

-- 
- T. Lund