[asterisk-users] dahdi fax catch-22

[Greg Woods]

I've got a Digium Wildcard TDM410P with one POTS line and three
extensions. One of the extensions is connected to a fax modem. This kind
of works, but there's a gotcha. If I set faxdetect=incoming in
chan_dahdi.conf, then incoming faxes do get routed to the modem and this
all works, but outbound faxes fail, with a message like this:

[Oct 29 21:57:09] WARNING[16732][C-00000000] app_dial.c: Unable to
create channel of type 'DAHDI' (cause 17 - User busy)

If I set faxdetect=no, then outbound faxes work, but of course incoming
faxes do not get routed to the modem. I'm guessing that what is
happening is that the "outbound" call coming in from the modem's channel
is an "incoming" call on that channel, asterisk detects the fax and
tries to route it to the same channel, resulting in busy. 

Is there any way around this catch-22? Is there some way to set
faxdetect=incoming only on the one POTS line channel?

The only alternative I can think of would be a kludgy Radio Shack-style
solution like a manual switcher, that switches the modem between the
connection to the dahdi channel (receive) and a direct connection to the
POTS line (send). I'd really like not to have to resort to that.

Thanks,
--Greg