txFax using Zap channel

I’m am trying to send a fax (a tiffg3 file ) using asterisk 1.4 running on ubuntu out via a zap channel and ISDN to a fax machine.

i get this error:
[Jun 27 11:17:07] WARNING[20810]: channel.c:3059 set_format: Unable to find a codec translation path from unknown to unknown
[Jun 27 11:17:07] WARNING[20810]: app_txfax.c:266 txfax_exec: Unable to restore read format on ‘Zap/1-1’

can anybody suggest what configuration I am failing to do , or point me in the right direction for a howto on txfax using zap ( I’ve found plenty on rxfax using sip )

thanks ( any hints would be useful)

ISDN ports aren’t appropriate for sending fax messages. They don’t have the correct signalling.

You should consider sending the fax using something that’s designed to send the fax. Specifically a fax modem (analog) or a card like a Dialogic card (digital) with fax DSPs built into it.

Sorry if i wasn’t clear, this is a primary rate E1 trunk - Faxing is now working ( I needed to set faxdetect=both in zapata.conf before the channel definition ).
However it is not 100% reliable with broadcast fax, is there a variable I can check to tell me if the fax was successful ?