8.3. fax passthrough with BRI Cards [under construction]
The utility program capifax, which is part of the capi4linux package, contains a bug: it uses the ISDN service designation "SPEECH" for transmitting fax data. In fact, "SPEECH" shall only be used for audio transmissions (eg. ordinary phone calls). The correct ISDN service designators for fax transmission are "FAX23" and "AUDIO31KHZ".
in hylafax, there is an option to accept speech anyway. in capi.conf change the option AcceptSpeech to 1.
Warning, if you are using chan_misdn, then preemptive kernel has to be disabled. (otherwise when you start asterisk, asterisk will hang up after loading chan_misdn). Possible also SMP support has to be disabled.