A high level of quality assurance for fax reception is required at medical clinics since faxing is the primary technology used for communication between participant's pharmacies and their prescribing physician at the clinic. A combination of SpanDSP, Asterisk call files, Asterisk MixMonitor() application, and Nagios provides a solution.
The SpanDSP project offers a modem connect tone library capable of parsing individual fax tones from an audio stream. Using this library I was able to write a simple CED tone check for nagios (based on spandsp's fax_decode test).
A remote asterisk server, with PSTN connectivity provided by callcentric, generates a call file via cron which calls the target fax number, records both channels of the call, then processes the recording with the custom nagios CED tone check.