Inbound FAXes are processed in two stages as depicted in Figure 37-1. In the first stage, a detached process running the channel program FAX_TO_DATA accepts from the FAX modem the raw data constituting a FAX. This data is then handed off to the DATA_TO_BITMAP channel. In the second stage, the DATA_TO_BITMAP channel, running in the PMDF queues, processes the raw data converting it to a specified image format and then either sends it as e-mail to a designated address, spools it to a printer queue, or stores it as a file in a designated directory.

It is important to keep in mind that received FAXes are nothing but bitmaps and contain no special, machine readable information indicating to whom they are addressed. DTMF (Dual Tone, Multiple Frequencies) or DID (Directed Inward Dial) techniques may be used to implement automated routing of received FAXes. Presently, the ZyXEL series of modems and the DCE FaxBox/30 are the only FAX modems supported by PMDF which supports DTMF or DID routing. See Section 37.3.3 for further details.

Short of DTMF or DID techniques there are, at present, no reliable, automated techniques for routing received FAXes: the bitmaps comprising each received FAX must be viewed in order to determine who their intended recipients are. This does not mean that some automated processing may not be attempted. Indeed, PMDF-FAX provides a hook for those sites wishing to undertake such endeavors. This hook is explained in Section 37.3.5.