About the FAX CSID/TSID on OSX 10.6.8 Snow Leopard

Call me a dinosaur. Here it is August 2014, and I am still using an Indigo iBook G3 running OSX 10.2.8 (Jaguar) on my home network because it can be used as a FAX machine. (And, well, for the approximately biannual Internet outage wherein I need to revert to dial-up and share the connection … which works surprisingly well for most day-to-day stuff. But I digress.) I've been running the long-discontinued PageSender software which was actually pretty nice, but the other day, it failed to bother to send a PDF. I figured it was a good idea to retire the iBook for its modem duties and just buy a USB modem. I opted for a USRobotics USR5637 56K USB Modem (from TigerDirect because I've been buying stuff from them since the 1990s).

It installed pretty easily and I was able to add it as a FAX modem per the System Preferences:Print & Fax page. One thing that I noticed was there was no place to enter the Called Subscriber ID (CSID) which is usually the same as the Transmitting Subscriber ID (TSID) and what I always thought was called the "Station ID" although my physical FAX machine's instructions simply refers to "Entering your name and phone number." In short, when you send a FAX, your phone number and TSID appear at the top of the page (and you can view the CSID of the FAX you just called). But in OSX 10.6.8 (Snow Leopard), there is only a space for "FAX Number".

My first reaction was to try and install PageSender to no avail: the installer failed to start on Snow Leopard.

So then I started digging. I started a free FAX account so I could experiment. I set the FAX number to my real FAX number and sent a FAX successfully. Both the FAX number and TSID appeared as that number. Next, I took a peek at the internal options: I opened a terminal session and (well, after some digging) entered:

defaults read /Library/Preferences/com.apple.print.FaxPrefs

Which resulted in:

{
EmailFax = 0;
FaxNumber =
(my FAX number);
PrintFax = 0;
PrinterID = "
(my default printer)";
ReceiveFaxID = "USRobotics_56K_Modem";
RingCount = 1;
SaveFax = 1;
SavePath = "
(my FAX receive folder)";
"device-uri" = "fax://dev/cu.usbmodem0000001";
}

It appears, therefore, that there is no place to enter a proper CSID/TSID. Tinkering with the preferences again, I tried entering text into the FAX number field—assuming it was indeed a substitute for the CSID/TSID. Indeed, this replaced "FaxNumber" in my FaxPrefs.

I looked around for modem logs, but that wasn't an option … only some error logs existed which could be accessed through the wackadoodle CUPS HTTP interface. If you have OSX, you can probably link to http://127.0.0.1:631/ and muck around with things you probably shouldn't touch.

Another thought was to try setting the CSID directly in the FAX modem. Once upon a time, Hayes-compatible modems connected through RS-232 interfaces and had internal non-volatile memory to store settings, although back then, the S-registers could only contain one byte and it was rare to find more than tens of bytes of storage inside a modem. I found an old article on Apple.com which defined a clunky way to do it and it got me to access the modem. At first I couldn't see what I was typing, so I entered an ATE1 to enable command echo. Man, that takes me back … the first time I typed it was somewhere around 1987 and the last time was probably more than 20 years ago.

There exists a "standard" Hayes-compatible AT command +FLID="local ID" which is used to set the local ID in a TSI or CSI frame. But it's only supported with modems that have Class 2 FAX support: AT+FCLASS=? returns 0,1,8 which apparently means the USRobotics modem supports data (0), Class 1 FAX (1), and voice commands (8). The latter of which interestingly implies I could use it as an answering machine … maybe.

Now that I'm invested a couple hours in, I thought I'd crack open the modem's internal documentation. Indeed, it has no support for the +FLID command which I already confirmed. Alas, the AT commands appear to be a dead-end as well.

In the end, I decided to leave the modem alone and just use my FAX number as a station ID. It is sufficient and effective—and it certainly wasn't worth the hours of fooling around … but once I get started on a short project like this, I like to see it through to the end.

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