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One of my earliest communications controllers, and one in which I had by far the most involvement, was VSI-FAX. This is by far the leading commercial UNIX facsimile system, with more than 40,000 server installations worldwide. At one time we supported more than 30 UNIX platforms and have since ported to Windows NT as well.
Conceived in 1988 by my then-partner David Droman, I perfected the first public demonstration late in that year, with commercial release in early 1989. Our first platform was the AT&T 3B2 due to our company's close relationship with AT&T, but over the years expanded to support more than thirty different UNIX platforms. I performed all those ports.
I have been responsible for development of every modem driver ever shipped, though the company refers to these drivers as FIMs (Fax Interface Modules). From the early days on the AT&T 3B2 - with notoriously underpowered serial hardware - to supporting the fantastic high-end Brooktrout TR114 family of intelligent fax cards, my experience in class 2/2.0 fax modems and UNIX serial communications is very broad.
Though fax modems often support flow control to regular the flow of data through them, the fax protocol does not: this means that once a fax starts to arrive, the FIM must be able to accept the data at full speed. UNIX serial input queues are typically 256 bytes large, and when they overflow, the entire buffer is discarded without notice. On a busy system, this can be quite a challenge.
Furthermore, for many years, we never met a platform with a bug-free serial subsystem. Though "regular" serial terminals and printers usually worked quite well even for low-end hardware, a modem driver exercised the serial I/O system in ways that were not typical: our software was notorious for finding bugs. All of these had to be worked around, sometimes with a great deal of effort.
Our first modem was the Fujitsu dexNET 200, which was a quasi-class 3 device (lots of smarts, easy to control), and we expanded to support the outstanding modems from Multi-Tech Systems. We had an excellent relationship with the company, and (in particular) their chief fax engineer. Multi-Tech has long been the favorite vendor for UNIX class 2 fax modems due to their peerless firmware.
The port to Windows NT meant that we could then support the TR114 family of smart fax cards from Brooktrout Technology. These multichannel devices were very intelligent and offloaded a great deal of the work from the main CPU, and were able to do much better image compression and (especially) call control.
Facsimile is ultimately based around images, and our software handled many kinds: I was responsible for nearly all imaging aspects.
Early in the product's life, I was responsible for not only development but technical support as well, and my team routinely scored "11 out of 10" on customer surveys for satisfaction with our support. We were targetting the VAR (Value Added Reseller) market, and we knew that if our VARs knew they could count on us to help them support our product, they would actually sell our product. My team learned from me: I was never "out to lunch" for a customer if I was actually in the office to take a support call, and we knew that "technical support" was as much about "support" as it was about "tech".
I was not responsible for writing the end-user product manuals, but I prepared much of the dealer training materials as well as very extensive documentation for technical support. My 100-page The Service Class 2 Specification and VSI*FAX Class 2 FIM technical manual - first written in in 1992 - is still in use today.