ado@elsie.UUCP (Arthur David Olson) (12/04/88)
We have Hayes 2400-baud modems that are used for both dialin and dialout. If I use the commands AT&D2 AT&W with the Hayes, things are set up so that whenever DTR from the computer drops, the modem "hangs up, assumes command state, and *disables auto-answer*" (emphasis added). This is a Good Thing; it means that when we stop the computer to do backups (or when the computer stops after a mid-night power outage and the reboot fails) the modem can stop answering the phone, avoiding useless call charges to other systems. If I use the commands AT&D3 AT&W with the Hayes, things are set up so that whenever DTR from the computer drops, the modem resets; "note that initializing the modem recalls the user profile. . ." This is a Good Thing; it means that after someone logs in at 300 baud and hangs up, the modem can revert to 2400 baud (if you've set that up in the user profile) so that the next caller can establish a high-speed connection. (The modems do dialin and dialout using Chris Torek's scheme a la SunOS 4.0. So fiddling with the "login:" message to rejigger the modem is out; the message won't be sent to the modem until carrier is detected. This also means you don't want to have the modem reset to non-auto-answer mode; you'll never get a chance to turn auto-answer on.) My ideal would be to have the modems * not answer the phone if DTR is absent * reset whenever carrier detect disappers though this ideal seems out of reach with the equipment in hand. My okay would be to have the modems * not answer the phone if DTR has dropped * reset whenever DTR drops --that is, combine the best of AT&D2 and AT&D3. While there are software approaches to dealing with the situation, I'd like to do things in hardware to make things easier at software upgrade time. If you know how to achieve either my ideal or my okay in hardware, I'd appreciate hearing from you by mail. -- Arthur David Olson ado@ncifcrf.gov ADO is a trademark of Ampex.