dave@onfcanim.UUCP (12/01/87)
I have "Call Waiting" on my phone line. Occasionally it might come in handy when I'm talking to one person and someone else calls. The main reason for having it, though, is so people can get through to me when I'm using the line with a modem. With the old, dumb 1200 bps modems, this works perfectly - the "beep" produced by an incoming call caused the modem to lose carrier, hang up, and then the phone would ring from the incoming call. I generally didn't lose any work either, since vi, mail, rn, and most other utilities do something reasonable on carrier drop. However, error-correcting modems don't seem to hang up from these short interruptions of carrier. Nor do you seen garbage on screen to warn you of what is going on - the modem just asks for a retransmission of the damaged data and continues on. Meanwhile, the person calling just hears a ring signal (rather than the busy signal they'd get without Call Waiting), causing them to think I'm not home rather than that I am home and they should try later. The two modems I've specifically seen this with are the Hayes V-series Smartmodem 2400 and the Telebit Trailblazer. The Hayes is configured with a carrier-loss-to-hangup delay of 1.4 seconds by default, which I reduced to 0.5 seconds, but it still didn't hang up. I tried reducing it below that figure, but I stopped using the modem before I found out if that worked. The Telebit modem doesn't hang up even with the carrier-loss-to- hangup delay set at 0.2 seconds; when it hears the beep it just does an equalizer retrain and continues on its way. I suspect that the register may only control hangup in non-PEP transmission modes. I don't know what to do about this, other than get a second phone line ($15/month). This is just a public service message to those who have one of (error-correcting modem, Call Waiting) and thinking of getting the other: they may not interact the way you'd like. Dave Martindale