Path: utzoo!attcan!uunet!hayes!tnixon
From: tnixon@hayes.uucp (Toby Nixon)
Newsgroups: comp.dcom.modems
Subject: Re: MODEM AND CALL WAITING
Message-ID: <2866@hayes.uucp>
Date: 12 Nov 90 13:04:48 GMT
References: <11464@j.cc.purdue.edu>
Organization: Hayes Microcomputer Products, Norcross, GA
Lines: 46

In article <11464@j.cc.purdue.edu>, zhou@brazil.psych.purdue.edu
(Albert Zhou) writes: 

> Since my phone is always busy with modem, I ordered a call waiting recently.
> However, it doesn't work well. Two problems:
>  	(1) The computer does not generate a beep as the telephone does
> when there is another call coming. Instead, the screen outputs some strange
> characters which can sometimes be ignored, especially when you are not
> really attending it.  Nevertheless, this is easily solved by writing a
> simple clock-interruption program to capture those characters and generate 
> some beeps.

Except for a very few modems (like the Hayes Personal Modem 1200 and 
2400) which have been specifically designed to handle Call Waiting, 
most modems consider the call waiting beep to simply be "line 
noise".  At best, on an error control modem, your data simply is 
delayed for a moment; at worst, if the interruption is long enough, 
you get disconnected.  Usually, you at least see a burst of garbage 
characters, if you're not using error control.

> 	(2) The second problem is harder. You cannot switch to another
> calling without hanging up the modem first. I think it is probably because
> I donot fully understand the mechanism of call waiting.

That's exactly right.  Without cooperation from the communications 
software, there's no way to suspend a modem call and switch to 
another call on the same line.  Modems transmit continuously, and if 
you take one of them off the line the other one will drop the call.  
The only way around this is to have a lot of cooperation between the 
comm software at each end, so that they can send messages saying 
"I'm going to drop carrier for a moment; please tell your modem to 
not go on-hook when I do, and reconnect when I come back."  Prodigy 
tries to do this, but almost no other network or BBS software has 
the capability.

In general, call waiting and modems are considered to be 
incompatible.  If you use your modem a LOT, the solution is to get a 
second phone line, not call waiting.

	-- Toby

-- 
Toby Nixon, Principal Engineer    | Voice   +1-404-449-8791  Telex 151243420
Hayes Microcomputer Products Inc. | Fax     +1-404-447-0178  CIS   70271,404
P.O. Box 105203                   | UUCP uunet!hayes!tnixon  AT&T    !tnixon
Atlanta, Georgia  30348  USA      | Internet       hayes!tnixon@uunet.uu.net