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From: dwl@hou4b.UUCP (D Levenson)
Newsgroups: net.dcom
Subject: Re: modem info
Message-ID: <1261@hou4b.UUCP>
Date: Tue, 8-Jan-85 16:10:32 EST
Article-I.D.: hou4b.1261
Posted: Tue Jan  8 16:10:32 1985
Date-Received: Wed, 9-Jan-85 05:24:33 EST
References: <1362GMS@PSUVM>
Organization: AT&T Information Systems Laboratories, Holmdel, NJ
Lines: 21

Q: Is there a modem compatible with call-waiting?

A: Many modems have an option (strapped, dip-switched, or
software-configured) known as "disconnect on loss of carrier".  This
is usually enabled by the factory-supplied defaults.  If you disable
this option *at both ends* then the modem will not break the line
connection when the carrier is interrupted by call-waiting. 
However, if the modem momentarily loses carrier, it may receive one
or more garbage characters when a call-waiting tone is applied. 
Also, your host computer's operating system may force the modem to
disconnect by dropping its DTR (data terminal ready) signal when it
senses the modem's dropping carrier detect. Finally, it is
desireable that the host treat loss of carrier as a disconnect and
logoff request from the user.  Overriding this feature, while
providing some imunity to call-waiting, may leave a port logged in
after a user has hung up without logging off.  Another user who
dials in shortly thereafter will find him/herself already logged in
as the previous user.  Definitely a security-hole.

-Dave Levenson
AT&T-ISL, Holmdel