Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site ulysses.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!smb
From: smb@ulysses.UUCP (Steven Bellovin)
Newsgroups: net.dcom
Subject: Re: Telco Hassles
Message-ID: <1125@ulysses.UUCP>
Date: Mon, 21-Oct-85 13:34:12 EDT
Article-I.D.: ulysses.1125
Posted: Mon Oct 21 13:34:12 1985
Date-Received: Tue, 22-Oct-85 05:54:12 EDT
References: <848@mcvax.UUCP> <843@vortex.UUCP>
Organization: AT&T Bell Laboratories, Murray Hill
Lines: 21

> First of all, I note that the original poster said the problem was with
> a 202C type modem.  This is a half-duplex modem, not used in "normal"
> applications with Unix, and implies that some specialized application
> was in use.  But in any case, regardless of the type of modem
> or the application that was running, the original poster said that the 
> computer on one end was rebooted, dropping all the dialup lines, at 
> intervals considerably shorter than the period of time telco claimed the 
> call was in progress.
> 
> This would seem to absolve software on those machines of responsibility
> for the problem.  If the modem on either side hungup, the phone connection
> would be broken (and charging stopped) within 30 seconds or less.

The problem with many models of 202 (I don't know for certain about the 202C
so I won't be that specific) is that there's no carrier present except when
transmitting.  Remember that this is a half-duplex modem, and hence does not --
nay, cannot -- transmit a tone when the other end is doing so.  It is thus
quite difficult to tell when the remote end has hung up, since all the local
end can do is (a) let its protocols time out when they don't get ackknowledgements;
or (b) *try* to detect dial tone or whatever other random noises your local
CO will throw at you when the far end has gone to sleep.