Path: utzoo!utgpu!watmath!onfcanim!dave
From: dave@onfcanim.UUCP (Dave Martindale)
Newsgroups: comp.dcom.modems
Subject: Re: About "+++" in-band escapes
Message-ID: <17584@onfcanim.UUCP>
Date: 26 Feb 89 01:46:23 GMT
References: <20335@lll-winken.LLNL.GOV> <20736@lll-winken.LLNL.GOV> <3695@phri.UUCP>
Reply-To: dave@onfcanim.UUCP (Dave Martindale)
Organization: National Film Board / Office national du film, Montreal
Lines: 25

In article <3695@phri.UUCP> roy@phri.UUCP (Roy Smith) writes:
>
>	Various people have been grousing about the "+++" in-band escape
>Hayes-like modems have to cut off a call.  While I agree in principle that
>there should be a way to turn it off (and a out-of-band way, like a dip
>switch), I wonder how much of a problem it is in practice.  On every modem
>I've seen, the escape signal is really "<one second pause>+++<one second
>pause>".  The odds of that happening by random are pretty damn small, and I
>would be amazed if it ever happened in any kermit, uucp, SLIP, or other
>machine-generated data stream.

The place where it *is* a real pain is with a modem connected to
a UNIX machine as a dialin line.

The user at home wants to escape temporarily into command mode *on the
modem at home* and types the escape sequence.  The home modem transmits
the +++ to the host, since it doesn't know it's an escape sequence
until after the second one-second pause.  The UNIX host *echos* the +'s
back to the answer modem, and puts it into command mode too.  From
that point, there is nothing you can do to get the answer modem out
of command mode.

So, you really need some way of turning off the in-band escape
sequence for a modem used as an answer modem.  Yet, if the same modem
is also used for dialout, you can't disable command mode entirely.