Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cwjcc!neoucom!wtm
From: wtm@neoucom.UUCP (Bill Mayhew)
Newsgroups: comp.dcom.modems
Subject: Re: I need help with setting MNP on my Telebit.
Summary: Problem not only on telebit modems .. MNP in general
Message-ID: <1489@neoucom.UUCP>
Date: 4 Feb 89 14:33:28 GMT
References: <367@twwells.uucp>
Organization: Northeastern Ohio Universities College of Medicine
Lines: 29


One must disable MNP protocol before dialing into a site that
echoes characters and also not equipped with an MNP modem.  The
reason is that the string of entrainment characters sent from both
the originate and receive ends are the same in the MNP protocol.
Thus if the other end is unix and puts up a login: prompt with
echoing enabled, login will echo back the entrainment sequence to
your modem, as login thinks that you are entering your userid.
The result is that your modem thinks the other end has MNP when in
fact it does not.  If you are using a modem that has level 3 or
higher MNP, you'll be locked out for the remainder of the call, as
the modem will try to switch over to synchronous operation.  So
much for stupid design features!

The way around the bug is to set S92 appropriately for whatever
site you are dialing out to in your chat script.  You can probably
safely leave MNP enabled for dial-ins without incident.  It is only
a bug while dialing out to a non-MNP site.

On a modem that doesn't have defeatable MNP (does such a thing
exist?), a way to get around the MNP bug would be to prevent the
other host from echoing anything for seven seconds after its modem
goes off hook.  If your own modem doesn't receive an entrainment
sequence within seven seconds of trying its own sequence, it is
supposed to assume the other end is a garden variety modem.

--Bill
  wtm@impulse.UUCP
  ...!lll-winken!scooter!neoucom!impulse!wtm