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From: tnixon@hayes.uucp
Newsgroups: comp.dcom.modems
Subject: Re: Reliable and Compression Protocols -- how do they sync up?
Message-ID: <3914.280d941c@hayes.uucp>
Date: 18 Apr 91 12:42:04 GMT
References: <9104170413.AA03912@ucbvax.Berkeley.EDU>
Organization: Hayes Microcomputer Products, Norcross, GA
Lines: 39

In article <9104170413.AA03912@ucbvax.Berkeley.EDU>, ho@HOSS.UNL.EDU
(Tiny Bubbles...) writes: 

> Say I have a dumb modem and I'm calling a smart modem, oh, for example,
> a Microcom QX-series MNP 10/LAPM modem.  (Real hypothetical, huh? :-) )
> 
> I advise people not to type *anything* for 2.5 seconds after the dumb
> modem reports a connect to prevent being mistaken for an MNP modem.
> But is there anything (like spaces, backspaces, returns) that would
> actually cause a modem like that to screw up?  I ask that because it
> seems to have happened to a few people, and nobody knows why.

The MNP Link Request frame starts with the ASCII characters SYN, 
DLE, STX.  Nothing else you type could be mistaken for an MNP frame, 
so it shouldn't cause the modem to "screw up".  Some modems look for 
certain _specific_ characters (like ^C, or CR) to force an immediate 
fall back to non-error-control mode, but, again, this is the desired 
result, not a "screw up".  Can you describe the problem in greater 
detail -- what are you observing that is undesirable?

> Also, some el-cheapo internal modems, most of them using very old
> chipsets, can't connect to the Microcoms *at all*.  Is this a problem
> with other V.32 modems, or just Microcoms, or just our setup?

Who knows.  It could be that the "el-cheapo" modems don't respond 
fast enough to the unscrambled binary one (USB1) signal sent to 
initiate V.22bis/V.22/Bell 212 modulation, so the Microcom modem 
(assuming it is the answering modem) goes on to try V.32 again, and 
the connection fails.  But if the "el-cheapo" modem is this far out 
of compliance with the applicable standards, you'd see the problem 
with ANY of the newer V.32 Automode modems, not just Microcom.

	-- Toby

-- 
Toby Nixon, Principal Engineer    | Voice   +1-404-840-9200  Telex 151243420
Hayes Microcomputer Products Inc. | Fax     +1-404-447-0178  CIS   70271,404
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