Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!cs.utexas.edu!usc!apple!netcom!mcmahan
From: mcmahan@netcom.UUCP (Dave Mc Mahan)
Newsgroups: comp.sys.amiga
Subject: Re: modem help me
Keywords: meode
Message-ID: <11663@netcom.UUCP>
Date: 6 Jul 90 03:21:44 GMT
References: <1990Jul4.212217.8205@cbnews.att.com>
Distribution: na
Organization: Dave McMahan @ NetCom Services
Lines: 56


 In a previous article, itch@cbnews.att.com (richard.m.brack) writes:
>
>I am planning on buying a 2400 baud modem soon.  I have an Amiga2000
>with 2 floppy dirves and a 40 meg hard drive.  I would like
>some advice.  
>
>First of all, is there really any difference between modems (like
>from different manufacturers)?

Yes.  Like all things, you usually get what you pay for.  The big thing with
modems are speed, features, and error performance.  Speed is stated up front.
The other two things are semi-hidden.  Personally, I like my Everex Evercom
24E+ modem, but it is external and you wanted an internal.  Error performance
is usually stated in error rate (1 bit in XXXX) at a given signal/noise
ratio.  The S/N ratio is usually stated in dB (deciBels).  Don't try to
compare the error rate vs. S/N ratio of modems operating at different speeds.
For that, you need to find the figure called Eb/N0 (Energy-per-bit/Noise
Density) and this is tough to come by with dial-up modems, in my experience.
Makers of phone modems don't quote it, they stick with the error rate at a
specific S/N ratio.  Unfortunately, it's quite likely that two makers will
pick different S/N ratios where their modem works well, comparatively.  The
best thing to get is a curve showing all possible error rates at given S/N
ratios, but good luck trying to get that info too.  I don't think it can be
had.

>I was considering a Supra 2400zi, any comments?  Also I noticed a 
>Supra 2400 plus with MNP; what's this MNP stuff all about?

MNP (MicroCom (sp?) Networking Protocol) is a family of error detection and
correction algorithms installed in the modem.  When your modem connects with
another, it tries to determine if the other has MNP capability and what level
it has (Usually MNP capability is stated in levels.  3, 4, and 5 are common.
I have heard of modems running at level 10 and higher).  The higher the level,
the more the modem does.  Starting at level 5, compression is thrown in too.
This makes the effective transfer rate higher for some things.  It won't speed
up the transmission of files that are already compressed.  You also have to
have your computer-to-modem link running faster than the bit rate of the modem
to support the higher throughput.  You also have to make sure that the modem
on the other end is MNP capable.  When the MNP link is established, the link
will occur at the highest MNP level supported by both modems.  If you have an
MNP-5 modem and the one you are calling is MNP-3, you will only get the
features of an MNP-3 link.  If the other end has no MNP level or it isn't
enabled (via the AT command set extensions each modem comes with) you get a
regular old link.  MNP capability is something you pay for.  Level 5 is about
the highest level in common use today.  In my experience, BBS systems I call
don't have MNP modems so for me it has been a waste of money to date.  I hope
that in the future this changes.  With MNP capability of the proper level,
you really don't need to use protcols like X-Modem or Z-Modem, since the
MNP modem you use gaurantees correct transmission of the data.

>RichBrack



   -dave