Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!snorkelwacker!mit-eddie!mit-amt!mjkobb
From: mjkobb@mit-amt.MEDIA.MIT.EDU (Michael J Kobb)
Newsgroups: comp.sys.mac.hardware
Subject: Re: 2400 baud modems
Summary: Brief response
Message-ID: <1648@mit-amt.MEDIA.MIT.EDU>
Date: 16 Feb 90 09:55:26 GMT
References: <5282@ur-cc.UUCP> <3967@hub.UUCP>
Reply-To: mjkobb@media-lab.media.mit.edu (Michael J Kobb)
Distribution: comp
Organization: MIT Media Lab, Cambridge MA
Lines: 31

In article <3967@hub.UUCP> 6600bike@hub.UUCP (Puneet Pasrich) writes:
>I hope this is the right place to post this...
>I have a 2400 baud modem, but I don't _really_ know what that means.
>Could someone fill me in on how to convert baud to data transfer?
>Something like, how long will it take to receive a 1meg file, assuming
>no data loss, no packet problems, etc. at 2400?  What's the "formula"?

  This question is more complicated than it seems on the surface.  "baud" as I
understand it, relates to the frequency with which the carrier signal of the
modem is modulated.  Since phone lines have a limited frequency range, there
is a limit to how high you can go with baud rates (and 2400 is getting up
there, I believe, especially since you have to fit two signals in; I believe
that 2400 actually requires the modems to filter their own signal out to find
the other modem's, but I may be confusing that with 9600).  For speeds <=2400
baud, it's fairly safe to assume ~1bit/baud, so a 2400 baud modem does
~2400bps on a really good day.  Using ZTerm, I usually get a K every 4 seconds
or so, and ZTerm is claiming 96% efficiency, so that means that, roughly
speaking, it would take about 4096 seconds, or ~68 minutes to download a
megabyte.

  It is possible to increase the bps on a given baud rate, for example, using
compression algorithms like MNP5 (yay, Paul!), which can give an effective
throughput of 4800bps on a 2400 baud signal.  You can also do weird things
with the encoding of the data streams to get 9600 and 19200 bps rates out of a
normal phone line, and I understand that MNP6(?) is now able to push nearly
38400bps on a normal phone line (I want two of these, and X for my Mac, and
I'll be a happy person!)

  I hope that this helps, and I entreat the more knowledeable out there to
correct me (here, please) if I've screwed up somewhere...

--Mike