Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!usc!polyslo!rcfische
From: rcfische@polyslo.CalPoly.EDU (Raymond C. Fischer)
Newsgroups: comp.sys.mac.hardware
Subject: Re: 2400 baud modems
Message-ID: <25ddc211.6a53@polyslo.CalPoly.EDU>
Date: 17 Feb 90 21:28:49 GMT
References: <5282@ur-cc.UUCP> <3967@hub.UUCP>
Reply-To: rcfische@polyslo.CalPoly.EDU (Raymond C. Fischer)
Organization: Cal Poly State University -- San Luis Obispo
Lines: 35


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"?

Despite postings that indicate otherwise, baud is NOT synonymous with
bits-per-second.  But since the two are often confused, you usually
can assume bps when reading baud.

Baud indicates the number of signal changes per second.  With the old
110 bps modems, a high pitched tone indicated a 1 bit and a low pitched
tone indicated a zero bit.  (this is called FSK for frequency shift keying).
Thus, 110 baud = 110 bps = 10 characters per second (since each character
is sent as 11 bits).

New modems are fancier.  Using a combination of PSK (phase shift keying)
and ASK (amplitude shift keying) a 2400 bps modem manages to encode 4 bits
into each signal change.  Thus, with a signalling rate of 600 baud, the
modem is able to send 2400 bps.  1200 bps modems also work at 600 baud,
but are not as clever about encoding bits, using only PSK to encode 2 bits
per baud.

Usually characters are sent at 10 bits/character (1 start, 8 data, 1 stop)
and so at 2400 bps you transfer 240 characters per second.  Doing some
rounding, this means about 1K bytes in 4 seconds, or about 7 minutes to
transfer 100k bytes, or roughly 6 seconds to fill a 24x80 screen full of
text.

Answer your question?

Ray Fischer
rcfische@polyslo.calpoly.edu