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From: lee@sed170.HAC.COM (John Lee )
Newsgroups: comp.sys.amiga
Subject: Re: "baud" == "bits"/"second"
Message-ID: <295@sed170.HAC.COM>
Date: 7 Jul 89 23:50:42 GMT
References: <42300@bbn.COM>
Reply-To: lee@sed170.UUCP (John Lee (ird))
Organization: Hughes Aircraft Co., El Segundo, CA
Lines: 55

In article <42300@bbn.COM> denbeste@BBN.COM (Steven Den Beste) writes:
>The term "baud" DOES mean "bits per second", not "characters per second".
>We use it just like we use "herz" as a synonym for "cycles per second".

	Not quite.  "baud" means "symbols per second" as Stephan Holmstead
	reported in his fine article.  Note that symbols != characters here.
	A "symbol" is actually an abstraction that stands for 1 or more bits,
	i.e., a phase shift of x degrees with an amplitude change to y% in
	the signal represents a particular sequence of one or more bits.
	Hence, if a symbol represents only 1 bit, then a 1200 _baud_ modem
	is indeed a 1200 bits per second modem, but if a symbol represents
	8 bits (as a Trailblazer might), then a 1200 _baud_ modem is actually
	a 9600 bits per second modem.

	The term "baud" has always been confusing, ever since the term
	originated when characters (not ASCII, more like paper tape) were
	only 5 or 6 bits.  One could never tell what the character rate
	was by the baud alone.

	By the way, Stephan said that it is impossible for a modem to do
	9600 baud.  What's the theoretical limit?  What's the actual
	baud rate of those MC68000-controlled 30,000+ bps high-speed
	modems that spread dozens of simultaneous channels across the
	ordinary voice-line telephone spectrum?  

>The person who reported that "baud" means "characters per second" is simply
>wrong.

	You're right.

>As a laboratory demonstration, I have a 2400 baud modem, and I run DNET.
>(Great stuff, Matt!) For those of you who do not know, DNET uses the line fully
>during downloads - no pauses waiting for acknowledgements. WHen downloading I
>get about 10K per minute transfer rate. (And, as the old joke goes, I'm
>THANKFUL for it. Just wait'll I have kids and they complain about how slow
>their T1 line is.)
>
>10240 bytes per 60 seconds = 171 bytes per second
>                           = 1710 bits per second
>
>The rest is DNET's blocking and protocol and escaping. I'm not getting anything
>like 2400 BYTES per second.

Gee, are you sure there's nothing else going on?  That's only 71.25%.  I don't
think DNET uses 28.75% of the bandwidth for its protocol.  2400 bps modems
are really 240 characters per second.  I've timed it out of curiosity when
I was doing straight ASCII dumps.

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