Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!mcsun!sunic!tut!santra!kampi.hut.fi!jmunkki
From: jmunkki@kampi.hut.fi (Juri Munkki)
Newsgroups: comp.sys.mac.hardware
Subject: Re: 2400 baud modems
Message-ID: <1990Feb17.205855.27079@santra.uucp>
Date: 17 Feb 90 20:58:55 GMT
References: <5282@ur-cc.UUCP> <3967@hub.UUCP> <1990Feb17.130612.1828@chinet.chi.il.us>
Sender: news@santra.uucp (Cnews - USENET news system)
Reply-To: jmunkki@kampi.hut.fi (Juri Munkki)
Distribution: comp
Organization: Helsinki University of Technology, FINLAND
Lines: 44

In his article magik@chinet.chi.il.us (Ben Liberman) writes:
>In article <3967@hub.UUCP> 6600bike@hub.UUCP (Puneet Pasrich) writes:
>>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"?
>
>Baud = bits/second.  Usually (8 bits/char., no parity bit, 1 stop bit, 1 start
>bit) there are 10 bits in every character sent, so
>
>    2400 baud = 240 characters per second
>
>    1 megabyte = 1,048,576 bytes = 4,369 seconds at 2400 baud = 72 min. 50 sec.

Actually bauds measure the modulation rate and can be totally different
from the bits per second (bps) data transfer rate. Older modems usually
transfer one bit at a time so it's quite common to say that baud=bps.
Faster modems transfer multiple bits at a time so the baud rate doesn't
say much about the actual transfer rate.

Then you have to take into account even newer modems that pack data and
correct errors. For binary data the transfer rate can be quite different
than what you get with just 7 bit ASCII.

The third thing that you have to account for is the speed of the protocol
that you are using. Plain kermit or xmodem waste a lot of time because the
data length/packet length ratio is quite low. I recommend using ZMODEM
where you can get about 90% efficiency on an error-correcting modem.

Basically what I'm saying is that even if someone says that a modem is
9600 baud, that person doesn't really mean baud, but bps unless the modem
uses a very special phone line that can carry that much bandwidth. You
can then merrily divide this rate by 10 to get an approximation of how
fast characters might be transfered. For actual file transfers, you need
to account for packet overhead. It's quite safe to add 10%, since most
protocols aren't all that optimal anyway. If you are using an old kermit
implementation and tranfering a binary file, expect to double the time.

The above is of course nit-picking and probably doesn't interest you if
you aren't already interested in splitting hairs. :-)

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|     Juri Munkki jmunkki@hut.fi  jmunkki@fingate.bitnet        I Want   Ne   |
|     Helsinki University of Technology Computing Centre        My Own   XT   |
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