"Juha Saarinen" <juha@saarinen.org> wrote:
>%-> One byte is 8 bits, therefore:
>%-> 56 kbit/s = 56/8 kbyte/s = 7 kbyte/s
>
>You would normally have a start/stop bit with serial modems, so
>dividing by 9 instead is a better approximation (~6.2KBps).

It's not that simple. The actual transmission (as long as error
correction is enabled) is normally synchronous, with framing done at a
block level, not at the character level. Thus normal modem transmission
is eight bits per character, plus framing and checksums per block, minus
the savings from compression, which is heavily dependent on the type of
data being transmitted -- already compressed data gets very little
benefit from compression while textual material (including HTML pages)
generally does.

Simple asynchronous serial comms usually transmits ten bits per
character, a start bit, eight data bits and a stop bit. There are
variations of course depending on how many bits per character you send
(anywhere from 5 to 8 can be used), whether you have a parity bit, or if
you need one or two stop bits. But for asynchronous IP transmission,
only eight bits, no parity and one stop bit is really the only sensible
combination.

I'm sure Josh can go into the modem stuff in more detail.

-- don

This message is part of the NZ ADSL mailing list.
see http://unixathome.org/adsl/ for archives, FAQ,
and various documents.
To unsubscribe: send mail to majordomo@unixathome.org
with "unsubscribe adsl" in the body of the message
Received on Mon Dec 11 11:29:17 2000