On Mon, 11 Dec 2000, Don Stokes wrote:

> Thus normal modem transmission is eight bits per character, plus
> framing and checksums per block, minus the savings from compression

MNP3 and later let you be rid of the overhead of start/stop bits; you can
have a 2400 bps modem, running (really - no compression) at 2900 bps.

IOW, even if you enable error correction (whether V.42 or MNP4) on your
modem, and *disable* compression, you'll get a win. That's why even when
you're transferring something uncompressable, you can actually exceed the
physical line rate.

Much of xDSL is directly descended from so-called "PCM modem" technology;
ironically PCM upstream in V.92 was descended from xDSL technology - the
client modem has to assess the analog line's electrical characteristics,
and then belt out a wavery, sloppy waveform that the analog line will
contort by its very nature into a nice clean step-wave by the time it hits
the codec in the exchange.

--
Josh Bailey (josh@vandervecken.com - Berkeley, CA, USA)
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