Re: connection speed when using pon
On Sunday 30 January 2005 21:22, John Hasler wrote:
>> No, these are meaningfull numbers alright, and thats the actual
>> speed the data is moving.
>But they do not take into consideration the compression done by the
Oh, but it does. If it weren't for the compression used in the
modems, the working baud rate would be limited to 1/4 or less of
whats achieved. Both v42.bis and MN5 play a role in this, a very
heavy role. Even at 9600 baud, v42.bis is needed just to get that.
The rest of it is of course in the odd phase shifted keying as a way
to pack more than one bit per cycle of the audio tone that is
actually sent down the wire. That phase shift keying is the major
reason you don't hear the individual tones of the code anymore, but a
quite raucous, nearly white noise occupying the whole 300-2500 hz
bandwidth of a voice grade line, if the line is listened in on.
Some bandwidth is of course used in error corrections, and when the
error corrections begin to impinge on the data rate, thats when the
modems will call a temporary halt, tell us users hey we're busy hold
up a few seconds, while they get together and negotiate a new, more
robust but slower modulation method. Conversely, if the error rate
drops to zilch for a while, they'll stop, and renegotiate a faster
modulation method, up to the theoretical maximum of 57k in the
download direction on a really good line.
Much of this error correction is also because modern modems are
capable of compareing what they send to whats comeing back slightly
later in the form of echos, and adjusting their internal digital
filter taps to cancel the echos that inevitably come back from poor
junctions and terminations in every box that cable goes thru between
you and the CO. Once at the CO, then its generally into radios or
microwave stuff and in pretty good shape, but that 'last mile' of
copper is, figuratively speaking, pure hell for a signal as complex
as these modems can generate. Its got to be a lot better than what
it takes for you to recognize your friends voice for a modem to
Todays 56k dual mode modem that runs on a couple of watts from a wall
wart, has more computing power in it than your dads whole computer
had 15 years (or even less) ago.
>I suggest that the OP look at the pppstatus package.
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Copyright 2005 by Maurice Eugene Heskett, all rights reserved.