> the KXTD is encoding the modem signal (analog) into
> digital and then back
> into analog which goes to the central office where
> it gets converted back
> into digital for delivery to your ISP (digital)
> where its "converted" back
> into analog (internally) for the modem
first part is correct, but once it is digital at the
CO, it must stay that way right to (and thru) the ISP.
ISP's run digital modem banks for 56 k operation with
PRI lines.
> which is why you cannot get one 56k modem to talk to
> another 56k modem on
> an analog line with anything usually faster than
> 33.6
two 56 k modems NEVER connect faster than 33.6 k to
each other. 56 k service is asymetric, server to user
can be up to 56 k, but user to server cannot be over
33.6 k To operate 56 k, the isp modem is a server
side 56 k modem (not like the 56 k modem in your pc -
but they are available in a bri version as well as
pri).
the nasty details, there are two 33.6 k data
channels,
one channel is outbound and the other is inbound
(full-duplex). and this is if the line is clean enough
to support the 33.6 k each way. the additional speed
from the isp to your pc is created by filling the
usable "holes" below, between, and above these two
channels with MORE bits, which is added to the 33.6k
channel. this is done with multifrequency(multi-tone)
modulation, which won't survive a-to-d and d-to-a
conversions. Which is what happens in a digital phone
system, the extension is analog, the internal
switching is digital and the co line is analog again.
you've done stripped off the extra speed that was
stuffed in the holes.
on the kxtd, there is a way to get 56 k speed. use
bri isdn lines! the digital internal switching goes
out the digital isdn line to the isp. no extra
conversions in the way. (i have never seen a kxtd
locally with a bri card, i think australia is the only
place they are common.)
>there has to be one and only one conversion form
> analog to digital in the
> whole system before it hits the isp
-larry
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