[PLUG] (no subject)

[John Meissen]

> That's like calling ethernet analog because it operates over copper. The 
> equipment at either end (the DSL transceiver and DSLAM) are sending digital 
> signals to each other. They share the wire that analog signals traverse, 
> but they ignore those signals as out of band noise.

The purpose of the DSLAM is to aggregate the DSL circuits and transfer
the digital content to a frame-relay setup inside the phone company.
The data is then delivered to the ISP over standard T-1 or better.
Standard voice circuits use bandpass filters to eliminate anything
over 2Khz. DSL takes advantage of that by using carriers at higher
frequencies.

You can run your own DSL circuit without a DSLAM by getting a dry
pair (like an alarm circuit) between two locations and putting a
DSL modem at each end. Bob Cringley described such a setup in one
of his columns. <http://www.pbs.org/cringely/pulpit/pulpit20010823.html>

Regular modems are sending digital data to each other, too. It's just
modulated on top of an audio carrier. In fact, that's what "mo-dem"
is from - modulator/demodulator.

I'm not familiar enough with ethernet to say for certain, but I thought
ethernet line drivers directly drove the wires with the digital signal,
rather than encoding it onto a carrier.

john-

 > 
> I'm not as familiar with cable as DSL, but I was under the impression that 
> it operates in much the same way, which is why you needed to be upgraded to 
> the new (digital) head end at the cable company to be able to get either 
> digital cable, cable phone, or cable modem.
> 
> At 12:49 PM 5/10/2002 -0700, you wrote:
> >That's not true. DSL and ISDN operate over analog telephone circuits.
> >Remove the little filter(s) that come with your DSL modem and you'll
> >probably be able to hear the carrier. Cable modems use an RF carrier,
> >still analog. Theory of operation and carrier frequencies are
> >definitely different from your standard modem, but they're still
> >analog.
> 
> Russ Johnson
> http://www.dimstar.net
> 
> 
> Fashion is a form of ugliness so intolerable that we have to alter it
> every six months.
>                  -- Oscar Wilde
> 
> 
> 
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