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There is DSL and there is DSL.
The original concept of DSL service was to use Data Over Voice to provide
high speed service for residential customers. However, the reality of the
POTS network is that only something like 20% of all existing phone lines
are useable for xDSL service.... at any speed.
Most people think they have a single continuous piece of copper from their
home to their CO. This was once true, but anyplace you see one of those
green distribution boxes at curbside, you've got a DSLAM - a T-circuit from
the CO to the box and multiplexed copper circuits from there to the
customer. New Developments, Industrial Parks, Apartment buildings suffer
some interesting problems with DSL service as a result.
Remember -- DSL service is not digital like ISDN, it's simply an analog
modem!!! (You can, in fact, run DSL service OVER an ISDN line.)
COVAD and Connective Communications, that I know of, offer a version of DSL
service which rides on top of dedicated tuned loops - like ISDN or 56K,
or T1, etc.
One of the best sources I have found, for detailed info on how DSL really
works is Paradyne. (They make modems, etc.)
Their DSL source book comes in PDF
http://www.paradyne.com/sourcebook_offer/sb_pdf.html
and HTML formats
http://www.paradyne.com/sourcebook_offer/sb_html.html
--
===<Tru64 UNIX-SIG Chair>===
www.tru64unix.org
T.T.F.N.
William H. Magill Senior Systems Administrator
Information Services and Computing (ISC) University of Pennsylvania
Internet: magill@isc.upenn.edu magill@acm.org
magill@upenn.edu http://pobox.upenn.edu/~magill/
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