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ADSL (thing)
See all of ADSL
, there is 1 more in this node.
(
thing
)
by
pihwlook
Thu Sep 07 2000 at 19:12:39
A
symmetric
D
igital
S
ubscriber
L
ine is a form of
DSL
. Collectively, all types of DSL are reffered to as
xDSL
. xDSLs are all considered "
last mile
" technologies.
Voice-band
modems
and
ethernet
both fall into this category, also. These technologies bring an internet connection from the high-speed backbone lines of major networks(for instance,
fibre optic
lines) that connect high traffic nodes (not
nodes
, nodes).
The primary limiting factor of
ADSL
(in fact, xDSL) is the distance from the remote end (that's your house) to the
Central Office
(
CO
) end (thats the
phone company
). If that distance is 18000 feet or less (a more practical number is 15000), then chances are the service will be available to you pending the phone company installs the
correct equipment
at the
CO
.
The
line rates
can be up to 8Mbps (8,000 kbps - think about it in relation to a 56kbps modem that you may have used) for the downstream and 800kbps upstream. Of course, any
service provider
would charge you a
pretty penny
for those speeds. The
going rate
is 256 upstream by 256 downstream for $50+/mo. "800 upstream and 8000 downstream", you say? "Sounds
asymmetric
", you say? Well, hence the name.
A brief
description
of
how
it all works follows.
Telephones
were
invented
. They run on one pair of
copper wires
, which are
twisted
to reduce
interference
with other phone lines. These are called
twisted pair
s.
ADSL
runs on your
standard
,
everyday
,
run-of-the-mill
twisted pair
phone line. Every
medium
, and by
medium
I mean a material used to
propagate
a signal from point A to point B, has a certain range of
frequencies
that it will
propagate
. The
copper
in a
twisted pair
has a certain
frequency
range.
Phones
traditionally
use a very small portion of that; when they were invented, someone decided to use the
smallest
frequency
range they needed for a decent
quality
sound. This leaves a -
ton
- of extra
frequencies
on the
copper wire
just sitting there,
hanging out
.
Some smart guy
a long time ago said, "Hey, we can send
data
over
phone line
s just like we send
voice
data
when we
talk
on the
phone
.
Voila
, the first
modem
(MOdulator/DEModulator) was born. Then
some smart guy
(presumably not the same
fellow
who I just
mentioned
) about 10 years ago said, "
Hey
, why don't we use that extra space for
something
."
Voila
,
xDSL
is
invented
, utilizing the previously
untouched
frequencies
of the
copper wire
s that run practically everywhere these days, yet leaving
POTS
(
Plain Old Telephone Service
) untouched.
Types of xDSL
DSL
SDSL
A modem is better than nothing
Acronym
Desperate guys who 'talk' me for no apparent reason
DSLAM
Installing DSL
broadband
last mile
DHCP
twisted pair
US West
VDSL
Asynchronous Transfer Mode
asymmetric
modem
microfilter
Verizon Online
Boon