An ISP of their own (was RE: [rescue] Being jobless)

Phil Stracchino alaric at
Wed Jul 30 14:41:50 CDT 2003

On Wed, Jul 30, 2003 at 12:48:51PM -0500, Joshua D. Boyd wrote:
> On Wed, Jul 30, 2003 at 01:03:13PM -0400, Phil Stracchino wrote:
> > On Wed, Jul 30, 2003 at 12:56:30PM -0400, Steve Sandau wrote:
> > > The old T1 in the last building just arrived as 4 copper wires from the 
> > > demark just like the phone lines. Dunno what "format" that was, but 
> > > there was no internal electronics at all..
> > 
> > That would be HDSL.  1.5 megabits over two pairs, 2 megabits over 3
> > pairs, maximum range about 20,000 feet.
> How is HDSL different from ADSL?  I know that it is 1.5 both ways, but
> other than that?  I'm within 20k feet of my CO, and they refuse to give
> me 640k or 1.5mbit ADSL service.

There's a lot of different flavors of DSL ....  the four most common
(and that I have any significant knowledge of) are ADSL, SDSL, HDSL and
VDSL.  In most of them, the bandwidth you can get is a function of your
distance from the CO.

ADSL (Asymmetric Digital Subscriber Line) is the one most commonly used
for consumer-grade DSL.  It has much higher data rate for download than
for upload, and drops dead at about 12,000 feet, but it's cheap and runs
over a single wire pair.

SDSL (Symmetric Digital Subscriber Line) is the next level up.  It's set
up differently (though I couldn't tell you exactly what the signalling
protocol difference is; IANANE), and geenrally offers lower bandwidth
than ADSL, but offers the same bandwidth in both directions and can
reach out close to 20,000 feet, also over a single pair.

HDSL (High-rate Digital Subscriber Line) is next in line.  Like SDSL,
it's symmetric and good to about 20,000 feet, but uses multiple pairs.
You can get either 1.5 megabits over two pairs (four wires), or 2
megabits over three pairs (6 wires).  It's the 2-pair version that's
most commonly installed as a T1 local loop.  If you see someplace
selling a 2-megabit T1, it's really 3-pair HDSL.

VDSL (Very high rate Digital Subscriber Line) is symmetric again, but
has a much shorter range than any of the others.  I don't recall
exactly; my best recollection is that maximum range for VDSL is 6,000
feet, but you can get 6 to 8 megabits depending how far within that
6,000-foot limit you are.

If you're within 20,000 feet, try shopping around for SDSL.  Check or  When we moved from Milpitas to Tracy,
PacBell originally gave us a CO distance estimate of 12,500 feet (we
checked *before* we bought the house).  "Yippee!" we said, "768k SDSL."
Then when we bought the house and actually tried to get service
installed, they revised their range estimate first to 16,000 feet, then
to 19,500.  At that range, PacBell's ADSL offerings dropped dead 7,000
feet short of the house, but Megapath and New Edge were able to get us
208k SDSL service.

(It was originally configured at 400k, and it actually *worked* at 400k
pretty well, except when it intermittently dropped carrier.  Then it
would take it up to 20 minutes to reconnect.  It wasn't long-term stable
at over 208k.)

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