A little Microsoft humor...

[Lloyd Kvam]

On Sun, 2007-05-20 at 16:47 -0400, Ben Scott wrote:
> Lloyd Kvam <python at venix.com>  wrote:
> >> So far as I know, T1 connections use DSL between the central office
> >> and your premises.
> 
>   Eh.  This implies that "DSL" actually means something specific.  It
> generally doesn't.  There are a bunch of "flavors" of DSL, and they
> don't all work the same way.  Further, there is often disagreement
> over what the "flavors" are, so terms are not always equivalent across
> markets.  (It's similar to how terms like "SCSI-3" gets applied to
> connectors, cables, speeds, and other things, with no consistency,
> because "SCSI-3" is just a standards document that covers all of that.
>  The terminology gets abused.)
> 

I was informed that Verizon has been using two-pair HDSL when possible.
This provides approximately 750 Kb per pair.  I can confirm that they
run two pairs from the punch block to the line card.  I have no obvious
way to verify that it is truly HDSL on the wires.

Google found these (DS1 HDSL)
http://www.jdsu.com/france/technical_resources/product_documents/outline/TT-DS1-HDSL-WS.pdf
http://honolulu.hawaii.edu/cet/courses/courses_tele_fiber.htm

Also you are quite right about the utter semantic mess that DSL acronyms
represent.  That's why I simply said DSL (Digital Subscriber Line) which
is pretty generic.

>   There are some flavors of DSL that re-use older equipment in new
> ways.  In particular, the line cards for both ISDN and T1.  Line cards
> just transmit bits; they don't really "interpret" much.  So there are
> DSL flavors which use ISDN or T1 line cards.  The defunct Vitts called
> these "SDSL" (symmetric DSL) and "HDSL" (high-speed DSL),
> respectively.  I don't know if Verizon even offers these services.  I
> know that most asymmetric DSL being delivered by Verizon in this area
> is a 1-pair (2-wire) system, while a T1 is a 2-pair (4-wire) system,
> so the Verizon ADSL I've seen is not the same thing as a T1.
> 
> On 5/20/07, Bill McGonigle <bill at bfccomputing.com> wrote:
> > That brings up an interesting scheme - I've been told more than once
> > that even if you can't get DSL in your area you can always order a T1
> > anywhere.  If they're being provisioned on DSL lines these days, I
> > wonder if I could order a T1, have them fix the induction coil
> > problems on our backhaul to get it out here, then cancel the T1.
> 
>   There are multiple factors in play.  DSL is usually offered as a
> low-price, consumer product, while DS1s are usually higher price,
> business class products.  Businesses are willing to pay a lot more, so
> the telcos are willing to do a lot more.
> 
>   When line quality is bad, T1 installation will often involve running
> a brand new copper pair (or reconditioning existing pairs) the entire
> distance from the CO to the demarc.  This is typically billed per foot
> and can run into the five figures if you're sufficiently far out in
> the woods.
> 
>   T1 also allows for extenders (in-line amplifiers).  If they reach
> the distance limit, they install an extender on the pole.  They'll run
> a separate power pair if needed.  This is also expensive, and -- more
> significantly -- just not done for consumer DSL.
> 
>   So even assuming you didn't get hit with an early cancellation fee,
> you'd likely end up with a line that was still not useful for DSL, due
> to the distance limits mentioned above.  There's also the fact that
> the telco could probably just say, "That's a T1 line, not a DSL pair.
> Even if we *could* run DSL over it, we're not going to.  It was
> installed for a T1, and we're not going to let it be used for anything
> else but."
> 
> -- Ben
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-- 
Lloyd Kvam
Venix Corp.
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Lebanon, NH 03766-1358

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