[lug] DSL Technical ?'s

[Timothy Klein]

Jeremy,

I think you are running primarily into a business decision on Qwest's
part.  The technology is sure there, but Qwest has decided it is not
cost efective to supply DSL to just anyone who asks.  They are picky
about who they will supply to.

Now, at the lengths you are mentioning for your line, there is a high
possibility that you are not on a copper pair at all, but rather a "pair
gain" pair.  This means that your line first rides to a central
distribution point (Cross Box) as a digital signal on some kind of
T1-type carrier ( that might be conditioned copper, or fiber).  Usually
96 virtual "pairs" are put onto a few actual copper pairs (can't
remember the number, something like 4 pairs) by using a digital signal
rather than the plain old low frequency analog pots signal.  At the
cross box, these digitial signals are converted back the to the analog
signal that your phone line expects, and then another, much shorter
segment of copper connects your house to the cross box.  DSL will not
work over one of these pair gain arrangments, as it basically tries to
do the same thing as the pair gain is already doing:  put a higher
frequence digital signal on the line.  Now IDSL is just an ISDN line,
that behaves like a DSL.  The speed you were getting on your SDSL is
only slightly faster than ISDN, so I would not be at all surprised if
you were on some kind of ISDN-type arrangement, eg, the DSL was working
through a pair gain system.

Which companies will choose to offer you DSL is largely based on
econimics, non techicalities, though.  Any one *could* offer you some
kind of high speed net access, the question is do they *chose* to.  Does
the company think it is a good business decision to do so?  Covad,
Rythyms, Jato and the like were hungry for customers, and thus willing
to deploy whatever technology they could to get a customer.  Qwest is an
entrenched monopoly, so they can afford to be much pickier about which
customer's the choose to serve.

So, to summarize, DSL needs a clean copper pair, less than 18K long,
with less than a few thousand feet of bridge tap, and no loid coils.

An ISDN line needs either the above, OR a pair gain pair.  There are a
couple of variety of DSL's that are really just ISDN type services that
will work this way.

The other new piece to the puzzle is the now deploying 'Remote DSLAMS'.
This is how DSL will be offered at the full speeds when the customer is
served by pair gain.  It moves the DSLAM to a box out next to the cross
box.  Thus your pots signal goes to the CO on one channel, and you DSL
goes to the ATM network on another.

Any way, I'm babbling.  I know a lot about this stuff, as I work with
these issues all day at a telecom. 

If you were interested, you could email me off list, and I could tell
you exactly what your situation was if you were willing to give me the
phone number or address involved.

HTH

Tim

* Jeremy Hinegardner (jeremy at mlug.missouri.edu) wrote:
> Hi all,
> 
> Some background info:
> 
> I have a few ?'s for the sage's of DSL.  As of recently I
> had a Rhythms 192kbps SDSL line to my home.  Since Rhythms
> has basically gone belly-up my ISP (Megapath) is going
> the motions to switch me over to Covad.  But it seems that
> Covad is unable to provide SDSL service to me and they
> are installing an IDSL line.  
> 
> I called Qwest and they say they are unable to provide me
> DSL service at all.  But according to their documetation
> http://www.qwest.com/disclosures/netdisclosure459/co_data.html
> my CO (BLDRCOMA) has RADSL equip installed.
> 
> I've checked the distances, estimates vary from 15500' to 
> 16500' and both fall well within the range of Qwest's  
> maximum for ADSL (17500').
> 
> So now for my questions:
> 
> 1. Why can't Qwest provide any DSL service? Is it because (a)
>    They don't provide SDSL service at all and don't have the
>    equipment at the CO? or (b) bridges/tap/etc on my line
>    to prevent ADSL from working?  
> 
>    Part of this question is why cannot Qwest just use the
>    existing copper pair that is in place for my SDSL and
>    treat it as a phone line to run ADSL over?  Both types
>    can run over the same line configuration right? I mean
>    I basically have an additional phone line at my house
>    when they installed the SDSL circuit right?  It just
>    happens to plug into Rhythms' DSLAM instead of Qwest's.
> 
>    An additional interesting note on this one is I was 
>    originally with Jato last fall (which also went out of
>    business) and from what they said, my SDSL circuit was
>    actually installed by Qwest.
> 
> 2. Why can't Covad provide SDSL service to me.  They do
>    provide SDSL service.  Is it because they just don't
>    take SDSL service to 16000'?  And if that is the case 
>    What is the technical reason why?  If Rhythms was able
>    to provide a satisfactory SDSL service to 16000' why
>    is Covad unable to?  They are both in the same CO right?
> 
> 3. I know there are several ISP's who are on this list and
>    I would like to know if any of them would be willing to
>    try an experiment.  Basically the Homebrew SDSL option
>    talked about at http://www.odessaoffice.com/sdsl.htm
> 
> I've tried getting these answers (1 and 2) from a few other
> sources but with no avail.  I really appreciate the level 
> of information available on this list and I hope you guys 
> can help me out.
> 
> Thanks,
> 
> -jeremy 
> 
> ============================================================
> Jeremy Hinegardner		    jeremy at mlug.missouri.edu
> _______________________________________________
> Web Page:  http://lug.boulder.co.us
> Mailing List: http://lists.lug.boulder.co.us/mailman/listinfo/lug
==============================================
== Timothy Klein || teece at silverklein.net   ==
== ---------------------------------------- ==
== "Hello, World" 17 Errors, 31 Warnings... ==
==============================================