DSL help plz.

ME dugan at libwais.sonoma.edu
Tue Dec 28 17:39:31 PST 1999

On Tue, 28 Dec 1999, Rick Moen wrote:
> Quoting ME (dugan at libwais.sonoma.edu):
> > This is not just from me, this is from PacBell and 2 northbay xDSL
> > providers.
> I beg your pardon, but it is not:

OK, I will admit that if pacific bell is wrong on this, then so am I.
I have had disagreements with them on ISDN where their web pages were
inaccurate, so this will not be thge first time.

> > Please check http://public.pacbell.net/faq/dsl_faq.html

> Obviously, this refers to aDSL.  Unfortunately, many parties who should
> know better use the terms "DSL" and aDSL synonymously.

This is what happens when I assume that the internet service
provider-telcos know what they post on their web pages.

> > Mention of "both ways" is full duplex. I believe that most xDSL are not
> > ale to upload and download at max speeds simutaniously.
> Allow me to refresh your memory:  We were speaking specifically of SDSL.

I disagree, we were speaking of DSL (as the subject states) which includes
all forms of DSL. Follow this thread and you can see this is the case.
ADSL has been mentioned as well as HDSL, and SDSL. I do not recall VDSL,
but now it has been.

> > On the original issue of latency, that does not describe bandwidth, they
> > are two different animals.

> That is true but not relevant to the present discussion.

I was not the first person to bring up the issue of latency, but was
re-addressing it since it was an item left un-contested and uncorrected by
anyone else.

> > If your xDSL cable provider offers you 2Mbps SDSL, you need clarification:

> To refresh your memory, (1) Best Internet (over Northpoint cabling service)
> provides approximately 1.1 Mbps service over an SDSL line to my place of
> residence, 744 Harrison, San Francisco.  (Again, the initial "S" stands 
> for "symmetric".)  Separately, (2) At my former firm, I had a 2 Mbps HDSL
> line over existing CAT3 cabling across the office building, internal to
> the firm's LAN.

In some ways you are lucky to be in SF to get multiple varieties of DSL.

There is also another company in RP offering SDSL service that is not
pacific bell. They are trying to target businesses. The SDSL offered
locally to remote locations can push about 384kbps both ways, but the
marketers offer it as a "near Mbps speeds"

I do not recall their name, but there are not many telcos up here for
choices. Possibly other members of this list may know their name...

> I hope that alleviates any confusion.

Yes, we are working towards a more complete picture. If we keep this up,
we will have a more complete picture!

Two questions:
Do you state that marketing of SDSL includes the common accepted
definition that Bandwidth is marketed as a meaure of the max Transmit (or
received) rates, not a sum of the two?

I have not examined how the various forms of DSL are able to transmit and
receive at the Data Link Layer. Is it possible for both sides to transmit
information at the same time at the data link layer or are they limited
by TDM to only have opportunity to tranmit when their time window is open?

If they are true TDM, then at the datalink layer they are half duplex, but
are able to synthesize what would appear to be full duplex for the higher


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