Hello...Pat,
Finally found the article Chipcorder posted with my favorite line regarding DMT & CAP. This article is to my knowledge, the first
confirmation of Telcos bias to DMT. IF it is true that what is
good for DMT is good for Amati, then I would suggest this is quite good.
Q:What kind of speeds are you expecting to deliver, and will it vary
with the length of the loop?
[Bell South]
A:We're expecting to offer a data service at up to 6 Mbps downstream
into a personal computer and about 768 kilobits per second upstream.
With our copper loops in the network today, the speed would vary,
depending on the length of the loop. It would also vary based on what
you call disturbances -- AM radio stations, etc. ADSL uses the full
spectrum above the 3-kilohertz band, and so it is susceptible to other
things operating in that band.
That's why we're going to use adaptive bit rate -- Discrete Multitone,
or DMT -- and that is very important from an operational perspective.
We originally thought we would be able to find a sweet spot [in the
spectrum] where we could be certain that the signal would be clean.
But given the characterization of our copper plant, and because of the
variability of loop lengths, we decided it would be better to use DMT
and its adaptive rate characteristics, which will give the customer
the maximum speed possible at that time.
Q: In making your ADSL push, you chose DMT technology over Carrierless Amplitude Phase, or CAP, technology. Why?
A: The DMT approach was selected because, first, that is what our
selected supplier has been focused on, and secondly, it is the
standard. Also, its design naturally lends itself to the adjustable
bit rate capabilities, which we think are important. CAP can do that,
but DMT in its fundamental design was set up to do that.
I'm not in any way demeaning CAP. When you look at the combination of
availability, cost, performance and the design, our selection was DMT.
zdnet.com
Cheers,
Daniel |
