xDSL is a very different technology. It requires a direct copper loop
from the user to the xDSL server. That generally means CO colocation to
terminate customer copper. Also, some of the newer technologies - the
Nortel/Rockwell 1-Meg Modem, and the Lucent WildWire 1.5-Meg system are
designed to be upgrades to the telco switch. New media cards for the
DMS or 5E series of switches.
I'm going to pull these numbers from memory, so I hope I don't botch them.
xDSL ranges from Ascend's IDSL (ISDN DSL) system at 128K (which has been
less than a widespread success) to VDSL - or Very-high-speed DSL. I forget
the rating on that, but it is multi-Mbps.
SDSL and HDSL are commonly used today. SDSL - or Single-pair DSL is 768Kbps.
HDSL is used widely to provide T1 circuits and is 1.544Kbps.
ADSL is the one in the news of late. GTE is rolling out ADSL service
agressively, as are many of the RBOCs. ADSL is Asymmetrical DSL. It
generally provides 640Kbps upload speeds and 1.5Mbps to 8Mbps download
speeds. The download speed is highly dependent on distance from the CO.
RADSL is Rate Adaptive DSL - and is really a superset of ADSL. It provides
for an automated way to determine the best performance for the line,
whereas ADSL is general set when installed and fixed at that speed.
VDSL is the top performer but is very short distance, generally useful
only between buildings in a campus.
You can see that with the performace of xDSL lines you need a very high
performace chassis to handle the data flow. And a 10base ethernet would
be quickly overwhelmed. xDSL is something a future chassis will be
better suited to address.
But again, the need for direct, uninterrupted copper to the customer is
a major limiting factor. What is general envisioned is that the RBOC
or CLEC will put xDSL servers in place in their COs - they you would have
to buy carrier service from them. They would connect the xDSL line to
the customer and backhaul the data to your network for termination.
-MZ
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