[EFM] RE: [EFM-Copper] [Fwd: Existing Loop Lengths]
Troy,
While the data you attached is a marketing document, the U.S. distribution
curve appears to align well with the Telcordia loop survey (reference
below).
Furthermore, during our reach debate at the LA meeting, I incorrectly quoted
Telcordia's loop length/coverage statistics. I stated that 12kft reach
covers 85% of the loops in North America. Upon further review, I noted that
the Telcordia Loop survey (which can be viewed at
http://www.ieee802.org/3/efm/public/may01/stanley_1_0501.pdf ,slide 6) is
normalized to 26AWG wire. Therefore, a reach of 12kft of 24AWG wire
(approximately 9kft of 26AWG wire), would only cover about 70% of the
market.
This survey only shows working length, which does not include bridged tap
lengths. Because 78% of loops contain bridged taps, and 70% of bridged taps
are <1000ft in length, which impact xDSL performance, a given performance on
12kft of 24AWG, without bridged taps, will actually cover a much smaller
portion of the market.
Comparing echo cancelled ADSL performance on 8kft of 26AWG wire, to
performance on CSA Loop #1, which contains 7.7kft of 26AWG wire, and a 600ft
bridged tap, you see the downstream bandwidth drop from 8.6Mbps (with 10
self Disturbers) to 1.6Mbps (with 10 self disturbers). To get the same level
of performance, with no bridged taps, the loop length would have to be
extended to 14kft of 26AWG wire. Thus, for a given rate, the reach with a
bridged tap is only 60% of the reach without one, for this case. If this
same ratio held, then achieving 9kft (26AWG) reach w/o bridged taps could
give 5.5kft reach with, which would only cover about 45% of the market.
Thus, to reliably reach real-world working lengths of 12kft of 24AWG wire,
one would have to design for a reach of 20kft, 24AWG, without bridged taps.
Regards,
Patrick
-----Original Message-----
From: Troy Manary [mailto:troy@xxxxxxxxxxx]
Sent: Thursday, October 25, 2001 2:30 PM
To: Copper
Subject: [EFM-Copper] [Fwd: Existing Loop Lengths]
I posted this to P2P but it is probably as useful, if not more so, to
copper heads too.