Bob's experience with ADSL2+
"The involvement of BT's team has significantly
overcome my original reservations and improved my broadband
speed."
Bob's update, 21st May
2009
"Following on from
my original comments
on ADSL2+, the involvement of BT's team has significantly
overcome my original reservations and improved my broadband
speed.
"BT were able to reduce the Target Noise back
to the original 6dB and I now have a stable connection
with rates of 4097 kbps down and 784 kbps up. This is an
improvement of about 330 kbps in both down and up speed
from the previously stable ADSL1 and my BRAS has increased
from 3 to 3.5 Mbps accordingly.
"Over the last week
I have monitored the modem Bitloading data and have recorded,
as anticipated, only data up to bin 197 (850 kHz) so that
the ADSL2+ part of the spectrum remains out of range. (This
would apply to most members of this group where their line
attenuations are in excess of 50dB).
"(Note: For
downloads, ADSL1 uses the 224 bins from 32 to 255 (138 to
1100 kHz), and ADSL2+ uses the ADS1 range plus an additional
256 bins (138 to 2200 kHz). These additional bins suffer
higher line losses than the lower ADSL1 frequencies so that
only those with low exchange distances can expect to benefit
from the higher download speeds (up to 24 Mbps) with ADSL2+).
"At my higher downstream rate the variation in Noise
Margin has increased to about 5dB depending upon time of
day. The minimum Noise Margin I have measured is 0.7dB which
surprisingly the router seems to cope with without any signs
of packet loss. Before the upgrade, I would be aware of
packet loss when the Noise Margin fell below about 2dB so
perhaps ADSL2 is more resilient to low Noise Margins or
perhaps the new TI DSLAM performs better than the Alcatel
version. My typical Noise Margin daily variation is shown
below.
"Using my modem I have also been able to extract
the spectrum of my neighbouring pub's ISDN connection. The
induced crosstalk can be seen to consists of a carrier at
384 kHz with 60 kHz sidebands (see
bitloading.pdf). The amplitude
is the number of bits the spectrum is reduced when the crosstalk
is present.
"Finally, as part of my investigation,
I requested Interleave to be turned off. This has significantly
improved my latency and I have not seen any degradation
in data rates."
Bob
|