Over time, I've been reporting how my "attainable bandwidth" has been decreasing. As this has happened, my SNRM figure has been dropping. And I have believed this to be caused by increasing crosstalk as usage increases.
My history is, roughly, as follows:
Date Attain Actual SNRM 01/2012 90 40 02/2012 91 40 02/2012 85 80 7.3dB * 80/20 package turned on 03/2012 84 80 7.1dB 06/2012 83 80 6.9dB 07/2012 82 80 6.6dB 09/2012 82 80 6.5dB * Voice fault occurs around here 11/2012 81 80 6.3dB 12/2012 78 80 5.4dB 01/2013 76 80 4.6dB 05/2013 72 80 3.0dB
It has stayed synchronised since the beginning of December, perfectly stable, running at 80Mbps, even as the SNRM has dropped to 3dB.
Last week, I finally bit the bullet, and decided to re-sync my line, even though I expected my sync speed to drop to below 72Mbps.
Imagine my surprise, then, when it resync'ed at 80Mbps with an attainable value of 83Mbps. Over the week since, this attainable figure has dropped some, but is still higher than it was earlier this year.
Date Attain Actual SNRM 05/2013 83 80 6.7dB 05/2013 79 80 5.6dB
I finally managed to turn some of my graphs into animations to highlight the line conditions. It looks like there has been hardly any change whatsoever.
So - is a dropping "max attainable" speed really a reflection on the crosstalk on the line? What else would cause it to drop over time?