@ Kitz and Roseway,
Continuing with the saga, the line remains a little unstable with the SNRM varying between 5 dB and 11 dB.
As to be expected the noise margin increases when the sync speed decreases.
The modem has reset itself several times and occasionally I've done a manual reset.
This often produces a sync speed up in the 600 kbps range, but then the modem resets itself back down to 448.
With a line of this length (attn'n 63.5 dB) I believe the observed noise margin patterns to be normal usually.
Perhaps what's surprising is the almost flat noise lines before these events started.
I assume that, as part of the initialisation after a reset, the modem negotiates with the DSLAM and the noise discrimination logic between the two define the tones and bit loading which then is also reflected in the current sync speed.
This logic then continues to monitor the individual tones loading them as has been determined until there is a major loss of data, whereupon the modem decides to reset itself.
I did just wonder if there was a sort of positive fault with the noise discrimination logic falsely giving the previous flat lines ?
I'm always a bit sceptical in these situations where you are observing the equipment and systems themselves rather than with independent test equipment.
However that would clearly be difficult to do when you're relying on the modem and DSLAM to be self-regulating in an inherently noisy environment.
Any corrections, comments or ideas would be welcomed.
Kind regards,
Walter
