I have an ADSL2+ line with O2, which has some very odd behaviour! Normally it is very stable, and is up for 2-3 months or more without dropping. However, if it drops (or I unplug router etc) it is very unstable for a few weeks (e.g. disconnecting several hundred times in one day).
These unstable periods are linked with a fluctuating upstream SNR - between 3.0-6.0, but occasionally dropping to zero. In fact it's possible to watch it drop from 6.0-0.0 and then disconnect.
When it is stable the SNR is about 6.0-7.0, as is the downstream most of the time.
I mentioned this to tech support - who dismissed it, as the upstream SNR cannot cause the line to disconnect. I should mention this is with all the usual tests - different filters, into test socket etc - making no difference.
My question therefore is what affects the upstream SNR (but not simultaneously the downstream) and can this cause stability issues?