Factors affecting Upstream SNR

Hey all,

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?

Thanks

The upsream is at a lower frequency than the downstream therefore can be targetted by lower-frequency RFI.

I have had my upstream capped at 427 Kbps, and that gives me an SNR of 16.2
At this capped rate my snr can still drop as low as 6 then back up again after about 10 mins
BT have done all kinds of tests and the line shows as fault free, Yet they can still see the SNR jump about like junkie going cold turkey

Have you tried Routerstats to graph the upstream SNR, to see if you can spot any pattern?

My line does this about twice a year.
Upstream NM hits the floor and the router goes into a resync loop. Check the line with a corded phone and there is noise. Report to O2, jump through hoops, remote line check and problem goes away. So it's either O2's kit or a very intermittent HR line fault.

Thanks - that makes sense, although I'm at a loss what could be causing it for a few days and then fine for months! I can't spot any pattern in time of day etc, it truly seems to be random.