Three weeks in - still up and down

[#1]

Yesterday I was feeling pleased. I was syncing at a bit above 5000, my profile was up to 4500 (not wonderful in absolute terms, I know, but for my line it's good). Then I looked at my computer just after midnight and found that the router was having another episode like the one I described here: http://community.plus.net/forum/index.php/topic,76159.0.html
The router was breaking the connection every minute (precisely every minute, I think). The sync rate was listed as 5036, but the downstream SNR was an interesting -2db. I don't think I've seen a negative SNR before.
Anyway, I reset the router and it came back up steady, with a normal SNR of 9db. Only now I was syncing at 3749. Sigh - I switched it off and went to bed.
This morning I switched it on again, and I'm back to a reassuring sync of 5186, with an SNR of 9db. The only problem is that my profile has dropped to 3000, and I'll now have to wait for it to rise again (if it does - I have a feeling that at some stage the DSLAM is going to decide to play it safe and not raise the profile).
Anyway, experience (not just last night) shows it's always a bad idea to reset the router late in the evening. For whatever reason, the sync rate on startup is always much lower at that time.
Upstream is (apart from during problem periods as described above) always fine, typically syncing at 775.
My downstream attenuation is around 39, so I know in theory I should be able to get a faster connection, but I'd be happy with a stable profile of 4000 or so. Until yesterday evening I thought things were settling down. Can I blame the weather?
Graham

[#2]

Same thing happened again last night. From the way the router restarts the uptime count on the ADSL line instantly (and precisely every minute) I don't think the line is actually being reset. From some stats sent to me by PlusNet staff after I first reported the problem last week (I thought it was a one-off then) it looks like the line is just seen as down at the PN end. When it's happening my WAN IP address is shown as 0.0.0.0 and obviously I can't connect to anywhere.
What I'd really like to know is what causes a negative downstream noise margin of -2db. Has anyone else seen this?
In the meantime my profile's sunk to 2500, though I'm currently (since resetting the line this morning) syncing at 5047 with a downstream noise margin of 9db. Until recently I thought my line was more stable since I joined the trial, but now that doesn't seem to be so.
Graham

[#3]

Do you use DMT to monitor the line? It's worth doing just out of interest. My own findings on my line with an attenuation of 50dB is that I can sync early afternoon at 4300Kbps and this is 80% of the attainable rate of 5378Kbps. Then during the evening using the DMT tool I can see that I losing all the upper bins and reducing the attainable rate down to 4500Kbps at 1am. If I lose sync at this time then the sync rate will be 80% of 4500Kbps giving 3600Kbps.
I believe that the DLM system would work if the 80% of the attainable rate is applied when the sync rate is at it's best but this should be increased to 95% when the line is at it's worst. But perhaps this will happen but need several months for the DLM to learn. Perhaps this is happening as others are seeing the same sync rates no matter the time of day. Mine are still changing slightly between 4200 to 4368Kbps with a couple in the 3600Kbps which cause my profile to go from 3500 to 3000. Actually in the 21 days I have been on the trial I only had 3 days at 3500Kbps.
Regarding the -2dB margin most modems are not very good returning negative numbers so most would only see 0dB. Its a margin, the average minimum SNR across the bins is approximately 35dB. This is the minimum SNR that the modem believe that it can maintain the connection. So with the a 6dB margin the modem will sync at a speed that will give a SNR of 41dB. So when the SNRM drop to -2dB then the average SNR across the bins will be 33dB.

[#4]

Thanks, again (you also replied to a related query elsewhere). I haven't tried DMT yet. I did try to get another monitoring program to work (routerstats lite) but I couldn't get it to work with my router (ZyXEL P660HW-61 - apparently not quite the same as some other P660 variants which allegedly do work with it). My router's also not listed for DMT, but I could give it a go.
Graham

[#5]

Well, after a bit of trial and error I've got a version of DMT that half works with my router. I had to use v5.22, which does talk to my ZyXEL but which only works with 'Annex B' connections - I think the UK uses Annex A. (Is this the difference between PPPoA and PPPoE?) It's also only in German, but luckily I can handle that. It doesn't show my sync speeds, but it does show SNR, attenuation, etc., and it knows I'm running ADSL2+ and which processor my router has. I'll need to look at the figures in the boxes on the right some more before I begin to understand them.
Graham

[#6]

Well, monitoring the line with DMT was certainly instructive! The logfile doesn't show sync speeds, as I mentioned earlier. But the combination of SNR and IP address tells a story.
8.30pm, start monitoring. Speed=5047, SNR=9
SNR drops steadily, down to SNR=1 by 9.35pm
SNR stays around 0, but shows -2 at 10.15pm
At this point I do a manual resync to stop the line from failing.
After this, speed=3458, SNR is between 6 and 9
SNR drops to 4 and 5 around 1.40am (for 15 mins), but comes up again to 7. Then drops to 3-4 around 2.50am and comes back up again.
SNR stays between 4 and 7 until around 4.40am, when it starts rising steadily to 10-11.
At 7.10am there's a resync, not initiated by me. New speed is 3684, and SNR stays at 10-11. (No idea why this resync happened then.)
At 9.10am, after having had a good look at the log, I initiate a resync. Speed is now 5158, SNR=9.
Apart from the bits in the early hours, which I don't know about, this pattern seems to fit what's been happening during the past few days.
Graham

[#7]

On the advice of PN support I've now raised a fault with the faults team. What a lot of hoops to jump through in the automated process, and you can't provide full info.
Looking at the times when my SNR margin drops and then rises, I'm wondering about interference from street lighting. If that's the case, there's probably not a lot that can be done.
Graham

[#8]

My first advice will be to remove the ring wire. From another thread where you have described your wiring I would suggest just removing the ring wire from the master. I know that this is not a NTE but the only options than to do it yourself is to pay large sums of money to Openreach to do it. The only 2 wires that need to be connected are 2 and 5 the others can be remove by gently pulling the wire upwards.
Normally you should not need to do the extensions as there should be no electrical path from the ring wire back to the Aand B pair.
As for noise street lighting probably do play a large part but I personally believe it also crosstalk from other ADSL users as this will explain the decrease in SNRM between midnight and 1am when all the P2P downloads kick in.