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[Paul C]

Hi I'm on a long line about 10km but luckily thick copper line attenuation 55dB and until a line fault I was getting sync  of up to 4.2M @ 3db SNR (7800n).
The line had a bit of a line fault but it was working well, until I lost a leg POTs phone not working but down load down to 1.9M. Open reach fixed the line faults, But now I have a spike on the SNR of about 3db and BT keep changing the target SNR I think due to the errors up to 2000 error seconds an hour, currently I'm at 12dB - 3dB tweak.
Strange the spike is positive for about 10 seconds 16 times an hour like clock work ? could it be to a split pair somewhere?
Has anyone come across this problem before, SNR trace attached.

[sevenlayermuddle]

I'd advise tweaking the SNR in these circumstances.

By tweaking it you will temporarily get a faster connection, but you will also get a higher error rate.   BT's DLM will interpret that higher error rate as 'instability' and will raise your target margin all the more, and you'll end up with a slower connection.

Fluctuations of a few dB are quite normal, the reason for the 'margin' is to a accommodate these fluctuations.   BTW's  DLM start off with a margin of 6dB even for the shortest and most stable of lines; a margin tweaked to 3dB, on a long line, is probably pushing your luck too far.

[kitz]

Curious.   How long has it been spiking like that for?  What modem are you using?

On occasion we see spiking like that on some VDSL lines after a power outage.  It doesn't seem to be related to modem model as we have seen it on the HG612, Billion and Zyxel modems. 


Over the past couple of months I've seen several patches of similar on my own line.
It usually starts at about 4-5am when the router will resync, then when it comes back up it starts the spiking... although mine is not as bad as yours (1-2db).
Usually the advice is to reboot the router and it comes back up fine.   
However that didnt work for me a couple of weeks ago until I left it switched off for a couple of hours. - see here.

I had it happen again last night - a reboot has stabilised it some, but its still jittering a tiny bit.   I'm currently waiting until tomorrow to check on something on my phone bill, because I think that the time it started last night may have been when I phoned a friend, but that certainly wouldn't account for the others which all started at 4-5am.   

[Paul C]

Hi thanks for that after I post this I'll turn it off over night and see what happens I had to sample every 5 seconds to see the regularity as the duration is so short. 

[aesmith]

That screen print shows upload speed of only 96K, does that indicate anything wrong?   On my line the upload speed was only ever knocked back from 448K during a really serious fault.

[4candles]

As far as one can tell from the SNR trace, the interval between spikes seems as near as dammit to 3 minutes.


Probably coincidence, but ISTR that 3 minutes was one of the standard timing pulses distributed round an exchange. No idea if that's still the case.   



It's certainly regular enough to be certain it's man-made.

[tickmike]

Have you gone around your house and outside with a medium wave radio tuned to 612Khz to check for REIN ?.