Strange Downstream SNR Margin

Hi guys,

I can only think this is caused by some interference, but does anyone who has better understanding of this than myself know what could be causing this? Should I be concerned?

https://i.gyazo.com/71f0472065c8f24c21e64b8714a7f8bb...

Cheers!

William

Not this again.

It's dropped from what, 4.2 to 3.8 a few times? If it didn't cause any issues at the time, then no it's nothing to be concerned about.

I think you need to switch off all your monitoring software and stop looking for faults.

I've turned on the monitoring software for diagnosis. There's a fault there, but it's very low scale. I should probably investigate it but it's not affecting service yet.

Edited by deleted (Sun 19-Mar-17 17:00:24)

Particularly on ADSLx, less so on FTTC, downstream noise margin is very likely to fall by anything up to 3dB overnight. The interference hitting the copper between you and the DSLAM/MSAN is greater at night.

A simple fact. It's to do with reflections off one of the atmospheric belts when the sun is down. Which is why it is always recommended to connect well inside daylight hours for highest speed, and at night for greatest stability.

Think about it. For decades the default sync-time noise margin was 6dB. SpeedTouch modems would lose connection if it went below 3dM. Netgear would hold it as low as 0dB or even sometimes -1dB.

Why did BT Wholesale Sky and TalkTalk all set it at 6dB? Because it was deemed to be the lowest safe level. Nowadays with improved modem technology at both ends, BT Wholesale allow DLM to set connection time SNRM at 3dB. Openreach are trialling 3-5dB as you know for VDSL2.

It's a safety margin. It is expected to fall. It is rarely a fault, and if it is there will be much more serious and noticeable symptoms that a slight overnight decrease. Remember this page?

I understand the normal fluctuations in SNR margin, but this is different, the downstream SNR margin is regularly fluctuating in short intervals.

Edited by deleted (Sun 19-Mar-17 17:34:08)

Is it service affecting?

Yes, in terms of throughput.

Edited by deleted (Sun 19-Mar-17 21:26:30)

Sudden drops of snrm always makes me think of close by equipment interfering with the modem/router when switched on

DECT phones are particularly suspect in my case. Cause exactly what we see on the graph linked in the OP.

Dodgy microwave seals perhaps. Who knows?

In reply to a post by WilliamGrimsley:

Yes, in terms of throughput.

Have you got evidence if that? At the specific times?