Speed down from a stable 80/20 to an IP Profile change of 49/11

[#1]

Won't be firmware, since this issue has existed since I had modified the ECI /r. Actually, I recall the HG612 doing the SNR damage (raised from 6db to what it is now, 20db) 
The firmware I compiled myself (OpenWrt) from trunk, and I've used the latest Lantiq drivers/firmware, which shouldn't be a problem.

[#2]

Oh interesting, at some (probably distant) point in the future, if I may, I'll get back to you for some more info. but I've got a lot of other more pressing things to get on with. Good luck with the engineer visit, btw.

[#3]

Sorry for the delayed response.
I can see you've got a engineer booked for tomorrow afternoon.
Let us know how you get on.

[#4]

Hi Matthew, thanks. Just wondering if the engineer will get the notes? If he's coming to the door, or just sitting in his van to do the reset? The ticket bot seems automated and when I replied to the ticket with a date and some extra information, it booked it anyway.

[#5]

The engineer should have the notes on their devices (I think they all use iPhones these days).
He/she will come to the property and attach his portable tester to the master socket and test it from there.
If a reset is needed they'd have to contact the Openreach helpdesk to get this authorised.
In addition your issue isn't caused by DLM as your profile is "0.128M-60M Downstream, Error Protection Off - 0.128M-17M Upstream, Interleaving On" and your currently syncing at 49mbps.
From what I can see it looks more like a fault on the line.

[#6]

Interesting. I noticed that from the ticket update.  
I always thought it was DLM raising my SNR due to the disconnections, which in turn has lowered my sync speed.
Previous SNR was 6.xdB both ways
now it's 20.6dB down and 15.2dB up.
I've noticed this morning my line resynced at 5AM, on retrain it slightly raised my upstream from 12Mb/s to 15Mb/s however it's added some extra interleaving depth and a delay from 4ms to 8ms
SNR raised some more for the upstream, from 13dB to 15.2dB which doesn't make sense to me given the speed improved so it should have been lowered.

[#7]

What did you actually do with the ECI modem? I'm wondering if that's also part of the issue here.
DLM doesn't touch the SNR margin - the target is always 6db.

[#8]

Quote from: jsamuel

Previous SNR was 6.xdB both ways now it's 20.6dB down and 15.2dB up.

Is it possible these are line attenuation figures and not SNRM's?

[#9]

A change from an ECI to an HG612 caused the issues, I'm not sure why though.
DLM issues a change in target SNR if the line has dropped x amount of times the previous day. It thinks the line is unstable but in reality just a loss of power.
My attn is  8.9dB down & 10.2dB up

[#10]

Quote from: jsamuel

DLM issues a change in target SNR if the line has dropped x amount of times the previous day.

Nope.

[#11]

Where did you get that from? It doesn't make sense atall..
Obviously if DLM sees the line as unstable it will first try to interleave, and if that doesn't work then banding which causes an SNR raise. 
I think the confusion there is ADSL's DLM changes the SNR directly, where as VDSL's DLM uses banding.

[#12]

That will probably have come from an Openreach document. 21CN can use banding as well as Target SNRM.
Yes a banded speed can result in a higher actual SNRM, but the Target stays the same, just doesn't have any impact because of the banding.

[#13]

FTTC DLM uses banding to cap a line, obviously this will also increase snrm, but the snrm target is always 6db, however the banding has higher priority than the snrm target.

[#14]

All is good. The engineer & his apprentice came and reset DLM. The line synced at a full 80/20 again, but the profile appears to be at 72/20. Not too bothered, perhaps it'll sort itself out in the next few days.
Noise margin dropped significantly, and is still dropping hopefully to a normal level.
My ping appears to be 6ms now, a nice improvement from 20ms.