I think I've got most of it from what people have said now thanks, I guess you can't really tell as I don't have the graphs before the speed drop but as I mentioned at the start I was at 53meg download and 15 upload and am now on 32/8 ish, is it possible to tell what caused the large drop, I realise cross talk would be involved but can you tell from the graph how much speed I've lost because of the power drop enforced (as in the bits missing from that big V shape on the bitloading graph, is it a set amount of speed per bit or not, i've no idea about bits if you couldn't tell ).
Looking at your band plans, you are connected to an ECI cabinet DSLAM.
It's not at all unusual to see such a V shape in the bitloading graph.
We think it's due to power cut back at those lower frequencies, to avoid swamping any ADSL connections that may have significantly weakened signals due to the original PCP cabinet being a long way from the exchange.
I'm connected to a Huawei cabinet DSLAM & I see a similar V shape.
I am over 5 km from the exchange & around 1.1 km from the cabinet.
I could only achieve around 1 Mbps sync speed on ADSL & at first, I achieved up to 35 Mbps on VDSL2.
Since then, I have been hit by increased crosstalk & I'm now lucky to get around 20 Mbps sync speed (currently 18.73 Mbps).
Over time (24/7 logging) I have seen a number of occasions where my DS SNRM would drop quite suddenly by 1 or 2 dB & various errors would increase for a few days before the connection would resync.
At the resync, SNRM would increase back to the target 6 dB, but sync speed would always be 1 or 2 Mbps lower.
QLN on my connection has also worsened at a similar rate.
I also noticed that my D3 band is not being used, Attenuation to high i'm guessing, could maybe that of been used before but the crosstalk took it over a threshold and I lost speed from that??, and if so do we know what the threshold is or is it not set?, the reason I ask is that my upstream U2 band is at 58 so wondered if I'm about to lose that.
Maybe the D3 band was used previously, but as you suggest, attenuation is now too high.
Attenuation is around 67.8 dB for my D2 band & I only get a small amount of bitloading from that band, so the cut off point is possibly somewhere around 70dB.
Line attenuation shouldn't really vary much (slightly increased during warmer weather), so unless there has been a permanent deterioration of line conditions, it probably hasn't changed much.
I suspect that crosstalk is the main factor in your reduced sync speeds, worsening QLN & SNR, and/or reduced power.
I think BT
could use power of up to 14.5 dBm for profile 17a VDSL2 connections, but choose to restrict it to something like 12 dBm anyway & when crosstalk is likely to be caused is a factor, DLM reduces it even further.
Do you have any older graphs or even raw telnet data at all from when you achieved higher sync speeds for comparison purposes?
1 thing I did notice that when I was on an earlier firmware version for the router that often my bits per carrier on the bitloading graph would plummet every few hours and then go back up to then normal levels, any idea what would of caused this to happen?? (I should have the rest of the graphs saved somewhere if they are needed).
I think that was simply down to a 'glitch' in the modem's previous firmware version(s).
I noticed that when I updated to the latest firmware ....038m that the issue stopped, I also noticed the all the shared bits/tones all became just download ones and not upload was that changed in the latest firmware do you know??.
Yes. 'Shared' tones disappeared when firstly the DSLAM band plans changed, shortly followed by another slight change via the remotely applied modem firmware updates.
You may/may not have also noticed that DS Line & Signal attenuation values no longer match exactly for the majority of connections, unlike with the older firmware.
We have no idea how accurate the reported values are, but they do at least now show a difference.
It is perfectly feasible to have low Line attenuation, but due to the effects of crosstalk or other 'noise' interference, worsened QLN & worsened Signal attenuation as a result.
FWIW, I have attached a recent snapshot montage from my connection for comparison against yours.