Weird connection behaviour (FTTC)

Hi, long time lurker but I needed to join and get some of your opinions as to what's happening. Bear with me here as this has been going on a while!

I have had the 80 down/20 up since it became available to me in 2016(ISH), it's always connected at around 50-55 down and 12-15 up, I was fine with this.

Over the last 18 months or so it's been going haywire, faster download speeds up to 69-70 down but this came withprolonged periods of disconnections daily and reconnecting back at similar speeds. It was annoying, engineer came out but couldn't find any fault while he was here but replaced the master socket and said he'd reset the monitoring computer anyway. This stabilised it for about a week before it started again, this progressed to the upload speed tanking to less than 1mb up so I'd have to manually reconnect until it got to a usable speed but still lower than usual, around 5-6 up.

3 more engineer visits, none could find any issues as it never disconnected while they were there. For no reason at all, in around November last year it stabilised back to it's 50 down 12 up and was rock solid for weeks. I was relieved that it seemed to have sorted itself out but now it's back to speeding up the download speeds and disconnecting. The last engineer suggested that it might be some sort of interference but the disconnects are never at the same time so probably not, or that some sort of connection was broken in the cabinet but he couldn't do anything until he found a fault, which never happens while they are here.

I was originally with BT and moved to Plus net and then Vodafone for the last couple of years.
I'm desperate to move to FTTP (another story, the battle to get my street included while the surrounding streets are done is infuriating), anyway I checked the fibre checker for my address and Vodafones own checker(!) says I am unable to get any form of broadband and to get 4g instead.

Sorry for the essay but does anyone have any suggestions?

Is there any sort of line statistics available from the modem/router you connect to the master socket with?

It sounds like the DLM (dynamic line monitoring) keeps trying to lower the downstream noise margin from the default 6dB to a lower value (5, 4 and 3dB are all viable). On some lines this can cause instability as it gives less spare noise margin.

Without some kind of line stats it's a guessing game.

In reply to a post by j0hn83:

Is there any sort of line statistics available from the modem/router you connect to the master socket with?

It sounds like the DLM (dynamic line monitoring) keeps trying to lower the downstream noise margin from the default 6dB to a lower value (5, 4 and 3dB are all viable). On some lines this can cause instability as it gives less spare noise margin.

Without some kind of line stats it's a guessing game.

What John said.

So this is what's currently on it the router page:

DSL Uptime 9 hours, 57 minutes and 11 seconds

Line Coding DMT
Status Connected
Number of Cuts 18
Link Power State L0

Line Quality

Downstream Upstream

Current Rate 65205 kbps 9540 kbps

Maximum Rate 65257 kbps 12917 kbps

Signal-to-Noise Ratio 3 dB 8.6 dB

Attenuation DS1 16.6 dB, DS2 41.3 dB, DS3 61.8 dB US0 6.0 dB, US1 31.9 dB, US2 48.4 dB

Power 12.6 dBm 7.6 dBm

CRC Errors in last 597 minute(s) 242 2444

K (number of bytes in DMT frame) 0 0

R (number of bytes in RS code word) 10 16

S (RS code word size in DMT frame) 0.1192 0.7922

D (interleaver depth) 8 1

Delay 0 ms 0 ms

Sorry for the formatting, I'd post a screenshot but I don't seem to have the option to. The other thing I forgot to add is that this is the second router, it was swapped out after one of the engineer visits but made no difference. When the connection goes down, I also get kicked off the WiFi, is that normal? I thought it would just not connect to the internet but I would stay connected to the home network.

Edited by WhiskyJamJar (Mon 11-Mar-24 19:45:24)

Yep, as suggested, DLM has set your target SNR to 3db … this is giving you a higher sync rate, but is proving unstable due to the error rate.

It needs hard pinning to 6db snr profile. Openreach can do this.