FTTC DLM query

[Andrew600]

Following a landline disconnection caused by contractor incompetence, Openreach turned up this morning to sort it out.

Broadband wasn’t affected and remained up at full 80/20 speed.

In the process of fixing the landline he disconnected the broadband at the cabinet which at first reconnected at 80/20, but after a few minutes it resynced automatically at 72/20 and the maximum data rate is now only 74 mbps compared to the normal 85 or so.

SNR has increased to 6.4 instead of 3.

The OR guy said he thought DLM had got upset and intervened, to give it 24 hours then to give him a call if it doesn’t recover and he will reset it. I’m grateful he gave me contact details to be honest.

Question is does this make sense and is a DLM reset the thing to do if it doesn’t sort itself out.

Thanks for any thoughts.

[licquorice]

Just leave things alone and DLM will revert to 3dB snrm in steps.

Resetting won't help as it will just reset to the default 6dB snrm which is the situation you are in now.

You certainly won't be able to tell the difference between 72M and 80M in the real world anyway.

[imjolly]

Yes the resets/disconnections have triggered the DLM to increase the noise margin resulting in drop in connection speed.  This will correct itself automatically given a stable connection and 7/10 days

[Andrew600]

Thanks both. I’ll leave it alone.

Glad I posted now. I had no idea the default was 6dB, and a loss of 10% speed will have no effect at all for my usage anyway.

Thanks for the replies. Much appreciated.

[Andrew600]

Sorry to be a pain about this. It’s just ticked over 10 days up time with no DLM intervention yet.

Is it time for a hub restart?

Stats:-

DSL uptime:10 days,00 Hours06 Mins08 Sec

Data rate:19.999 Mbps / 72.038 Mbps

Maximum data rate:25.005 Mbps / 74.131 Mbps

Noise margin:15.3 / 6.3

Line attenuation:5.3 / 9.4

Signal attenuation:5.2 / 10.8

[licquorice]

Unfortunately, if DLM hasn't dropped your noise margin to 3dB by now it isn't going to. A hub restart won't do anything to prompt DLM.

Not what you want to hear, but there is absolutely nothing you can do to invoke 3dB margin.

[Andrew600]

Thanks @licquorice 

Yep, not what I wanted to hear. 
I wonder what the OR contractor, then an OR engineer did to provoke this. It’s been at 3dB and 80/20 for longer than I can remember, so something fairly significant happened. It was without any doubt a contractor foul up, but it will remain an unsolved mystery.

At least, as you suggested, the impact on my day to day use is zero, so it doesn’t really matter. It’s just the numbers annoying me.

[licquorice]

DLM seems to be very flaky and temperamental I'm afraid. Probably no consolation, but my line has been banded at 44M with 9dB margin for months despite being totally stable.

You could try one restart of the hub but I would be extremely surprised if it kicked DLM into life.

[Andrew600]

You were right.
A hub restart made no difference at all. 
Once is enough. I won’t be doing another. I’ll just live with it and hope it sorts itself out one day.

I hope yours improves soon. 🤞

[licquorice]

If it has kicked DLM, you won't see an immediate change. It will still need to see that your line will cope with reducing SNRM before it does so. Check again in a few days, but I'm very doubtful it will.