Broadband restricted speed?

[pddco]

Hello. I’ve got BT Fibre 2. Had it for years. No issues. Until recently. Up until about a month ago I was consistently getting 75Mbps down and 18 Mbps up. As reported by my Sam Knows Whitebox and an occasional test through MyBT. Now it’s 60Mbps down and 18 up. Not a dramatic decrease but just wondering why? Quiet line test fine. The only thing I can think of is that I’ve  just been doing some decorating in the hall and perhaps unplugging the hub probably more than I should. Could it’ve upset DLM - Or whatever it is that monitors the connection. If that’s the case how long must I wait for my normal service to be resumed. I’ve looked at the hub admin and it shows a possible 75Mbps. Can I ask the 150 team to restore it? Realising of course that a refusal often offends. Thanks

[imjolly]

If you have been switching the hub off and on a few times a day for a few days then I expect the DLM to have seen your line as unstable and increased noise margin resulting in drop in connection speed.  A stable connection for a few weeks and your noise margin should start to reduce and speed increase

[pddco]

Thanks @imjolly  Hmmm, I wonder what it’s metric is.  Clearly it doesn’t take years of previous good behaviour, or current line conditions, into account. Or perhaps a 15Mbps cut is quite generous as it’s a first offence. But weeks seems a bit harsh…. Oh well, meanwhile can I see the noise margin figure that’s been set and compare with what it should ideally be? 

[imjolly]

You need to go to hub manager the advanced setting then technical log information. The normal noise margin should be about 6db and I expect yours to be higher

[licquorice]

Yes, your hub stats should show the current value and target will be either 6dB or 3dB depending on cabinet type you are connected to.

[pddco]

Well, I had a look and indeed noise margin is up. 

Just curious, but if I restart the hub will I it retrain and perhaps reduce the margin? How dynamic is DLM?

 

[imjolly]

You need a stable connection for noise margin to reduce. Resetting hub will not help and could make matters worse with higher noise margin and lower speed

[licquorice · Accepted solution]

Do not be tempted to restart the hub, that will just make things worse.

https://kitz.co.uk/adsl/DLM_system.htm is quite an old description of DLM but gives you an idea of how it works.

[pddco]

Well @licquorice it may not have been me unplugging the hub a few times after all. That all happened over 4 weeks ago. And today I’ve noticed the noise margin has actually increased. My download speed has  reduced to 52 Mbps (from 75 originally). I had to do the 17070 quiet line just to check again  (from the test socket)  But there’s no obvious crackling / noise. Looking at the logs after about 9 days of  DSL uptime the hub had a soft restart around 1 am. Anyway. I’ve raised a fault but seems odd. Like I say, I’ve had years of stable 75/19Mbps but over the past month or so it’s gradually got worse. 

 

[imjolly]

your connection speed is 67mb just as it was when you previously posted hub stats so the recent drop in connection has not change that but your noise margin has increased slightly.  download speed can fluctuate and is not guaranteed