DLM setting level too low after "fault"

Had my BT Infinity 2 officially enabled yesterday but thought I'd plug in the Smart Hub (Home hub 6) early hours Sunday morning to try my luck and low and behold, it connected at 46Mbps - much lower than the 68 to 80 estimate and even the 54MBps guaranteed minimum but since the offcial activation date wasn't until the next day I didn't think much of it and went to bed assuming it'd be correct at some point the next day.

Completely out of the blue, 2 OpenReach engineers knocked on my door yesterday morning saying there's a fault on my line resulting in their servers always showing me as dropping the connection. They then proceeded to fit a new faceplate and went on their merry way. However I was still syncing at 46Mbps; the engineer said he was surprised I could connect at all but made no mention of the slow speed.

Fast forward to the day after, which is obviously today, and the speed is now 45Mbps, it hasn't moved up; in fact it's dropped 1Mbps, probably as I rebooted the router a couple of times during the day?

Anyway, I was now worried the DLM has "settled" on this lower speed so I called BT and they advise to turn off the router and turn it back on after half an hour, which will apparently force a retrain of the line. I did this some 5 hours ago and I'm still connecting at 45Mbps, I've not rebooted since tho as that seems to make the connects lose a few Kbps.

My line stats look pretty good to me, but I'm not really up on VDSL:
DSL uptime:
0 Days, 4 Hours 47 Minutes 41 Seconds

Data rate:
14.27 kbps / 44.71 kbps

Maximum data rate:
14273 / 44709

Noise margin:
6.1 / 6.4

Line attenuation:
16.5

It looks like the 45Mbps is an artificial cap? Those stats to me suggest the line is capable of much more?

Does turning the modem off for half hour force a retrain?

Should I wait a couple of days or speak to them again tomorrow?

Edited by deleted (Tue 23-Aug-16 22:27:28)

If the attenuation is right, you probably can get more - and the estimate of 68-80 seems to match that.

However, with only 6dB of noise margin, your line is running as fast as it can right now. The sync speeds and noise margins don't suggest an artificial cap.

If there is more to be gained out of the line, then there would have to be a fault with the copper somewhere. However, I'm not really au-fait with trying to debug a line via the HHx devices, so someone else might offer help...

Ah, I didn't think that's how the Noise Margin worked when it's capped? I figured it'd always sync at the cabinet at 6dB then the cap is implemented after that? Like it'd sync at 60Mbps at the cabinet but DLM thinks this is too fast due to previous errors so reports a max attainable of 45Mbps to the router?

I just found it a coincidence my actual speed is exactly the highest attainable.

Also, BT tested my line both this morning (the engineer) and remotely and found no fault (after changing the faceplate).

I'm confused now haha

EDIT: A noisy line would increase the Noise Margin wouldn't it? For example, max attainable would report, say, 70Mbps at 6dB but the NM would be increased to, say, 9dB resulting in a connection of, again only an example, 50Mbps.

I may have this all wrong lol

Edited by deleted (Tue 23-Aug-16 23:09:32)

Have you tested into the test socket to rule out internal wiring/setup as being the cause of the low speeds?

I got the same speeds using the faulty and the new faceplate, not sure if that makes a difference? The speeds are also the same with and without a filter and/or a phone connected.

The faceplate on now is brand new and fitted by a BT engineer yesterday morning.

But no, I haven't tried that as yet. You think that might help?

There's one way to find out

lol true.

It's slightly better:

Data rate:
17.85 kbps / 49.51 kbps

Maximum data rate:
17850 / 50369

Noise margin:
6.1 / 6.3

Line attenuation:
16.1

You need an engineer visit. However you're unlikely to get one without waiting the 10 mythical days.

Hey, I came from ADSL, 50Mb is magical to me

I'll contact them tomorrow. If it is a fault the annoying thing is there was an engineer here yesterday morning and he said it tested fine. Odd.

This increase could just be the DLM that I apparently "reset" some 6 hours ago, no?

I'll leave it and see if it increases overnight.

Best way to think of it, noise margin is effectively how much noise the line can tolerate before it drops out.

The target is usually 6db, this is on a good line. Here lets imagine the line drops out when the noise margin hits 1db. The line can tolerate effectively 5db of noise / interference before it drops out. Interference may be a lamp post turning on, a washing machine in your home close to the phone wiring etc.

Now let's take a problematic line. At 6db noise margin the line drops out. It continually loses connection. DLM intervenes here and sets a noise margin of say 9db or 12db.

Now at a 12db noise margin, the line can tolerate 11db of noise before dropping out.

The issue, at a higher noise margin the line syncs slower.

Now looking at your line the noise margin is 6db and is not indicating that DLM is capping the speed. It might just be the estimate you were given was off or that there is a line fault somewhere.

Certainly there is not a DLM fix that will give you 10Mbps more, as if that was the case your noise margin would be say 15db not 6db.