FTTC speed fault (SamKnows white box evidence)

[#1]

I've just had the monthly report email from Samknows; I have one of their white boxes in as I'm taking part in the UK speed measurement trial.
I notice that the speed nosedived from around 62Mb/s on 4th Feb to around 36Mb/s on 5th Feb and it's been constant around that mark since. Upstream has been steady at about 17.7Mb/s and latency and packet loss both around where I'd expect them to be.
There's been no change in the line profile (just checked with support to confirm that) so there's obviously something amiss somewhere.
I trust these numbers more than I'd trust a web-based speed checker as it's entirely hardware based and the white box is wired in to my home network in the "approved manner".
I'm less than 100m from the cabinet that's providing our FTTC service and there have been no other changes in-premise.
Anyone else got any similar views?
--
David

[#2]

The speeds in your report card email are averages. Log in to the SamKnows performance monitor, and drill it down by hours instead of days. On my connection it's at full speed for most of the day and painfully slow at peak time. On average therefore it looks like a much slower speed than the line is actually running at.

[#3]

Thanks for the reply. I know they're averages, but the graph did a reasonable impression of a cliff edge on 4th Feb. The monthly average shows 38Mb/s and the numbers since hover around 33Mb/s because the average is weighted by the higher  figures at the start of the month (I'll take my stats hat off now).
The weekly figures are also consistent with the 33 to 35Mb/s readings I've been seeing since early Feb.
Looking by hour tells exactly the same story. It isn't a gradual decline which you'd (intuitively) expect to see as service load increases, it's a sudden and dramatic reduction as if something changed:
4th Feb
00h00 : 62.15
06h00 : 69.06
12h00 : 62.07
18h00 : 37.64
19h00 : 37.71
20h00 : 37.77
21h00 : 37.79
etc
On the preceding day, the lowest was 55.92Mb/s and generally bounced around the 60Mb/s mark
Sorry, but this doesn't look much like an averaging problem to me.

[#4]

Given the time of day it occurs, it looks more like it might be this problem.
EDIT: Or has it stayed at that low of 37 ever since since 6pm on 4 Feb?

[#5]

Thanks bright. I'd seen that thread...
Nope, since 4th Feb, it's been constantly around 35Mb/s. It looks like a profile change from 80 to 40. It's not dependant on time (well it hasn't been since 4th Feb!).
Support reckon it's not a profile issue though.

[#6]

You said there has been no change in the line profile, but what value is the profile currently?
You can check the BT IP profile by using the BTW speed tester and clicking "Further Diagnostics" after the 1st test completes.
Your Plusnet line profile should match the BT profile - you can check the Plusnet profile at https://portal.plus.net/my.html?action=data_transfer_speed (you need to log into the Members Centre first). It's the figure shown as Current Line Speed.

[#7]

Phone exchange:
MOSBOROUGH
Estimated line speed:
80Mb (Accurate to within +/- 1Mbit) - Checked on 2012-12-19 20:01:42
Current line speed:
78 Mb
The PN support chappie agreed with these numbers when I rang earlier. I can't run the BT speed tester remotely so I will try that tonight

[#8]

The line profile has been changed down to 38Mb. Damn and blast.

[#9]

Given it dropped so suddenly it does suggest a line fault of some sort. Might be worth trying to get the line to re-sync, which should reset the profile. The best way to achieve that is log into the router management interface and manually drop the PPP session. Then power off the BTOR modem, leave it off for at least 10 minutes (so the DLM doesn't think there's a problem with the line), longer if you want to be extra safe. Then turn on the modem again, wait for the DSL light to go green. Then re-enable the PPPoE session in the router. That should cause the new BT IP profile to be notified to Plusnet's systems. The BTW speed tester should then tell you if there's been any improvement in the profile.
Given that you're only 100m from the cabinet, I'm surprised you were only getting around 62Mbit/s before 4th Feb. I would have expected your line should sync at pretty close to the max.

[#10]

Thanks bright. I'm going to do that now.