Why would there be sudden downgrade of line speed?

Well I hope this is the right place to ask but I'm a bit confused.

on BT Broadband, we've previously had up to 300+Kb/s download speeds quite consistently but a couple of weeks ago this suddenly dropped to 150Kb/s, regardless of the time of day.

I've run a test over at http://speedtester.bt.com/ and have seen that our rated line speed has been significantly downgraded (I believe it was about 4000kbps previously, but it's been a while since I ran this test until now), down to this:
Download speedachieved during the test was - 1142 Kbps
For your connection, the acceptable range of speeds is 400-2000 Kbps.
Additional Information:
Your DSL Connection Rate :1664 Kbps(DOWN-STREAM), 448 Kbps(UP-STREAM)
IP Profile for your line is - 1250 Kbps

Also, here's the stats from the BTHomeHub:

Uptime: 26 days, 21:03:29
Modulation: G.992.1 annex A
Bandwidth (Up/Down) [kbps/kbps]: 448 / 1,664
Data Transferred (Sent/Received) [GB/GB]: 9.00 / 179.30
Output Power (Up/Down) [dBm]: 11.5 / 17.0
Line Attenuation (Up/Down) [dB]: 28.0 / 49.0
SN Margin (Up/Down) [dB]: 22.0 / 10.0
Vendor ID (Local/Remote): TMMB / ALCB
Loss of Framing (Local/Remote): 0 / 0
Loss of Signal (Local/Remote): 1 / 0
Loss of Power (Local/Remote): 0 / 0
Loss of Link (Remote): 0
Error Seconds (Local/Remote): 53 / 0
FEC Errors (Up/Down): 0 / 130,191
CRC Errors (Up/Down): 0 / 2,775
HEC Errors (Up/Down): 0 / 2,400
Line Profile: Interleaved

A little background info - the HomeHub is connected to the master socket on the floor below with an off-the-shelf extension cable. I recognise this is far from ideal but essentially I'm asking why the line rating might change suddenly. The physical setup of the systems involved on my end haven't changed in this time.

Any advice you can give would be greatly appreciated

Chances are there's been a burst of noise on the line which caused you to lose sync.

BT's Dynamic Line Management has kiwered the sync speed in order to try and stabilise the line.

Restart the Home Hub and post the stats taken immediately afterwards.

Done and Done - Does that make more sense to you? Or did you want me to run the other test as well?


Uptime: 0 days, 0:01:48
Modulation: G.992.1 annex A
Bandwidth (Up/Down) [kbps/kbps]: 448 / 4,864
Data Transferred (Sent/Received) [KB/KB]: 155.00 / 314.00
Output Power (Up/Down) [dBm]: 11.5 / 19.5
Line Attenuation (Up/Down) [dB]: 28.0 / 49.0
SN Margin (Up/Down) [dB]: 22.0 / 6.5
Vendor ID (Local/Remote): TMMB / ALCB
Loss of Framing (Local/Remote): 0 / 0
Loss of Signal (Local/Remote): 0 / 0
Loss of Power (Local/Remote): 0 / 0
Loss of Link (Remote): 0
Error Seconds (Local/Remote): 0 / 0
FEC Errors (Up/Down): 0 / 6
CRC Errors (Up/Down): 0 / 0
HEC Errors (Up/Down): 0 / 0
Line Profile: Interleaved

I was under the impression that the DLM should take a maximum of 5 days to start re-adjusting the sync speed?

Or am I just tradgically out of date? :/

The sync speed only changes when you lose sync or when you restart the router. You had a low sync event which caused your BT IP profile to drop. The BT IP profile is only raised when it sees a stable higher sync. Since you didn't restart the router after the low sync (to get back to a normal sync) the profile remained unchanged.

As John says .

The first thing I looked at was your sync speed, the second was the noise margin, the third was the attenuation, and the fourth was the router uptime. A restart had to be the first thing to try.

Depending on which exchange you are on, you may get an almost immediate IP Profile rise, or it may be two-three days. Some exchanges (I don't know which) are trialling a faster-reacting DLM.

those stats now look fine,

when did the line slow down? was it when we had thunder storms last week?

I thought about that, but it slowed down about 2-3 weeks ago. I usually shut everything down during electrical events just as a precaution, I live on top of a hill about 50m from the local lightning conductor. Don't know why I didn't do that this time XD

Alrighty then!

Everyone's been giving some good advice. I'll give it a few days and let y'all know how it went, for better or for worse

Thanks again everyone!