Power Cut Temp Speed Increase.

[biffab]

This is an odd one. Two weeks ago my local area suffered a total power cut for 10 mins. When power was restored my Infinity 2 with HH6 was reporting Download of 79.99 and Upstream of 20. As I normaly run at 68/20 I was very happy as previously the best I had acheived was 72/20. I even ran a speedtest to check the figures being reported were accurate and they were. For the last two weeks I have been running at this speed with no issues at all. 

My HH6 has just rebooted itself ( as it does every 14 days) and my speeds are back running at 68/20. Does anybody have any ideas why this would happen ? For info I do power recycle my HH6 every couple of weeks where I leave it off for an evening and why cant I get 79.99/20 all the time as obvioulsy capable of it.    

[Webby · Accepted solution]

Crosstalk.

When your router reconnected you were likely one of the first on the cab to connect, so no crosstalk (interference from other users) present.

You'd probably have noticed that a couple of days after connecting your SNR was low, due to the increased interference on the line.

After the reboot, your modem has synced with the cab using a 6db noise margin and due to the additional "noise/crosstalk" the DSLAM in the cab was only happy to connect at 67meg.

[biffab]

Thanks Webby that makes sense. I thought it would probably be something to do with crosstalk and I was just lucky to connect early.

[brummygit]

I've noticed exactly the same. I usually sync at 60/13 but 2 or 3 times now after power cuts I sync at 79.99/20. The connection SNRM soon drops and whilst stable, eventually when the inevitable resync occurs at some point I'm back where I started. Powering down my house doesn't do it - it's something external to my property.

I always used to sync at about 77/20 until one day in Dec 2015 when I suffered a sudden drop that then recovered for a couple of weeks th following February and never since other than after a power cut. Multiple calls to BT never solved anything. After swapping me onto different pairs they just declared that it was the fastest my line would go even though the distances should have me at pretty much max speeds. The were seeing the speed decrease at the first point the cable exits the ground to overhead poles.

I'm not so convinced I'm seeing crosstalk, but rather some other interference. In my case my cab is right by a set of traffic lights which were upgraded to more sophisticated sensors in the December my troubles started. It seems that whatever is affecting my sync speed is consistently slower to restart after a power cut.

[Webby]

If your speed goes up after a power cut, but the SNR then drops, the issue is crosstalk.

[brummygit]

Why can't it be an alternative source of electrical interference causing this effect?

The reason I ask this is that the problem wasn't a gradual reduction as my cabinet became more heavily subscribed, but rather a change on a single day that introduced the speed reduction. I believed that crosstalk was a problem then gradually built as the cabinet became more heavily utilised?

[Webby]

One single subscriber can cause a 10-15meg drop if it's in the "wrong" place in the cable bundle.