Is this crosstalk/DLM/interleaving slowing my connection.

Got BT Infinity 2 in August 2014 - sync'd at 78.12Mbps down and 19.53Mbps up and has been like that up until recently. I am 77m from the cabinet (Openreach engineer told me).

However, since 17th March, the downspeed has dropped a few meg.

Old stats from 8th March:
(50413.530000) PPPoE is up -​ Down Rate=79995000Kbps, Up Rate=19999000Kbps; SNR Margin Down=8.3dB, Up=24.1dB

New stats from 22nd March:
PPPoE is up -​ Down Rate=76777000Kbps, Up Rate=19999000Kbps; SNR Margin Down=8.6dB, Up=22.4dB

Done the BT livechat, but they just keep going on about how many devices attached to wifi/is this a wired or wireless connection.

Does cross talk affect short lines and does it affect upload as well?

Here's the results from my phone number on the BT ADSL Checker:

FTTC Range A (Clean) 80 80 20 20 -- Available
FTTC Range B (Impacted) 80 57.8 20 5 -- Available

At a loss as to what to do next.

Help!

Edited by deleted (Tue 24-Mar-15 16:27:25)

Personally I would carry on enjoying the good connection and not worry about a few meg. You might find it will go back up again in a few weeks. Does a couple of meg make any real difference to your usage or just to your speed tests?

At a loss as to what to do next.

I would suggest nothing.

I suugest you watch it like a hawk, just in case it starts on a gradual slowdown.

If you have a Homehub 5A you can use Routerstats Hub to monitor it for you. Not sure if it works with a 5B.

Edited by deleted (Tue 24-Mar-15 17:04:07)

The quick answer is - yes, crosstalk affects even short lines; Crosstalk is at its worst where the signal is at its strongest ... which, for downstream, is in the tie pair from FTTC cab to PCP. And in the upstream, is as soon as your drop wire joins the D-side.

As take-up increases, crosstalk increases - so you should expect some degradation - in SNRM at least, and possibly in speed.

Of course, on such a short line, crosstalk is unlikely to take your speed down from 80Mbps. Your SNRM ought to be a long way above the target of 6dB, so you should have plenty spare - and you would then see crosstalk as a reduction in SNRM instead.

However, perhaps your engineer figures aren't quite right. I'm 100m from the cabinet, and I get 80/20 sync speeds. However, I get an SNRM value of 11.5dB down and 15.8dB up.

Now, the striking thing about the stats is this ... your speed has dropped, but your SNRM hasn't. Those 2.6dB spare ought to be worth around another 8Mbps.

Perhaps a resync will restore the speed.

Or ... perhaps you have been hit by DLM, and the use of FEC and interleaving has stolen some of your bandwidth for error correction. This could happen if your lines is getting errors, and need not be caused by crosstalk (but it could be caused that way).

Looks like "problem" was G.INP got enabled on my local PCP - and the homehub went into panic mode.

Got a HG612 modem off eBay, flashed it with custom firmware - put that in front of the homehub and now sync at 79999 and 20000

Happy days.