I will correct
"BT engineers dont like trying to resolve crosstalk as pair swaps, replacing budles with less dense bundles etc. is time consuming so they wont accept faults raised on the issue, unless the crosstalk drop off is very extreme".
I dont know why you deliberately misled the poster in your reply, but I corrected it.
I'm not sure that counts as "correcting".
Let me correct it myself:
-
"BT's engineers can't do anything about crosstalk"
- "BT's engineers can't do anything
meaningful about crosstalk"
- "BT's engineers can't do anything
predictable about crosstalk"
- "BT's engineers can't do anything
long term about crosstalk"
- But it is plausible that they
might, temporarily.
1) "Fixing" crosstalk is an impossible game
Engineers can indeed perform pair swaps
in an attempt to alter the impact of crosstalk.
However, there is no engineering tool available to them to say which pairs will get less crosstalk or more crosstalk. And no way to predict the crosstalk tomorrow.
All they can do is try other pairs, to see if things change. All with no guarantee, because the other pairs might have worse crosstalk, or worse crosstalk might appear tomorrow, courtesy of a new subscriber, or might have their own latent fault.
2) Pair swaps cannot eradicate all crosstalk
The first leg that VDSL2 signals must pass is the tie pair to the PCP - where every single pair will ultimately be carrying signals. And, even though it might be a short leg, is also the one where signal strength is highest, and induced crosstalk is at its worst.
A pair swap within the D-side cannot ever eradicate this portion of crosstalk.
3) The jobs Openreach accept aren't likely to be pure crosstalk.
Openreach will only accept jobs, where the only fault indication is one of low speed, when that low speed is in the bottom 10th percentile of the nationwide pool of that type of line.
Some of these lines will be ones with extreme crosstalk; some will be lines with real copper faults, but the user never reports a low speed. However, I suspect a lot of them really suffer from a latent copper fault that cannot be detected by the automatic test tools.
When an engineer turns up, he won't be looking for crosstalk, or trying to "fix" crosstalk. He will be looking for a latent copper/aluminium fault. And will attempt to fix such faults as he can do in a limited timespan - if you'r lucky.
If his work fixes nothing, then a procession of further engineers will all attempt to do the same thing. None of them will look for crosstalk.
Only in the absence of anything else to do will they then consider a pair swap. But, in some places, they won't even do that.
If you are amongst this bottom 10% (so get an appointment at all), and you don't have a hidden line fault (after many engineers), and your issue is really pure, extreme, crosstalk, and you are very persistent as you run through that procession of engineer visits, then you might be very lucky, and persuade someone to perform a pair swap. You might then be lucky further, and find a pair with less crosstalk. At least temporarily - until a new subscriber is added.
Bottom 10%; No fault; Persistence; Luck; More Luck. Permanent, ongoing luck.
Yes: getting anyone to look at "extreme crosstalk" is a time-consuming affair. But there is never, ever, a permanent guaranteed solution. Not without vectoring.
Perhaps my correction should read:
-
"BT's engineers can't do anything about crosstalk"
- "BT's engineers can't do anything about crosstalk. They can
do plenty of things, but they cannot guarantee a positive outcome."
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