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[WWWombat]

Don't know about the geometry in the bundle of course. But crosstalk is going to be symmetrical, in a smoothed-time fashion, because the lines are never operated independently.

I think a lot of D-side cables come as 100-pairs, but those are subdivided into 25-pair binders. Within the binder, pairs probably twist around somewhat so the neighbours change slightly over distance. The binders, as a whole, probably twist too, so neighbours on the outer edges likely change too.

Overall, though, crosstalk happens most between pairs in the same binder of 25-pairs. That is visible in crosstalk heatmaps.
http://forum.kitz.co.uk/index.php/topic,17836.msg328503.html#msg328503

Looking at the image on that page, and focussing on one line at a time, it looks like there are maybe 6 or 7 of the highest "red" disturbers.

[WWWombat]

Cool broadband might make a comeback with G.Fast. It employs the idea of discontinuous transmission if you have nothing to send.

[S.Stephenson]

Is cool broadband required so the vectoring engine isn't under stress?

[Weaver]

@S.Stephenson - Could you clarify your question?

[S.Stephenson]

Well there will be no crosstalk when the lines aren't transmitting anything, so the load on the engine should be lower than if it had to vector always on lines.

[ejs]

I'm not so sure about G.fast, but the vectoring engine might be under more stress if the signal levels for different lines keep changing, depending on if they've got any data being sent or not. With VDSL2, what would happen is that when one line disconnects or re-trains, then the vectoring engine would have to re-calculate the crosstalk cancellation for all the remaining lines. I thought that was why a low power mode wasn't particularly wanted for VDSL2, because it would make the crosstalk levels more changeable.

With an always on VDSL2 line, the amount of crosstalk it causes should be fairly constant, so it would be easier for the vectoring engine if it stays constant.

[Weaver]

I agree with ejs. It doesn't work like that.