I am pretty sure that is probably due to power cutback.
That wouldnt account for the huge losses in speed that all of us have seen over time.
I suspect even BT may have been surprised at just how much crosstalk has affected VDSL. All the laboritory testing in the world cant foretell what will happen in the field.
When I first got vdsl & after my line fault was fixed my max attainable was something like 10400, by the time Id taken the HG612 off it had dropped to 86000 - thats what 18Mbps? Putting on the ZyXel gave me a boost back up to the region of 8990.
Power cutback on VDSL means that ADSL is less impacted by any VDSL lines, but conversly means that ADSL will impact on VDSL, however not as noticable though because VDSL has more tones to play with. Its the very long lines which cant use all of the D1 tones that will likely notice impact from adsl crosstalk the most.
However adsl is already in place, so we perhaps dont notice this as much because adsl crosstalk will be there from day 1. We see degredation from other VDSL lines as they joint the cab and theres been some fairly big losses reported immediately a neighbour gets vdsl.
My reasoning is:
- You have line A and line B.
- Line A gets VDSL. Line B remains on ADSL.
- User B decides to get FTTC
- Line A speed reduces.
Now if ADSL was a bigger disturber than VDSL... then Line B's speed would have gone up not down.
Line B on VDSL is a bigger threat of crosstalk to Line A, because Line B is now 'contending' in the same frequencies as Line A.
Would I be right in presuming that any services running in the opposite direction away from the cabinet, therefore in a separate bubdle of cables, will have little or no effect on crosstalk at my end?
hmmm Im really not sure tbh BE.. you ask some good questions.. but if its on the same line card I guess it would be possible.
It happens with adsl, so I would have thought the theory was the same with vdsl.
I wonder if a single user in my bundle went on holiday just before midnight 29th May (at 23:53 to be precise), switching off their modem/router.
Sorry I wouldnt like to say for certain (not much use am I with your questions :/ )... but yes it is possible.
Crosstalk is known to affect the shortest lines the most - their power back off profile is higher, so they see larger decreases in speed from x-talk, especially if the disturber is on profile med or long.
However.. a line which is unable to use all of the sub carriers will still be affected but to a lesser extent of speed loss. Like you say, in cases like yours - Every little helps.
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btw BE, your difference in signal and line attenuation niggles at me a little for a reason I cant explain. Is there still such a large difference immediately after a sync?
