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Cross talk and sync speed lost

artfulbodger
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Registered: ‎16-01-2015

Cross talk and sync speed lost

Apologies if this is an open ended and impossible to answer question - but can anyone explain how much sync speed can be lost in general with crosstalk please? I mean, is there a ball park figure of how much each additional connection in the cabinet can bring down the sync speed?
21 REPLIES
Estragon
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Re: Cross talk and sync speed lost

Short answer, No!
Long answer, someone more technical will no doubt answer. It can be one new connection knocks several Mbps off you, when a dozen others didn't make any significant difference. Or the one that does the damage could be the first, and the next dozen don't make it much worse.
artfulbodger
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Re: Cross talk and sync speed lost

Mmmm ... ok, Estragon. So a loss of 1Mbps after a simple phone line fix, off a full 80 that's been there for years, could be something and nothing? (please don't laugh, I know this is not the end of the planet and other folk are suffering much worse, but I'm just curious).
Cheers.
danludlow
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Re: Cross talk and sync speed lost

I assume that crosstalk is an issue created away from the cabinet?
In other words, screening the coppers in the cabinet won't make any difference?
Terranova667
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Re: Cross talk and sync speed lost

It's hard to say how much you can loose because it varies so much, some loose speed over time in small amounts and some loose a chunk in one go in a very short period as i did,  I lost 10Mb down 65mb to my current 55Mb and half my upload from 10Mb to 5Mb since joining Plusnet in March 2014 the loss on the download came within the first three months of joining the loss on upload came about 7 months after joining so you can imagine i wasn't best pleased.
It's why i hope that Vectoring gets rolled out someday soon as it eliminates crosstalk and then hopefully my full speed will return.  
As for your loss, 1Mb loss could be crosstalk or maybe due to very low interleaving being applied it's hard to say, and I wouldn't laugh a loss is a loss in my book although there are some members here who would say other wise.  

Terranova667
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Re: Cross talk and sync speed lost

@danludlow crosstalk happens within the fibre cab itself it comes from the interference that the other connections make it's why it varies so much depending on how many are connected in the cab and where abouts in the bundle of connections in the cab you are, some are lucky and not effected or get a very small hit others sadly can be hit very hard, like i said above Vectoring can eliminate crosstalk just as G.INP helps with noise interference on a line.  
sjptd
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Re: Cross talk and sync speed lost

I don't think interleaving would ever make such a small decrease.  As OP has had solid 80, we don't know what attainable speeds he has had.  Unless he has an unlocked modem, any higher attainable will show up as 80 sync.  It may be that it started at well above 80, and has been gradually dropping, and it has just passed the 80 threshold.
artfulbodger
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Re: Cross talk and sync speed lost

Thanks Terranoa. I'm suspecting it could be a very low level of interleaving as well. Is there a way of detecting it? Every time I've asked PN they've categorically said there is zero interleaving and no "faults". Would love to see what's actually sitting on the line. Even a couple of forced re-syncs haven't recovered anything (which is what PN advised immediately after the phone problem had been fixed). I know the engineer on the day said he had found a "loose connection" in the cabinet for my line (whatever that meant?) - the line remained on the 80/20 profile for a couple days after, then dropped inexplicably? Could he have shifted the pairs to a new card? (can't believe he would've done without doing a corresponding SNR reset, surely?)
artfulbodger
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Re: Cross talk and sync speed lost

I've got an unlocked HG612. The attainable speed was always 81 (infact I remember seeing 82 shortly after upgrading it for G.INP).
As I say it was a couple of days after the OR engineer fixed a "loose connection" in the cabinet for a phone line problem that things dropped. The connection has dropped a few times since, but with no loss of sync or drop in profile.
artfulbodger
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Re: Cross talk and sync speed lost

Just witnessed the strangest thing - re-synched the modem 3 times within 20 minute intervals and each time the line rate went up: 79.19, 79.27, and finally 79.36. I didn't dare re-sync anymore incase DLM kicked in, but can anyone explain what's happening and if I had carried on would I have regained the 80mbps? (probably not and highly inadvisable I bet!)
sjptd
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Re: Cross talk and sync speed lost

All of those figures are so close together as makes no significant difference.  It will depend on the exact situation at the time of any resync, which can easily vary by 1% or so over even a few seconds.
danludlow
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Re: Cross talk and sync speed lost

@Terranova667 So if all the crosstalk interference is created within the cabinet, why can't it be tackled there with cable routing practices, screening and use of screened cable? even greater distances between connections etc? Why not give a couple of Universities some cabinets and have them look at the problem, with a decent reward for achieving a solution. Devise some clever countermeasures perhaps? As someone watching from the touchline, this interference looks predictable and a rather predictable own goal.
Terranova667
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Re: Cross talk and sync speed lost

That's a question for people far more technical than me 
jafreer
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Re: Cross talk and sync speed lost

Surely crosstalk can occur outside the cabinet? Anywhere that twisted pairs are in close proximity to each other? If my own twisted pair and my neighbour's twisted run up the street in a bundle, and we both have fibre, then crosstalk can affect the speeds? Just curious.
Estragon
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Re: Cross talk and sync speed lost

It is hoped the crosstalk issue will be solved by using vectoring. Openreach are trialling it. I expect there will several threads about it here. There certainly are on thinkbroadband forums. Plus some News Articles on the thinkbroadband Main site.