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Author Topic: Curious paper  (Read 7673 times)

Blackeagle

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Re: Curious paper
« Reply #15 on: April 18, 2014, 06:14:49 PM »

Moreover, sometimes tones 410-415 are used, sometimes not, sometimes tone 478 is used, sometimes not.

Thank you very much for your time
konrado5

But this is by design.  What you describe is exactly how ADSL is supposed to work.  If there is noise on the line, some tones (where the noise is located) aren't going to be used, or if they are, the bitloading will be vastly reduced.  Whilst the 'notch' in your graph is obvious, nobody here can offer an explanation as to why it is there. We simply don't know.

In any case, even if you resolved that notch, I doubt that you would see much improvement in speed.

As I see it, you have 3 options from here.  You can either :-

1) Accept your line for what it is, complete with 'notch', and agree your speed isn't that bad.
2) Assume your ISP has, for some unknown reason, fitted a filter, and change ISP.
3) Keep asking what/why/how/if questions that nobody here (and I know of no other forum with more highly qualified experts than this one) can answer.

I hesitate to say it, but you seem to have a 'bee in your bonnet' regarding the condition of your line.  I can sympathize with you but as far as I can see, there is nothing you can do about it.  You need to accept this, and move on.

With no ill will intended,

BE
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konrado5

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Re: Curious paper
« Reply #16 on: April 18, 2014, 06:19:46 PM »

Quote from: Blackeagle
I doubt that you would see much improvement in speed.
I'd have 3 mbps raised synchronization rate (I've had 3 mbps more before my ISP changed DSLAM).  Changing ISP doesn't satisfy my curiosity regarding to cause of notch.
Quote from: Blackeagle
But this is by design.  What you describe is exactly how ADSL is supposed to work.
I know it is the way how ADSL works. I only question is it possible it is delibarately setted on ADSL2+. I suspect only way to delibarately disabling particular frequiences on DSLAM is disabling particular tones eg. 415-477 and not sometimes 415-476, sometimes 410-477.
« Last Edit: April 18, 2014, 06:27:36 PM by konrado5 »
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Blackeagle

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Re: Curious paper
« Reply #17 on: April 18, 2014, 07:12:49 PM »

 :wall:
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kitz

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Re: Curious paper
« Reply #18 on: April 18, 2014, 09:25:13 PM »

Apologies - I cant recall that QLN, but having looked at it now, then I'd concur with b*cat in that it very likely excludes crosstalk/RFI/EMI.   

That spike smack bang in the middle is peculiar and it almost looks like the surrounding tones could be blocked out to prevent some sort of overspill, but Im only guessing at that.

I do however recall suggesting to you many months ago (and several times) the possibility of your ISP deliberately excluding these tones, but your replies seem to suggest this wasnt the case and/or your ISP denied that it was using any form of masking on these tones.

TBH Ive seen so many graphs and had so many discussions with you that my head spins sometimes.

As others have pointed out, often the ISP themselves may not even have a clue that these masks are in place, its not an area that their front-line staff who we speak to even have any training or knowledge about, as its left to techies who never see the light of day, nor disclose what they have done in public. You probably know (or should know by now) more information about adsl technology than most ISP staff.

I keep mentioning to you how BE (a UK isp) did something similar with tones 476 - 499 which after much debate with them they said it was to protect against maritime transmissions(?) which were affecting some areas.  It took years before a proper explanation came forward and was admitted why they were doing it, but we as consumers could do nothing about it - even if we werent in an affected area.


>>> I'd have 3 mbps raised synchronization rate

It would take all those tones to be fully or near fully bitloaded to gain that much, dont forget that over-time you will also be expected to loose a certain amount of speed from crosstalk.  This is inevitable as more users join your dslam.  Its highly unlikely that tones in the 400+ region would gain full bit loading.


Unfortunately konrado, when we try and help and discuss the gap, you bring up small irrelevancies such at the minute attenuation changes which are normal, then we get distracted and annoyed by you bringing up something which isnt relevant and is normal.   

I appreciate that you have the special ability to focus at length on certain aspects & talent to concentrate on problem solving likely far exceeds most of us here put together - but please try to understand that it becomes confusing for us when you focus in the wrong area and it throws the rest of us off the scent, and thats why we get frustrated when you repeat questions about areas that are normal.  People on here do try and help, but we do have a limited amount of time and knowledge that we can spend trying to explain things to you as most of us have occupations or real life responsibilities that must come first. There also comes a point when our knowledge is exhausted. 
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konrado5

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Re: Curious paper
« Reply #19 on: April 18, 2014, 09:32:47 PM »

I found probable cause:
http://forum.kitz.co.uk/index.php?topic=13856.0
Quote from: kitz
I keep mentioning to you how BE (a UK isp) did something similar with tones 476 - 499 which after much debate with them they said it was to protect against maritime transmissions(?) which were affecting some areas.  It took years before a proper explanation came forward and was admitted why they were doing it, but we as consumers could do nothing about it - even if we werent in an affected area.
Was it SNR very low nearly 476-499 tone?
« Last Edit: April 18, 2014, 09:37:13 PM by konrado5 »
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konrado5

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Re: Curious paper
« Reply #20 on: April 18, 2014, 09:43:38 PM »

Quote from: kitz
but your replies seem to suggest this wasnt the case and/or your ISP denied that it was using any form of masking on these tones.
Because you've written:
Quote from: kitz
     However I notice a slight dip in snr both before and after which could point to radio/EMI interference being the cause.
Moreover, there aren't always the same tones not used, sometimes 410-477, sometimes 411-476, sometimes 415-470.
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kitz

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Re: Curious paper
« Reply #21 on: April 18, 2014, 10:16:33 PM »

Now Im really just theorising on this...  so do not take it as gospel.  Take the following as a random thought and not fact.

BUT after having seen that spike of yours smack bang in the middle, that indicates to me some sort of disturbance even if those tones are blocked out either side...  now what IF there is some noise spread from that tone, that could explain why sometimes the tones at each edge of the block are in use and sometimes not, because they are sometimes affected sometimes not.  It could also explain the U shape either side.

However I dont know Im afraid.   If Im talking garbage, someone can correct that thought.  This is an area where we may never know unless your ISP confirms it.   They may be like BE and deny the reasons for a while.




Id also need to see bitloading & SNRm per tone & QLN & Hlog from the same sync to dismiss the theory - but I really dont know if I could bear to look again, because the boy who cried wolf springs to mind.  We've previously been distracted too much by you focussing on minute changes in the overall attenuation and bombarding us with things that arent relevant and are normal, and I dont think it would get us any further anyhow.
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konrado5

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Re: Curious paper
« Reply #22 on: April 18, 2014, 10:22:19 PM »

I sincerely apologize for bombarding with minute changes.
I've found identical PSD (probably) graph here with U shape:
http://www.itu.int/rec/T-REC-G.992.5-200305-S/en
On page 26 of PDF. It seems it is PSD mask for 400-483 tones. DSLAM doesn't block tones but it significantly lower power ouput. It explains the U shape of bit-loading and SNR graph.
« Last Edit: April 18, 2014, 11:14:03 PM by konrado5 »
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konrado5

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Re: Curious paper
« Reply #23 on: April 19, 2014, 12:42:14 AM »

burakkucat: You rather excluded PSD masks. Do you have the same belief after looking at above?
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burakkucat

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Re: Curious paper
« Reply #24 on: April 19, 2014, 01:01:29 AM »

Quote
I've found identical PSD (probably) graph here with U shape:
http://www.itu.int/rec/T-REC-G.992.5-200305-S/en
On page 26 of PDF. It seems it is PSD mask for 400-483 tones. DSLAM doesn't block tones but it significantly lower power ouput. It explains the U shape of bit-loading and SNR graph.

Taking the above link shows me a screen, as in the first image below. Selecting the PDF file, downloading it and looking at page 26 I do not see a PSD mask (the second image, below).

I really do not know what to think. To be honest, I would prefer to forget about the whole issue. I am so utterly confused.  :'(
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konrado5

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Re: Curious paper
« Reply #25 on: April 19, 2014, 01:04:37 AM »

I thought about 26 page of PDF file (18 page of text). Sorry for misunderstading.
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konrado5

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Re: Curious paper
« Reply #26 on: April 19, 2014, 01:13:22 AM »

I attach screenshot.
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burakkucat

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Re: Curious paper
« Reply #27 on: April 19, 2014, 01:31:07 AM »

Thank you for the clarification. Looking at page 18 of the PDF file, I now see the curve to which you refer.

Yes, it does seem to be a possible explanation of what you observe. It also ties in with the sudden fall to the noise floor, as seen in your QLN graph.
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konrado5

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Re: Curious paper
« Reply #28 on: April 19, 2014, 01:42:49 AM »

I'm happy that I resolved the crux. Unfortunately the ISP tech staff probably didn't heared about PSD masks. I don't know if they change it.

Thank you very much for your time.
konrado5
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kitz

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Re: Curious paper
« Reply #29 on: April 19, 2014, 01:58:01 AM »

Ive just spent a bit of time reading and trying to understand what it is saying and yes I agree it does look exactly like what you are seeing.

That specific type of HAM masking isnt something that Im aware of that is in use by any of the UK ISPs (BE did a total block rather than the U-interface mentioned in that document). 

Having read the document it would appear to be a specific filter for the HAM band and bearing in mind that one of the guys posted a document just last week showing that your gap was specific to the Amateur Radio (HAM) band for Poland, then I think its fair to assume that what you are seeing is a dslam mask against Amateur Radio broadcasts in Poland.

Well done for finding that document, because Im quite sure that it is an explanation for what you are seeing.   
As regards for getting it lifted, Im afraid to be the bearer of bad news in that its highly unlikely it will be lifted.  It will have been put in place by the dslam owners, and therefore unlikely that even the frontline staff of your ISP will know its there.

The only thing that is surprising is that none of their other customers have noticed.   But then again not everyone looks at their stats in such detail, and from what you have told us, its unlikely many will have routers that have the ability to plot QLN graphs to be able to spot it.

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>> Warning - while you were typing a new reply has been posted. You may wish to review your post.

B*cat and yourself have since replied since I started reading and typing this, but Im going to leave it as it was.
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