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Author Topic: Unused tones and.....  (Read 6397 times)

renluop

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Unused tones and.....
« on: May 24, 2013, 08:59:07 PM »

I've noticed that certain tones do not get used by my connection. Curious, as too often I am, I've been trying to google what those tones might relate to with no particular luck.

However, in a thread over in the PN forum a member quoted a substantially similar list of the unused ones. Here are both lists.

Code: [Select]
My unused tones
110
128
188
191
243
277
278
291
314
315
316
331
332
end of range is 333

other forum list

110   
127   
156   
188 
191   
243   
291


That set me wondering if there is anything special about the listed items. Is there?

DSLstats shows my connection as not interleaved, and there are CRC errors, DS 1790 in ~7.5 hrs, and ES/hr 143 ( has risen during time connected).

All seems well though, but are those stats, in deed nothing to worry about; else what do they suggest?
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ryant704

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Re: Unused tones and.....
« Reply #1 on: May 24, 2013, 09:14:22 PM »

Can be a whole host of reasons...

The main reason I believe is to due with how long your line is, if it's too long the modem will not be able to receive data from tones as the signal will fade too quickly. This is why you will get the full 80Mbps at 100 meters from the cabinet compared to 1000 meters and only receive 25Mbps. It's due to the line being too long to receive higher frequency's... I'm sure some will be able to describe it a lot better than I have. It could also be due to noise levels (SNR, QLN, etc) local to you so the DLM doesn't use it as it will be unstable.

The amount of CRC errors there are nothing to worry about really.
« Last Edit: May 24, 2013, 09:16:30 PM by ryant704 »
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c6em

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Re: Unused tones and.....
« Reply #2 on: May 24, 2013, 09:21:09 PM »


I remember contributing to the PN discusssion.........
We compared ADSL2+ DMT spectrums from around the country - same gaps: so it's not regionally/location specific
We compared ADSL1/20CN and ADSL2+/21CN connections on the same line - the gaps were NOT there on 20CN but WERE there on 21CN.
So again that ruled out local conditions/interference

We gave up and concluded it was something specific to the 21CN DSLAM's.
(in between trying to get rid of those who claimed loudly and forcibly that it was due to medium wave radio)
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Black Sheep

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Re: Unused tones and.....
« Reply #3 on: May 24, 2013, 09:23:15 PM »

Asbo will hopefully be able to answer this conclusively.
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asbokid

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Re: Unused tones and.....
« Reply #4 on: May 24, 2013, 10:47:52 PM »

Just a guess, but could it be a DSL tone blackout plan for an RFI cancellation scheme?  It is configured in the TR129 line-profile of a Huawei MA56xx DSLAM. But not sure how or why certain  tones are chosen for universal blackout.   Some tones in a geographic locality would be affected similarly by RFI  but how could that be replicated across the country?  Perhaps just a poorly configured blackout plan that was once valid to a locality but without much consideration was rolled out nationally.

cheers, a
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guest

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Re: Unused tones and.....
« Reply #5 on: May 25, 2013, 07:58:43 AM »

Interesting. ColinS has a thread going a couple of boards up called "The worried well" where his friend has similar tones missing - and he's on a BT DSLAM too.
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renluop

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Re: Unused tones and.....
« Reply #6 on: May 25, 2013, 08:12:58 AM »

Are all cases on same type? Mine's is IFTN/71BE!
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c6em

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Re: Unused tones and.....
« Reply #7 on: May 25, 2013, 08:43:39 AM »


Indeed a valid question...but as I recall we couldn't get any further on that one as several like me were using routers/modem units that do not support the 'vendor enquiry command' within the telnet cli.
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ColinS

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Re: Unused tones and.....
« Reply #8 on: May 25, 2013, 09:12:11 AM »

Are all cases on same type? Mine's is IFTN/71BE!
I can confirm that the friend of mine that rizzla referrred to is on an IFTN:0X718C8/v0x71C8 DSLAM/MSAN and AFAIK an Orange Livebox (don't know what version, but I could ask)
[Edit] Make that was on an Orange Livebox; currently using the HG612 in ADSL2+ PPP router mode.
« Last Edit: May 25, 2013, 10:47:02 AM by ColinS »
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kitz

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Re: Unused tones and.....
« Reply #9 on: May 25, 2013, 11:39:22 AM »

Very quick reply as I overslept and have to be out in 2 mins :(

Likely that 110 will be the Adaptive Pilot tone for your particular line.
Tones 300+ ish will very likely be due to length of line and not enough SNR at that frequency.

As regards to the rest, theres nothing special about them that I know that is defined within the dsl standards. -
DMT tones not in use.

There are DSLAM specific tones which may be marked by the provider as being permanently cancelled. (Passive RFI suppression using Masks). - Be* for example on tones 476-499.  I am not aware of any other provider doing this.


However - There is a technology called Active RFI cancellation, which has the ability to detect tones which have RFI and selectively marks those tones as unusable.  The way I understood it, is idea being blocking out one tone prevents noise bleed /Xtalk to other tones . I wasnt aware of it being used on adsl/adsl2+ in the UK...   Thats not to say it isnt being! Possible with FTTC though?   

Really got to go now and dont have time to search, but if someone wants to look further into Active RFI cancellation because I believe there may even be 'RFI profiles' that can be loaded
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ColinS

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Re: Unused tones and.....
« Reply #10 on: May 25, 2013, 04:52:45 PM »

Really got to go now and dont have time to search, but if someone wants to look further into Active RFI cancellation because I believe there may even be 'RFI profiles' that can be loaded

Here http://books.google.co.uk/books?id=m77kZl71gysC&pg=PA400&lpg=PA400&dq=active+rfi+cancellation+adsl&source=bl&ots=wx6uTaqkS4&sig=GebI7HlJ00d1o43-ED9H5PaosyY&hl=en&sa=X&ei=TdygUZS-EqWo0wW89oHwAw&ved=0CDYQ6AEwAQ#v=onepage&q=active%20rfi%20cancellation%20adsl&f=false

** Health Warning ** Not exactly bed-time reading!  ???
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burakkucat

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Re: Unused tones and.....
« Reply #11 on: May 25, 2013, 05:47:23 PM »

 :hmm:  Hmm . . . looking at a succession of pages from the book so referenced reminds me of what I have seen on the backs of old envelopes, etc, within Asbokid's domain.  ;)
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renluop

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Re: Unused tones and.....
« Reply #12 on: May 25, 2013, 08:00:03 PM »


Indeed a valid question...but as I recall we couldn't get any further on that one as several like me were using routers/modem units that do not support the 'vendor enquiry command' within the telnet cli.
I see, but perhaps there might be a friend whose eqpt does give info.

I'd have the cheek to ask. ;D
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c6em

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Re: Unused tones and.....
« Reply #13 on: May 25, 2013, 08:27:26 PM »


Yes, and the local friend's router does not support the cli command either.

No one else round here (village 400 houses) is the slightest bit interested in broadband, or of bringing superfast/fibre broadband whatever here, or of registering on the BT bring it here faster site, or of the BDUK process locally.
Nor are they interested in monitoring much less improving their sometime dire connections they have from ADSL2+: mostly due to their cr*p house wiring.

Unlike Walter who seems to be deluged with disgruntled residents my proactive attempts to drum up support for wanting FTTC have been met with total disinterest.
Not suprisingly the exchange is deemed economically unviable despite being currently one of the biggest non FTTC converted ones in the county with several smaller ones already done.

Its a fairly upmarket village and to be honest I doubt the residents spend much time either on the web or watching TV.
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kitz

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Re: Unused tones and.....
« Reply #14 on: May 26, 2013, 12:53:43 AM »

Really got to go now and dont have time to search, but if someone wants to look further into Active RFI cancellation because I believe there may even be 'RFI profiles' that can be loaded

Here http://books.google.co.uk/books?id=m77kZl71gysC&pg=PA400&lpg=PA400&dq=active+rfi+cancellation+adsl&source=bl&ots=wx6uTaqkS4&sig=GebI7HlJ00d1o43-ED9H5PaosyY&hl=en&sa=X&ei=TdygUZS-EqWo0wW89oHwAw&ved=0CDYQ6AEwAQ#v=onepage&q=active%20rfi%20cancellation%20adsl&f=false

** Health Warning ** Not exactly bed-time reading!  ???

Yea gawds... ur not kidding :o

I just started to have a look, but I saw all the equations and a lot of unavailable pages...  and since it is my bedtime reading on the ipad.. it didnt exactly inspire me to read it Im afraid. :(

Instead i'm going to summarise something that I can recall from several years ago when I first went on Be* and no-one at the time really knew much about the missing gap in tones, which is when I researched it.

Because it was so long ago, I could be wrong, but I will expand a little on my above post to a basic summary of how I understood it to work. Im using my own words as Im not an electronics person so Im happy to be corrected with correct phrases if any of what Im saying isnt quite correct. 

I seem to recall the theory behind active RFI cancellation was that when RFI was detected at a particular tone, that frequency was not used.   By cancelling that sub-channel and taking it out of use, the effects of the noise was less likely to bleed over to the neighbouring frequencies.  Taking the tone out of use results in some loss of bit loading, but should makes up for it with a cleaner neighbouring tones.

The downside of constantly monitoring for active RFI cancellation is that it can be put pressure on the modem processing power and cause delay. 

So enter a kind of hybrid -  if RFI is found to be affecting certain tone(s)*, then apply one of a set of pre-defined masks.  These masks are up to the dslam owner to define...  ie BTw or the LLU provider...  so they can cancel 'sets' of known problematic frequencies.

*I'm guessing that this would have to be done during the sync process, but it means once the mask is applied then the modem doesnt have to work as hard by actively monitoring each tone.

Im not saying this is what is happening... but it could explain what some users are seeing.    It wouldnt be too hard for BTw to get their mits on known profiles of problematic frequencies.

Over to someone else to do the technical jargon...  I need sleep..   g'nite. :)
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