Kitz Forum
Broadband Related => Broadband Technology => Topic started by: renluop on May 24, 2013, 08:59:07 PM
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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.
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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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.
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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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Asbo will hopefully be able to answer this conclusively.
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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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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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Are all cases on same type? Mine's is IFTN/71BE!
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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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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.
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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 (http://www.kitz.co.uk/adsl/adsl_technology.htm#tones_not_used).
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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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 (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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: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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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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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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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 (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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However, in a thread over in the PN forum a member quoted a substantially similar list of the unused ones.
PS... can you link to that post please... If I get chance I'd like a looksee... not sure when though, as Im mega busy over the next 5-6 weeks :(... and then if I survive them.. i'll prolly want some 'me time' and catchup on household chores. :D
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Hi! I'll try to find it, but I did not keep details and recently cleared my history in Chrome: helpful NOT! :(
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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.
Which, maths aside, is a concise and accurate summary of what they describe at various places in that book. :graduate: ;D
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havent read the whole thread...so sorry if Iam late with this... but don't certain Dslam's /Msan's use some tones for communication to the router and not for data transfer? my neighbours BT ADSL2+ looks identical to my dads Talk Talk LLu ADSL2, same tones disabled, on my old o2/LLu connection there were a whole bunch together in the upper part of the spectrum..
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yes gaps varies on dslam vendor.
on adsl max days with BT they used TI dslams and another vendor (forgot which). Imo the TI dslams were the better ones to have. I was initially on the other vendor (fujitsu?) and I had a large gap between upstream and downstream tones unused as well as alot of bitswapping issues.
I finally after ages got a managed cease and reprovide (thanks aaisp) which moved me to a TI dslam, that had a smaller gap and also bitswapping worked correctly.
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Whilst this subject has been brought up again, I saw something only last month that for the very first time actually admitted why Be had blocked those specific tones. It was because they had seen local RFI interference in some of their new exchanges... and they just rolled out the same profiles to all exchanges when they expanded.
I dont have access now to the Be* forum to be able to quote from where I read it nor what it said exactly.
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The only thing I can find quickly, from ages ago (2008 or earlier), is:
Hi,
A number of members have questioned why there are specific tone or frequency gaps visible on the network.
We carry out extensive testing with our network vendor to produce a fast, stable network. As part of this testing, we have identified a number of frequencies that commonly affect the stability of broadband lines, usually due to significant fluctuation of noise in these frequencies. This can affect the stability of a broadband line. This results in certain frequencies which have been identified as causing significant stability or noise issues being masked out - tones 476 to 499 fall into this category.
We expect that for short customer lines, that these frequencies would produce 500kb/s to 1mb/s. On longer lines these speeds would be insignificant as these frequencies are unlikely to be in use. However, our analysis indicates that this is likely to produce less stable lines.
As we centrally manage out exchange equipment, we deploy the same profile to all our exchanges. Managing profiles on individual exchanges or customer's lines is very difficult to support and as the profiles are centrally managed, may require hundreds of thousands of different profiles.
We believe, with our equipment vendor, that we have selected the best profile that we can use through the UK.
We will continue to work with our vendors to maximise the performance and stability of the network.
regards,
_________________
Brett Coles
Head of Member Services
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very good :)
i thought it was a bit odd? - I managed 16.6Mb without those tones, wondered what I would have got with em... thinking back I think it may have been about 700k-1Mb because it was a fair chunk.
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I dont have access now to the Be* forum
Yes you do. ;) http://www.beusergroup.co.uk/ and click on the forum link.
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Thank you HP, I hadnt seen that particular post, but thanks to your link to the login I found the post that I had seen. :)
I thought it was slightly more recent than it actually was because siteguru's post (https://avatar.bethere.co.uk/forum/viewtopic.php?t=44226) saying it was the first decent answer he'd seen, was still at the top of the section.
He pointed to this post (https://avatar.bethere.co.uk/forum/viewtopic.php?p=382306#382306)
Fri Sep 21, 2012 9:30 am
Unblocking tones 476-499
When first developing the network, we experienced some intermittent noise source around 2 MHz in the London area, the source of which remains a mystery. To eliminate the bit errors it caused on the lines we decided to mask out the tones with a 0.5 – 1Mbps on very short lines, and negligible on longer. Since we can still maintain competitive speeds with these tones masked, we prefer to leave them masked; in any event, removing them would require extensive testing to ensure no net negative customer impact.