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[kitz]

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. 

[renluop]

Hi! I'll try to find it, but I did not keep details and  recently cleared my history in Chrome: helpful NOT!

[ColinS]

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.  

[snadge]

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..

[Chrysalis]

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.

[kitz]

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.

[HPsauce]

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

[snadge]

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.

[HPsauce]

I dont have access now to the Be* forum

Yes you do.  http://www.beusergroup.co.uk/ and click on the forum link.

[kitz]

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 saying it was the first decent answer he'd seen, was still at the top of the section. 
He pointed to this post

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.