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Standard User lexden16
(newbie) Wed 27-Jul-11 14:22:29
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ADSL2+ - Is this Unusual?


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I switched to ADSL2+ at the end of Feb. Despite estimates of 15Mbps on various ISP websites, I initially got an IP of 7150 which rose to an IP of 10000 after I followed advice on this site and fitted a NTE5 faceplate. My initial stats were a downstream LA of 16 and SNR of 15. My ISP's response to my concerns was 'noisy line'.

At the end of May (3 months on), my downstream SNR fell to 12 and a month later it fell to 9. Yesterday, my router log showed that there had been a disconnection and the box had re-booted with a downstream SNR of 6. The cumulative effect of this is that my connection rate is now 15991 and IP 14108. My stats are now downstream LA/SNR of 18/6 and upstream 6/6 with a fairly low error rate.

I am not complaining, I just wish that I understood what was going on. I can only assume that something has changed and my line conditions over the past 5 months have improved.

I also note that ISP speed estimates for my line have fallen by 2Mbps to 13 since my ADSL2+ service began.
Standard User orly
(fountain of knowledge) Wed 27-Jul-11 16:09:04
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Re: ADSL2+ - Is this Unusual?


[re: lexden16] [link to this post]
 
An SNR of 6 is what you want.

What you've seen is the line gradually improving (lower SNR is better) and the speed therefore increases.

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Standard User lexden16
(newbie) Wed 27-Jul-11 18:25:16
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Re: ADSL2+ - Is this Unusual?


[re: orly] [link to this post]
 
In reply to a post by orly:
An SNR of 6 is what you want.

What you've seen is the line gradually improving (lower SNR is better) and the speed therefore increases.


Yes, I understand that but thank you anyway. What I do not understand is why when my line has been pretty stable for 5 months it has taken so long for BT's 'systems' to reduce the target SNR and what would cause a line to gradually improve? I accept that it is likely that I will never know.


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Administrator MrSaffron
(staff) Wed 27-Jul-11 19:14:19
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Re: ADSL2+ - Is this Unusual?


[re: lexden16] [link to this post]
 
Because it looks for stability for a few weeks, and lowers in 3dB steps

Its not a gradual improvement of the line, line is probably the same as it was some time ago, just the BT systems taking their slow automated path towards a low target SNR margin

Andrew Ferguson, andrew@thinkbroadband.com
www.thinkbroadband.com - formerly known as ADSLguide.org.uk
The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User lexden16
(learned) Wed 27-Jul-11 19:37:11
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Re: ADSL2+ - Is this Unusual?


[re: MrSaffron] [link to this post]
 
In reply to a post by MrSaffron:
Because it looks for stability for a few weeks, and lowers in 3dB steps

Its not a gradual improvement of the line, line is probably the same as it was some time ago, just the BT systems taking their slow automated path towards a low target SNR margin


I don't recall ever seeing anything about BT systems taking months to make line SNR adjustments. Based on what I have seen over the past 5 months, I am sure that you are right. That said, it does make a mockery of the latest OFCOM announcement on broadband speeds and the right to 'opt out' of contracts. Arguably, in some cases, 3 months is not long enough for the line monitoring process.

I shall now keep my fingers crossed that everything remains as it is now. - at least until FTTC arrives at the end of the year. Thanks again.
Administrator MrSaffron
(staff) Wed 27-Jul-11 19:41:48
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Re: ADSL2+ - Is this Unusual?


[re: lexden16] [link to this post]
 
Line monitoring and DLM is a constant thing reacting to changes, i.e. for BT it never switches off

An ISP can force a change in target noise margin manually, just most cannot be bothered

Andrew Ferguson, andrew@thinkbroadband.com
www.thinkbroadband.com - formerly known as ADSLguide.org.uk
The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User RobertoS
(sensei) Wed 27-Jul-11 22:45:46
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Re: ADSL2+ - Is this Unusual?


[re: lexden16] [link to this post]
 
It's supposed to work as described here, Section 4. The fact it has taken so long could be due to continuing noise and/or errors, but still within the boundaries of what is allowable on a 6dB target margin.

Unfortunately there doesn't seem to be any information about what the noise and error parameters are.

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Standard User IamQ
(experienced) Thu 04-Aug-11 17:36:39
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Re: ADSL2+ - Is this Unusual?


[re: MrSaffron] [link to this post]
 
In reply to a post by MrSaffron:
i.e. for BT it never switches off


It can however be set to not tamper with your line profile in any way. (I have this set on a number of lines) It may take some hard work with your ISP depending who they are. Most including BTWS will tell you they can't change the DLM settings but they can if you find the right department and go through the correct channels.

The only problem with DLM set to leave well alone is that any problems, errors, noise *will* cause you problems as the DLM won't try and compensate for it and leave you with LoS events, or lots of re-transmitted segments and other lovley errors. In some cases that is better than having a line that 'flaps' all the time.

Edited by IamQ (Thu 04-Aug-11 17:36:59)

Standard User lexden16
(learned) Sat 06-Aug-11 15:46:52
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Re: ADSL2+ - Is this Unusual?


[re: IamQ] [link to this post]
 
And 10 days on, there was a further forced resynchronisation at 07:40am today and my downstream SNR reduced from 6 to 3 with the connection rate rising to 17.8Mbps downstream. I am of course pleased to see that my connection is now performing as various ADSL Speed Estimators predicted it should 6 months ago; however, I am still curious to know what has changed. My ISP still believes that the problem was noise on the line. What I can say with almost 100% certainty (after removing bell wires, DECT phones, fitting a filtered faceplate, trying 3 routers and roaming the house with a MW/SW battery radio) is that the problem was on BT's side of the test socket. That said, I could never prove this to be the case.

Thanks again for all the help and advice given so freely on this site.
Standard User 2pods
(member) Sat 06-Aug-11 18:19:43
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Re: ADSL2+ - Is this Unusual?


[re: lexden16] [link to this post]
 
I'm in the same boat, mine started off good, dropped to a profile of 11000, then eventually went up to a profile of 15000, THEN was droped to a sync of 10000 with a 12db NM.

After phoning my ISP, trying three three routers, various filters, cables etc, they came to the conclusion that it's a wiring problem.

So, I have to find out where it's coming from.
I have an iPlate, with a BT hard wired extension so I don't know exactly what I can do.

ZeNLite
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