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Standard User buteo54
(newbie) Wed 30-Nov-11 18:54:28
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SNR 12.5dB after 21CN conversion


[link to this post]
 
After conversion to 21CN my SNR is stable at about 12.5db and my line speed is 2600k, using ADSL, not ADSL2+. I reckon I should be getting well over 3000k with a more reasonable SNR of 6 or 7 dB, more in accordance with the BT estimator for my line.

Can anyone comment on this? Eclipse support are saying that they can't influence SNR with 21CN, it's all done automatically by a DLM (Dynamic Line Monitor). They're treating it as a line fault because they can see a lot of retrains after the change last Friday, but these retrains were due to me connecting and testing my new TP-Link router and installing and testing a new ADSL splitter faceplate for mt NTE5. I'm convinced my line is as good as it's going to get because Openreach came out and remade all the joints on my line only 3 weeks ago.

Maybe the retrains are what made the DLM bump up my SNR; so how long do I have to wait for it to come down?

BT Line Speed Estimation

Fixed ADSL: 1024 kbps (1 Mb)
DSL Max: 2500 kbps (2.5 Mb)
21CN WBC : 3500 kbps (3.5 Mb)

Details from TP-Link TD-W8960N v3:
adslctl: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 8000
Max: Upstream rate = 676 Kbps, Downstream rate = 2912 Kbps
Channel: INTR, Upstream rate = 544 Kbps, Downstream rate = 2624 Kbps

Link Power State: L0
Mode: G.DMT
Trellis: ON
Line Status: No Defect
Training Status: Showtime
Down Up
SNR (dB): 12.3 10.0
Attn(dB): 61.0 31.5
Pwr(dBm): 17.8 12.8
G.dmt framing
K: 83(0) 18
R: 8 8
S: 2 8
D: 16 4
Counters
SF: 11787904 11787862
SFErr: 3139 0
RS: 400788748 100195824
RSCorr: 30098 0
RSUnCorr: 26586 0

HEC: 2546 0
OCD: 2 1
LCD: 0 0
Total Cells: 1240169923 0
Data Cells: 1354830 0
Drop Cells: 0
Bit Errors: 0 0
Administrator MrSaffron
(staff) Thu 01-Dec-11 14:55:46
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Re: SNR 12.5dB after 21CN conversion


[re: buteo54] [link to this post]
 
Providers can get margins altered and have lines retrained, whether their support see the option on their computer is another issue.

Have you tried ADSL2 mode? That can give an extra 0.5Meg, ADSL2+ mode is not going to give any more than ADSL2 mode anyway.

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 buteo54
(newbie) Thu 01-Dec-11 17:46:22
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Re: SNR 12.5dB after 21CN conversion


[re: MrSaffron] [link to this post]
 
Thanks for the idea - it was a good one.

But it wouldn't train at all in ADSL2 (I issued a adsl configure --mod 2 through the CLI to the Broadcom chipset). Looks like they've disabled ADSL2 on my line...

Also thanks for the info about what the ISP can do. I wonder if there's a service charge every time they ask BT to do something so it's better for Eclipse to fob me off with a 'we can't do anything' than actually fix the issue?

I guess I could resort to using adsl configure --snr commands to reduce the SNR and increase the speed - but I'm concerned that because this works by applying a factor to the SNR from the DSLAM - this is correct, isn't it? - if I do this the DLM will just set an even higher SNR to try to restore the status quo. It would be much better to get a sensible target configured in the DSLAM.

Any more advice from experts who know how this works greatly appreciated...


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Administrator MrSaffron
(staff) Thu 01-Dec-11 21:40:26
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Re: SNR 12.5dB after 21CN conversion


[re: buteo54] [link to this post]
 
If error rates are low, and it is holding sync the automatic systems may allow the target SNR to reduce in time, so give it three weeks and if still the same come back to me and will try and get BT Wholesale to tweak you down to 9dB or 6dB

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.
ISP Representative Eclipsestaff
(isp) Fri 02-Dec-11 09:17:59
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Re: SNR 12.5dB after 21CN conversion


[re: buteo54] [link to this post]
 
Hi buteo54,

I agree that the SNR does look a little high, but its difficult to tell if this is because the target itself has been set high, or if there is something else happening over your line.

Would you be able to PM me your account details, so I could take a look at it?

I wonder if there's a service charge every time they ask BT to do something so it's better for Eclipse to fob me off with a 'we can't do anything' than actually fix the issue?


There isn't a charge for this sort of thing.

Andy

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The above post has been made by an ISP REPRESENTATIVE (although not necessarily the ISP being discussed in the post).
Standard User buteo54
(newbie) Fri 02-Dec-11 20:09:28
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Re: SNR 12.5dB after 21CN conversion


[re: Eclipsestaff] [link to this post]
 
Thanks for the offer, but it seems I've already convinced Eclipse support that my line really is very stable and not failing all the time: "I have checked your line and can see its stable, with a target SNR of 12db. I have therefore initated an SNR retrain on your line to attempt to bring the target SNR level down."

So, I'm going to wait to see what happens in the next 10 days.
Standard User buteo54
(newbie) Mon 05-Dec-11 12:30:26
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Re: SNR 12.5dB after 21CN conversion


[re: buteo54] [link to this post]
 
In reply to a post by buteo54:
Thanks for the offer, but it seems I've already convinced Eclipse support that my line really is very stable and not failing all the time: "I have checked your line and can see its stable, with a target SNR of 12db. I have therefore initated an SNR retrain on your line to attempt to bring the target SNR level down."

So, I'm going to wait to see what happens in the next 10 days.


Well, after 3 days nothing has happened at all, so I'll PM my account details...
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