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Standard User boothroyd
(newbie) Sat 23-Jul-16 13:12:35
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DLM & Noise Margin


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For a couple of years until a month ago I had a good line at 14 Meg on a Noise Margin of 6dB. Good for a rural area, 1.7km from exchange. ADSL2+.

A month ago I started getting chronic multiple disconnects/connects, deemed to be caused by intermittent severe crackle on the phone line, causing voice calls to deteriorate and disconnect. I swopped over 4 modem/routers (have plenty as repeaters), ADSL filters, checked with multiple phones, did umpteen quiet line tests etc etc all in test socket. 4 BTOR engineers later, they had between them found and corrected (a) squirrel chewing the cable (b) HR at exchange (c) HR at Cabinet (d) incomplete connection in JB at top of a pole. Last engineer found a clean line so requested the Openreach Broadband people to check the broadband.

They did that, and now my WAN has been up for a continuous 25 hours at 6.5 Meg on a Noise Margin of 19- 20 dB (and attenuation 27.5 dB). I was told (had to ask) that the BB engineer had found 'a loose wire on the B-RAS of the DSLAM'. Although the description might not be quite right it sounds plausible.

So my questions to you knowledgeable folk are:
1. I am leaving the modem/router connected now I have at last apparently got this sorted. I hope that the DLM will gradually take the Noise Margin back down and my speed will increase again. Do I need to reboot the modem/router in order for it to reset to a higher speed, or does it re-synch all by itself at higher speed and lower margin?

2. Would a 'loose wire on the B-RAS' have been causing that intermittent loud crackle causing phone line disruption.

3. Not directly related, but I have had instances where sometimes unplugging a phone from socket causes the broadband to disconnect. What would cause that, is it common?

Will be interested in your thoughts, particularly on Q1.

Thanks, cheers
Standard User RobertoS
(elder) Sat 23-Jul-16 13:16:39
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Re: DLM & Noise Margin


[re: boothroyd] [link to this post]
 
A noise margin of 19-20dB is not a DLM setting value. Normally I would suggest a single re-sync, but in this case I would close down the router, preferably closing the PPP session first, and leave it off for about 30 minutes. Then see what the stats look like after restarting and let us know.

Kindness isn't going to cure the world of all its awfulness but it's a good place to begin. Daisy Ridley.
My broadband basic info/help site - www.robertos.me.uk. Domains, site and mail hosting - Tsohost.
Connection - AAISP Home::1 80/20. Sync 59500/14989kbps @ 600m. - BQM

Edited by RobertoS (Sat 23-Jul-16 13:17:21)

Standard User boothroyd
(newbie) Sat 23-Jul-16 15:19:36
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Re: DLM & Noise Margin


[re: RobertoS] [link to this post]
 
Thanks. OK. I turned off modem/router for 30 mins then restarted. I then booted up at 6 Meg like before and Noise Margin of 19.8 dB like before. But then it disconnected and reconnected 3 times within a couple of minutes, each time 6 Meg/19-ish dB. Now it has settled for 20 minutes at 6656 kbps/Line Attenuation 27.5 db/Noise Margin 19.9 dB, all much the same as before the reboot.

Are you sure that the DLM does not vary the Noise Margin - as a consequence of changing the speed? Whilst in the midst of the disconnects a couple of weeks ago the ISP changed the Target Noise Margin to 15 dB to try to overcome likely high resistances. That might still be set but I would have thought that after fixing the fault Openreach would have reset the Target Noise Margin to the usual 6 dB and then let the DLM set the speed, which would yield an appropriate noise margin.

I am quite prepared to accept 6 Meg to keep stability if the DLM will gradually increase the speed back upwards again. [3 of my modems are DG834G v4's with DGTeam Firmware so I could frig the Noise Margin from my end but I don't want to go there (if at all) until the synch is well settled by the DLM (assuming that the Target Noise Margin has been set properly].

Key question is, if the DLM decides to change the speed after a period of stability, does it force a disconnection/reconnection at the changed speed and changed Noise Margin? If so, perhaps it would be best to leave the connection alone, and just wait. At least it seems to be working again.


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Administrator MrSaffron
(staff) Sat 23-Jul-16 15:22:23
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Re: DLM & Noise Margin


[re: boothroyd] [link to this post]
 
If still getting the disconnects like you described then DLM is not going to lower the target noise margin, and even if it was reset you'd probably end up quickly back to where you are now.

Suggesting is maybe that even if a loose wire has been fixed, there may be some issue with the connection, evidenced too by the phone ringing causing the odd disconnect

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
(elder) Sat 23-Jul-16 15:42:01
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Re: DLM & Noise Margin


[re: boothroyd] [link to this post]
 
Openreach do not set the noise margin on ADSLx. Only on FTTC. On ADSLx it is BT Wholesale or an LLU supplier.

The highest BTW setting I believe is 15dB, though I did once hear a possibility of 18dB. To be higher than that suggests the sync speed has been capped. As Andrew says, things are not normal on your line.

It is very unusual for the speed to be capped, so causing the noise margin to rise. The normal behaviour is the other way round. I can't directly answer your question therefore about it auto-adjusting - but certainly the normal behaviour unless the noise margin has been "fixed" rather than set at 3/6/9/12/15 is that it does auto re-sync when it drops it by 3dB. In 10-14 day steps.

Kindness isn't going to cure the world of all its awfulness but it's a good place to begin. Daisy Ridley.
My broadband basic info/help site - www.robertos.me.uk. Domains, site and mail hosting - Tsohost.
Connection - AAISP Home::1 80/20. Sync 59500/14989kbps @ 600m. - BQM
Standard User boothroyd
(newbie) Sat 23-Jul-16 17:29:13
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Re: DLM & Noise Margin


[re: MrSaffron] [link to this post]
 
Thank you both. Since I rebooted just the once today at Saturday, Jul 23,2016 14:25:12 it connected and reconnected 3 times during a few minutes, and it has later connected and reconnected 5 times since. I am posting this while it is connected for a short time!

I am now back to where I was a month ago! It is mega-tedious, it was all right until I rebooted! The ISP is Entanet (Vivaciti via Entamet via BTW). I will let this run for 24 hours then give them a call and see what they say, they seem to be pretty good nowadays.

I have tried different routers, and done all sorts of things to make sure that it is not my equipment or wiring......
Standard User b4dger
(knowledge is power) Sat 23-Jul-16 18:15:17
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Re: DLM & Noise Margin


[re: RobertoS] [link to this post]
 
In reply to a post by RobertoS:
Openreach do not set the noise margin on ADSLx. Only on FTTC.
I didn't know Openreach control DLM on FTTC. Any link to an authoritative source?

Standard User RobertoS
(elder) Sat 23-Jul-16 18:31:57
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Re: DLM & Noise Margin


[re: b4dger] [link to this post]
 
BT SIN 498

BT Wholesale cannot control it, as it is an Openreach service open to all CPs. (BTW/Sky/TalkTalk/Vodafone. Maybe some Zen).

Don't get confused by the IP Profile side of things, which is purely a BT Wholesale artifice. Not part of FTTC DLM.

Kindness isn't going to cure the world of all its awfulness but it's a good place to begin. Daisy Ridley.
My broadband basic info/help site - www.robertos.me.uk. Domains, site and mail hosting - Tsohost.
Connection - AAISP Home::1 80/20. Sync 59500/14989kbps @ 600m. - BQM
Standard User b4dger
(knowledge is power) Sat 23-Jul-16 18:38:02
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Re: DLM & Noise Margin


[re: RobertoS] [link to this post]
 
Looks like this is the link: http://www.sinet.bt.com/sinet/SINs/pdf/498v7p1.pdf

Standard User boothroyd
(newbie) Tue 09-Aug-16 10:11:10
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Re: DLM & Noise Margin


[re: boothroyd] [link to this post]
 
Postscript: A couple of hours after writing the original question that Saturday, the router started disconnecting and reconnecting again until we were disconnected completely with a dead line. I walked around outside and noticed that our neighbour had decided at long last to prune a tree growing up into the phone line on a shared BT/electricity pole (the one where the squirrel had been chewing the cable 6 weeks ago). His yanking about of the branches had damaged an inline overhead connection box & cable.

4 days later, Openreach reconnected us. We are now up to 13 meg on a noise margin of 9dB. How long that will last is anyone's guess.
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