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[Weaver]

My line 1 is set to 6 dB downstream target SNRM and 9db upstream, supposedly. This morning, for god only knows what reason, the line dropped at around 9:25 am and resynched with a d/s SNRM of 3dB which was wrong. I have no idea why it resynched and I have no idea why it was at 3dB, not the 6dB that is on record in clueless.aa.net.uk

This then caused me a load of problems with Zoom as the error rate was too high.

I’ve just forced an SNR reset, and the SNRM is now 6.5 dB d/s / 9.0 dB u/s, just as it should be.

[burakkucat]

Just one of those little mysteries with no obvious reason.

[Weaver]

I looked at this further and all lines had ended up at 3dB d/s at some earlier time. I would have to go back through all the logs to work out when the SNRM changed for each line. Line 2 anyway did not change this morning, it was at least a few days earlier than this; I didn’t go back far enough to find it.

[burakkucat]

A while ago, you were running each circuit with a DS target SNRM of 3 dB. Could it be that one of your auto-magic scripts made the change? (Perhaps you forgot to disable the helper.) 

[Weaver]

No, I haven’t developed that technology yet. Good thought though. There are two things here; why drop a line? Could be various reasons but I’m thinking that it is unreasonable, and secondly why forget what the downstream target SNRM is?

I decided a few weeks ago that I had to raise the downstream target SNRM to 6dB from the long-term 3dB because of unreliable performance with Zoom.

[burakkucat]

xDSL technology is both:

• miraculous
• mysterious

At times it is impossible to rationalise what has taken place. I strongly suspect that this is one of those times.

[Weaver]

At least I can fix it with an SNR reset. But I don’t want it to happen again as it causes too many errors.

This is what we want to see (for the first time ever); the report from my DSL links’ summary tool:

Summary of DSL links’ wellbeing and error counts
=====================================

--------------------------------------------------------
 ***                                                                                    ***
 *** All is well ! No errors or problems detected.  : -)  ***
 ***                                                                                    ***
--------------------------------------------------------

--
* Modems with a few errors:  None

__

[Weaver]

This has happened twice more. Always in the early morning. The latest was line 1 only and at 6am, and that time that is an exact multiple if an hour makes me thing that it is related to management systems - something within BT or AA. I’m wondering now if this is the resync to do with the 10 day training period. this latest time it put the downstream SNRM of line 1 down from the target 6 dB to 3, but left the upstream alone at my chosen elevated 9 dB target.

I’ll have to ask AA. It’s not like it is a major problem, just a bit odd.

[ejs]

Perhaps it's the DLM doing it's thing. Doing a reset to set the target SNRM to whatever value does not disable the DLM, and does not prevent the DLM from changing the target SNRM.

[Weaver]

Yes, I had thought about DLM. It’s weird DM increasing the error rate though isn’t it? By reduce the SNRM? I’m lost. If so, I could get AA to fix that by turning off the DLM, iirc.

[Weaver]

I asked AA to look into it. They haven’t come back to me yet with no ideas as to why it might be happening. It happened to me again this morning: 6dB d/s down to 3dB.

@ejs Does DOM sometimes decrease the SNRM ? (I can understand that after a fault of course, during recovery.)

Does this mean I should ask AA to turn DLM off ? Can that even be done with a BT ADSL2 line?

[burakkucat]

. . . I should ask AA to turn DLM off ? Can that even be done with a BT ADSL2 line?

It would be worth a try. "Yes" & "yes", I believe, are the answers to your two queries.

In the case of my TalkTalk supplied ADSL service, I have had the DLM disabled from about month seven. My circuit is far more stable (and usable) without the interference of an automoron.

[Weaver]

I thought it was possible with ADSL2. AA said they can’t turn DLM off. That sounds odd, the person I talked to might be thinking about VDSL2 too much. Also I thought that they once turned off DLM for me, on line 4. But perhaps I’m just going mad, and my memory is shocking. Isn’t that one of the advantages of TT though? I had it in mind that TT is unrepresentative.

[meritez]

disabling DLM is possible over TTB ADSL:

[burakkucat]

. . . the person I talked to might be thinking about VDSL2 too much.

I strongly suspect that is the case.

. . . perhaps I’m just going mad, . . .

I haven't seen any obvious signs.

Isn’t that one of the advantages of TT though? I had it in mind that TT is unrepresentative.

For their ADSL services, they own all the equipment. So it was just the case of me making the request for an appropriate someone to tweak the my circuit setting via the MSAN, located in the exchange at EABSE.