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High downstream SNR

jab1
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Re: High downstream SNR

OK, @Gandalf, but as I said, I'm away for three weeks from next Wednesday, so I'll persevere with what I have until I get back, then swap the final bit of kit my side when I return and see if that has any effect before we start kicking BT/OR.

I'd hate to have them come, blame that, and cost me £65.00.Smiley

John
summers
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Re: High downstream SNR

Am very surprised that "Stable" when down to a 14dB margin. @Gandalf what is the mean time between errors? on 14dB I'd expect the MTBE to be probably up at the 6000s level, that on "Stable" should kick it down to a better margin.

What i think our problem is we don't know how the DLM sets the target margin. I  don't, kitz doesn't seem to know either, does plusnet know? Or is it only open reach that know?

By using a standard openreach DLM setting i hoped that openreach would set all settings to something sensible, that didn't allow such jumps in margin ...

jab1
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Re: High downstream SNR

Yup, I was hoping that too, @summers, but it seems the DLM, a bit like most of BT/OR work to a different and weirder set of rules than everyone else.Wink

As I said above, I haven't really got time to spend on this before I go away, so I'm going to suffer in silence for the next week, and re-visit the problem when I get back in January.

Thanks for your continued interest.

 

John
ejs
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Re: High downstream SNR

Or maybe, just maybe, not every single drop in the connection is the DLM's doing!

jab1
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Re: High downstream SNR

They aren't @ejs - but I do know which are from this end. I spent long enough with our  IT department when I was working to learn that in times of problems, you keep a record of what happens at your end, just in case BT/OR (or even PN) try to wriggle a bit too much.

John
ejs
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Re: High downstream SNR


@jab1 wrote:

DLM threw another hissy-fit and decided to rack the SNR up to 14.8!!


 

They aren't @ejs - but I do know which are from this end.

 

How do you know which are and which are not due to the DLM?

 

Also, what were people expecting the DLM to do now that it's been put on a more stable setting? If this time it is the DLM that's put the target SNRM up to 15 dB, then that's what the DLM is going to do if you put it on the Stable setting. It's not some magic setting that will make the line more stable without making it slower.

jab1
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Re: High downstream SNR

@ejs I'm not going to get into an argument with you - I have better things to do with my life - but as I said previously, and you have conveniently snipped from your reply, anything that is done in-house, which may (or may not) invoke DLM is recorded, and if required, can be referred to.

Also, for your information the Openreach engineer who visited me last Tuesday was very knowledgeable and thorough and spent quite a while checking both internally and externally, and was satisfied everything my side of the DP was working as it should be.

Also FYI, I understand that if the DLM raises the SNR there must be a reason, and I am quite aware that a higher SNR will reduce the speed.

The aforementioned engineer was familiar with this area, and I quote (as near as I  remember 'Round here, 6dB margin should give you a stable 8/8.5Mb/s connection speed, anything lower will give you a higher speed, but not stable'.

John
summers
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Re: High downstream SNR


@ejs wrote:

Also, what were people expecting the DLM to do now that it's been put on a more stable setting? If this time it is the DLM that's put the target SNRM up to 15 dB, then that's what the DLM is going to do if you put it on the Stable setting. It's not some magic setting that will make the line more stable without making it slower.


Previously @Gandalf set the MTBE Green zone to 86400s = 1day. Now "Stable" sets the MTBE Geen zone at 6000s.

So the "stable" setting goes into green zone sooner than the previous custom settings. When in green zone it should decrease the target SNR margin.

So  "stable" gave the possibility at setting at a higher target SNR margin.

Hence my hope (I say "hope" rather than "expectation") is "Stable" would give higher speeds than custom.

So what do you disagree with in this logic?

ejs
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Re: High downstream SNR

The only purpose for those custom thresholds was to prevent the DLM making any changes, the line was supposed to be permanently Amber, and the target SNRM kept constant at whatever someone set it at. Comparing this to any other policy seems rather pointless. Custom should give and keep whatever speeds you get with the target SNRM set at whatever it was set to. This could be more or less than whatever speed it ends up on once after the DLM finishes changing things under any other policy. In this case, the custom thresholds didn't appear to work.

It'll be quite unlikely to get an MTBE above 6000. Some lines/modems might find it quite difficult to keep the MTBE above 300.

summers
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Re: High downstream SNR

Yes, but we know that the DLM is making changes to the SNR target margin. This was happening when the MTBE and MTBR were always set to amber. So we known that something else was making the SNR target margin changes.

Now using a standard DSLAM setting of "stable" and one would hope that it set all possible parameters that change the SNR target margin, but this seems not to be the case.

Yes getting the MTBE below 6000s is a chalange, on my line (which is longer than here) the MTBE is always over that, indeed my MTBE only drops off very slowly with target margin setting, FEC varies strongly, but there seems something underlying that causes the occasional Error at most margins.

Hence why the question to @Gandalf as to what the measured MTBE was when the line switches down to ~15dB of Margin (which is its lowest setting IIRC), if that is always over 6000s, then yes we can understand why the line doesn't go green and switch to higher margin. However still doesn't help us understand how the DLM is setting the target margin.

So should this be an investigation into what is going on? None of us yet seem to understand what is causing the changes here ...

Gandalf
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Re: High downstream SNR

@jab1, there seems to be something underlying behind the issues you're seeing so when you're back I think it may be best to arrange another engineer to investigate things further.

From 31st October 2022, I no longer have a regular presence here as I’ve moved on to a new role.
Anoush Mortazavi
Plusnet
jab1
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Re: High downstream SNR

I agree, @Gandalf and will certainly be revisiting this aggravating issue in the New Year. I'm saving this thread to remind me what has happened and to remind me - although I'm sure I don't really need it for that purpose Wink

John
Gandalf
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Re: High downstream SNR

No problem, hope you have a good new year!

From 31st October 2022, I no longer have a regular presence here as I’ve moved on to a new role.
Anoush Mortazavi
Plusnet
ejs
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Re: High downstream SNR


@summers wrote:

Yes, but we know that the DLM is making changes to the SNR target margin.

No, we did not initially know if it was the DLM responsible for all those drops in connection with a re-connect at a slower speed. It looked like the DLM left the target SNRM at 3dB, and then presumably something else knocked out the connection (maybe SHINE), whatever it was had gone by the time the modem had finished re-connecting, leaving it at a lower speed and higher current SNRM, without the DLM changing anything. Then a modem reboot or some other re-connection would restore the speed and 3dB current SNRM. I think a lack of clarity on what's causing the connection drops, and a fixation on the DLM, is not helpful. Yes the line might survive whatever was causing the connection to drop if it wasn't connected at a 3dB SNRM. It's now been made even less clear, because it might have now been the DLM on the Stable policy increasing the target SNRM all the way up to 15dB.

summers
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Re: High downstream SNR

Now I'm confused. Doesn't the DLM set a target margin level which it gives to the DSLAM. Then when the connection is negotiated when bringing up the connection it is brought up at exactly the target  margin. This is the only way I've been able to understand my link. But this says that the speed can only change due to an action by the DLM, as I believe it is the only part that can change the target margin level.