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Author Topic: SNR reduction, giving DLM a real chance...  (Read 10355 times)

sevenlayermuddle

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Re: SNR reduction, giving DLM a real chance...
« Reply #15 on: August 22, 2009, 04:43:39 PM »

Well well,

Guess what, I never thought I'd see the day, but I just noticed DLM's given me back 3dB, I'm back on a 12dB margin! :thumbs:

I don't know when that happened, but it was still 15dB when I looked a couple of days ago.  It does look like just over two weeks with an actual SNRM of about 18-20dB (thanks to a lousy initial sync), with a corresponding error rate less than 20 ES per day on avreage, has done the trick for DLM.

I'm predicting that it won't, but will be happy to eat my words if it does. :-\
Munch, munch  :-[

ALong with my 12dB margin, I'm back at 3552 kbps, which with my 56dB line means several (say, 5-10) ES per hour.  So I'm guessing DLM won't give me any more, but I'm going to leave it alone (untweaked) for another two or three weeks.  If nothing gives,  then I think I'll try another experiment, which will be to 'adversely' tweak my SNR to a higher level than DLM's target, and thus get my error rates right down again.

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roseway

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Re: SNR reduction, giving DLM a real chance...
« Reply #16 on: August 24, 2009, 02:41:17 PM »

It will be very interesting to see if it does go further. Some time ago I went through the same process and it went all the way back to 6 dB eventually, but my ES levels were very low.
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sevenlayermuddle

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Re: SNR reduction, giving DLM a real chance...
« Reply #17 on: August 24, 2009, 09:10:42 PM »

It will be very interesting to see if it does go further. Some time ago I went through the same process and it went all the way back to 6 dB eventually, but my ES levels were very low.


Well I'll definitely let you know.  I'd actually quite like to be able to remove my 'SNR tweak' for good, but I'd want a 9dB target for that.

I'll also be intersted to see whether my hard-won DLM improvement is any more permanent than the improvement brought about by BTw's manual override, following a request from my ISP.  That 'improvement' evaporated after 48 hours, reverting back to 15dB again.

One thing I'm tempted to deduce from my own, yours, and some others experience is that, if the line's stable enough, then 14 days does seem to a critical period over which DLM samples the line before reacting.  Mine took about 17 days, but I recall a big thunderstorm at or about day 3, which possibly caused a brief increase in error rates that restarted the 14 day clock.
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roseway

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Re: SNR reduction, giving DLM a real chance...
« Reply #18 on: August 24, 2009, 10:33:34 PM »

Yes, my margin went down at about 15-day intervals.
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  Eric

kitz

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Re: SNR reduction, giving DLM a real chance...
« Reply #19 on: August 25, 2009, 05:20:32 PM »

>> but I just noticed DLM's given me back 3dB, I'm back on a 12dB margin

OMG..  I thought 7LM was going to be stuck at 15dB for eva and a day.  Congrats on some improvement at least.
Like you say it will be interesting to see if there are any further developments.

Please do keep us informed.
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sevenlayermuddle

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Re: SNR reduction, giving DLM a real chance...
« Reply #20 on: August 25, 2009, 07:36:13 PM »

Actually Kitz, it just dawned on me that it's been about  year.  In fact, driving home I began counting, and thought it might have be exactly 365 days.. now that would have been a dramatically interesting coincidence!  In fact, checking back over my emails to ISP, it was about 2 weeks short of the year, so no real coincidence at all.

One curiousity, I have noticed a couple of unexplained spontaneous resyncs over the past few days, following that margin drop.    I strongly suspect they were exchange-initiated as my line hasn't lost sync in months, even at much higher speeds than I have now.  But I don't run anything like routerstats (shame on me) :-[ so I've no real evidence of it.  I almost wondered if my ten-day training period might be getting re-run but, presumably, if that were the case I'd have gone back to 6dB initially, not 12dB?
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kitz

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Re: SNR reduction, giving DLM a real chance...
« Reply #21 on: August 26, 2009, 02:22:15 PM »

>> if that were the case I'd have gone back to 6dB initially, not 12dB?

I would have thought so.
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sevenlayermuddle

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Re: SNR reduction, giving DLM a real chance...
« Reply #22 on: September 16, 2009, 01:23:02 PM »

To recap the last few weeks...   One day in early August, following a power cut, my router synced at the default target margin of 15dB but, as often seems to happen after a power cut, the sync speed was much lower than I'd normally get at 15dB.  Correspondingly, once the the noise had settled,  the actual SNR soon rose to about 18 dB.  With such a high margin, my error rates became very low, averaging no more than 20 ES per day.

After a littler over 14 days with these low errors, DLM rewarded me with a 3dB target reduction to 12dB.

That 3dB reduction was on 22 Aug.  Since then, with a 12dB margin, my error rates have been not bad, averaging about 150 per day.  But that's not been good enough for DLM as I've had no additional reduction in target, despite having let it maintain continuous sync for the last 19 days in case it helped.

So, I've now bravely tweaked my margin again, 'adslctl configure --snr199',  which has got me an 18.5dB margin, and obviously a  loss in sync speed.  But I suspect there will also be a big drop in errors.

It'll be interesting to see, in a little over two weeks time, whether DLM has responded favourably to the lower error rates. ;)

One thing I've already noted is that the earlier reduction has stayed with me.  That contrasts with the manual reduction which I persuaded by ISP to get done year ago, and which evaporated 48 hours later.  I've seen similar accounts elsewhere of manual overrides quickly reverting. I do wonder whether BTw's DLM interface actually enforces a 48 hour timeout on manual overrides, or at least there may be a tick box for it  somewhere on the GUI, that the operators either ignore or don't understand?


edited to get the dates accurate
« Last Edit: September 16, 2009, 01:39:21 PM by sevenlayermuddle »
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roseway

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Re: SNR reduction, giving DLM a real chance...
« Reply #23 on: September 16, 2009, 04:05:09 PM »

You're certainly a rare beast, 7LM, to tweak your margin up. :) But it's almost certainly the right thing to do, to try to get DLM to lower the target further. If it does get to 9 dB, I think I would probably leave it there, because it looks as though your error rate increases quite rapidly with lower noise margins.
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sevenlayermuddle

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Re: SNR reduction, giving DLM a real chance...
« Reply #24 on: September 16, 2009, 04:36:29 PM »

If it does get to 9 dB, I think I would probably leave it there, because it looks as though your error rate increases quite rapidly with lower noise margins.

Yes, I totally agree, 9dB is probably right for my line, and when it was at 15dB target that's as far as I ever tweaked it.  In fact most of my neighbours' seem to have settled at 9, and my line was happy (and so was I) at a DLM target of 9dB for as long as I can remember, before I stupidly upset DLM by too many deliberate resyncs one afternoon whilst experimenting with wiring changes.  I really just want to get back to where I was before that happened, without future tweaking.

As an aside,when I tried 'adslctl configure --snr 200' it didn't seem to sync at the first attempt, so I gave up after a few seconds. Rather than keep trying, and maybe trigger alarms in DLM, I then tried '--snr 199' and that worked.  I don't know whether '--snr 200' would have worked if I'd tried again, or waited longer.  As you infer, it's probably not something people do often.  The router's a DG834GT with standard f/w, so I believe 200 should have worked. :-\

- 7LM
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roseway

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Re: SNR reduction, giving DLM a real chance...
« Reply #25 on: September 16, 2009, 04:58:03 PM »

Quote
The router's a DG834GT with standard f/w, so I believe 200 should have worked.

Yes, I would have expected it to work, although it's not something I've ever tried. I use a DG834GT with the DGTeam firmware (which gives a slider control in the web interface to make this tweak) and the slider permits values up to 300.

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  Eric

sevenlayermuddle

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Re: SNR reduction, giving DLM a real chance...
« Reply #26 on: September 23, 2009, 10:25:53 PM »



Some time this afternoon, my router resynced itself at 15dB.  So I've just removed my +6dB tweak (with a power-off reboot), and whad'ya know, my target's back at 9dB.

The interesting thing about this is that it's only taken a week of that high margin, whereas I think we've concluded from my past experience and other previous reports that 14 days seems to be DLM's normal 'proving' time.  I deduce from that that the error rates have been averaged over 14 days, and the low errors of the past 7 days averaged with the slightly higher errors of the previous 7 days, were enough to satisfy it.

Also, there were a couple manual resyncs 7 days ago when I set the +6dB tweak, but that doesn't seem to have spoiled anything. My error rates over the past week have been around 50-70 ES per day, against about 150 ES per day for previous weeks.  So it may be the case that DLM looks for a rate between these two before reducing the margin.   I guess DLM may also have been influenced by the fact the margin reported by my router was consistently very high compared to the DLM configured target. 

What a shame BTw won't just tell us exactly what DLM looks for before reducing the margin,  so we wouldn't have to guess.  But regardless of DLM's secrets, I feel that I've finally tricked it into reducing my margin when it clearly had no natural inclination to do so.  Tonight, 7LM's a happy bunny, and feeling somewhat chuffed. :lol:  :thumbs:

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roseway

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Re: SNR reduction, giving DLM a real chance...
« Reply #27 on: September 23, 2009, 10:44:06 PM »

That's very interesting 7LM. :thumbs:
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  Eric

jeffbb

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Re: SNR reduction, giving DLM a real chance...
« Reply #28 on: September 24, 2009, 05:46:02 PM »

Hi
The mysteries of the DLM my error rates are < 3 ES /day yet it takes Much longer than 14 days to drop my target SNR by 3 db it has taken up to 2 months . still waiting for it to give me back another 3 15 days and counting  ::)

Regards Jeff
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sevenlayermuddle

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Re: SNR reduction, giving DLM a real chance...
« Reply #29 on: September 24, 2009, 08:10:13 PM »

Hi
The mysteries of the DLM my error rates are < 3 ES /day yet it takes Much longer than 14 days to drop my target SNR by 3 db it has taken up to 2 months . still waiting for it to give me back another 3 15 days and counting  ::)

Regards Jeff

Jeff, I'm fascinated.

Another possibility is that my reduction was earned by what DLM saw as 'stability' in my SNRM.  That wouldn't be an unreasonable prerequisite for a target reduction.  Now, my SNR wasn't particulary stable - fluctuating by 2- 3dB night to day.  But thanks to my adverse tweak, it was always (for the past 7 days) an awful lot better than DLM may have expected it to be.  I wonder if maybe that's more important than error rates?

7LM
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