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Author Topic: 21CN DLM/Banding Question  (Read 1013 times)

aesmith

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21CN DLM/Banding Question
« on: February 07, 2018, 01:08:13 PM »

Hi,

Some quick questions on 21CN DLM and banding in particular.   Does anyone know (1) what's the highest noise margin that 21CN will apply in response to line error?  (2) does DLM apply banding in response to errors, or only in response to excessive disconnections.   And finally, can the ISP over-ride either target noise margin and/or banding?

Thanks, Tony S
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ejs

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Re: 21CN DLM/Banding Question
« Reply #1 on: February 07, 2018, 08:40:34 PM »

The highest target SNRM is 15 dB.

I don't know, and I'm not sure if anyone (publicly) knows, if the DLM takes different actions in response to errors and in response to retrains. The banded profiles do have higher than usual INP values available.

The ISP can easily set / reset the target SNRM and rate band.
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aesmith

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Re: 21CN DLM/Banding Question
« Reply #2 on: February 08, 2018, 09:33:57 AM »

Thanks, and if the ISP sets the band and/or target SRNM, do the stay set?

Reason for asking is that for the last year we've been reliant on using the router config to over-ride BT DLM to maintain the proper speed.  A&A had said that they can't fix SNR target on 20CN as we were then, but they'd have more control on 21CN.  We've just been moved onto 21CN, still in the 10 day training period.  A&A now a little vague about what can be done, I can see error messages back from BT in response to their attempt to set band and SNR, but that maybe because it's within that 10 day period.

Meanwhile performance on 21CN is absolute crap.

20CN was typically just over 4 meg, for example
   "Down Sync=4224kb/s LoopLoss=55dB SNR=5dB"

On 21CN it just seems worse in all parameters for example ..
  ADSL2+  "Down Sync=3068kb/s LoopLoss=57dB SNR=4.4dB"   
  ADSL 2   "Down Sync=3068kb/s LoopLoss=53dB SNR=3.9dB"

Just getting a bit concerned that we've been sold a pup and far from improving things, 21CN is a big step backwards.  Should I go a step further and disable ADSL 2 as well, effectively reverting to 20CN type modulation?
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kitzuser87430

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Re: 21CN DLM/Banding Question
« Reply #3 on: February 08, 2018, 02:19:05 PM »

Hmm. I am waiting for a 21CN "upgrade" as well.

Do you know if you were interleave/fastpath on g.dmt;

 have you any quiet line/hlog graphs from before the upgrade....

Just found you on MDWS your bits/tone shows where you are losing speed.

What modem are you using and what exchange equipment has been installed.

I have an nagging thought about an unsolved  line problem on your rural line, by your error seconds pre and post move to 21CN.

Ian
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aesmith

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Re: 21CN DLM/Banding Question
« Reply #4 on: February 08, 2018, 04:33:51 PM »

Cheers.  It's a Billion 7800DXL, I don't what type of kit is in the exchange.   Errors come from an electric fence which affects (according to BT) all users on the 50 pair cable with no solution available.   On 20CN we dealt with the situation by over-riding target SNRM on the router and there was an obvious relationship with lower SRNM giving higher synch speed, higher SNRM with lower synch.  What we have now is the sort of speed that 20CN would reach at 12dB SNRM, but even at that low speed the stats are showing what looks like an unhealthily low margin.
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ejs

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Re: 21CN DLM/Banding Question
« Reply #5 on: February 08, 2018, 06:02:29 PM »

Thanks, and if the ISP sets the band and/or target SRNM, do the stay set?

Not usually, but there should be ways to make the settings stick. The original way is to set custom DLM thresholds, if the red threshold is 1 and the green threshold is 86400, then the MTBE and MTBR cannot be less than the red threshold or more than the green threshold, therefore the ILQ should always be amber and the DLM shouldn't change anything. Later BT seemed to keep announcing there would be some new way to turn off the DLM, but most recently they stopped making the documentation publicly available.

3068k looks suspiciously near the top of the 3Mb band, and I'm not sure you can always trust the SNRM while banded to accurately indicate what would be possible if not banded.
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aesmith

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Re: 21CN DLM/Banding Question
« Reply #6 on: February 08, 2018, 06:54:43 PM »

3068k looks suspiciously near the top of the 3Mb band, and I'm not sure you can always trust the SNRM while banded to accurately indicate what would be possible if not banded.
I certainly hope it's not indicative, the link's now down to only 1.2dB @ the same 3070k.

Interesting thing is that when the speed/margin changed, the errors virtually disappeared.  Now that's not just due to speed, because the speed actually increased at that exact time.  Going by the DSL Stats logs it went from  ..
 Current Downstream Sync Rate is now 2990kbps @ 11.4db SNRM. Attainable is 3192kbps.  (Around 2,000 ES per hour)
To ..
 Current Downstream Sync Rate is now 3069kbps @ 3.4db SNRM. Attainable is 4876kbps (almost no errors)

So something's been done in addition to the speed change.  Unless it's coincidence and that change corresponded with something happening to the electric fence - that does happen from time to time, sometimes when it's wet weather the errors disappear.
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tickmike

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Re: 21CN DLM/Banding Question
« Reply #7 on: February 08, 2018, 09:59:37 PM »

Hi.
I am on 21CN ADSL2 and I told my isp 'Eclipse' business that I wanted the target set to 3dB on down stream, they could only alter the down, up is still 6dB.
Max:   Upstream rate = 892 Kbps, Downstream rate = 6356 Kbps at 96/2 interleaving d/up.

Sometimes on a re-boot of the modem it will go to 6dB/6dB or higher and the I force it down with DSLstats advanced tweaks. it is about 2.5 D/5.9 up SNRM
Line attenuation (dB):     52.0   D   30.6  up

You will have to wait for the 10 days training to finish .
« Last Edit: February 08, 2018, 10:07:15 PM by tickmike »
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aesmith

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Re: 21CN DLM/Banding Question
« Reply #8 on: February 09, 2018, 06:57:00 PM »

Earlier someone asked what kit was in the exchange, does the following shed any light from DSL stats ..

DSLAM/MSAN type:           TSTC:0x0510 / v0x0510
Modem/router firmware:     AnnexA version - A2pD039f.d24m
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ejs

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Re: 21CN DLM/Banding Question
« Reply #9 on: February 09, 2018, 07:11:48 PM »

Is that the same as what it was on 20CN? If so, perhaps the 21CN / WBC upgrade was more about the backhaul than the DSLAM/MSAN. I think TSTC indicates the oldest and worst type of 21CN DSLAM/MSAN.
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burakkucat

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Re: 21CN DLM/Banding Question
« Reply #10 on: February 09, 2018, 10:11:19 PM »

DSLAM/MSAN type:           TSTC:0x0510 / v0x0510

TSTC ---> Texas Insturments

If you scroll down close to the bottom of the main site "Line Stats - Explanation" page there is a table which shows that the DSLAM could be either Marconi, Ericson or Huawei.
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j0hn

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Re: 21CN DLM/Banding Question
« Reply #11 on: February 09, 2018, 11:12:48 PM »

A&A are pretty good at checking what equipment is in the exchange, and if there are alternative DSLAM/MSAN's you could be connected to. The knowledgeable staff will be able to advice what performs better.
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aesmith

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Re: 21CN DLM/Banding Question
« Reply #12 on: February 10, 2018, 07:09:22 PM »

Is that the same as what it was on 20CN? If so, perhaps the 21CN / WBC upgrade was more about the backhaul than the DSLAM/MSAN. I think TSTC indicates the oldest and worst type of 21CN DSLAM/MSAN.
I'll have to check back and see if I've got any record.  The DSL behaves differently, for example connecting at ADSL2 or ADSL2+ depending on my modem settings, alsi the line attenuation has dropped by 2dB and the upstream synch increased from the 20CN 448k to (currently) 828k.  It would be very disappointing if it's really the oldest and worst kit, since it's only just been made available at this exchange.  Does this imply that BT's really lost interest in 21CN and just stuffing in any gear to get exchanges off 20CN?
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ejs

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Re: 21CN DLM/Banding Question
« Reply #13 on: February 10, 2018, 08:33:50 PM »

I guess it either means that yes, BT did recycle some older kit from elsewhere, or alternatively perhaps the existing 20CN DSLAM hardware was already capable of ADSL2+ so they upgraded the backhaul and re-configured the existing DSLAM.
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aesmith

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Re: 21CN DLM/Banding Question
« Reply #14 on: February 12, 2018, 07:26:09 PM »

Well aside from 21CN vs 20CN issues, my link seems to have blown it's brains out this afternoon with noise margin crashing down to zero, bursts of up to thousands of CRCs per minute, and consequential retaliation by BT in slowing it down first to 2000 odd, then half an hour later dropping again to 1539k.   Not a symptom I've seen before, our electric fence has never given more than one or two CRCs per second and those didn't interfere with throughput in the slightest.   Hope it's something that can be fixed as 1500k is hardly worth keeping.
« Last Edit: February 12, 2018, 07:28:27 PM by aesmith »
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