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a DLM question

crowroad
Grafter
Posts: 40
Registered: ‎01-04-2013

a DLM question

I wonder if I might tap the experience here on the forum regarding DLM on FTTC lines?
My FTTC installation was on 26/03/2013 and went without a hitch.  The BTOR engineer indicated that its attainable rates were such that I could expect the full 80/20 Mb/s.  Distance to the cabinet is ~150m.
Everything in the garden was rosy for 11 days until a clearly audible if minor noise fault developed on the line starting on 06/04/2013.  I suspected at the time that perhaps someone was doing another installation in my cabinet.  However, on 08/04/2013, I experienced no less than 17 resyncs in a 2hr period around lunchtime, followed by a further 9 resyncs in a half-hour period later around tea-time. Sad All of these were of generally short duration so the PPP connection was not lost in most cases.
Obviously this upset DLM as much as it did me!  As I expected it took action to protect my service, increasing my DS SNRm resulting in a sync rate of 35/20 Mb/s.
Typical stats on the state of the line before this are in the first attachment below.
The voice fault disappeared as suddenly as it had appeared, and pleased with this, DLM increased the sync rate first to 54/20 Mb/s on 11/04/2013, and then to 67/20 Mb/s on 14/04/2013.
But there it has remained. Huh Stats for a continuous uninterrupted 14day period to 27/04/2013 are in the second attachment below.  DS ES for the entire 14day period averages just under 16/hr on fastpath, but DS SNRm remains high at 12dB while attainable rates have been close to their original values throughout.
So, how long might I have to wait before DLM views the line as stable once more and restores it back to the full 80/20 it had for the 11days prior to this single anomalous day? I'm willing to be patient.  Smiley
31 REPLIES
Plusnet Alumni (retired) orbrey
Plusnet Alumni (retired)
Posts: 10,540
Registered: ‎18-07-2007

Re: a DLM question

Sorry to say this but I'm afraid we honestly don't know - it's a fairly new technology and we're not sure how the DLM system works as yet :/ Likewise we don't actually have any control over it like we do on ADSL2+/ADSL.
Sorry it's not good news, really hope it picks up and lowers your SNR soon.
crowroad
Grafter
Posts: 40
Registered: ‎01-04-2013

Re: a DLM question

Thank you Matt.  Smiley  That's OK, I guess we're all learning the hard way.  It is rather unfortunate (though nobody's fault, as such) that possible disturbance when BTOR has to work in the same cabinet can have this undesirable effect.  Had the resyncs not come in bursts like that I might have noticed the first few, and simply powering off the modem for a few days might have avoided this altogether.
I intend to power off the modem for at least an hour today and then see what sync we get.  I doubt it will be any worse, and there is the possibility it just might improve things. However, patience is a virtue, so perhaps we'll see.  Undecided
dick:quote
crowroad
Grafter
Posts: 40
Registered: ‎01-04-2013

Re: a DLM question

Well Matt, it seems neither patience nor a stable line with a low (recoverable) error rate will ever make an impression on this DLM.
Here we are more than a month later, and this 67Mb/s IP profile cap (along with a 15dB US and 12dB DS SNRm) is still solidly refusing to relent.  If I was that kind of suspicious person  Roll eyes I might think that a cap has been applied solely to make it match a BTOR 'estimate' that was way too conservative for a 150m D-side, as shown at the time of installation.
Perhaps it is about time someone enquired of BTOR just exactly how FTTC DLM actually works?
Plusnet Staff
Plusnet Staff
Posts: 6,346
Thanks: 31
Fixes: 5
Registered: ‎26-11-2011

Re: a DLM question

Hi crowroad,
I think that's my job. I'll investigate and let you know, I can't give a timescale on how long it will take me to find out this information but I will update this thread once I have more information for you.
Chris Pettitt
Cloud Environments Engineer
crowroad
Grafter
Posts: 40
Registered: ‎01-04-2013

Re: a DLM question

Thank you Chris, that's very kind of you.  I love a volunteer!  Smiley
I'm in no rush. I'm not going anywhere, and neither is my cap for the moment!  Grin
But it was really just a question, as there is no fault here on the line itself to be 'fixed'.  Smiley
Cheers.
Community Veteran
Posts: 19,102
Thanks: 443
Fixes: 21
Registered: ‎31-08-2007

Re: a DLM question

In the absence of any other suggestions, as you've had a solid connection for this long -
Log in to the Router, go to the Internet box, and click Disconnect to drop the PPP(oE) Internet session. Wait about a minute and power down the Router. Wait about a minute and power down the Modem. Leave the Modem off for an hour minimum. Switch it on again in daylight hours (noise levels tend to be lower). Wait until all the lights have stabilised and sync is established. Power up the Router. Log in and click Connect to establish a new PPP session. See if that does any good - no guarantees mind!
crowroad
Grafter
Posts: 40
Registered: ‎01-04-2013

Re: a DLM question

Thank you A1 for your helpful suggestion.  Smiley
Sadly, I have already executed this procedure twice in the last month - at least a week apart - but with no beneficial effect.  As you said, no guarantees.  Sad
Cheers.
Community Veteran
Posts: 19,102
Thanks: 443
Fixes: 21
Registered: ‎31-08-2007

Re: a DLM question

Can you hear/have you heard any crackling or other noises on the line when using the phone? Have you had any problems with incoming or outgoing calls?
crowroad
Grafter
Posts: 40
Registered: ‎01-04-2013

Re: a DLM question

No, not since the brief period described in my original post above, a month ago now.  DLM has taken no further action on this line since 14/04/2013.
This is the nub of this DLM connundrum.  I understand, and to a degree I am grateful, that DLM reacted on that occasion to protect my fibre service as much as it could in the face of what was probably somebody working in my cabinet and inadvertantly distubing my line.  I also am happy that DLM started to back off again as it saw that the disturbance was anomalous and had gone.  The problem is that it stopped backing off before it returned the line to where it was immediately prior to this 'eventful' day.  Sad
There will always be problems of this nature that are outwith the control of the EU or the ISP.  A 'good' DLM would take whatever protective steps are merited by a disturbance, but then continue to monitor the situation, and progressively restore 'normal service' when that has passed.  My (rhetorical) question is why hasn't it done that?  What makes it think this is where it should stop when there are no unrecoverable, and next to no recoverable, errors on the line?  I'm still on fastpath, with no INP.  SNRms are large, and there is clearly a profile cap in place.  If it had capped it at 60Mb/s, then that would have qualified as a fault with BTOR - 25% reduction in previous line rate for more than 14 days.  So, for 7Mb/s, I don't have a fault, I just have a 13 Mb/s reduction in DS line rate - which to put it into perspective, is as much as this line got when it was on ADSL2+; so the reduction is equivalent to having lost all of the ADSL service I previously had - which nobody would be happy about if that was all you had.  It seems that because you still get a reasonable rate (one that perhaps others would be glad of, I appreciate), that an inexplicable loss of (not attainable but) actual DS line rate is just something to be endured.  Death by a series of <24% cuts, as it were.  Smiley
I really wouldn't mind, well I mean I could accept this, if there was some good reason for it.  But, I can't see one.
Thank you though for trying to eliminate the most obvious causes.  Help is always appreciated. Smiley
Community Veteran
Posts: 19,102
Thanks: 443
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Registered: ‎31-08-2007

Re: a DLM question

Oh well, see what Chris Pettitt comes up with. The only thing I can see is that DLM probably is being a bit fussy about the HEC & ES errors you currently have and is going to take a bit longer to change the sync speed. It might be Banded.  As you probably know the chances of getting any sort of reset on FTTC is about the same as winning the Lottery  Huh
crowroad
Grafter
Posts: 40
Registered: ‎01-04-2013

Re: a DLM question

As I said earlier, your help is  very much appreciated A1   Smiley
Fussy DLM?
Current DS ES are ~601 a day, or 0.695%, i.e. on average ~1 every 144 secs, at 67Mb/s, and as you know an Error Second is not a second of errors.  Wink
SES are zero.
Current HEC are ~2630 a day, or ~3.05%
The fact that it doesn't see the need to apply interleaving suggests that these corrected error rates are well within the expected rates of a line on fastpath.
As you wisely say, let's see what Chris can find out.  Smiley
Community Veteran
Posts: 19,102
Thanks: 443
Fixes: 21
Registered: ‎31-08-2007

Re: a DLM question

Fibre DLM can be, note, I said can be, quite aggressive. Now whilst I don't disagree that those errors rates seem as though they may be well within expected limits for Fastpath and in other circumstances DLM wouldn't lower your sync speed, it doesn't mean that it is going to rush and raise your sync speed. Unless Chris discovers something out of the ordinary, even if DLM has banded your speed at the moment, it will be a case of twiddle your thumbs. BTW, info on Fibre Banding does not seem to be available, I did a quick search earlier with no luck, but I'm quietly cursing because I could have sworn I read something recently with the speeds and never noted it  Sad
crowroad
Grafter
Posts: 40
Registered: ‎01-04-2013

Re: a DLM question

Quote from: Chris
I think that's my job. I'll investigate and let you know,

Chris,
Do you think you could possibly find and post the details (including the name and timestamp ) of the profile applied by OR to my line?
It may reveal some information useful in understanding what might be happening here.
I believe it may look something like this (just not the same as this):
Profile Name  67M-80M Downstream, Interleaving Off - 20M-20M Upstream, Interleaving Off
Time Stamp    2013-04-14T05:00:00

Thank you.
Plusnet Staff
Plusnet Staff
Posts: 6,346
Thanks: 31
Fixes: 5
Registered: ‎26-11-2011

Re: a DLM question

Sure can...
33M-67M Downstream, Interleaving Off - 10M-20M Upstream, Interleaving Off
2013-05-21T14:44:05
I'm still working on the DLM information, before I post about it, I want to make sure that it's correct!
Chris Pettitt
Cloud Environments Engineer