DLM - "What it is and how it works"

This is the most comprehensive ISP document I've come across so far regarding FTTC DLM (from Plusnet): FTTC DLM - What it is and how it works

Can people say how accurate they think this is?

I thought this was an interesting statement:
"Any changes made by DLM are executed between 3am-5am"

I would say the 3-5am statement is wrong. Every DLM intervention I've had has come at 8:01am.

Are you sure that was DLM intervention and not a broken VDSL connection; eg from a big burst of noise.

Pretty sure my interventions have happened between midnight and 7am.

If DLM finds that your line is erroring enough to cause the quality of your service to become poor, it will act and either apply Interleaving or reduce the �speed band� that you�re set within.

I'm sure many will argue that this is often not the case and that DLM is far too quick to make changes that add lag and slow speeds,based on error rates,It often intervenes where is doesn't need to
In other words what it considers to be above normal error rates may not be noticeable to the end user, and if left they may never do so, the errors are often not enough to cause problems with throughput or instability. dlm is triggered way before the line is actually impacted

Edited by tommy45 (Mon 06-Oct-14 15:38:52)

In reply to a post by tommy45:

In other words what it considers to be above normal error rates may not be noticeable to the end user, and if left they may never do so, the errors are often not enough to cause problems with throughput or instability. dlm is triggered way before the line is actually impacted

It depends what you are doing with the data.

If everything is transferred under a protocol that notices the failure and gets a re-transmission, such as TCP (used by downloads) then you'll just get a drop in throughput. If the error rate gets high enough, the throughput drops dramatically, but for more normal error rates, you'll barely notice the difference.

If, however, it is transferred under a protocol that does not re-transmit, you just get gaps in the transmission. For most people, this happens to the protocols used for streaming audio & video, and for online gaming. As the error rate increases, the gaps become more noticeable (and, for streaming, the glitches they cause to the audio and video become more intolerable). Any errors here are noticeable to the eye and ear, even if they don't cause you to miss the plot. We humans are rather less tolerant of these errors than a computer is to a re-transmitted packet.

Under FTTC, DLM is undoubtedly tuned so as to give a good experience for streamed video - and particularly to make sure that subscription TV gets somewhere close to broadcast quality. That means it has a lower tolerance to errors than would be needed for "just" downloading.

But not everyone has an internet connection in order to watch tv, that imo isn't what the internet is for, though if government has it's way it will become just for that and a platform for it's own uses ,

Did adslmax see any issues streaming tv or you tube videos prior to dlm kicking in? even if he did see buffering it doesnt necessarily mean it was due to an increased error rate, as buffering can be caused by a number of other things, even software for instance the ff add-on "you tube HD" that would cause almost all you-tube video streams to stop at 14 seconds from the start then there is network congestion, to and from and including the CDN it's self

If the info about the error rates that he posted are factually correct and not misreported in any way by the modem in use , i wouldn't consider the figures excessive or likely to adversely impact his connection in any way as the majority of connections on Fast Path will generate some errors it's that fact that BT OR's DLM parimiters are far too sensitive ,and are causing missery too many that isnt really nescercary, by using interleave and INP to mask what they should be fixing(underlying line fault,crosstalk,ect) if they are really that concerned about providing quality

Edited by tommy45 (Mon 06-Oct-14 17:53:56)

I dont think its too sensitive on error counts but it programmed badly.

e.g. it reacts "after the event" so if you get 400k CRC for a 20 min period at 7.45pm whilst streaming eastenders, DLM doesnt react, but instead wait until the next early morning. Which if its a one off event is too late.
It seems to have little intelligence if the need to adjust the line is long term or not.

I would handle DLM like this.

If ES or UAS goes over 15 min threshold, adjust the line parameters immediately.
Set the recovery period for 24 hours for each day the events reoccur. So if the threshold is only breached for one day, 24 hours later the line is reverted, however if its 2 days in a row, then it needs 48 hours of green status before it can be reverted and so on.
Add a gaming mode, in the gaming mode, banding takes priority over interleaving if adjustments needed.

Edited by Chrysalis (Mon 06-Oct-14 18:28:44)

My DLM was resync at 8:56am on the Saturday and again last night at 2:33am. From 79999k to 72000k and now at 67000k

Edited by adslmax (Mon 06-Oct-14 19:48:01)

Are those exact numbers, or the nearest "000"?