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Openreach Give UK ISPs More Control of Broadband DLM Profiles

Wednesday, October 28th, 2020 (5:18 pm) - Score 11,664
blowing fibre optic cable to fttc cabinet

Openreach (BT) has informed ISPs with Fibre-to-the-Cabinet (FTTC / VDSL2) and G.fast broadband lines that they will “soon” be deploying functionality that allows providers who wish to purchase this to amend Dynamic Line Management (DLM) profiles on customer lines, which sounds as if it may be more flexible than prior approaches.

The current DLM system is used to control the speed and stability of copper based broadband lines (ADSL, VDSL2, G.fast), which in practice means that your speed may go up or down depending upon how stable / error prone (interference etc.) DLM thinks the line is.

In the past broadband providers have had very little control over DLM profiles for hybrid-fibre lines, although since 2017/18 we have seen a number of changes to improve that (e.g. remote DLM resets, albeit with caveats). Following on from those we now have the new Amend Dynamic Line Management (DLM) Profile functionality, which allows ISPs to “request a DLM reset on any FTTC service that you own.”

Openreach Statement

While this functionality will be at no additional cost to consume in-life, there is an onboarding charge.

The development costs associated with delivering this functionality will initially be split evenly between the CPs purchasing this functionality upon release. If an additional CP wishes to purchase the solution at a later date, they will pay an even split (re-calculated across all CPs) which Openreach will also rebate equally to the CPs who had previously purchased the functionality to maintain an even cost to all CPs.

The related price notification for this change suggests that it will be introduced from 26th November 2020. The ability to reset DLM profiles is often helpful when trying to resolve banding problems and other issues that can disrupt service speeds. Hopefully the new approach will be cheaper and more accessible.

Leave a Comment
28 Responses
  1. A_Builder says:


    Can they turn DLM off?

    I say this as DLM can be triggered by line noise from industrial plant at specific times. Those specific times may not impact the user but as DLM picks up the real problem It then manages global speed downwards – unnecessarily.

    Just a though…..

    1. adslmax says:

      I hope so! Option for DLM to be turned off permanent

    2. Alex Atkin says:

      I doubt it. The problem with turning DLM off is it may impact more than one line due to crosstalk. So while your specific line might improve, it could potentially make anyone further from the cabinet less stable.

    3. NE555 says:

      “DLM off” is more or less what “banding” is: set a fixed speed which the modems are not allowed to negotiate above (although they can go below, if line conditions don’t allow the requested speed to be maintained)

      It’s unclear from this article whether the DLM control provided to ISPs includes being able to set (or remove) banding.

    4. Jay says:

      DLM “off” is nothing like banding.

      Banding is still a DLM profile. Banding can be applied at systems of different sites levels.
      It still contains error protection within the DLM profile (G.INP High or Low, Interleaving High or low or fastpath).

      Capping sync is only 1 out of half a dozen params that DLM controls.

    5. Jay says:

      Dozens of speed levels*

      Site needs an edit button.

  2. Charles Pullin says:

    My uplink speed in the past year has gone down from 1.2mbit to 0.3 -0.5mbit and is causing issues with a number of service including the BT App. BT say they have tried to improve to 1mbit as promised at the last service upgrade but cannot. They say only a 4G home bub will improve the unlink data speed. This is financial increase of £240 annually which the cause is not my fault. Is this a normal practice now when BT cannot meet their contract terms ?

    1. TB says:

      Unfortunately broadband is still a “best efforts” service and “guaranteed” sync speeds can’t always be met, even if they have been faster in the past. Unless there is a underlying fault that is causing the slow speeds then there aren’t many options left if you’re a long way from the exchange. Consider their 4G suggestion but possibly look at an alternative 4G provider, you can get 4G hubs that will accept a SIM card from any network giving you the choice to look for the best value deals.

  3. adslmax says:

    Bit cheeky from Openreach to charged customers for any DLM Request per application but no metion of price yet?

    Is there an option to turn off DLM? I do hope so!

    1. Alex Atkin says:

      There has to be something to discourage ISPs resetting it willy nilly on lines, potentially making other lines on the cabinet go awol in the process.

    2. Phil says:

      Yes you need to discourage it as what will happen is first line support will just constantly issue a reset to get the customer off the phone ASAP without ever showing any interest in actually fixing the underlying problem. In the majority of cases the DLM has gone a bit awry because of an underlying fault or issue and the reset is what you do once the fault has been cleared.

  4. bob says:

    i hope talk talk will use it. as id like to request speed profile interleaving OFF. 4 months now im on interleaved and it wont give me back fast path 🙁
    i also wonder if its possible that this application can be added to our account pages so the customer can pick and choose what setting they want.

    1. Alex Atkin says:

      I do not believe there is a DLM profile that mandates Interleaving off, its still going to assess your error rate and adjust it accordingly.

    2. bob says:

      well speed profile will make it less likely it will apply interleaving and if it does, at least we can just reset it. nobody knows what options there will be until its released i guess.

    3. Jay says:

      Error protection off, is the DLM profile for fastpath.
      It certainly exists.

    4. bob says:

      jay, yes it exists however its currently linked to the error limits of the speed/standard/stable profiles which are extremely unforgiving 🙁

  5. Mike says:

    Gave up with FTTC getting worse over time and went with 4G, and I highly suspect DLM is the reason why.

    1. Alex Atkin says:

      To be fair 4G can be much worse. My Three connection has been anywhere from 2Mbit, 20Mbit to 50Mbit over the last year. When I’ve wanted to use it, its been pretty much unusable and their customer service is either closed or busy, so I never got around to complaining.

      They have upgraded my local tower recently and touch-wood it seems to have stabalised to 50-80Mbit. But it doesn’t alter the fact I’ve been paying for a next to useless service for over a year, as prior I had it in my mobile and had the same problem everywhere I tried using it even before the pandemic.

      Even though my FTTC has gotten slower over the years, its infinitely more reliable than 4G has been. I couldn’t run a VPN over the 4G due to these issues.

    2. Jack says:

      @Alex Atkin your issue with Three is more Three specific than something wrong with 4G. Three’s network does not have the backhaul required to make it work well in these situations.

    3. Mike says:

      Three is very location dependent, it can range from very good to terrible, that’s why for home use I recommend EE, it’s worth the premium.

  6. Rahul says:

    DLM is a big deal especially on unstable EO lines under ADSL!

    When I had ADSL EO Line until last year, I always had problems with my internet connection dropping out. Regardless of 3dB or 6dB noise margin profiles connection will relentlessly drop-out without avail. DLM would never stabilize at no point because the Openreach DLM would never go above 6dB by default.

    Changes of Microfilters, removing orange ring wire, connecting via test socket and routers did not help. What did help however, at that time was telling my ISP to manually cap noise margin to 9dB! That was the only time under ADSL when my connection was stable. But at a drawback, a drop from 16-18Mbps to 11-13Mbps.

    Now I have FTTC finally upgraded last year and since February this year I have FTTC with TalkTalk and since then my connection has been rock solid even under a 3dB noise margin profile I had max 80/20 sync speeds without drop-outs!

    This problem stems from the fact that if you had ADSL and a very long copper line (1000+ meters to exchange) it is more prone to picking up noise and interference. While on FTTC the nearest street cabinet being around 300 meters or so slashes out most of the copper length eliminating most of the noise from the line.

    Of-course there’s still no guarantees that connection will be reliable unless you had a cabinet that is isn’t too distant from your property.

    This is why most of us crave FTTP as it is a much more reliable and future proof technology that is not dependent on DLM and thus will not result in speed fluctuations.

    Btw, turning off DLM is not the solution for most people either. Because let’s say you are able to sync at max speeds with a lower SNR profile but the line wasn’t stable. Turning off DLM will result in endless drop-outs. Turning off DLM permanently is only good for those who are absolutely certain that their connection is stable regardless of how low their SNR is.
    Under ADSL I could get 18Mbps with 3dB profile but what would be the point if it drops out relentlessly? In this case 12Mbs at 9dB is a better option. I would never sacrifice reliability over speed. I’m lucky that under FTTC I no longer have issues at max speeds.

    As long as we have copper, DLM will always be a thing as it needs to determine how reliable your connection will be under the max speeds that your line can handle efficiently.

    1. bob says:

      i had bt adsl years back and the dlm definitely did flip to 9db and 12db profiles when i restarted my modem too many times

    2. Rahul says:

      @Bob: Not in my case! Regardless of how many times I restarted my router or the amount of times the drop-outs did occur. The SNR set point defaulted back to either 3dB or 6dB.

      Somehow there was no way to manually increase the SNR past 6dB without calling the ISP manually. This happened with Sky, Be Unlimited* and then with Plusnet.

      Each time after I had switched to any ISP. Even after the 10 days interleave, the vicious cycle did not stop.

      It is like DLM is interpreting the connection as stable and increases the speed back up and dropped SNR from 6dB to 3dB but few hours to a couple of days later when the connection dropped the same issue occurred. 6dB, 3dB, 6dB, 3dB speed increased, speed dropped and so on, but no permanent end to it.

      This is the observation I have seen for over a decade when observing router stats. Only a few years ago I diagnosed that the only solution was call the ISP, raise SNR to 9dB and that took care of the problem.

      Hence why I was always so worried when I found out that I was going to be upgraded to FTTC instead of FTTP I feared that the same issue was going to carry over.

      Thankfully, FTTC has eliminated this problem once and for all! This time my connection no longer drops and DLM is stable and no longer gets triggered.

      The BT Openreach engineer who came to install new pre-filtered NTE5c Faceplate MK4 in February as part of the FTTC upgrade admitted that there were many complaints over the years and reassured that with FTTC now this problem is gone for good. I was still skeptical but it appears that indeed the issue has finally been solved. But in the past the Openreach engineers could never diagnose the line problem when they came to my flat.

    3. Jay says:

      The ADSL DLM is a very different beast and is run by BT Wholesale.
      Completely unrelated to the OpenReach FTTC DLM which is by design a hands off system.

    4. Rahul says:

      @Jay: This is true. Openreach FTTC DLM is different in a sense that it does not use 9 or 12dB noise margin profiles. Fortunately the reliability issues are naturally rectified on FTTC so a 3dB or 6dB SNR profile does not pose any problems as interference’s and noise is usually filtered out at the cabinet as well as reduced risks due to reduced copper line length.

      The problem with DLM as a whole, however, is that it is always going to be potentially problematic. In the event for example due to power failure or constant router reboots this will trigger DLM once again as the system fails to interpret the line as stable.

      Then another 10 days the internet might drop out. This happened to me a few months ago on FTTC only because of TalkTalks firmware update that triggered DLM to wrongly think my line was unstable. Speed normalized on return and the connection was reliable once again after 10 days or so.

      These are my complaints with the DLM system. When the whole of the UK eventually gets upgraded to FTTP, DLM will be history as it will no longer be needed.

  7. Paul M says:

    Will this allow me to trade download speed for better upload? From 40/5.5 to say 35/10?

    1. A_Builder says:


  8. Andrew says:

    Any news/reports as to whether this has been rolled out to any of the ISPs yet? I’m interested in Sky in particular.

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