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FTTC: What is DLM and how does it work?

Chat Champion

I think that many using this forum would, like me, welcome a  clear understanding of DLM as it applies to the services that TalkTalk provide.


I am looking for a guide like this:

Maybe that guide applies equally to TT lines, but I am not sure.  Please can someone advise?


These are some of the key facts that I glean from the article:


"ZEN....provides our Fibre Optic Broadband (FTTC) services on the “Speed” option. A connection should drop no more than 20 times in a 24 hour period, and should error no more than 2 times per minute.."

(Zen have DLM configured to use the "speed" option.  The article describes two other options that prioritise stability over speed allowing fewer drops and errors.)


"If your line suffered a temporary problem and no issues occur again then the DLM system will act to improve the speed of the service. This would happen after 9 days of stable service (within the thresholds) if the problem only occurred once."


"If the DLM system improves the line and a problem returns it would need to see an additional 8 days of stability before improving the service again. This would mean the connection would need to be stable for 17 days (within the thresholds) before the DLM system would try and improve the performance again. If the problem repeats itself the DLM system can increase the required stability period up to a maximum of 64 days. "


  1. I would be grateful if someone can confirm that TalkTalk uses the same DLM parameters as described in the article and my extracts.

  2. The article suggests that the only things that cause DLM to change things are connection drops and errors.  Is there anything else?

  3. I have a DLINK 3782.  How can I monitor errors and connection drops?
    1. If my uptime shows as 24hrs does this mean that I have not dropped connection (as defined in DLM)? 
    2. What "event(s)"  within the router log that would indicate a dropped connection?
    3. Do the errors that DLM is monitoring get reported on my router?  If so then which statistic(s) is this?  I can see ES, SES, UAS, FEC, CRC.   
    4. These stats are of course total numbers since the last Router reset or DLM intervention.  Is there a way I can monitor whichever of them really matters (CRC?) by time - so I can identify patterns?

I have asked about monitoring the error conditions using the 3782.  I am sure that the same info for other TT provided routers would be welcomed by the community.


Thanks in advance for your help,






Not applicable



You have accidentally (or deliberately) stepped into a veritable minefield. BT supply and manage virtually every aspect of fibre infrastructure and performance for all ISPs, so the system is common for all ISPs.  I don't think anyone outside BT Openreach technical understand all aspects of DLM. I think TT use the "standard" option and this is common to all TT lines (a TT rep can probably confirm this).


Probably a good starting point for understanding is this Kitz write up :-


Kitz DLM


As to how any specific TT router reports these stats will have to be explained by a TT representative. But TT's ability to mange fibre is very limited and any particular parameter is probably best ignored unless you have identifiablble problems (IMO).


Far too easy to get hung up on things you can't manage or control with DLM.

Chat Champion

Thanks, nice link - will study it!

(I do have identifiable problems - trying to understand the cause - and to do that to understand what I can meaningfully monitor and try to spot patterns in.  However this thread is not the place to discuss the specific issues.)