To DLM or not to DLM?

[see BT reply at end]

Having recently posted on the small differences between BT and TT (TalkTalk) back-haul for us as an ISP, it is interesting news that apparently BT are stopping their DLM (Dynamic Line Management) according to a story in The Register.

We are awaiting comment from our BT account manager to confirm this.

If true this creates an interesting difference. For us, DLM is usually a pain - we see the major issues that it can create when it is not working as intended. This is why we like TalkTalk where we have no DLM but direct control of the profiles.

On TalkTalk our end users can log in to our control pages and adjust their line, with immediate effect, and can make changes as needed. Interestingly, TT are talking of offering DLM as a feature soon which may have uses on some lines, or for an initial period on a line as an option.

However, if BT stop their DLM, then we have a problem as the controls on BT lines are much harder. There is an option to set some of the settings, but they have a very annoying lock out when used meaning you cannot make another change for 10 days. This makes it impossible to tweak a line without the risk of breaking it totally. At present, if you set it wrong the DLM will kick in, usually within hours and at least make it work, but with no DLM, a 10 day lock out makes the controls almost useless.

BT will have to provide the same level of instant direct control as we have with TalkTalk and used to have with BE, or there will be major problems with BT lines.

Let's see what BT say...

Update: No word from BT yet, but ispreview confirm that BT think this will not have any impact, so DLM will continue.

Update from BT:

"BT has been defending a claim brought by ASSIA since November 2011. They had asserted three patents against BT but during the proceedings, they had to narrow their allegations and withdraw one of these patents entirely.

"In January 2014, the High Court found BT was infringing on only a minor part of one patent, and the Court of Appeal, whilst invalidating the majority of the claims of ASSIA's other patent, ruled that BT's network infringes what remains of the other patent.

"Although BT was disappointed with the ruling, we have made minor changes to our programming which means these two decisions have no material effect on the operation or performance of our networks. "


  1. The updated ISPReview article indicates BT began disabling NGA-DLM last Friday at 6am, having failed to get a stay of the injunction long enough to remove just the specific feature under dispute.

    I guess that means current lines are now locked to whatever settings DLM last provided until BT pushes a release with the disputed feature removed.

  2. Why can't BT just licence the relevant patent(s)? That was the original intent of patents, that they could be licenced out. I know today the model is to not licence them and sue people when they infringe, but is the original model so completely dead?

    1. Three reasons.

      Firstly it's about negotiating the royalty rate. If a patent troll can go to BT and say "we have this key patent you need and can't work around" then they can get a lot of money. But if they go to BT and say "we have this patent you're using and you could work around it for X pounds, but you'll loose a network feature that brings you an extra Y pounds a year of profit" then BT aren't going to pay more than X pounds upfront plus Y pounds a year for the patent. So if BT deploy a workaround, THEN they can go back to the patent troll and negotiate for a much lower license fee.

      Secondly, the patent troll is suing for past damages. If BT can show the patent isn't particularly useful to them - "as soon as we learned of it we turned off our servers for a few days then disabled that feature" - then they're likely to have to pay less damages if they lose in court.

      Thirdly, there is probably a genuine dispute about whether the patent is valid and BT infringes. People filing patents have a delicate balance between "language so broad the patent has prior art" and "language so narrow that no-one is likely to infringe". The resulting language is usually quite broad and subject to interpretation. So it's impossible to know if a court will rule the patent invalid, or rule that BT doesn't infringe, or not. Obviously if BT don't infringe then they don't want to pay.


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