Surely openreach should updated dlm system to take no noticed of every years Xmas Lights
Interference is interference, it doesn't matter what's creating it, if you can't remove it you have to work within the limitations that presents.
DLM exists to automatically find the right settings to keep your line in sync if at all possible. Without it you'd have either no connection at all when the christmas lights are on, or a very unstable one that is resyncing constantly.
Before DLM we had much slower connections as they had to estimate what your line could take and have a huge safety margin. When I first got DSL I could only get 500Kbit, then later they allowed 1Mbit. I then upgraded to 2Mbit which they "accidentally" allowed to go through, even though they supposedly rejected the order due to my line being too long. Yet once I moved to Be Broadband my line was capable of 5Mbit, because I had very little interference.
People who weren't so lucky had huge problems with the their connections resyncing all the time and ISPs had to manually band lines and/or apply aggressive interleaving, which is why DLM was developed as once everyone and their cat had broadband it was no longer practical to do this manually. Plus people in general don't want to spend months reporting back to their ISP that their connection is still unstable as the line profile is tweaked.
In an ideal world seamless rate adaptation would handle all this, allowing the line speed to reduce and you to manually recover it by forcing a resync, but in the real world this unfortunately did not work reliably with all the DSL modems out there.
