REIN stands for, Random Electrical Impulse Noise, and it is very often the reason for those seemingly random disconnects on your ADSL connection.
This is the second Christmas since rate adaptive products from LLU providers and BT Wholesale have been used by millions of people in the UK which means the number of people who may see yet more disconnects over the Christmas period is a lot higher than in the past.
What many people may not know is that while a phone line will happily run a 0.5Mbps connection in the face of almost any form of random noise, run the same line at the maximum it will support and the safety margin decreases to the point that something as simple as a set of Christmas lights blinking on and off may be enough to cause disconnects, or slower speeds than previously experienced.
The moral is that if your ADSL starts to run slow and your Christmas lights are on, try switching them off and restart the ADSL modem to see if things improve. If they do, consider moving the Christmas lights. Things to avoid are running Christmas lights close to the telephone wiring, or plugging power transformers into the same power strip as an ADSL modem. It may actually be your neighbours lights that are the problem, so some delicate discussions could be required. If they have ADSL themselves, they may welcome some help in figuring out what the problem is.
In cases where the disconnects are not resolved by switching things off or moving it, then ensuring the telephone wiring inside your property is not picking up more noise than it needs to is a good idea. The simplest and fastest solution is to disconnect the ring wire on all your extensions and master socket. If you don't mind waiting for the postman to deliver it, fitting a dedicated ADSL faceplate to the master socket is a good project to keep you out of the shops. One final word, if you are using a flat ribbon type cable for connecting your ADSL modem, we would advise changing this for a cable that has twisted pairs. Twisted pair cabling is what BT use for the cable to your home and for BT installed extensions (unless your wiring is very old) and it helps to make the ADSL signal more immune to noise.