Deteriorating ADSL connection

I've been experiencing connectivity issues with my (Eclipse) ADSL service for a while, with the connection seemingly dropping under load (i.e. when trying to download anything substantial).

This being a long weekend and trying to think of the kind of questions an ISP might ask, I bought a new router/modem (ASUS DSL-N66U), replacing a NetGear DGND3300. I setup the new equipment, configured it easily enough, and all was fine. It didn't fix the connectivity issues but I was confident that it wasn't the hardware.

Next, I decided to simply the telephone wiring which leads to my DSL modem, in order to get closer to the master/test socket.

The master socket enters the house on one side of the living room, I have an (plugged, not wired, to the master) extension which takes the socket to the other side of the room. I then had a several metre long telephone cable into a surge suppressor, then a 5m long cable (passing through several floors) to the office which is on the 2nd floor of the house. I also had the base station of a cordless telephone and a Sky HD box plugged into the phone line.

I decided that I could do without the surge suppression but there's not much I can do about the length of the cable. So, to simply, I now have the same 5m cable running into an ADSL splitter/filter on the extension which itself runs about 3m to the master/test socket.

I thought that this would, at least, be an improvement. However, since making this change, all of the line statistics, as read from the modem, have deteriorated and I cannot retain a stable connection (drops every 10-50 minutes).

The SNR down was 14dB and is now 6dB (I thought that higher was better). The line attenuation down was 10dB and is now 21dB (lower is better). Previously the stats read 1 CRC error down and 0 up, now 100s accumulate over about 15 minutes. Finally the data rate has reduced from approximately 8192 kbps to 5024 kbps. Nothing other than the router is plugged into the phone line.

Any thoughts as to what I can do here? I've tried several different filters but can't really replace the phone cable easily (since it runs through 2 floors). Why would this apparent simplification (intended as an improvement) cause such unwanted consequences?

Are the cordless basestation and the Sky box still on the "Voice" (filtered) side of the filter after this change?

Normally you could to filter the connection at or near the master socket and run separate wiring from there so that only the router is on the ADSL (unfiltered) socket.

In your case depending on where the phone and Sky box are in relation to the wiring layout you may need more than one filter.

Thanks for your reply. I have tried with the phone connected to the "voice" side of the microfilter and also with the phone fully disconnected. (Sky box is currently disconnected).

After I posted, I connected an extension cord (currently across the living room floor) between the end of the wire leading to the modem/router and the master socket. Even though I had tried the same the day before, this seemed to do the trick and restored my previous line quality approximately (now about 11.5 SNR down and 6.5 attenuation).

This seems to isolate the existing extension as the root of the recent problem and, obviously, I can replace this. Alternatively, I could move the router to be very close to the master socket and route a Cat5e network cable across the living room to a nearby switch. Not sure what would be best.

However, I'm still getting the original problem of frequent disconnects under load (i.e. whilst downloading) so nothing has really improved.