Many years ago when Telecom first came out with the 128k/128k ADSL plan (JetStart it was called?), I started using ADSL. Sync speed has been very stable until some months ago (perhaps even longer), I start to notice the sync speed becoming unstable. I feel it's time I should do something about this.

My sync speed can fluctuation any where from about 1Mbps to the max speed ADSL1 can allow. I have a Dynalink RTA770W, it's quite old, but it has been serving me well. What confuses me is that the noise margin seems to increase linearly in the opposite direction of the sync speed. From that, it looks like the noise level is at normal level, but the router for some reason decides to sync at lower speed.

Only one of the phones in the house shares the same connection with the router. The phone of course goes through a filter. As I have requested a splitter to be installed when ADSL was first setup for me many years ago, I have not used filters for any other phones around the house. Further more, the technician who did the wiring told me I have two separate phone lines (I used to have two numbers), so he connected the router to the second phone line (if I understood him correctly).

If at all relevant, I used to have Sky installed, but have terminated it some time ago. The sync speed still fluctuates from time to time. Is this an indication of poor line quality, bad router or something else?