Firstly, DSL does not generally fluctuate in data rate unless: 1. There are bad connections between the subscriber and the DSLAM 2. The line was oversold ( customer too far in wire distance from the DSLAM to support the data rate "contracted" ) I have experienced this problem. After complaining for a year or so, my neighbor let it slip that another neighbor accidentally dug up the lines and severed a cable a year or 2 before. The phones were all screwed up for a couple days after said neighbor did his own splicing job and did not get it professionally repaired at the dig site. The wires were all re-assigned at the box at the end of the street. So for a couple days after every rain speeds were awful, but the more you use it the better it would get. This is a classic characteristic of wet lines. If the line were oversold, it would be pretty consistently bad. Upshot is, your ISP may not even be accountable if they don't own the lines and you will likely find disclaimers in the contract.