Where are you that you have Supervectoring? IOM?

well, I'm from Germany.
But as there isn't any other Draytek Forum, I decided to register here.

Chavell3 wrote:
Hey,
the problem is, that the router first connects with around 190mbit(and daily conection Problems) and after about 10 or more days the speed turns down to around 180mbit and working fine with that…
It seems it has something to do with the signal negotiation between router and the DSLAM.

Well, what difference does +/-10mbps make if you're already connecting at 180mbps?

You'd need to read up on how German DSLAMs work.

In the UK, if there is a period of stability/instability on the line, the DSLAM will automatically reduce/increase SNR. Since I'm on a Huawei cabinet, we started at 6db, but then this was gradually reduced to 3db. As there were more disconnections at 3db, the DSLAM would incrementally raise the SNR until fewer disconnections.

I have no experience with ECI cabinets, but read that the SNR on those is 6db, though Openreach, which is the company that manages the network here, were going to experiment with lower SNRs.