DSL is now working smoothly :-)

Thus, although it was possible in each case to connect the DSL router (ordinary RJ45 cable) and an analog telephone (RJ11 cable) directly and utilize parallel,
however, the Internet connection was aborted when you exit the call.
Therefore unfortunately had to call each of the DSL router to be restarted - particularly listless when just a permanent connection is needed ... :-(

This adapter is now the splitter between ISDN box and router / phone wired and interference are eliminated entirely :-)
Before: ISDN socket -> DSL router / phone
Now: ISDN socket -> This adapter -> splitter -> DSL router / phone

Thank so a perfectly-working, very cheap (currently 1.75 incl. Shipping) part now saves a lot of hassle.