Since modern routers don't check the header-checksum any more to increase performance I'm wondering what my computer is doing with defective data-packets?
Further reading links appreciated.
It requests the data packet again. Wikipedia has a nice article that explains the workings of the TCP (Transmission Control Protocol). This protocol makes sure that lost (or damaged) data packages are intercepted and a packet repeat is then requested. http://en.wikipedia.org/wiki/Transmission_Control_Protocol#Data_transfer