Bandwidth on Network Card

Hello,

How is performed the synchronisation regarding the bit rate transmition between the emitter and the receiver cards (for routers) ?

The related question is : is it possible to connect directly a network card whose transmission speed is higher than the receiver card ? If there is no CLOCK SYNCHRONISATION on physical hardware interface between the 2 routers, I think the receiver is (potentially) flooded ?

Thanks for help,

:o