Manifold differences are also possible on the physical and
medium-access layers. Some approaches foresee redundant media (Vnet/IP, TCnet), PROFINET IO uses dedicated builtin switches to reduce the data transmission jitter [14],
and EtherCAT and SERCOS III need dedicated controllers [12].
Ethernet Powerlink uses the traditional shared Ethernet and
places a master–slave scheduling system on top of it.
Common to many proposed networks is that they employ clock synchronization to support real-time applications