Determinism is the ability to respond in a consistent, predictable time delay. Ethernet, even if it can be a fast network, is not determinism as collision between messages can create unpredictable delay. Of course, if the load on the network is very low or if you use Ethernet switch, it is possible to considerate Ethernet as determinism for slow to mid speed system. Some other network technology was developed specifically for process control and they are really determinism. Don't be mix-up by marketing: determinism just mean that the delay are consistent and predictable, but give you any information relative to the speed of the network.