You can run Ethernet on any medium that has the capacity to transmit digital signals. It can be copper, optical, over-air laser, radio, on top of an analog carrier wave (ASK, FSK, PSK). The Ethernet traffic can be completely independent from the physical medium by using encapsulation (L2TP or any other protocol that encapsulates Layer-2). It can be pigeons carrying printouts of the Ethernet frames, scanned and reassembled at the destination. The same can be said about most Layer-2 protocols.

As long as the proper interfaces are present, the physical layer is completely transparent to the data link layer.

(edit) I should point out that Ethernet, specifically, transmits extra data before and after the frame (the preamble and inter-packet gap) that are used to configure the Rx circuit for reception, but the Layer-2 frame will be identical regardless of the medium.

[–] ulterno@programming.dev 0 points 2 hours ago

RFC 2549