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ASIC: - looks at frames - decides where they go - very smart, very dry, does not touch wires PHY: - negotiates link speed - handles encoding / signaling - pushes electrons (or photons), meaning bits without the PHY, an ASIC is just thinking thoughts with nowhere to send em

MII / GMII / SGMII / RGMII: - the private lil interface between the ASIC’s MAC & the PHY - sits inside the box, passing bits back & forth

tl;dr ASIC = brain thinking PHY = mouth speaking (although it does have logic of its own in there too) MII variants = internal nervous system Ethernet is teamwork actually

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caveat for “well, actually”s—MII is not a physical chip u can see on the board. the variants of MII are basically interface standards for signaling/clock frequencies BUT sometimes u can open up a switch & see traces on the board between the ASIC & PHY. that’s where your MII logic is applied :)

another caveat bc im sure someone is gonna ding me for this too: yes, an ASIC doesn’t need an ethernet PHY to talk to another component thats, say, on the same board. you could just have comms via MII between them. PHY is generally used to get stuff onto the wire/in the air as RF/whatever