Port protection

Anything leaving the board through a connector is exposed. A cable is an antenna, and a person touching the connector is a static discharge of a few kilovolts arriving at a pin rated for a few volts.

Protection is whatever is placed at the connector to absorb that before it reaches anything expensive: a TVS diode or diode array for the discharge, a common-mode choke or ferrite for the interference.

flowchart TB
    C["connector<br/>ESD, and whatever<br/>the cable picked up"] --> P["protection<br/>TVS diode,<br/>common-mode choke"]
    P --> X["transceiver"]
    X --> M["processor"]
    C -.->|"with no protection,<br/>this is the path"| X

The ordering is the point. Protection has to sit between the connector and the part it defends, so a board that has the right parts in the wrong order has no protection at all, and nothing in the netlist distinguishes the two.

That is why it is declared in a profile rather than inferred, the same as termination.

Where the course teaches it: chapter 10, a bus as a contract.