Still very much a thing in the world of optical networking ("rolling the cable", i.e. switching the two sides at one end to match tx/rx up correctly, is a commo

Still very much a thing in the world of optical networking ("rolling the cable", i.e. switching the two sides at one end to match tx/rx up correctly, is a common first step in debugging a link that won't come up -- standard fiber patch cables are effectively crossover cables but when you're running through patch panels, have multiple cables in the path, etc it can end up mismatched). Some plants have primarily switched to bidirectional (bidi) transceivers that transmit and receive on two different wavelengths on the same strand, but that also requires matching optics at the other end with the tx/rx frequencies reversed.