Most of the copper in a building is twisted pair: eight wires in four pairs, each pair twisted around itself. The twist is not decoration. It is the entire engineering. Two wires twisted together cancel each other’s interference. Alexander Graham Bell patented that idea in 1881 to keep streetlight noise out of telephone lines. We still use it.
Crosstalk is the enemy, signal leaking from one wire into the next. Tighter twists mean less crosstalk and a faster cable. Category ratings are the grade of that fight. Three numbers are worth saying out loud. Cat 5e does one gigabit to 100 meters. Cat 6A does ten gigabit to 100 meters. Cat 8 does forty gigabit, but only about 30 meters, which is why it is a data center answer and not a building answer. Cat 5e is the floor. Nothing below it belongs in a network today.
U T P (unshielded) is almost every cable in the walls. S T P (shielded) wraps the pairs in foil or braid for noisy places: factory floors, elevator shafts, runs beside power. Do not walk the whole Category table from one to eight. Six of those rows are obsolete telephone grades. Students need three facts, not eight rows. The twist is why the cable works. The Category number says how far and how fast before crosstalk ruins it.
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