Lockstep
A networking model where every client runs the exact same deterministic simulation and sends only each other's inputs, not the game state.
Instead of streaming the world, every client runs an identical, deterministic simulation and exchanges only the players' commands each turn; a tick is simulated only once everyone's inputs for it have arrived. Mark Terrano and Paul Bettner's famous GDC 2001 talk, "1500 Archers on a 28.8", explained why Age of Empires did this — sending the state of thousands of units was hopeless, but sending a handful of clicks fits any modem.
The price is steep: the simulation must be bit-for-bit deterministic across machines (floating point makes this miserable), and a single lagging player stalls everyone. Rollback netcode later kept the determinism but hid the waiting.