[Animats]

There was an era of "multiprotocol routers", which routed IP, Xerox Network Architecture, DECnet, and maybe TP4, PARC Universal Protocol, Microsoft Server Message Block, and IBM's SNA. Stanford built those, because they had many incompatible networks internally, and Cisco, being a Stanford spinoff, supported multiple protocols.

This burned a lot of effort in the late 1980s and 1990s. Much incompatibility. Attempts to use intermediate machines to help with protocol conversion. Attempts to build protocol converters. A need for O(N^2) different protocol converters. Some computer vendors had to be dragged, kicking and screaming, away from their proprietary networks. There was a lot of pressure from DoD to standardize.

Down at the wire protocol level, there were alternatives. Too many of them. IBM had Token Ring. Apollo had a different token ring. Datapoint had ARCnet. Industrial automation people liked RS422, which is still around. DEC had a triaxial coax system. ARPANET IMPs had their own strange parallel interface. Ethernet came in two coax forms before un-shielded twisted pair took over, plus a form of Ethernet which connected via a 15-pin D-sub connector. Sometimes you just skipped the Ethernet cable and plugged all the 15-pin cables into a multi-port repeater. Plus there were a bunch of photonic links.

Finally, IP won as the only long-haul packet format, RJ45 jacks handled most electrical interconnects, and most things just plugged in and worked.