MIDI is an excellent example of a “wire protocol” for sending control and data between devices.
The format is compact and provides a common base set of functionality across many different devices, while still extendable to allow full use of device-specific features.
MIDI provides an excellent reference model for features, requirements, and pitfalls to avoid when designing any communications system between to electronic devices.
MIDI 1.0 evolves … without sacrificing its roots.
https://www.midi.org/articles-old/details-about-midi-2-0-midi-ci-profiles-and-property-exchange