Depends on what you consider a "protocol". Morse code dates back to 1844 and is still in use. Hellschreiber is from the 1920s, still in use by some hams. You ca

Depends on what you consider a "protocol". Morse code dates back to 1844 and is still in use. Hellschreiber is from the 1920s, still in use by some hams. You can downlink slow scan TV (1957) images from the ISS sometimes. Except for Morse code, a lot of the older protocols used by hams are mostly for novelty, legacy, and price reasons as they can be cheaply implemented into just about any computer ever made. Morse code still has use in the military as a backup system for long range communications.