Very likely it's Bell 202 AFSK. This is specifically designed to run at audio fr...

		kevin_thibedeau on June 12, 2015 \| parent \| context \| favorite \| on: 1980s computer controls Grand Rapids Public School... Very likely it's Bell 202 AFSK. This is specifically designed to run at audio frequencies with 1200 Hz and 2200 Hz tones. You'd have to figure out how the higher protocol levels are implemented but it's probably going to fall within the realm of what is done with AX.25.