The early history of BAUDOT from the 1870's is really interesting, as Time Division Multiplexing was used to share a telegraph wire.
http://www.computer-timeline.com/timeline/emile-baudot/ has some background.
https://www.rtty.com/England/fiveunits.htm and https://en.wikipedia.org/wiki/Time-division_multiplexing.
Sam Hallis has this: http://www.samhallas.co.uk/repository/telegraph/b6_baudot_multiplex.pdf -
http://www.samhallas.co.uk/telhist1/telehist2.htm - worth a read
multiplexer showing sync ring
Enough of that!