Check out the SearchCIO-Midmarket article on TDM.
Time-division multiplexing is a technique/process that allows a link to be ‘sectioned’ in time slots, so different signals can be transmitted <i>almost </i>simultaneously using the same link. Each transmission uses the channel for a limited (and fixed) period of time (the time slot).
In synchronous TDM, all party’s clocks need to be aligned with some reference clock, which could be provided by one of the involved systems.
In asynchronous TDM, the timeslots are not fixed. They are assigned dynamically as needed.