Asynchronous time division multiplexing (ATD or ATDM) is a time division multiplexed access strategy in which the connected data stations do not have fixed reserved transmission capacities with periodic time slots as in synchronous time division multiplexing (STD).
In asynchronous time division multiplexing, the data streams to be transmitted are divided into information units of fixed or variable length and transmitted asynchronously. The information units are assigned via an identification number in the header with which each cell is provided.information for the control and the payload, the user data. The user data to be transmitted is buffered by an asynchronous multiplexer and is broken down into fixed data blocks and provided with the channel address before transmission. The transmission medium has time slots that can be freely assigned and in which the cells are transmitted. The transmission of cells with a fixed length is cell switching, while data packets with a variable length are data packet switching.