1. In communications systems, the creating of data links, circuits, or channels by (a) using a given set of physical equipment, (b) increasing the traffic capacity of the equipment to carry data, and (c) using various means to increase the traffic capacity, such as time sharing, frequency division, time division, space division, wavelength division, and phase shifting. Common abbreviationMUXing.Note: In radio, electronic, and fiber optic transmission systems, the two basic forms of multiplexing are (a) time-division multiplexing (TDM) and (b) frequency-division multiplexing (FDM). In fiber optic transmission systems, wavelength-division multiplexing (WDM) is equivalent to frequency-division multiplexing. 2. The combining of two or more information channels on a single common propagation medium. 3. Using a single transmission channel for two or more signals from different users. Synonym muxing. See also channel,  data,  digital multiplex hierarchy,  fiber optic transmission system,  frequency division,  group,  multiplex hierarchy,  phase shift,  propagation medium,  space division,  signal,  time division,  time sharing,  transmission,  traffic capacity,  user,  wavelength division. 4. In data transmission, a function that permits two or more data sources to share a common propagation medium, i.e., transmission medium, in such a manner that their transmissions appear to be simultaneous. See also data source,  data transmission,  function,  propagation medium,  simultaneous,  transmission. 5. In a given layer of an open system, a function that permits more than one connection in the given layer to be supported by one connection in the next lower layer. See also connection,  function,  layer,  open system. See asynchronous time-division multiplexing,  color-division multiplexing,  dense wavelength-division multiplexing,  frequency-division multiplexing,  heterogeneous multiplexing,  homogenous multiplexing,  optical multiplexing,  polarization-division multiplexing,  pulse-code-modulation multiplexing,  space-division multiplexing,  statistical multiplexing,  statistical time-division multiplexing,  synchronous time-division multiplexing,  time-division multiplexing,  wavelength-division multiplexing. Refer to Fig. O-10, S-12, T-5, W-3.