adm

Multiplexers that have the capability to insert and extract individual lower speed channels (e.g., DS-1, DS-2, or DS-3) into a higher speed aggregate bit stream. ADM (see Figure A-2) offers considerable advantage over traditional time division multiplexers (TDM). The process of bit stuffing to adapt to slight clocking variations can require that a DS-3 frame be demultiplexed into its DS-2 and then DS-1 frames, which must be broken down into 24 DS-0 channels in order to extract and route an individual DS-0 channel.When that is accomplished, the process must be reversed to reconstitute the DS-3, minus the extracted DS-0. Contemporary T-carrier muxes are capable of add/drop multiplexing in the absence of stuff bits. Used extensively in SDH and SONET networks,ADMs perform the additional functions of dynamic bandwidth allocation, providing operation and protection channels, optical hubbing, and ring protection. In wavelength division multiplexing (WDM), an optical add/drop multiplexer (OADM) performs the same add/drop function on individual wavelengths. See also channel, DS-1, DS-2, DS-3, hub, multiplexer, OADM, SDH, SONET, T-carrier, TDM, wavelength, and WDM.