A switched multimegabit data service (SMDS) is a connectionless telecommunications service allowing organizations to exchange large amounts of data over a wide area network (WAN) on a non-constant or burst basis. SMDS is usually provided by telephone companies as a value-added service.

SMDS extends the abilities of an organization’s local area network (LAN) over a wide area on an as-needed basis. If a regional office of a commercial bank only needs to send data once a day to the central headquarters, there is no need to have a dedicated wide area network (WAN) connection, which will be idle most of the day. SMDS offers a solution through use of public telecommunications facilities to periodically send a burst of data, but only when and as needed.