See Data eXchange Interface.

Data exchange Interface, an interface between a data device and a cell-based service DSU/CSU used to offload the process of cell creation and processing from a router or data system.

A generic phrase used in the full names of several protocols, all commonly used to allow a pair of DCE and DTE devices to share the implementation of a particular WAN protocol. The protocols all define the packet formats used to transport data packets between DCE and DTE devices.