CCDA: Cisco Certified Design Associate Study Guide, 2nd Edition (640-861)

An ITU-T standard that defines communication between DTE and DCE network devices. X.25 uses a reliable Data Link layer protocol called LAPB. X.25 also uses PLP at the Network layer. X.25 has mostly been replaced by Frame Relay.

A windowing environment developed at MIT for Unix workstations. Often referred to simply as X.

X Window is an open and nonproprietary bit-mapped graphics system, designed to be independent of both the display hardware and the underlying operating system. It is supported by all the major workstation vendors.

X Window implements a client/server environment, but with the sense of the terms reversed from today’s common usage.