Most Common Networking Terms and Acronyms – X

X terminal
Terminal that allows a user simultaneous access to several different applications and resources in a multivendor environment through implementation of X Windows. See also X Window System

X Window System
Distributed, network-transparent, device-independent, multitasking windowing and graphics system originally developed by MIT for communication between X terminals and UNIX workstations. See also X terminal.

X.121
ITU-T standard describing an addressing scheme used in X.25 networks. X.121 addresses are sometimes called IDNs.

X.21
ITU-T standard for serial communications over synchronous digital lines. The X.21 protocol is used primarily in Europe and Japan.

X.21bis
ITU-T standard that defines the physical layer protocol for communication between DCE and DTE in an X.25 network. Virtually equivalent to EIA/TIA-232. See also EIA/TIA-232 and X.25.

X.25
ITU-T standard that defines how connections between DTE and DCE are maintained for remote terminal access and computer communications in PDNs. X.25 specifies LAPB, a data link layer protocol, and PLP, a network layer protocol. Frame Relay has to some degree superseded X.25. See also Frame Relay, LAPB, and PLP.

X.400
ITU-T recommendation specifying a standard for e-mail transfer.

X.500
ITU-T recommendation specifying a standard for distributed maintenance of files and directories.

xDSL
Group term used to refer to ADSL, HDSL, SDSL, and VDSL. All are emerging digital technologies using the existing copper infrastructure provided by the telephone companies. xDSL is a high-speed alternative to ISDN.

XML
extensible markup language. A standard maintained by the World Wide Web Consortium (W3C). It defines a syntax that lets you create markup languages to specify information structures. Information structures define the type of information, for example, subscriber name or address, not how the information looks (bold, italic, and so on). External processes can manipulate these information structures and publish them in a variety of formats. Text markup language designed to enable the use of SGML on the World Wide Web. XML allows you to define your own customized markup language.

XOT
X.25 over TCP.

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