Glossary- X
A Data Communication Historical Series
By Bob Pollard

HOME                         INDEX

X-ON / X-OFF:

A protocol that adjusts the flow of information for asynchronous serial transmission

X STANDARDS:

   X. 1 through X.521: A numbered group of Standards and Regulations originated and approved by the International Consultative Committee for Telephone and Telegraph (CCITT) and other International committees.

   These Standards and Regulations would include, but not be limited to, the following principles, procedures and approved standards and regulations:

    Class of Service, routing principles and plans, numbering plans, connection procedures, grade of service, services and options, interface definitions, data terminal interface, overall architecture, conformance testing, abstract service definition conventions, encoded information type, conversion rules, message transfer system, message store, support of packet mode DTEs by ISDN, protocol specifications, interpersonal messaging system and multiplexing schemes, etc.

X.3:

ITU-T recommendation that defines various PAD parameters used in X.25 networks

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 a X.25 network: Virtually equivalent to EIA/TIA-232.

X.25:

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 Frame Relay has to some degree superseded X.25.

X.28:

ITU-T recommendation that defines the terminal-to-PAD interface in X.25 networks

X.29:

ITU-T recommendation that defines the form for control information in the terminal-to-PAD interface used in X.25 networks

X.75:

ITU-T specification that defines the signaling system between two PDN(s): X.75 is essentially an NNI.

X.86:

Refers to microprocessors that have or emulate the 32-bit Intel processor architecture:

X.121:

ITU-T standard describing an addressing scheme used in X.25 networks: X.121 addresses are sometimes called IDN(s).

X.3T9.5:

Number assigned to the ANSI Task Group of Accredited Standards Committee for its internal working document describing FDDI.

The American National Standards Institute (ANSI) committee responsible for defining the various specifications: Including Physical-layer Media-Dependent (PMD), Physical-layer Protocol (PHY), Media Access Control (MAC), and Station Management (SMT) that comprise the Fiber-Distributed Data Interface (FDDI) standard.

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.

X.509v3 CERTIFICATE:

   Version 3 of the ITU-T recommendation X.509 for certificate syntax and format: This is the standard certificate format used by Windows XP certificate-based processes.

   A X.509 certificate includes the public key and information about the person or entity to whom the certificate is issued, information about the certificate, plus optional information about the Certification Authority (CA) issuing the certificate.

<X-DELPHI>

A special HTML tag for internal Delphi Forums (forum promotions): It will display promotions a Forum host sets up in the Forum Control Center via the Promote menu. The promotions will display in web pages, Message Board welcome screens, and messages where the tag and accompanying HTML code are placed.

X TERMINAL: 

Refers to a terminal that allows a user simultaneous access to several different applications and resources in a multi-vendor environment through implementation of X Windows

X WINDOW SYSTEM:

Distributed, network-transparent, device-independent, multitasking windowing and graphics system; developed by MIT for communication between X terminals and UNIX workstations.

XAPIA:

X-400 Application Programming Interface Association

XCOM:

Extended Communications Search

XDMCP:

X Display Manager Control Protocol: Protocol used to communicate between X terminals and workstations running the UNIX operating system.

XDR:

External Data Representation: A standard for machine independent data structures developed by Sun Microsystems. Similar to BER

XDSL:
Refers to the digital subscriber line technologies: ADSL, HDSL, IDSL, RADSL, SDSL and VDSL.

XE:

1) VSC Execution Environment: a layer of software providing shared services for all application software on the VSC; and isolates higher-level software from operating system dependencies.

2) TransPath Execution Environment: Layer of software providing shared services for all application software on the Trans-Path and isolating higher-level software from operating system dependencies.

XGCP:

External Media Gateway Control Protocols: Includes SGCP and MGCP.

XHTML:

eXtensible HyperText Markup Language: Basically HTML expressed as valid XML. XHTML is intended to be used in the same places you would use HTML (creating web pages) but is much more strictly defined, which makes it a lot easier to create software that can read, edit and check it for errors, etc. XHTML is expected to eventually replace HTML.

XID:

Exchange Identification: Request and response packets exchanged prior to a session between a router and a Token Ring host. If the parameters of the serial device contained in the XID packet do not match the configuration of the host, the session is dropped.

XMISSION: Abbreviation for Transmission

XMIT:

Abbreviation for Transmit or Transmission

XML:

Extensible Markup Language: A widely used system for defining data formats. XML provides a system to define complex documents and data structures such as invoices, molecular data, news feeds, glossaries, inventory descriptions, real estate properties, etc. See Extensible Markup Language.

XMLRPC:

XML Remote Procedure Call: A protocol for client-server communication that sends and receives information on top of HTTP (Hypertext Transfer Protocol). The data sent and received is in a particular XML (Extensible Markup Language) format specifically designed for use with XMLRPC.

XMODEM:

A popular public-domain protocol for transferring files through asynchronous connections between personal computers. XMODEM is a half-duplex protocol, used on full-duplex circuits transmitting 128 characters per block. After information is sent, the sender waits for a reply before transmitting the next message.

XNS:

Xerox Networking Standard: Defines Xerox networking protocols that are similar to TCP/IP.

XNS / ITP:

Xerox Network Systems / Internet Transport Protocol: A communications protocol used in a LAN (Local Area Network) environment between networks, functioning similar to the TCP/IP.

XOT:

X.25 over TCP

XPFE:

Cross Platform Front End: A group of technologies used to create applications that will work and look the same on different computer operating systems. A widely used XPFE application is the Mozilla web browser and its derivatives, such as the Netscape web browser in version 7 and later. The primary technologies used in creating XPFE applications are Javascript, Cascading Style Sheets, and XUL (Executable User-interface Language).

X-REMOTE:

Protocol developed specifically to optimize support for the X Window System over a serial communications link.

XSL:

eXtensible Stylesheet Language

X-STREAM: Major public PSN in the United States operated by MCI: Formerly called TYMNET.

XTagATM:

Extended tag ATM

XUL:

1) Extensible User-interface Language: A markup language similar to HTML (Hypertext Markup Language) and based on XML (Extensible Markup Language). XUL is used to define what the user interface will look like for a particular piece of software and will define what buttons, scrollbars, text boxes, and other user-interface items will appear, but it is not used to define how those item will look as far as color.

2) An XML User-interface Language: XUL (pronounced zool, rhymes with cool) was created to make development of the Mozilla browser easier and faster. XUL is a XML language therefore all features available to XML are also available to XUL. This language was created for Mozilla applications and is used to define the user interface.