X - Symbol for reactance.
X band - A band of frequencies between 5,200 and 10,000 megahertz.
X.121 - In packet-switched networks, a CCITT recommendation that defines the international packet-switched networks numbering scheme.
X.21 - (In PDNs) A CCITT recommendation that defines a digital interface, using the 15-pin connector described in V.11.
X.21 bis - Use on public data networks of data terminal equipment that is designed for interacting to synchronous V-series modems; it is equivalent to RS-232 and V.24.
X.25 - A CCITT standard that defines the interface between a RDN and a packet-node user device (DTE); also defines the services that these user devices can expect from the X.25 PDN including the ability to establish virtual circuits through a PDN to another user device, to move data from one user device to another, and to destroy the virtual circuit when through.
X.28 - Defines the interface between PADs and non-packet mode OTEs.
X.29 - Defines the interface between PADs and packet-mode DTEs or other PADs.
X.3 - Describes the functions of the PAD and the various parameters which can be used to specify its mode of operation.
Xerox - The originator of Ethernet.
XHHW - A UL cable type. Cross-linked polyethylene insulated small diameter building wire rated 75°C wet and 90°C dry.
XHHW-2 - A UL cable type. Cross-linked polyethylene insulated small diameter building wire rated 90°C wet and dry.
XLP - Cross-linked polyethylene. Also written XLPE.
XNS (Xerox Network System) - A set of protocols that defines the network and transport layers of a network.
XNS/ITP (Xerox Network Systemís Internet Transport Protocol) - In LAN technology, a special communications protocol used between networks. XNS/ITP functions at the 3rd and 4th layer of the OSI model. Similar to TCP/IP.
XON/XOFF - 1. A form of software flow control in a DTE. A control character is transmitted over the primary data channel indicating that transmission should be suspended or reinstituted, depending upon the state of the DTEís buffers. 2. Control characters used for flow control.
XPM - Cross-phase modulation (interchannel nonlinear effect).
X-ray - Penetrating short wavelength electromagnetic radiation created by electron bombardment in high-voltage apparatus; produce ionization when they strike certain materials.