Ufer grounding - Steel reinforcement is used in place of copper wire ground due to the pH factor of concrete.

ultrahigh frequency (UHF) - Frequencies in the range of 300 MHz to 3000 MHz.

ultraviolet (UV) light - The portion of the electromagnetic spectrum in which the longest wavelength is just below the visible spectrum, extending from approximately 10 nm to approximately 400 rim.

Um - A global system for mobile telephony air interface component or radio link.

unauthorized access - In general, the use of any network resource without approval as established in the security policy.

unbalanced cable (circuit) - A cable (circuit) that is not equal in phase and opposite in magnitude (e.g., coaxial cables are unbalanced). Contrast with balanced twisted-pair cable.

unbounded medium - A term sometimes used to describe wireless. Contrast with bounded medium.

underfloor raceway - A pathway placed within the floor and from which wires and cables emerge to a specific floor area.

underground - Refers to conduit and maintenance hole systems installed below the surface of the ground.

underground cable - A telecommunications cable designed to be installed under the surface of the earth in a trough or duct that isolates the cable from direct contact with the soil. (T!A) Contrast with directburied cable.

underground entrance - Entrance facility using conduit or other types of mechanical pathways to provide out-of-sight service to a building.

unequal splitter - A device that asymmetrically splits a radio frequency signal between two outputs while maintaining dc continuity between all ports.

unicast - A technique for sending data to a single network device. A one-to-one mode of communication. See also broadcast and multicast.

unidirectional antenna - An antenna characterized by a very narrow focus and an extended reach. See directional antenna and omnidirectional antenna.

unidirectional signaling - Signaling that occurs in one direction. Contrast with bidirectional signaling.

UniFormat - A document produced by the Constructions Specifications Institute that is a classification system used to organize preliminary project descriptions, preliminary cost estimates, and drawings that detail filing.

unigrounded power system - A power system where only one point, usually the midpoint, of the supply transformer bank is grounded. The neutral conductor may or may not be carried along with the phase wires.

unintentional radiators - A device that intentionally generates radio frequency energy for use within the device or that sends radio frequency signals by conduction to associated equipment via connecting wiring, but which is not intended to emit radio frequency energy by radiation or induction.

uninterruptible power supply (UPS) - A device that is inserted between a primary power source and the primary power input of equipment to be protected to eliminate the effects of transient anomalies or temporary outages.

unistrut - See channel stock.

universal mobile telecommunications service (UMTS) - A third generation broadband, packet-based transmission of text, digitized voice, video, and multimedia at data rates up to 2 Mb/s, similar to wideband code division multiple access.

unknown user - All individuals who do not have existing identity profiles on the network they are attempting to access.

unlicensed frequency band - Radio frequencies that require no license. The unlicensed frequency requirements vary by country.

unlicensed multipoint - A radio system linking three or more nodes that does not require formal government license to install and operate (i.e., spread spectrum radio).

unlicensed national information infrastructure (U-NII) - Designated to provide short-range, high-speed wireless networking communication at low cost. Consists of three frequency bands in the 5 GHz band of 100 MHz each: 5.15 to 5.25 GHz, 5.25 to 5.35 GHz and 5.725 to 5.825 GHz.

unprotected system - A nonredundant wireless system that uses a single transceiver and antenna.

unshielded twisted-pair (UTP) cable - Cable made up of one or more pairs of twisted copper conductors with no metallic shielding. The entire assembly is covered with an insulating sheath (cable jacket).

unshifted singlemode - See dispersion unshifted.

unsoldered mechanical (UM) protection - Additional steel and polyethylene sheaths provided over the inner polyethylene cable jacket.

unusable floor space - Floor space that is typically used in support of the building occupants (e.g., core area, mechanical/ electrical rooms, hallways) but does not allow for occupancy of building tenants. Contrast with usable floor space.

uplink - 1. Signals transmitted from ground stations to satellites. 2. In demand priority access method, the communications channel between a connected end node and a repeater, or between a repeater and a higher-level repeater.

upload - To send information from the controller to the host computer.

upstream neighbor's address (UNA) - In token ring, the address of the device immediately preceding a given device on the ring communications path.

uptime - The time during which a functional unit is fully operational.

urban wire - Multiconductor cable, 19 AWG [0.91 mm (0.036 in)] or 22 AWG [0.64 mm (0.025 in)], with a center strand and no outer sheath.

usable floor space - Floor space that is capable of being used as a work area. (TIA) Contrast with unusable floor space.

user code - A unique designation assigned to a person who is expected to use the circuit, equipment, service, etc., serving a particular work area.

User Datagram Protocol (UDP) - An Open Systems Interconnection Reference Model Layer 4 connectionless protocol that is part of the Transmission Control Protocol (TCP)/Internet Protocol suite. UDP supports single packet data transmission with no guarantee of message delivery. See also Transmission Control Protocol (TCP) for contrast.

utility column - An enclosed pathway extending from the ceiling to furniture or to the floor that forms a pathway for electrical wiring, telecommunications cable, or both.

utility pole - A customer-owned outside plant pole owned by a private or municipal utility. See also pole.

utility tunnel - An enclosed passageway, usually placed between buildings, for the distribution of utility services.