Telecom Dictionary - Definitions of terms

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

U

UDP - Abbreviation for user datagram protocol. An Internet protocol for datagram service.

UHF - Abbreviation for ultra high frequency. See electromagnetic spectrum. Frequencies from 300 MHz to 3000 MHz. This is the part of the radio spectrum from 300 to 3000 megahertz, which includes TV channels 14-69. After the DTV transition, UHF TV will be changed to 470 to 698 MHz, which includes channels 14-51.

U Interface - For basic-rate access in an Integrated Services Digital Network (ISDN) environment, a user-to-network interface reference point that is characterized by the use of a 2-wire-loop transmission system that (a) conveys information between the 4-wire user-to-network interface, i.e., the S/ T reference point, and the local exchange, (b) is located in the servicing central office, and (c) is not as distance sensitive as a service using a T interface.

ULF - Abbreviation for ultra low frequency. See electromagnetic spectrum. Frequencies from 300 Hz to 3000 Hz.

Ultra High Frequency (UHF) - Frequencies from 300 MHz to 3000 MHz. See electromagnetic spectrum.

Ultra Low Frequency (ULF) - Frequencies from 300 Hz to 3000 Hz. See electromagnetic spectrum.

Ultraviolet (uv) - The portion of the electromagnetic spectrum in which the longest wavelength is just below the visible spectrum, extending from approximately 4 nm to approximately 400 nm. Note: Some authorities place the lower limit of uv at values between 1 and 40 nm, 1 nm being the upper wavelength limit of x-rays. The 400-nm limit is the lowest visible wavelength, i.e., the highest visible frequency, violet. See electromagnetic spectrum.

Ultrawideband - See UWB. 1. Referring to any radio or wireless device where the occupied bandwidth is greater than 25% of the center frequency or greater than 1.5 GHz. 2. A radio or wireless system that uses narrow pulses (on the order of 1 to 10 nanoseconds), also called carrierless or impulse systems, for communications and sensing (short-range radar). 3. A radio or wireless system that uses time-domain modulation methods (e.g., pulse-position modulation) for communications applications, or time-domain processing for sensing applications.

Unallowable Character - Synonym illegal character. A character, or a combination of bits, that is not valid in a given system according to specified criteria, such as with respect to a specified alphabet, a particular pattern of bits, a rule of formation, or a check code. Synonyms false character, forbidden character, improper character, illegal character, unused character.

Unassigned Cell - A cell identified by a standardized virtual path identifier (VPI) and virtual channel identifier (VCI) value, which has been generated and does not carry information from an application using the ATM Layer Connection.

Unauthorized Disclosure - Exposure of information to individuals not authorized to receive it.

Unavailability - A expression of the degree to which a system, subsystem, or equipment is not operable and not in a committable state at the start of a mission, when the mission is called for at an unknown, i.e., random, time. Note 1: The conditions determining operability and committability must be specified. Note 2: Expressed mathematically, unavailability is 1 minus the availability. Note 3: Unavailability may also be expressed mathematically as the ratio of the total time a functional unit is not capable of being used during a given interval to the length of the interval, e.g., if the unit is not capable of being used for 68 hours a week, the unavailability is 68/168.

Unbalanced Line - A transmission line, such as a coaxial cable, in which the magnitudes of the voltages on the two conductors are not equal with respect to ground.

Unbalanced Modulator - A modulator in which the modulation factor is different for the alternate half-cycles of the carrier. Synonym asymmetrical modulator.

Unbalanced Wire Circuit - A circuit in which the two sides are inherently electrically dissimilar.

Unbound Mode - Synonym radiation mode. For an optical fiber, an unbound mode. Note: In an optical fiber, a radiation mode is one having fields that are transversely oscillatory everywhere external to the waveguide, and which exists even at the limit of zero wavelength. Specifically, an unbound mode is one for which

where is the imaginary part (phase term) of the axial propagation constant, integer is the azimuthal index of the mode, n (a) is the refractive index, where a is the core radius, and k is the free-space wave number, k = 2/, where is the wavelength. Unbound modes correspond to refracted rays in the terminology of geometric optics.

Unbundling - In the context of the FCC's Computer III Inquiry, the process of separating individual tariffed offerings and services that are associated with a specific element in the CEI or ONA tariff from other tariffed basic service offerings.

Unclassified - Information that has not been determined pursuant to Executive Order (E.O.) 12958 or any predecessor order to require protection against unauthorized disclosure and that is not designated as classified.

Underflow - In computing, a condition occurring when a machine calculation produces a non-zero result that is smaller than the smallest non-zero quantity that the machine's storage unit is capable of storing or representing.

Underground Cable - A communication cable designed to be placed under the surface of the Earth in a duct system that isolates it from direct contact with the soil.

Underground Plant - Cable and wire plant, together with closures appropriate for the application, that is placed below ground in structures such as conduit or ducts.

Underlap - In facsimile, a defect that occurs when the width of the scanning line is less than the scanning pitch.

Undershoot - See overshoot. When the transition is from a higher value to a lower value, and the parameter takes a transitory value that is lower than the final value, the phenomenon is called undershoot.

Undesired Signal - Any signal that tends to produce degradation in the operation of equipment or systems.

Undetected Error Rate - Deprecated synonym for undetected error ratio. The ratio of the number of bits, unit elements, characters, or blocks incorrectly received and undetected, to the total number of bits, unit elements, characters, or blocks sent.

Undetected Error Ratio - The ratio of the number of bits, unit elements, characters, or blocks incorrectly received and undetected, to the total number of bits, unit elements, characters, or blocks sent. Synonyms residual error rate, undetected error rate [deprecated] .

Undisturbed Day - A day during which neither sunspot activity nor ionospheric disturbance causes detectable interfere with radio communications.

Unequipped Indication - A code placed in unequipped channels by originating equipment to indicate to path terminating equipment that the channel is intentionally unoccupied so that alarms can be inhibited.

Unexpected Frame - A valid frame that cannot be processed. The frame itself is perfectly legitimate. Its unexpected character is defined by two conditions: the specific type of frame and the state of the receiver. The layer-2 protocol states define the proper sequence in which frames are expected to occur. The receiver will compare received frames with its own protocol state to determine whether or not a valid frame is unexpected.

UNICOM station - Synonym aeronautical advisory station. An aeronautical station used for advisory and civil defense communications primarily with private aircraft stations.

Unidirectional - The condition where information flow is provided only in one direction.

Unidirectional Channel - Synonym one-way-only channel. A channel capable of transmission in only one direction, which cannot be reversed.

Unidirectional Operation - Operation in which data are transmitted from a transmitter to a receiver in only one direction.

Unidirectional Path - A path that logically connects a single path source with the associated path sink.

Uniform Encoding - An analog-to-digital conversion process in which, except for the highest and lowest quantization steps, all of the quantization subrange values are equal. Synonym uniform quantizing.

Uniform Linear Array - An antenna composed of a relatively large number of usually identical elements arranged in a single line or in a plane with uniform spacing and usually with a uniform feed system.

Uniform Quantizing - Synonym uniform encoding. An analog-to-digital conversion process in which, except for the highest and lowest quantization steps, all of the quantization subrange values are equal.

Uniform Resource Locator (URL) - The standard for giving an WWW Internet address (e.g. http://www.faxswitch.com)

Uniform-Spectrum Random Noise - See white noise. Noise having a frequency spectrum that is continuous and uniform over a specified frequency band. Note: Uniform-Spectrum Random Noise has equal power per hertz over the specified frequency band. Synonym additive white gaussian noise.

Uniform Time Scale - A time scale made up of equal intervals.

Uniform Transmission Line - A transmission line that has distributed electrical properties, i.e., resistance, inductance, and capacitance per unit length, that are constant along the line, and in which the voltage-to-current ratio does not vary with distance along the line, if the line is terminated in its characteristic impedance. Note 1: Examples of uniform transmission lines are coaxial cables, twisted pairs, and single wires at constant height above ground, all of which have no changes in geometry, materials, or construction along their length. Note 2: In a uniform transmission line, signal attenuation is a function of the length of the line and the frequency of the signal.

Unilateral Control System - Synonym unilateral synchronization system. A system of synchronization in which signals from a single location are used to synchronize clocks at one or more other locations.

Unilateral Synchronization System - A system of synchronization in which signals from a single location are used to synchronize clocks at one or more other locations. Synonym unilateral control system.

Unimode Fiber - Synonym single-mode optical fiber. An optical fiber in which only the lowest order bound mode can propagate at the wavelength of interest. Note 1: The lowest order bound mode is ascertained for the wavelength of interest by solving Maxwell's equations for the boundary conditions imposed by the fiber, e.g., core (spot) size and the refractive indices of the core and cladding. Note 2: The solution of Maxwell's equations for the lowest order bound mode will permit a pair of orthogonally polarized fields in the fiber, and this is the usual case in a communication fiber. Note 3: In step-index guides, single-mode operation occurs when the normalized frequency, V, is less than 2.405. For power-law profiles, single-mode operation occurs for a normalized frequency, V, less than approximately

where g is the profile parameter. Note 4: In practice, the orthogonal polarizations may not be associated with degenerate modes.

Unit Impulse - A mathematical artifice consisting of an impulse of infinite amplitude and zero width, and having an area of unity. Note: The unit impulse is useful for the mathematical expression of the impulse response, i.e., the transfer function, of a device. Synonym Dirac delta function.

Unit Interval - In isochronous transmission, the longest interval of which the theoretical durations of the significant intervals of a signal are all whole multiples.

Universal Personal Telecommunications Number - Synonym UPT number. In universal personal telecommunications service, the number that uniquely identifies a UPT user and that is used to place a call to, or to forward a call to, that user. Note: A user may have multiple UPT numbers, e.g., a business UPT number for business calls and a private UPT number for private calls. In the case of multiple numbers, each UPT number is considered, from a network vantage point, to identify a distinct UPT user, even if all such numbers identify the same person or entity.

Universal Personal Telecommunications (UPT) Service - A telecommunications service that provides personal mobility and service profile management. Note 1: UPT service involves the network capability of identifying uniquely a UPT user by means of a UPT number. Note 2: The general principles of UPT are given in ITU-T Recommendation F.850. Note 3: UPT and PCS are sometimes mistakenly assumed to be the same service concept. UPT allows complete personal mobility across multiple networks and service providers. PCS may use UPT concepts to improve subscriber mobility in allowing roaming to different service providers, but UPT and PCS are not the same service concept.

Universal Service Fund Surcharge - Telephone customers also may see charges on their local and long distance bills for universal service. Companies are required by the FCC to contribute to a federal universal service fund (USF). The USF helps to make phone service affordable and available to all Americans, including those with low incomes, those living in areas where the costs of providing telephone service is high, schools, libraries, and rural health care providers. These fees vary by amount and by company. USF surcharges may also be assessed at the state level.

UNIX - The most common multi-user operating system for servers on the Internet.

Unwanted Current - With respect to telecommunications plant, any current that is not intentionally supplied from the central office or from telephone equipment.

Upconvert - A process by which a digital, high-definition television takes a lower-definition picture and converts it into a higher-definition picture. This may be done by doubling each line as it is drawn on the screen, or by using advanced algorithms to interpolate the data between each lower-resolution line, filling in the missing image.

Update - The regeneration of a display to show current status, based on changes to the previously displayed data. Note: An update can be accomplished upon user request or by automatic means.

Upload - To transfer a file or information from your computer to another.

UPT - See Universal Personal Telecommunications Service.

UPT Number - In universal personal telecommunications service, the number that uniquely identifies a UPT user and that is used to place a call to, or to forward a call to, that user. Note: A user may have multiple UPT numbers, e.g., a business UPT number for business calls and a private UPT number for private calls. In the case of multiple numbers, each UPT number is considered, from a network vantage point, to identify a distinct UPT user, even if all such numbers identify the same person or entity. Synonym universal personal telecommunications number.

UPT User - In universal personal telecommunications service, a person who (or entity that) has access to universal personal telecommunications (UPT) services and who has been assigned a UPT number.

URL - See Uniform Resource Locator

Usage - Synonym occupancy. For equipment, such as a circuit or a switch, the ratio of the actual time in use to the available time during a 1-hour period. Note 1: Usage is usually expressed in percent. Note 2: Usage may be plotted versus time of day.

User - 1. A person, organization, or other entity (including a computer or computer system), that employs the services provided by a telecommunication system, or by an information processing system, for transfer of information. Note: A user functions as a source or final destination of user information, or both. Synonym subscriber. 2. [In security, a] person or process authorized access to an IS (information system); [an] individual defined, registered, and bound to a public key structure by certification authority.

User Datagram Protocol (UDP) - In the Internet Protocol suite, a standard, low-overhead, connectionless, host-to-host protocol that is used over packet-switched computer communications networks, and that allows an application program on one computer to send a datagram to an application program on another computer. Note: The main difference between UDP and TCP is that UDP provides connectionless service, whereas TCP does not.

User Name - Your user name, also called user ID or account name, is the same as your login name. This is the name by which you and your electronic mailbox are identified online.

User Information - Information transferred across the functional interface between a source user and a telecommunications system for delivery to a destination user. Note: In telecommunications systems, user information includes user overhead information.

User Information Bit - A bit transferred from a source user to a telecommunications system for delivery to a destination user. Note 1: User information bits do not include the overhead bits originated by, or having their primary functional effect within, the telecommunications system. Note 2: User information bits are encoded to form channel bits.

User Information Block - A block that contains at least one user information bit.

User Overhead Information - See overhead information. - Digital information transferred across the functional interface between a user and a telecommunications system, or between functional units within a telecommunications system, for the purpose of directing or controlling the transfer of user information or the detection and correction of errors. Note: Overhead information originated by the user is not considered to be system overhead information. Overhead information generated within the communications system and not delivered to the user is system overhead information. Thus, the user throughput is reduced by both overheads while system throughput is reduced only by system overhead.

User Part - A functional part of the common channel signaling system that transfers signaling messages via the message transfer part. Different types of user parts exist (e.g., for telephone and data services), each of which is specified to a particular use of the signaling system.

USF - Universal Service Fund. The National Exchange Carrier Association administers the USF. This is a mechanism designed to keep local exchange rates at reasonable levels, especially in high-cost, rural areas. The fund gets money from a surcharge on phone lines and uses those funds to offset telecommunication expenses in the high-cost areas.

UseNet Newsfeed - A huge, world wide "Users Network" of discussion groups, or newsgroups, connecting and sharing information from hundreds of thousands of machines.

Utility Program - A computer program that is in general support of the operations and processes of a computer. Note: Examples of utility programs include diagnostic programs, trace programs, input routines, and programs used to perform routine tasks, i.e., perform everyday tasks, such as copying data from one storage location to another. Synonyms service program, service routine, tool, utility routine.

UUCP Service (UNIX to UNIX Copy Program) - A method of transferring files between UNIX computers that includes Electronic mail.

UWB - Abbreviation for ultrawideband. 1. Referring to any radio or wireless device where the occupied bandwidth is greater than 25% of the center frequency or greater than 1.5 GHz. 2. A radio or wireless system that uses narrow pulses (on the order of 1 to 10 nanoseconds), also called carrierless or impulse systems, for communications and sensing (short-range radar). 3. A radio or wireless system that uses time-domain modulation methods (e.g., pulse-position modulation) for communications applications, or time-domain processing for sensing applications.

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