U

U Frame (Unnumbered Frame) - One of three SDLC frame formats. See also I Frame and S Frame.

U Interface - A two-wire (one pair) ISDN (Integrated Services Digital Network) BRI (Basic Rate Interface) telephone line. This popular type of digital telephone line has two B (bearer channels) and one D channel. For more information, see ISDN.

U Plane (User Plane) - One of the three entities of frame-relay network management. The three planes are: The User Plane (the U Plane defines the transfer of information), the Management Plane (the M Plane defines the LMI, Local Management Interface), and the Control Plane (the C Plane is delegated for signaling and switched virtual circuits). The U Plane is based on the ANSI TI.602 (LAPD) core aspect standard. It provides the interface between the end user and the network, bi-directional transfer of frames, frame-order preservation, congestion avoidance, and determines the priority of PVCs (Permanent Virtual Circuits).

U-Band (Ultralong Wavelength) Band) - The ITU-T standard optical transmission window in the wavelength range of 1,625–1,675 nm. See also wavelength and window.

U-mm Band - The band of frequencies designated by the IEEE between 300 GHz and 3000 GHz. For a table, see IEEE Radar Band Designation.

U-NII (Unlicensed National Information Infrastructure) - Radio spectrum in the 5 GHz range made available for use on an unlicensed basis in the United States. Indoor applications include wireless LANs (WLANs) such as 802.11a (Wi-Fi5) and HiperLAN. Outdoor applications include wireless local loop (WLL). See also 802.11a, HiperLAN, Wi-Fi-5, WLAN, and WLL.

U.S. Digital Cellular (USDC) - A digital cellular radio standard better known as Digital Advanced Mobile Phone Service (D-AMPS). See D-AMPS.

U - 1. In electricity, the symbol for potential energy difference, which is the work done to move a unit charge between two points in an electric field. In other words, the difference in voltage level between two points in an electric field. 2. U interface or Reference Point U in ISDN. See Reference Point U.

UA (Unnumbered Acknowledgement) - A command defined by the last three bits in the control byte of an unnumbered or “control” frame in the X.25 protocol being 110. The UA control frame is a response to a Set Asynchronous Balanced Mode (SABM) frame, which resets the entire link. See U Frame.

UADSL (Universal Asymmetric Digital Subscriber Line Lite) - See G.lite.

UART (Universal Asynchronous Receiver/Transmitter) - An integrated circuit, attached to the parallel bus of a computer, used for serial communications. The UART translates between serial and parallel signals, provides transmission clocking, and buffers data sent to or from the computer.

UBR (Unspecified Bit Rate) - A Quality of Service (QOS) defined by the ATM Forum for ATM Networks that allows any amount of data up to a specified maximum to be sent across the network. A connection would be rightfully commissioned as an UBR connection if it carried nontime sensitive data that could be retransmitted without a large inconvenience. The UBR quality of service does not guarantee freedom from cell loss or delay. Other QOSs defined by the ATM Forum for ATM connections include CBR (Constant Bit Rate), ABR (Available Bit Rate), and VBR (Variable Bit Rate).

UBR (Unspecified Bit Rate) - In asynchronous transfer mode (ATM), a best-effort class of traffic.Traffic parameters include peak cell rate (PCR) and cell delay variation tolerance (CDVT). No quality of service (QoS) commitment is made.ATM also defines available bit rate (ABR), constant bit rate (CBR), non realtime Variable Bit Rate (nrt-VBR), real-time Variable Bit Rate (rt-VBR), and variable bit rate (VBR) traffic classes. UBR traffic includes traditional computer applications such as file transfer and e-mail. See also ABR, ATM, CBR, CDVT, compression, nrt-VBR, PCR, QoS, real-time, rt-VBR, and VBR.

UCAID (University Corporation for Advanced Internet Development) - A not-for-profit consortium formed specifically to advance the development of Internet2.All nomenclature since has transitioned to Internet2. See also Internet2.

UCD (Uniform Call Distributor) - A less-expensive and less-smart version of an ACD (Automatic Call Distributor). The UCD receives incoming calls and equally distributes them among agents in a call center. For more details, see ACD.

UCS (Universal Character Set) - A joint initiative of the International Organization for Standardization (ISO) and the Unicode Consortium to develop a 32-bit character set capable of encoding all written languages. ISO 10646 defines the Universal Character Set (UCS), into which all Unicode Transformation Format (UTF) code sets map. UCS-4 is a four-octet code set into which UTF-32 maps and UCS-2 is a two-byte code set into which UTF-16 maps. UCS-1 encodes all characters in byte sequences varying from one to five bytes. See also bit, byte, code set, octet, and Unicode.

UDC (Universal Digital Carrier) - Also referred to as DLC (Digital Loop Carrier). A method of placing two analog telephone lines onto one digital copper pair. In areas where a telephone customer has requested an additional line and there are no additional copper pairs available, many telephone companies digitize the existing line to carry two. The central office routes the two telephone lines to a UDC trunk, which is then connected to the copper pair that carries the digital transmission to the customer’s premises. The telephone company installs a UDC adapter at the demarcation point, which converts the digital UDC transmission into two analog lines. The UDC carrier is DSL (Digital Subscriber Loop) based. UDC is a 2B1Q (Two Binary One Quarternary) line format that rides on a - 137-volt battery. If the UDC carrier fails, it will go into an override/bypass mode and switch the pair to a –52-volt battery to provide the original POTs service. The telephone number that will continue to work is line one, and line two can be set to call forward to line one. For a diagram, see DLC.

UDC Remote Unit - The electronic equipment placed at the customer end of the UDC pair that converts the digital transmission to analog telephone service. See UDC for operational details.

UDP (User Datagram Protocol) - A connectionless transport-layer protocol that helps make up the TCP/IP protocol stack. UDP is a simple protocol that exchanges datagrams/packets without acknowledgments or guaranteed delivery, requiring that error processing and retransmission be handled by other protocols. UDP is defined in RFC 768. An IP (Internet Protocol) transport-layer protocol that is sometimes used in place of TCP when transaction-based application programs are communicating (i.e., SNMP, Simple Network Management Protocol).

UGS (Unsolicited Grant Service) - A WiMAX quality of service (QoS) level involving a polling schedule designed for services that periodically generate fixed units of data. T1, E-1, and other services based on time division multiplexing (TDM) require UGS polling. See also E-1, QoS, T1, TDM, and WiMAX.

UHF (Ultra-High Frequency) - The part of the radio-frequency spectrum that ranges from 300 MHz to 3 GHz. It is used for broadcast TV and other radio communications.

UHF/VHF Splitter - Used to make a junction point or split a signal so that it will travel down multiple paths over coax. It is also called an RF splitter or splitter. For a photo, see RF splitter.

UIFN (Universal International Freephone Number) - A toll-free telephone number for international calling. A UIFN charges the cost of the call to the called party. Standardized by the ITU-T, the numbering convention for UIFNs is 800 + 8 digits. See also ITU-T and toll free service.

UL (Underwriters Laboratories) - A private company that certifies manufacturer’s products for safety.

UL (Underwriters Laboratories) - An independent, for-profit laboratory that has developed a large number of safety standards against which it offers testing and certification services for potentially hazardous products, including electrical equipment, marine products and life-saving devices, fire suppression and fire containment equipment, and heating, air conditioning, and refrigeration equipment. See Appendix A for contact information.

Ultra High Frequency (UHF) - The part of the radio-frequency spectrum that ranges from 300 MHz to 3 GHz. It is used for broadcast TV and other radio communications.

Ultra Large-Scale Integration (ULSI) - A classification of microchips that have more than 100,000 devices incorporated into their circuitry.

ultralong wavelength band (U-Band) - See U-Band.

ultraviolet (UV) - light See UV.

UMA (Unlicensed Mobile Access) - The original term for the Generic Access Network (GAN) standards. See GAN.

UMTS (Universal Mobile Telecommunications System) - Also known as Wideband CDMA (W-CDMA).A 3G digital cellular radio technology that is an upgrade to the pan-European Global System for Mobile Communications (GSM). UMTS is based on code division multiple access (CDMA) and operates over a carrier 5 MHz wide, compared to the 200 kHz carrier used for narrowband CDMA. UMTS specifications provide for both time division duplex (TDD) and frequency division duplex (FDD) modes of operation, with TDD largely used in Europe and FDD in the United States.The FDD specifications call for the downlink to run in the 2110–2200 MHz range and the uplink in the 1885–2025 MHz range. As is the case with all true 3G systems, UMTS specifications include 128 kbps for high-mobility applications, 384 kbps for pedestrian speed applications, and 2 Mbps (1.920 Mbps) for fixed in-building applications. In reality, UMTS currently caps the transmission rate at a theoretical 384 kbps. UMTS was first deployed in Japan (2000), where it is known as Freedom of Mobile Multimedia Access (FOMA). High Speed Downlink Packet Access (HSDPA), sometimes characterized as a 3.5G technology, is an upgrade to UMTS that increases theoretical downlink data rates to 14.4 Mbps. High Speed Uplink Packet Access (HSUPA), which remains in development, is expected to increase uplink speeds to a maximum of 5.76 Mbps. UMTS standards are published by the 3rd Generation Partnership Project (3GPP). See also 3G, 3GPP, carrier, CDMA, cellular radio, digital, downlink, FDD, GSM, HSDPA, HSUPA, narrowband, TDD, uplink, and wideband.

UMTS Terrestrial Radio Access Time Division Duplex 1.28 Mega chips per second Option (UTRA TDD 1.28Mcps Option) - See UTRA TDD 1.28Mcps Option.

UN (United Nations) - An association of nations with stated goals, including uniting the strength of nations to maintain international peace and security, and promoting the economic and social advancement of all peoples.With respect to telecommunications, the UN system of organizations includes the International Telecommunications Union (ITU), which establishes standards in the wireline and radio sectors, manages the global frequency spectrum, and works to improve infrastructure in developing nations. See also ITU.

UN/EDIFACT (United Nations/Electronic Data Interchange For Administration, Commerce, and Transport) - The international standard for Electronic Data Interchange (EDI), UN/EDIFACT is a United Nations recommendation that has been adopted by the International Organization for Standardization (ISO) and is predominant outside of North America. The competing X12 standard is dominant in North America. EDI standards specify data formats, character sets, and data elements. See also EDI, standard, UN, and X12.

unbalanced - Referring to a lack of electrical symmetry. A coaxial cable (coax) comprises two conductors.The center conductor(s) carries the carrier signal.The outer conductor generally is used only for electrical grounding, and is maintained at zero volts (0V). Therefore, coax is described as an electrically unbalanced medium.A balun (balanced/unbalanced) connector is used to connect (balanced) twisted pair and (unbalanced) coax cables. See also balanced and twisted pair.

Unbundled Network Element (UNE) - See UNE.

Unbundled Network Elements Platform (UNE-P) - See UNE-P.

unbundled service - The Telecommunications Act of 1996 specifies three ways that competitive local exchange carriers (CLECs) in the United States can provide competing local telephone service: build and interconnect, bundled wholesale purchase, and unbundled service. Securing unbundled service from the incumbent LECs (ILECs) essentially was a matter of selecting, on a case-by-case basis, from a menu of unbundled network elements (UNEs), including local loops, local exchange and tandem switches (including software features), interoffice transmission facilities, signaling and call-related database facilities, operations support systems (OSSs) and information, and operator and directory assistance facilities. When all elements from the menu are chosen, this approach is known as Unbundled Network Elements-Platform (UNE-P) and the effect is the same as the bundled service, but the total price typically is at a discount of 40–60 percent from retail prices. See also bundled service, CLEC, ILEC, and Telecommunications Act of 1996.

Under-Floor Raceways - Wire ducts that are designed to be used under raised-floor systems, like those in computer rooms.

underground cable - Cable designed to be place underground, either directly buried or in conduit. Underground cable must be specially designed to protect against moisture, rodents, cable-seeking backhoes, and other earth-moving equipment. See also conduit and direct bury cable.

Underwriters Laboratories (UL) - See UL.

undocumented feature - A euphemism for bug. See bug.

UNE (Unbundled Network Element) - The Telecommunications Act of 1996 specified three ways that competitive local exchange carriers (CLECs) in the United States can provide competing local telephone service: build and interconnect, bundled wholesale purchase, and unbundled service. Securing unbundled service from the incumbent LECs (ILECs) essentially was a matter of selecting from a menu of network elements, including local loops, local exchange and tandem switches (including software features), interoffice transmission facilities, signaling and call-related database facilities, operations support systems (OSSs) and information, and operator and directory assistance facilities. See also CLEC, CO, database, ILEC, local loop, OSS, signaling and control, tandem switch, and Telecommunications Act of 1996.

UNE-P (Unbundled Network Elements-Platform) - The Telecommunications Act of 1996 specified three ways that competitive local exchange carriers (CLECs) in the United States can provide competing local telephone service: build and interconnect, bundled wholesale purchase, and unbundled service. Securing unbundled service from the incumbent LECs (ILECs) essentially was a matter of selecting from a menu of network elements, including local loops, local exchange and tandem switches (including software features), interoffice transmission facilities, signaling and call-related database facilities, operations support systems (OSSs) and information, and operator and directory assistance facilities.When all elements from the menu are chosen, this approach is known as Unbundled Network Elements-Platform (UNE-P) and the effect is the same as the bundled service, but the total price typically is at a discount of 40–60 percent from retail prices. See also CLEC, CO, database, ILEC, local loop, OSS, signaling and control, tandem switch, and Telecommunications Act of 1996.

UNI (User Network Interface) - 1. An ATM Forum specification that defines an interoperability standard for the interface between ATMbased products (a router or an ATM switch) located in a private network and the ATM switches located within the public carrier networks. An ATM physical-layer interface (DS3, OC-N, STS-N, or STM-N) that provides physical-layer services to an NNI. It is also used to describe similar connections in frame-relay networks. See also NNI, Q.920/Q.921, and SNI (Subscriber Network Interface). 2. UNI (User Network Interface). Also called a cable voice port or voice port. In cable-TV networks, a device located at the telephone subscriber’s premises that modulates and demodulates the DS0 voice upstream and downstream channels. The modulated DS0 voice signal is sent by the HDT (Host Digital Terminal) located at the cable-TV head end. The voice port provides connection to the customer premises’ telephone wiring. Channel control between the head end and the customer site voice port can be maintained remotely, from the head end or other office. Because the voice service in cable telephony is provided via radio channels, the channels can be switched when a subscriber is experiencing static or radio interference on line. This would be equivalent to a pair change in a twisted-pair-based telephone network. A pair change cannot be performed by remote control and requires a technician on site. For a photo, see Voice Port.

unibit - Referring to a modulation technique that impresses a single bit on a baud, so that the bit rate is the same as the baud rate. Such a technique employs only two signal states. Binary phase-shift keying (BPSK) is an example of a unibit modulation scheme. Basic amplitude modulation (AM) and frequency modulation (FM) also are unibit in nature. See also AM, BPSK, dibit, FM, quadbit, and tribit.

unicast address - In Internet Protocol version 6 (IPv6), an address associated with a single interface that is associated with a single node, and can, in effect, identify the node. A unicast address can be of several types and here are also special purpose unicast subtypes, including IPv6 addresses with embedded Ipv4 addresses.A global unicast address is a conventional, publicly routable address that can be used in the Internet or any public domain.A link-local address is similar to an IPv4 private IP address, as it is not meant to be routed, but confined to a single segment.A site–local address is used by an organization that has not yet connected to the Internet. A loopback address is used when a host needs to send a packet back to itself. See also domain, global unicast address, interface, Internet, IPv4, IPv6, link-local address, loopback address, node, packet, router, and site–local address.

unicast - Referring to the transmission of a signal or packet from a single device to another single device over a circuit or network. See also anycast, anycast address, broadcast, global unicast address, and multicast.

Unicode (Universal code) - A set of standard coding schemes intended to replace the multiple coding schemes currently used, worldwide.The Unicode Consortium developed the original standard, Unicode Transformation Format-16 (UTF-16), in 1991 as a standard coding scheme to support multiple complex alphabets such as Chinese, Devanagri (Hindi), Japanese, and Korean. In the Japanese language, for example, even the abbreviated Kanji writing system contains well over 2,000 written ideographic characters; the Hirigana and Katakana alphabets add considerably to the complexity.As 7- and 8-bit coding schemes cannot accommodate such complex alphabets, computer manufacturers traditionally have taken proprietary approaches to this problem through the use of two linked 8-bit values. UTF-16 supports 65,536 (2 16 ) characters, which accommodates the most complex alphabets. Unicode accommodates pre-existing standard coding schemes, using the same byte values for consistency. For example, Unicode mirrors ASCII in UTF- 7 and EBCDIC in UTF-EBCDIC, specifically for IBM mainframes. UTF-8 supports any universal character in the Unicode range, using one-to-four octets (eight-bit bytes) to do so, depending on the symbol. UTF-32 uses four octets for each symbol, but is rarely used due to its inherent inefficiency.The Unicode Standard has been adopted by most, if not all, major computer manufacturers and software developers, and is required by modern standards such as CORBA 3.0, ECMAScript (JavaScript), Java, LDAP,WML, and XML. Unicode is developed in conjunction with the International Organization for Standardization (ISO) and Internet Engineering Consortium (IEC), which also define the Universal Character Set (UCS), into which the UTF code sets map. UCS-4 is a four-octet code set into which UTF-32 maps and UCS-2 is a two-byte code set into which UTF-16 maps. UCS-1 encodes all characters in byte sequences varying from one to five bytes. See also ASCII, code set, EBCDIC, IEC, and ISO.

Unicode Consortium - A not-for-profit consortium founded to develop and promote the use of the Unicode Standard. The consortium operates with the International Organization for Standardization (ISO), Internet Engineering Consortium (IEC) and World Wide Web Consortium (W3C) to refine the Unicode specifications and expand the character set. See Appendix A for contact information. See also IEC, ISO, Unicode, and W3C.

Unicode Transformation Format (UTF) - See Unicode.

unified communications - The ability to communicate in real time in the preferred mode (i.e., landline, cellular telephone, e-mail, or fax), unified communications incorporates presence technology, thereby allowing the user to indicate availability (e.g., available, unavailable, or out to lunch) and communications mode preference (e.g., business phone, cellular phone, text message, or instant message) to prospective callers. See also unified messaging.

unified messaging - Synonymous with integrated messaging and multimedia messaging.The integration of voice, audio, text, facsimile, image, and video messaging, ideally on a single messaging platform or on a suite of platforms interrelated in such a way as to be transparent to the end user. Unified messaging is intended to provide an end user with a single interface to a messaging system or suite of messaging systems that support all types of messages in all formats, and that can adapt the message format to match the limitations of the terminal device and network that the end user employs to access the messaging system. For example, a unified messaging system could convert a fax message into a voice message if the user calls from a conventional telephone over a landline, or into a text message if the user has access to a cellular telephone. Ideally, unified messaging works in both directions, enabling the recipient of the message to respond in an inverse manner. If, for example, a unified messaging system converted a fax message into a text message for a user who has access to a cellular telephone, unified communications allows the user to respond with a text message that the system will convert into a fax that it will send to the originator of the message. See also unified communications.

Uniform Call Distributor (UCD) - A less expensive and less smart version of an ACD (Automatic Call Distributor). The UCD receives incoming calls and equally distributes them among agents in a call center. For more details, see ACD.

uniform dialing plan (UDP) - Also known as coordinated dialing plan.An optional PBX feature for large, complex multisite PBX networks, UDP supports simplified station-to-station dialing, allowing multiple PBXs to share a single numbering plan wherein each station has a unique number comprising four or five digits.The end user need only dial those digits to be connected to another user, regardless of where the two are located. If the two are served by the same PBX, the call connection process is simple. If the two are served by separate PBXs, the call will be sent over a private facility such as a tie trunk if one is available. If the call is sent over a central office (CO) trunk for connection through the PSTN, the originating PBX will automatically insert the necessary country code, area code and central office prefix, or otherwise modify the dialed digits as necessary to, for example, direct the call to the DID number of the called party.

Uniform Resource Identifier (URI) - See URL.

Uniform Resource Locator (URL) - See URL.

Uninterruptable Power Supply (UPS) - A battery back-up system. When the power goes out, the UPS converts the DC battery power to AC power to run the system.

uninterruptible power supply (UPS) - See UPS.

unipolar - A digital signaling technique that makes use of a positive (+) voltage and a null, or zero (0), voltage to represent data in binary form, i.e., ones (1s) and zeroes (0s). See also binary and bipolar.

United Nations (UN) - See UN.

United Nations/Electronic Data Interchange For Administration, Commerce, and Transport (UN/EDIFACT) - See UN/EDIFACT.

United States Computer Emergency Readiness Team (US-CERT) - See US-CERT.

United States Digital Cellular (USDC) - A digital cellular radio standard better known as Digital Advanced Mobile Phone Service (D-AMPS). See D-AMPS.

United States Independent Telephone Association (USITA) - See USTA.

United States Telecom Association (USTA) - See USTA.

United States Time Division Multiple Access (US TDMA) - A digital cellular radio standard better known as Digital Advanced Mobile Phone Service (D-AMPS). See D-AMPS.

Unity Gain - 1. Gain (another word for amplification) in an electronic circuit that is equal to 1. In oscillator circuits, and some other radio receiver circuits that have a feed back (generate their own input), the amplification between the output and the input must be one. If the gain is not one, the signal will either diminish to nothing or be amplified beyond the saturation point of the active component (e.g., transistor) in the circuit. 2. In broadband networks, the balance between signal loss and signal gain through amplifiers.

universal ADSL (universal Asymmetric Digital Subscriber Line Lite) - See G.lite.

Universal Asynchronous Receiver/Transmitter (UART) - An integrated circuit, attached to the parallel bus of a computer, used for serial communications. The UART translates between serial and parallel signals, provides transmission clocking, and buffers data sent to or from the computer.

Universal Character Set (UCS) - See UCS.

Universal Code (Unicode) - See Unicode.

Universal Coordinated Time (UTC) - See UTC.

Universal Digital Carrier (UDC) - Also referred to as DLC (Digital Loop Carrier). A method of placing two analog telephone lines onto one digital copper pair. In areas where a telephone customer has requested an additional line and there are no additional copper pairs available, many telephone companies digitize the existing line to carry two. The central office routes the two telephone lines to a UDC trunk, which is then connected to the copper pair that carries the digital transmission to the customer’s premises. The telephone company installs a UDC adapter at the demarcation point, which converts the digital UDC transmission into two analog lines. The UDC carrier is DSL (Digital Subscriber Loop) based. UDC is a 2B1Q (Two Binary One Quarternary) line format that rides on a - 137-volt battery. If the UDC carrier fails, it will go into an override/bypass mode and switch the pair to a - 52-volt battery to provide the original POTs service. The telephone number that will continue to work is line one, and line two can be set to call forward to line one. For a diagram, see DLC.

Universal International Freephone Number (UIFN) - See UIFN.

Universal Mobile Telecommunications System (UMTS) - See UMTS.

Universal Plug and Play (UPnP) - See UPnP.

Universal Resource Locator (URL) - An Internet address. URLs consist of two parts. The first part is the protocol identifier and the second is the domain identifier. For example, in the address http://www.mcgraw hill.com, the “http://” specifies a request to fetch a Web page using the HTTP (Hyper Text Transfer Protocol) and the “mcgraw-hill.com” specifies a domain name (which converts directly into an IP address) on the World Wide Web (WWW).

Universal Serial Bus (USB) - A latter external bus standard that emerged in 1996. It supports data transfer rates of 12 Mbps, and can connect as many as 127 peripheral devices (mice, printers, video equipment, modems, and keyboards) simultaneously. USB is also able to support Plug and Play and can be hot pluggable. For a photo of a USB connector,see USB.

Universal Service Administrative Company (USAC) - See USAC.

Universal Service Fund (USF) - See USF.

universal service - The concept of making affordable basic telephone service available to everyone everywhere within a nation, state, or other governmental jurisdiction.The United States Communications Act of 1934 first established the concept and led to the formation of a fund known as the Universal Service Fund (USF), which was finally codified in the Telecommunications Act of 1996. In some cases, the concept has been widened to include other telecommunications services classified as information services, most especially Internet access.That is the case in the United States, where the Universal Service Administrative Company (USAC) administers programs that provide support for incumbent local exchange carriers (ILECs) in high-cost areas, assistance for low-income subscribers, discounts for telecommunications service to schools and libraries, and discounts to rural health care providers. See also Communications Act of 1934, Internet, Telecommunications Act of 1996, USAC, and USF.

University Corporation for Advanced Internet Development (UCAID) - See UCAID.

UNIX - An operating system similar to MS Windows, only it is designed to operate on RISC (Reduced Instruction Set Computers), like those made by Sun Microsystems. (It can work on Intel Pentium and other 586- based PCs, too.) UNIX performs all the functions that MS Windows does, only the icons look different and have different names. UNIX and RISC computers are used in conjunction with CTI (Computer Telephony Integration) applications, such as front-end processors and integrated voice-response systems, because of their ability to execute small instructions and tasks very quickly, and on a real-time basis.

Unlicensed Mobile Access (UMA) - The original term for the Generic Access Network (GAN) standards. See GAN.

Unlicensed National Information Infrastructure (U-NII) - See U-NII.

Unlisted Number - A phone number that is not listed in a telephone book, but can be found by calling directory assistance and giving the person’s name. The other type of private listing is an unpublished number, which is not listed in a telephone book and cannot be found by calling directory assistance.

Unpublished Number - See Unlisted Number.

Unshielded Twisted Pair (UTP) - Twisted-pair wiring that is unshielded, meaning it does not have a foil wrapping around the group of conductors within the jacket. Unshielded twisted pair is the most commonly used wiring for voice and data networks. Twisted-pair wire consists of pairs of color-coded wires. Common sizes of twisted-pair wire are 2 pair, 3 pair, 4 pair, 25 pair, 50 pair, and 100 pair. Twisted-pair wire is commonly used for telephone and computer networks. It comes in ratings of CAT 3 (for voice), CAT 4 (voice and 10-base-T), and CAT 5 (for 100-base-T and token ring). See also Plenum and PVC.

unsolicited grant service (UGS) - See UGS.

Unspecified Bit Rate (UBR) - A Quality of Service (QOS) defined by the ATM Forum for ATM Networks that allows any amount of data up to a specified maximum to be sent across the network. A connection would be rightfully commissioned as an UBR connection if it carried nontime sensitive data that could be retransmitted without a large inconvenience. The UBR quality of service does not guarantee freedom from cell loss or delay. Other QOSs defined by the ATM Forum for ATM connections include CBR (Constant Bit Rate), ABR (Available Bit Rate), and VBR (Variable Bit Rate).

unsponsored domain - In the Internet Domain Naming System (DNS), the original Top Level Domains (TLDs) that operate under policies established by the global Internet community, directly through the administration process of the Internet Corporation for Assigned Names and Numbers (ICANN). See also DNS, ICANN, Internet, sponsored domain,and TLD.

update - 1. A manipulation involving adding, modifying, or deleting data to bring a file or database upto-date. 2. A relatively minor release or version upgrade to an existing software product that adds minor features or corrects bugs. An update generally is denoted by a decimal fraction notation in the version number, such as 6.1 as an update to 6.0. See also bug, bug fix, patch, and upgrade.

upgrade - A new, enhanced, or more powerful version or release of a product.A software upgrade generally is denoted by a new version number, such as 7.0 as an upgrade to 6.0. See also bug, bug fix, patch, and update.

uplink - 1. The microwave radio link from the terrestrial transmit antenna to the satellite. See also downlink. 2. In a cellular network, the radio link from the mobile station (MS) to the base station (BS). See also downlink.

upload - To transfer a file copy from a local computer to a remote computer over a network. See also download

UPnP (Universal Plug and Play) - A Microsoft initiative that extends the PnP specification to networks. UPnP enables a PC to automatically recognize the presence of a new peripheral hardware device as it is connected to a network, locate the necessary support software (e.g., driver), and configure the device interface. UPnP is aimed primarily at home and small office users who need to network devices such as personal digital assistants (PDAs) and digital cameras. See also PnP.

UPS (Uninterruptable Power Supply) - A battery back-up system. When the power goes out, the UPS converts the DC battery power to AC power to run the system.

Upstream - In asymmetrical broadband transmissions, a reference to the bandwidth or information flow toward the service provider and away from the customer/subscriber. ADSL and cable-modem Internet services are asymmetrical. They consist of a larger downstream and smaller upstream component. Asymmetrical transmissions are best suited for enduser Internet services. See also ADSL and Cable Telephony.

URI (Uniform Resource Identifier) - See URL.

URL (Universal Resource Locator) - An Internet address. URLs consist of two parts. The first part is the protocol identifier and the second is the domain identifier. For example, in the address http://www.mcgraw hill.com, the “http://” specifies a request to fetch a Web page using the HTTP (Hyper Text Transfer Protocol) and the “mcgraw-hill.com” specifies a domain name (which converts directly into an IP address) on the World Wide Web (WWW).

US TDMA (United States Time Division Multiple Access) - A digital cellular radio standard better known as Digital Advanced Mobile Phone Service (D-AMPS). See D-AMPS.

US-CERT (United States Computer Emergency Readiness Team) - A team within the Department of Homeland Security charged with protecting the nation’s Internet infrastructure by coordinating defense against and response from cyberattacks. See also CERT, cyberspace, and Internet.

US - The ASCII control-code abbreviation for unit separator. The binary code is 1111001 and the hex is F1.

USAC (Universal Service Administrative Company) - A subsidiary of the National Exchange Carrier Association (NECA), USAC administers programs that provide support for incumbent local exchange carriers (ILECs) companies in high-cost areas, assistance for low-income subscribers, discounts for telecommunications service to schools and libraries, and discounts to rural health care providers. USAC accepts funds collected by the ILECs and the interexchange carriers (IXCs) and distributes designated funds in support of the following programs and organizations set up under the Telecommunications Act of 1996:

• Schools and Libraries Program: Also known as the E-rate Program.Administered by the Schools and Libraries Corporation (SLC) to make telecommunications service, Internet access, and internal connections affordable for eligible schools and libraries.

• Rural and High Cost Program: Subsidizes basic telephone service in high-cost areas of the United States and its territories.

• Rural Health Care Program: Administered by the Rural Health Care Corporation (RHC) to subsidize telecommunications and Internet service for eligible rural health care providers in highcost areas.

• Low Income Program: Lifeline subsidies to reduce the installation and monthly costs of basic telephone service for low-income consumers.

See also ILEC, IXC, LEC, Telecommunications Act of 1996, universal service, and USF.

USART (Universal Synchronous/Asynchronous Receiver/Transmitter) - The part of a computer’s serial communications port (most PCs have two) that converts the parallel data from the data bus into serial data to be sent to a device connected to the port, like a modem.

USB (Universal Serial Bus) - A latter external bus standard that emerged in 1996. It supports data transfer rates of 12 Mbps, and can connect as many as 127 peripheral devices (mice, printers, video equipment, modems, and keyboards) simultaneously. USB is also able to support Plug and Play and can be hot pluggable.

USDC (United States Digital Cellular) - A digital cellular radio standard better known as Digital Advanced Mobile Phone Service (D-AMPS). See D-AMPS.

User Datagram Protocol (UDP) - A connectionless transport-layer protocol that helps make up the TCP/IP protocol stack. UDP is a simple protocol that exchanges datagrams/packets without acknowledgments or guaranteed delivery, requiring that error processing and retransmission be handled by other protocols. UDP is defined in RFC 768. An IP (Internet Protocol) transport-layer protocol that is sometimes used in place of TCP when transaction-based application programs are communicating (i.e., SNMP, Simple Network Management Protocol). UDP usually carries noncrucial network information.

user ID (user IDentification) - The user name, or username, by which a person is identified to a computer system or network.A user commonly must enter both a user ID and a password as an authentication mechanism during the logon process. If the system or network is connected to the Internet, the username typically is the leftmost portion of the e-mail address, which is the portion preceding the @ sign. In the e-mail address ray@contextcorporation.com, for example, ray is the username. User ID is synonymous with username. See also password.

user interface (UI) - The portion of a computer program with which the user interacts, i.e., the interface between a user and a computer program.There are command-line interfaces, menu-driven interfaces, and graphical user interfaces (GUIs). See also GUI.

User Network Interface (UNI) - 1. An ATM Forum specification that defines an interoperability standard for the interface between ATM-based products (a router or an ATM switch) located in a private network and the ATM switches located within the public carrier networks. An ATM physical-layer interface (DS3, OC-N, STS-N, or STM-N) that provides physical-layer services to an NNI. It is also used to describe similar connections in frame-relay networks. See also NNI, Q.920/Q.921, and SNI (Subscriber Network Interface). 2. UNI (User Network Interface). Also called a cable voice port or voice port. In cable-TV networks, a device located at the telephone subscriber’s premises that modulates and demodulates the DS0 voice upstream and downstream channels. The modulated DS0 voice signal is sent by the HDT (Host Digital Terminal) located at the cable-TV head end. The voice port provides connection to the customer premises’ telephone wiring. Channel control between the head end and the customer site voice port can be maintained remotely, from the head end or other office. Because the voice service in cable telephony is provided via radio channels, the channels can be switched when a subscriber is experiencing static or radio interference on line. This would be equivalent to a pair change in a twisted-pair-based telephone network. A pair change cannot be performed by remote control and requires a technician on site.

User Plane - One of the three entities of frame-relay network management. The three planes are: The User Plane (the U Plane defines the transfer of information), the Management Plane (the M Plane defines the LMI, Local Management Interface), and the Control Plane (the C Plane is delegated for signaling and switched virtual circuits). The U Plane is based on the ANSI TI.602 (LAPD) core aspect standard. It provides the interface between the end user and the network, bi-directional transfer of frames, frame-order preservation, congestion avoidance, and determines the priority of PVCs (Permanent Virtual Circuits).

user - 1. End user.The living, breathing human being who actually uses a computer or application to perform processes that yield end results. 2.The person, organization, process, device, program, system, or other entity that exploits another person, organization, process, device, program, system, or other entity.

username - Synonymous with user ID. See user ID.

USF (Universal Service Fund) - A fund established in the United States to support the concept of universal service, as first described in the Communications Act of 1934.The USF traditionally was intended to subsidize the cost of providing service to high-cost areas, defined as areas where the cost of providing service is at least 115 percent of the national average.Thereby, the USF ensured that even the most remote, sparsely populated, and impoverished areas of the United States had access to good quality basic voice telephone service at reasonable cost. In effect, it was a national cost-averaging scheme designed for the benefit of society.The USF extended over time to support the provisioning of lifeline service to those end users who cannot afford the cost of basic telephone service.The Telecommunications Act of 1996 codified the USF, extending its benefits to subsidize Internet access to schools and libraries, and telecommunications networks to link rural health care providers to urban medical centers in order to provide access to advanced diagnostic and other medical services. Under the direction of the Federal Communications Commission (FCC), the National Exchange Carrier Association (NECA) governs the USF, which actually is administered by the Universal Service Administrative Company (USAC), a NECA subsidiary. USAC accepts the collected funds from the local exchange carriers (LECs) and interexchange carriers (IXCs).The LECs collect USF fees from both IXCs and subscribers.Those fees are embedded in the access charges to the carriers, and generally are billed to subscribers as a separate line item.The LECs net out their approved USF requirements, retain a percentage as reimbursement for billing and administrative costs, and pass any remaining monies to USAC. Cellular providers contribute to the USF, usually on the basis of an average assumed percentage of interstate and international traffic.Voice over Internet Protocol (VoIP) providers also contribute to the fund for VoIP to PSTN calls; peer-to-peer VoIP-to-VoIP calls remain untaxed. In the United States, each of the individual states also has a USF, or something similar. Many other countries do, as well. For example,Australia formally established a Universal Service Obligation (USO) in 2001 and South Africa established the Universal Service Agency (USA) in the Telecommunications Act of 1996. See also access charges, cellular radio, Communications Act of 1934, FCC, IXC, LEC, lifeline service, NECA, PSTN, Telecommunications Act of 1996, universal service, USAC, and VoIP.

USITA (United States Independent Telephone Association) - See USTA.

USOC (Universal Service Order Code) - A code that defines different equipment and services within Regional Bell Operating Companies (RBOCs). Different RBOCs have different meanings for each code, as far as services, but the USOC codes for equipment has remained the same since the old Bell System (pre-1984).

USRT (Universal Synchronous Receiver Transmitter) - The part of a computer’s serial communications port (most PCs have two) that converts the parallel data from the data bus into serial data to be sent to a device connected to the port, like a modem.

USTA (United States Telecom Association) - A trade association of United States telecommunications carriers and suppliers, the USTA lobbies Congress, regulatory agencies, and other policy makers on behalf of its membership. USTA has its roots in the National Telephone Association (1897), which later changed its name to the United States Independent Telephone Association (USITA) and represented the interests of independent (i.e., non-Bell) telephone companies.When the break-up of the Bell System was decided in 1982, USITA admitted the newly divested Baby Bells as full members and changed its name to USTA. See Appendix A for contact information.

USWest A Regional Bell Operating Company (RBOC). - Their territory includes the States of Washington, Oregon, Idaho, Montana, Wyoming, North Dakota, South Dakota, Minnesota, Iowa, Nebraska, Utah, Colorado, Arizona, and New Mexico.

UTC (Universal Coordinated Time) - Also known as Zulu (Z) Time.The International Telecommunications Union (ITU) struggled to develop an initialization for a universal time coordinated among all nations of the Earth. English speakers preferred CUT (Coordinated Universal Time). French speakers preferred TUC (Temps Universel Coordonné). So, the ITU managed to reach a consensus that totally satisfied neither group, but resolved the stalemate. UTC is based on the average of multiple atomic clocks, many of which are cesium clocks, which are the standard on which the SI second is based. UTC sometimes is referred to as GMT (Greenwich Mean Time), which is archaic. See also ITU, second, SI, and Zulu Time.

UTF (Unicode Transformation Format) - See Unicode.

utility - 1. A computer program dedicated to the management of a computer system, a utility is narrowly focused on a task such as maintaining a database, improving the efficiency of computer storage, searching for viruses, encrypting and decrypting data, and compressing and decompressing data. 2. A company that performs or provides an essential public service, such as electric power, natural gas, sewer, telephone, or water.

utilize - A frilly word that means to make use of something. People who want to sound smarter than they really are utilize utilize. I just use use.

Utopia - From the Greek ou, meaning not, and topos, meaning place, and translating literally as no place.The word was first used by Sir Thomas More (1516) in his book Utopia as the name of an imaginary island that was the home of a perfect political and social system. In contemporary usage, utopia refers to an ideal place, state of being, or situation. (Note: Utopia sounds like no place I’ve ever been. If there were such a place, someone surely would foul it up. If not it would get so crowded that nobody would go there any more.)

UTP (Unshielded Twisted Pair) - Twisted-pair wiring that is unshielded, meaning it does not have a foil wrapping around the group of conductors within the jacket. Unshielded twisted pair is the most commonly used wiring for voice and data networks. Twisted-pair wire consists of “pairs” of color-coded wires. Common sizes of twisted-pair wire are 2 pair, 3 pair, 4 pair, 25 pair, 50 pair, and 100 pair. Twisted-pair wire is commonly used for telephone and computer networks. It comes in ratings of CAT 3 (for voice), CAT 4 (voice and 10-base-T), and CAT 5 (for 100-base-T and token ring). See also Plenum and PVC.

UTRA TDD 1.28Mcps Option (UMTS Terrestrial Radio Access Time Division Duplex 1.28 Mega chips per second Option) - The 3rd Generation Partnership Project (3GPP) designation for Time Division-Synchronous Code Division Multiple Access (TD-SCDMA), a 3G cellular radio standard under development by the Chinese Academy of Telecommunications Technology (CATT), an agency of the People’s Republic of China (PRC). See also 3G, 3GPP, cellular radio, and TD-SCDMA.

UV (UltraViolet) - The portion of the electromagnetic spectrum in the frequency range of 1–30 PHz and with a wavelength of 380–10 nm. UV light has no applications in telecommunications other than to make it possible for you to enjoy the full impact of psychedelic posters from the 1960s while you are contemplating what to do next. UV is the most dangerous portion of the spectrum in causing sunburn because the energy of a photon is proportional to its frequency (e = h × f), where h is Planck’s constant (6.6 × 10 -34 joule-second). See also electromagnetic spectrum, frequency, Hz, and wavelength.