Fiber Optics Illustrated Dictionary Type of Service ToS. Type of Service is both a ge- neric concept in networking and a specific parameter related to Internet Protocol communications. It de- scribes and determines various networking param- eters related to speed, security, format, etc. As with many types of network services, there may be trade- offs between speed, flexibility, and security, depend- ing upon how ToS is specified at any particular time or on specific types of networks. ToS is now man- dated by the Requirements for Internet Hosts speci- fications described in the various relevant Requests for Comments (RFC) documents. At the present time, support for ToS is somewhat uneven and there are known problems on some prevalent systems. In Internet Protocol (IP), a byte in the IP header sup- ports Type of Service information. The byte is divided into the precedence field, the lOS field, and a re- served bit, only one of which may be set at a time. It is recommended that routers be cognizant of the ToS value for a route in the routing table. If the routing protocol does not support ToS header settings, the ToS must be assigned the default value of zero (0). Physical Link Security Type of Service was described as an RFC by D. Eastlake in May 1993. It was sub- mitted as an experimental protocol providing a ToS 952 to request maximum physical link security in addi- tion to existing types ofservices in the Internet Pro- tocol (IP) Suite. This ToS requests protection against surreptitious observation by agents labeled as outside the traffic. When transporting SNA network traffic over TCPIIP networks, there are issues with preserving the SNA Class ofService (CoS) parameters. Cisco addressed this issue by developing a data-link switching en- hancement (DLSw+) to improve response time and the effective use of bandwidth while supporting SNA Type ofService (ToS) over TCPIIP to ensure preser- vation of SNA CoS traffic parameters and aid net- works in prioritizing SNA traffic. Programmers have created tables and software utili- ties to streamline the processing ofToS settings. For example, iptables allows a table to be constructed with predetermined values that can be matched to the data grams being processed. Thus, only those with matching patterns are processed. Masking utilities are available for accomplishing a similar task, but with more power and flexibility. In NIKHEF ping code, TOS bits can be set to enable the user to set priorities for the ping query. Settings are between 0 and 255. See RFC 1455, RFC 1812. © 2003 by CRC Press LLC u symb. A letter sometimes substituted for Jl (micron) when special symbol sets are not available. See mu. U interface In ISDN, a number ofreference points have been specified as R, S, T, U, and V interfaces. To establish ISDN services, the telephone company typically has to install a number ofwire lines and de- vices to create the all-digital circuit connection nec- essary to send and receive digital voice and data trans- missions. The U interface is a full-duplex link that works over a single pair (2-wire) cable. It interfaces a line termi- nating switch in the telephone switching office with a small interface device called a Network Termina- tion device (NTI or NT2) at the customer premises. In the U.S., the NTI converts the 2-wire U interface into a 4-wire SIT interface which, in turn, can sup- port multiple devices in a single bus loop configura- tion, such as atelephone, computer, or facsimile ma- chine. Alternately, in parts of Europe, the NT2 inter- faces with an S interface. See ISDN interfaces for a diagram. Ureference pointAdemarcation point in ISDN ser- vices installed in North America, where the local loop connects with the NT 1 device. See U interface. See ISDN interfaces for a diagram. USeries Recommendations A series of lTU-T rec- ommended guidelines for telegraph switching. These guidelines are available for purchase from the lTU- T. Since lTU- T specifications and recommendations are widely followed by vendors in the telecommunica- tions industry, those wanting to maximize interoper- ability with other systems need to be aware of the information disseminated by the lTU - T. A full list of general categories is in Appendix C and specific se- ries topics are listed under individual entries in this dictionary, e.g., T Series Recommendations. See V Series Recommendations. U-band Astronomical emanations ranging from 3200 to 3950 A that are usually detected with U po- larimetric filters from the U, B, V + R, I Johnson- Cousins broadband photometric system. U-band fre- quencies are emitted by some celestial bodies and help us gain apicture ofour universe. V-band energy emanating from some galaxies has been detected and U-band flares are occasionally recorded. U-band, optical In optical communications, an ultralong-wavelength ITU-specified transmission band in the 1625 to l675-nm range. Distributed- feeback and continuous-wave laser diodes are avail- able in U-band frequencies. U-band systems are not as common as C-bandIL-band, but it has been sug- gested that U-band signals may be multiplexed with S-band signals in dense wavelength division multi- plexed (DWDM) systems in much the same way. ItV~T .• (j·.Seti~I~~tJ.D1endafl4Jbs u-c user-central. In ADSL, the standardized inter- face between the twisted-pair local loop to the sub- scriber premises and the plain old telephone service (POTS) splitter on the network (usually the central office) side of the link. U-C 2 is a less-standard inter- face between the POTS splitter and the ATU-C (net- workADSL Transmission Unit). While functionally 953 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary Sampling ofUL Standards Related to Telecommunications UL No. Descriptions of UL Numbers from Underwriters Laboratory UL 1409 Low-Voltage Video Products Without Cathode-Ray-Tube Displays: Antenna signal amplifiers, CATV adapters and digital converters, channel balancers and processors, distribution amplifiers, commercial TV cameras, disc players, electronic viewfinders, internal distribution amplifiers, laser disc players, modulators, picture tube degaussers, power packs, power supply-battery chargers, satellite receivers and dish controllers, single-channel converters, teletext and television decoders, television descramblers, tuner adapters and power supplies, UHF amplifiers, tuners, and converters, VHF amplifiers and tuners, video printers, video- production -processing, -receiving, and -recording equipment, and video tape recorders. UL 1418 Cathode-Ray Tubes: Bonded frame, laminated, prestressed picture tubes (CRT), rebuilt picture tubes, picture tubes for business equipment, dental, and medical equipment. UL 1410 Television Receivers and High- Voltage Video Products: Household and commercial television receivers and monitors, and health care facility television equipment. UL 1412 Fusing Resistors and Temperature-Limited Resistorsfor Radio- and Television-Type Appliances: For use in appliances that do not involve potentials greater than 2500V peale UL 1414 Across-the-Line, Antenna-Coupling, and Line-by-Pass Capacitors for Radio- and Television- TYpe Appliances: For nominal 125- and 250- V, 50- to 60-Hz circuits, includes double protection capacitors rated 1.0 B5F maximum. UL 1419 Professional Video and Audio Equipment: Video tape recorders, audio/video editing equipment, audio/video receiving and processing equipment, signal transmission equipment, television cameras, video digitizers, video monitors, metering equipment, and similar equipment. UL 1492 Audio-Video Products and Accessories: Audio and video products intended for use on supply circuits. Audio products and accessories intended for household use and involved with the reproduction or processing of audio signals. Video products that are intended for household or commercial use, that receive signals in ways such as off the air, through a CATV IMATV cable system, from a video-recorded medium, and from image-producing units. Auxiliary products and accessories intended for use with audio or video products wherein the auxiliary and accessory products are separate and do not perform the desired function, but are used in addition to or as a supplement to products mentioned above. Cellular telephones and similar transceiving devices used on a vehicle, boat, or the like, where the telephone interconnects to the telephone network through a radio transmitter and receiver. Portable audio or video products of the types described above that are intended for use with a vehicular, marine, or any other battery circuit as the power supply means. UL 6500 Audio/Video and Musical Instrument Apparatus for Household, Commercial, and Similar General Use: This standard applies to the following apparatus that is to be connected to the supply mains, either directly or indirectly, intended for domestic and commercial and similar general indoor use and not subject to dripping or splashing: radio receiving apparatus fQr sound or vision; amplifiers; independent load transducers and source transducers; motor- driven apparatus which comprise one or more of the above-mentioned apparatus or can be used only in combination with one or more of them, such as radio-gramophones and tape recorders; other apparatus obviously provided to be used in combination with the above- mentioned apparatus, such as antenna amplifiers, supply apparatus and cable-connected remote control devices; battery eliminators; electronic musical instruments; electronic accessories such as rhythm generators, self-contained tone generators, music tuners and the like for use with electronic or nonelectronic musical instruments; video apparatus intended for entertainment purposes in health-care facility locations; cellular telephones and similar transceiving devices used on a vehicle, boat, or similar location where the telephone interconnects to the telephone network through a radio transmitter and receiver; portable audio or video apparatus intended for use with a vehicle, marine, or any other battery circuit as the power supply means. UL 1685 Vertical- Tray Fire-Propagation and Smoke-Release Test for Electrical and Optical-Fiber Cables: Limits for each fire test to make the tests equally acceptable for the purpose of quantifying the smoke. The cable manufacturer is to specify, for testing each "-LS" (limited- smoke) cable construction, either the UL vertical-tray flame exposure or the FT4/IEEE 1202 type of flame exposure. The same test need not be specified for all constructions. Cont 954 © 2003 by CRC Press LLC similar, the U-C is distinguished from the U-R inter- face due to the asymmetry of the link. See U-R. U-DSL The U interface in a Digital Subscriber Loop (D8L) system. V-law, Jl-law A pulse code modulation (PCM) cod- ing and companding data ITU- T standard used in au- dio systems on computer multimedia peripheral cards. This takes some of the load ofspecialized ap- plications off the central processing unit (CPU). It is often implemented in addition to A-law companding and is suitable for compression of voice communi- cations. Note, this is technically J,l-law, but many key- boards don't support the Mu (J,l) character and so it is altematelywritten as Mu-Iaw or U-Iaw. In fact, it's even sometimes written M-Iaw since the Greek sym- bol for uppercase J,l is M. See A-law, Mu-Iaw. U-plane In ATM networking, as it applies to Broad- band-ISDN reference model, the U-plane is the user plane, a higher-level plane including all of the ATM layers, which bears user application information. It sits adjacent to the C-plane (control plane) and shares physical and ATM layers with the C-plane. The M- plane (management plane) enables the transfer of in- formation between the C- and U-planes. In ATM net- working as it applies to Frame Relay bearer services, the U-plane parameters, such as throughput, maxi- mum frame size, etc., are negotiated through the C- plane. Synchronization and coordination between the U-plane and C-plane are described in ITU- T Recom- mendation Q.923. See the Appendix for more detailed information on ATM. U-R user-remote. In ADSL, the standardized inter- face between the twisted-pair local loop to the sub- scriber premises and the plain old telephone service (POTS) splitter on the premises. U-~ is a less stan- dardized interface between the POTS splitter and the ATU-R (premises ADSL Transmission Unit). While functionally similar, the U-R interface is distin- guished from the U -C interface due to the asym- metry of the link. See U-C. U.K. Education & Research Networking Associa- tion UKERNA. The trading name for the JNT Asso- ciation, which has managed the development and operation of the Joint Academic Network (JANET), since 1994, under agreement with the Joint Informa- tion Systems Committee (llSC) of the U.K. Higher Sampling of UL Standards Related to Telecommunications, cont. ULNo. Descriptions of UL Numbers from Underwriters Laboratory UL 1577 Optical Isolators: Optically isolated switches and insulation systems, photocouplers. UL 1651 Optical Fiber Cable: Single and multiple optical-fiber cables for control, signaling, and communications as described in Article 770 and other applicable parts of the National Electrical Code. UL 1690 Data-Processing Cable: Electrical cables consisting of one ormore current-carrying copper, aluminum, or copper-clad aluminum conductors with or without either or both (1) grounding conductor(s) and (2) one or more optical-fiber members, all under an overall jacket. These electrical and composite electrical/optical-fiber cables are intended for use under the raised floor of a computer room (optical and electrical functions associated in the case of a hybrid cable) in accordance with Article 645 and other applicable parts of the National Electrical Code. UL2024 Optical Fiber Cable Raceway: Covers the following types of optical fiber cable raceways and fittings designed for use with optical fiber cables in accordance with Article 770 of the National Electrical Code: Plenum. Evaluated for installation in ducts, plenums, or other spaces used for environmental air in accordance with the National Electrical Code as well as general purpose applications; Riser. Evaluated for installation in risers in accordance with the National Electrical Code as well as general purpose applications; General Use. Evaluated for general purpose applications only. UL 1459 Telephone Equipment: Cordless telephones, key systems private branch exchange equipment, telephone answering devices, dialers, and telephone sets. UL 1863 Communication Circuit Accessories: Telecommunications equipment such as jack and plug assemblies, quick connect assemblies, telephone wall plates, cross connect enclosures, network interfaces, and connector boxes. UL 1950 PracticalApplication Guidelines On-Line Service (PAGOS): A reference service providing information for understanding and applying the requirements ofUL Standards for Safety. Of interest is the UL 1950 Standard for Safety of Information Technology Equipment, Including Electrical Business Equipment. 955 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary and Further Education Funding Councils. Thus, UKERNA has responsibility for the education and research communities' networking programs in the U.K. It further researches and develops advanced electronic communications facilities. See JANET. UA See User Agent. UAC User Agent client. See User Agent. UART See universal asynchronous receiver-trans- mitter. UASs unavailable seconds. A measure of duration, in seconds, during which a service or entity is not available. UAT See user acceptance testing, user application testing. UAWG See Universal ADSL Working Group. UBR See unspecified bit rate. UCA See Utility Communications Architecture. UCC See Uniform Commercial Code. UCF See UNIX Computing Forum. UCITA See Uniform Computer Information Trans- actions Act. UCM 1. universal controller module. 2. See Univer- sal Call Model. Uda, Shintaro One of the designers of the Yagi-Uda antenna, a sensitive, directional antenna which worked in the higher frequency ranges and became the model for thousands ofantennas that came later and are still in use. See Yagi-Uda antenna. UDLC See Universal Digital Loop Carrier. UDP See User Datagram Protocol. UECT See Universal Encoding Conversion Tech- nology. UFO 1. See UHF Follow-On. 2. unidentified flying object. UHF See ultra-high frequency. UHF Follow-On, Ultra-High Frequency Follow- On UFO. A U.S. Naval, Air Force, and Command communications satellite constellation intended to supersede the aging FLTSAT and LEASAT satellite systems. The system is designed to provide interim Global Broadcast Service (GBS), EHF, and Ka-band transmissions. UFO provides more modem capabili- ties and more secure communications than the older satellite communications systems. Increased channel capacity is available with Demand Assigned Multiple Access (DAMA) technology. UFO is intended to pro- vide global coverage of four significant geographic areas, including the U.S. and three major oceans. See FLTSAT. UHTTP See Unidirectional Hypertext Transfer Pro- tocol. m I. Unix International. Aconsortium ofcomputer software and hardware vendors promoting the devel- opment and implementation of Unix, and of related and other open software standards. See Unix, UNIX. 2. See user interface. uk.telecom An online USENET newsgroup estab- lished in August 1991 to discuss topics related to tele- communications in the U.K Topics include services, prices, technical specifications, equipment function- ing and options, ISDN, and the various telephone carriers providing services. 956 mffiRNA See u.K. Education & Research Network- ing Association. UL See Underwriters Laboratories Inc. U1ex, Georg Ludwig (1811-1883) A German chem- ist, Ulex is remembered for having discovered Ulex- ite, the "TV rock," a unique mineral that projects light through its structure by internal reflection. Ulex found this rock in Chile in the mid-1800s. The mineral was named in his honor by renowned geologist/mineralo- gist James Dwight Dana (1813-1895), a correspon- dent of Darwin. See Ulexite. U1exite Afibrous substance of hydrated sodium cal- cium borate hydroxide. It is named for its discoverer, Georg Ludwig Ulex. Ulexite is a borate from the class of carbonates. The natural substance is found in the American southwest, South America and Kazakhstan. It ranges from translucent white to transparent and the chains of sodium, water, and hydroxide are linked in an interesting way. Like Iceland spar, Ulexite is asomewhat brittle, com- plex mineral with unique optical properties; when it has a veined structure, it can channel light through its fibers. For example, if a I-in. chunk of polished Ulexite is placed over an image, with the fibers per- pendicular to the image plane, the image is channeled through the mineral and projected virtually un- distorted upon the opposite (top) surface, much to the delight of the viewer. This capability has caused it to be dubbed the "TV rock." Synthetic versions ofUlexite are fabricated in a va- riety of marbled colors to have aesthetic appeal while still retaining some of the optical qualities of the natu- ral substance. Synthetic Ulexite may be coated on one side to maximize its light transmission properties. See Iceland spar. ULP See upper layer protocol. Ultra Sniffer A kit-based, handheld radio commu- nications receiver designed to facilitate radio direc- tion finding, especially for "fox hunts," during which hobbyists get together to try to find a hidden trans- mitter. This unit, from VK3TJNNKJXAJ, is a little larger than adeck of cards. It is attached to a 2-m cen- ter beam with three elements attached in the center at 90° from the center beam. The unit is designed to overcome some of the limitations of other radio di- rection finders in terms of overcoming interference and selective tuning without increasing complexity (and knobs). See fox, sniffer. ultra-high frequency UHF. A designation for a range within the radio frequency spectrum commonly used for broadcast communications, which ranges from 300 to 3000 MHz. ultra-high frequency (UHF) antenna Acategory of antennas which are designed to take advantage of the particular characteristics of ultra high frequency (UHF) waves. Because of the wavelength differences between UHF and very high frequency (VHF) waves and the relationship of the rods on the antenna to the length of the wave, it is possible to make UHF an- tennas relatively small, with more branching elements compared to VHF antennas. However, as UHF tele- vision broadcast signals are generally weaker than © 2003 by CRC Press LLC those from VHF, there is a greater potential for loss, and they must be designed and installed with greater care to be effective. See antenna, combination anten- nas, VHF antennas. ultraviolet Electromagnetic radiation with shorter wavelengths, between the violet part of the visible spectrum and X-rays. Although it cannot be seen by humans, ultraviolet radiation is of commercial sig- nificance because it can degrade many types of ma- terials and pigments. Commercially, it is used in a variety of lamps, such as arc lamps, and can be used to remove data from erasable/programmable com- puter chips. In astronomy, ultraviolet sensing devices use ultra- violet radiation focused through a spectrograph to study the characteristics of celestial objects. Tele- scopes and some satellites are equipped with this capability. The Hubble Space Telescope and the International Ultraviolet Explorer satellite enable study of objects using ultraviolet light near the vis- ible spectrum. The Johns Hopkins Ultraviolet Tele- scope extends the range to the far ultraviolet, that is, the region further from the visible spectrum. See in- frared. umbrella antenna An antenna that resembles an umbrella in that the lines extend out and down from a central pole. UML See Unified Modeling Language. UMPIX The USOC code for telephony-related main- tenance plan, tier 1, per line. VMSP See Unified Memory Space Protocol. VMTS See Universal Mobile Telecommunications Systems. unattended call A situation that occurs when, for example, an automatic dialing system dials a line, then tries to pass the call to the first available human agent, but no agent is available. Consequently, the call is abandoned. This type of calling occurs in the tele- marketing industry and the call is terminated in or- der not to irritate a potential customer. Unattended calls are also used by collection agencies and the sys- tem hangs up if no agent is available or if the call is answered by an answering machine, thus not imping- ing on the agent's time. unattended systems Devices or systems which func- tion without a human operator or without significant human attention except for installation and routine maintenance and upgrades. Unattended systems have become prevalent since the late 1970s, when com- puter automation became inexpensive enough to in- corporate into a wide variety of components and ma- chines. Computer bulletin board systems were some of the frrst information-rich systems to function 24 hours a day, and phone systems now are frequently automated with menu selections and voice mail op- tions. Recently, faxback systems allow users to re- quest product information or technical support in the form of fax documents. The system logs the phone call, gets the customer's document selections from a list of options, then dials back the user's fax machine and transmits the requested documents. Unattended systems generally function 24 hours per day at a sig- nificant cost savings over human operators. Many businesses are willing to give up personalized service in favor of the economy offered by automated sys- tems. See Auto Attendant. unbalanced line A transmission line with two con- ductors (such as coax or a telephone circuit) with unequal voltages with respect to the ground. In phone circuits, this is generally an undesirable condition. unblanking The portion of the sweep in a cathode- ray tube (CRT) where the beam is turned on, with pulses from the generator. See blanking. unbundled Products or services which are sold sepa- rately. For example, a company may release a graph- ics card/monitor combination as a package deal, and later unbundle the items, that is, allow them to be sold separately in order to clear the products, get a higher return, or respond to market demand for one product over the other. Contrast with bundled. Unbundled Network Elements UNE. Telephone network services that are sold or leased through com- petitive local exchange carriers (CLECs) as un- bundled services from an incumbent local exchange carrier (!LEC). These physical and functional ser- vices, when broken down (unbundled) into discrete components, make it possible for them to be mixed and matched into a variety of new services that may be optionally resold or leased to endusers by a vari- ety of providers. UNEs came about as a result of the competition-supporting provisions of the Telecom- munications Act of 1996. UNEs include such aspects as local loops, switches, information (databased) ser- vices, etc. The UNE model and Congressional decisions regard- ing UNE were controversial. In 1997, AT&T re- sponded to a Circuit Court decision that defeated key provisions of the Federal Communications Commission's (FCC's) rules on UNEs. AT&T's po- sition was that the rulings could open the door to com- petitive restructuring of existing services and mo- nopolization of new services by competing provid- ers, but at a higher cost, which would not result in the desired competitive benefits to users. Unbundled Network Elements - Platform In tele- phony parlance, UNE-Platform (UNE-P) services are combinations of Unbundled Network Elements (UNEs) that provide finished (end-to-end) services to Competitive Local Exchange Carriers (CLECs) that are functionally equivalent to retail service of- ferings. UNE-P products are intended only for resale to endusers, not for the use of carriers themselves. Examples of UNE-P services include plain old tele- phone service (POTS), public access line (PAL), ISDN Pri and Bri, digital switched service (D8S), and Centrex services. UNC See Universal Naming Convention. underfill In semiconductor circuit assembly, mate- rial that seals components or fills holes or gaps, of- ten around solder joints where chips attach to circuit boards. Underfill may insulate from possible electri- cal shorts or may provide structural support. It may also help prevent abrasians and corrosion. Underfill requires extra materials and time, and may need to 957 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary be cured, and thus is not always used, even when it might improve fabrication quality. underfill, optical A situation in which the amount or intensity oflight present does not fully fill an ap- erture or grating structure or meet operational mini- mums of a component. If apoint light source is much narrower than an opening through which it is shin- ing, the opening is said to be underfilled. Similarly, ifa light source is smaller than the acceptance cone of a light-carrying component, it is said to be underfilled. In grating structures, which have differ- ent geometries depending upon the direction of the incident light, the structure may be optimally filled or overfilled in one plane and underfilled in others. In coupled optical fibers, particles or back reflection may result in loss of light at the junction and under- fill of the succeeding link in the light path. There is a relationship between the F number (aper- ture diameter) and an illumination target (grating, mirror, light pipe, etc.) such that a higher F number may underfill the aperture. Sometimes underfilling is desired and may improve resolution. At other times it may result in incomplete or ineffective function- ing of a system. See acceptance cone, overshoot. Undersea News Service An international submarine fiber optics news service that features selected press releases from major newswire services, compiled and published by KMI Corporation. See KMI Corporation. undershoot See overshoot. Underwriters Laboratories, Inc. UL. UL is a not- for-profit organization established in 1894. It provides conformity, safety, and quality assessment services and publications to a variety of organizations, includ- ing manufacturers. In addition, UL provides educa- tional materials, input to international safety systems, and assistance to various regional authorities. UL publishes a catalog of its standards and the stan- dards themselves in print, on microfilm, CD-ROM, and diskettes. The UL also sponsors a UL Standards Electronic BBS (accessed directly, or through the Web). The majority of the UL published standards have been approved as American National Standards by the American National Standards Institute (ANSI). UL has a number ofpublications of interest to pro- fessionals in the communications industry, including WireTalk for the wire and cable industry. http://www.ul.com/about/wtalk/index.htrnl UL provides ISO 9000 standards quality registration through its accredited RvA, Registrar Accreditation Board (RAE) and other international quality affilia- tions. It provides information on new international environmental management standards through ISO 14001. The full UL catalog is available on the Web, but the Sampling of UL Standards chart shows some tele- communications-related UL Standards which may be of interest and which provide an idea of the types of use and safety issues concerned. http://www.ul.com/ Underwriters LaboratoryInc. assessment The UL provides a number ofconformity assessment services for product certification. These include listing, clas- sification, field engineering, and various types of safety and performance testing. The UL Conformity Assessment services chart shows some of the services relevant to telecommunications. Underwriters Laboratory Inc. Mark UL Mark. UL provides a number of listing marks to indicate that products or systems have been evaluated by UL and conform to certain specifications. Those shown in the UL Listing Marks chart are relevant to telecommu- nications. UNE See Unbundled Network Elements. UN! User Network Interface, User-to-Network Inter- face. As specified by the ATM Forum, an ATM network UL Conformity Assessment Services Related to Telecommunications Service Brief Description Listing Service A UL Listing Mark indicates that representative samples have been tested and evaluated according to nationally recognized safety standards. Classification Service A UL Classification mark indicates that products have been evaluated for certain properties under specified conditions. Component Recognition A service for factory-installed components in complete products. Certificate Service A service for completely installed systems. Field Engineering Service A service for installed products without UL Listing Marks or UL Classification Marks. Testing Environ. Products Evaluation of innovative environmentally friendly products. LAN Cable Performance Safety evaluations and evaluation of LAN cable according to industry performance specifications, including TlAIEIA standards. Energy Efficiency Electrical appliances are certified according to U.S. or Canadian standards for energy efficiency through the UL Energy Verification. SDS Verification Testing Verification of input/output products to Honeywell's Smart Distributed System (SDS) for compatibility of components to an industrial control communications network. 958 © 2003 by CRC Press LLC switch which interfaces user equipment to private or public ATM network equipment, or connects between Customer Premises Equipment (CPE) and public net- work equipment. See PMP, PCR, OeD, SCR. Unicamp A group at the State University of Campinas, Brazil, formed in 1975 to deveop optical fibers for TELEBRAS (Telecommunica~oes do Brasil). The majority of optical fiber produced in Brazil is based upon research in optical communica- tions, nonlinear optics, and other phenomena re- searched by Unicamp. unicastA type oflntemet Protocol (IP) address iden- tifier for a set of interfaces. Unicast transmits a single Protocol Data Unit (POD) to a single destination (un- like multicast, where it may go to multiple destina- tions). The fonnat of the ATM subinterface unicast command is: atm smds-address <address>. See anycast, IPv6 addressing, multicast. Unicode A character-encoding standard to support text-encoding in data files. Unicode, Inc. was origi- nallya collaboration between Apple and Xerox, who produced the original specification. They were later joined by Adobe, Aldus, Borland, ffiM, Microsoft, NeXT, Novell, Sun, and others. Unicode has been rolled in with an ISO specification as a subset of ISO 10646. Unicode is loosely based upon the widely sup- ported Ascn standard, but in a greatly extended fonn to include major world languages not represented with Roman characters, including Cyrillic, Greek, Arabic, Hebrew, Japanese Kana, Chinese bopomofo, Korean hangul, and others. Symbols, punctuation marks, mathematical symbols, and technical symbols are also supported. Unicode uses a 16-bit character set, supporting over 65,000 characters. Each charac- ter is assigned a unique 16-bit value. No special modes or control or escape sequences are needed. Unicode comprises the first 65,536 code points of the ISO 10646 standard; the rest are reserved for future use. See Unicode Consortium. Unicode Consortium A nonprofit association founded in 1991 to promote and support the accep- tance and implementation of the Unicode character- encoding standard. The Consortium publishes a pam- phlet on the Unicode specification. The Unicode Technical Committee, descended from Unicode, Inc., now functions as part of the Consortium to actively maintain the standard. See Unicode. unidirectional Moving, responding, or transmitting in one direction, or in only one direction at a time. Unidirectional Hypertext Transfer Protocol UHTP. A robust, unidirectional IP multicasting re- source transfer protocol suitable for one-way broad- casting over the Internet or over the television verti- cal blanking interval. The protocol allows many view- ers to simultaneously access the broadcast site. See broadcast data trigger. unified memory architectureA system o~ which the video display drivers are integrated into the mother- board, and system random access memory (RAM) is used to buffer graphics displays, rather than having them as separate systems. Some systems use this very effectively, providing graphics coprocessor chips, and allowing greater video graphics memory and more control over memory for programmers, applications, and users. On other systems, this type ofintegration slows down the graphics rendering and overloads the CPU. This is not the fault of the concept, but rather a result of how it is implemented. Unified MemorySpaceProtocol UMSP. Aconnec- tion-oriented network protocol corresponding to the session and presentation layers of the Open Systems Interconnect (OSI) model. UMSP was submitted as an Experimental RFC by A. Bogdanov in December 2000. UL Listing Marks Related to Telecommunications Listing Mark Brief Description UL Listing Mark Commonly seen, and indicates that samples of the product conform to UL safety requirements according to UL published standards for safety. C-UL Listing Mark Canadian market products evaluated according to Canadian safety requirements. Classification Mark Products evaluated for specific properties under specified conditions. These usually consist of industrial and building materials and equipment. C- UL Classification Mark Classification Mark products intended for the Canadian market. Recognized Specific to components used in products sold as complete units, and thus Component Mark not usually seen from the outside. There is also a Canadian version. International emc-Mark Products which conform to electromagnetic compatibility requirements of Europe and/or U.S. and/or Japan and/or Australia. Field Evaluated A product which is evaluated in the field rather than in a laboratory. Product Mark Facility Registration A facility which has passed UL quality assurance standards, Mark specifically ISO 9000-series and ISO 14001 (environmental). 959 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary UMSP uses transport layer service for reliable deliv- ery (with acknowledgment data). UMSP creates a network environment for organizing 128-bit address space distributed among Internet nodes. The proto- col defmes connections management algorithms and network primitive formats; it does not control local node memory. Connection parameters may be set in a number of ways and systems with high protection levels may be configured without restricting appli- cation functionality. See RFC 3018. unified messaging See integrated messaging. Unified Modeling Language UML. Awidely used modeling language for specifying, constructing, vi- sualizing, and documenting the artifacts of software systems. UML is intended to streamline and simplify the process ofsoftware design. It is a product of the Object Management Group. See Object Constraint Library, Object Management Group. Unified User Interface Dill. In the Envisat satellite data communications services, the Dill is a single interface to User Service Facilities that enables us- ers to access Envisat data services from any station or access node using a standard Web browser. The UUI interprets the browser commands to the service functions in the Envisat-l Payload Data Segment (PDS). Uniform Commercial Code UCc. An adopted code for conveying, clarifying, and permitting commercial activities within the provisions of the UCC Act as they apply to commerce within the 50 U.S. states and some of its territories. The Act sets forth the terms and con- ditions for commercial policies and activities de- scribed within the Act, concepts applicable to law, including actions, contracts, and remedies related to commercial endeavors and disputes. The UCC does not strictly dictate the terms ofcontracts and agree- ments between parties, but it helps to provide guide- lines and default terms that provide a measure of con- sistency and security for those conducting commer- cial transactions. The Permanent Editorial Board for the Uniform Commercial Code provides oversight and permission for the distribution ofUCC informa- tion. The Board publishes reports and drafts related to UCc. See Uniform Computer Information Trans- actions Act. Uniform ComputerInformation Transactions Act UCITA. This was formerly an Article of the Uniform Commercial Code. However, with the growth and prevalence ofconcerns specific to computing, it was felt that there was a need for a separate, related Act. This became especially true when a large amount of electronic commerce began to flow across the Inter- net. UCITA is a uniform commercial code for soft- ware licensing and other computer information-re- lated transactions adopted by the National Conference of Commissioners on Uniform State Laws in July 1999. See Uniform Commercial Code. http://www.ucitaonline.com/ uniform line A line which has essentially identical electrical characteristics throughout the transmission path. Uniform Resource Agent URA. An architecture for an agent system to provide Internet information ac- cess and management. Encapsulation of protocol- specific actions enables the addressing ofhigh-level Internet activities. It is a structured mechanism for abstracting characteristics of desired information and distancing access processes from the client. The URA system was submitted as an experimental RFC by Daigle et al. in October 1996. See RFC 2016. Uniform Resource Characteristic URC. A data for- mat for including meta-information, information out- side the resources in question, for the identification and location of these resources on the Internet. See Uniform Resource Identifier. When URCs were pro- posed, in the mid-1990s, it was suggested that they be used in conjunction with Uniform Resource Names (URNs) instead ofURLS, to remove location dependencies. Uniform Resource Identifier URI. A means to iden- tify resources on the Internet. Because of the size and structure of the Internet, these resources may exist in one or more locations concurrently or may at times not be available at all. The syntax and encoding of the names and addresses of objects has been gradually developed since 1990, Common Uniform Resource Locator (URL) Schemes Scheme Name Type ftp File Transfer Protocol Files and directories http Hypertext Transfer Protocol Internet resources, Web pages gopher Gopher Protocol File directories in Gopherspace mailto Electronic mail address Internet electronic mail address news USENETnews Newsgroups and individual articles nntp USENET news using NNTP access Alternate means of accessing news telnet Reference to interactive sessions Interactive telnet remote logon sessions wais Wide Area Information Servers WAIS databases, searches, documents file Host-specific file names Accessible files from various hosts pro spero Prospero Directory Service Resources on the Prospero service 960 © 2003 by CRC Press LLC with URIs used to manage registered protocols or name spaces. A URI uses network protocols to ex- press an address which maps onto an access algo- rithm. This is important because the Internet functions with many different protocols for the transmission and sharing of data. In most cases, the data can be converted to accommodate diverse formats. How- ever, some types of information are impractical to convert, such as names and addresses of resources. By creating a type of object that can be labeled for recognition and retrieval and a name space in which these objects can reside, access and use of this infor- mation can be facilitated. A Uniform Resource Lo- cator is an example ofa URI. One of the more interesting developments on the In- ternet has been the establishment of broadcasting channels over which video and audio radio and tele- vision programming can be viewed through Web browsers and various other specialized software pro- grams. This has necessitated the definition and orga- nization of URIs appropriate for digital broadcasts. See Uniform Resource Characteristic, Uniform Re- source Locator, Uniform Resource Name, RFC 1630, RFC 1736, RFC 1737, RFC 2396, RFC 2838. Uniform Resource Locator URL. A compact string representation for a resource available on the Inter- net. URLs have been in use since 1990 as Universal Resource Identifiers in WWW. A URL is a means to locate resources, by providing an abstract identifica- tion of its location. Generally, a URL follows this format: <scheme>:<scheme-specific-part> Examples: http://www.abiogenesis.com/telecomdict ftp://www.peanut.org/ Scheme names consist of a sequence of lowercase characters from a to z, numerals 0 to 9 and the char- acters "+" (Plus), "." (period), and "." (hyphen). It is recommended that upper case be treated as lower case in resolving a URL. A number of specific schemes for particular proto- cols are standardized or commonly used and there is a process for registering new ones. Common schemes (typed in lower case when used in a URL) are shown in the Common Schemes chart. See RFC 1630, RFC 1738, RFC 1808, RFC 2396. Uniform Resource Name URN. Similar in concept to Uniform Resource Locators as a means to iden- tify a resource or unit of information on the Internet, but intended to manage an object space of names ex- pected to have a longer shelf life. URNs provide a globally unique means of identifying information about a resource or access to the resource itself. Func- tional specifications for URNs were proposed by Sollins and Masinter and presented as a Request for Comments in 1994. See Uniform Resource Charac- teristics, Uniform Resource Identifier, RFC 1737. Uniform Resource Name Namespace for Object Identifiers URN Namespace for OIDs. On the In- ternet, an Object Identifier is a tree of nodes, syntac- tically described as a series of delimited digits. For example, the Internet OlD is 1.3.6.1. The OlD name- space specifies how an Object Identifier (ASN.l) is encoded as aUniform Resource Identifier. The ISO/ IEC Joint Technical Committee is the declared reg- istrant of the namespace. The scheme was originally submitted by M. Mealling as an Informational RFC, in November 2000, and up- dated in February 2001. See RFC 3061 which obso- letes RFC 3001. Uniform Resource Name Namespace for Public Identifiers URN Namespace for PIDs. Anamespace designed to enable Public Identifiers to be expressed in Uniform Resource Identifier (URI) syntax. Within XML, a public identifier is a simple string and, his- torically, public identifiers are not legal URIs in the context of the Web. The URN namespace enables public identifiers to be encoded in URNs in a reli- able, comparable way through introduction ofa for- mal public identifier namespace (publicid). The URN namespace scheme was submitted as an Informa- tional RFC by Walsh et a1. in August 2001. See RFC 3151. uniformity The capability of a broadcast or other communications medium to deliver a steady and con- sistent signal within the desired range. uninterruptible power supply UPS. A safety and steady-service device which protects equipment and data by guaranteeing a sufficient and steady source of electrical power in the event that other power sources are interrupted or lost. UPS systems may take their current from an alter- nating power supply while the system is up, store charges from this source, and then switch to an alter- nate source, such as a direct current storage battery or separate alternate current generator in the event of power disruptions to the normal supply. UPSs are used on computers, phones, lighting sys- tems, and in emergency centers. :~~~r s;~eg~~,c~~~~fa~~;e[~ ~~~~~~~ ~:~~~~!. queues, backup file systems, and applications which are reading or writing to storage media at the time of a power outage. UPS systems can prevent loss of files in the process of being saved and prevent possible corruption to the medium on which they are being written. unipolar Having only one pole, direction, or polar- ity. unique useridentifier UUI. An administrative func- tion for uniquely recognizing or storing data on be- halfof an individual user. This may be a name, num- ber, symbol, token, or biometric equivalent, depend- ing upon the system. A username is a type of UUI commonly used to enable access to restricted com- puter systems. UUIs are used in association with thou- sands of different types of secured systems and ser- vices. The New Zealand Customs Service, for ex- ample, uses a UUI system to register users and to administer their EDI clients using the Customs Computerized Entry Processing System. unit vector In mathematics/geometry, a vector 961 © 2003 by CRC Press LLC . transmission band in the 1625 to l675-nm range. Distributed- feeback and continuous-wave laser diodes are avail- able in U-band frequencies. U-band systems are not as common as C-bandIL-band, but it has been sug- gested that U-band. unit (CPU). It is often implemented in addition to A-law companding and is suitable for compression of voice communi- cations. Note, this is technically J,l-law, but many key- boards don't support the Mu (J,l) character and so it is altematelywritten as Mu-Iaw or U-Iaw. In fact, it's even sometimes written M-Iaw since the Greek sym- bol for uppercase J,l is M. See A-law, Mu-Iaw. U-plane In ATM networking, as it applies to Broad- band-ISDN reference model, the U-plane is the user plane, a higher-level plane including all of the ATM layers, which bears user. LLC similar, the U-C is distinguished from the U-R inter- face due to the asymmetry of the link. See U-R. U-DSL The U interface in a Digital Subscriber Loop (D8L) system. V-law, Jl-law A pulse code modulation (PCM) cod- ing and companding data ITU- T standard used in au- dio systems on computer