Fiber Optics Illustrated Dictionary - Part 104 pdf

Fiber Optics Illustrated Dictionary WTD Wireless Telecommunications Bureau. An organization of the Federal Communications Commis- sion (FCC). WTLS See Wireless Transport Layer Security. WTO World Trade Organisation. An international organization established in 1994. As the Internet has become a significant vehicle for domestic and international commerce, the WTO has become involved in discussions about electronic commerce and in the debate regarding intellectual property and domain name registration. The functioning of the WTO has been scrutinized by critics who are concerned about ensuring that there is adequate accountability built into the function and makeup of the organization. WTPF See World Telecommunication Policy Forum. WWV A U.S. Government National Institute of Stan- dards and Technology (NIST) radio facility providing time and frequency standard voice announcements at a variety of high frequency (HF) broadcast wavelengths. WWVH operates 24 hours a day, 7 days a week from a radio station in Colorado. The time is announced by a male voice based upon a 24-hour clock at the Greenwich meridian. WWYH broadcasts on 5,10, and 15 MHz at 10,000 watts and on 2.5 MHz and 20 MHz at 2500 watts using individual transmitters for each frequency. WWV uses five half-wave vertical antennas. Modulation is double-sideband amplitude modulation (AM). See WWVB,WWYH. WWVB A U.S. Government National Institute of Standards and Technology (NIST) radio facility providing time and frequency standards broadcast at 60 kHz with 50 kW of power from Fort Collins, Colo- rado. WWVH operates 24 hours a day, 7 days a week. Unlike WWV and WWYH, this is not a voice an- nouncement service, but rather a reference based upon a stable radio frequency transmission that can be traced to the national standard. At WWVB, a time code is synchronized with the carrier for continuous broadcast at a rate of I bps using pulse-width modulation. The time code bits are pro- duced by reducing and restoring carrier power, thus creating a low/high binary system that is used to represent decimal numbers. In this manner, the time code conveys the current year, day, hour, minute, and second along with flags that indicate Daylight Savings Time (DST) and leap year/leap second status. WWVB uses two top-loaded dipole antennas utiliz- ing four towers in a diamond configuration with ca- pacitance cables suspended between the towers. Commercially available clocks and wristwatches that derive their time from NIST-based WWVB broadcasts can be used within the continental U.S. There are also software clients that enable Internet-con- nected computer users to synchronize their computer time with NIST time. This type ofcapability will become increasingly important as auction sites, stock sites, and other types of time-sensitive public network-based electronic commerce services become more widely used. See binary coded decimal, WWV, WWYH. 1022 WWVH A U.S. Government National Institute of Standards and Technology (NIST) radio facility providing time and frequency standard voice announcements at a variety of high frequency (HF) broadcast wavelengths. WWVH operates 24 hours a day, 7 days a week from a radio station in Hawaii. The service includes time announcements, standard time inter- vals, time frequencies, time corrections, BCD time code, and various weather and Global Positioning System (GPS) reports. The time is kept within 1 mi- crosecond of Coordinated Universal Time (UTC), but will become delayed as it propagates out from the source. In other words, there is lag time (travel time) from the radio station to the receiver that is depen- dent upon distance and atmospheric conditions. There can be delays up to 10 or 40 milliseconds, depending upon whether the user is listening through a radio receiver or a telephone receiver. The time is announced by a female voice ("At the tone the time will be II''') based upon a 24-hour clock at the Greenwich meridian. Since 1964, the female voice has been that of Jane Barbe, whose recorded messages are used on millions of telephone and time- related products. WWYH broadcasts on 5, 10, and IS MHz at 10,000 watts and on 2.5 MHz at 5000 watts using individual transmitters for each frequency. The 5-, 10-, and IS-MHz frequencies use phased-array vertical dipole antennas (driven 90° out of phase), whereas the 2.5-MHz frequency uses half-wave vertical antennas. Modulation is double-sideband amplitude modulation (AM). See Barbe, Jane; WWV; WWVB. WWW See World Wide Web. WWWC See World Wide Web Consortium. WYGIWYD (pron. wiggy-wid) Abbreviation for "what you got is what you deserve." In other words, if you made a bad decision on your own behalf or one you communicated to others to direct their work, you should accept the responsibility and the conse- quences. WYPFIWYG (pron. wip-fee-wig) Abbreviation for "what you pay for is what you get." The concept applies as much in fiber optics and computer technology as anywhere else. If you buy a cheap system, you may pay more later for adding extra memory, sound cards, graphics cards, hard drive controllers, CD- ROM drives, etc. The same applies to network server software. WYSIWYG (pron. wiz-ee-wi~) Abbreviation for "what you see is what you get.' A desktop publishing term that refers to a computer display ofa document or image that looks on the screen the way it would look on the intended output device, usually a printer. The term became prevalent when desktop publishing programs on the Macintosh could be printed on Adobe PostScript-capable printers, begin- ning in the mid-1980s. Up to this time, 9-pin dot matrix printers were prevalent and no matter how nice a document looked on the screen, it rarely looked that spiffy on the dot matrix printout. WZI See World Zone. © 2003 by CRC Press LLC x, x 1. symb. an unknown, situational, derivable, or arbitrary quantity. Commonly used in mathematics and software programming, written both lower- and uppercase, and often italicized as in 4 +x = 10. The symbol is also often used in product identification to indicate a family ofproducts, e.g., xDSL for the family ofDigital Subscriber Line services. 2. abbrev. cross. 3. abbrev. exchange. 4. abbrev. external. 5. abhrev. trans- (prefix). 5. The USOC Federal Com- munications Commission (FCC) code for complex multiline or series jack. 6. colloq. See X Window System. Xaxis, x axis A geometric convention for coordinate systems (e.g., Cartesian coordinates) designate the horizontal axis as the X axis. When graphing pro- cesses that may occur over time, the X axis is often used for the time variable. X Consortium A group that continued the development and management of the X Window System, now part of the Open Group. See X Window System. X Cut An X cut creates a crystal plate with the plane perpendicular to the crystalsX axis. X cutA type of cut used with piezoelectric crystals. Crystals are used in radio wave detection and timing applications, and their piezoelectric properties are partly detennined by their shape and size. See crystal, quartz, piezoelectric, X-ray goniometer, Y cut, Y bar. X Protocol A low-level client/server standard communications protocol that handles window manipulation routines for the graphical user interface (GUI) X Window Systems. See X Window System. XSeries Recommendations A set oflTU-T recommended guidelines for interconnecting networks and network devices. These are available for purchase from the lTU-T and a few may be freely downloadable from the Net. This is a large category; some of the X Series Recommendations of particular interest are listed in the following charts, organized into three categories. See Appendix C for a general list of the different categories. See also individual listings under G, I, Q, and V Series Recommendations. X Window System, The X Window System, X Windows, X, X.tt Hardware-independent founda- tion software for the development ofgraphical user interfaces (GUIs) based upon a client/server model. The X Wmdow System is a nonproprietary, distributed, multitasking, network-transparent protocol that has been implemented on many different Unix-based systems. Originally used as a graphics display protocol for text-based UNIX platforms, developers are rec- ognizing and exploiting its ability to enable popular ass to run on a UNIX workstation or, conversely, to run UNIX applications on popular hardware platforms, and to run applications from within Web browsers. Development tools such as Motif facilitate the quick design ofX GUIs. The X Protocol is an X Windows System client/server protocol and the X server is a client/server process that controls a display device on the system. X Windows code for noncommercial purposes is freely downloadable from The Open Group Web site. As ofversion XIIR6.4, commercial users must pay alicense fee to continue support for development ef- forts. See Athena project. http://www.opengroup.org/ XWindow System 11 Release 6.x (X 11 R6.x) A sub- stantial initiative by The Open Group to enable the X Window System to be used to create and access interactive World Wide Web applications through the X Window System and a downloadable plugin. Ap- plications linked to the Web using XIIR6.x can be found, accessed, and executed with the same Web browsing utilities used to access current static HTML documents. This may become a very significant means of networking through the Internet. See X Window System. 1023 © 2003 by CRC Press LLC Fiber Optics III us trated Dictionary lTU-T X Series RecommendatioDs Prevalent Formats X.25 Definitions of the procedures for exchanging data between user devices (DTEs) and network nodes in a public switched packet data network (PSPDN) in order to provide a common interface across a variety of systems. X.2Sis a layered packet transmissions protocol commonly used in wide area networks (WANs). AversionofX.25 specifically designed for packet radio. has been developed as AX.2S. X.400 An international ISOIITU-T series of standards. for electronic messaging architecture for the exchange of data between computer systems. X.400 was published by the ITU~T in 1984.·The standard wasjointly rewritten by.ISO and lTU-Tin1988. X.400 does notstipulate the fonnatting ofdata. It provides guidelines for intemetworking various messaging systems,•addressing individual messages,. and· describing. message contents. Within X.400. there are also substandards and recommendations to X.400, some of which are: X.402 describes the overall architecture;X.420 describes email· transfer; X.43S defines the electronic movement of Electronic Data Interchange (ED I); and X.440 describes ··voice messaging ·· See Electronic Data Interchange. X.445 Asynchronous· Protocol Specification (APS). A commercially promoted multiple media client/server extension of the X.400 standard that facilitates the exchange of digital data overpublic phone networks rather than X.25 standard leased lines. X.SOO .Adirectory serviceprotocol for building distributed global directories. It was developed in response toa.need to design directories that would not experience the same problems and bottlenecks thatwere developing with many of the large databases being accessed by thousands or millions of users on the Internet X.SOO employs decentra1izedmaintenance, searching capabilities· for · complex queries, homogenous global namespace, and a structured standards-based information framework. 1024 Recommendations of Particular Interest X.I International user classes afservice in, and categories of access to, public data networks and integratedservices digital networks (lSDNs). Includes information on access to leased or switched circuits by data terminal equipment (DTEs) in various modes, access by facsimile terminals, and access to Frame Relay systems. X.6 Multicast service definition. Service defmitions and capabilities of a multicast service providing a common model for the description of service elements. Interface specifications and protocol elements are not specified by X.6. X.31 Support of packet mode terminal equipment by an ISDN. Service and signaling procedures definitions operated at the Srr-reference point of an ISDN for subscribing packet mode terminal equipment and terminal adapter functionalities to support existing X.25 terminals at the R- reference point of the ISDN. X.7S Packet-switched signaling system between public networks providing data transmission services. A description of packet-switching signaling systems among public data networks. X.76 Network-ta-network interface between public data networks providing the Frame Relay data transmission service. A description of interface interconnections between Frame Relay networks and.public data networks, Layer, data transfer, and signaling information are provided. X.77 Internetworking between PSPDNs via B-ISDN. Definitions of procedures for intemetworking thatinclude reference configurations, protocol stacks, and signaling procedures. X.121 International numberplanfor public data networks. A description of the design, characteristics, and applications of the Ilwnbering plan for public data networks. The International Number Plan was developed to facilitate th~ linking of public data networks with the © 2003 by CRC Press LLC 1025 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary 1026 © 2003 by CRC Press LLC ••. I3rie~;t.isfinmp~!:.fRpttt1e:r .EXampl~sj . OOI'l~~::iJ :.::/ .: :: ' .::: .: -"::'."':".::- : : > : :. ~:'.' • '. ~:13:S.··.'·:·:!SI.1~n:·.·~~:s~ce.! ••• ~aela!:·~Q.·.ffirougI;tp~f~·.' ·~· .;".< Description u.s. wholesale banking standard for transaction authentication. Financial Institution Key Management standard for wholesale transactions. Defines protocols for the transfer of encryption keys using symmetric techniques. U.S. standards for digital signatures based upon the Digital Signature Algorithm (DSA) using the SHA-l hash algorithm. U.S. standards for digital signatures based upon the RSA algorithm based upon the MDC-2 hash algorithm. Certificate management encryption schemes. A draft standard for key agreement based upon the Diffie-Hellman algorithm. A draft standard for key transport based upon the RSA algorithm . X9.9 X9.17 Title X9.31 X9.30 X9.44 X9.42 X9.57 X Window System history X was originally developed by Robert Scheifler and Ron Newman from the Massachusetts Institute of Technology (MIT) and Jim Gettys ofDigital Equipment Corporation (DEC) to provide auser interface for the Athena Project. It has been further developed by The X Consortium and is now trademarked and managed by The Open Group. See Athena project, X Window System. X9 standards An important set of standards defined by the American National Standards Institute (ANSI) for the financial industry that has many ramifications for secured transactions over computer networks. The X9 standards cover such aspects as personal identification number (PIN) management, electronic transfer of funds, transaction processing, security mechanisms. Abrief summary of some of the X9 security- related standards includes See RSA Security Inc. X.25 Awidely implemented, significant, connection- oriented, packet-based communications protocol used in local and wide area networks. The protocol was developed in the mid-1970s, when analog networking over noisy copperconnections was optimized for voice rather than data communications. It helped to fulfill a growing need for a common language to interconnect local area networks that often used pro- prietary network protocols and for error mechanisms that could overcome the problems associated with marginal connections. In 1976, the CCITT (now the ITU) recommended X.25 for international data exchange. It was approved and subsequently revised every 4 years or so. In general, X.25 is a three-layer model that includes a physical level, a link level, and a packet level that are, in turn, associated with the lower physical, data, :' . . ':-:. ;.:':. ' :':;"::'" : ., ~ ' .:'" ''':::.~;:: >::i;.:~:·:'~:.:.,:·" . ~: ,.:.,.: .:::::.: .'. 1027 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary and network layers of the hierarchical Open Systems Interconnect (OSI) model. Basic Overview ofX.25 Levels Name Level # Description Physical 1 The electromechanical, procedural, and functional interfaces between the data terminal equipment (DTE) and the data circuit-terminating equipment (DCE). This level is specified by lTV -TX and V Series Recommendations that apply to modems and interchange circuits (e.g., X.21). Link 2 Also called the frame level, the link level ensures reliable data transfer between the DTE and the DCE in an efficient, timely manner. It synchronizes transmitter/receiver interactions, and detects and handles errors. A number of link access protocols may be implemented at the link level. Packet 3 Also called the network level, the packet level creates the network data "chunks" with appropriate controll error information and user data payload. Various virtual circuit (VC) and datagram services are handled at this level. Data is formatted into X-25 data packets by "packet- izing" the data into smaller chunks and adding the appropriate protocol information into each packet header. Error mechanisms are also included to enable retransmission if packets are lost. X-tO ProtocolA protocol for sending radio frequencies (RF) signals over power line carriers (PLCs). In other words, a radio frequency-emitting device can be plugged into a wall socket and the protocol will enable device control signals to be sent through the wiring (over the alternating current power curve) to compatible devices set to the same settings as the controlling devices. Lately, wireless X-I O-compatible transmitters are being added to commercial catalogs, with transmission ranges of up to about 100 feet. See CEBus, LONWORKS. X-bandAn assigned spectrum in the microwave frequencies of approximately 8 to 12 GHz with wavelengths ofjust a few centimeters. X-band signals are not significantly hindered by the Earth's atmosphere unless a lot of moisture (e.g., rain) is present. X-band frequencies are used by military satellites and deep- space vehicles. See band allocations for a chart of assigned frequencies. X-Bone A system designed to facilitate and automate the rapid deployment and management of multiple overlay networks. X -Bone is an overlay technology 1028 combined with teleconferencing-style coordination and management tools. X-Bone provides a virtual networking infrastructure that is configurable. While X-Bone is intended to be implemented with networks running more advanced systems, such as IPv6, some of the automatic tunneling services can be deployed to a limited extent on IPv4 systems. See 6bone, Mbone, overlay network, X-Bone xd. X-Bone xd An X -Bone directory tool for performing a number of tasks including the coordination of re- source sharing at the local site, the support of local daemons through authentication, configuration, and creation of IP-encapsulation tunnels between daemons, and the provision ofa user interface and API for users or programs wishing to manually parameter- ize and override overlays. See X-Bone. X-dimension ofrecorded spotIn facsimile transmissions, a means of describing variation density in tenns of the minimum density. The largest center-to-center space between recorded spots is measured in the direction of the recorded line. This can also be as- sessed perpendicular to the recorded line as the Y-dimension ofa recorded spot. The same principles can be applied to assess the scanning spot. X-ray Aradiant energy within the spectrum of high energy, invisible, ionizing electromagnetic radiation that ranges about 0.08 nm in wavelength, between ul- traviolet light and gamma rays. X-rays were somewhat naively and irresponsibly used in early radio signal and human anatomy experiments. These prac- tices are now used with great care due to the damag- ing influence ofX -rays on living cells. X -rays are used in many medical, industrial, and fabrication applications. See X-ray goniometer; Roentgen, Wilhelm Konrad; scintillator. X-ray goniometer An instrument for detennining the position of the axes in a quartz crystal. X-rays are aimed at the atomic planes of the crystal and the re- flected rays are evaluated. Since crystals are physi- cally manipulated to alter their oscillating properties and often cut in very thin slices, it is important to know the orientation of the crystalline structure be- fore cutting. See quartz, X cut, Y cut. X-ray spectrometer An instrument that is used, by means ofreflected rays and evaluation of the result- ing diffraction angles, to study the characteristics and composition of materials, including crystals. See X- ray goniometer. X/Open A global, independent organization of computer manufacturers founded in 1984. X/Open seeks to promote an open, multi vendor Common Applica- tions Environment (CAE) to enhance application portability. This is a good concept, as it allows software developed by different vendors to run on a variety ofplatforms, leaving the choice of equipment up to the individual purchaser. See Common Appli- cations Environment, Open Systems Interconnection. X/Open Federated Naming A naming mechanism from the X/Open group for developers to access network naming services and to provide integration with industry-accepted naming services such as X.SOO, Domain Name Service (DNS), DCE, and others. © 2003 by CRC Press LLC X/Open PortabilityGuide XPG. A guide document- ing the X/Open common applications environment system. XA extended architecture. XA-SMDS See Exchange Access SMDS. XAPIA X.400 Application Program Interface Asso- ciation. See X Series Recommendations. Xaw The Athena Widget set. A set of widgets distributed with the X Window System, which began as Project Athena. See Athena, X Window System. Xbar abbrev. crossbar. See utility pole. XBase, XbaseA generic designation for applications that read and/or write dBase-compatible files. XC abbrev. cross connect. XCA extended communication adapter. XcoralA multiwindow text editor for the X Window System, that can be used in conjunction with a mouse. XCVR abbrev. transceiver. xd See X-Bone xd. XDL An object-oriented extension to the lTU- T-defined Specification and Design Language (SDL) for telecommunications systems. See Specification and Design Language. XDMA Xing Distributed Media Architecture. A commercial streaming media architecture for delivery of live and on-demand audio-video from Xing Technol- ogy Corporation. It is built around standards such as TCP/IP and MPEG, and supports multicasting to multiple simultaneous users over local area networks (LANs) and wide area networks (WANs). XDMAcan be implemented over ISDN networks for services such as news and distance learning. XDMCP X Display Manager Control Protocol. A protocol used to communicate between X terminals and UNIX workstations. XDR See External Data Representation. xDSL Generic term for a variety of digital subscriber line technologies, which include ADSL, EDSL, and HDSL. See digital subscriber line and individual listings for further information. XENIX A Unix implementation best known as being from the Santa Cruz Operation, Inc. (SCO), it was originally codeveloped by International Business Machines (IBM) and Microsoft as XENIX-ll for Intel machines. SCO is now marketing UnixWare 7. xerographic printer A printer that uses the same basic electrostatic mechanisms and techniques as a xerographic copier. The information is imaged onto a drum with lasers, the printing medium is passed across the drum and picks up the dry transfer toner, which then fuses the toner to the printing medium. Xerox Corporation One of the first companies to see the commercial benefits of new photocopying technology developed by Carlson in the early 1940s. When still a relatively new, small company, Xerox took a chance on the new photocopying invention that had been passed up by other companies. Xerox is now known throughout the world for its technology, especially in the replication industry, and many people refer to all photocopies as "xeroxes." See pho- tocopy for further information and an illustration of Carlson's patent. Xerox Network Services XNS. A multilayer, distributed file network architecture developed by the Xerox Corporation which is somewhat similar to TCP/IP. Unlike many networks from other vendors, XNS per- mits a user to use files and devices from a remote machine as if they were on a local machine. XNS functions compatibly with the third and fourth layers of the Open Systems Interconnection model (OSI). Xerox PARe Xerox Corporation's Palo Alto Re- search Center. This research center provided enor- mous impetus to early computer companies and software developers (e.g., Apple Computer Inc., Micro- soft Incorporated), especially those developing object-oriented systems and graphical user interfaces (GUls). PARC researchers invented mice and various laser printing technologies, developed Smalltalk; they generated one good idea after another throughout the 1970s and early 1980s, yet surprisingly few of these were commercially implemented or marketed through Xerox. Charles Simonyi, one of the early founding members ofPARC, was the demonstrator of the Alto, apioneer desktop computer that inspired many of those fortunate enough to see it in the early days. Later, Simonyi was hired by Microsoft to move the company into graphical applications. XFN See X/Open Federated Naming. XFR abbrev. transfer. XGA 1. See extended graphics adapter. 2. See extended graphics array. Xi'an The capital of the Shaanxi province in north- west China; firms in this region are major suppliers of broadband and optical networking products, including ADSL and fiber optic cables and components. XID exchange identification. In data networking, XIDs are request and response packets exchanged prior to communications between arouter and a network host. XID is used for device discovery, address conflict, resolution, and sniffing. The XID packet includes the parameters of the serial device, and a connection can only be negotiated if this configuration is recognized by the host. XIP abbrev. execute in place. A means to access memory and execute code on PCMCIA cards without having to load them into system memory first. See PCMCIA. XIWT See Cross-Industry Working Team. Xlib X Library. A program interface for the X Win- dows System. Xmission, Xmit abbrev. transmission, transmit. XML See Extensible Markup Language. XModem A widely used error-correcting network file transfer data transmission protocol developed by Ward Christensen in the late 1970s. XModem utilizes 128-byte packets, so files of various lengths will be padded to adjust the packet length and may be longer than the original file. The filename is not sent with the transmission. YModem, a successor to XModem, with support for longer data packets and file at- tributes, was developed by Chuck Forsberg. XModem is often used with computer modems to transfer files to and from bulletin board systems over 1029 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary traditional phone lines. XModem is not fast, but it has error correction and it's reasonably reliable. It's well supported, an important consideration since both ends of the connection have to agree on a protocol. Many service bureaus use XModem for file transfers, how- ever, check if they have ZModem, which is faster and capable of restarting an interrupted transmission from where it left off. See Kermit, YModem, ZModem. XModem-lK, XModem-K A variant of XModem that manages data in 1K (I 024-byte) packets. See XModem. XModem-CRC XModem with 16-bit cyclic redun- dancy checking (CRC) error detection mechanisms, instead of checksum. XModem-CRC can communicate with XModem versions that use checksum for error correction. XMP X/Open Management Protocol. XMS See Extended Memory Specification. XMT abbrev. transmit. XMTR abbrev. transmitter. XNMS MlCOM's commercial mM-licensed Intel- based desktop computer packet data network (PDN) network management system software. XNS See Xerox Network Services. XO abbrev. crystal oscillator. See crystal detector, quartz. XONIXOFF transmission on/transmission off. Com- mon flow control signals used between two commu- nicating devices or software programs, typically through modems. Since many transmissions media are inherently slow, there may be a delay between receiving a block of data and resuming transmissions. XONIXOFF signals allow the communicators to signal when to stop sending data and when to resume, in order to prevent loss or corruption. XONIXOFF is also known as software flow control. In newer high-speed modems, flow control may be handled by hardware, often in conjunction with specific types of cables. Flow control signals are not limited to modem communications. Ifa user is working on a terminal that understands XONIXOFF commands, usually signi- fied by Ctrl-S (stop) and Ctrl-Q (resume), then it is possible to suspend a listing or other activity and resume when it is convenient. Xover abbrev. crossover. XP AD external packet assembler/disassembler. XPG See X/Open Portability Guide. Xponder transponder. Xpress Transport Protocol XTP. A flexible, high- performance commercial multicast protocol to support a wide variety of applications from wide area networks (WAN s) to multimedia and realtime embedded systems. It was developed by an international group of representatives from academia, industry, and the government from 1987 to the early 1990s and was described by Strayer et al. in the early 1990s. It has been adopted as part ofMIL-STD-2204 (Survivable Adaptable Fiber Optic Embedded Network). XTP brings together the functionality ofUDP, TCP, and TP4, in addition to transport multicast, group management, Quality of Service (QoS) negotiation 1030 capabilities, rate and burst control, and error and flow control mechanisms. It is designed to operate over any network or datalink layer or may be implemented directly over anATMAAL. It can run in parallel with other transport protocols and thus can increase functionality without giving up interoperability. It is ex- pressly intended to separate the communication para- digm from error control policies. The protocol sparked interest in the development of a public domain version at Sandia National Labora- tories. This protocol is distinct from the lightweight eXpress Transfer Protocol originally developed by Protocol Engines, Inc. See multicast, XTP Forum. XRB transmit reference burst. xref abbrev. cross reference. XRF Extended Recovery Facility. XSI X/Open System Interface Specification. XSMP X Session Manager Protocol. XT 1. abbrev. crosstalk. 2. ffiM Personal Computer XT. SeeffiM. Xtalk abbrev. crosstalk. xterm A popular terminal emulator for the X Win- dow System that has been ported to several other op- erating systems. Xtenn lets you have more than one terminal window active at a time through a single modem, each with its own input/output process running independently of the others. XTP 1. See eXpress Transfer Protocol. 2. See Xpress Transport Protocol. XTP ForumA nonprofit group promoting the development and distribution of Xpress Transport Proto- col (XTP). A number of significant vendors, including Apple Computer, Hughes Aircraft, Lockheed Martin, Northrop-Grumman, Philips Research, and Silicon Graphics are involved in this effort, in col- laboration with XTP Forum Research Affiliates from universities and military labs around the world. XWA The callsign issued to ahistorically significant Canadian radio station, it stood for X-peri mental Wireless Apparatus. XW A was issued its first experi- mental license by the Department of Naval Service, in 1918, following about 3 years of discussion (and presumably some preliminary experiments). The first general broadcast licence was issued in Sep- tember 1919 to XWA as part of the Marconi Wire- less Telegraph Company. Broadcasts apparently began in December 1919. The pioneer broadcasts were primarily musical and, since few consumer radios existed at the time, the listeners were amateur radio enthusiasts. In May 1920, XWA aired its first regu- larly scheduled broadcast and the radio industry evolved quickly, with XWA becoming station CFCF in November 1920. See CFCF, radio history. XWindows, XWS See X Window System. XXXX A designation for the last four digits in a telephone number, usually used when the numbers are not yet known (or assigned). It represents any number between 0 and 9. XY cutA means of angle-cutting a piezoelectric crystal such as LGS so its electrical characteristics are between those of an X cut and a Y cut. See quartz, x- ray goniometer, X cut, Y cut. © 2003 by CRC Press LLC y symb. yocto See yocto Y 1. symb. admittance. The ease with which alternating current (AC) flows through a circuit, as opposed to impedance. See impedance. 2. Syrnbolforytbium. See ytbium. 3. symb. yotta See yotta 4. A general purpose programming language distributed from the University ofArizona in the early 1980s that is se- mantically similar to C, but without C pointers and structures. Y antenna A single-wire antenna with leads con- nected in aYshape, with the top part of the Ycorre- sponding to the transmission line. Since the top of the Y is closed, causing it to resemble the Greek "D" (delta), the Yantenna is sometimes also known as a delta matched antenna. This style ofantenna is commonly used for very high frequency (VHF) and frequency modulated (PM) signals. Yaxis, y axis Areference baseline or vector within a coordinate system, most often associated with rect- angular or Cartesian coordinates. The Y axis is oriented vertically by convention, perpendicular to a horizontal X axis in a two-dimensional system, and perpendicular to the Z and X axes in a three-dimensional system. See Cartesian coordinates, X axis, Z axis. Y bar A type of cut used with piezoelectric crystals in which the plane of the long direction is parallel to the crystal's Y axis. See Y cut. Ycable,YconnectorAcable or cable connector that splits from a single line or bundle into two usually equivalent lines or bundles. Sometimes called a Y splitter. Y cables are frequently used in audio applications to split a mono signal into two jacks (not the same as real stereo) to connect systems with different inputs and outputs, or to combine a stereo signal onto one jack. Y cables are also used to split power sources, as when adding an extra drive to a computer system. Depending upon the application, the Ycable mayor may not cause a degradation of the transmission once the signal is split. AY cable mayor may not be combined with other connectors or convert- ers. AY cable is usually functionally the same as a T cable, except that the "y" angle of the split is nar- rower than 180 degrees. See converter. Y cut A type of cut used with piezoelectric crystals. Crystals are used in radio wave detection and timing applications, and their piezoelectric properties are partly determined by their shape and size. See crystal, detector, quartz, piezoelectric, X cut, X-ray goniometer, Y bar. YCut A Y cut creates a crystal plate with the planeper- pendicular to the crystal sYaxis. YSeries Recommendations A series ofITU-T recommended guidelines for global information insfrastructure and Internet protocol aspects. These guidelines are available as publications from the lTU-T for purchase on the Net. Since lTU-T specifications and recommendations are widely followed by vendors in the telecommunications industry, those wanting to maximize interoperability with other systems need to be aware of the information dissemi- nated by the ITU-T. A full list of general categories is listed in Appendix Cand specific series topics are listed under individual entries in this dictionary, e.g., G Series Recommendations. See Y Series Recom- mendations chart. Ysignal Amonochrome (it's actually more descrip- tive to say grayscale) signal luminance transmission. When combined with a color signal, luminance provides brightness to the image. The relative absence ofaluminance signal is used to represent black, while the highest level of power applied to the luminance signal is used to represent white, with shades of gray in between. See Y IC. 1031 © 2003 by CRC Press LLC . frequency. The 5-, 1 0-, and IS-MHz frequencies use phased-array vertical dipole antennas (driven 90° out of phase), whereas the 2.5-MHz frequency uses half-wave vertical antennas. Modulation is double-sideband amplitude modulation (AM). See Barbe, Jane; WWV; WWVB. WWW See World Wide Web. WWWC See World Wide Web Consortium. WYGIWYD (pron. wiggy-wid). In other words, if you made a bad decision on your own behalf or one you communicated to others to direct their work, you should accept the responsibility and the conse- quences. WYPFIWYG (pron. wip-fee-wig) Abbreviation for "what you pay for is what you get." The concept applies as much in fiber optics and computer technology as anywhere else. If you buy a cheap system, you may pay more later for adding extra memory, sound cards,. Fiber Optics Illustrated Dictionary WTD Wireless Telecommunications Bureau. An organization of the Federal Communications Commis- sion (FCC). WTLS See Wireless Transport Layer Security. WTO World Trade Organisation. An