Fiber Optics Illustrated Dictionary - Part 104 pdf

Crystals are used in radio wave detection and timing applications, and their piezoelectric properties are partly detennined by their shape and size.. Recommendations of Particular Intere

Fiber Optics Illustrated Dictionary

WTDWireless Telecommunications Bureau.An

or-ganization ofthe Federal Communications

Commis-sion (FCC)

WTLSSee Wireless Transport Layer Security

WTOWorld Trade Organisation.Aninternational

organization established in 1994 As the Internet has

become a significant vehicle for domestic and

inter-national commerce, the WTO has become involved

indiscussions 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

WTPFSee World Telecommunication Policy Forum

WWV AU.S Government National Institute

ofStan-dards and Technology (NIST) radio facility

provid-ing time and frequency standard voice

announce-ments at a variety of high frequency (HF) broadcast

wavelengths.WWVHoperates 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

us-ing individual transmitters for each frequency WWV

uses five half-wave vertical antennas Modulation is

double-sideband amplitude modulation (AM) See

WWVB,WWYH

WWVBA U.S Government National Institute of

Standards and Technology (NIST) radio facility

pro-viding time and frequency standards broadcast at 60

kHzwith 50 kW of power from Fort Collins,

Colo-rado.WWVHoperates 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

car-rier 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

rep-resent decimal numbers In this manner, the time code

conveys the current year, day, hour, minute, and

sec-ond 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

broad-casts 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

be-come increasingly important as auction sites, stock

sites, and other types of time-sensitive public

net-work-based electronic commerce services become

more widely used See binary coded decimal, WWV,

WWYH

WWVH A U.S Government National Institute of Standards and Technology (NIST) radio facility pro-viding time and frequency standard voice announce-ments at a variety of high frequency(HF)broadcast wavelengths.WWVHoperates 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 ofCoordinated 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, depend-ing upon whether the user is listendepend-ing through a ra-dio receiver or a telephone receiver

The time is announced by a female voice ("At the tone the time will beII''')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 oftelephone 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."Inother 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 ap-plies as much in fiber optics and computer technol-ogy as anywhere else Ifyou 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 publish-ing term that refers to a computer display of a docu-ment or image that looks on the screen the wayit 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 ma-trix printers were prevalent and no matter how nice a document looked on the screen,itrarely looked that spiffy on the dot matrix printout

WZI See World Zone

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

fam-ily of Digital 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

X axis, x axis Ageometric 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

develop-ment and managedevelop-ment ofthe 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

per-pendicular to the crystalsX axis.

X 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 detennined by their shape and size See

crys-tal, quartz, piezoelectric, X-ray goniometer, Ycut, Ybar

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

X Series Recommendations A set oflTU-T recom-mended guidelines for interconnecting networks and network devices These are available for purchase from the lTU-T and a few may be freely download-able from the Net This is a large category; some of the X Series Recommendations ofparticular 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 un-der G, I, Q, andVSeries Recommendations

X Window System, The X Window System, X Windows,X, X.ttHardware-independent founda-tion software for the development of graphical user interfaces (GUIs) based upon a client/server model The XWmdow System is a nonproprietary, distributed, multitasking, network-transparent protocol that has been implemented on many different Unix-based sys-tems Originally used as a graphics display protocol for text-based UNIX platforms, developers are rec-ognizing and exploiting its ability to enable popular ass torunon a UNIX workstation or, conversely, to run UNIX applications on popular hardware plat-forms, and to run applications from within Web browsers Development tools such as Motiffacilitate the quick design of X GUIs

The X Protocol is anXWindows 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 of version XIIR6.4, commercial users must pay

a license fee to continue support for development ef-forts See Athena project http://www.opengroup.org/ XWindow System 11 Release 6.x(X11R6.x) Asub-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

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Fiber Optics IIIustrated Dictionary

lTU-T X SeriesRecommendatioDs

Prevalent Formats

X.25 Definitions of the procedures for

exchanging data between user devices

(DTEs) andnetwork nodes in a public

switched packetdatanetwork (PSPDN)

in order to provide a common interface

across a variety ofsystems X.2Sis a

layered packettransmissions protocol

commonly used inwidearea networks

(WANs) AversionofX.25 specifically

designed for packetradio has been

developed as AX.2S

X.400 Aninternational ISOIITU-T series of

standards for electronic messaging

architecture for the exchange ofdata

between computer systems X.400 was

published bythe ITU~Tin1984.·The

standard wasjointly rewritten by.ISO

and lTU-Tin1988

X.400 does not stipulate 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 andrecommendations to

X.400, some ofwhichare: X.402

describesthe overall architecture;X.420

describes email· transfer;X.43Sdefines

the electronic movement ofElectronic

Data Interchange (EDI); and X.440

describes ··voice messaging ·· See

Electronic Data Interchange

X.445 Asynchronous· Protocol Specification

(APS) Acommerciallypromoted

multiple media client/server extension of

the X.400 standard that facilitates the

exchangeofdigital data overpublic

phonenetworks ratherthanX.25

standardleased lines

X.SOO A directory service protocol for building

distributed global directories It was

developed in response toa need to

design directoriesthatwouldnot

experience the same problems and

bottlenecks that were developing with

manyof the large databases being

accessedbythousands 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

Recommendations of Particular Interest

X.I International user classes afservice in, and categories ofaccess to, public data networks and integrated services digital networks (lSDNs).

Includes information on accesstoleased

or switched circuits by data terminal equipment (DTEs)in various modes, accessby facsimile terminals, and access

to Frame Relay systems

X.6 Multicast service definition.

Service defmitions and capabilities of a multicast service providingacommon model for the description of service elements Interface specificationsand protocol elements are not specifiedby X.6

X.31 Support ofpacket 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 equipmentand 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.

Adescription 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,datatransfer, and signaling information are provided

X.77 Internetworking between PSPDNs via B-ISDN.

Definitions ofprocedures for intemetworkingthatincludereference configurations,protocolstacks, and signalingprocedures

X.121 International number plan for public data networks.

A description of the design, characteristics, and applications ofthe Ilwnbering planfor public data networks The International Number Plan was developed tofacilitateth~

linking ofpublic data networks with the

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Fiber Optics Illustrated Dictionary

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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 theSHA-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 Xwas originally devel-oped by Robert Scheifler and Ron Newman from the Massachusetts Institute ofTechnology (MIT) and Jim Gettys of Digital Equipment Corporation (DEC) to provide a user 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 Animportant set ofstandards defined

by the American National Standards Institute (ANSI) for the financial industry that has many ramifications for secured transactions over computer networks The X9standards cover such aspects as personal identifi-cation number(PIN)management, electronic trans-fer of funds, transaction processing, security mecha-nisms A brief 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 network-ing over noisy copper connections was optimized for voice rather than data communications It helped to fulfill a growing need for a common language to in-terconnect 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,

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Fiber Optics Illustrated Dictionary

and network layers of the hierarchical Open Systems

Interconnect (OSI) model

Basic Overview of X.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 bylTV-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 Protocol Aprotocol for sending radio

frequen-cies (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-bandAnassigned spectrum in the microwave

fre-quencies of approximately 8 to 12 GHz with

wave-lengths ofjust a few centimeters X-band signals are

not significantly hindered by the Earth's atmosphere

unless a lot ofmoisture (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 Asystem designed to facilitate and automate

the rapid deployment and management of multiple

overlay networks X-Bone is an overlay technology

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 xdAnX-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 dae-mons, and the provision of a user interface and API for users or programs wishing to manually parameter-ize and override overlays See X-Bone

X-dimension of recorded spotInfacsimile transmis-sions, a means ofdescribing variation density in tenns

of the minimum density The largest center-to-cen-ter 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-di-mension ofa recorded spot The same principles can

be applied to assess the scanning spot

X-ray A radiant 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 some-what 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 of X-rays on livdamag-ing cells X-rays are used in many medical, industrial, and fabrication ap-plications 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 spectrometerAninstrument that is used, by means of reflected 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 ofcom-puter manufacturers founded in 1984 X/Open seeks

to promote an open, multivendor Common Applica-tions Environment (CAE) to enhance application portability This is a good concept, as it allows soft-ware developed by different vendors to run on a va-riety of platforms, 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 net-work naming services and to provide integration with industry-accepted naming services such as X.SOO, Domain Name Service (DNS), DCE, and others

X/Open Portability GuideXPG Aguide

document-ing the X/Open common applications environment

system

XA extended architecture

XA-SMDSSee Exchange Access SMDS

XAPIAX.400 Application Program Interface

Asso-ciation See X Series Recommendations

XawThe Athena Widget set A set of widgets

dis-tributed with the X Window System, which began as

Project Athena See Athena, X Window System

Xbarabbrev.crossbar See utility pole

XBase, XbaseAgeneric designation for applications

that read and/or write dBase-compatible files

XC abbrev cross connect.

XCA extended communication adapter

XcoralAmultiwindow text editor for the X Window

System, that can be used in conjunction with a mouse

XCVRabbrev. transceiver

xdSee X-Bone xd

XDLAnobject-oriented extension to the

lTU-T-de-fined Specification and Design Language (SDL) for

telecommunications systems See Specification and

Design Language

XDMA Xing Distributed Media Architecture

Acom-mercial streaming media architecture for delivery of

live and on-demand audio-video from Xing

Technol-ogy Corporation.Itis 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 ofdigital subscriber

line technologies, which include ADSL, EDSL, and

HDSL See digital subscriber line and individual

list-ings for further information

XENIX A Unix implementation best known as

be-ing 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 printerA 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 thedrytransfer toner,

which then fuses the toner to the printing medium

Xerox CorporationOne ofthe first companies to see

the commercial benefits of new photocopying

tech-nology 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 ServicesXNS Amultilayer, distrib-uted 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 lay-ers of the Open Systems Interconnection model (OSI)

Xerox PAReXerox Corporation's Palo Alto Re-search Center This reRe-search center provided enor-mous impetus to early computer companies and soft-ware developers (e.g., Apple Computer Inc., Micro-soft Incorporated), especially those developing ob-ject-oriented systems and graphical user interfaces (GUls) PARC researchers invented mice and vari-ous laser printing technologies, developed Smalltalk; they generated one good idea after another through-out the 1970s and early 1980s, yet surprisingly few ofthese were commercially implemented or marketed through Xerox Charles Simonyi, one of the early founding members ofPARC, was the demonstrator ofthe Alto, a pioneer 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 ex-tended graphics array

Xi'anThe capital of the Shaanxi province in north-west China; firms in this region are major suppliers

of broadband and optical networking products, in-cluding ADSL and fiber optic cables and components XID exchange identification.Indata networking, XIDs are request and response packets exchanged prior to communications between a router and a net-work host XID is used for device discovery, address conflict, resolution, and sniffing The XID packet in-cludes the parameters ofthe serial device, and a con-nection can only be negotiated if this configuration

is recognized by the host

XIPabbrev. execute in place A means to access memory and execute code on PCMCIA cards with-out having to load them into system memory first See PCMCIA

XIWT See Cross-Industry Working Team

XlibX Library A program interface for the X Win-dows System

Xmission, Xmitabbrev.transmission, transmit XML See Extensible Markup Language

XModemAwidely 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

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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 ifthey have ZModem, which is faster and

capable ofrestarting an interrupted transmission from

where it left off See Kermit, YModem, ZModem

XModem-lK, XModem-KA variant of XModem

that manages data in 1K(I024-byte) packets See

XModem

XModem-CRCXModem with 16-bit cyclic

redun-dancy checking (CRC) error detection mechanisms,

instead of checksum XModem-CRC can

commu-nicate with XModem versions that use checksum for

error correction

XMPX/Open Management Protocol

XMSSee Extended Memory Specification

XMT abbrev.transmit

XMTR abbrev.transmitter

XNMSMlCOM's commercial mM-licensed

Intel-based desktop computer packet data network (PDN)

network management system software

XNS See Xerox Network Services

XOabbrev. crystal oscillator See crystal detector,

quartz

XONIXOFFtransmission 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 ofdata and resuming transmissions

sig-nal when to stop sending data and when to resume,

in order to prevent loss or corruption

In newer high-speed modems, flow control may be

handled by hardware, often in conjunction with

spe-cific types ofcables

Flow control signals are not limited to modem

com-munications If a user is working on a terminal that

understands XONIXOFF commands, usually

signi-fied by Ctrl-S (stop) and Ctrl-Q (resume), thenitis

possible to suspend a listing or other activity and

re-sume when it is convenient

Xover abbrev.crossover

XPAD external packet assembler/disassembler

XPGSee X/Open Portability Guide

Xpondertransponder

Xpress Transport ProtocolXTP Aflexible,

high-performance commercial multicast protocol to

sup-port a wide variety of applications from wide area

networks (WANs) to multimedia and realtime

embed-ded systems It was developed by an international

group ofrepresentatives 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

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 canrunin parallel with other transport protocols and thus can increase func-tionality 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 XRBtransmit reference burst

xref abbrev.cross reference

XRFExtended Recovery Facility

XSIX/Open System Interface Specification XSMPX Session Manager Protocol

XT1 abbrev crosstalk 2 ffiM Personal Computer XT.

SeeffiM

Xtalkabbrev.crosstalk

xtermA 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 mo-dem, each with its own input/output process running independently of the others

XTP1 See eXpress Transfer Protocol 2 See Xpress Transport Protocol

XTPForumAnonprofit group promoting the devel-opment and distribution of Xpress Transport Proto-col (XTP) A number of significant vendors, includ-ing 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 XWAThe callsign issued to a historically significant Canadian radio station, it stood for X-perimental Wireless Apparatus XWAwas issued its first experi-mental license by the Department ofNaval 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 be-gan in December 1919 The pioneer broadcasts were primarily musical and, since few consumer radios existed at the time, the listeners were amateur radio enthusiasts.InMay 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, XWSSee X Window System

XXXX Adesignation for the last four digits in a tele-phone number, usually used when the numbers are not yet known (or assigned) It represents any num-ber between 0 and 9

XYcutAmeans ofangle-cutting a piezoelectric crys-tal such as LGS so its electrical characteristics are be-tween those of an X cut and a Y cut See quartz,

x-ray goniometer, X cut, Y cut

ysymb yocto- See yocto-.

Y 1.symb admittance The ease with which

alternat-ing 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 of Arizona 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 a Y shape, with the top part of the Y

corre-sponding to the transmission line Since the top ofthe

Y is closed, causing it to resemble the Greek "D"

(delta), the Y antenna is sometimes also known as a

delta matched antenna This style ofantenna is

com-monly used for very high frequency (VHF) and

fre-quency modulated (PM) signals

Y axis,yaxis A reference baseline or vector within a

coordinate system, most often associated with

rect-angular or Cartesian coordinates The Y axis is

ori-ented 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-dimen-sional 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

Y cable, Y connector A cable 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

appli-cations to split a mono signal into two jacks (not the

same as real stereo) to connect systems with

differ-ent 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 Y cable

mayor may not cause a degradation of the

transmis-sion once the signal is split A Y 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

YcutAtype 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 crys-tal, detector, quartz, piezoelectric, X cut, X-ray go-niometer,Ybar

YCut

A Y cut creates a crystal plate with the plane

Y Series Recommendations A series ofITU-T rec-ommended 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 specifi-cations and recommendations are widely followed by vendors in the telecommunications industry, those wanting to maximize interoperability with other sys-tems need to be aware of the information dissemi-nated by the ITU-T A full list of general categories

is listed in Appendix C and specific series topics are listed under individual entries in this dictionary, e.g.,

G Series Recommendations See Y Series Recom-mendations chart

Y signal A monochrome (it's actually more descrip-tive to say grayscale) signal luminance transmission When combined with a color signal, luminance pro-vides brightness to the image The relative absence ofa luminance 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 YIC.

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