Because expert systems often handle different types of data, different types of input, and process the formation in different ways from other types of in-formation repositories, they som
Trang 1Fiber Optics Illustrated Dictionary
and input/output peripherals are event-driven or event
initiators
eventual Byzantine agreement EBA In EBA, a
number ofcoordinated processors (with some specified
upper value for faulty processors) agree on a state or
value among those considered to be reliable Thus, a
state of mutual agreement is negotiated among
nonfaulty processors in a fault-tolerant system, but
the processing does not have to be simultaneous See
Byzantine agreement and Byzantine Generals
prob-lem for a history and fuller explanation
EWOS See European Workshop in Open Systems,
Open Systems Interconnection
EWP electronic white pages Anelectronic database
of personal, and sometimes business, phone and
ad-dress listings There are many EWP lookup services
on the Web
exa- E A prefix for an SI unit quantity of 1018, or
1,000,000,000,000,000,000 It's a gargantuan
quan-tity See zeta-,
atto-ExCa Exchangeable Card Architecture An open
socket architecture extension to PCMCIA 2.0 for use
on Intel x86-based computers, introduced by Intel in
the early 1990s The software specification provides
standardized socket, card, and client services ExCA
allows interfacing ofPCMCIA devices with
comput-ers, particularly mobile computcomput-ers, which are more
likely to have PCMCIA slots See Personal Computer
Memory Card International Association
exception I error or unusual occurrence, such as an
abnormal signal, data falling outside a certain
speci-fied range or a deviation from normal program
ex-ecution Common exception conditions in
program-ming include stack overflow and divide-by-zero
er-rors In software development, exception handlers can
be included in the code to detect and manage error
conditions and resume program execution 2 In ATM,
a connectivity advertisement in a PNNI complex node
representation that represents something other than
the default setting of the node representation
excess burst size See burst size, excess
excess noise, current noise Undesirable noise that
results from current passing through semiconductor
components
exchange Acentral location for making connections,
directing traffic, and redirecting traffic A public
tele-phone switching office or regional system is often
called a telephone exchange
exchange access Defined in the Telecommunications
Act of 1996, and published by the Federal
Commu-nications Commission (FCC), as
" the offering of access to telephone exchange
services or facilities for the purpose of the
origi-nation or termiorigi-nation of telephone toll services."
See Federal Communications Commission,
Telecom-munications Act of 1996
Exchange Access SMDS XA-SMDS, Exchange
Access Switched Multimegabit Data Service A
con-nectionless, cell-switched, security-enabled data
transport service for extending network features
through standard interconnections with interexchange
carriers (IXC) XA-SMDS is similar in structure to
ATM and is designed so that migration to ATM may
be possible as ATM becomes more widely imple-mented Multiple node local area networks (LANs) and wide area networks (WANs) can be intercon-nected without installing a dedicated path, at speeds ranging from 1.17 to 34 Mbps XA-SMDS is a pub-lic level service, with a universal addressing plan, so various XA-SMDS networks can intercommunicate
as desired
exchange carrier EC A telecommunications pro-vider operating under specified territorial and oper-ating parameters designated within the industry Exchange Carriers Association ECA An organiza-tion established to support the interests and account-ing administrative concerns of long-distance tele-phone companies
Exchange Carriers Standards Association ECSA More familiarly known as the Alliance for Telecom-munications Industry Solutions (ATIS) since 1993, the Washington, D.C.-based ECSA was established
in 1983 to develop and promote standards related to the needs ofvarious telecommunications carriers The ECSA works in conjunction with a number of com-mittees, including the Carrier Liaison Committee (CLC), Information Industry Liaison Committee (IILC), and Telecommunications Industry Forum (TCIF) See Alliance for Telecommunications Indus-try Solutions for more information
exchange line The connection between a telephone subscriber and the local telephone switching ex-change See local loop
Exchange Message Record EMR An industry stan-dard for the exchange of sample, study, and billable data messages among local exchange carriers (LECs) Exchange Service ES Basic subscriber phone ser-vice with a unique local telephone number and ac-cess to the public switched telecommunications net-work Includes residence and business services and private branch trunk line services Private lines and Special Access services are not considered to be Ex-change Services
excitation The application of an external stimulus to
a system resulting in a reaction or response The ap-plication of a charge, potential, or electromagnetic influence
excitation voltage The minimum or sufficient volt-age required for a circuit to be functional
exciton An excited state in a crystal substance with the characteristic of moving and recombining holes and electrons See p-njunction, quantum
execution In a software process, the carrying out of preprogrammed, realtime, or heuristic steps in order for the program to run through its instructions or logi-cal structure It mayor may not be an interactive process
execution time A measure of the time in steps, min-utes, or machine cycles that a process, or a particular computer instruction, takes to be carried out Executive Cellular Processor ECP In wireless Mo-bile Switching Centers (MSCs), the capabilities for intelligent call handling, mobility management, and system control and configuration In Lucent
Trang 2and Management Platforms (OMPs), comprise the
Access Manager
EXFO Electro-Optical Engineering, Inc.Expertise
in Fiber Optics A publicly traded leading designer
and manufacturer ofglobal fiber optic test,
measure-ment, and automation solutions for
telecommunica-tions The products are aimed at handheld and
modu-lar instruments telecommunications markets and
high-performance optical instrument component lab
users and systems vendors In August 2001, EXFO
announced an agreement to acquire Avantas
Net-works Corporation, a pre-revenue company
develop-ing data communications and telephony testdevelop-ing
systems
exosphereAregion beyond the Earth's surface at the
edge of the atmospheric "envelope" surrounding the
planet See ionosphere
Expanded Interconnection ServiceEIS
Acolloca-tion arrangement, in which the switch services for a
private branch are located within the premises ofthe
local telephone carrier
expansion slotsPeripheral slots in an expansion bay
or a computer intended for the placement of
control-lers, cards, and other device interfaces, usually
com-prised ofprinted circuit boards, which are used to
ex-tend a system VESA, EISA, ISA, MCA, and PCI are
various common standards for the electrical and
trans-missions protocols used with slot peripherals for
per-sonal computers
expert systemAn expert system is a type of
infor-mation-handling approach which grew out of
artifi-cial intelligence research Various types of expert
systems exist for information creation, storage, and
manipulation An expert system is one that involves
the manipulation and creation ofinformation in a way
that is rule based and evaluative, rather than search
and query The traditional means of providing
infor-mation to computer users is through a database, which
usually involves storing and retrieving the data on a
keyword basis, but an expert system can take in a
richer mix ofinputs, or nontraditional inputs,
includ-ing natural language queries, visual queries, or other
contextual input An expert system also incorporates
the combined knowledge of many experts in that it
is not just a collection offacts but may further include
data relationships, means of analyzing and
evaluat-ing the data, and other pertinent evaluative
charac-teristics Expert systems grew out ofefforts to mimic
the ease and naturalness of human communications
through machine interfaces, in order to enhance the
usefulness of computers
Because expert systems often handle different types
of data, different types of input, and process the
formation in different ways from other types of
in-formation repositories, they sometimes require
dif-ferent programming languages than those commonly
used for commercial applications Cobol, Fortran, C,
and BASIC are used for many programs used in
busi-ness and educational settings However, because
ex-pert systems often require a different programming
approach, good text parsing languages like Perl, and
like LISP and Prolog may be used
Of the various types of products that have evolved from artificial intelligence research, expert systems are some ofthe most commercially successful results
explicit congestion notificationECN An IETF IP standard proposed in the late 1990s for detecting and managing end-to-end network transmissions and con-gestion Acongestion experienced (eE) bit in the
header serves as a data congestion indicator in
con-:~~~~:ra~:~~~ ff~g~l~6ea~~::t:~~pa::,~~~o~: ••• livery ofdelay-sensitive applications, such as
broad-casts on the Web, or for improving security and in-trusion detection One might expect a trade-off in transmission efficiency from having to encode and detect the ECN; however, in testingithas been found that bulk and transactional data transmissions may be more efficient when packets are marked rather than dropped See random early detection,~C 2481, RFC 2884
explicit forward congestion indicatorEFCI In ATM networking, a traffic flow control congestion,
or impending congestion, indicator contained in the ATM cell header The congestion signal is sent to the end destination to adjust accordingly See cell rate, leaky bucket
Explicit RateER A network congestion feedback mode provided in available bit rate (ABR) service
Network rates that can be received are indicated within Resource Management cells See cell rate
ExplorerSee Microsoft Explorer
Explorer IThe first successful U.S satellite launched
on January 31, 1958 Its mission was scientific, and
it included instruments to measure radiation in space
At first, it was thought that the instruments might be defective, as the readings were much higher than ex-pected' but the measurements were later verified
Explorer 8The first NASA satellite launched by the United States The Explorer 8 was launched on No-vember 3, 1960, to study the ionosphere
exportTo save information in a format that is not the native format ofthe application doing the saving For example, a word processed document may be saved
in ASCII to facilitate transfer over a 7-bit network
This procedure is often done to create a version of a file which is compatible with other applications or transport mechanisms Exporting is usually done through a conversion filter, and there may also be fil-ters for importing
exposureContact with radiant energy, bacterial or viral toxins, or chemicals Sun exposure can cause fading, burning, melting, or other chemical reactions
Exposure to radiation from X-rays or laser light can can cause burns, deep cellular damage, chemical changes, or death to biological organisms at high doses Exposure is a concern in industrial environ-ments for both equipment and humans It is also a consideration in medical environments, where expo-sure to viruses, bacteria, X-radiation, chemicals, and other contaminants or hazards may cause harm See CDRH classification
Trang 3Fiber Optics Illustrated Dictionary
express circuitAninterurban phone carrier circuit
connected without multiplexing equipment
eXpress Transfer Protocol XTP A lightweight
net-work protocol originally developed by Protocol
En-gines, Inc., in the late 1980s In its early development
it was sometimes also called Xpress Transfer
Proto-col It is a reliable, realtime,transfer layer (combined
network and protocol layer) protocol It was designed
to be implemented as a VLSI chip set XTP is
de-signed for parallel processing and the various
func-tions such as address translation and flow/rate/error
control can be executed in parallel XTP utilizes
con-trol packet and information packet frame formats In
multicast mode, one-to-many transmissions can be
supported Protocol Engines, as a company, was no
longer able to continue development after the early
1990s, but interest in XTP as a protocol continued
from outside the company
The protocol is used in the European RACE and
DeTeBekom projects The XTP collaborators are the
University of Dresden, The University of Salzburg,
and the University ofOttawa Anumber ofextensions
were added to the XTP 3.6 standard to support
Qual-ity of Service (QoS) This version is known as XTPX
(XTP eXtended) It might be best to abbreviate it as
eXTP rather than XTP to distinguish it from the
com-mercial multicasting protocol known as Xpress
Transport Protocol The author was unable to find
clarification as to whether the Xpress Transport
Pro-tocols had its origins in the eXpress Transfer
Proto-color whether the protocols were developed
indepen-dently
extended ASCII Acolloquial designation for a
vari-ety of noncompatible 8-bit character code
designa-tionsinwhich the first 128 characters conform to the
ASCII standard, but the subsequent 128 characters
(which mostly include symbols and accented letters)
are variously assigned by different developers
Extended-defmition Television See
Enhanced-defi-nition TV
Extended Digital Subscriber Line EDSL Aversion
of Digital Subscriber Line (DSL) services that
sup-ports 23 B channels and one 64-Kbps D channel
transmitted over a single line See Digital Subscriber
Line, Primary Rate Interface
extended graphics adapter EGA A color graphics
standard introduced by International Business
Ma-chines (ffiM) in 1984, considered the successor to
color graphics adapter (CGA) EGA was widely
implemented by third party developers on Intel-based
personal computers EGA could display up to
640 x 350 in 16 colors Actually, to say "16 colors"
is stretching it a bit because, in fact, there were eight
colors, plus eight half-intensity versions of those
same colors, rather than 16 colors selected for their
usefulness to a limited palette Not long after, ffiM
introduced PGA, which had slightly better vertical
resolution than EGA (640 x 400) but was otherwise
not a significant evolution See color graphics adapter
extended graphics array XGA A 1024 x 768-color
graphics format used in liquid crystal display (LCD)
data projectors
Extended Industry Standard Architecture EISA
A 188-pin bus interface specification to succeed Industry Standard Architecture (ISA), which in tum succeeded the IBM PC/AT bus specifications EISA supports bit memory addressing, and 16- or bit data transfers EISA was designed to support 32-bit Intel 80386 and 80486 processors The specifica-tion works with various system resources, including input/output ports, memory, and DMA channels
On EISA boards, configuration is done with EISA Configuration Utility (ECU) software, rather than through hardware, using a CFG file supplied with the board EISA boards, while faster, are somewhat physically compatible with legacy boards, preserv-ing the old AT pin specifications on the upper 98 pins The rest are used for the EISA bus signals The slot into which an EISA card is inserted is assigned a unique address so that the system can recognize and initialize the interface
EISA is widely supported by many manufacturers but
is being gradually superseded by newer formats extended play A designation for a technology that plays beyond that generally expected to be the maxi-mum limit Historic phonograph cylinders played for two or three minutes, but some companies found a way to make them play for four minutes on standard equipment, thus creating extended play albums Extended SuperFrame ESF A frame format for 1.544 Mbps communications (2.048 in Europe with
30 channels) evolved from DS-I in 1962 and Super-Frame in 1969, widely used in T1systems ESF pro-vides improved error correction and can be serviced without taking down the entire system Twenty-four frames are combined to create one Extended Super-Frame Six frames are used for frame synchroniza-tion, six for error tracking, and twelve for Facility Data Link (FDL) Signaling is accomplished through robbed bits in frames 6, 12, 18, and 24, except in transparent mode, in which the 24th channel is used
in order to provide Clear Channel Signaling (CCS) Facility Link Data (FDL) is used to transmit to tele-phone monitoring stations
extended time division multiple access E-TDMA
A type ofdigital transmission scheme favored by cel-lular providers over older analog-based systems See time division multiple access
Extensible Markup Language XML XML is a markup meta language that allows more flexibility and complexity of presentation than HyperText Markup Language (HTML) and is not limited to Web publishing Like HTML, it is based upon the Stan-dard Generalized Markup Language (SGML - ISO 8879) Some have promoted it as the successor to HTML, but the industry has not yet formed a con-sensus on this possibility XML has been recom-mended for use with the International Development Markup Language and is integral to the WebDAV Distributed Authoring Protocol
XML MIME entities are offour types: document en-tities, external DTD subsets, external parsed enen-tities, and external parameter entities
In Jan 2001, Murata et a1 submitted a Standards
Trang 4to facilitate the exchange ofXML network entities.
XML MIME entities contain information to be parsed
and processed by the receiving XML system and may
include system-level commands The proposed new
media types were intended to overcome problems
inherent in trying to adapt SGML text/sgml and
ap-plication/sgml media types for use with XML The
new media types follow the conventions of the IETF
media types tree, for consistency, and include
text/xml Preferred over application/xml
for unprocessed, readable documents (as with plaintext)
Use of the parameter is op-tional but recommended
application/xml Use of the parameter is
op-tional, but recommended, to distinguish between the recom-mended utf-8 or utf-16 charac-ter sets; otherwise the default is us-ascii
text/xml-external-parsed-entity
application/xmI-externaI-parsed-entity
application-xml-dtd
See IDML Initiative HTML, SGML, World Wide
Web Consortium See RFC 1874 for SGML media
types See RFC 3023
extension, file nameA suffix, often preceded by a
period, as a subsection delimiter on systems that
re-quire it, and as a visual locator on systems that don't
Ithelps to indicate the file format, such as txt, bmp,
.tiff, ilbm, frame, wrd,etc File extensions need not
be restricted to three characters except on some
sys-tems with older types of file structures.Inthe
mid-1980s most types of computer platforms (Atari,
Macintosh, Amiga, Sun, Apollo, NeXT, SGI, etc.) did
away with the mandatory period and three-character
limitation, as did Intel-based machines running OS/
2 and Microsoft Windows NT Surprisingly, many
consumer Intel-based desktop computers running
Microsoft Windows retained the limitation until 1996
and even later on some of the machines running
legacy software
extension, phoneAnextra phone line that uses the
same phone number as the originally installed phone
with which it is associated
Exterior Gateway ProtocolAnInternet protocol
developed in the early 1980s for the exchange
ofrout-ing information between autonomous systems See
RFC 827
External Data RepresentationXDR A standard
representation for platform-independent data
struc-tures for remote procedure call systems, developed
by Sun Microsystems See RFC 1014
External EnvironmentIn the X/Open Architectural
Framework Technical Reference Mode, the External
Environment is one of five basic elements The EE
Application Platform (AP) exchanges data The EE links to the AP through the External Environment Interface (EEl) Printers, scanners, other computers
in a network, public switched telephone networks (PSTNs), human operators, etc are all common ele-ments ofthe EE See External Environment Interface external environment interfaceEEL Generically,
a transmissions linking device between a local device (e.g., personal computer) and outside devices (key-boards, mice, printers, scanners, public phone ser-vices, surveillance cameras, packet radio transmis-sions, etc.) Serial, parallel, SCSI, IDE, USB, Apple-Talk Data Bus (ADB), Ethernet, and Firewire periph-eral cards are examples of some common external environment interfaces on commercial computing systems
External Environment Interface EEL In theXI
Open Architectural Framework Technical Reference Model, the External Environment Interface is one of five basic elements and one of two basic interface types It provides the data link between the applica-tion platform and the external environment (EE) The
EE is comprised of the various entities and systems with which the application platform exchanges data Thus, the EEl may link to various devices such as printers, modems, scanners, keyboards, mice, moni-tors, etc Open systems EEl standards facilitate inter-operability among platforms interconnected through the EEl See Application Program Interface external memoryAny memory outside the direct access memory peripherals or chips in a system Thus, information stored on punch cards or paper tape would be considered external memory, as would re-movable cartridges or tapes Chip memory and in-ternal hard drives would be considered inin-ternal memory
extinction potentialThe lowest voltage level at which plat current in a plat will flow in a gas-filled electron tube
EXTN Extension.Anindustry abbreviation designat-ing the last four digits of a phone number A 10-digit number is expressed with symbolic characters as: NPA-NXX-EXTN
extraneous emissionAny emission in addition to, or external to, the desired emission Thus, emissions outside the case of a computer system or outside the sheath of an insulated wire are considered extrane-ous Since these emissions can interfere with radio transmissions (radio broadcasts, intercoms, cordless phones, etc.), they are strictly regulated by the Fed-eral Communications Commission (FCC), and elec-tronic components must conform to stated emission requirements
extranetA larger network, based upon Interworking technology, for connecting local area net-works (intranets) and other authorized users within
a virtual 'closed loop' system The extranet is seen
as having the potential to significantly support and change electronic commerce and to take some of the traffic load offthe Internet Those promoting the con-cept suggest that it will enable customers to connect
Trang 5Fiber Optics Illustrated Dictionary
more directly to vendors than is typical in the
cur-rent Web-based system and that security will be more
easily supported on the system Extranets will
poten-tially be used for monitoring transactions, accessing
databases, requesting product information, etc For
example, bookstores might be connected directly to
book distributors, to expedite orders, shipments, and
account handling
Marshall Industries, Federal Express, and Dell
Com-puter are some of the early adopters of the extranet
concept Extranets are also seen as a way to give
pri-0rity services to elite customers For example, Charles
Schwab & Company has developed SchwabLink
Web, a redesigned online trading and research
ser-vice available only to the company's top 5,000
invest-ment manager customers The system is Java-based,
conforming to CORBA and InterORB Protocol
standards
The original use of the term has been attributed to
Bob Metcalfe in 1996, though a number ofelectronic
commerce work groups may have begun using the
term around the same time Steven Telleen was
de-scribing intranets in 1994, with a definition that is
now more commonly expressed with the term
extranet Telleen described intranets as an
"infrastruc-ture based on Internet standards and technologies that
supportssharin~ofcontent within a limited and
well-defined group.'
The concept of an extranet is not new, even if
cur-rent implementations represent a significant
evolu-tion In the earliest days of telegraph and telephone
technology, it was not unusual for related businesses
to have direct connections to one another without
going through the local switchboard exchange, and
later incarnations ofthis system used leased lines and
sometimes hot lines for direct connections between
building complexes or cooperating businesses
extremely high frequency EHF The frequency
spec-trumdesignated as 30 to 300 GHz, typically used for
satellite communications These very short
wave-lengths can be apprehended with small antenna
as-semblies See band allocations for a chart
extremely low frequency ELF The frequency
spec-trumdesignated as 30 to 300 Hz Waves in this range
are extremely long and not of much practical use for
communications with our present technologies (the
same was formerly said of microwave frequencies, and they are now widely used) See band allocations for a chart
extrinsic semiconductor A type of semiconductor that includes impurities that contribute to its electro-magnetic properties, usually to enhance them See doping
extrusion 1 Forming by forcing through an open-ing, which may contribute to the shape ofthe extruded material Extrusion is often accompanied by a heat-ing or coolheat-ing process in order for the extruded ma-terial to retain the desired shape 2 A means to pro-duce or apply insulating materials to wire or cable
by forcing plastic or other materials through an open-ing
eye phone 1 A project by a NolWegian group, Me-dia Lunde and Tollefsen, Ltd (MeMe-diaLT), that designs products for the visually impaired MediaLT plan to use video telephony as a communication channel to
a sighted eye 2 A body-worn helmet or laser-to-retina transmission system associated with electron-ics for communications The user views images on the inside surface of the eyepiece, on a tiny screen next to the eye, or through a direct projection on the retina Anumber of companies have produced work-able systems ofdifferent types This technology is of special interest to the virtual reality (VR) community, and research is fueled in part by demand from the games-playing community, with spinoffs for business markets and handicapped individuals Potentially an eye phone can be integrated with a mobile commu-nications link to the Internet (stock market day trad-ers would probably love this kind of system) 3 A visual interface on a computer system equipped with
an Internet phone that enables calls to be clicked and controlled through a computer mouse/pen-type inter-face This is a less common use ofthe phrase and will probably fade away as Internet phone technology be-comes more familiar and common, but it may con-tinue to be applicable to phone interfaces that can be controlled by eye movements (e.g., by someone with quadriplegia)
eyelet Asmall, washer-like flat cylinder or short tube for threading or supporting various wires, cables, or other narrow parts
EYP See electronic yellow pages
Trang 6femto- 3 symb focal length (usually italicized) See
focal length 4 symb frequency See frequency.
F 1.abbrev Fahrenheit See Fahrenheit 2 abbrev.
fiber 3 symb filament 4 symb off with N as the
corresponding symbol for on 4 symb 15 in the
hexa-decimal number system The symbols used are 0 1 2
3 4 5 6 7 8 9 ABC D E F Thus, "A" in hexadecimal
represents" 10" in the familiar decimal system, and
"F3" represents "18" in decimal Hexadecimal
nu-merals are sometimes preceded with "X" or "OX" to
indicate that the subsequent digits are represented in
the hexadecimal system For example, "15" in
deci-mal may be represented as"OXOF.'~ See the ASCII
chart in the Appendix for a list ofdecimal,
hexadeci-mal, and octal equivalents up to 127 decimal
F Block Federal Communications Commission
(FCC) designation for a Personal Communications
Services (peS) license granted to a telephone
com-pany serving a Major Trading Area (MTA) The
li-cense grants pennission to operate at certain
FCC-specified frequencies See A Block for a chart of
fre-quencies See C Block for a history and a more
de-tailed explanation
F connector A small coupling connector used at the
end ofcoaxial cable that is common in video editing,
broadcast components, and local area network (LAN)
cables The F connector is recognizable by its center
pin or plug opening for the center pin that is
com-monly seen on consumer television sets and on the
cables run to the house by local television cable
pro-viders 75-ohm F connector cables are commonly
used for TV, VCR, satellite, and radio frequency (RF)
device connections See connector for a diagram
F-ES The designation for a fixed, Le., nonmobile, end
system in a digital cellular network The F-ES can
both send and receive data and typically receives data
from a mobile end system (M-ES)
F region Aregion of the Earth's ionosphere in which
F1 and F2 regions tend to fonn The F1 region is
ac-tive in daytime The F2 region is commonly used for
the propagation of radio waves, due to its high
ion-ization levels See ionospheric subregions for a chart
F link In Signaling System 7 (SS7), a fully
associ-ated transmission link directly connecting two
signal-ing endpoints The F link connects the host directly
trol Point (SCP) without passing through intermedi-ate Signal Transfer Points (STPs) For security rea-sons, F links are generally used for local applications rather than for links between networks
F port, fabric port On a Fibre Channel network, a fabric-attached loop or node that connects point-to-point to an N port.Incommercial products, the F port may be self-discovering See FL port
F Series Recommendations A series of ITU-T rec-ommendations that provides guidelines for nontelephone telecommunications services These guidelines are available as publications from the
ITU-T for purchase Since IITU-TU-ITU-T specifications and rec-ommendations are widely followed by vendors in the telecommunications industry, those wanting to maxi-mize interoperability with other systems need to be aware ofthe information disseminated by the ITU-T
A full list of general categories is listed in Appendix
C, and specific series topics are listed under indi-vidual entries in this dictionary, e.g., A Series Rec-ommendations See ITU-T F Series Recommenda-tions chart
Ionospheric Regions
Topside beyond F region
F region ca 150+ km
E roglon ca 95·150 Ian
o region ca 75·95 km
Earth
An illustration of the general ionospheric regions enveloping Earth These regions vary with tempera-ture and distance The F2 region is particularly im-portantfor reflecting radio waves over long distances.
Trang 7Fiber Optics Illustrated Dictionary
F-number Anumeric expression of the luminance
associated with an aperture Smaller F numbers are
typically associated with higher luminance Larger
apertures are generally associated with higher F
num-bers up to the maximum luminance available For
lenses, the F number is the ratio of the focal length
to the diameter ofthe aperture On camera lenses, the
F number associated with the maximum aperture is
often inscribed on the lens casing See candela, }stop,
luminance
.fstopAnexpression of the open region of an
aper-ture that admits lightina fixed or adjustable lens
as-sembly as in a camera or other imaging device The
scale is commonly used with optical lenses to
indi-cate the amount of light entering a sensing or
imag-ing device (based upon the diameter of the aperture)
Lower numbered fstops indicate larger openings, hence a wider diameter and more room for light to enter Typical 35mm camera fstop settings range from 4 to 22
There is a relationship betweenfstop openings and the depth of field of the image in most lens assem-blies (e.g., cameras) A wider aperture (lower.fstop)
images over a broader area ofthe lens and thus is
sub-ject to greater curvature A smaller aperture typically focuses through the central part ofthe lens, thus hav-ing less curvature over the extents of the image The fstop is often balanced with the shutter speed to fur-ther control the imaging factors Some imaging de-vices (e.g., consumer cameras) can balance fstops and shutter speeds automatically See F-number, focal length
MESSAGEHANDLINGSERVlCES
DIRECTORYSERVICES
TELEGRAPH SERVICE
F.l-F.19
F.2Q-P.29
FJ6-F.39
F.40 F.58
F.59-F.89
F.96-P.99
F.IO().lF.I04
F.I05~F.I09
MOBILE SERVICE
F.I1o-P.159
TELEMATIC·SERVICES
F.16o-F.199
F.20o-F.299
F.30G-F.349
F.3SG-R.39,9
Description
Operating methods for.the international public telegram service The gentex network
Message switching Theinternationaltelelllessage service Theintemationaltelex service Statistics··and.publicationsonintemational telegraph services Scheduled and leased communication services
Phototelegraph service
Mobile services and multidestination satellite services
Public facsimile service Teletex service Videotex service General.provision~JQrtelematic services
DOCUMENTCOMMU'NICATION
F.SSo-F.579 Documentcommunication
F.58o-F.S99 Programming communication interfaces
DATA TRANSMISSION SERVICES
AUDIOVISUAL SERVICES
ISDNSERVICES
UNIVERSAL PERSONAL TELECOMMUNICATlON
HUMAN FACTORS
F.60o-F.699 F.70o.-F 799 F.80o-F.849 F 85G-F.899 F.9OO'-F.999
Trang 8applied to a plant that produces computer chips or
optical components
fabricAgeneric term for describing the interlinked!
interwoven architecture or nature of a network's
physical and logical interdependencies AFibre
Chan-nel fabric is a system with interconnecting Nx-ports
capable ofrouting frames using only D-ID data in
Fe-2 signaling protocol fame headers
The term is especially applicable to systems in which
the speed oftransmission across a network link, such
as Fibre Channel, is near to, or exceeds, the speed of
the processor in the machines that are being linked
Thus, the network as a whole begins to take on some
of the characteristics of a machine organism, as
op-posed to discrete machines simply sharing
informa-tion over much slower links With intelligent routing
algorithms, it becomes impossible in a larger network
to fully know or predict the routes that data will take
when being transmitted across the communications
links Taken as a whole, fabric-related networking is
an interesting evolutionary development in digital
technology and will change not just the speed
ofcom-puting, but its very nature
fabric/fibre loop portSee FL port
fabric portSee F port
Fabry-Perot interferometerAdetection instrument
with an optical cavity composed of highly reflective
surfaces that can be variably separated When
illu-minated with highly coherent light from a laser, the
reflectors will bounce the light back and forth If the
reflecting waves resonate in phase, amplification of
the wave, or resonance, occurs and the wave assumes
enough power to "escape" through the reflective
mir-rors and stimulate a phototube that converts the light
energy to electricity in order to measure and display
its characteristics The resonant process is sometimes
called constructive interference due to the
amplify-ing effect of the interaction between the waves
To work effectively, the distance between the
reflec-tive surfaces is set in a mathematical relationship to
the wavelength ofthe laser input (hence the variable
separation of the reflective surfaces) An integral
number ofhalfwavelengths is related to the distance
between the reflective surfaces See Fabry-Perot
la-ser
Fabry-Perot laserF-P laser Areasonable-cost
semi-conductor laser component with a constant index of
refraction that lases simultaneously at different
wave-lengths; in other words, it emits a wider frequency
spectrum than a distributed-feedback laser
Fabry-Perot laser diode amplifiers can be used to
electro-optically modulate a signal and can be monolithically
integrated with quantum well transistors See
distrib-uted-feedback laser, Fabry-Perot interferometer
faceAgeometric surface oriented toward the viewer,
another component, the host system in general, or a
radiant energy source Thus, the endface of a fiber
optic filament is the end where light enters and!or
exits the fiber The face of an imaging surface is the
surface that is oriented toward the image and,
gener-ally, the source of illiumination (which may be
face modelA graphically modeled image of facial features, particularly eyes, lips, nose, and the general contours of the face These images can be used in conjunction with computer applications for videophone, graphical answering services, simula-tions, police identification, artistic works, educational applications, and computer animations Just as we now have synthesized speech for responding to user inquiries, we may someday have computer generated facial images responding to videophones and other interactive electronic devices, in effect, electronic
ply of and demand for anthropomorphic imaging technologies
face timeTime spent in a face-to-face encounter, as
in social or business interchanges A few years ago, one would never have thought to include this in a dic-tionary, but with so many human exchanges now be-ing carried out remotely, by email, videoconferenc-ing, etc., the distinction is becoming more significant
Infact, in the future, you might not know what a per-son looks like, even ifyou communicate with him or her audio/visually through a fast link, since people might design virtual environments and avatars to take their place in such encounters, projecting a personal image rather than an image of what they look like in real life and avoiding face time altogether
faceplateAt its most basic level, a protective plate, usually ofplastic or metal, that fits over the front sur-face of a console or other device, which may have openings to accommodate various knobs or dials or sensors The faceplate may be engraved, painted, or otherwise labelled to indicate settings The term is also used to describe protective plates that have
built-in connectors and sometimes some basic, compact electronics associated with those connections Face-plates for supporting connections to wire or fiber-based data, voice, and video couplers may need to meet NEMA standards for electrical boxes
Incable networks, specialized faceplates can be used
to upgrade passive taps to addressable taps to facili-tate connection and disconnection ofsubscriber links
Single- or multiple-gang faceplates canbe used in conjunction with fiber optic adapters (e.g., ST adapt-ers)
In fiber fabrications testing, specialized microscopes may be equipped with a faceplate for inserting and steadying common fiber optic connectorsto facilitate inspection ofthe ends See bezel; faceplate, fiber op-tic
faceplate, fiber opticAplanar surface comprised of
an array of aligned fiber optic filaments that serves
as an electromagnetic energy-guiding surface Unlike traditional electrical faceplates that are mainly used
as a protective surface, a fiber optic faceplate is a so-phisticated component assembly that may replace or complement lens components for transmiting a sig-nal from an input to an output surface It may inten-sify the signal for imaging applications and may be customized for various thermal expansion or
Trang 9radiation-Fiber Optics Illustrated Dictionary
resistant tolerances.Itcan guide various
electromag-netic phenomena, including X-ray emissions and
vis-ible light for use in X-ray crystallography cameras,
dental X-ray technologies, and biometric sensing
sys-tems, when coupled with CCD and CMOS
compo-nents In a molecular microscope, a fiber optic
face-plate can be used on an interfaced camera to
com-pensate for interference from the monochromatic
la-ser light source
For some applications, a fiber optic faceplate may be
used with or in place of a traditional energy-emitting
component, such as a scintillator, providing higher
resolution and lower scattering It is capable of
im-aging areas (up to about a square foot) without the
curvature distortion characteristic oflenses The
im-aging area on a CCD array coupled with a fiber optic
faceplate may be divided into quadrants to facilitate
independent processing (e.g., timing) of sections of
the imaging area
When combined with electrical components, a fiber
optic faceplate may be vulnerable to heat from nearby
electrical discharges (e.g., sparks).Anaccumulation
of tiny indentations in the surface would gradually
compromise the utility of the plate Some assemblies
include components for monitoring electrical spikes
or conditioning the power source to avoid this
prob-lem
See faceplate, fiber optic taper, phototube,
scintilla-tor
Fiber Optic Faceplate Bonded to Components
A basic jiber optic faceplate consists of tightly
packed, coherently aligned opticalfibers (left) bonded
to electronic sensing technology (e.g., CCD imaging
components) Attaching the faceplate to the image
sensing components must be done with extreme
preci-sion to prevent signal loss or distortion - chemical
gluing and oil coupling are two common bonding
methods.
facetIntransmission technologies, a planar
geomet-ric surface that reflects or refracts radiant energy The
term usually connotes more than one facet as in a
multifaceted grating, lens, or resonating cavity Thus,
the facets of a gem may prismatically refract light,
the facets of a blazed grating may selectively reflect certain wavelengths, and the facets of a parabolic antenna may reflect radio waves toward a centtral feedhorn
facilities An installation designed for a particular purpose The term typically encompasses related buildings, equipment, and operations, though some people use it loosely to include the personnel as well Facilities of significance in telecommunications in-clude broadcast sending and receiving stations, com-puter terminal rooms, Internet link facilities (which may include tens of thousands of modems or terminal devices), and other wiring and access installations facilities-based carrier FBe Phone carriers that use their own facilities and switching equipment to pro-vide phone service, often long-distance service Con-trast this with those who lease or resell services from established carriers, although even facilities-based carriers enlist other can-iers as needed
facility-associated signaling FAS In ISDN net-works, a type of signaling in which the D channel is
at the same primary rate interface (PRI) as an associ-ated set ofB channels In contrast, in nonfacility-as-sociated signaling (NFAS) the B channels are sepa-rate from the D channel PRI Delivery of FAS is through a link access protocol FAS over Internet Pro-tocol is essentially the same as FAS over ISDN, but uses Internet Protocol (IP) as the transport mecha-nism See channel-associated signaling
facom A distance radio navigation system or mea-suring system Facom is a means of analyzing local signals and received signals using the low frequency band for distances up to several thousand miles to determine distances See band allocations
FACOM fully automatic computer A series of com-mercial large-scale computing systems first intro-duced in the mid-1970s by Fujitsu Limited, at about the same time the first microcomputers were being developed for commercial distribution The FACOM M-190 is significant for being based upon large-scale integration (LSI) semiconductor circuitry that was new at the time.In1981, Fujitsu released a large-scale general purpose system, FACOM M-380/382, the same year its first fiber optic communication systems were delivered
facsimile device, fax device A device for sending an image transmission through wireless or wireline phone transmissions The word 'facsimile' implies an exact copy, though on some of the cheaper fax ma-chines, that's wishful thinking
The two most common ways to transmit and receive facsimiles (faxes) are through dedicated fax machines and through fax modems Often a fax generated on one type of system will be received on the other type The most common form offax machine is a dedicated system resembling a small printer that connects to a phone line It sends faxes by scanning a piece of pa-per fed through the machine Received faxes are printed in much the same way as they would be on a computer printer Some faxes use continuous feed thermal paper, though more commonly now fax ma-chines can work with sheet-fed plain paper Many
Trang 10ers See facsimile modem.
facsimile formats In order for facsimile (fax)
ma-chines to exchange data, a number of international
standards have been defined for image encoding and
transmission In addition to this, dialup modem
trans-mission protocols with compression and error
correc-tion for fax/modems, called the V Series
Recommen-dations, are used for data transfer in conjunction with
fax formats Tag Image File Format (TIFF) is an
im-portant raster image encoding format widely used in
facsimile transmissions, with TIFF-FX as an offshoot
of TIFF developed specifically to facilitate faxing
over computer networks
Since a high proportion offacsimile transmissions are
still basic black-and-white text documents, guidelines
have been established for the encoding of minimal
black-and-white images and text These formats also
have the advantages ofsmall file sizes and fast
trans-mission speeds The Profile S and Profile F subsets
ofthe TIFF specification support the transmission of
basic black-and-white documents
Basic Facsimile Formats
Class 1 EIAITIA (EIA-578) standard for
basic computer fax/modem
interface
Class 2 EIA/TIA standard for extended
computer fax/modem interface
which includes AT commands
Group 1 Single page transmission in six
minutes Common in the 1970s
Group 2 Single page transmission in three
minutes Common in the late 1970s
Group 3 (There is also a Group 3 bis, or
Group 3 enhanced format.) 14,400
bps facsimile protocol Two
resolution modes include 103 x 98
dpi (standard), and 203 x 196 dpi
(fine) Compression is supported
This is the most common protocol
used with fax machines and fax
modems, either Class 1 or Class 2
SeeVSeries Recommendations
V.27 Single page transmission in
under 30 seconds
Group 4 ISDNBfacsimile protocol adopted
in 1987 but not widespread in
subsequent years
For metric equivalents and higher
resolutions (e.g., 400 x 400), added
in the early 1990s, reference the
ITU-T T.30 recommendations
Over the years, Group 3 has become the de facto
stan-lines, supporting two basic resolutions commonly
called standard andfine Three compression schemes
are commonly used in Group 3 transmissions: Modi-fied Huffman (MH), ModiModi-fied READ (MR), and Modified Modified READ (MMR) (Group 3 and Group 4), with MH the most common
Due to the limitations of data transmissions over phone lines with traditional modems, black-and-white imaging and bit- and stream-oriented transmis-sions predominate However, as the Internet increases
in importance and accessibility, byte- and
file-ori-E~~:~;:~:1~~ii:::r::~:i~:!~~!i.
channel network fax transmissions to appropriate servers and devices (e.g., a fax device can be assigned
an email address) and other means ofdocument trans-missions have evolved alongside traditional facsimi-les Faxing over computer networks is of great inter-est to individuals and businesses, asitfrequently saves long-distance phone charges There are pro-posed and standardized formats for including fax in-formation in existing email as opposed to distinct fax-over-Internet formats
Another approach is to send original "facsimiles"
such as word-processed files as email attachments
When viewed or printed, the files contain all the col-ors, text, images, symbols, and formatting found in the original files up to the capability of the display
or printer upon which it is viewed, which is almost invariably higher quality than a traditionallow-reso-lution, black-and-white fax transmission Even ifthe file is printed on a fax machine that doubles as a printer,itwill not be skewed or smudged (or blank)
as are many scanned and manually transmitted fax documents
Adobe Portable Document Format (PDF) has become
an important vehicle for disseminating high-quality PostScript documents over the Internet, in essence, providing a high-quality "facsimile" that is the same
as the original as opposed to being a lower-quality copy With the wide availability offree PDF readers, PDF may supersede facsimile formats for many types
of documents and forms (many state governments now use PDF for informational brochures and license application forms) For people who don't like to look
at documents on computer screens or who require a physical printout on a fax machine, PDF files sent over the Internet (or over phone lines) could be fed
to a dedicated reader on a PostScript-capable fac-simile machine, resulting in perfect copies of the original (no smudging or blurring) at whatever reso-lution is available on the printer (most consumer la-ser printers now image between 400 and 1000 dpi)
Thus, the very concept ofa fax transmission is chang-ing, as more and more documents are created in elec-tronic formats that can be transmitted directly, with-out first being scanned and encoded!decoded In other words, legacy faxes, based on the current lossy scan-encode-transmit-decode scheme, may largely
be superseded by future faxes based on lossless