A layer in a laminate which may be planar or spheri-cal with a lower refractive index than its associative conductive materials, as in a fiber optic transmission cable, such that inciden
Trang 1Fiber Optics Illustrated Dictionary
circuit switching A type of end-to-end transmission
system common in phone connections In the process
of setting up the connection, a number of resources
are allocated to that specific call, most of which are
tied up until the call is completed and the connection
terminated One advantage ofthis system is that it can
guarantee a certain level ofperformance
Adisadvan-tage is that the resources are tied up whether or not
there is active communication See message
switch-ing, packet switching
circular antenna Ahorizontally polarized, half-wave
dipole antenna formed into the shape of a circle
ex-cept that the terminating ends do not touch to make a
continuous loop
circular magnetic wave A magnetic wave in which
the lines offorce describe a circular pattern
circular polarization An electromagnetic wave
whose lines of flux are oriented in a plane, usually
horizontal or vertical, or where the "edge" ofthe field
describes a circular shape Circular polarization is
used in antennas, where electricity serves to
uni-formly rotate the electromagnetic field through the
antenna It is possible to use one circularly polarized
wave to communicate with another, or the circularly
polarized wave can be manipulated to yield linearly
polarized waves perpendicular to one another
circular scanning Scanning in which the sweep of
the sensor and/or the display monitor describes a full
3600 arc, which can be pictured as a cone shape
spreading out toward the direction of the region
be-ing scanned (e.g., some types of radar)
circulator I A process or device that moves
some-thing from hand to hand, or device to device 2 In
microwave transmissions, a multiterminal coupling
device in which the transmission is passed down
through adjacent terminals 3 In radar transmissions,
a device that alternates the signal between the
trans-mitter and the receiver 4 In data communications, a
mechanism for allocating or transferring information
or control among ports
CISC See Complex Instruction Set Computing
CISCC Collocation Interconnection Service Cross
Connection
Cisco lOS Cisco Internetwork Operating System.An
OS incorporated as part of the CiscoFusion
architec-ture to help the system administrator centralize,
in-tegrate, install, and manage internetworks
Cisco Systems Inc A significant vendor of routers,
switchers, and related hardware and software for
net-work systems The author gained a greater
under-standing of the function and implementation of
net-work routing systems through Cisco seminars
CiscoFusion ACisco Systems intemetworking
archi-tecture that integrates scalable, stable, secure
tech-nologies with ATM, local area networks (LAN), and
virtual local area networks (VLANs)
CiscoView Agraphical device-management
applica-tion that dynamically provides administrative,
moni-toring, and configuration information for Cisco
inter-network devices
CISE See Computer and Information Science and
Engineering
CISPR See International Special Committee on Ra-dio Interference
CITA See Canadian Independent TelephoneAssociation CITEL Inter-American Telecommunications Com-mission
citizens band radio, citizens radio service CB ra-dio Radio frequencies set aside for the use of rela-tively low power consumer radios and radio control-lers (for model cars and planes) These have a lim-ited range (up to about 10 or 15 miles for mobile units), although sunspot activity and local weather can sometimes provide some surprisingly long con-nections when broadcasting conditions are optimal
In the United States, CB radios are commonly used
by truckers, travellers, and radio hobbyists Commu-nications over 150 miles are prohibited by the Fed-eral Communications Commission (FCC) The fre-quencies originally allocated by the FCC were around
27 Mhz, but have been changed to around 463 to 470 MHz Before computer bulletin board systems and the Internet, CB radio was a popular means of com-munity interaction Not all countries are free, and ci-vilian use of radios is not permitted in some regions
of the world See OSCAR, AMSAT
CITR Canadian Institute for Telecommunications Research
CITRIS See Information Technology Research Center
CITU See Central IT Unit
City and Suburban Telegraph Company The first company in Cincinnati, OR to provide direct com-munication between homes and businesses, incorpo-rated in 1873 In 1878, it contracted with the Bell Telephone Company of Boston, MA to provide Bell services in the Queen City area and, in 1882, con-tracted with American Belltoprovide long-distance services Its first payphone was installed in 1904 and mobile phones were introduced in 1946.In1952, it became the first Bell company to provide 100% dial service The company became Cincinnati Bell Tele-phone in 1971
CIV See cell interarrival variation
CIVDL See Collaboration for Interactive Visual Dis-tance Learning
CIX See Commercial Internet Exchange
CJC See Canadian Journal ofCommunication.
CKAC The first Canadian television broadcasting station, which began experimenting with mechani-cal television transmitted over wires in 1926 ABaird disc camera and Jenkins scanning disc television re-ceiver were early inventions that were tried around this time Sound and images were transmitted sepa-rately so the sound could be played on a radio re-ceiver Shortwave bands were used for the images Alphonse Ouimet, who later became the president of the CBC, was a technician for the first historic CKAC broadcast in 1931, a musical performance that was sent out to 20 viewers See Canadian Broadcasting Corporation
CL symb left-hand circular or indirect polarization.
cladding I Acoating, something that overlays, a pro-tective covering, sheath 2 A substance, such as
Trang 2such as pressure rolling or extruding Aprocess
some-times used in producing transmission cables 3 A
layer in a laminate (which may be planar or
spheri-cal) with a lower refractive index than its associative
conductive materials, as in a fiber optic transmission
cable, such that incident light is reflected away from
the cladding rather than passing through Glass and
plastics are commonly used as fiber cladding
mate-rials but planar laminates may use other matemate-rials as
well Depending upon the materials and their
refrac-tive indexes, there are effecrefrac-tive ratios between a
clad-ding layer (as in a fiber bundle) and an inner
conduct-ing core as well as limits established by economics
and whether the cable needs to be flexible Different
cladding arrangements have some interesting effects
on light transmission in a fiber cable For example,
the materials in the cladding may be designed to
re-flect some wavelengths and absorb or transmit
oth-ers The cladding may also be designed so that it
be-comes thin at certain bend radiuses to emit rather than
reflect light (thus radiating modes exceed guided
modes) This may seem impractical, but it allows the
fabrication of illuminated "fabric" sheets by weaving
the fibers over a warp layer that deliberately bends
the fiber filament at periodic intervals See index of
refraction, spilling, stray light, total internal
reflec-tance, V number
cladding alignment splicerCAS Aprecision
indus-trial tool for preparing a variety of types of cladded
fibers (single-mode, multimode, dispersion-shifted,
etc.) for assembly and installation The device
pro-vides a tension and alignment mechanism (e.g., a
groove) to facilitate precise splicing of cleaved fiber
filaments It may optionally have fiber end angle
measurement, defect detection and pigtail
continu-ity assessment capabilities Passive alignment
sys-tems (on two axes) provide cladding alignment rather
than core-to-core alignment A CAS typically uses
heat (fusion splicing) to join fiber filaments into a
continuous waveguide Automatic units can create a
splice in about 10 to 20 seconds (not including a
technician's assessment of the visual display of the
splice and its accompanying data parameters)
A CAS typically includes a small built-in display or
a connection to a computer display to provide an
im-age of the assembly and alignment in the X and Y
coordinates, usually magnified about100times This
enables a technician to visually inspect the assembly
Since there are many different splice modes,
depend-ing upon the type of fiber and components, the unit
may be preprogrammed or programmable for quick
setup Depending upon the splicing capabilities, it
may be possible to store and retrieve a log of
splic-ing activities, includsplic-ing the selected splice modes, arc
conditions, estimated efficiency (e.g., loss estimates),
and optional comments Stand-alone units may log
from ca 300to 1000splices Units with computer
connections could provide unlimited logging with
re-movable mass storage, which may aid companies in
monitoring quality control, production changes, staff
training statistics, etc See cleave, fusion splice
ding layer, such as a metal wire with a bonded coating, or a two-glass cladded fiber cable, the di-ameter that includes the cladding layer.Ina perfectly round fiber, this can simply be measured; however,
as the cable may be elliptical, the diameter may be calculated by taking the average of the smallest cir-cular outer diameter and the largest circir-cular inner di-ameter
Cladding&Core Ratios in Optical Cables
In single-modefibers (A), the cladding thickness (1)
is typically much larger than the diameter ofthe tiny
the relationship is typically reversed The core has a higher diameter in relation to the cladding thickness, providing room for multiple wavelengths to travel along the waveguide.
The ideal ratio depends upon manyfactors, includ-ing the cable materials, the wavelengths transmitted, and the degree ofbend that might be expected of the cable during installation.
cladding glassA type of glass or other transparent material used in fiber optic cables that has a lower refractive index than the glass used in the inner core
cladding modeIn a transmission through a cladded conductor, a signal conducted through the outer clad-ding in addition to any signals that may be transmit-ted through the cladded core See cladding beam
clamping 1.Holding within an established operat-ing, baseline, or midline range in a circuit, in order
to maintain various processes or electrical charges at stable or safe levels 2 In a cathode-ray tube (CRT),
a process that establishes a level for the picture dis-play at the beginning ofeach scan line within a frame
clamping voltageAnestablished level of voltage around, under, or over which an electrical device is pennitted to operate For example, clamping voltages can be used to establish a range within which a de-vice operates, by setting them so that any fluctuations above or below that voltage will cause a system shut-down or other protective reactions
Clark cellAtype ofhistoric low-volt energy cell us-ing mercury and zinc amalgam in the cathodes and anodes
Clark, David(ca.1943- )David Clark has been a chairman and active participant in various Internet as-sociations, including the IRTF and lAB He has par-ticipated in numerous research efforts in high speed, very large networks, and network video applications, and various development efforts including the Swift
? : '
-;, :::~.~.,.F .z~
-,tt
Trang 3Fiber Optics Illustrated Dictionary
operating system, Multics and Token-Ring local area
networks (LANs)
Clark, James "Jim" H.(1944- ) Formerly ofSGI,
in 1994 Clark co-founded Mosaic Communications
Corporation with Mark Andreessen, which later
be-come Netscape Communications, distributors of the
most broadly used browser applications on the World
Wide Web See World Wide Web
Clarke, Arthur C.(1917- ) An English-born
scien-tist and writer With remarkable prescience, Clarke
anticipated the age of satellites and long-distance
communications He was talking about it as early as
1942, while still in his twenties, and published an
ar-ticle about it called "Extra-Terrestrial Relays" in
Wireless Worldin 1945 Clarke further wrote detailed
descriptions of geostationary satellite orbits and
sat-ellite transmitting and receiving stationsin the 1950s,
years before the first Sputnik was launched.Inthe
1960s, he collaborated with Stanley Kubrick in the
making ofthe movie 2001: A Space Odyssey (1968),
which has since become a classic See satellite,
Sputnik I
Clark, George Howard(1881-1956) A
Canadian-born American telegraph operator and significant
col-lector of historical radio artifacts, Clark worked for
the Boston and Maine Railroad A scrapbook
enthu-siast as a child, Clark began collecting wireless
ra-dio materials in 1902 In 1903, he graduated from
MIT in Electrical Engineering, specializing in radio
work He then worked for the Stone Telegraph and
Telephone Company in Boston.In1915, while in the Navy, Clark helped devise a classification system for blueprints, photographs, documents, and generaldata
In 1918, he adopted the system for organizing his ra-dio collection and coined the term "Rara-dioana." In
1919, he joined the staff at the Marconi Telegraph Company ofAmerica and later the Radio Corporation ofAmerica (RCA) Clark devised the 'type number system' used by RCA for classifying equipment (e.g., vacuum tubes) From 1922 to 1934, he was in charge
of exhibits of radio apparatus at shows and fairs on behalf of RCA In 1928, he started a radio museum for RCA The museum collection was turned over to the Rosenwald Museum in Chicago, IL and the Henry Ford Museum in Dearborn, MI Clark's collection began to assume some importance when patent in-fringement cases came to court and the documents provided substantive evidence about the radio industry
At his death, the collection was given to MIT and, in
1959, turned over to the Smithsonian Institution See Clark, George H Radioana Collection
Clark, George H Radioana CollectionAnarchive
of historical radio memorabilia and documents col-lected primarily between 1900 and 1935 by radio engineer George H Clark It was transferred from the Massachusetts Insti tute of Technology to the Smithsonian's National Museum of American His-tory in 1959 It is one of the most extensive collec-tions of wireless radio history in the U.S., compris-ing more than 276 linear feet of shelf space at the Amplifier Operations and Emissions Class Categories
Amplifier Categories Description
ClassAamplifier A single-ended circuit in which output current flows during the input cycle, as
related to the grid bias and grid voltage Provides good fidelity at low receiving levels
Class AB amplifier Acircuit in which output current flows for more than half, but less than the
full, duration of the input cycle Better efficiency than a ClassAamplifier but also has higher power requirements
Class B amplifier Acircuit in which output current flows for half of the input cycle More
efficient than ClassAor Class AB but has higher power requirements and can't be configured as a single-ended circuit
Class C amplifier A circuit in which output current flows for somewhat less than half of the
input cycle This provides high efficiency but also has higher power requirements
Emissions Categories Description
ClassAOemission Incidental radiation emanating from an unmodulated carrier wave
transmission
ClassA1 emission A low-speed carrier wave (as those used for early telegraphy) unmodulated by
an audio signal
Class A2 emission Anamplitude-modulated carrier wave modulated by low audio signalst~
transmit simple tones or Morse code
ClassA3emission Anamplitude-modulated carrier wave modulated by audio signals so
intelligible conversation can be transmitted
Trang 4tion includes biographical information on the
pio-neers developing radio and photographs and
docu-ments on the growth and operations of radio
compa-nies, particularly National Electric Signaling
Com-pany and RCA Interestingly, the collection is
ar-ranged according to a Navy filing system devised in
part by Clark in 1915 See Clark, George Howard
CLASSCustom Local Area Signaling Services
Tele-phone subscriber calling options including, but not
limited to, Automatic Callback, Call Trace, Callerill,
Selective Call Rejection In the past, when demand
for these services was lower, they were billed
indi-vidually, depending upon which ones were selected
More recently, phone companies have been offering
monthly flat rate bundles on a variety of these caller
options
Class, facsimileFor information on Class 1and Class
2 facsimile standards and related concepts, see
fac-simile, formats
Class, IPSeeIFClass
class of serviceCoS A general designation for an
agreed or specified level of functioning or security,
which varies from industry to industry In
telecom-munications, network configuration and tuning and
sometimes billing levels are established according to
class of service parameters See quality of service
Classical IPA set of specifications for an
asynchro-nous transfer mode (ATM) implementation model
described in the early 1990s by the Internet
Engineer-ing Task Force (IETF) for local area internetworkEngineer-ing
In Classical IP implementations, IP headers are
pro-cessed at each router, creating latency and limiting
throughput Due to the increase in demand for
multi-media capabilities, ClassicalIFis showing its age
One of the limitations of Classical IP is that direct
ATM connectivity exists only between nodes with the
same IP address prefix See ATM models for a chart
of some historic and new ATM models See
RFC 1577
Classmark Anelectronic designation that identifies
privileges and restrictions associated with a
particu-lar communications line or trunk See class ofservice
CLC 1.Carrier Liaison Committee.2.Competitive
Local Carrier
cleaning arcAbriefelectrical spark generated by an
electrode for the purpose of removing particulate
matter from a surface Cleaning arcs are used in
fu-sion splicers for cleaning the ends of fiber optic
fila-ments prior to joining since any undesired particles
in the joint could interfere with light transmission
See fusion splicing
clear 1 In computer monitor displays, to blank a
screen, applications window, or tenninal window The
clearcommand provides a clean slate, a visual
work-ing space without clutter, obsolete information, or
dis-tractions 2.In programming, to set a storage
loca-tion (a buffer, address, etc.) to a zero state, blank state
(as with space characters), previous state, or default
state 3.Incommunications, a clear signal is one
with-out noise or interference and of sufficient volume or
intensity to be heard or seen distinctly
transmission line that is used entirely for communi-cation, and no control or other signaling bits are be-ing transmitted In other words, all the resources are available for the infonnational communication 2 In radio communications, a station that is permitted to dominate a frequency and broadcast at a certain power level or up to a certain distance (e.g., 750 miles) during a specified time of day A type of ex-clusive frequency arrangement
clear to sendCTS.Ahandshaking signal provided when the communication has been set up over a se-rial link, and the called modem is ready to receive information See RS-232
clearanceIn electrical installation, the shortest dis-tance between separated live conductors, or between live conductors separated from physical structures,
or between live conductors separated from associated grounds See gap
cleavage planeA planar direction in a material in which the molecular bonds that hold the substance together can be more readily cleaved Many materi-als have a "grain," a general direction in which the fibers or lattice structure are aligned Thus, most pa-per tears more readily in one direction than another and a number of materials used in electronic compoents will cleave more readily depending upon the orientation of the material with respect to the cleaver For example, birefringent materials, those with a molecular structure that is the same in two planes and different in a third, will generally cleave more readily when nicked, broken, sawed, or sliced across the plane in which the bonds are weaker Knowledge ofthe composition ofmaterials and their cleavage plane is useful in materials science and ma-terials and component fabrication See cleave
cleaveTo cut or break a cable or component so the broken surface meets certain needs, as in junctions, solder joints, or optical connections With basic elec-tricity-conducting wires, the angle or cleanliness of the break in a line is not usually critical, as wire can
be readily wrapped or soldered in place without sig-nificant loss to the signal However, with layered wires or certain electronic components, where a smooth or straight surface might be important to the electrical contact, or in fiber optic cable, where rough edges can degrade the light-carrying properties ofthe fiber, a precise cleave is critical
Wire is usually cleaved with scissors, knives, or spe-cialized cutters, depending upon the gauge of wire and the importance ofa clean cleave Fiber optic fila-ments are usually cleaved with mechanical blades, but some systems use ultrasonics for the very precise cleaves desired for fusion splicing See cleavage plane, cleave angle, cleaver, crimp, fiber optic; fu-sion splice
cleave angleThe angle at which a surface is cut rela-tive to a reference Cleaving is often done prior to creating a glued or fused joint or adding a connector, but it may also be used to provide an unimpeded exit path for an optical signal (e.g., a fiber optic sign or lighting fixture)
Trang 5Fiber Optics Illustrated Dictionary
Cleave - Basic Types
that produce a cleaner cleave and claim that polish-ing is not necessary For complex bundled assemblies, polishing may still be necessary
1
C
C _ _
B A
There are a number ofways to cleave a wire or cable, depending upon the materials Wires andplastics can often be cut all the way through with a knife (A) or
me-tallic compounds often cleave better ifnickedfirst and bent until they break at the point ofthe nick (B) (the effectiveness ofsnapping depends partly upon the di-rection of the grain) Glass may break more cleanly and evenly ifnicked or scored (C) and then snapped Nicking and snapping often provides the best cleave for fiber optic filaments.
Fiber optic cleavers come in many shapes and sizes Some resemble microscope components, with view-ing and testview-ing capabilities, some have computer in-terfaces for magnifying or analyzing diffraction pat-terns in the filament that has been cleaved, some sup-port polishing components, and some are compact units resembling staplers Sizes range from handheld
to table-top Mid-sized cleavers for field work may have tripod mounts for securing in a mobile lab or
an outdoor or in-plant location where there is no flat workspace for setting up the cleaver
Since fiber scraps can get in the way and present a safety hazard (the shards are small and sharp) a tray for collecting the fiber end scraps is sometimes in-cluded with cleaving devices It is important to shield the eyes with safety goggles and to remove any fila-ment shards not discarded into trays when working with cleavers
The angle ofa cleave will influence the amount of
surface area that is availablefor connecting orfusing
a fiber optic filament The smaller the angle, the
greater the surface area This has advantages and
dis-advantages A larger surface area may provide added
strength in certain directions and a strongerfuse, due
to the larger surface area, but it also is more difficult
to cut and match and creates a larger area in which
contaminants or aberrations in a joint can interfere
with light transmission.
A straight (90") angle is used when the filament is
being terminated, hand spliced, or spliced with a
ma-chine that is set to rotate the two ends independently
prior to splicing Angle cuts must be carefully matched
gap that interferes with light propagation.
Cleave Angle Effects
y
- - - - x
Inwires and fiber optic filaments, the angle is
mea-sured relative to the lengthwise conductive core and
is usually described and handled in two planes Thus,
if the core is horizontal (in the X plane), the cleave
angle is described in terms of its angle as it rotates
through the X-V plane There's no reason why the
angle in the Z plane couldn't also be described, but
in most fabrication technologies for wire and cable
splicing and attachment, the Z plane is kept at right
angles to the X reference for simplicity (and because
there's usually no added benefit in altering Z angles)
Cleave angles vary depending upon the materials
being cut, the cleaver, the purpose of the cleave, and
any tension factors that may act upon a cable that is
to be cleaved and spliced A900cleave may be easier
to cut and fuse and may provide a better unimpeded
path for signals due to the smaller fused
cross-sec-tion, but an angled cleave (e.g., 45°) may provide a
stronger connection due to the larger fusing area and
may withstand better forces against the fused joint
For end-emitting fiber filaments intended for signage,
artworks, or lighting fixtures, an angled cleave can
influence the shape and the amount of light that
es-capes from the endpoint See cleave
cleaver, fiber optic A device specifically designed
to provide the precise, clean cleaves required for
fus-ing fiber optic filaments together, or for attachfus-ing
connectors to a fiber filament Tolerances are usually
within 0.5°
Traditionally, optical fibers to be coupled with other
components were cleaved and then polished to
pro-vide the cleanest surface possible at the terminal ends
However, some manufacturers now promote products
Trang 6diameter range and type of fiber to be cut (glass or
plastic) There may be different blade heights and
ro-tations to accommodate different sizes See cladding
alignment splicer, crimp, interferometer
Cleave Area and Strength
In fiberfilaments, cleaves intendedfor splicing must
be clean and precise to prevent inte171lption or back
reflection ofa light signal passing through the joint.
The angle ofthe cleaves to bejoined should match (in
most cases) tofacilitatefusion Narrower angles (e.g.,
45 0
from perpendicular in the orientation shown
above) create larger surface areasfor fusion and may
resist breakage from forces in certain directions, but
may also influence the lightguiding properties ofthe
joint if the angles don~match rotational
characteris-tics of the fiber (e.g., in polarized cables) Angle
cleaves are generally more difficult to cut and splice,
especially with hand tools.
CLECSee Competitive Local Exchange Carrier
Clerk-Maxwell, JamesSee Maxwell, James Clerk-
click tonesA signaling system common on phone
systems, especially wireless phones, that alerts the
user that the call is being processed
clickstreamslangAdescription ofthe flow ofevents
and sites visited when a user navigates the Internet,
particularly the Web, which is connected through
clickable hyperlinks Product vendors have an intense
commercial interest in monitoring user behavior and
maneuvering users to their sites
cleavage clientA system or application that serves
the user but that may seek or require information or
operating parameters through a host with a higher
pri-ority or greater capabilities In the past, host and
cli-ent have had almost opposite meanings for some
computer administrators, but for consistency in this
dictionary, and because the trend is in this direction,
client is defined as the adjunct or subservient system
or application See host
client applicationIn a client/server computer
soft-ware application, the client is typically the
applica-tion used by the user to communicate to a source or
destination through a related higher priority or more
powerful (or just different) server program The
Net-of a common client application that communicates
to Web sites through a Web server, handles the traf-fic, and provides some measure of security
client operating systemOn a network, the operat-ing systems run on client machines, user tenninals, and subsidiary machines These do not have to be the same as the server operating system A good server can handle a variety of client OSs and network be-tween them seamlessly, using standard network pro-tocols For example, you may have a network that is configured with a Sun workstation and Sun operat-ing system (SunOS, Solaris) as the main server, with
a number of different client platfonns connected to
it, running different client operating systems and op-erating environments, such as Linux, Apple Computer'sas x,Be Inc.'s BeOS, or Microsoft Win-dows
client/server modelA computer processing method
of improving efficiency, and sometimes security, by selectively distributing activities In human enter-prises, there is often amanager with an overall knowl-edge of the work to be done, security clearance, and the authority to designate tasks and respond to re-quests.Inconjunction with the manager are workers with knowledge of specific tasks and needs, lower security clearance, and instructions to report their findings and to direct their questions and requests for resources to the manager A client/server model on a computer system is similar to this.AnISP's Web server has the logic and security clearance to accept requests from many Web browsers, and to fetch the infonnation and serve it back to the browsers which then fonnat and display the information for the user Most networks work on client/server models, where the server handles administrative details, file man-agement, and security, and the client machines, usu-ally tenninals or desktop computers, handle input and output, local processing, and display
CLIPcalling line identification presentation (e.g., as
in ISDN Q.81 and Q.731 number identification ser-vices)
clipboardIn most operating systems, and in some software programs, an area of memory or a file on a hard drive designated to hold information (usually images or text, but may also be sound or video clips)
that has been cut by the user for later retrieval Most
clipboards store only one clip at a time, with subse-quent clips over-writing previous ones, so that only the most recent can be retrieved Some clipboards can handle multiple clips, and some store the informa-tion on disk for later retrieval On the Macintosh, for example, a user can save clips by copying or cutting them and storing them in the Scrapbook Clips can
be retrieved later by paging through the clips, select-ing those desired, and copyselect-ing and pastselect-ing them back into an application
Clipper chipAmicroprocessor chip that provides se-curity encryption features that can be incorporated into electronic devices The Clipper chip has become the focal point for broad and heated debates over the privacy of global communications The U.S federal
Trang 7Fiber Optics Illustrated Dictionary
governing bodies had initiated plans to include the
chip in consumer telecommunications products, to
secure conversations from anyone but the
govern-ment The plans were initially announced in 1993
through the White House Escrowed Encryption
Ini-tiative The system was designed by the National
Security Agency (NSA) Three versions of the
pro-posal, Clipper I, II, and III were promoted between
1993 and 1996
Most people agree that there is a need for voluntary,
widely available encryption options for government
and private use, and vendors agree that standards
pro-vide a means for them to distribute products with
intercompatibility But on this issue, concern has been
expressed about how the government is intending to
implement and enforce encryption policies, and on
their assertion that the system will work only if made
mandatory There has been a considerable outcry
from vendors and the public, who questioned the
ro-bustness ofthe technology, and who are gravely
con-cerned about too much power being in the hands of
too few people
In spite of the negative feedback, the Department of
Commerce approved the Escrowed Encryption
Stan-dard (EES) as a voluntary Federal Information
Pro-cessing Standard (FIPS) in 1994 One of the
require-ments would be that every Clipper chip would have
its unique key registered with the federal government
and held in split form by two federal escrow agents
(NIST and the Treasury Department), creating
acces-sibility for the federal government to wiretap secure
communications The debate over the chip, privacy,
and law enforcement led in the fall of 1994, to the
Encryption Standards and Procedures Act, which
de-scribed federal policy governing the development and
use of encryption technology for unclassified
infor-mation Back references were made to The Computer
Security Act of 1987
The public responded in many ways to the various
proposals regarding the Clipper chip Some sought
to point out flaws in the process and design; others
created free user-encryption programs that would
de-feat the Clipper system One of the more significant
challenges to the system was the X9 Accredited
Stan-dards Committee (ASe) announcement that it would
develop a competing data security standard based
upon triple-DES The ASC sets data security
stan-dards for the U.S financial industry
The Clipper chip uses a nonpublic encryption
algo-rithm called SKIPJACK which cannot be read offthe
chip and is designed so that it cannot be reverse
en-gineered According to the EES, when two devices
negotiate a communication, they must both have
se-curity devices with Clipper chips and must agree on
asession key, which may be a public key such as RSA
or Diffie-Hellman The message is then encrypted and
sent with a law enforcement access field (LEAF), a
serial number, authentication string, and a family key
When received, the LEAF is decrypted, the
authen-tication string verified, and the message decrypted
with the key See Capstone chip, LEAF, Pretty Good
Privacy, SKIPJACK
information, such as graphics, text, sound or video, usually for later retrieval or insertion elsewhere See clipboard 2 In graphics programs, the process ofre-moving parts of an image, or of the display outside some designated boundary, usually the outer margin
of a picture, or of an application's window
Informa-tion that is clipped mayor may not be retained in
memory Often a program will retain the information, even if the user can't see it, so the user can quickly restore the information or scroll quickly through the image without recreating it or having to wait for the computer to reread it from disk 3 In audio, a brief loss of sound, especially at the beginning or end of a transmission due to limitations of the technology (limited frequency range, direction flipping, ramp-up time) 4 In audio communications, especially phone calls over satellite links, the equipment may be oper-ating part of the time in half duplex mode, transmit-ting in only one direction at a time, so gaps in the con-versation may cause a switch in the other direction and clip part of the conversation
CLIRcalling line identification restriction (e.g., as
in ISDN Q 81 or Q.731 number identification services)
CLLISee Common Location Language Identifier
various gravity (sand, weights) or oscillating mecha-nisms (radioactive decay, emissions, crystal vibra-tions) to track time Quartz crystals have extremely consistent vibrations that are sometimes used to make very accurate clocks 2 A device that provides regu-lar signals for use as a timing reference On a
com-puter, instruction speeds are expressed in clock cycles.
indi-cated on a clock and True Universal Time See Co-ordinated Universal Time
per-formance out of a computer instead of having to re-place the system With constant demands for faster systems, balanced by the high cost of replacing a sys-tem that may be only a year old or less, some manu-facturers have provided versions of the CPU chip or accelerator accessories that effectively double the speed of the CPU This does NOT mean performance
is doubled The CPU is only one part ofa system, and the bus rates, coprocessing chips, sofrware design, op-erating system parameters, and other factors, will af-fect the actual performance increments to a great ex-tent In other words, the speedup is usually more on the order of20% or so but, for graphics computations
or resource-hungry sofrware, that might be an impor-tant 20% Sometimes it's worth it; it depends upon the cost of the doubler
the speed of a central processing unit (CPU) or other processing chip, usually expressed in megahertz Mi-crocomputers in the 1970s ran at clock speeds rang-ing from about I to 4 MHz In the 1990s , they ran at about 200 to 300 MHz Current microcomputers in consumer price ranges run at over 700+ MHz
Clock speed is not equivalent to system speed.
Doubling the clock speed doesn't mean doubling the
Trang 8slightly more, and sometimes it is three or four times
more Determining the overall speed of a computing
system is complex and requires evaluation ofthe
gen-eral architecture of the system, the efficiency of the
operating software, the amount of memory, the
in-clusion of coprocessing chips, and the type of
appli-cation being run
For example, the author's first 8-kilobyte RAM (yes,
kilobyte, not megabyte), 1.8-MHz system ran
tele-communications software and word processors very
effectively at typing speeds of over 80 wmp A
fea-ture-rich, well-written graphical word processor can
run very efficiently on an 8-MByte RAM, 10-MHz
system The same software running on a 16-MByte
233-MHz system often is notperceptuallyfaster
be-cause text entry, at its basic level, is not a computing
intensive application
In contrast with basic word processing,
computing-intensive applications, however, can be dramatically
affected by clock speed A stock 1.8-MHz system is
essentially incapable ofdoing 3D ray-tracing in a
rea-sonable amount of time, whereas an older Amiga
computer with a clock speed of only 7.16 MHz can
render a complex 3D scene in 3 or 4 days, faster than
many 25-MHz computers with different
architec-tures Amigas with 40-MHz accelerator cards can
ren-der the same scene in 3 or 4 hours, and dedicated
graphics systems, running on parallel processing
sys-tems, or current Silicon Graphics Machines, for
ex-ample, can accomplish the same feat in minutes or
seconds
Since computing speed is important to computer
elec-tronics designers, a number of measures have been
established to provide information for comparing
chips, systems, or architectures These benchmark
tests are not absolute measures of clock speed, but
they provide some information that is helpful and they
generate some pretty entertaining controversy See
benchmark, clock doubling, Dhrystone, Whetstone
clonen 1 Duplicate, exact copy, genetically
identi-cal individual 2 A software program or device
con-figured to masquerade as another device, either for
diagnostic purposes, interim use, or fraud
clone fraudA method of gaining entry to a system,
or using a device, by simulating a user, serial
num-ber, or access code Cellular phones are particularly
susceptible to clone fraud, as it is not difficult to
pro-gram a legitimate serial number into another cellular
unit See tumbling
closed architectureAproprietary design that is
sup-ported and enhanced by peripherals that conform to
its particular specifications, and that may not be
manufactured by third party vendors, except perhaps
by obtaining special permissions or paying royalties
Contrast with open architecture
closed captioningCC A broadcast technique for
transmitting text, usually to be superimposed over a
corresponding television image CC is provided
mainly as an aid for the hearing impaired, although
in some cases it may also be used to provide subtitle
translations It is typically sent on the vertical
blank-be required to interpret the signals
closed circuitAbroadcast circuit in which the send-ing and/or receivsend-ing components are limited to a cer-tain frequency range or power level Thus, a closed circuit radio system within a complex may be set to send and receive FM signals at 89 hertz Aradio sta-tion may have permission to broadcast at only 91.7 hertz on frequency modulated (FM) signals.In con-trast, an open circuit is one that is not restricted to a narrow frequency range, as a CB radio, for example, which may be set to pick up signals broadcast over a variety of channels
closed circuit broadcast, closed circuitTV Aradio
or television transmission that is broadcast to a small
or restricted audience, often within a specific build-ing complex or campus Low power frequency modu-lated (FM) ranges are often used for this type oftrans-mission because they are not as strictly regulated as higher power transmissions
closetA room, cabinet, or case used for terminating blocks or patch panels for wiring configurations The closet serves a variety of aesthetic, safety, organiza-tion, and security purposes
cloud networkFrame Relay network connections are now offered as a lower cost alternative for small busi-nesses and educational institutions, and a cloud re-lay is one connectionless option ofthis type in which resources are shared, usually among four or five small subscribing organizations
CLPcell loss priority Aone-bit ATM networking cell header toggle indicating the relative importance of the cell CLP is important as there are various mecha-nisms in ATM for prioritizing cell traffic, or discard-ing cells in congested situations See cell rate CLRSee cell loss ratio
CLTPSee Connectionless Transport Protocol
CLTSConnectionless Transport Service
cluster1 In cellular communications, a unit consist-ing of a group of adjacentcellswithin which chan-nels are not reused See cell, cellular phone, mobile phone 2 A set of workstations or terminals in the same general physical or virtual networked grouping These may share more than physical connectivity; they may also have shared devices that manage pro-cessing input and output, or specialized requests of the cluster See cluster controller 3 Acombined unit
of disk storage allocation, usually consisting of four
or more sectors
cluster controllerAdevice controlling communica-tions input/output for multiple connected devices
clutterWave reflections from obstructions such as terrain and buildings, which may show up as echoes
or unidentifiable blips on a radar screen, thus inter-fering with scanning
CMA See Communications Management Association CMCSee connection management controller CMISee coded mark inversion
CMIP See Common Management Information Protocol
CMOLCMIP Over LLC (Logical Link Control) See Common Management Information Protocol
Trang 9Fiber Optics Illustrated Dictionary
CMOS Complementary Metal Oxide
Semiconduc-tor A semiconductor chip that combines p-channel
and n-channel MOS in a single substrate with
push-pull circuits Slow, but noise resistant, and good for
battery-operated devices CMOS RAM needs a small
stream of constant power to preserve information
stored in its memory, which is typically supplied by
a lithium battery (available in photography and
elec-tronics stores) Default settings and sometimes video
card and other peripheral parameters may be stored
in CMOS RAM linked with a lithium battery on a
computer's motherboard See PRAM
CMOT CMIP Over TCP See Common Management
Information Protocol
CMR See cell misinsertion rate
CMRS/PMRS commercial mobile radio
service/pri-vate mobile radio service The Federal
Communica-tions Commission (FCC) was directed, through the
Omnibus Budget Reconciliation Act of 1993, to
auc-tion radio spectrum for CMRS Unfortunately, the
initial spectrum allocations in the C and F blocks,
intended for small businesses, did not work out well
in practical use After numerous discussions and
bankruptcy lawsuits, the FCC announced the cancel-
lation of certain licenses and began to reauction
por-tions of the C and F Block radio spectrum, beginning
in 2000 See A Block for a chart of frequencies See
Omnibus Budget Reconciliation Act
CMTS Cellular Mobile Telephone System
CMYK A color model widely used in the paper
print-ing industry The initials signify cyan, magenta,
yel-low, and black, which are the four colors combined
as tiny dots inprocess color printing jobs to
simu-late all hues and black Black is included because the
combination of the first three does not give a dark,
rich, black pigment Metallic colors cannot be
pro-duced within this color model, and extra runs through
the press or spot application of metallics on a
multicolor printer are necessary to accommodate
me-tallic effects Computer publishing software often
seeks to simulate these colors on the monitor in
or-der to provide WYSIWYG in the [mal printed result
CN complementary network
CNA I Centralized Network Administration A
means of consolidating network-related connections
in a single location, usually a wiring closet or panel,
rather than distributing them in various parts of the
premises 2 Cooperative Network Architecture
CND I Calling Number Delivery 2 Calling
CNET Centre National d'Etudes des
Telecom-munication, now France Telecom R&D
CNG A calling tone emitted by facsimile machines
that lasts about half a second and repeats as many
times as the software dictates, to signal its presence
and to try to establish a negotiation with a receiving
fax machine Most machines default to about 45
sec-onds oftone sequence before they disconnect, ifthere
is no successful connection This time may not be
enough for some systems or for a long-distance
con-nection and some fax machines and fax modems have
an option for extending it
Most fax machines now automatically dial and emit the CNG However, some of the older fax machines,
or bargain basement varieties, still require a human operatortodial the number The operator must then wait to hear a fax response and start the fax machine CNG by pressing a button This method is a problem
if the system that has been dialed has a sensing de-vice to route incoming calls to a phone, modem, or fax machine depending upon the tone If a human dials the line as a voice call, the switcher will route it
to a phone, and then starting the calling fax's CNG does no good, as the phone has no way ofrouting the call back thJough the switcher to the fax machine However, with increasing automation and decreas-ing cost of better fax machines, this problem is be-coming less prevalent
CNIS Calling Number Identification Services CNR I See Complex Node Representation 2 cus-tomer not ready
CNRI Corporation for National Research Initiatives
CO I cash order 2 See central office 3 command-ing officer
co-channel interference CCl A quantitative expres-sion of inteference in a communications circuit when multiple channels are arranged in such a way that they may interfere with transmission on a neighboring or associated channel This concept is especially impor-tant in wireless communications in which increasing numbers of subscribers are being accommodated within limited frequency allocations
One way to reduce CCI is with guard bands, but the tradeoff is lost bandwidth Another way of reducing CCI is with adaptive beam forming See antenna, smart
COAM See Customer Owned And Maintained coaxial cable A transmission cable consisting essen-tially of an irmer conducting core surrounded by a conducting tube, each insulated and all wrapped to-gether in an outer protective sheath The inner core
is a metallic conductor surrounded by a metal shield, that acts as aFaraday cage, with a dielectric
mate-rial interposed between them Typically, the signals are propagated in one direction along the conduct-ing core
Coaxial cable was an important development for the transmission of telegraph, telephone, and television signals as it was found to conduct radio frequency (RF) signals well By the late I940s, much ofthe east-ern United States was interconnected with coaxial cable
Coaxial cables are typically described in terms oftheir impedance; values from 50 to 95 ohms are com-mon The video industry makes extensive use of75-ohm coaxial cables for interfacing cameras, frame synchronizers, and recording decks.Incomputer net-working, 75-ohm cables are used for unbalanced E I connections Higher impedance 100- to 120-ohm twisted-pair wire is used for balanced EI connections, and subrate cabling in trunk/circuit lines
coaxial omniguide A lightguiding cable based upon layered film mirror technology developed at MIT in the late 1990s in a project led by Francis W Davis
Trang 10Omniguide Communications to further develop and
market a transmission cable based upon the
technol-ogy that would reflect a wider range ofwavelengths
in a smaller space without changing the polarity or
creating pulse distortion characteristic of traditional
cables
COBOLCommon Business-Oriented Language A
verbose, high-level programming language once
widely used for business applications and still taught
in business schools, but which is slowly being
re-placed by other languages See OO-COBOL
CoBRAA commercial, portable, ISDN analyzer for
installation, maintenance, and troubleshooting of
ISDN Basic or Primary Rate networks, from
Consultronics Consultronics now markets the
CoBRA-CQ as a portable local loop test set for ISDN,
ADSL, G.lite and other formats
COBRAA frequent misspelling of CORBA,
Com-mon Object Request Broker Architecture See
CORBA, Object Request Broker
COBRASCosmic Background Radiation Anisotropy
Satellite
COCOTcustomer-owned coin-operated telephone
See payphone, private
CODconnection-oriented data
code 1 A system of symbols, cyphers, characters,
images, movements, sounds, or other meaningful
marks or actions that serve to represent ideas and
lan-guage in a way that is not commonly understood or
recognized Not all symbolic forms of
communica-tion are considered to be codes For example,
Ameri-can Sign Language is not understood by many, but it
is not considered a code in the sense that
informa-tion on learning it is readily available in schools and
libraries
Social changes can alter the perception of whether
something is a code Before the development of the
printing press and public education, text and reading
were mainly restricted to the elite political leaders,
and common people probably considered it as a sort
of code The use of coded information is common in
wartime, or with politically or economically
sensi-tive infonnation Some codes are exceedingly
sophis-ticated and difficult to break Until recently, most
analog communications have not been coded to
pro-tect privacy, due to the difficulty of doing so With
recent digital technology, it has become much easier
to code communications, and many software
devel-opers and equipment makers are adding encoding to
their products Many satellite communications, cell
phone messages, and computer data communications
are now encoded 2.Anabbreviated means
ofrepre-senting information in order to save time in its
tran-scription or transmission, or to send it over limited
transmissions devices, and sometimes also to shield
it somewhat from prying eyes Shorthand is a type
ofcode intended to save time in taking oral dictation
Drumbeats or smoke signals are two types of codes
designed to abbreviate information so that it is
prac-tical to transmit through these basic means
Basic telecommunications codes have been in
devel-telegraph code in 1832 Morse (Vail) code is a widely used alphabet coding system developed in the early 1830s It is still often used in telegraph and radio com-munications, particularly in countries with limited ac-cess to computer equipment See semaphore, Baudot code, Hollerith, Morse code 3 Computer program-ming code is a system oflinguistic and symbolic char-acters and syntax that serves to represent computer instructions so they can be run directly by the ma-chine or compiled into mama-chine-readable form
Code designations in packet networkingSee Link Control Protocol codes
Code Division Multiple AccessCDMA A digital, wireless communications service based upon spread-spectrum technology, which claims to provide about
10 times the capacity of analog Access to the local exchange is wireless
This technology was originally used in military sat-ellites for its security features and resistance to jam-ming Now more widely used in commercial appli-cations, it provides access to many users at a time without the multiple user interference associated with other modulation techniques The same frequencies
in adjacent beams can be reused by assigning vary-ing spreadvary-ing codes to users The method offers au-thentication of the source transmitter and is very se-cure against eavesdropping
Frequency reuse logistics in AMPS and DAMPS sys-tems are eliminated in CDMA by assigning codes to users so they can share carrier frequencies The sys-tem capacity is not fixed but is influenced by the ac-cumulated noise and interference associated with power levels and simultaneous users
CDMA, supported by companies like Sprint and PrimeCO, is somewhat similar to TDMA, with some-what less built-in support for private branch applica-tions B-CDMA is also in development as a propri-etary technology by a group of vendors supporting InterDigital Communications See B-CDMA, spread spectrum
Technique Description DS-CDMA Spread spectrum technology in
which codes are used to modulate information bits such that each code is assigned to prevent the overlap of signals from user to user The receiver regenerates the code and uses the information to demodulate the transmission FH-CDMA Agroup of changing frequencies
are modulated by the information bits in a two step process First, the carrier frequency is modulated, and these modulated frequencies further modulate frequencies while still keeping them independent