The physical layer is independent of the actual medium used and thus the layer model applies equally to electrical voltages in wired lines, radio waves in wireless transmissions, and las
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and others The OSN architecture is intended to
fa-cilitate the interoperability and accessibility of data
via industry-standard networks.
Open Trading Protocol OTP See Internet Open
Trading Protocol.
Open Video System OVS A regulatory distinction
for video services carried by Local Exchange Carriers
(LECs), for example, who are not recognized as
lo-cal cable service providers per Federal
Communica-tions Commission (FCC) guidelines and regulaCommunica-tions.
Thus, a local exchange carrier (LEC) could become
an OVS operator, but was also required to provide nondiscriminatory access on a portion of its channel capacity to unaffiliated program providers By 2000,
25 OVS operators had been certified to serve 50 areas.
The mid-1990s was an important time during which technological advances made it possible for a wider range of types of providers to offer a broader range
of telephony and cable programming options to their subscribers In addition to this, the Telecommunica-tions Act of 1996 opened the doors for tekos to offer
ISO/Open Systems Interconnection (OSI) Reference Model
From bottom to top, seven layers have been defined for OS I, ranging from physical and data layers through presentation and applications layers, thus following a low-level to high-level an'angement com-mon in many computer architecture models The selection of the layers was based on subdivisions cho-sen to distinguish well-defined functions and various levels of abstraction In general, layers are re-lated to services provided by the layers below In actual implementations, the situation is a little more complex and many variations with sublayers or lesser-used layers exist.
Layer Function Number Purpose, Implementation
Application Layer 7 User interfaces, applications programs, emulation, and other higher-level
software implementations.
Presentation Layer 6 Character sets, text handling Data conversion into standard formats for
transmission over a network or conversion from the transmitted format
to something that user applications can understand Encryption and other means of data security are also handled at this layer.
Session Layer 5 Connection and session mechanisms for facilitating intercommunication
between networks File transfers, program sharing, data sharing, and basic traffic direction are managed at this layer to provide an orderly exchange of information (e.g., management of simultaneous requests from different users that might affect data integrity).
Transport Layer 4 Process-to-process communications, addressing, and a number of
end-to-end services The data are packaged into packets in preparation for transmission Identification is added so that disassembled packets that may travel different routes can be reassembled at the destination Local network addresses may be defined at this layer Error handling not already managed by lower levels may be handled here with respect to reliability and data integrity.
Network Layer 3 Host-to-host communications and basic transfer units (packets), network
addressing, forwarding, and routing Addresses may be provided by the Network Layer to the Transport Layer.
Data Link Layer 2 Activation, handshaking, interfacing, and other basic communications
intended to initiate, regulate, and terminate a communications session Common functions at this level include the management of wired connections (modems, Ethernet, etc.) or wireless transmissions, although the actual physical medium used is handled by the Physical Layer transparently to the Data Link Layer Low-level error handling, data synchronization, and flow control are managed at this layer.
Physical Layer I The transmission medium, electromagnetic properties, and other
physical aspects associated with getting the signal from one place to another such as cables, devices, buses, signaing, etc The physical layer
is independent of the actual medium used and thus the layer model applies equally to electrical voltages in wired lines, radio waves in wireless transmissions, and laser light beams in fiber optic cables.
Trang 2or to develop wireless cable systems Together, these
conditions resulted in blurred distinctions between
cable and telephone companies since many services
were now being offered over the same media Thus,
regulatory authorities were asked to clarify some of
the issues and the FCC Cable Services Bureau became
involved in this process
On the other side of the equation, in 1996 the cable
providers expressed concerns about telcos not being
regulated in the same way as cable companies were
by the Cable Act Organizations such as the National
Cable Telecommunications Association argued that
the FCC exceeded its authority by preventing cable
operators from switching to become Open Video
Sys-tems (OVS) providers, as defined by the FCC
In January 2001, the FCC presented its seventh
An-nual Report on competition in the video markets The
document confinned that cable TV was still the
domi-nant video delivery technology, but with a declining
market share ofa couple ofpercentage points per year
Cable service rates increased slightly more than the
rate of inflation in general over the study period.
In-terestingly, it was found that few telephone
compa-nies had sought OVS certification since 1996 See
Telecommunications Act of 1996, Video Dial Tone
operandA quantity or information which is being
manipulated For example, in mathematics, if you
divide 200 by 10, then 200 is the operand In
com-puter algorithms, data, or the address of the data to
be operated upon, are passed to an instruction in
or-der for the instruction to act upon the data
operating environmentThis has two meanings,
de-pending upon the context It is used in a limiting
con-text to describe an operating system which isn't fully
integrated or fully multitasking It may be
task-switching, or it may have a graphical user interface
on top of a text-based operating system not fully
implemented as multitasking Many vendors have
claimed multitasking operating systems which were
not really so.In its second, broader context, it refers
to the environment surrounding an operating system,
that is, the system, the software that runs it, the
periph-erals and applications that support it, etc.An
operat-ing environment, in this broad sense, may encompass
more than one operating system
operating systemOS The most important software
on a computer is that which lies between the user
ap-plications and the hardware It's not possible to
con-trol the CPU, manage memory, access a disk drive,
send images to a monitor, or transmit data through a
network connection or modem without an operating
system The operating system handles interrupts,
tim-ing, the movement of data from one register to
an-other, and all thenitty-grittyoperations that are
typi-cally not seen or understood on a technical level by
most users
Microcomputer operating systems began to be
devel-oped in the 1970s The early ones were text-based
One of the first widely used, popular operating
sys-tems was CP1M,designed by Gary Kildall CP1Mwas
the forerunner of QDOS, and hence, MS-DOS, and
TRS-DOS, UltraDOS, and other TRS-80 operating systems shared many common properties with CP/
M Kildall also later designed a multitasking operat-ing system and a graphical user environment (GEM)
In the early 1980s, Apple created proprietary operat-ing systems for their Apple and Macintosh lines of computers, featuring the first widely distributed graphical operating system descended from pioneer-ing work at Xerox PARCo This concept was so suc-cessful that it has since been adapted by virtually all subsequent vendors, including Atan, Commodore Amiga, Apollo, Sun Microsystems, Microsoft, SGI, The X Windows System, and NeXT It's difficult to find a computer now that doesn't have a graphical user interface on top of, or in conjunction with a text operating system, or which is fundamentally agraphi-cal operating system The various versions of Win-dows are popular on consumer-level, Intel-based sys-tems
A number of multitasking systems were developed
in the late 1970s and early 1980s, but the first widely distributed commercially successful preemptive multitasking operating system on a microcomputer was AmigaOS, introduced in 1985 Most ofthe work-station level computers had multitasking operating systems by the early or mid-1980s, and the other ven-dors began to follow this lead in the late 1980s, most notably OS/2 (Operating System 2), originally devel-oped jointly by IBM and Microsoft Many other op-erating systems released around this time were task-switching rather than fully multitasking Microsoft Windows has since become widespread on personal computers, with Windows NT, originating out of the OS/2 collaboration, used on many server systems Unix is one of the most robust, earliest, and most important operating systems A high proportion of institutional computing operations, much scientific research, and many Internet hosts run on Unix sys-tems Unix is freely distributable, powerful, flexible, dependable, well-supported, and runs on most com-puters Linux is a popular implementation ofUnix (as
is BSD), available from a number ofcommercial and free distribution sources Along with Apache, a freely distributable server software, Unix!Apache systems are used by thousands ofInternet Services Providers
to provide gateways to the Internet through the Web
An operating system runs a computer, and comput-ers are increasingly delegated control tasks beyond those humans can handle alone or in cooperation with one another Navigational aids on aircraft are a good example Fighter jets traveling at hundreds of miles per hour move too quickly for the human nervous system to react in time to control every aspect of the plane's behavior, so computerized systems handle many functions on the pilot's behalf Extrapolate that type of control to appliances, houses, security sys-tems, currency exchange, intelligent vehicle syssys-tems, and every aspect ofhuman society that will someday
be controlled by computers through a 24-hour Inter-net connection to all the other computers in the world Given this broader outlook on our probable future,
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the importance of carefully choosing a reliable
oper-ating system cannot be overemphasized Buying the
cheapest system or the most popular system, or
passively allowing the choices to be made by
profit-based corporations is, in the long run, a more
far-reaching decision than selecting a President or other
political leader Why? Because a President who does
a badjob can be voted out.Anoperating system that
does a bad job cannot be disabled if it has been
del-egated important tasks such as running medical
equipment, automated transportations systems, or
en-vironmental controls Once a fighter plane has been
designed with a dependency upon computer control,
you can'tjusttumoffthe software in mid-flight
Simi-larly, if 5 or 10 years from now a family's financial
transactions, medical prescriptions, education, and
travel arrangements are handled by a computer
op-erating system through the Internet, it may no longer
be possible totumoffthe computer at will That bears
thought and forethought and suggests that open
source operating systems coexisting with
commer-cial products can help maintain balance See BSD,
Linux, Mac OS X, Microsoft Windows, NeXTStep,
OS/2, Solaris, SunOS, Unix, UNIX
operational load1 The full power requirement ofa
facility, which may be expressed in terms ofaverages
or maximums 2 The administrative and personnel
requirements of an organization when in full
op-eration
operatorAnindividual with system access privileges
hierarchically higher or more powerful than general
users Atelephone operator can manage calls and
cess services and control mechanisms that are not
ac-cessible by regular phone subscribers A chat room
operator can include or exclude specific users or set
other restrictions or standards of use A system
op-erator has access to monitors, security devices,
soft-ware programs, and other computer operations
mechanisms not available to regular users
operator, telephoneAnindividual who handles the
routing ofcalls from callers to callees and provides a
variety of types ofassistance such as directory
assis-tance, long-distance procedures, billing options, etc
Many of these processes have now been automated,
but in the early days, the telephone operator had
com-plete responsibility for connecting, monitoring, and
disconnecting calls through manual patchcords He
or she was also implicitly expected to provide
emo-tional support, emergency information, local news
and gossip, and business tips In fact, the position of
the phone operator included so much power (over
connections to alternate business options) and
infor-mation that a direct dial system was invented
ex-pressly to bypass the operator! Later switchboard
systems required a higher level of concentration and
expertise as many more lines would be serviced and
the switchboards included lights to indicate
connec-tions and incoming calls, switches, cards for
record-ing toll calls, and more
While the names of the very first telephone
opera-tors have probably been lost to history, George
Willard Coy is generally credited as the first telephone
operator and Emma Nutt as the first female telephone operator Nutt was instated following the relative fail-ure of male telegraph operators to adapt to the task
of courteously handling customer voice calls Nutt apparently moved from a telegraph office to the phone exchange in Boston, hired in September 1878
by A Graham Bell She was paid a salary of $1 0 per month for a 54-hour work week (minus lunch) This was a year ofgreat expansion, during which the New England Telephone Company was formed to sellli-censes to telephone company operators in the New England area Ms Nutt apparently could remember every number in the directory
Preferred Voice has created a synthesized voice speech attendant for delivery ofinformation services named EMMA in honor ofMs Nutt
Records are spotty, but a small selection of notable first telephone operators for their regions prior to about 1913 is shown in the Selection of Pioneering
"First" Telephone Operators chart See Call Girls, Strowger switch, switchboard, telephone history Historic Telephone Switchboard&Operator
A telephone operator staffing the first switchboard
in Idaho Springs, Colorado, wearing a headset Manual switchboards still exist on islands, in remote areas, and in many undeveloped nationas In North America the main telephone system operates with high-speed digital switching circuits {Denver Public Library Collection; copyright expired by date.}
operator-assisted callAny phone call in which the caller contacts the operator to handle somepartofthe transaction or connection, rather than direct dialing There are usually surcharges associated with opera-tor-assisted calls
operator console, computerIn computer networks,
a console is a computer terminal which allows access
to management and administrative functions that monitor and control the network Common operations carried out on the console include user password as-signments, new user account allocations, virtual con-figuration ofdevices and the network topology, selVer configuration, etc Often the operator console is in a
Trang 4least, is password protected to prevent unauthorized
users, or well-meaning but uninformed users from
accessing lower level system functions that could
in-terrupt the functioning of the network
operator console, phoneIn telephony, the main
console of a multiline phone system The operator
console often is programmable and may include a
hands-free earphone set
Operator Service ProviderOSP Previously called
Alternate Operator Services A competitive provider
of operator-assisted long-distance calls, especially
third-party billing, collect, etc., which usually leases
the services of existing phone networks Large
ho-tels sometimes provide AOS services to hotel guests
for a premium See splashing
OPREOperations Order Review
OpsAbbreviation for operations, operators,
opera-tor services, and system operaopera-tors This is a
particu-larly common abbreviation on Internet chat systems,
where the operators (ops) or channel operators
.(chops, chanops) enforce accepted behavior on chat
channels See operator
OPSoff-premises station
optical amplifierA type of device used as a cable
repeater on fiber optic transmission lines, which
func-tions without converting the optical signal Early
ver-sions were based on semiconductor lasers Most are
now erbium-doped fiber amplifiers (EDFAs), that is,
directly doped silica fibers, with the principal
param-eters defined by atomic composition
optical attenuatorA coupling component, usually
of a standardized type (e.g., FC- connector) that
at-tenuates the energy of the passing optical signal by a
certain amount OAs are compact, low-power
com-ponents available in fixed, variable, and
computer-controlled models Multiple OAs may be combined
into multichannel arrays to meet the needs of
com-plex networks
Thus, a fixed or variable amount ofloss is
intention-ally induced in the received optical signal to adjust
the signal to the desired level This is useful for
switching, gain tilt, modulation, and power control
optical burst switchingOBS A mechanism
pro-posed in 1999 by Chunming Qiao and Myungsik Yoo
for managing bursty network traffic on the Internet
The research, supported in part by a National Science
Foundation (NSF) grant, is intended to streamline
network switching in anticipation ofhigh-speed
end-to-end optical networks of the future The system
combines aspects of optical circuit switching and
packet/cell switching While transition technologies
are expected to combine optical networks with
elec-trical switching, at some point there may be second
generation all-optical networks that can be
estab-lished as a layer beneath Internet Protocol (IP) OBS
anticipates this evolution in technology
Many broadband transmissions are inherently bursty
(e.g., multimedia), as apparently are large numbers
of self-similar traffic streams Thus, a system more
efficient for this situation than optical circuit
switch-ing was sought The researchers have observed that
setup time and overhead, but that this approach has limitations as well In OBS, a control packet is trans-mitted to set up a connection, followed by a data burst before the connection acknowledgment is received, essentially a one-way reservation system In addition, data burst buffering at intermediate nodes is elimi-nated, reducing the wait for processing of control packets Signaling is out-of-band See Just-Enough-Time, Optical-Label Switching
optical bypassIn a Fiber Distributed Data Interface (FDDI) token-passing network, port adaptors can be equipped with optical bypass switches to avoid seg-mentation which might occur if there is a failure in the system and a station is temporarily eliminated
Normally, optical signals pass through the bypass switch uninterrupted, but ifa station fails and is elimi-nated from the ring, the optical bypass can reroute the signal back onto a ring before the signal reaches the failed station, thus providing fault tolerance for the system
The optical bypass switch is attached to the FDDI port adaptors between the attachment station and token-passing ring See A port, dual attachment station
optical carrierOC 1 In general, a signal carried over optical media that is intended to provide con-trol signals, information, or other signal data Com-monly lasers are used to provide carrier signals that may be given information content through electro-optical modulators (e.g., a quadrature amplitude modulator) See carrier, modulation 2 A series of optical network transport levels defined in conjunc-tion with SONET See SONET Optical Carrier Trans-port Levels chart
optical channel data unitODV.Aunit ofdata in an optical transmission network In an ITVT G.709 optical transport network, for example,ODV over-head resides in columns 1 through 14 of three rows ofthe frame It provides connection monitoring, path supervision, and client signal adaptation
optical character recognitionOCR Asoftware pro-cess, or combination of hardware scanning devices and software, which evaluates marks on a page and determines whether they have the predefined char-acteristics of text, symbols, and images, depending upon the software
Most OCR programs use a combination ofintelligent algorithms and character tables to process marks
These marks are typically text and character symbols, although some programs will also recognize math-ematical and logical symbols ifthese are added to the program dictionary or the user dictionary Some programs can automatically discern columns of text and images, and divide the page up appropriately, handling the regions separately Once the document has been "recognized,' the characters and symbols are converted to a common format, such as ASCn or one of the many flavors of extended ASCII, and stored as a file that can be further edited with a text editor, word processor, or desktop publishing pro-gram In its strictest sense, OCR just recognizes the characters; software which handles images as well is
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calledoptical document recognition However, most
OCR applications these days have some document
processing and image recognition functions, so the
phrase is used broadly here
Most of the early work on pattern matching
algo-rithms used in character recognition was done in the
late 1950s and the early 1960s By 1963, ffiM had a
system that could recognize Roman and Cyrillic
char-acters at the rate of about 50 words per minute, the
speed of a moderately competent typist, and faster
than most typists can type information with many
numerals See optical document recognition, scanner
Sample Optical Choppers
Optical choppers range from simple, regular
pat-terns, to combinations of two or more blades (top
right) High-precision choppers may have hundreds
or thousands ofchopping segments (upper left).
optical chopper Acomponent for interrupting a beam
of light, often at very fast speeds Chopping can be
accomplished with shutters, tuning forks, rotary discs/
blades, or etched crystalline plates Applications for
choppers range from special lighting andarteffects
to highly-precise scientific applications and experi-ments Scientific choppers typically have a data in-terface to a display component or computer Tuning fork choppers are intended to be used at a spe-cific frequency and have small apertures at high fre-quencies, compared to rotary choppers Despite the frequency and aperture limitations, tuning forks are robust and have many applications and can be used
in a wide range of operating conditions
Disc or rotary choppers resemble pinwheels in the sense that they have divided segments rotating around
a central axis like a rotary fan Most are mounted with ball bearings, but some are available with magnetic suspension
Choppers can be fabricated as high precision instru-ments with highly accurate divisions in the chopping segments and carefully controlled rotational axes and speeds The number of "slots" on a chopper may range from 2 to 2000+ and some choppers provide variable speeds for the rotations of the wheels It is also possible to design chopper blades to chop more than one frequency at a time by having two sets of slots in the same wheel It may be possible to option-ally phase-lock the chopper to an internal clock or to
a user-supplied external clock A monochomator for dispersing light waves may be coupled directly to choppers with an appropriate coupling head Choppers may consist of coated gels or glass or one
or more blades, depending upon the application When there are two blades, one may be fixed while the other rotates The alignment of the blades deter-mines whether a beam is passed or blocked The beam need not be completely blocked With a general pur-pose scientific chopper with just two blades, it is pos-sible to have chopping frequencies ranging from about 4 to 5000 Hz With a gel chopper, different types or colors of coatings may selectively pass or chop certain frequencies
Piezoelectric choppers are small enough to fit on a chip for use in integrated circuits In conjunction with
a collimated laser source, they may be used as com-pact optical sensors
SONET Optical Carrier (OC-) Transport Levels
Trang 6erational frequencies Disc choppers with
inter-changeable blades and rotational speeds can support
many applications See knife-edge focusing, Ronchi
grating
Piezoelectric Semiconductor Chopper
In the quest.{or ever smaller components,
piezoelec-tric choppers have been developed, such as the one
illustrated here, designed by H Tohiyoshi.
Incident light (A) encounters a chopper plate (B)
made from anisotropically etched Z-cut quartz, with
chopper slits perpendicular (normal) to the surface
ofthe component Light passing through the slits
ac-tivate photosensitive detectors (C).
optical combinerIn general fiber optics terms, any
system for aggregating optical cables in adjacent
waveguides or for combining two or more optical
sig-nals for transmission through a single waveguide
Optical cables are typically aggregrated to facilitate
installation and maintenance Optical signals are
combined for a variety of reasons Transmission
through a single rather than multiple waveguides can
be cost-effective Broadcast services available to all
service subscribers may be combined with targeted
services requested by individual users at appropriate
pointsinthe network Combined signals may be
use-ful for research purposes for studying optical
effi-ciency, interactions, and various sources of loss
As a fiber optic network component, the term more
specifically refers to devices that combine or
com-bine and regenerate comcom-bined optical signals with a
minimum of loss and interference in the coupling/
combining process Combiners may be passive or
actively integrated with switching mechanisms
An arrayed waveguide grating (AWG) can combine
(or separate) multiple wavelengths An active
self-switching combiner, as an example, takes signals
from two or more ports and physically couples them
so they are proximate, then phase-shifts the signals
through optical amplifiers and brings them together
in a combined signal See multiplexing
optical combiner, projectionA projection surface
other functions, images, or physical environments
For example, in military jets, the windshield may serve as a transparent viewing window as well as a projection surface for certain cockpit status displays
The same concept is applied to head-worn optical dis-play systems, some ofwhich have small transparent screens that enable the viewer to see ahead while at the same time viewing a small projected image (in some systems, the image may pass through the com-biner to be projected on the viewer's retina)
Combiner projection technologies are useful any-where information needs to be superimposed on a transparent surface so that the viewer can see both the projected image and the environment behind the projected image Thus, they could be used with a video camera to project an image of the area behind
a viewer so the viewer could see front and back at the same time or they could project status informa-tion over a video image or real-life environment In terms of innovative networking possibilities, they could project a Web page coupled with a GPS reader that shows a map and local landmarks at the specific site at which a person is standing with a body-worn computer linked to the Internet
Optical Communications DemonstratorOCD A NASAlJPL laser-based extraterrestrial communica-tion system capable of transmitting at speeds up to
flector, which controls the orientation ofa Q-switched diode-pumped laser communicating in the downlink direction The ground station detects the light signal using silicon avalanche photodiodes This is seen as
a possible alternative to radio wave communications that are more apt to be distorted due to Doppler shift effects See Laser Communications Demonstration System
optical computerA type of processing hardware based on photons rather than electrons This is a more experimental technology than is used with traditional computers, but it has possible advantages, particularly
in speed and resistance to interference over current technologies, and may become more prevalent in the future
optical connectorsConnectors specially designed to couple fiber optic cable junctions so they interfere as little as possible with the path of the optical beams passing through the connectors The connectors are usually used at points where the fibers connect with routing or switching circuitry, or with the optical in-terface to the system itself Optical connections have
to be well-engineered, as they must handle very pre-cise beams and paths, and often must maintain the proximity and orientation of a bundle of optical fi-bers Connectors for blown fiber installations are easier to install and maintain than a number of other types offiber attachments See blown fiber
optical coreThe light-carrying central region of a fiber optic filament, commonly made from silica and germania
optical couplerSee coupler
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optical coupler module OCM A component that
provides functions in conjunction with coupled fiber
optic cables such as branching/joining, multiplexing/
demultiplexing, and filtering OCMs are often
modu-lar and may be customized for operating wavelength
and the size and number of fiber filament
optical cross connect OXC Optical connection
com-ponents oftelecommunications carrier networks that
help operators manage the larger amounts of
band-width enabled by newer capacity-increasing
tech-nologies OXCs began to become generally available
in the late 1990s
OXCs can facilitate network administration by
en-abling a network to be more readily reconfigured or
restored using optical switches OXCs can handle
data streams in the terabit ranges and work with a
range of wavelengths and bit rates, making it easier
to quickly effect rerouting Currently OXC
compo-nents are part ofthe optical portion ofmixed wire and
optical fiber networks, but as the optical market
grows, demand for OXCs will likely increase See
lambda switching
optical detector Asubstance or circuit which detects
and converts electromagnetic waves in the form of
optical waves Solar panels contain substances that
allow the conversion of light into electricity, which
are widely used in the satellite industry to provide
power for telemetry adjustment of orbits See solar
panel
optical disc Any of a number of technologies used
to store digital data which is subsequently accessed
by light, usually a laser beam pickup The
informa-tion on an optical disc is commonly stored in a series
ofpits, that is, indentations in a metal disc coated with
a plastic substrate The placement, size, and
proxim-ity of these pits is defined in part for the
specifica-tion for the type of optical technology Newer
tech-nologies have been developed to increase the
information capacity of a disc, as in digital
video-discs (DVDs) that are slightly thicker, to bring the
disc closer to the laser pickup, with slightly smaller,
tighter pits Compact discs, videodiscs, PhotoCDs,
and DVDs are popular forms ofaudio and visual
stor-age media Optical discs are also used for computer
data storage, particularly for backups
optical document recognition ODR Asoftware
pro-cess or combination of hardware scanning devices
and software, which evaluates the various elements
on a page to determine whether they are
distinguish-able as text, images, symbols, or lines, and identifies
them accordingly The ODR in its simplest sense does
not interpret the text into characters; it merely
iden-tifies page layout elements: images, columns, page
numbers, text, etc However, in commercial products,
it is commonly combined with optical character
rec-ognition (OCR) capabilities in order to optically
iden-tify and interpret areas that are text into characters
that can be edited with a word processor, text editor,
or desktop publishing program ODR is a somewhat
more complex process than OCR; together they
com-prise powerful tools which are a part ofimage
docu-ment managedocu-ment and processing
ODR is particularly valuable for converting archived image information (e.g., microfiche) into documents that can be desktop published, or archived in data-bases for faster and more efficient search and re-trieval See image document management, optical character recognition, scanner
optical eye pattern measurement procedure An optical fiber test procedure standardized within TW EIA-526, developed by the Optical Fiber Communi-cations System subcommittee It describes param-eters for measuring the repetitive temporal charac-teristics of a two-level intensity-modulated optical waveform at an optical interface Rise time, fall time, overshoot, and extinction ratio may be determined from the measured eye pattern The waveform itself may be tested against a reference waveform mask to determine standards compliance
optical fiber A flexible, light-conducting, filamen-tous plastic or glass medium used for optical signal transmissions Optical fiber is typically from 2 to 125 J.lm thick, and is capable ofcarrying a variety ofhigh-speed, wide bandwidth transmissions with relatively low loss, when correctly installed Unlike wire, fiber
is not subject to electromagnetic interference or most ofthe types ofradiant eavesdropping techniques that can be used on wire This has made it very popular for backbone, hazardous area, and multimedia instal-lations It also does not present the same potential fire hazard as wire electrical cables
Two common types of optical fiber include step-in-dex fibers and graded-instep-in-dex fibers Step-instep-in-dex fibers have two layers: a lower refractive outercladding
layer and an inner core with a high refractive index Graded-index fibers also are less refractive toward the outer edge, but rather than being two layers sand-wiched together, as in the step-index fibers, the re-fractivity in the material overall decreases gradually
in relation to its distance from the innermost point of the cylinder
Fiber can be bundled without the electrical interfer-ence common to bundled wires; a group of fibers works together to provide greater capacity Single-mode fiber transmissions, in which the signal can only follow one path through the filament, can travel greater distances without repeaters See multimode optical fiber, single mode optical fiber
optical fiber cable See fiber optic cable
optical fiber ribbon A bundled fiber assembly in which individual fibers are laid side-by-side to form
a flat ribbon or strip This is convenient ifthey are to
be installed in narrow areas such as inside walls or under carpeting This way of arranging fibers is less common than bundling them into a cylindrical shape optical handwriting recognition OHR Aspecialized form of character recognition designed to separate joined shapes and recognize variations of particular letters, in addition to other generalized optical char-acter recognition (OCR) functions Most OHR sys-tems have to be trained to recognize a particular style
of handwriting, since there is so much variation in the letter forms in the way different people write optical insertion loss OIL The coupling-associated
Trang 8Number Line Rate Frame Rate Speed
In commercial implementations, OTUs are built into SONEr optical transport platforms
1992 OSTA develops technology "roadmaps," sta-tistical illustrations of optical storage progress and trends, to define compatible product classes It is not
a standards-development organization per se, but it develops specifications and provides input to other organizations regarding practical implementations of optical storage standards In July 2001, OSTA an-nounced the development and approval of a new specification for organizing compressed audio files
on optical disc, called MultiAudio The intent is to ensure that discs with compressed audio files (e.g., MP3) are as straightforward and standard Red Book CDs The format specifies a table of contents access mechanism for CD and DVD playlists and media playback See MultiAudio, MultiPlay
http://www.osta.org/
optical time domain reflectometerOTDR An in-strument for reflecting light through a fiber optic waveguide to determine loss and integrity of the fi-ber light path OTDR measurements may be uni- or bidirectional Unidirectional measurements may be misleading ifthere are diameter differences from one fiber joint to the next However, if the light will be traveling only in one direction and the OTDR is mea-sured in the same direction, this may be sufficient If the light is being alternately transmitted in two di-rections along the fiber optic path, bidirectional av-eraging (taking measurements from each end of the fiber path) will provide more complete data for as-sessing the lightguide See bidirectional averaging optical transport networkOTN As defined in ITU
G Series Recommendation G.709, OTN isan inter-face that builds upon previous SDH and SONET tech-nologies to provide layered network services, but improves upon previous technologies with better op-tical channel management in the opop-tical domain and forward error correction (FEC) to increase the dis-tance over which data signals can be transmitted G.709 standardizes the management ofoptical chan-nels (wavelengths) without conversion to electrical through newer bubble and micro-electromechanical systems (MEMS) technologies See optical transport unit
optical transport unitOTU In the ITU-T G.709 framing structure, a frame in which each row con-tains 16 forward error control (FEC) blocks of 16-byte interleaved codecs for a total of4x16=64 FEC blocks Currently three line and frame rates are de-fined
48.971ms 12.191ms 3.035ms
2,666,057.143 20.420 10,709,225.316 82.027 43,018,413.559 329.489
OTUI OTU2 OTU3
cables are connected into ports The loss is due to a
number of factors, including the quality of the cable
assembly, the diameter and type of fiber (some are
more subject to loss than others), the snugness of the
fit, the amount of strain associated with the
connec-tion, and the ambient environment In product
litera-ture,low optical insertion losstypically refers to the
precision ofthe fit and resistence to strain in the joint
between the connector and the port There is
some-times a tradeoffbetween ease ofuse and reconnection
and loss
Optical Internetworking ForumOIP An open trade
organization fostering the global development and
deployment of interoperable optical data switching
and routing technologies Membership includes
ser-vice providers, equipment manufacturers, and end
users http://www.oiforum.com/
optical label switchingSee optical-label switching
optical modulation depthOMD An expression of
the degree ofmodulation in an optical data
transmis-sion system OMD is usually expressed in
microme-ters as a percentage per channel (e.g., 4% or 20%) at
a specified frequency range The OMD may have to
meet certain standards (e.g., SONET)
Fiber optic CATV transmitting components may have
controls for operator adjustment ofOMD Poor
ad-justment can result in reflections or clipping See
modulation
optical network unitONU A device for
connect-ing a userwitha fiber optic network The ONU creates
a physical link and conversion services, ifnecessary,
between the central office optical wavelength and the
home or office optical wavelength, which may be
different frequencies
A number ofONUs are typically aggregated at a host
digital terminal Groups of host digital terminals are
similarly aggregated at a control tenninal, located at
the central office of the local exchange
In spring 2002, companies such as Salira began
of-fering multiple-customer ONUs so that individual
units for each customer were no longer necessary
optical scannerSee optical character recognition,
scanner
Optical Society of JapanOS1 Founded in 1952 as
a division of the Japan Society of Applied Physics
(JSAP), it is now the biggest division of JSAP with
almost 2000 members OSJ publishes theJapanese
Journal ofOpticsand theOptical Review.Itprovides
educational support, technical working groups, and
conferences for its members and sponsors a number
of awards for excellence in the field of optics
http://annex.jsap.or.jp/OSJ/index-e.shtml
optical spectrum analyzerOSA Adesktop
diagnos-tic instrument for measuring the power ofa light
sig-nal at each of its emitted frequencies.Itincorporates
a diffraction grating to split out the wavelengths (in
much the same way a prism splits white light into its
constituent colors) and measures the power level of
each wavelength See reflectometer, tracer
Optical Storage Technology AssociationOSTA An
international trade association promoting the use of
Trang 9Fiber Optics Illustrated Dictionary
In "digital wrapper" implementations as introduced
by Lucent Technologies, data is encapsulated in an
optical transport unit frame similar to a SONET
pro-tocol frame so that any type ofnetwork traffic (ATM,
IP, etc.) may be handled and forwarded over existing
SONEr networks The OTU provides FEC
informa-tion at the end of the frame to ensure the suitability
of the optical signal for high-speed transmission
optical-label switchingOLS.Anetwork switching
system developed under the direction ofSJ Ben Yoo
through a DARPA ITO-sponsored research project
It was first proposed by Yoo in1997and developed
independently at around the same time as
Multi-protocol Label Switching (MPLS)
OLS is a means of implementing packet-switching
protocols over optical media OLS is a scalable
ul-tra-low-latency multiprotocol optical
routing/switch-ing system that shares some characteristics with
MPLS Underlying OLS is the packet-switching
fab-ric comprising rapidly tunable wavelength conversion
capabilities and scalable arrayed-waveguide grating
OLS is built upon this with a forward look to next
generation all-optical Intemetworks
OLS routing uses an optical header with a label in
the header to determine the packet forwarding The
data are heldin the fiber path while the header is
ex-amined and may be replaced for the next leg in the
transmission path
OLS project goals as of2000included router
con-nectivity in excess of1024x1024and aggregate
switching bandwidth of almost a
peta-bits-per-sec-ond The multiprotocol optical routing is intended to
be interoperable with circuit-, burst-, flow-, and
packet-switched networks See label switching,
Multiprotocol Label Switching, optical burst
switch-ing
OQPSKoffset quadrature phase shift keying See
quadrature phase shift keying
Orange Book Aset of standards for Compact Disc
readable (write once) optical media The previous
Red and Yellow Book standards established the
ba-sic standards for recording audio and computer data
to a Compact Disc The Orange Book extended these
capabilities to enable multisession recordings to be
created (though they are not recommended as
mas-ters) Red and Yellow Book data can be combined on
one disc in whatever order is desired See Blue Book
ORBSee Object Request Broker
ORBCOMMOrbital Communications
orbitThe path described by a moving body in
more-or-less stable balance with the gravity of the body
being orbited so that it continues in that path for a
significant period oftime (usually at least a few hours
or days, although orbits ofartificial satellites can last
for years in a stable orbit) The Earth is in orbit around
the Sun, and the Moon is in orbit around the Earth
When the balance is lost and the orbit becomes
smaller as the orbiting body is drawn inward, it is said
that the orbit is decaying Many types of orbits
(or-bits at different heights, with differently shaped paths)
are used in telecommunications with artificial
sat-ellites
Early communications satellite orbits tended to be circular or low and somewhat flatly elliptical (and tended to decay quickly) Communications were hin-dered by the necessity of locating the orbiting satel-lite and keeping it in range before it passed around
to the other side ofthe Earth Later satellites were put into higher, more stable orbits, which were often geo-stationary; that is, the orbit was synchronized with the movement ofthe Earth so that the location of the satellite was roughly above the same location at all times The amount by which an orbit deviates from a
circle is referred to as its eccentricity See
geostation-ary, satellite
Elliptical Orbit
Satellite orbits tend to be circular or moreflatly el-liptical, and may befurther controlled so that the sat-ellite spends a greater part ofthe orbit over ocean or land masses, depending upon whether it is serving marine or terrestrial communications needs.
The orbits are often described in terms oftheir dis-tance from the Earth as low, medium, and high Earth orbits (LEO, MEO I HEO) Geostationary orbits are a type ofhigh Earth orbit in which the satellites move-ment is paced such that it remains in the same posi-tion relative to the Earth.
Orbital Sciences CorporationCommercial devel-opers of global satellite communications services Orbital Sciences is a space and information systems company which designs, manufactures, and markets space-related infrastructures and products See OrbLink
OrbLink Aglobal broadband commercial satellite communications network being developed by Orbital Sciences Corporation for deployment around2002 The designers intend to use the newest technology
to construct broadband services that can be offered
at lower prices than existing services OrbLink is based on seven medium Earth orbit(MEO)satellites orbiting at9000kIn in an equatorial orbit, transmit-ting in extremely high frequency radio bands Ser-vices will include digital voice, data videoconferenc-ing, computer networkvideoconferenc-ing, imagvideoconferenc-ing, and other broad-band applications
Pending Federal Communications Commission (FCC) approval, intersatellite communications will
be at65.0to71.0GHz at speeds up to15Gbps, sup-porting high-capacity intercontinental trunking Two-way digital connections will be between37.5to38.5 GHz and47.7 and48.7 GHz bands up to about 1.5Mbps
The seven satellites, plus one spare, are based on
Trang 10technology, acquired through a purchase of CTA
Incorporated's space system business Each satellite
will support 100 spot beams As an economic note
on the dynamics of new telecommunications
tech-nologies, the total cost ofbuilding and deploying the
orbital network, according to Orbital Sciences,
com-pares to the cost of installing two transatlantic fiber
cables, which provide only about 10% of the
trunk-ing capacity of the proposed satellite system
Orckit CommunicationsAdeveloper and
manufac-turer of high-speed local loop communications
sys-tems and participant in a number ofnetwork standards
working groups Orckit partners with Fujitsu Network
Communications, Inc
order entryThe inputting, usually by voice or
key-board, ofa customer request for a product or service
On the World Wide Web, Webformsare often
avail-able for customers to put in their own order entry
These Web applications are ofteninthe form of
shop-ping carts in which the customer browses various
Web pages and enters each product desired into the
shopping cart (order batch) The order is typically
pre-processed by a CGI and then sent to the appropriate
order fulfillment personnel for shipping and billing
Other automated systems allow customers to carry
out a complete ordering transaction over a touchtone
phone by using the keypad to enter codes and digits
See Automatic Call Distribution
Organization of American StatesOAS The OAS
Web site provides information on the group
http://www.oas.org/
Organizationally Unique IdentifierOUI Aglobally
unique 24-bit Ethernet address identifier for LANs
and MANs managed and assigned by the IEEE
Reg-istration Authority online or by phone The OUI is
assigned as a three-octet field in the SubNetwork
At-tachment Point (SNAP) header, identifying an
orga-nization which further creates unique six octet
num-bers Together they constitute a distinct Media
Ac-cess Control (MAC) address or Ethernet address See
Ethernet, IEEE, Token-Ring
originate/answerOn a computer data modem, when
the user wants to dial out to connect to another
com-puter, a bulletin board, or an Internet access point,
the commands for controlling the phone line and
di-aling the desired number come from the originating
modem "Originate mode" sets up a sequence of
events which checks for a dial tone, dials, and
hand-shakes with the receiving modem to establish the
con-nection rate and protocol (or hangs up if the line is
busy or is dropped) The receiving modem is set to
"answer mode' so it detects an incoming call,
an-swers it, and participates in the rate and protocol
ne-gotiation Most of this is automatically handled
through a terminal software program, but it may be
necessary to set originate or answer through menu
selections, or direct commands through the software
to the terminal program
originate restrictionA secwity or specialized use
restriction on a phone line which causes it to work
only for incoming calls Outgoing calls are blocked
to public areas to prevent people from monopolizing
or misusing a phone line Sometimes the originate re-striction applies only to long-distance calls or calls outside a private branch exchange
In some circumstances, the local phone company will partially disconnect a line by setting an originate re-striction ifthe subscriber is behind in the payment of the phone bill After paying the bill, it is usually nec-essary to request restoration of full service, as it is seldom done automatically
originatorInitiator, caller, inventor, introducer, founder The person, entity, device, or station that first communicates a message or starts an action or pro-cess
OrionA broadband data satellite service provider aiming at international common carriers and indi-vidual companies
ortho-correctionIn satellite imaging, a correctional adjustment for distortion resulting fromt~rrain. orthogonal frequency division multiplexOFDM
A multicarrier modulation system which is similar to discrete multitone in that it utilizes Fourier transforms
of data blocks OFDM is suitable for Digital Sub-scriber Line (DSL) services See Digital SubSub-scriber Line, discrete multitone
OS XSee Mac OS X
OS/2Operating System/2 International Business Machines' 32-bit preemptive multitasking text and object-oriented graphical operating system targeted for Intel-based microcomputers in the late 1980s It was originally developed for IBM by both IBM and Microsoft Corporation, and version 1.0 was released
in 1987 to succeed MS-DOS When an upgrade to OS/2 was well under way, Microsoft pulled out to concentrate on their own operating system in com-petition with IBM Many of the same concepts that were part of OS/2 were incorporated into Microsoft Windows NT, which was marketed as a direct com-petitor to OS/2
In 1991, ffiM released OS/2 version 2.0 Version 2.1 added support for multimedia and Windows 3.1 ap-plications OS/2 had some commercial success in the early and mid-1990s, but by 1996, through aggres-sive advertising and bundling programs, Windows was better known and more widespread in North America In spite of this, there are many strong sup-porters of OS/2, including a worldwide network of Team OS/2 Groups It is still a popular choice in Western Europe and Canada Team OS/2 information for OS/2 users is available at their Web site See Team OS/2
OS/2SMP OS/2 Symmetric Multiprocessing This version of IBM's OS/2 supports systems with mul-tiple processors, making it suitable for Internet ser-vices, graphics, and corporate applications, particu-larly those which operate as various types ofresource servers in a networked environment See OS/2 OS/2 WarpOperating System/2 Warp By version 3 ofmM's OS/2 operating system, their operating sys-tem product was called OS/2 Warp The Warp ver-sion added increased support for various peripheral