Spread spectrum is used for a number of reasons: it can reduce overall interference with other radio sig-nals, can be more difficult to detect, intercept, or de-code, and more difficult
Trang 1Fiber Optics Illustrated Dictionary
ofboth store-and-forward and realtime facsimile
pro-tocols (ITU-T T.37, T.38)
spoofing, network In network traffic routing, a
means ofrerouting, or otherwise changing the
desti-nation of a transmission by mimicking the
destina-tion through responses, signals, or other
identifica-tion Spoofing has legitimate purposes, such as
test-ing and modeltest-ing, or overcomtest-ing problems oflatency
in slower devices, but often the spoofing is intended
to gain unauthorized access to a system or to
imper-sonate a system and send substituted information
Reports of malicious spoofing on the Internet began
to emerge in the mid-1990s
Spoofing can be set up at the beginning of a session
or can be inserted into a session after it has been
es-tablished The first method may be harder to detect,
while the second may be a means to eavesdrop on
information the source system thinks it is sending to
the original destination, which is now the spoofed
destination In general, the spoofing is carried out by
impersonating a trusted destination IP address The
spoof can sometimes be detected if the IP address is
found to originate on the local system rather than on
an external system
Spoofing occurs for many reasons It can enable a
user to intercept programs or information or it can
be used to send bogus responses to requests from the
originating system It can also compromise the
abil-ity of a system to carry out its normal functions A
denial of service attack is a situation in which a
ser-vice (e.g., a Web server for a stock quote or online
auction system) is made unavailable to normal users
By setting up a loop that ties up or floods the system,
for example through a half-open connection that
over-flows, denial ofservice can be achieved This doesn't
usually compromise the information on the attacked
system, but may harm it by denying legitimate users
access The host system may not be aware ofthe
prob-lem until customers begin to complain
Since the mid- and late-1990s, various dynamic
rout-ing techniques and packet traffic monitors have aided
in preventing and detecting spoofing See Computer
Emergency Response Team, Computer Incident
Ad-visory Capability
spoofmg, Web site This is a subset ofnetwork
spoof-ing that specifically spoofs or impersonates a Web site
at another location A vulnerability exists within
browser software supporting HTML frames
preva-lent in the late 1990s Subsequent versions
ofbrows-ers have been updated to help prevent this type of
spoofing (e.g., Netscape Communicator 4.51)
Web site spoofmg is usually a malicious activity
in-tended to mislead, inconvenience, or harm A Web
site can be spoofed to make a site look bad (e.g.,
ma-ligning a commercial site) by inserting insulting,
poorly designed, or shocking images or text into an
otherwise normal-looking site Spoofing can also be
similar to the Trojan Horse concept wherein
some-thing desirable appears to be offered (but not given)
to the user in order to gain entrance to a location or
information repository The user may think he or she
is getting a free product sample, for example, when
the spoofed site is actually capturing names and mail-ing addresses (in fact this type of fraud can be car-ried out on a nonspoofed site, as well)
Not all Web site spoofs exploit browser vulnerabili-ties Some of them rely upon human trust and error One type of Web spoof impersonates the layout and functions of another Web site and mayor may not spoof the original IP address or domain name (Web sites are sufficiently high in information content that
an IP address or domain name change may not be no-ticed by the user)
For example, in summer 2000, someone spoofed the login page for the PayPal online financial system, which enables users to conduct online monetary transactions through user accounts The Web page was designed to clandestinely capture names and passwords The perpetrators then sent out bulk email that looked like a legitimate PayPal notification with
a clickable Web address embedded in the email mes-sage However, the embedded URL didn't link to
www.paypal.com, it linked to www.paypaI.com with
a capital "i" rather than a lowercase "1" People couldn't easily see the deliberate misspelling and anyone who linked to the site and tried to log on gave away his or her login name and password This could then be used to access the real PayPal account to en-able the perpetrators to transfer funds Fortunately, the fraud was discovered quickly, before significant harm was done This kind of spoofing has a good chance of landing the perpetrators in jail
spool v An acronym for "simultaneous peripheral
operations on line," a means of running scanners, printers, plotters, video capture systems, or other peripherals while other computing tasks are ongoing
In earlier nonmultitasking computer systems the ac-ronym was misleading, since spooling was a way of saving information in a file so it could run as a batch job later, rather than as a simultaneous process Spool-ing as we know it now more accurately reflects the acronym.Itis a technique for improving efficiency
by accommodating the different operating speeds of
a number of types of peripherals and processes by scheduling and optimizing the exchange of hand-shakes and data transmission Spooling is especially popular for creating files that will be printed as a background task or sometime later (e.g., overnight, when printers aren't so busy, or when the computer isn't engaged in CPU-intensive functions)
On multitasking systems, it is not necessary to wait for a print, plot, or other peripheral job to finish to continue word processing or drawing, but it may slow current processes Thus, the system may schedule the printing job to run while the user is away from the keyboard or engaged in computing tasks requiring less processing power The resource management software routines can be designed to sense when re-sources are available and carry out the print job On single-tasking or task-switching systems, however,
with peripherals that don't support a queuing system,
wait time can be a problem while a file is processed
or printed For example, plotters tend to print rather slowly If the user must wait for 25 minutes while a
Trang 2plot to a software spooling process (or a hardware
spooling buffer) and plotting it at a convenient time,
the user can continue working uninterrupted
spot ofAragoIn1818, Augustin Fresnel, after whom
the Fresnel lens is named, submitted a thesis on
dif-fraction to a competition sponsored by the French
Academy of Science At the time, the wave theory of
light was not scientifically accepted and Simeon
Pois-son endeavored to shoot down Fresnel's thesis on the
basis that his theory would predict that a bright spot
would appear in the shadow behind a circular
obstruc-tion Dominque Arago, a member ofthe judging
com-mittee, took the time totrythe experiment and
veri-fied Fresnel's prediction It is sometimes called
Poisson's bright spot, but it is more fitting that it be
called the spot of Arago See diffraction; Fresnel,
Augustin
spread spectrumA technique used with
radio-fre-quency-generating systems to spread the emitted
wavelengths over more than one frequency, in either
predefined or random patterns (or a combination of
these) In telecommunications, spread spectrum is
generally divided into frequency hops, a system
de-veloped over 50 years ago by Hedy Lamarr, and
di-rect sequencing, which utilizes the noise-like
char-acteristics of pseudorandom sequences to control a
phase modulator
At the sending end, specific types ofnoise are
incor-porated into the signal, which is spread over a wider
frequency range At the receiving end, a lower
band-width version of the original signal is recovered
Spread spectrum is used for a number of reasons: it
can reduce overall interference with other radio
sig-nals, can be more difficult to detect, intercept, or
de-code, and more difficult to jam, thus providing
sev-eral types of security not possible with
single-fre-quency transmissions There are tradeoffs when
us-ing spread spectrum More bandwidth than normal
is required to transmit the signal
Spread spectrum broadcasts are not only used in
co-vert or private communications, but are now also used
as a means to optimize increasingly limited
broad-cast space due to increased demand In the United
States, unlicensed spread spectrum transmitters are
permitted to broadcast within specified frequency
ranges As an example, the 900-MHz cordless
tele-phones and a number ofwireless local area networks
(LANs) operate in the unlicensed spread spectrum
frequencies
Pseudonoise, or direct sequence spread spectrum, is
a technique used in local area wireless networks
(LAWNs) Redundant data bits calledchipsare
in-corporated into the transmissions and the receiver
must have knowledge of the spreading code to
re-move the added chips and decipher the incoming
mes-sage The insertion ofchips provides a means to
pro-vide more frequencies within a given area, with a
tradeoff in speed The throughput of this type of
sys-tem is about 2 to 8 MHz
The Federal Communications Commission (FCC)
regulates the amount of time that may be spent on
902 to 928 MHz, the frequency hop on a particular channel must not exceed 0.4 seconds once every 20 seconds Similarly, in the 2.4- to 2.484-GHz range, the interval is not more than once every 30 seconds
Recommendations are also being drafted by the IEEE See frequency hopping, spread spectrum clocking
spread spectrum clockingIn electronics, many com-ponents emit radiation The smaller and more tightly these components are bundled, the more likely there
is to be undesirable electromagnetic interference (EMI) from neighboring parts This is especially true
in precision very large-scale integration (VLSI) elec-tronic components generating high clock frequencies
Spread spectrum clocking is a means ofspreading the spectral emissions generated by the clock signals to reduce the overall EMI This is often done through frequency modulation (FM) See spread spectrum
spreading lossIn a beam of radiant energy, loss as-sociated with the geometrical spread of the energy
as distinct from absorption and scattering Thus, the peak power level that emanates from the energy source is reduced as the energy propagates outward
Itis also known as energy spreading loss (ESL)
To better understand this, imagine the light from a flashlight beam gradually spreading as it travels away from the source When the beam hits the upheld palm
of a friend standing several feet away, the strength
or power of the light is lower than if the palm is in front of the light a few inches away The rest of the light will spread around the palm, passing it by, even ifno absorption or other type of loss occurs Acous-tic energy, like electromagneAcous-tic energy, exhibits spreading loss, because it radiates outward, which makes spreading loss an important consideration in sonar technologies as well
When spreading loss occurs in energy forms travel-ing through the air, it may be termed free air loss
Spreading loss can vary as frequencies vary and as frequency compositions vary For example, spread-ing loss in a coherent beam of laser light is far less than the spreading loss in a beam from a flashlight
Spreading loss becomes greater as the distance from the source increases (e.g., a radar echo traveling to-wards a target will exhibit spreading loss not only on the way to the target but also on the way back).Itis especially important to account for spreading loss in very remote sensors, such as satellite imaging systems
Range-spreading loss associated with satellite imag-ing sensor data may be compensated for, based upon distance, incident angle, and known characteristics
of the sensing medium Some commercial satellite image products are routinely processed for range-spreading loss (e.g., synthetic-aperture radar products)
In fiber optic transmissions, spreading loss is reduced
or mitigated in a variety ofways, including reducing the number of components and installing active re-lays Spreading loss in a number of media can also
be compensated for by redirecting the spread energy back into the main beam See absorption, attenuation, scatter
.'::.~.
lJ
Trang 3Fiber Optics Illustrated Dictionary
company, Sprint was one of the early companies to
make dialup access to nationwide ISPs affordable, in
the early 1990s
Sprint began as a small telephone company in
Abilene, Kansas, founded by Cleyson L Brown, in
1899 The Brown Telephone Company provided an
alternative to the Bell system and grew and was
re-organized as United Utilities By the 1950s, it was
the second-largest non-Bell company in the U.S In
1972, the name was changed to United
Telecommu-nications By the late 1970s, the company began
in-stalling fiber optic links and soon after established
UNINET, then the third largest commercial packet
data network in the world In the mid-1980s, Sprint
became known for its long-distance services Sprint
established the first coast-to-coast, national fiber optic
data and telephone system as Sprint International
af-ter which United Telecommunications became Sprint
Corporation, in 1992
In 1995, Sprint moved into the mobile market by
ac-quiring wireless licenses for 29 major trading areas
auctioned by the Federal Communications
Commis-sion (FCC) In 1998, Sprint introduced ION,
simul-taneous voice, video, and data services over existing
connections
There was an unsuccessful attempt to merge Sprint
and WorldCom, a merger that did not receive U.S
government approval Thus, Sprint focused its efforts
upon building Sprint PCS into a major wireless
ser-vices vendor
SPSSee Standard Positioning Service
be-tween a pry bar and a long-handled, short-bladed
spade The handles may be D-shaped or ball-shaped
and the blades may be replaceable These are useful
for breaking up tough soil clots for installing utility
poles in areas where it is not practical or possible to
bring in mechanized diggers (they're also handy for
scraping asphalt lumps and old roofing or siding
ma-terials and for making holes in thinner patches ofice)
spur1 Afoot spike worn by line workers to improve
contact and traction when manually climbing utility
poles to carry out maintenance, testing, or repair 2 A
tributary or offshoot from a main line, as in a
rail-road track or communications spur line Spur lines
may run to the end of a cuI de sac, a pier, or other
tenninal point where there is an obstruction or no
fur-ther need for the line to continue
launched by the Russian Federation on 4 October
1957, studied the ionosphere and heralded the space
age It transmitted in a frequency range just above
global frequencies for standard time signals, so that
those listening in, which included Earth stations all
over the world and a large number ofamateur
enthu-siasts, would be able to monitor and report the status
of the satellite The project was announced in print
by the Russian Federation several months before its
launch so that results ofcommunications from the
sat-ellite could be reported See Radio
retrieval of a living creature, Laika, a dog, was car-ried out by the Russian Federation in Sputnik 2 on 3 November 1957 This craft also studied space radia-tion and used a slow-scan TV camera to relay images
to the ground
SQL Structured Query Language A widely used, structured data sublanguage coding system for que-rying database infonnation (e.g., Oracle) Most pro-fessional database programs support SQL-format files or can import/export SQL instructions SQL emerged from technical descriptions of relational databases documented by computing professionals such as E.F Codd Based upon this model, ffiM de-veloped SEQUEL, the forerunner to SQL In 1979, Relational Software, Inc introduced a commercial implementation of SQL that became integral to the Oracle database program The company later became Oracle Corporation
SQL has been supported and standardized by a num-ber ofprominent organizations, including ANSI and IS/IEC Embedded SQL comprises SQL statements within a procedural programming language as well
as certain extensions to standard SQL statements
devel-oped by Joan Daemen and Vincent Rijmen Paulo Barreto and George Barwood developed a fast imple-mentation of the algorithm for the Pentium II that is available on the Web Square was used as the basis for the development of Rijndael, an important sys-tem used by the U.S government See Rijndael
Srsymb strontium See strontium.
SRsymb left-hand slant polarization (ITU).
recogni-tion and translarecogni-tion applicarecogni-tions programming inter-face (API) developed by the SRAPI Committee, a Utah nonprofit corporation consisting of some well-known vendors of various audio and multimedia products http://www.srapi.com/
SRGPSee Simple Raster Graphics Package SS7 See Signaling System 7
No 13 ABritish automatic IVF signaling system for transmitting supervisory telephone signals between private branch exchanges (PBXs)in the 2280-Hz fre-quency Using the two-wire section ofa transmission path, signals may be sent in one direction or the other (but not both at the same time), although some imple-mentations use four wires for two-way signaling
No 15 ABritish private telephone line signaling sys-tem designed to operate in the 2280-Hz frequency Each line has two transmitting lines and two receiv-ing lines such that it is suitable for settreceiv-ing up a wide-area network (WAN) with two or more private branch exchanges (PBXs) and the appropriate wiring and in-terface cards BTNR 181 is the British Telecom Sig-nal Systems SSAC 15 standards description
SSBSee single sideband
SSCSSee Service Specific Convergence Sublayer
Protocol
Trang 4ST Ports&ST- Connector - Basic Parts
ST2+ is anATM-based, connection-oriented Intemet protocol for communication among ST2+ agents The protocol is designed to extend UNI 3.1/4.0 signaling functions, to reduce certain signaling limitations, and
to manage resources more efficiently in ATM and non-ATM networks The protocol specifies the inter-action between ST2+ and ATM on three planes that correspond to the lTU-T B-ISDN Protocol Reference Model:
user Specifies encapsulation ofthe ST2+
DATA PDU into the AAL-5 PDU
management Specifies the Null FlowSpect,
Con-trolled-Load Service FlowSpec, and the Guaranteed Service FlowSpec mapping for UNI 3.1 traffic
control Specifies encapsulation ofthe ST2+
SCMP PDU into the AAL-5 PDU, the relationship between ST2+
SCMP and PVC management (for ST2+ data), and the interaction be-tween ST2+ SCMP and UNI 3.1 signaling
See byte-stream protocol, STll, RFC 2383
Aconnection-oriented Internet protocol which brings together SCMP (for signaling and control) and ST (streaming protocol) A connection must be set up between
deal oflntemet traffic is connection-oriented, in that the receiving system doesn't have to be determined
to be online before a transmission is sent ST2 has an IPv5 designation See ST2+, RFC 1819
STA 1 See spanning tree algorithm 2 Science and Technology Agency Japan's research and develop-ment support, to plan and coordinate national science and technology Founded in 1956
stage A designated platform or work area that is sometimes housed in a special enclosure or room to provide the right environment for the work to be carried out A microscope stage is the region where the sample is held in place for viewing A fiber optic fusion splicing stage is the region where two fila-ments are aligned and spliced
stand alone, stand-alone, standalone A system or device providing a self-contained service or function, independent ofother major components See turnkey system
standard cellA fragile, special-purpose cell provid-ing very small amounts ofelectrical current (1.019V) for short periods
standard network variable type SNVT (pron.
snivit) A common variables framework element
::'::~::""""""'.Y":"'''::''''''''''': : : , ":'"
::, :\l~~· \, 'l~~~~;
2 See System Services Control Point
SSD 1 Secret Service Division 2 Service Selection
Dashboard (Cisco Systems) 3 shared secret data
Encryption infotmation shared between negotiating
systems for purposes of security In mobile
commu-nications environments, SSD is divided into
authen-tication procedures (SSD-A) and
privacy/confiden-tiality (SSD-B) with SSD infotmation shared between
a user mobile handset and an Authentication Center
(AC) and sometimes also a Visitor Location Register
(VLR) SSD is documented inANSI-41
SSL See Secure Socket Layer
SSPSee Service Switching Point
SSRPSee Simple Server Redundancy Protocol
SSTVSee slow scan television
ST1 See Scheduled Transfer 2 signaling tetminal
3 straight-tipped 4 systems test
ST- ports (top) and their associated connectors are
standardizedjiber optic coupling components that are
widely used.
The basic components in the ST- connector include
(bottom image, left to right) a strain relief boot (to
prevent excessive bending), sometimes a crimp sleeve,
a2.5mm-ferrule connector, which may have a
bayo-net mount, and a dust cap The necessity for a crimp
sleeve depends upon the clamping or bonding method.
The size ofthe hole to accommodate the fiber varies
with the diameter ofthe fiber to be inserted.
ST-connector A common, standardized connector
for coupling fiber optic cables ST- connectors may
vary in the details of their appearance but are
essen-tially mechanically the same They are fabricated in
a variety ofmaterials including metal (e.g., stainless
steel), plastics, or ceramics
ST2+Aconnection-oriented, routable,
multicast-capable Intemet protocol for providing native ATM
circuits for applications that require bandwidth
guarantees and Quality of Service (QoS) ST2+ is an
updated version of STII (ST2), specified in 1996,
which has an Intemet Protocol V.5 (IPv5)
designa-tion See ST2+1UN1, RFC 1946
ST2+1UNI Stream Protocol Version 2+.An
evolu-tionary descendent ofsmand a version of a previous
ST2+ providing native ATM support for ST2+, this
Trang 5application program
Standards that influence application portability by describing and defining interoperability between applications software and the computer operating system Consideration is given to systems,
communications, information, and human-computer interactions
platform external
Standards that influence system portability and interoperability, that is, the behavior of information processes which interact with their external environment Data portability and user interfaces are important
considerations
Conformance to these standardization concepts pro-vides a framework for vendors to develop and dis-tribute products and services compatible with those
of other vendors, and provides users with some as-surance that products purchased from different ven-dors will work together
in a computer system that is ready to take over ifthere are problems with the first, or if extra computing power is needed on an irregular basis The standby processor is usually a hot standby device, that is, it can come online without turning the system off or interrupting its functioning to a substantial degree Sometimes the second processor is not idle, but is used for less intensive computing operations, while still remaining ready if it needs to come online as a substitute for the main processor In some cases, the standby processor does low-level maintenance work
on updating its databases and file structures, so that
if the primary processor goes offline, the file infor-mation is known by the standby processor
Standby processors are most commonly used.in high-end systems that require a high degree of reliability Examples would include medical or navigational ap-plications where people's lives might be in danger if there were a processor failure
many consumer electronics Camcorders, calculators, laptop computers, and various other devices that rely
on limited battery power will often have timing mechanisms that monitor idle time, that is, time dur-ing which the device receives no input from the user When the idle time expires, the device is powered down or put in a minimal power-consuming mode,
in order to save battery life 2 The amount of time a fully charged battery-powered unit can remain on before the battery runs out This applies to many de-vices, including cell phones, cordless phone·s, short-range radios, laptop computers, etc Standby time is often used as a marketing statistic to characterize a system and generally refers to idle time, rather than
Fiber Optics Illustrated Dictionary
designed to support interoperability The term is
es-pecially associated with the LONWorks control
au-tomation system, though it is applicable in a general
sense to other types of network devices where
pre-defmed network variables have been associated with
various units within the system (e.g., degrees, meters,
volts, etc.)
Standard Performance Evaluation Corporation
SPEC Anonprofit organization supporing the
estab-lishment and maintenance of standardized, relevant
benchmark computer performance evaluation tools
that can be applied to various high-performance
sys-tems http://www.specbench.org/
pre-cise location data signals transmitted from Global
Positioning System (GPS) satellites This signal is
available without charge for private and commercial
use and is not encrypted It provides information
about the functioning ofthe satellite and its
approxi-mate location Combined with infonnation from three
or four other satellites, the user can pinpoint a
loca-tion with horizontal and vertical accuracies up to
about 100m and 340 nsec of time, depending upon
the quality and accuracy of the receiving equipment
See Global Positioning System, Precise Positioning
Service
Australian standards organization with strong
inter-national activities focused on supporting
business-to-business services based on knowledge sharing The
organization was established in 1922 as the
Austra-lian Commonwealth Engineering Standards
Associa-tion and became the Standards AssociaAssocia-tion of
Aus-tralia (SAA) in 1988 Other changes were made, and
the organization was incorporated as Standards
Aus-tralia International in 1999
SAl generates revenues through normal business
ac-tivities and government-funded contributions to the
national interest It makes innovative use of the Web
to develop and distribute intellectual property
Through a large number of technical committees, a
staff of almost 300, and thousands of voluntary
ex-perts, SAIl maintains over 6000 standards
Council of Canada is a federal Crown corporation
responsible for promoting efficient and effective
vol-untary standards in Canada for the health, welfare,
and economy of Canada The SCC works in
coop-eration with, and manages, the National Standards
System The SCC coordinates input from the SCC to
the International Organization for Standardization
(ISO) and the International Electrotechnical
Commis-sion (IEC) See Canadian Standards Association,
Telecommunications Standards Advisory Council of
Canada http://www.scc.ca/
framework for describing and classifying information
processing standards by the Institute ofElectrical and
Electronics Engineers, Inc (IEEE).Withinthe reference
model, general sets of requirements are developed
The reference model divides standards into two
cat-egories:
Interface Type Description
Trang 6talk time on a cell phone) is typically less if many
features are used
physical relationships and movements in real life as
well as diagrammatic representations on display
sys-tems such as computers and oscilloscopes Very large
standing wave patterns are described by astronomers
when talking about the movement, relationships, and
symmetry of galaxies
measure-ment of a standing wave which is commonly used in
transmitter and transmission line testing and
mainte-nance When cables are affected by moisture, wear,
and loose connections, an impedance mismatch may
occur which can be detected through the amplitude
ratio ofa standing wave The transmitted wave is used
as the signal source for measurement by an inline
SWRmeter
This research laboratory is the source of many
pio-neer ideas and developments in artificial intelligence
and general concepts related to computers SAIL
con-tributed to the development ofthe LISP programming
language The SAIL facility also developed the SAIL
programming language, an ALGOL-like language
created in the early 1970s The SAIL facility was
closed down in 1990
practical alternating current generator, after it was
pioneered by Elihu Thomson Thus, the first Stanley
alternating current (AC) distribution system came
into being in 1885, 3 years after Thomas Edison
opened the first direct current (DC) power utility
company.Inconjunction with Elihu Thomson and
Sebastian de Ferranti, Stanley also developed the
transformer See Alexanderson alternator
Transit Access Point This is a persistent
communi-cations infrastructure project funded largely by the
National Science Foundation to facilitate the
opera-tion and interconnecopera-tion of advanced internaopera-tional
networking systems It supports applications,
perfor-mance measurement, and technology evaluation, and
facilitates the flow ofnetwork traffic to international
collaborators The project is managed at the
Univer-sity of Illinois Electronic Visualization Laboratory
See STAR TAP International Advisory Committee
http://startap.net/
STAR TAP International Advisory Committee A
committee ofinternational member groups connected
to STAR TAP or interested in joining STAR TAP
which overseesSTAR TAPpolicies and operations
Members are affiliated with a wide variety of
orga-nizations including CERN, SURFnet, TransPAC,
iCAIR, and Euro-Link See STAR TAP
of reflecting surfaces at high powers by using
illu-mination from a star as a reference Astar test typically
uses the entire telescopic instrument rather than just
the reflecting mirror or lens components The pattern
from a perfect optical test resembles a top view of a
and light values Ifthe lens is misaligned or aberrant, the pattern may appear eliptical, off-center, or blurred Since a star test is done with the full assembly,itcan also be used "on the fly" to make corrections The star test is sometimes used as a followup to the Ronchi test See DaB test, Ronchi test
in which remote systems and nodes are connected point-to-point to a central system, and not to one an-other Unlike some topologies with redundant con-nections, ifthe central system on a star network fails, the entire network is unable to intercommunicate One advantage is that problems are easier to isolate, another is centralized administration and security A star system provides the option of physically isolat-ing the server from unauthorized access Star topolo-gies are used in many phone and data networks See hub, topology
Johannes Stark, in 1913, following several years of research into Doppler effects in rays He observed the application ofan electric field could induce the split-ting of spectral lines when he was studying the spec-trumofhydrogen Further investigation indicated that the spectra decomposed into several components, some of which were linearly polarized through the influence of a strong electric field and that this effect could be observed in substances other than hydrogen Thus, at the atomic level, it appeared that the influ-ence of an electrical field produced different results from that of a magnetic field See Zeeman effect
who studied the influence ofelectrical fields on spec-trallines Stark was awarded the Nobel Prize in phys-ics in 1919 for his discovery of the Doppler effect in certain rays and ofthe distortion properties ofan elec-trical field on spectral lines See Stark effect
mechanism to release the receiving line relay and permit the receiving arm to move
Howard L Krum for use with permutation code tele-graph systems
security and traffic management technique used in packet-based networks to selectively control network traffic based on information contained in packet head-ers Many routers are equipped to support packet fil-tering Dynamic packet filtering is a means of dy-namically handling the traffic management after a stream of packets has passed through, to minimize the number of security gaps that might be left open
by static packet filtering Stateful packet filtering is
a form of dynamic packet filtering that applies pro-tocol-specific filtering rules and monitors state and context information associated with a network ses-sion This may, in some cases, improve security (or appear to improve security), while still having some limitations and drawbacks associated with direct connections to internal hosts and no direct user au-thentication See spoofing
Trang 7Fiber Optics Illustrated Dictionary
weather phenomena and related atmospheric
electri-cal charges Proper grounding can help reduce static
interference See interference, noise
600 B.C when Thales recorded that a "fossilized
veg-etable rosin" (amber), when rubbed with silk,
ac-quired the property to attract very light objects to
it-self See mutual capacitance
to investigate static electricity and its effects Static
generators still are valuable as educational tools See
static, Van de Graaf generator
Im-ages are often embedded as static objects in word
pro-cessed documents, and can only be edited by
locat-ing the source document, changlocat-ing it in the original
context, and updating the static location (or
reinsert-ing it into the document as a static or dynamic
ob-ject) Contrast with linked object
ran-dom access memory chip which is often used in com-puters in conjunction with dynamic RAM (DRAM)
as they have different characteristics Unlike DRAM chips, SRAMs do not need to be refreshed while in operation, thus providing fast access As with many other types of memory chips, they require power to retain their information See dynamic RAM
and stored in a table or other form of database in a network router or high-end switcher (the distinction between routers and switchers is not as great as it
routing, but is not suitable for all types of installa-tions Static routing works well in small systems or those in which the routes are fixed and known, whereas dynamic routing is suitable for large, chang-ing, distributed networks
telecommuni-cations device selVice office, console, or workstation
switching stations which commonly provided 48V direct current (DC)
station clockAcentralized timing clock which provides
a local reference for broadcast or other
telecommu-Static Electricity Generator
discharging rods
conducting rods
with brushes
collecting
forks
revolving
glass plates
drive wheel
Leyden jar
This excellent example ofa static generating machine mounted on a base with Leyden jar condensers
on either side is on exhibit in the American Radio Museum.
discharging rods _ _- - _ ):======(
revolving glass plates
Leyden jar
This schematic diagram shows the basic components of a static generator which functions in essen-tially the same way as the one shown in the photos above A Leydenjar is positioned at each side, with the revolving plates in the center The discharge rods are shown across the top.
Trang 8information may be actively transmitted from the
sta-tion clock to other equipment In broadcast stasta-tions
in North America, the idiosyncrasies of black and
of different media, even though they might use the
same time-code basis Thus, the playing time of a
broadcast may be considered compensated when it
has to be adjusted to match the station clock
In networks, internal clocks and station clocks are
used to provide timing information
In very precise timing situations, such as in
astro-nomical observatories, cesium-beam station clocks
may be used for timing purposes
STE 1 See Section Terminating Equipment 2
Sta-tion Terminal Equipment 3 Spanning Tree Explorer
arranged in series, when not sending, an operator
would close a switch to short the key contacts in
into a steady mark condition.
computing, stealth products or processes intended to
be active without detection, such as a viewing portal
or recording system that allows people or processes
to be monitored without their knowledge
Account-ing, audit, orjob performance applications are
some-times run in stealth mode System operators often run
stealth processes to monitor regular or unauthorized
activities on computer networks or individual
ma-chines Hackers use stealth measures to break into
computer systems or to investigate processes or
switching systems
name systems, a stealth server is similar to a slave
server in that it is an authoritative server, but differs
in that it is not identified in the name server's
regis-ter and thus would be visible to other servers only if
explicitly known by a static identifier See slave
server
inventor who designed and built Norumbega castle
in 1886 near Penobscot Bay, Maine He invented
im-portant aspects of duplex telegraphy that were
pat-ented in 1872 (U.S #126,847 and #132,933) Stearns'
system was initially used on the Franklin Telegraph
Company lines and later on the Western Union lines
He sold the rights to duplex telegraphy to Western
Union Thomas Edison later extended the concept to
create a quadruplex system in which two
communi-cations could be sent in two directions at the same
may have introduced duplex telegraphy even earlier,
but the author was unable to find any solid
documen-tation to confirm this
Documents such as Stearns' Western Union
member-ship cards and the Stearns patents of 1872 to 1874
(and reissued patents of 1880 to 1882) are in the
West-ern Union Telegraph Company Collection, 1848 to
1963 See Frischen, Carl; Gintl, Julius; duplex
telegraphy
who experimented with an Earth conductivity method
to send wireless communications over distance in the 1830s Steinheil was born in Alsace, but settled in Munich, Germany With Gauss, he proposed the use
of rail lines as a conduit for returning electrical sig-nals Steinheil developed a magnetic recording tele-graph that marked high and low dots on a ribbon of paper (very similar in concept to Vail's code used on the Morse telegraph a few years later) In 1836, he contributed to the development ofstandards for mea-surement In 1839, he pioneered electric clocks and
reported some of his telegraphic discoveries in
An-nals ofElectricity, Magnetism, and Chemistry.Ten years later he was involved in the organization oftele-graphic communications in Austria He is also known for inventing optical technologies See conductivity method See Sommering, Samuel Thomas
Ger-man-born American electrical engineer acknowl-edged for his genius in the investigations oflightning, alternating current phenomena, magnetism, and other discoveries which led to the development of safer power distribution systems and better motors, gen-erators, and electrical appliances
supporting a rung, intended to assist a climber in find-ing footfind-ing while climbfind-ing, as in a high-voltage line supporting tower As towers age, the bolts tend to rust
or even disappear altogether, causing risk to the climber, unless the bolts are maintained and replaced when needed Tower maintenance workers are cau-tioned to place their gloved hands on the side sup-porting structures rather than on the step bolts, in case
of a slip or fall
au-tomatic telephone switching system developed in
rotating blades for setting switching connections In competition with this, AT&T developed the first com-mercial panel switch in 1921 This type ofswitch was widely used until the mid-1970s, when crossbar switches superseded most panel switches and many step-by-step switches Step-by-step switches must be modified to support touchtone dialing See Callender switch, crossbar switch, Lorimer switch, panel switch
provides voltage conversion from a higher to a lower level This type of system is commonly seen on util-ity poles carrying primary power to secondary power users and individual drop points See diagram
layers with differing refractive indexes The core has
a slightly higher refractive index than the cladding, which causes the light to be reflected back into the core to continue along the waveguide Stepped index
is essentially an abrupt transition (though it need not
be a large difference to be effective), in contrast to graded index fiber in which the refractive index de-creases gradually as the distance from the center in-creases See graded index
Trang 9Fiber Optics Illustrated Dictionary
Stepdown Transformers on Utility Poles
Stepdown transformers are common components of
utility poles carrying primaly power between
substa-tions (upper) and secondary power for residential/
small business subscribers (lower) Here the
connec-tions are shown between the higher-voltage
conduc-tors all the crossamls to the three transfomlers
at-tached with brackets to the pole to the conducting lille
for the secondmy power fed via connecting lines to
the adjacent buildings [Classic Concepts photo.}
that is independent of scale The name is related to
raidan,which is an SI unit for plan angle Both may
be expressed in meter units
derived from a conical shape radiating out from the
center of the sphere with the area at the portion
bounded by the cone at the surface of the sphere equal
to the radius squared
measure-ments In conjunction with watts, the steradian is a
standard unit of luminous intensity See candela,
lu-minous intensity, spat
Stibitz Complex Number Calculator The first
re-lay calculator, released in 1939, developed at Bell
Laboratories
math-ematician and researcher at Bell Telephone
Labora-tories who developed relay arithmetic devices in the
mid-1930s Stibitz began to study binary circuits and
the various applications of binary systems This led
to Stibitz's subsequent development, in collaboration
with Samuel B Williams, of an electromagnetic
re-lay calculator, the Complex Number Calculator,
which could manipulate complex numbers By 1940,
this machine had become the Bell Labs Model I and
was incorporated into the telephone network in such
a way that it could be remotely accessed, setting an
early precedent for future network systems Stibitz
ofScientific Research and Development Stibitz' con-tinued interest in calculating machines and comput-ers led to the awarding of a patent for a computing system that was a forerunner of modern digital com-puters, in February 1954 (U.S #2,668,661)
In 1997, the American Computer Museum launched
an annual award to honor living pioneers of the com-puter and information age and named it in honor of George R Stibitz
STL I Standard Telegraph Level 2 Studio-to-Trans-mitter Link
stock ticker A type of early stock reporting machine, somewhat resembling an anniversary clock with me-chanical parts within a glass globe on a round base This machine used a paper tape and telegraphic line hookup to provide fast reporting of stock activities with alphanumeric characters In many ways, stock tickers led to asynchronous telecommunications Stoke's shift A loss of energy during an excited state ofan electron where internal forces bring the excited electron to the first level singlet In observations of fluorescence, the difference between the peak exci-tation wavelengths and the emission wavelengths The concept of the Stoke's shift is important in a number of fields related to telecommunications, including spectroscopy In fiber optics, it applies to shifts that occur in doped in-fiber amplification tech-nologies that help overcome signal loss through at-tenuation See Stoke's theorem
Stoke's theorem A theorem pertaining to vector cal-culus that describes a relationship between surface integrals over an open, spatially oriented three-dimen-sional surface and closed line integrals along the
to be mathematically reduced to line integrals and vice versa This is useful for analyzing vector fields
in electromagnetics It is related to Green's theorem, which provides relationships between closed path line integrals and plane integrals for curves lying in a two-dimensional plane
(1989), an account of computer espionage by foreign infiltrators as experienced by Stoll, who was deter-mined to track down the source of a tiny, but puz-zling accounting error, and found much more This account ofremote hacking was only the tip ofthe ice-berg in terms ofwhat was subsequently learned about computer penetration into unauthorized systems, computer theft, and fraud and thus has become a clas-sic nonfiction techie thriller
step back and looks at the pros and cons of digital technologies and how they have affected our world
electron-ics experimenter and amateur radio enthusiast who,
in 1957, suggested the amateur construction of a re-lay satellite capable of two-way communications This idea was in advance of its time, preceding the widespread use of electronic transistors and the con-struction of government two-way communications satellites, and inspired the development of the OS-CAR satellites Stoner wrote about his ideas for
Trang 10In 1971, along with Pierre Goral, Stoner formed
Stoner-Goral Communications (SGC) to sell radio
equipment, 70% ofwhich is not exported outside the
the advancement ofamateur radio until his death He
and head, for a time, of the National Amateur Radio
Association His callsign was W6TNS
phrase for new systems for handling large amounts
ofdata stored on a variety oftypes ofmedia, accessed
by a variety ofremote users on a network The model
ofa single hard drive and floppy drive on a dedicated
workstation is impractical for heterogenous,
high-capacity storage; high-demand storage needs on
evolving local area and distributed public networks
A SAN is a general effort to efficiently organize,
ad-minister, and evolve storage solutions for
heterog-enous network environments This more general
con-cept is distinct from network access storage (NAS),
which implies the consolidation of network storage
resources SAN is a broader concept, encompassing
many different types of solutions for handling
stor-age devices and data-need dynamics
SAN is also more narrowly defined by commercial
vendors as storage devices optimized for use on
dis-tributed networks See network-attached storage
electricity, since it does not provide power
immedi-ately, but rather is charged up and then used Car
bat-teries are typically lead-acid storage cells that derive
their power from a generator when the car is running,
then store the power for later starting of the vehicle
or operation of its electrical system when the motor
is not running See solar cell
store-and-forwardAtechnique for temporarily
hold-ing infonnation until the conditions are right for
trans-mitting the data to the receiver This method is very
common on data networks, where a router, local
net-work, or individual machine may be offline or down
The data may be held indefinitely and transmitted
when conditions are right (the right time, when
traf-fic is lower, when the recipient is online, etc.), or may
be bounced back to the sender after a certain interval
or number of tries It may even be abandoned,
de-pending upon its nature and priority level
that store and forward information when conditions
sta-tions, both Earth and satellite stasta-tions, the conditions
for transmitting a received signal may not be
opti-mal right away, due to weather, political unrest, high
traffic levels, or the movement of a satellite out of
transmissions range The message is thus not sent
until conditions improve or the satellite comes into a
favorable position in orbit
in 1891, to specifically describe an electric charge
by the Brookfield Glass Company in 1909 See
Point See Signaling System 7.3 Spanning Tree Pro-tocol
STPC 6800 An early Motorola MC6800-based com-puter kit from Southwest Technical Products Corpo-ration It featured 2048 bytes of static memory, a se-rial interface, case, and cover in the fall of 1975, and sold for $450 without a monitor or keyboard See Altair 680, SPHERE System
util-ity pole insulator that French inventor C Priestley submitted for a patent in 1910 The Ohio Brass com-pany acquired the rights and the patent was granted
in 1912 It was in production, with variations, for
liver insulator due to the brown or tan coloring and
the blobby dimpled saddle shape that allowed the conductive line to be fed through a channel connect-ing the dimples The dimple channel configuration provided some protection in case the insulator broke,
as it could still hold the cable See saucer insulator, suspension insulator
that fits over cables in sections where there may be pressure or pulling strain against the cable Strain re-lief boots are often fitted over the point of coupling between a cable and cable jack See ST- connector
When two or more of these strands are combined or twisted around one another in the same bundle, it is
of reasons; it can make it more flexible and it may alter the electrical characteristics ofthe wire for some particular purpose
telephone networking products, particularly Frame Relay switching systems and network management control software based on open, standards-based in-terfaces for integrating with other vendors' products
or wavelengths of observational interest Undesired stray light may reach a viewing component or detec-tor from a number of sources, including external re-flected light, light scattered from imperfections in optical mechanisms, or flaws in grating corrugations Interference gratings have been found to be much less susceptible to stray light effects than ruled gratings, especially when the grating corrugations are densely configured
reliable network transport protocol designed to trans-port public switched telephone network (PSTN) sig-naling messages over Internet Protocol (IP) networks SCTP was submitted as a Standards Track RFC by Stewart et al in October 2000
SCTP operates over connectionless packet networks such as IP It is modeled as a layer between the SCTP user application and a connectionless packet network service in the context of an association between two