Fiber Optics Illustrated Dictionary - Part 88 potx

single sign-on SSO.Anetwork security and manage-ment strategy to help reduce the number ofpasswords needed to access a variety of software and hardware resources on a network.. Thus, whe

Fiber Optics Illustrated Dictionary

poles The top and bottom mounting surfaces are

metal, while the layers of "skirts" down the body of

the insulator are fabricated out ofsilicone rubber over

a fibre-glass core Silicone rubber is nonconductive,

light, water-repellant, resistant to ozone and

ultravio-let degradation, and easy to fabricate in a variety of

shapes and sizes, making it an alternative for glass

and ceramic insulators

SIM4 Historically one of the early desktop

computers, introduced over 2 years before the Altair,

but several months after the Kenbak-1, in 1972, by

the Intel Corporation, which was around the same

time Hewlett Packard introduced the HP 9830 The

single-board Intel computer was based upon a 4004

processor and was available in at least two models,

the SIM4-01 and the SIM4-02 The SIM4-02 could

be inserted into an Intel MCB4 chassis and

pro-grammed through a programmer card See Altair,

Kenbak-1, Micra!

SIMMsingle inline memory module

SimonA historically remarkable computer project

described in Edmund C Berkeley's book Giant

Brains or Machines That Think in 1949 and in Radio

Electronicsarticles in the early 1950s The name was

based on Simple Simon It was basically a desktop

logic calculator that could be built for about $300

(about $4000 in today's money) In his book,

Berke-ley describes it as " so simple and so small, in fact,

that it could be built to fill up less space than a

gro-cery store box, about 4 cubic feet."

The Simon was an electromechanical assembly for

performing different calculating experiments, but it

can probably be considered the first desktop

comput-ing kit considercomput-ing the size of computer behemoths

at the time Simon was a papertape computer based

on 129 relays and a stepping switch In Berkeley's

description, a two-hole tape reader was used to input

numbers and operations and a four-hole tape reader

was used to input instructions, but Berkeley points

out that relays and other input modes apply just as

well Problems were entered in binary and answers

were displayed on front panel lights (a design aspect

used by many early microcomputers until the

mid-1970s)

With assistance from William A Porter, Robert A

Jensen, and Andrew Vall, Berkeley got a basic

ma-chine working Considering that most people didn't

know what a computer was in those clays, it is

amaz-ing that Berkeley wrote about "machines that think"

in November 1949 and published plans for actually

building the Simon in 1950 Apparently more than

400 plans for the Simon were sold over the next

de-cade

Simon's little-cousin successor was the GENIAC, a

computing "game machine" developed by Berkeley

in the mid-1950s with documentation by his partner

Oliver Garfield (until a dispute split the name from

the technology) See Altair; Arkay CT-650;

Berke-ley, Edmund C.; GENIAC; Kenbak-l; Simplac

SimplacA design for a transistor-based computer

presented as a collaborative progress report

docu-mented by Edmund C Berkeley through Berkeley

Enterprises Laboratory in 1956 Milt Stoller had re-sponsibility for the logical design ofthe machine The machine was intended to have registers for three bi-nary digits The author is not sure whether this com-puter ever came to fruition Berkeley had a lot of in-terests in robotics and artificial intelligence and was always beginning new projects See Simon, GENIAC

Simple Discovery ProtocolSDP An experimental minimal request/response multicast network recourse discovery protocol developed by Martin Hamilton SDP payloads are application-dependent SDP is not intended for bulk data transfers, due to the size of UDP packets

Simple File Transfer ProtocolSFTP A simple file transfer protocol that fills the need for a specifica-tion that is easier to implement than File Transfer Protocol (FTP) It provides file transfer capabilities combined with user access control, listing of direc-tories, traversing direcdirec-tories, file renaming, and file deleting.Inother words, it incorporates the most com-mon and necessary functions ofFTP See RFC 913 Simple Gateway Monitoring ProtocolSGMP De-veloped in the mid-1980s and demonstrated in 1987, SGMP later evolved into Simple Network Manage-ment Protocol (SNMP)

Simple Internet TransitionSIT A set of Internet protocol mechanisms for hosts and routers designed

to smooth the transition between IPv4 and IPv6, its successor SIT eases the transition by supporting in-cremental upgrades of hosts through upgrading the DNS server with support of existing addresses SIT employs a number of mechanisms to achieve inter-operability and compatibility including:

• embedding of IPv4 addresses within IPv6 ad-dresses

• encapsulation of IPv6 packets in IPv4 headers for transmission through IPv4 legacy routers

• dual IPv4/IPv6 protocol stacks model for hosts and routers

• header translation for IPv6 only routing topolo-gies

simple line code SLC A means of transmission through four-level baseband signaling that filters the baseband and restores it at the receiving end Simple Mail Transfer ProtocolSMTP Atransmis-sion subsystem-independent electronic mail protocol which establishes and negotiates communications between sender and receiver (or multiple receivers) across transport service environments Transmissions may be direct, depending upon the transport service,

or may pass through relay servers

When a user mail request is generated, the sender-SMTP establishes a two-way transmission channel

to the intermediate or ultimate destination-SMTP SMTP commands are then sent between the two ends Once a transmission channel is established, a lock-step negotiation of the transmission and identifica-tion of the recipient or recipients is carried out, and the mail data sent, with a terminating sequence to indicate the end When successfully received, the

email, RFC 821.

Simple Multicast Routing ProtocolSMRP A

rout-ing protocol from Apple Computrout-ing, Inc which is

used for AppleTalk network data from applications

such as their QuickTime Conference, which in tum

is used for videoconferencing, electronic

whiteboard-ing, etc

Simple Network Management ProtocolSNMP

SNMP evolved from, but is not backwardly

compat-ible with, the Simple Gateway Monitoring Protocol

(SGMP) Essentially, SNMP communicates

manage-ment information between network managemanage-ment

sta-tions and the agents in the network elements (NEs)

SNMP was designed for TCP/IP-based network

en-vironments and manages nodes on the Internet

SNMP was originally designed as an interim solution

with the intention that it follow generally along Open

Systems Interconnection (OSI) guidelines Over time,

they were found more different than originally

envi-sioned

Along with MIB and SMI, SNMP has been

desig-nated by the lAM as a full Standard Protocol with

"recommended" status The SNMP Extensions

work-ing group was formed to evaluate and further develop

the SNMP definition, with the mandate of retaining

its simplicity See RFC 1157

Simple Raster Grapbics PackageSRGP A

low-level graphics package which incorporates features

from a variety ofgraphics systems (such as GKS and

PRIGS standards, The X Window System, Apple

QuickDraw) SGRP typically functions as an

inter-mediate layer between the applications program and

the display device

Simple Security and Autbentication Layer

ANet-work Working Group-proposed standard for

provid-ing a quick method of negotiatprovid-ing an authentication

mechanism, even ifthe client has minimal knowledge

of the system See RFC 2222

Simple Server Redundancy ProtocolSSRP A

net-work protocol which provides resiliency for LANE

services onATM-based local area networks (LANs)

SIMULAobject-oriented programming language

designed by O Dahl and K Rygaard at the

Norwe-gian Computing Centre between 1962 and 1967 It

was intended for discrete event simulation, but

gradu-ally became a general-purpose programming

lan-guage SIMULA was one of the early languages

in-corporating object-oriented concepts A number of

versions of SIMULA have been developed over the

years, with compilers for specific systems such as

Control Data Corporation systems as well as IBM

360/370and UNIVAC computers

The Association ofSIMULA Users (ASU), formally

established in 1973, supports the development and

use ofthe language and is one ofthe earlier computer

users groups

simultaneous voice/dataSVD A number of

ana-log and digital techniques and standards which

per-mit liper-mited use of simultaneous voice and data

through regular phone lines with computer voice/data

modems These might be considered medium level

videoconferencing, but they allow whiteboarding and switching between voice and data as needed (alter-nate voice/data [AVD]) SVD is accomplished through multiplexing.Inanalog SVD, voice is mul-tiplexed with data in digital SVD; data and digitally compressed voice are multiplexed into a digital data stream

The ITU-T has established standards, draft standards, and specifications related to SVD These are periodi-cally reviewed and updated to reflect improvements

in modem technology V.61 has been specified for 14,400 bps standard for analog SVD, and V.70 for 28,800/33,600 bps for digital SVD

simulatorA software program, or software/hardware combination that models, reconstructs, or mimics an environment or situation, which may be real or imag-ined Simulators are used in many areas of scientific research to enact scenarios; to test, confirm, or inves-tigate hypotheses; to compare or contrast the effects ofvarious changes to a system; or to monitor the evo-lution ofa system Simulators are also popular in the entertainment industry Flight simulators have been developed into interactive, environmental video games with helmets, moving seats, and more, to pro-vide a strong emotional/intellectual/tactile experi-ence Virtual reality simulators go a step farther, cre-ating 3D effects which appear to inhabit the space around the user, sometimes so convincingly that the user will duck to get out of the way of a virtual im-age

Sinclair ZX81The successor to the ZX80, the ZX81 personal computer was introduced in spring 1982 and sold for under $200 (without monitor; it could be hooked up to a television set) It sported 8 kbytes of

display It was also available as a kit for under $100 sine waveA fundamental waveform presentinalmost all vibratory motion, which can be represented as a

sine curvewith periodic oscillations in which the amplitude of displacement at each point in the wave

is proportional to the sine of the phase angle of its displacement In telecommunications, the sine wave

is important in many representations, but especially

in alternating current (AC) circuitry and in represent-ing sound See oscilloscope

sine galvanometerAnearly current-detecting instru-ment in which the coil is rotated until the reading needle again registers zero This type is subject to interference from the Earth's magnetic field See gal-vanometer

SINGARSSingle Channel Ground and Airborne Radio Systems Atactical radio system See Enhanced Trivial FTP

single line repeaterA mechanism for allowing two-way communication on a single line by pennitting the transmission to be alternately broken in one di-rection in order to initiate or resume communication

in the other direction This is accomplished by an ad-ditional holding coil on each relay which can open

Fiber Optics Illustrated Dictionary

or close independent of whether the main circuit is

open See half-duplex

single sideband Transmissions created by

manipu-lating frequencies that are selected from one side of

the modulation envelope of a transmission wave to

recreate the original baseband transmission Much of

the credit for the development of single sideband

technology, which is essential to frequency division

multiplexing, belongs to John R Carson, a

mathema-tician with AT&T, and later Bell Laboratories, who

mathematically demonstrated the relationship

be-tween the information in the sideband signals and the

original baseband

Sideband frequencies were not originally used

be-cause of problems with noise Later, as technology

improved and the demand for airspace grew, sideband

transmissions became more interesting, and Carson

demonstrated in 1915 that one sideband could be

sup-pressed from the transmission and the other could

even be transmitted without the carrier wave Due to

its predictable characteristics, the original baseband

wave could then be mathematically rebuilt at the

re-ceiving end In a sense, this was a type of"wave

com-pression" accomplished by removing extraneous and

redundant information The significant advantages

included lower power requirements for the

transmis-sion and a narrower wave overall (i.e., requiring less

bandwidth), leaving more room for other

transmis-sions See frequency division multiplexing

single sign-on SSO.Anetwork security and

manage-ment strategy to help reduce the number ofpasswords

needed to access a variety of software and hardware

resources on a network

Single UNIX Specification Developed within the

Common Applications Environment by the X/Open

Company, the Single UNIX Specification is a

collec-tion of documents which includes interface

defini-tions, interfaces, headers, commands, utilities,

net-working services, and X/Open Curses This

specifi-cation is distinct from the AT&T licensed source-code

commercial product and is intended as a single stable UNIX specification for which portable applications can be built It provides vendors a means to provide

a "branded" product and assumes voluntary confor-mation to the specification Basic components within the Specification are shown in the Single UNIX Specification chart See Unix, UNIX

single wire circuit Atransmission path used in early telegraph lines and still used for telephone service in some rural areas The single wire circuit relied on the conductive characteristics ofthe Earth to ground the circuit and complete the return path

single-frequency signaling, SF signaling A tele-phony signaling system in which transmission is through a single designated frequency such as 2600

Hz in the U.S and 2280 Hz in the U.K SF signaling tends to be used in certain microwave transmissions and in two- or four-line wired networks SF ing is an in-band signaling scheme in that the signal-ing is transmitted in the same band or channel as the data or voice communications When a phone system

is on-hook, the designated signaling frequency is transmitted; when it is off-hook, the frequency is in-terrupted Variations in signals can be produced within a single frequency by varying the level of the tones (as expressed in decibels - dB).Inthe U.S., a high level of-8 dB and a low level of-20 dB are stan-dard as these are levels that can be readily recognized

by the electronics in a phone receiver

single-mode optical fiber Asingle mode fiber optic transmissions cable has a relatively thin core acting

as a waveguide such that light is reflected and propa-gated at a consistent angle Athinner core has advan-tages and disadvanadvan-tages over multimode fiber Sig-nals cannot be sent at a multiplicity of angles in the tiny fiber core, but distortion is minimized and trans-missions can reach longer distances Thus, where multimode fiber in data network installations is limited to about 2 lan, single-mode fiber can trans-mit to about 15lan.For other types oftransmissions, Single UNIX Specification - Components

XPG4 System Calls and Libraries Internationalized, covering POSIX 1 and POSIX.2

callable interfaces, the ISO C library and Multibyte Support Extension addendum, the Single UNIX Specification extension including STREAMS, the Shared Memory calls, application internationalization interfaces, and other application interfaces.

XPG4 Commands and Utilities V2 Covering the POSIX.2 Shell and Utilities and a large

number of additional commands and development utilities.

XPG4 Internationalized Terminal Interfaces Including the new extensions to support color and

multibyte characters.

XPG4 C Language

XPG4 Sockets See sockets.

XPG4 Transport Interfaces (XTI)

200 lan.

Signals are usually transmitted through single-mode

cables with laser diodes, in order to get the precise

alignment needed for the fine filaments, and received

at the other end with a photodiode detector This

de-tector translates the signals back into electrical

im-pulses

Single-mode fiber is divided into two general

catego-ries: non-dispersion-shifted fiber (NDSF) and

disper-sion-shifted fiber (DSF) DSF, in turn, is

subcategorized as zero-dispersion-shifted fiber

(ZDSF) and non-zero-dispersion-shifted fiber

(NZDF) In DSFs, the core-cladding has been

fabri-cated to shift optimal dispersion to higher

frequen-cies There are limits to how much ofthis type

ofcom-pensation can be implemented, however, as shifting

frequencies may interfere with other frequency

"win-dows" traveling in the same lightguide, as in

multi-mode fiber NZDF is intended to overcome this type

of interference by shifting the zero-dispersion point

above the range of wavelengths that have been

opti-cally amplified See multimode optical fiber

sink1 Adevice to drain energy from a system Heat

sinks are common on devices or components which

run hot and need to be cooled for safety and to

main-tain operating temperatures 2 Apoint where energy

from a number ofsources is directed, and then drained

away 3 Apoint in a communications system where

information is directed

sinterTo cause to become a coherent mass without

melting, through the application of heat 1 In fiber

optics, sintering ofsooty deposits such that they form

a clear substance is part of the process of creating

preforms from which optical fibers may bedrawn

See boule, preform, vapor deposition 2 In the

con-struction ofmultilayer electronic components,

sinter-ing is part of a direct-write process developed by

Sandia researchers for precision printing of ceramic

and metallic substrates with an ink-filled nozzle rather

than traditional screening or etching processes The

direct-write process enables a high degree of

preci-sion and flexibility in the design of the components

The electronic inks are heated at low temperatures

to evaporate fluids and the remaining dried metal or

ceramic medium is fired to sinter the powders

Ink-written components have potential applications

as conductors, voltage transformers, radio frequency

filters, resistor networks, and other applications

Sioussat, Helen Johnson (1902-1995)Sioussat was

the Director of the Talks and Public Affairs

Depart-ment of CBS radio from 1937to1958 Her

exten-sive correspondence with many ofthe radio and

tele-vision broadcast pioneers is historically significant

and has been preserved in the Library of American

Broadcasting at the University of Maryland

Librar-ies See Broadcast Pioneers Library

SIPP Simple Internet Protocol Plus One of three

candidate protocol proposals eventually blended into

IPv6 by the Internet Engineering Task Force (IETF)

SIR See substrate-incident recording

SIS Standardiseringen i Sverige The Swedish

SITSee Simple Internet Transition

SITA See Societe Internationale de Telecom-munications Aeronautiques

site licenseAlegal arrangement granting specific use

or distribution permission of a copyright product to

a specified location, firm, or other entity A site li-cense is a common method for specifying and con-trolling software use and distribution within a firm, particularly if the firm wishes to install the software

on a network for access by multiple users or on sev-eral user machines within the organization Typically, software companies will offer site licenses with the first copy and installation ofthe product priced at one level, and discount subsequent installations This is common in educational institutions For example, the first copy might cost$1000and permit installation

on up to five machines, with subsequent installations,

in groups offive, at$200each Network licenses typi-cally specify how many users may simultaneously ac-cess the software, and the software itselfmay moni-tor and control access Distribution ofany sort, other than as specified by the license, in most cases is a criminal offense See piracy

SkanovaA wholesale network provider within the relia Group, Skanova operates the largest broadband network services network in Sweden

skin1 Outer protective layer A skin is often used to isolate conductive materials and/or to provide insu-lation and, sometimes, identification through the use

of colored or marked skins

skin antennaAn antenna used on aircraft, in which

a region of the metal craft is delineated and isolated

on its edges by insulating materials

skin effectIn electricity, a situation in which the

cur-~?l~:~::r~;~:~~:Eini~~~~~ [_ penetration to the core of the wire It may increase

the effective resistance in long wires and interfere with transmissions in the high frequencies used in broadcast transmissions

skinningStripping an outer protective layer This is commonly done with wires to expose the conductive material within in order to make a connection

skip distanceThe distance traveled by a reflected radio wave from the transmitter to the point at which

it reaches the Earth's surface or the receiving antenna

This distance is affected by the frequency ofthe wave, the angle at which it passes into the ionosphere, and various atmospheric characteristics and conditions

See ionospheric wave, radio

skip selection Incomputer software applications, a selection that halts the current process, or lets it fin-ish in the background, and allows the user to continue

to the next menu or activity without waiting In au-tomated voice or tone systems, especially menu-driven touchtone phones, a key press that allows con-tinuing to the next selection, menu, or local phone number without waiting for completion of the cur-rent message

skip zoneSee zone of silence

Fiber Optics Illustrated Dictionary

SKIPJACK The name ofa symmetric encryption

al-gorithm which is the basis of the Escrowed

Encryp-tion Standard (EES) incorporated into the Clipper

chip SKIPJACK can be usedtoencrypt a TELNET

stream It has also been described for use in

conjunc-tion with FTP Security Extensions and Key Exchange

Algorithm (KEA) to provide for mutual

authentica-tion and the establishment of data encrypauthentica-tion keys

See Clipper chip, RFC 2773, RFC 2951

skunkworkscolloq.A facility in which clandestine

or time-pressured activities take place in an

environ-ment which is closed off to increase security

Gov-ernment operations, sensitive research, and

high-tech-nology design often operate in environments that are

without sunlight or adequate ventilation, and in which

the participants are working long hours (without

much free time for personal hygiene)

One ofthe most famous skunkworks was a

Lockheed-Martin research "lab" established by Clarence

"Kelly" Johnson in a small desert facility scraped

to-gether from salvaged materials.Itwas a tight, intense,

jet aircraft research and engineering operation dubbed

the Skonk Works after an AI Capp cartoon moonshine

operation, while its official name became the

Ad-vanced Development Projects (ADP) division Later

the name was changed to The Skunk Works and the

lab was moved to a location northeast of Los

Ange-les, California

The term is more than an amusing historical name; it

is also at the heart of some of the significant disputes

about domain names on the Internet Lockheed owns

the service mark for The Skunk Works and initiated

lawsuits in the mid-1990s against Network Solutions,

Inc for registering variations of the name on the

be-half of parties other than Lockheed It was decided

at the time that a domain registrar supplies a service

rather than a product and that NSI was thus not

li-able for contributory infringement against the mark

sky maps Charts of the electromagnetic radiation in

the radio frequencies emanating through space and

around Earth Much pioneer work in this area was

conducted in the 1930s and I940s by Grote Reber,

an amateur radio operator, using a home-built 32-foot

parabolic antenna Cosmic frequencies can

some-times be detected when the ionosphere is temporarily

affected by the burn ofa spacecraft or deliberate

seed-ing with elements such as barium

The phrase is also generically used to describe

im-ages ofthe sky as humans see it looking up from Earth

with or without telescopes Some interesting utilities

on the Web now enable users to enter a location and

date/time to calculate and display a sky map that can

be printed or downloaded John Walker provides

ac-cess to "Your Sky" free on his Fourrnilab site See

radio astronomy http://www.fourmilab.to/

sky wave See ionospheric wave

SkyBridge A medium Earth orbit (MEa) satellite

system from Alcatel providing commercial

satellite-based networking solutions to service providers

Bridge was established in 1997 In March 200 I,

Sky-Bridge announced that it would also be implementing

broadband communications services through

geostationary satelli tes

SkyCell Communications Limited An Indian cel-lular services provider incorporated in 1992 It is the first Indian cellular company to receive company-wide ISO 900 I certification

SKYCELL An American Mobile Satellite Corpora-tion (AMSC) satellite telephony communicaCorpora-tions service providing coverage for the North American continent and nearby islands, catering to mobile workforces, traveling executives, and government agencies The company also offers a continent-wide regional dispatch service providing digital broadcast capabilities to up to 10,000 mobile users

Skynet A U.S domestic communications satellite service purchased in 1997 from AT&T by LORAL Space & Communications, Ltd Skynet originated in the Echo satellite and Project Telstar efforts in the 1960s Telstar 5 was launched 2 months after LORAL's acquisition and positioned at 97° west Soon after, Satmex was merged into the firm, form-ing the LORAL Global Alliance Orion Network Sys-tems, Inc was acquired in spring 1998 Telstar 6 was lawlchedinMarch 1999 at 93° west; Telstar 7 was launched in September 1999 at 129° west It has been called the most powerful communications satellite in Telstar history and has been joined by further satel-lites later named Telstar 10 and 12

Skynet provides news, television broadcasting, dis-tance learning, videoconferencing, and other data transmission services to about 85% of the populated regions of the world

SL Symbol for left-hand slant polarization (lTD)

SL Mail A commercial SMTP and POP3 mail server daemon for Windows NT 4.0 from Seattle Lab, Inc slamming A reprehensible trade practice in which a long-distance supplier switches a person's long-dis-tance service without his or her explicit informed consent In the early 1990s, some companies did this

by phoning potential subscribers and having them verifY their name and address over the phone and then signing them up without actually asking for consent Since that time, more stringent customer consent is required before a change in the service can be initi-ated, and the customer usually must initiate the re-quest, or the company making the change must ob-tain written authorization or outside verification SLAR See side-looking airborne radar

slave I A subsidiary structure, system, process, or device which takes direction or data from a master Many computer peripherals are slave devices 2 In programming, slave processes are sometimes used to gather and report information to a master controlling process 3 In communications circuits, slave con-soles, subsidiary switching centers, and substations are often used to supply low-density populations or workstations some distance from the main control-ler or switching center

slave server In distributed networks using domain name systems, a slave is an authoritative server, iden-tified in the name server's register, which retrieves zones using zone transfer See stealth server sleeve A covering to protect cables, bars, and other

air, and moisture and may provide electromagnetic

shielding The term is used for shorter lengths

ofpro-tective shielding Alonger length, that protects a span

of wire or fiber optic cable, is more often called a

jacket.A sleeve is used for identification (e.g., color

coding) or to protect fragile sections such as areas

where the jacket has been opened (e.g., for splicing

cable)

Sleeves are often made of plastic, though flexible

metallic sleeves may be used to provide additional

strength or electromagnetic shielding Plastic sleeves

are sometimes designed so that they will shrink

around the covered component when exposed briefly

to heat to further ensure a tight seal Some have a resin

adhesive coating on the inside to ensure good

con-tact Transparent sleeves can facilitate inspection of

a joint after the sleeve has been installed See cable,

fusion sleeve

slide contactAsmall sliding ball or tab attached to a

thin rod that acts as a contact mechanism on a tuning

coil Tuning coils were used in early radio sets to

se-lect a frequency A radio might come with several

tuning coils for selecting various frequencies, as

de-sired See tuning coil

SLIPSee Serial Line Interface Protocol

SLM1 See spatial light modulator 2 System Load

Module

slot1 In programming, a time or data "opening" into

which other processes or data can be inserted 2 A

physical opening for connectors or wires/cables

which is typically narrow and rectangular The slots

on the back of a computer allow external connection

access to peripheral cards such as serial, graphics, or

network interface cards (NICs) See slot types 3 In

building structures, an opening that may be built into

a wall or floor in order to enable cables to be fed

through the building

slot typesMost computers and switching stations

have slots into which electronics peripheral cards can

be inserted In order for third-party suppliers to be

able to develop options for consumers, a number of

standards have been adopted for the shape and

elec-trical configuration ofthese slots Most ofthese slots

are long, narrow-edge card configurations, with two

to six slots in the typical desktop computer Many

computers will accommodate two different card

for-mats The software drivers for the cards inserted into

these slots are sometimes supplied on diskettes, to be

loaded on the system, and are sometimes supplied in

hardware, on chips on the actual card Some of the

more common card slot types include PCI, ISA, ESA,

ZORRO,and PCMCIA

Slotted ALOHASee ALOHA

slottingIn setting up a network, the assignment of a

circuit to available channel capacity

slow scan television, slow scanTV SSTV Atype of

black and white TV signal which can function within

a narrow spectrum, similar to single-sideband

trans-missions for voice SSTV has been used since the late

1950s by amateur television and radio operators to

send series of images over radio frequencies SSTV

verter or on a computer monitor with the appropriate interface

In the U.S., SSTV uses frequencies ranging from about 3.845 to 145.5 MHz to transmit a series ofim-ages which can be captured through a dedicated sys-tem or through a computer linkup Interface circuits for setting this up are in the hobbyist price range Hicolor mode can provide color images up to

320 x 240 in thousands of colors Even higher reso-lution 640 x 480 24-bit images (millions of colors) can be transmitted, but they take 7 or 8 minutes, com-pared to low-resolution black and white images that take only 7 or 8 seconds

Radio broadcasting is regulated throughout the world; those interested in SSTV technology will have to be licensed, usually for voice grade channels, by local regulatory authorities

Arelated technology is amateur TV (ATV) which re-fers tofast scan amateur television See amateur

tele-vision

SLPSee Service Location Protocol

SLR1 send loudness rating 2 single lens reflex

Smsymb.samarium See samarium

Small Computer System Interface SCSI (pron.

sCllZzi) Astandardized interface specification which provides a means for the central processing unit (CPU) and main circuitry on the motherboard to com-municate with computer devices that are interfaced

to the system This requires standardization of elec-trical circuitry and data protocols because peripheral devices are manufactured by many different compa-nies One of the most common of these formats is SCSI, which is widely used to interconnect hard drives, scanners, cartridge drives, digitizers, CD-ROM drives, and more

The SCSI standard is approved by the American Na-tional Standards Institute (ANSI), and several en-hanced versions have appeared (variously called SCSI-2, extended SCSI, SCSI-3, wide-SCSI, etc.) SCSI typically consists of a SCSI controller on a motherboard or a peripheral card, which is terminated and usually designated as zero or six, depending upon the system and one or more peripheral devices, set

to SCSIillnumber zero through five or one through six, depending upon which one is reserved for the motherboard, and terminated at the end of the last device The devices can be hooked up end-to-end, that

is, daisy-chained Each SCSI controller can chain up

to seven devices, with the motherboard or main con-troller counting as one The cable for SCSI devices

is either a 50-pin edge connector or a 25-pinD con-nector (or a hybrid cable with an edge concon-nector at one end and pin connector at the other) SCSI-3 cables are wider

Only one device can be assigned to each SCSIill Conflicts or lack of termination will cause failure to recognize a device or spurious errors Many systems expect CD-ROM devices to be set toill3, although there is no inherent reason whyill3 has to be assigned

to only this type of device Scanners often default to SCSIill4 Theillnumber will determine the priority

Fiber Optics Illustrated Dictionary

setting for loading the device, thus boot disks are

usu-ally assigned a number closest to the number of the

controller In other words, if the controller on a

motherboard is zero, then the boot hard drive should

probably be set to one and a relatively low-use tape

drive to five or six

SCSIillsettings are sometimes on the outside ofthe

device, with a thumb-turn switch or DIP switch, and

sometimes on the inside, with DIP switches or

jumpers

Termination is accomplished either by placing a

physical terminator in one of the cable connection

slots, by setting DIP switches, or by setting jumpers

inside the device Automatic termination is available

on some devices, which means that if the device

senses that it is the last device in the chain, it will

minate automatically These types of automatic

ter-minators are sometimes specific to the slot There will

be two slots on the back ofmost SCSI devices so that

they can be chained Take care to follow instructions

for which one to connect if the device is last in the

chain and intended to terminate automatically

Most SCSI devices can only work with cables up to

about 6 feet in length, and 3 feet or shorter is

gener-ally recommended Newer Fibre Channel Standard

technologies can support longer connection lengths,

allowing SCSI devices to be centralized in an

opera-tions room or wiring closet

SCSI controllers are standard in many consumer and

workstation computer systems, including Macintosh,

Amiga, server-level ffiM-licensed desktop

comput-ers, NeXT, Sun, SGI, some HP systems, and DEC

Most of these systems include an internal SCSI

con-troller (for up to six hard drives and internal CD-ROM

drives, etc.) and an external SCSI controller (for up

to six scanner, printer, external CD-ROM, external

hard drive devices, etc.) Thus, a total of 12 devices

can easily be daisy-chained to these systems without

any modifications to the operating system or the

hard-ware, other than perhaps adding a software device

driver and cabling.Inthe author's experience, SCSI

is a good format The inexpensive 8-year-old

Motorola 68040-based computer used for the

illus-trations for this dictionary has two SCSI connectors

(internal and external) with eight SCSI/SCSI-2

de-vices attached (scanner, tape drive, cartridge drive,

six-disc CD-ROM drive, and four different kinds of

hard drives) These are chained to the two

control-lers and worked together the first time they were

con-nected without any compatibility problems

SCSI drives are incorporated in mirroring and

redun-dancy combination drive/backup systems such as

re-dundant array ojinexpensive disks(RAID) systems

These drives can be conveniently hot-swapped in and

out if a drive fails and needs to be replaced, with the

information rebuilt by the controller and software

when the new drive is installed

For consumer desktop Intel-based, IBM-licensed

computers that come standard with IDE drives, a

SCSI controller card can be added to the system to

accommodate SCSI devices However, on this type

ofsystem, it is important to detennine whether

appro-priate device drivers are available for the peripheral, that there is no contention with the IDE drive, and also that any appropriate IRQ issues are settled Small Scale Experimental MachineNicknamed

"Baby," this historic computer was developed in the mid-1940s, based upon tube memory, a form of ran-domly accessible data stored in a Williams-Kilburn cathode-ray tube Baby was a binary small-endian system that supported 32-bit words and a main ran-dom access storage capability of 32 words, which could be extended to 8192 words It used several tubes for different functions, including a storage reg-ister that is still used in modern computers, the "ac-cumulator," a couple of instruction tubes, and a tube for displaying the contents ofthe other tubes Asimple keyboard was used to set the bit sequences

The project was undertaken by T Kilburn and G Tootil1with equipment support from the Telecommu-nications Research Establishment (TRE) The system was initially used in 1948 for mathematical calcula-tions that were laborious to execute by hand See Williams-Kilburn tube, Manchester Mark1 small vocabularyInspeech recognition,ithas been found that software can be designed to recognize a variety of voices, without special training of the sys-tem, if the total vocabulary of the recognition is kept small These small vocabulary systems work well in specific environments such as stock buy/sell systems While definitions ofsmall vary, recent systems ofthis type typically recognize 200 or fewer words Smallhouse, Charles "Chuck"Anamateur radio enthusiast (callsign WA6MGZ [now W7CS]) who contributed substantially to the first three OSCAR sat-ellites' design and construction See OSCAR SmalltalkAn object-oriented computer exploration and development language developed through the Xerox Corporation in the 1970s It was evaluated by four Xerox-selected companies in 1980, before be-ing broadly distributed By the mid-1980s, commer-cial versions of Smalltalk-80 were being released for

a variety of platforms including mM licensed per-sonal computers and Apple II systems Smalltalk has been favored by developers working in object-ori-ented programming environments and artificial intel-ligence applications See Palo Alto Research Center

SMAPSee Service Management Access Point

SMARTSelf-Monitoring, Analysis, and Reporting Technology A preventive system implemented in data protection schemes such as RAID which uses predictive failure analysis to anticipate possible fail-ures Impending problems are communicated to the controller, which signals a warning so that faulty drives may be examined or replaced prior to any fail-ure which might occur See redundant array of inex-pensive disks

Smart CardA compact, thin card with embedded data It may contain a microprocessor, memory, or both It typically resembles a plastic credit card Ear-lier Smart Cards incorporated a magnetic strip, but more recent cards may include a set of contacts em-bedded in the card

There are various ways to categorize Smart Cards

without direct physical contact Acontact sensor can

consist of a reader with a slot or a sensing surface

upon which the card is placed Slot sensors generally

require that the card be swiped across the surface to

register the information Basically the card is being

scanned for information Contactless cards typically

incorporate tiny wireless transmitters and may

in-clude an antenna to increase the transmission range

of the signal There are also hybrid cards For

ex-ample, a wireless transmitter may be included for

opening entranceways at a worksite while a second

contact surface may be used to transmit more detailed

information about the person holding the card when

it is swiped through a card reader

The common standard for Smart Cards is in the ISO

7816 series A number of financial agencies have

agreed upon a common specification for

communi-cations between Smart Cards and Smart Card

read-ers, similar to the serial communication that occurs

between computers and computer peripherals This

makes it possible to exchange virtually any type of

data between readers and cards and increases the

pos-sibility ofprogrammable universal cards for the

con-venience of users The downside of universal cards

is that, if they are stolen, a great deal of information

may be in the wrong hands However, various

encryp-tion and other security measures are being developed

to help protect Smart Card users against theft

The cards can also be categorized on the basis of the

types of data contained on the card (information or

algorithms) and whether they are reprogrammable

(write once, read many (WORM) or rewritable)

Since a Smart Card is somewhat like a tiny floppy

disk or a very tiny computer, the range of uses to

which it can be applied is exceptionally broad It

could not only facilitate telephone access for

travel-ers, but could potentially keep track of where and

when the calls were made This information is

valu-able for corporations logging sales transactions, for

example, and keeping records for the taxation

depart-ment ASmart Card could also help present and track

prescriptions, employee purchases, medical histories,

allergy shots, pet vaccination histories, automobile

histories, and much more Smart Card application

interfaces have been introduced by a number of

de-velopers and a lot of interest in programming Smart

Cards with Sun's Java language arose in the late

1990s.Itis likely that Smart Cards will become a

ubiquitous part of daily life, replacing many of the

paper notepads and "dumb" cards now used by

con-sumers and professionals

Smart Card historyThe essential concept of the

Smart Card was patented in 1974 by K Arimura in

Japan andR.Moreno in Europe In the 1980s and

1990s, Smart Cards came into common use for many

types of financial transactions, mobile

communica-tions devices, long-distance phone services, and

au-thorized entry systems

Smart Card Industry AssociationSCIA A trade

association supporting and promoting the

develop-ment, utilization, and understanding of Smart Card

SMASH ProjectA project dedicated to developing mass storage devices for multimedia applications for home use This is intended to promote commercial offerings of video services to the home, with part of the goal of SMASH to provide a labeling algorithm system in the storage system to provide vendor copy protection Thus, data on the storage device can be set so that it can only be stored or copied once

SMASH seeks to develop realtime labeling methods for compressed video Common schemes for this in-clude spatial or discrete cosine transform (DCT) The SMASH Project also introduces two new realtime labeling techniques that can be used in conjunction with MPEG-l or MPEG-2 format video information

See watermark

SMAS Switched Maintenance Access System A legacy telephony network system from Anritsu Com-pany The older systems (e.g., cross bar access sys-terns) are gradually being updated or phased out

SMATVSatellite Master Antenna Television Asat-ellite communications distribution system designed

to send transmissions to hotels, motels, apartments, etc Since these are sent mainly to commercial estab-lishments, they are often used as marketing leaders

or as pay-per-view revenue-generators

5MB See Server Message Block protocol

5MBProjectA project for preserving the history of the Server Message Block (SMB) protocol while pri-mary materials are still available The first definition ofNetBlOS was released by ffiM in a Technical Ref-erence in 1984 By the late 1980s, 5MB File Sharing Protocol extensions were being published by Micro-soft http://samba.org/

SMDS See Switched Multi-Megabit Digital Service

play distortion in which the image is blurred and ap-pears stretched in the horizontal direction 2 Low-level frequency distortion in an audio signal 3 In digital imagery, distortion of details resulting from sampling frequencies or compression algorithm com-promises, so transitions which normally would be sharp and crisp in the original image exhibit blurring

or smear

smectic liquid crystalSLC The molecules ofnem-atic liquid crystals have a certain amount of orienta-tion order but generally lack posiorienta-tion order At cer-tain transitional temperatures, these materials may acquire a certain amount of positional order, called the smective phase Thus, the material has some of the properties ofliquids, but tends to form somewhat positional layers, resulting in a two-dimensional nem-atic liquid crystal Depending upon the tilt and light-directing properties ofthe smectic liquid crystals, they may be subdivided into different types

If the SLCs are encouraged to form a chiral orienta-tion resulting in a helical orientaorienta-tion (as in the Schadt Helrich effect) they can be selectively used to modu-late light to tum it on or off

This form of liquid crystal has faster response time

Fiber Optics Illustrated Dictionary

and better contrast ratio than nematic crystal displays

See nematic liquid crystal, Schadt-Helfrich effect

SIMIMESecure Multipurpose Internet Mail

Exten-sion An IETF working group (inherited from theSf

MIMEConsortium) Internet messaging standard for

the transmission of secure network communications

Unlike PGPIMIME, SIMIME public keys are

distrib-uted via X.509 digital certificates SIMIME can

sup-port 12S-bit encryption, although not all

implemen-tations will use the fulll2S bits See PGPIMIME

SMPTESee Society of Motion Picture and

Televi-sion Engineers

SMPTE Registration AuthoritySMPTERA.A

for-mat and specification authority for technologies

re-lated to the motion picture and television industries

For example, the SMPTERAis approved by IEC and

ISO for the registration ofMPEG-related format

iden-tifiers See Society ofMotion Picture and Television

Engineers

SMPTE time codeA standard developed by the

So-ciety of Motion Picture and Television Engineers

which provides synchronization for information

re-corded on audio and visual video tapes SMPTE time

code digitally encodes hours, minutes, seconds, and

frames

SMPTE time code is recorded onto audio tracks and

video tracks as follows: in audio as Longitudinal time

code (LTC); in video as Vertical interleave time code

(VITC)

A time code word consists of SO bits (zero or one)

per video frame, with 2400 bits per second

corre-sponding to 30 frames per second for North

Ameri-can TV.InEurope, 2000 bits per second corresponds

to the standard of 25 frames per second See drop

frame, Society ofMotion Picture and Television

En-gineers

SMR See Specialized Mobile Radio

SMRP See Simple Multicast Routing Protocol

SMS I See Service Management System 2 See

Short Message Service

SMS/800A centralized interactive computer system

dedicated to coordinating network services related to

toll-freeSOO/S76/etc numbers These are managed

in a central database-equipped mainframe computer

from IBM that updates locally deployed databases

Access is through dialup, Internet, and dedicated

con-nections with various security systems in place to

re-strict access to authorized users TheSMS/SOO

sys-tem supports a 24-hour-a-day, 7-day-a-week public

service

Within the SMS/SOO system, a Responsible

Organi-zation (Resp Org) is an entity authorized to manage

and administer a toll-free number customer using the

SMS/SOO system Bell Operating Companies (BOCs)

administer theSMS/SOO system under the SOO

Ser-vice Management System Functions Tariff

The SMSfSOO system tracks the availability ofall

toll-free numbers and permits Resp Orgs to access the

database to search for available numbers and to

change the status of existing numbers The North

American Numbering Plan (NANP) Administrator

issues instructions to carriers for making toll-free

numbers available or unavailable Resp Orgs are as-signed a logon ID code from a BOC and must meet certain certification requirements Logonillrequests are processed by the SMSfSOO Management Team in New Jersey

Numbers are obtained by Resp Orgs from a common pool, with specific SOO number requests honored based upon availability on a first-come, first-served basis at the time the request is received in theSMSI

SOO Reservation Queue Specific numbers may be reserved for a potential subscriber for upto45 cal-endar days If the period expires, the number is des-ignated a spare A Resp Org may reserve up to 2000 numbers, or up to 7.5% of the total available num-bers, whichever is greater Certain numbers are re-served for special purposes (e.g., hearing impaired) and are considered Closed Resp Orgs are limited to

a maximum of up to 3% of available numbers that are reserved at any given time Resp Orgs must be willing and able to provide troubleshooting assistance and maintenance personnel There is a customer record administration charge for each toll-free num-ber assigned or reserved

Hoarding of toll-free numbers by Resp Orgs is ex-pressly forbidden within the Federal Communications Commission (FCC) Tariffguidelines Acquiring more numbers than are intended for immediate use by a subscriber, or the sale of a toll-free number for an additional fee, contravenes the FCC's responsibility

to promote the fair allocation and orderly use of toll-free numbers

The SMSfSOO Software Support organization pub-lishes the Service Management System (SMS)/800 Mechanized Generic Interface Specification

(SR-4592 - Feb 200 I) See SOO http://www.smsSOO.com

SMS/800 historyTheSMS/SOO system originatedin

1967, when AT&T introduced an inward Wide Area Telecommunications Service (INWATS) for business subscribers who wanted to purchase bulk calling to enable customers to reach them from a wide geo-graphic region In 19SI, computerization made it practical to introduce a centralized database for man-aging national services such as SOO numbers and to assign parameters to specific numbers This, inturn,

made it possible to make the service more flexible and powerful At about the same time, smaller com-panies and competing phone carriers were comput-erizing their customer databases

When the Judge Greene divestiture proceedings led

to the breakup of the Bell System in 1984, SOO ser-vices were required to be opened up to competitors This necessitated the development of more sophisti-cated software to handle the management of data-bases from Bell Operating Companies (BOCs) and independent competing carriers

Number portability soon became an issue, with so many competing phone carriers now offering SOO services.In1991, the Federal Communications Com-mission (FCC) mandated that SOO numbers must be able to be moved among carriers according to the carrier selection of the subscriber

By the mid-1990s, SOO-number designations were

sult, additional prefixes were released, to be assigned

as the need arose See SMS/800

SMS/SOO Management TeamAteam

ofadministra-tors, consisting of a representative from each of the

regional Bell Operating Companies (RBOCs),

re-sponsible for SMS/800 services The team is

head-quartered in New Jersey

SMS/SOO Mechanized Generic InterfaceMGI A

means to interface with the SMS/SOO centralized

to11-free number database The MGI facilitates the

trans-fer of number and customer record administration

between the SMS/800 and Responsible Organization

(Resp Org) computer system over a network

connec-tion.Itis a two-way interface delivered over a

five-layer protocol model The transport service is

sup-ported over the physical, packet, and link layers for

error-free communication The user program layer

(UPL) supports specific applications messages

Before active status on the SMS/800 system is

granted, the MGI must be put through four test phases

to confirm data communications integrity per

spe-cific field and laboratory testing requirements

Atest-ing logonillis assigned for the test period of about

4 months Once access is authorized, an active login

illcode is assigned See SMS/800

SMTPSee Simple Mail Transfer Protocol

SnSymbol for tin (AN 50)

SNASee Systems Network Architecture

SNA Control ProtocolSNACP A protocol which

handles the configuration and enable/disable

func-tions at the ends of a point-to-point link Subdivided

into two protocols that independently negotiate SNA

with or without LLC 802.2 Similar to Link Control

Protocol See See RFC 2043

SNACPSee SNA Control Protocol

snakeAcabling aid consisting ofa flexible, long, thin

cord of metal or plastic used to feed wire and cable

through conduit or through structures (ceilings, walls,

attics, etc.) where space is tight, or access is limited

See birdie

SNAPSee SubNetwork Access Protocol

snap-hookAloop-shaped connector with a normally

closed hook that can be opened to add objects to the

hook with the hook snapping closed automatically

after insertion Snap hooks may be locking or

non-locking Rock climbers are familiar with a number

of types of snap hooks and similar hooks are used by

workers who climb utility poles or towers to do

in-stallations or maintenance/repair Snap hooks are also

handy for slinging wire bundles and hanging up

equipment that needs to be securely held Contrast

with Jhook.

sneak currentsLow-level undesired currents which

seep into circuits and may, ifcontinued long enough,

cause damage Sneak currents are those which do not

cause immediate harm and are not sufficient to

trig-ger safety mechanisms such as normal fuses and

breakers Sneak currents can result from causes such

as worn sheaths and insulators, incorrect wiring,

tem-porary contact due to settling, etc See sneak fuse

sneak fuseAspecial low-level current detection fuse

detected See sneak currents

Snell, Willebrord(1580-1626) Amathematician and astronomer from the Netherlands, who succeeded his father as a mathematics professor at the university of Leiden Snell established a variety of methods for measuring the Earth, establishing some of the basic tools of geodesy He further refined basic principles

of light and predicted how light rays would act in an environment such as a glass rod

In 1703, C Huygens published Dioptrica in which

he refers to Snell's observations about refraction made in 1621 For a time, R Descartes was thought

to be the originator of the mathematics of refraction, but it appears he got his information from Snell The explanation of the phenomenon came to be called Snell's law Snell's observations were important be-cause refractive behavior is nonlinear and thus not easy to measure or mathematically describe unless the relationships are understood See refraction, Snell's law

Snell's lawAdescription ofthe relationship between the angle of incidence and the angle of refraction in propagating radiant energy when it encounters a ma-terial of differing density This relationship was ver-bally described by Willebrord Snell in 1621 In 1658, Fermat showed how Snell's law was generalizable to any propagating radiant energy traveling through any medium See absolute refractive index; Brewster's angle; refraction; Snell, Willebrord

Snell's Law of Refraction

Snell described howpropagating radiant energy (I) refracts when it encounters a medium ofhigher den-sity (R) The energy is bent toward the surface normal

of the medium such that the angle of incidence (a)

and the angle ofrefraction (13) remain in constantpro-portion to one another in terms of the sines of the angles.

SNI See Subscriber Network Interface

sniffer1 colloq nose 2 A synthetic or electronic

substitute for a nose, such as a chemical testing kit used for drug detection and identification by the U.S Customs service 3 A utility for peeling or ferreting out information, such as particular statistics from a log file 4 Anetwork traffic monitoring tool used for diagnostics and sometimes unauthorized snooping