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 of silicone 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!. SIMM single inline memory module. Simon A historically remarkable computer project described in Edmund C. Berkeley's book Giant Brains or Machines That Think in 1949 and in Radio Electronics articles 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 considering 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. Simplac A design for a transistor-based computer presented as a collaborative progress report docu- mented by Edmund C. Berkeley through Berkeley 862 Enterprises Laboratory in 1956. Milt Stoller had re- sponsibility for the logical design of the 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 Protocol SDP. 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 Protocol SFTP. 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 directories, file renaming, and file deleting. In other words, it incorporates the most com- mon and necessary functions ofFTP. See RFC 913. Simple Gateway MonitoringProtocol SGMP. De- veloped in the mid-1980s and demonstrated in 1987, SGMP later evolved into Simple Network Manage- ment Protocol (SNMP). Simple Internet Transition SIT. 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 TransferProtocol SMTP. A transmis- 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 © 2003 by CRC Press LLC recipient sends an OK reply. See electronic mail, email, RFC 821. Simple MulticastRouting Protocol SMRP. A rout- ing protocol from Apple Computing, 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 Protocol SNMP. SNMP evolved from, but is not backwardly compat- ible with, the Simple Gateway Monitoring Protocol (SGMP). Essentially, SNMP communicates manage- ment information between network management 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 ofretaining its simplicity. See RFC 1157. Simple Raster Grapbics Package SRGP. 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 LayerA Net- work Working Group-proposed standard for provid- ing a quick method ofnegotiating an authentication mechanism, even if the client has minimal knowledge of the system. See RFC 2222. Simple ServerRedundancy Protocol SSRP. A net- work protocol which provides resiliency for LANE services onATM-based local area networks (LANs). SIMULA object-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 360/370 and UNIVAC computers. The Association ofSIMULA Users (ASU), formally established in 1973, supports the development and use of the language and is one of the earlier computer users groups. simultaneous voice/data SVD. A number of ana- log and digital techniques and standards which per- mit limited use of simultaneous voice and data through regular phone lines with computer voice/data modems. These might be considered medium level applications, since they do not support full realtime videoconferencing, but they allow whiteboarding and switching between voice and data as needed (alter- nate voice/data [AVD]). SVD is accomplished through multiplexing. In analog 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 ofscientific research to enact scenarios; to test, confirm, or inves- tigate hypotheses; to compare or contrast the effects of various 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 ofa virtual im- age. SinclairZX81 The 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 ~l~~~~~~l~~~:~;~r~iE~:~~~{i~i:; • display. It was also available as akit for under $100. sine waveA fundamental waveform present in almost all vibratory motion, which can be represented as a sine curve with periodic oscillations in which the amplitude ofdisplacement 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 galvanometerAn early 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. SINGARS Single Channel Ground and Airborne Radio Systems. A tactical radio system. See Enhanced Trivial FTP. single line repeaterAmechanism 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 863 © 2003 by CRC Press LLC 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 ofa 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 of passwords 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 circuitA transmission 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 of the 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 signal- 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). In the 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 A single 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. A thinner core has advan- tages and disadvantages 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 multi mode fiber in data network installations is limited to about 2 lan, single-mode fiber can trans- mit to about 15 lan. For other types of transmissions, Single UNIX Specification - Components Components Notes 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) 864 © 2003 by CRC Press LLC longer distances are possible, sometimes up to 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 of this type of com- 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 ofwavelengths that have been opti- cally amplified. See multimode optical fiber. sink 1. A device 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. A point where energy from a number of sources is directed, and then drained away. 3. A point in a communications system where information is directed. sinter To cause to become a coherent mass without melting, through the application of heat. 1. In fiber optics, sintering of sooty deposits such that they form a clear substance is part of the process of creating preforms from which optical fibers may be drawn. See boule, preform, vapor deposition. 2. In the con- struction of multilayer 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 ofpreci- 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 1937 to 1958. Her exten- sive correspondence with many of the 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 standards institute located in Stockholm. SIT See Simple Internet Transition. SITA See Societe Internationale de Telecom- munications Aeronautiques. site licenseA legal arrangement granting specific use or distribution permission ofa 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 of the product priced at one level, and discount subsequent installations. This is common in educational institutions. For example, the first copy might cost $1000 and permit installation on up to five machines, with subsequent installations, in groups offive, at $200 each. Network licenses typi- cally specify how many users may simultaneously ac- cess the software, and the software itselfmay moni- tor and control access. Distribution of any sort, other than as specified by the license, in most cases is a criminal offense. See piracy. Skanova A wholesale network provider within the relia Group, Skanova operates the largest broadband network services network in Sweden. skin 1. Outer protective layer. A skin is often used to isolate conductive materials and/or to provide insu- lation and, sometimes, identification through the use ofcolored or marked skins. skin antenna An antenna used on aircraft, in which a region of the metal craft is delineated and isolated on its edges by insulating materials. skin effect In electricity, asituation 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. skinning Stripping an outer protective layer. This is commonly done with wires to expose the conductive material within in order to make a connection. skip distance The 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 of the wave, the angle at which it passes into the ionosphere, and various atmospheric characteristics and conditions. See ionospheric wave, radio. skip selection In computer 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 zone See zone of silence. 865 © 2003 by CRC Press LLC 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 used to encrypt 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 encryption keys. See Clipper chip, RFC 2773, RFC 2951. skunkworks colloq. Afacility 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 of the 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. It was 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 I 940s 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 ofaspacecraft or deliberate seed- ing with elements such as barium. The phrase is also generically used to describe im- ages of the 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. Sky- Bridge was established in 1997. In March 200 I, Sky- Bridge announced that it would also be implementing broadband communications services through 866 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 communications 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 lawlched in March 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 Acommercial SMTP and POP3 mail server daemon for Windows NT 4.0 from Seattle Lab, Inc. slamming Areprehensible trade practice in which a long-distance supplier switches aperson'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 amaster 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 © 2003 by CRC Press LLC long narrow components. A sleeve helps keep out dirt, air, and moisture and may provide electromagnetic shielding. The term is used for shorter lengths of pro- tective shielding. A longer 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 ofplastic, 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 ajoint after the sleeve has been installed. See cable, fusion sleeve. slide contactA small 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. SLIP See Serial Line Interface Protocol. SLM 1. See spatial light modulator. 2. System Load Module. slot 1. 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 ofa 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 types Most 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 of these slots. Most of these 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. SlottedALOHA See ALOHA. slotting In setting up a network, the assignment ofa circuit to available channel capacity. slow scantelevision, slow scan TV SSTV. A type 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 can be viewed on a television set with a scan con- 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. A related techno logy is amateur TV (ATV) which re- fers to fast scan amateur television. See amateur tele- vision. SLP See Service Location Protocol. SLR 1. send loudness rating. 2. single lens reflex. Sm symb. samarium. See samarium. Small Computer System Interface SCSI (pron. sCllZzi). A standardized 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 SCSI ill number 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-pin D con- nector (or a hybrid cable with an edge connector at one end and pin connector at the other). SCSI-3 cables are wider. Only one device can be assigned to each SCSI ill. Conflicts or lack of termination will cause failure to recognize a device or spurious errors. Many systems expect CD-ROM devices to be set to ill 3, although there is no inherent reason why ill 3 has to be assigned to only this type of device. Scanners often default to SCSI ill 4. The ill number will determine the priority 867 © 2003 by CRC Press LLC 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. SCSI ill settings are sometimes on the outside of the 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 ter- minate automatically. These types of automatic ter- minators are sometimes specific to the slot. There will be two slots on the back of most 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. In the 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 ifa 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 of system, it is important to detennine whether appro- 868 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 Machine Nicknamed "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 of the other tubes. A simple keyboard was used to set the bit sequences. The project was undertaken by T. Kilburn and G. To o til 1 with 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 Mark 1. small vocabulary In speech recognition, it has 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 of small vary, recent systems of this type typically recognize 200 or fewer words. Smallhouse, Charles "Chuck" An amateur radio enthusiast (callsign WA6MGZ [now W7CS]) who contributed substantially to the first three OSCAR sat- ellites' design and construction. See OSCAR. Smalltalk An 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. SMAP See Service Management Access Point. SMART Self-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 in ex- pensive disks. Smart Card A 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. © 2003 by CRC Press LLC Some require contact with a sensor and some are read without direct physical contact. A contact 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 of programmable 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. A Smart 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. It is 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 history The essential concept of the Smart Card was patented in 1974 by K. Arimura in Japan and R. 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 Association SCIA. A trade association supporting and promoting the develop- ment, utilization, and understanding of Smart Card technologies. http://www.scia.org/ SMASH Project A 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. SMATV Satellite Master Antenna Television. A sat- 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. 5MB ProjectA 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. ~~~t~~f:~ri~:::::: :e:::~i:~ ::~~ ::~ II 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 crystal SLC. The molecules of nem- atic liquid crystals have a certain amount of orienta- tion order but generally lack position order. At cer- tain transitional temperatures, these materials may acquire a certain amount ofpositional order, called the smective phase. Thus, the material has some of the properties of liquids, but tends to form somewhat positional layers, resulting in a two-dimensional nem- atic liquid crystal. Depending upon the tilt and light- directing properties of the 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 orientation (as in the Schadt Helrich effect) they can be selectively used to modu- late light to tum it on or off. This form ofliquid crystal has faster response time 869 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary and better contrast ratio than nematic crystal displays. See nematic liquid crystal, Schadt-Helfrich effect. SIMIME Secure Multipurpose Internet Mail Exten- sion. An IETF working group (inherited from the Sf MIME Consortium) Internet messaging standard for the transmission ofsecure 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. SMPTE See Society ofMotion Picture and Televi- sion Engineers. SMPTE Registration Authority SMPTE RA. A for- mat and specification authority for technologies re- lated to the motion picture and television industries. For example, the SMPTE RA is approved by IEC and ISO for the registration ofMPEG-related format iden- tifiers. See Society ofMotion Picture and Television Engineers. SMPTE time code Astandard 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. In Europe, 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/800 Acentralized interactive computer system dedicated to coordinating network services related to toll-free SOO/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. The SMS/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 atoll-free number customer using the SMS/SOO system. Bell Operating Companies (BOCs) administer the SMS/SOO system under the SOO Ser- vice Management System Functions Tariff. The SMSfSOO system tracks the availability of all 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 870 numbers available or unavailable. Resp Orgs are as- signed a logon ID code from a BOC and must meet certain certification requirements. Logon ill requests are processed by the SMSfSOO Management Team in New Jersey. Numbers are obtained by Resp Orgs from acommon 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 the SMSI SOO Reservation Queue. Specific numbers may be reserved for a potential subscriber for up to 45 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 history The SMS/SOO system originated in 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 acentralized database for man- aging national services such as SOO numbers and to assign parameters to specific numbers. This, in turn, 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. In 1991, 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 © 2003 by CRC Press LLC running out, due to the increasing demand. As a re- sult, additional prefixes were released, to be assigned as the need arose. See SMS/800. SMS/SOO Management TeamA team of administra- tors, consisting ofa 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 Interface MGI. 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. It is 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. A test- ing logon ill is assigned for the test period of about 4 months. Once access is authorized, an active login ill code is assigned. See SMS/800. SMTP See Simple Mail Transfer Protocol. Sn Symbol for tin (AN 50). SNA See Systems Network Architecture. SNA Control Protocol SNACP. A protocol which handles the configuration and enable/disable func- tions at the ends ofapoint-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. SNACP See SNA Control Protocol. snakeA cabling 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. SNAP See SubNetwork Access Protocol. snap-hookA loop-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. sneakcurrents Low-level undesired currents which seep into circuits and may, if continued 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. sneakfuse A special low-level current detection fuse specifically designed to trigger if sneak currents are detected. See sneak currents. Snell, Willebrord (1580-1626) A mathematician 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 lawA description of the 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 ofRefraction Snelldescribed how propagatingradiantenergy (I) refracts when it encounters a medium of higher den- sity (R). The energy is benttoward the surface normal of the medium such that the angle of incidence (a) andtheangle of refraction (13) remain in constantpro- portion to one another in terms of the sines of the angles. SNI See Subscriber Network Interface. sniffer 1. 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. Autility for peeling or ferreting out information, such as particular statistics from a log file. 4. A network traffic monitoring tool used for diagnostics and sometimes unauthorized snooping. 871 © 2003 by CRC Press LLC . 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. 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 of this type of com- 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 ofwavelengths that have been opti- cally amplified. See multimode optical fiber. sink 1. A device 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. A point where energy from a number of sources is directed, and then drained away. 3. A point in a communications system where information is directed. sinter To cause to become a coherent mass without melting, through the application. databases. Access is through dialup, Internet, and dedicated con- nections with various security systems in place to re- strict access to authorized users. The SMS/SOO sys- tem supports a 24-hour-a-day, 7-day-a-week public service. Within the SMS/SOO system,