Set is another name for a telephone.
SET. Secure Electronic Transaction. A developing, open specification for handling credit card transactions over any sort of network, with emphasis on Internet and the World Wide Web. Rather than providing the merchant with a credit card number, you send the information to them in encoded form. The merchant can't see the encrypted credit card number, but can forward the transaction request to the credit card company or clearing- house where the information is decrypted and verified . Only the financial institution has the key to unlock the encrypted account information. The financial institution responds to the merchant request with a digital certificate which serves to verify the authenticity of the parties and the overall legitimacy of the transaction. SET ensures that no one else (e.g., hackers) can gain access to your credit card information. It also ensures that an unscrupulous ecommerce merchant can't take advantage of your credit card number. The theory is that you don't always know with whom you are dealing in Cyberspace.
A caching technique where each block of main computer memory is assigned to a location in each cache set where the cache is divided into multiple sets.
Set Copy allows the duplication of programming settings from one telephone to another.
STB. The electronics box which sits on top of your TV, connecting it to your incoming CATV or MMDS (Microwave Multi-point Distribution System) TV signal and your TV's incoming coaxial cable. Set-tops, or converter boxes, vary greatly in their complexity, with older models merely translating the frequency received off the cable into a frequency suitable for the television receiver while newer models can be addressable with a unique identity much like a telephone or a node on a computer network. That identity can be addressed from the cable headend. This allows the CATV operator to turn individual channels on and off, such as pay channels. See DOCSIS and Digital Video Broadcast.
SouthEastern Telecommunications Association, a user group .
Search for ExtraTerrestrial Intelligence. A federally funded project which uses arrays of radiotelescopes to search the heavens for signs of intelligent life as evidenced by radio transmissions. SETI is based on rationale laid out in a "Nature" article by physicists Philip Morrison and Guiseppe Cocconi and first implemented by Frank Drake, a Cornell astronomer . As radio waves propagate infinitely at the speed of light in the pure vacuum of space, the thinking is that at least traces of intelligent life can be identified, even though they will be of millennia long past since other stars and galaxies are thousands or millions of light years away. Promoted as a far less expensive technique than that of space travel, the project is interesting but in jeopardy as results have been nil over the last 25 years or so. See Grid Computing and SETI@home.
Search for ExtraTerrestrial Intelligence at home. A project sponsored over the Internet by the Planetary Society and the University of California at Berkley. The project harnesses home computers to sift through the billions of radio signals from the cosmos that pass the Earth each day in the hope of finding signals that have emanated from intelligent life on other planets. The PCs download the program and run it against a record of signals detected by the Aricebo radiotelescope in Puerto Rico. As each PC works on the analysis, a screen saver of sorts displays a 3-D graph charting its progress. Once the analysis is completed, the results are uploaded to UC Berkley over the Internet, and another set of data is downloaded. http://planetary.org or http://setiathome.ssl.berkley.edu. See also Grid Computing and SETI.
See Accounting Rate System.
See Set Top Box.
Single Frequency. A method of inband signaling. Single frequency signaling typically uses the presence or absence of a single specified frequency (usually 2,600 Hz). See Signaling.
SuperFrame: A DS1 framing format in which 24 DSO timeslots plus a coded framing bit are organized into a frame which is repeated 12 times to form the superframe.
Shared Frame Buffer Interconnect, a specification that makes it possible for hardware manufactures to produce a single-board video-graphics adapter for the PC.
Switch Fabric Controller.
Start Frame Delimiter. A binary pattern at the end of eight octets of timing information in an Ethernet frame that tells the receiving station that the timing information is over, and all subsequent signal represents an actual frame. The pattern is two 1s after a long string of alternating one, zero, one, zero, etc. The one octet SFD field is 10101011 in binary.
Small-Form-Factor Connector. An optical fiber connector used to join single fibers together at interconnects or to connect them to optical cross connects. SFF connectors are smaller than FC and SC connectors, which makes them easier to use in high- density applications such as fiber-to-the-desktop. In fact, SFF allow two optical fibers to be connected in the same space occupied by the copper -based, eight-position modular RJ-45 footprint. Size matters! See also FC Connector, RJ-45, SC Connector, and ST Connector.
Simulated Facility Group.
Serializer/Deserializer Framer Level 5 is a standard electrical interface for 40- gigabit per second transponders and framer devices that promise to drive down communications cost even further. The SFI-5 Implementation Agreement was approved by the Optical Internetworking Forum in June, 2002.
Service for French Internet Exchange. See IX.
Structured Full-Text Query Language. A proposed standard for full-text databases. The primary focus of the proposed standard is interoperability of CD-ROMs. SFQL is based on the SQL (Structured Query Language) standard for relational databases. See also SQL.
System Fault Tolerance. The capability to recover from or avoid a system crash. Novell uses a Transaction Tracking System (TSS), disk mirroring, and disk duplexing as its system recovery methods . System Fault Tolerance as a Novell NetWare term means data duplication on multiple storage devices. If one storage device fails, the data is available from another device. There are several levels of hardware and software system fault tolerance. Each level of redundancy (duplication) decreases the possibility of data loss.
Scalable Fault Tolerant Architecture.
Study Group. The ITU-T has formalized committees studying future telecommunications standards. These groups are called Study Groups.
Signal Ground. Ground lead used in E&M signaling types II, III, IV. See also SB and E & M.
Signaling Gateway. An agent which serves to resolve differences in signaling and control mechanisms between circuit-switched and packet-switched networks, SGs are defined in the overall protocol stack of MGCP (Media Gateway Control Protocol). See also MGCP.
See Simple Gateway Control Protocol.
Standard Generalized Markup Language. A text-based language for describing the content and structure of digital documents SGML was developed by Tim Berners-Lee, who is generally recognized as the father of the World Wide Web. HTML, which has gained fame as the language used to create Web pages on the Internet, is a descendant of SGML. SGML documents are viewed with transformers , which render SGML data the way Web browsers render HTML data. SGML was adopted by the International Standards Organization in 1986. SGML allows organizations to structure and manage information in a cross-platform, application-independent way. It tags documents as a series of data objects rather than storing them as huge files. Theoretically, SGML can reduce errors, slice costs and speed work. SGML attempts to separate the informational content of a document from the information needed to present it, either on paper or on screen. See also HTML and XML.
Simple Gateway Monitoring Protocol. Network management protocol that was considered for Internet standardization and later evolved into SNMP.
Serving GPRS Support Node. See GPRS.
Secure Hash Algorithm 1. Algorithm that takes a message of less than 264 bits in length and produces a 160-bit message digest. The large message digest provides security against brute-force collision and inversion attacks. SHA-1 [NIS94c] is a revision to SHA developed by NIST that was published in 1994. See NIST.
A dead spot in a communication area where radio communication is difficult or impossible .
Shadow BIOS ROM is a concept I first found in Toshiba lap- tops which use Flash ROM to hold the machine's BIOS. When you start the machine, the BIOS copies itself from the flash ROM to the Shadow BIOS area. Accessing the BIOS from the Shadow BIOS is much faster than from flash ROM. I learned later that Compaq actually started what they called shadowing the BIOS. According to InfoWorld, Compaq did it because PC-compatible systems available at the time could have no more than 16 megabytes of RAM. Compaq decided to use the memory address at the top of the 15- megabyte physical address space for the shadow RAM.
The most common type of color picture tube in which the electron beam is directed through a perforated metal mask to the desired phosphor color element.
A process used in many 386 machines to map ROM BIOS activities into faster 32-bit RAM memory. Shadow memory must be loaded with BIOS routines each time the computer boots. See also Shadow Bios ROM.
A measurement of the quality of information in a message represented by one or the other of two equally probable, exclusive and exhaustive states. See Shannon's Theorem.
Professor Claude Shannon was a distinguished mathematician who spent a number of years working at Bell Telephone Laboratories. During that time (1948), he published a paper entitled "A Mathematical Theory of Communication" in the Bell System Technical Journal. The paper showed conclusively that all information sources (e.g., telegraph keys, people speaking, and television cameras ) have an associated "source rate" that can be measured in binary terms (i.e., a series of 1s and 0s) and that can be expressed in bits per second (bps). Although the contemporary technology wasn't sufficiently advanced enough to take advantage of these findings, they eventually became the basis for digital technologies as diverse as modems, magnetic storage, and all variety of digital transmission systems. Other impressive contributions in mathematics and cryptography followed. Shannon, a distant relative of Thomas Edison, also was remembered within the scientific community for his wacky inventions , such as the rocket- powered Frisbee; the gasoline- powered pogo stick; Theseus, the maze solving mechanical mouse; and THROBAC (THrifty ROman numberical BAckward-looking Computer), a calculator that performed mathematical calculations in the Roman numerical system.
Technology Review Magazine of July/August 2001 wrote of the "Reluctant Father of the Digital Age," Claude Shannon, "The entire science of information theory grew out of one electrifying paper that Shannon published in 1948, when he was a 32-year-old researcher at Bell Laboratories. Shannon showed how the once-vague notion of information could be defined and qualified with absolute precision. He demonstrated the essential unity of all information media, pointing out that text, telephone signals, radio waves, pictures, film and every other mode of communication could be encoded in the universal language of binary digits, or bits ” a term that his article was the first to use in print. Shannon laid forth the idea that once information became digital, it could be transmitted without error. This was a breathtaking conceptual leap that led directly to such familiar and robust objects as CDs. Shannon had written "a blueprint for the digital age," says MIT information theorist Robert Gallager, who is still awed by the 1948 paper. Claude Elwood Shannon died on February 24, 2001. See also Shannon's Law and Shannon-Fano Coding.
A statistical compression technique developed independently in 1949 by Shannon and Weaver, and Fano. Shannon-Fano coding reduces the average length of the code required to represent symbols and characters , such as the letters of an alphabet, through the use of variable-length code words. The method divides the entire set of symbols into two equal, or almost equal, subsets , based on the statistical probability of occurrence of the set of symbols in each subset. Within each subset, the symbol with the greatest frequency of occurrence is represented with the shortest code word, i.e., the fewest number of bits. The symbol with the lowest frequency of occurrence is represented with the longest code word, i.e., the number of bits increases . The codewords used to represent the symbols in the first subset all begin with a binary "0," and those in the second subset with a binary "1." With each subset, the symbol with the greatest frequency of occurrence is represented by only a "0" or "1." Additional binary digits are added to represent the less frequently occurring symbols Huffman coding is a related method. Note that this general approach was developed many years ago, as exemplified by Morse Code, in which the most frequently letters of the English alphabet are represented by the fewest number of dots and dashes. See also Compression and Huffman Coding.
Developed by Claude Shannon of Bell Labs and R.M.
Fano of MIT. A compression algorithm based on the ASCII character set, and supporting 256 values. The frequency of occurrence of each symbol in a set of symbols is tallied. The list is divided and subdivided, with the most frequent symbols being represented by the fewest number of bits. Shannon-Fano coding is used, along with other compression algorithms, in the implode (compression) algorithm of PKZIP, for instance. See also Compression.
A theorem defining the theoretical maximum at which error-free digits can be transmitted over a bandwidth-limited channel in the presence of noise. The rough equation works out to about 10 bits per Hertz of bandwidth in practical analog circuits, making the Shannon limit about 30,000 bps for voice-grade lines. According to ZhongJin Yang, a Ph.D. engineer with Lucent Technologies, "Shannon's Law" should be "Shannon's Theorem". Generally speaking, he wrote me, there is no law in mathematics. There are only theorems. Mr. Yang points out that mathematics is not an experimental science, and all laws are from experiments. The conclusion from logical derivation is a theorem. I stand corrected, thanks to Mr. Yang. Now comes the hard part. We've got to correct the rest of the world.
In any event, Shannon's Law is the mathematical theorem used in the A-Law encoding technique used in E-carrier transmission systems. The Nyquist Theorem, a similar but incompatible approach, is used in North American T-carrier systems. See also E-Carrier; Nyquist Theorem; Shannon, Claude; and T-Carrier.
The theoretical limit of information through a channel is called the Shannon Limit (after Claude Shannon, who began information theory). You approach the Shannon Limit by adding redundant bits to the information you send, manipulating them in a standard way to arrive at the correct information, although noise distorts it. The Viterbi algorithm (symbol correction), turbo coding (bit correction), and Reed-Solomon (byte correction) are standard methods of FEC (forward-error correction).
The focusing of a microwave radio beam by the transmitting dish to provide maximum signal strength at the receiving dish. In most microwave systems, the transmitting antenna sits inside a concave, reflective metal dish, and transmits the signal into the dish. The dish reflects and shapes the signal towards the receiving antenna, much like the mirror inside a flashlight reflects and shapes the light signal. See also Microwave.
The process by which signals are modified between networks for interface purposes, at least in some instances. For example, the analog signal originating from your premises might be shaped so that it fits properly into the digital channel of a DLC (Digital Loop Carrier) system. Each channel of the DLC is 64 Kbps wide, which is voice-grade bandwidth in digital terms. The assumption is that the analog signal is 4 KHz wide, which is voice- grade in analog terms. If the analog signal exceeds 4 KHz, it is shaped down to 4 KHz before it is converted to digital format at the DLC in order that it will fit into the 64 Kbps channel. This all works just fine unless the analog signal intentionally is wider. DSL (Digital Subscriber Line) technology for high-speed Internet access is much wider than voice grade and, therefore, will not work over conventional DLC. See also DLC and ngDLC.
An ATM term. N ordered pairs of GCRA parameters (I,L) used to define the negotiated traffic shape of a connection.
A network inserted in a circuit for improving or modifying the wave shape of the signals.
To make resources, such as directories, files, printers, and ClipBook pages, available to network users.
A feature of Microsoft's NetMeeting. See NetMeeting.
In a database a shared lock is created by non update (read) operations. Other users can read the data concurrently, but no transaction can acquire an exclusive lock on the data until all the shared locks have been released.
Simultaneous use of a single computer by multiple users.
See Line Sharing.
Portion of memory accessible to multiple processes.
Dial-out users share resources. Any authorized user attached to the network can dial out a port on the dial-up switch, reach a modem and go for it. Benefits: Reduced costs, improved management and security; It eliminates the need for separate modem and separate modem phone lines.
A path or channel that can be used for a number of interconnecting functions; e.g., a tandem trunk that can be used to interconnect Office A, via the tandem office, with Offices B, C, or D. See Dedicated Path.
Any device, data, file or program that is used by more than one other device, program or person. For Windows NT, Windows 95 and Windows for Workgroups, shared resources refer to any resource that is made available to network users, such as directories, files, printers, and named pipes.
A multimedia concept. Shared screen applications enable two or more workstations to display the same screen simultaneously. For example, two users sharing a screen can work on the same spreadsheet. Changes made by one user can be seen by the other as they are made. Shared screens can be implemented in two ways. One way enables people to view each other's screen while one person makes changes. The other way enables people to run the same application on both screens so that both users can make changes simultaneously .
Providing PBX-based communications and processing services to the unaffiliated tenants and/or the building manager/owner of a commercial building in a standalone or campus environment.
Providing centralized telecommunications services to tenants in a building or complex.
Traditionally, PCs used a special bank of memory for the video circuitry , called Video RAM, or VRAM, that was separate from the main memory used for all the other tasks the computer performs . Having separate memory in a separate location is a good thing. However, some cheaper PCs steal part of main memory for use with their video circuitry. This can impair performance by degrading the amount of main memory the computer can use. Because of that, computer ads often reveal only in tiny type that the video memory is shared. Walt Mossberg of the Wall Street Journal warns that "a related jargon term is "integrated graphics" or "integrated video." This refers to a cheaper, less capable type of video circuitry that is bolted onto the computer's main circuit board rather than residing on a separate video card."
A multimedia concept. Shared whiteboards enable you to "mark-up" a screen using a mouse or stylus input device and have the results show on other screens, often communicating over long distance telephone lines. The concept is similar to a traditional whiteboard mark-up process where everyone has a different color marking pen to circle, write, or cross out items. The background board can be a window from the workstation such as a spreadsheet, image, or blank canvas, or it can be the entire workstation screen. The shared whiteboard can be used for either real-time or store-and-forward collaboration. In the store-and-forward scenario, the mark-ups can be implemented in a time-delayed fashion so everyone can follow the entire step-by-step process.
Imagine you write software. You've just written a great program. You now want to sell it. You have two choices. You can take advertisements, sell it to retailers, get distributors to carry it, hire salespeople, etc. In other words, go the commercial route. This is expensive and requires a major marketing / sales budget. The other choice is to go the Shareware route. This involves giving away your software on various bulletin boards , on many Web sites, in "shareware" direct mail catalogs. People download the software for free and try it. If they like it, they will send you money. They will do this because you offer them an instruction manual, a new version of the software that doesn't blast "unregistered" on the splash screen when you load the software, or an upgraded version of the software, with more features, or a chit that assuages your guilt at using unpaid-for software that someone worked real hard on.
Self Healing Alternate Route Protection. A system typically employing redundant cables (often fiber) that carry traffic between two separate local exchange carrier offices along divergent paths.
Symmetric High-Bitrate Digital Subscriber Loop, the first multi-rate, symmetric digital subscriber loop to be standardized. SHDSL enables symmetrical data transmission of 192 kBps to 2.3 MBps on a single copper wire pair or 384 kBps to 4.6 MBps on two pairs. Hence, it supports applications previously supported by E1 and T1 ISDN and by HDSL and SDSL. The relevant recommendations on SHDSL are ITU G991.2, ETSI TS 101-524 and ANSI T1E1.4/2001-174 G:SHDSL.
A computer imaging term. A tool for distorting a selected area vertically or horizontally.
The outer jacket (usually metal or plastic) surrounding copper and fiber cables that prevents water damage to the cables inside.
Let's say that you have two sheaths of fiber, each of which contains ten fibers and runs for one mile. That is one route mile (total distance of all fibers), two sheath miles (two sheaths running one mile), and twenty fiber miles (20 fibers running one mile).
The useful life of components when not in use ” such as being stored on a shelf as spare parts or in a warehouse awaiting shipment. Batteries tend to have the shortest shelf life of most telecommunications components. Today, the shelf life is less a problem of shelf decay and more a problem of technological obsolescence.
A shelf registration is a filing by a corporation that awaits approval from the Securities and Exchange Commission with no specific dates of the offering. Essentially the SEC approves the deal with a wide latitude but no particular timeframe. A shelf registration could also give the issuer, the corporation, a wide ability to issue either debt or equity.
Software that is bought, then placed on the shelf, but never used. In the June 17, 2002 issue of Business Week, AMR Research, Inc. argued that only half the corporate software bought in the Spring of 2002 was actually ever installed and used. See also feedware, hookemware, hyperware, meatware, seedware, shovelware, smokeware, slideware and vaporware.
An outer layer of a program that provides the user interface, or the user's way of commanding the computer. Instead of presenting the user with a bland C prompt, i.e. C:> the shell presents a list of programs that the user can choose from, making it easier, allegedly, to figure out which program to run. The problem with shells is that they often take up precious memory. That memory might better be used in actually running a program faster, or more efficiently .
An Internet term. A type of interface on a dial up connection in which you log in to the host computer and use a command shell to get to the Internet. Shell accounts are typically text-based-only interfaces controlled by host servers which normally don't allow for use of graphic Web browsers.
Sheriff is a word that originated from Shire Reeve. During early years of feudal rule in England, each shire had a reeve who was the law for that shire, that is, he was the "shire reeve." When the term was brought to the U.S. it was shortened to "sheriff."
A metallic layer consisting of type, braid, wire or sheath that surrounds insulated conductors in shielded cable. The shield may be the metallic sheath of the cable or the metallic layer inside a nonmetallic sheath. Shields reduce stray electrical fields and provide for safety of personnel. See Shield Effectiveness, Screen, and Microwave Absorber.
The relative ability of a cable shield to screen our undesirable radiation. Frequently confused with the term shield percentage, which it is not.
Two insulated wires in a cable wrapped with metallic braid or foil to prevent the wires acting as antennas and picking up external interference (e.g. a local TV station).
A cabling system comprising wires which are separately insulated, and twisted together in a spiral manner. In addition, each pair is wrapped with metallic foil or braid, designed to insulate (i.e., shield) the pair from electromagnetic interference. See STP for a full explanation. See also SSTP.
The metal- backed mylar, plastic, teflon or PVC that protects a data-communications medium such as coaxial cable from Electromagnetic Interface (EMI) and Radio Frequency Interference (RFI).
The process by which electrical conductors are wrapped with metallic foil or braid to insulate them from interference and thus provide high quality transmission. Many devices can cause interference to cables (i.e. multiple conductors) carrying telecommunications conversations. Such things include high voltage AC power lines, machinery with motors, machines which make rays of some type (X-Ray systems, TV sets etc.). By wrapping conductors around the cable cores, these cables are less likely to be affected by these outside forces and the noise they create on telephone lines. Shielding will also lessen the chance that the information movement along the cable will interfere with signals on other, adjacent cables. The need for shielding stems from this phenomenon : If you send an electrical signal along one pair of cables, those cables will give off a small amount of electrical energy ” called magnetic radiation. That radiation will cause electromagnetic interference with a cable close by. If you "shield" the pair carrying the electrical signal, you will cut down the susceptibility of those cables to interference from other cables. LANs should always be installed with the best quality shielded cable. They will run better with shielded cable. Never skimp on the quality of the cable you're installing for LANs. Most telephones don't require shielded cable unless the cable serving them is passing through some area of high electromagnetic interference.
The movement of data to either the right or the left of an existing position in a data field.
The code control function of converting the characters from upper to lower case, or vice versa.
To shift programs to a lower level of government without providing the means with which to pay for those programs.
This button acts exactly like a Shift button on a typewriter or computer. It gives the key you're touching a second meaning ” either a capital letter or a second set of speed dial buttons , etc.
The control character which defines the shift function.
A call center term. A template from which the program can create schedules during a scheduling run. Each shift definition is a record in a Scenario giving more or less precise instructions on shift length, time of day, breaks, and how extensively such schedules can be used in meeting staffing requirements.
A register in which a clock pulse causes the stored data to move to the right or left one bit position. See Zero Stuffing.
Another term for a Universal Asynchronous Receiver/Transmitter (UART). See also UART.
You're selling something on an auction on the Internet. In order to push the price up you bid against the people who are bidding. This is called "Shill bidding."
A shim is a piece of software. The term is associated with calls to communications protocols such as TCP or IP for communications services. The shim inserts itself into the logical space between a program asking for service and the program, such as a TCP-conforming communications program, able to provide the service. The function of a shim is to intercept calls made by higher level programs, such as applications, to translate them, and to pass them off to some other piece off software -perhaps IPX. The program requesting the service is fooled by the shim into thinking it is receiving the service from the software it addressed. This term courtesy Frank Derfler. Thank you Derf.
MPLS term. When an IP packet (layers 2-7) is presented to the LER, it pushes the shim header between layers 2 and 3. Note that the shim header is neither a part of layer 2 or layer 3; however, it provides a means to relate both layer 2 and layer 3 information. The Shim Header consists of 32 bits in four parts - twenty bits are used for the label, three bits for experimental functions, one bit for stack function, and eight bits for time to live (TTL). It allows for the marriage of ATM (a layer-2 protocol) and IP (a layer-3 protocol).
Any exposed copper wire that may cause a electrical short.
See Marine Telephones.
A term that describes the ability of two protocols to coexist with one neither having any knowledge of the other, nor being affected by it. For example, OSI Layer 2 (Data Link Layer) ATM switching and signaling protocols can coexist with Layer 2 and Layer 3 (Network Layer) MPLS (MultiProtocol Label Switching) protocols.
In the 16th and 17th centuries, everything had to be transported by ship. It was also before commercial fertilizer's invention, so large shipments of manure were common. It was shipped dry, because in dry form it weighed a lot less than wet. But once water hit it, it not only became heavier, but the process of fermentation began again, of which a byproduct is methane gas. As the stuff was stored below decks in bundles you can see what could (and did) happen. Methane began to build up below decks and the first time someone came below at night with a lantern, BOOOOM! Several ships were destroyed in this manner before it was determined just what was happening. After that, the bundles of manure were always stamped with the term "Ship High In Transit." This meant to stow it high enough off the lower decks so that any water that came into the hold would not touch this volatile cargo and start making methane. Thus evolved the term "S.H.I.T," which has come down through the centuries and is in use to this very day. You probably did not know the true history of this word. Neither did I. I always thought it was a golf term. See also Camel Droppings.
A sudden stimulation of the nerve and convulsive contraction of the muscles caused by a discharge of electricity through the body. The severity depends on the amount and duration of the current and whether the path of the current is through a vital organ.
A radio disc jockey who uses profanity, libelous statements against minorities and sundry incitement to violence and lewd behavior. All of this is used to attract a listening audience.
A mark made on your neck by someone standing on your shoulders. This definition contributed by Steve Hersee, founder of Copia International, a great fax server company. Steve does circus work and trains cheer leaders as a hobby.
A shoebox is a housing device with a power supply to support external peripherals. When the user's main computer case is filled to capacity, an external device is needed to handle the overflow. Hence a shoebox.
A circuit impairment that exists when two conductors of the same pair, which normally make up an operating electrical circuit, touch or are connected.
A broadcast station that transmits on frequencies of 6-25 megahertz . These waves are shorter than those sent out by AM stations but longer than those of the Very-High frequency FM radio and television stations .
See Shopping Bot.
Also called a shopping agent. Bot is a shortened form of robot. A shopping bot or agent is a piece of software that prowls the Web on your behalf in search of bargains in products you specify. Want a cheap sweater, a cheap car, a cheap airline ticket, your shopping bot will go out and find it ” theoretically. Of course, it ain't always that easy. Shopping bots are run by companies on the Web, who use them as ways to attract people to their sites so they can sell advertising or get a piece of your shopping bill.
Shopping cart is the electronic equivalent of a shopping cart in a supermarket . You're on a Web site, buying something, let's say computer equipment. You choose a monitor you like. You say "buy it." It drops into
A high-speed common channel in the AT&T ISDN packet controller over which all messages between sending and receiving devices pass.
A near zero resistance connection between any two wires that disrupts transmission where two pairs are involved usually called a "cross." It disrupts transmission and may cause an excessive current flow. In AC electricity, a short circuit is an unintended connection between two supply conductors (i.e.: HOT and Neutral conductors.) A short circuit will usually cause high current flow and will operate the over current protection (fuse or breakers) to interrupt the circuit.
A carrier event that occurs when the activity duration is shorter than the ShortEventMaxTime (84 bits).
Between a few hundred yards and 20 miles. Many people would argue with this definition.
A data set designed for use in communicating data up to distances of 25 miles over a dedicated unloaded copper pair. Many people would argue with this definition.
Short Message Service SMS or S.M.S. A means by which short messages can be sent to and from digital cell phones, pagers and other handheld wireless devices. Alphanumeric messages up to 160 characters can be supported. That's adequate for stock quotes, short e-mail, bank account balances , buying movie tickets on line, updates on traffic conditions, answers to quizzes posed by the teacher and other really short messages. Europeans, who have relied on digital cell phones for years, love to send short text messages by tapping on their telephone dialing pads. Europeans don't use the Internet for sending email as much as Americans do. SMS is defined in IS-41C. Some cell phones announce the arrival of a new message with three short beeps, two long ones, and three short ones ” Morse code for SMS. American telecommunications regulations, which encouraged different mobile operators to choose different, incompatible technologies, are also responsible for the dearth of texting in America. Only in 2003 did the largest American operators agree to pass text messages between their networks ” an agreement still only patchily implemented. In addition, not all handsets sold in America support two-way texting: many older models allow only incoming messages. And texting is not included as standard in most subscription packages, but as an extra for which customers must pay a few dollars per month or rather exorbitant amounts per message. In contrast, email for most Americans is free. See also IS-41 and Wireless Application Protocol (WAP).
Short Reach refers to optical sections of approximately 2 km or fewer in length. The sections may be interoffice or intraoffice in nature. An example application of SR is that of the interconnection of routers, cross-connects, and DWDM equipment within a CO (Central Office) or POP (Point Of Presence) over POS (Packet Over SONET) interfaces. A POS interface launches a single optical signal commonly running at SONET speeds of OC-3 (155 Mbps), OC-12 (622 Mbps), or CO-48 (2.488 Mbps). See also VSR (Very Short Reach).
SMPP. A protocol, developed by Logica Aldiscon, that provides the capability to deliver email and voicemail between wired and wireless networks.
Investors who make bet that a company's stock will decline. They often sell the company's stock short, or they buy put options on the company's stock.
See Short Tones.
First, we invented touchtone, also called DTMF, Dual Tone Multi Frequency tones. You'd punch your number with tones, instead of dialing them. Then someone thought you could control telephone response gadgets, like voice mail, interactive voice response, etc. with touch tones. For these gadgets to work, they had to "hear" the tones you sent. No one really set standards as to the minimum length tone they would hear. But it was generally conceded that they were to be 120 milliseconds . So some manufacturers of telephone equipment started to make phone equipment that, if you pushed a touchtone button, the machine would only sent a touchtone of 120 millisecond duration. That was called a short tone. It wasn't very useful because the manufacturers quickly discovered that many pieces of equipment couldn't respond that quickly. And the manufacturers got complains that their customers couldn't call their voice mail, their bank, etc. As a result, some manufacturers of equipment brought out new hardware (replacing the old) to allow you to send "long tones," which are now defined as touchtones that last for as long as you hold down the button ” just as it is (and has always been) on a normal single line, non-electronic, non-digital telephone. Isn't progress wonderful? See also DTMF for a much longer explanation of tone dialing.
A routing algorithm in which paths to all network destinations are calculated. The shortest path is then determined by a cost assigned to each link.
You're standing at a pay phone. You punch in your credit card numbers to make your long distance call. There's a fellow standing behind you. He's carefully watching what you're doing. He is memorizing the digits you have punched in. When you are through, he will write them down and sell them to someone else, who will use them to make fraudulent long distance phone calls. Our friend is indulging in a new " occupation ." It's called "shoulder surfing."
A term used to refer to the tendency of early CD-ROM disc producers to shovel anything they could to fill up their voluminous CD-ROM discs. They did this so they could tout all the great value they were offering in their CD-ROM discs. See also Hookemware, Hyperware, Meatware, Slideware, Vaporware and Bundle Fodder.
A child who is more talented than yours.
This is the trade name for those annoying little images you sometimes see drifting across your computer screen and which interfere with your viewing the Web page underneath. It belongs to United Virtualities, who say it was named after the middle daughter of the company founder. In April they announced another technology, Ooqa Ooqa (which daughter is that named after?), which changes your browser's toolbar in response to any Web ad you click on. This definition from Wired Magazine.
Signaling Handoff Point, a type of equipment which acts as a gateway between two dissimilar Signaling System 7 networks, allowing information exchange between the two networks.
State Historic Preservation Officer. In compliance with Section 106 of the National Historic Preservation Act, this investigation reports on the "no effect/no impact or impact" of proposed telecommunication sites on Historic Properties/Communities.
A device to destroy paper, plastic...in fact anything confidential that, if it fell into the wrong hands (a competitor, the public, the police, etc.), could harm the company wishing the item destroyed. The shredding business came into public renown with the Enron scandal in the winter of 2001/2002. According to the Wall Street Journal, shredding may date as far back as the age of papyrus. John Wagner, founder and chief executive of Allegheny Paper Shredders Corp., Delmont, Pa., traces its modern practice to the 1920s, when an American inventor got the idea for a document shredder from a hand- cranked Bavarian noodle cutter .
Software that requires no customization. So called because it comes in a package that is plastic shrink-wrapped. Of course, so does non-shrink wrap software, or software that has to be customized for your use. But this is a dictionary that explains what words mean. It doesn't explain the lack of logic behind the naming of those words.
A call center term. A group of Scenario budget assumptions that define the percentage of the time employees are scheduled to work but are not available to handle calls because of absence, breaks, vacation, non-productivity, training, and other activities.
An expert in testing coins is called a shroff.
Short Hold Time.
Secure Hypertext Transfer Protocol. An extension of HTTP for authentication and data encryption between a Web server and a Web browser.
A conductor joining two points in an electrical circuit so as to form a parallel or alternative path through which a portion of which the current may pass. For example, a shunt might be applied to a main circuit to connect a control circuit for purposes of regulating the amount of current passing through the main circuit.
A means by which traffic is switched or diverted from one network to another. For instance, a number of manufacturers are developing devices intended to be positioned logically between central offices (COs) and the connected local loops . Such devices would identify data traffic destined for the Internet or an Intranet, most obviously by means of recognizing the dialed telephone number as being associated with a remote access server supporting IP (Internet Protocol) traffic. At that point, the traffic is routed over a packet network, rather than the circuit-switched Public Switched Telephone Network (PSTN). Thereby, IP traffic's significant contribution to congestion in the PSTN are mitigated. See also Circuit Switching, IP, Packet Switching and PSTN.
An arrangement of apparatus or circuits in which the total current is subdivided. Same as Parallel Circuit.
Also written Si/Ge. Silicon Germanium (not Geranium, which is a flower). Si-GE is a chip technology announced by IBM in the fall of 1998. Cheaper. Faster, etc.
Satellite Industry Association. An operating arm of SBCA (Satellite Broadcasting and Communications Association of America). Formed in 1995, the SIA promotes the role of satellite technologies and applications in the National and Global Information Infrastructure, and acts to inform policy makers , regulators, legislators, the press and the public about the capabilities and benefits of satellite communications. Members include service providers, manufacturers, launch service companies and ground equipment suppliers in the US. www.sia.org.
Securities Industries Association.
A CATV (Community Antenna TeleVision) term. A siamese pair is a connection between a coaxial cable and a twisted pair cable in order that CATV provider can connect to devices such as telephones and PCs which do not have coax interfaces and, thereby, to provide POTS (Plain Old Telephone Service) and Internet access, as well as CATV access. A number of large CATV providers have upgraded their old analog, one-way, coax-based transmission systems in order to operate as CLECs (Competitive Local Exchange Carriers), as well as entertainment TV providers. See also CATV, CLEC, ILEC, and Sidecar.
Service Independent Building Blocks, a term coined by Bellcore and the ITU-T for the Intelligent Network. Creation of SIBBs will in theory make it easier for non-software specialists to create new services by mixing and matching SIBBs. SIBBs are like software objects ” capsules of reusable software that can be combined together to create wondrous and complex new computer telephony services.
Service Initiation Charge. This is a charge to a client by a carrier for the initiation of a new telecom service such as the installation of a new T-1 line or a Frame Relay PVC.
System IDentification number. A five digit number that has been assigned to identify the particular cellular carrier from whom you are obtaining service. This number identifies your "home" system.
A lower or higher frequency signal which is created when one signal is used to modulate another signal.
The band of frequencies to the right or left of a channel's center frequency. See Sideband.
A call center term. The process whereby a supervisor or other qualified party listens in on the calls of an agent by sitting at their side. The supervisor is able to listen to both sides of the conversation, usually via double jacking, which is plugging a headset into the agent's phone and listening in on the line.
A metallic, single pair circuit arranged to derive a phantom circuit. The phantom circuit is derived by center tapping a repeating coil in each of two side circuits.
Any hour that is not the Busy Hour. A telephone company term: An amount of time equal to one hour that is time consistent and adjacent to the CBH (Component Busy Hour). This one hour period must have average weekly usage equal to at least 90% of the CBH during the busy season and 80% of the CBH during the nonbusy season .
A minor lobe of an antenna pattern as distinguished from the main lobe(s) of an antenna pattern.
The frequencies on either side of the main frequency in an RF (Radio Frequency) signal. In the early days these sideband frequencies were not used because they were too " noisy ," unreliable and were not needed. Now, technology has improved and frequencies are in short supply, more and more transmission vendors are making use of their sidebands, and thus substantially broadening the throughput of their existing transmission paths. Sideband technology has made great strides especially in through-the-air microwave transmission.
An add-on module for a CATV (Community Antenna TeleVision) set-top converter box. A sidecar essentially is peripheral equipment for interactive, two-way access to the CATV provider's network. The sidecar allows you to gain access to an interactive program guide, to access the Internet through a built-in cable modem, and to access the PSTN (Public Switched Telephone Network). In order to provide a full range of capabilities, the CATV provider, of course, must have enhanced the cable system to support two-way transmission, packet-switched data access to the Internet, and circuit-switched access to the PSTN. A number of CATV providers have done so in order to position themselves as CLECs (Competitive Local Exchange Carriers), in competition against the ILECs (Incumbent LECs) in voice and data. In order to improve on the quality of transmission and to provide more bandwidth, many also have upgraded their coaxial cable transmission systems to hybrid systems, incorporating fiber optic transmission facilities in the high-capacity trunk segments of their network. See also CATV, CLEC, ILEC and Siamese Pair.
Complete rotation of a celestial object about its axis. The sidereal year of the Earth is approximately 365 days. A sideral day is approximately 24 hours.
A part of the design of a telephone handset which allows you to hear your own voice while speaking. The idea is to let you know that the telephone you're speaking on is working. Too much sidetone becomes an echo and is bad. Too little sidetone makes the channel unerringly quiet and people start to think it's busted.
Security Industry Digital Network.
Standard Image Format. See MPEG.
SONET Interoperability Forum. A voluntary industry group established to define and resolve issues of SONET implementation. SIF was formed by Southwestern Bell in 1991; Bellcore and other RBOCs soon joined. SIF now is open to membership of any interested party, including vendors, service providers and end users. SIF works under the umbrella of ATIS (Alliance for Telecommunications Industry Solutions). www.atis.org/atis/sif/index.html See also ATIS.
Signaling Information Fields. A SS7 term. See Signaling Information Fields.
Special Interest Group. A SIG is an ongoing discussion group held electronically via PCs. A SIG focuses on one area of interest. Members phone in with their PCs, read messages posted, contribute their wisdom, ask questions, etc. SIGs are ways people get up-to- date accurate information on a subject. SIGs are run on most BBS (Bulletin Board Systems). SIGs are to bulletin boards what on-line services call conferences or forums.
Special Interest Group. In this context, a SIG is a voluntary organization which is dedicated to the advancement of a particular technology, standard or technique. Examples include the ATM Forum, CDPD Forum, Frame Relay Forum and SMDS Interest Group.
SMDS Interest Group. A defunct consortium of vendors and consultants who were committed to advancing worldwide SMDS as an open, interoperable solution for high-performance data connectivity. On June 16, 1997, the Board of Trustees announced that the group was disbanded, turning over all responsibilities to regional organizations. The Board declared that its mission had been fulfilled.
Signaling Transport. See Sigtran.
Signature File. A file that automatically is appended to every e-mail message you send. The sig file commonly contains your name, title, company, telephone number, fax number, and return e-mail address. See also vCard.
A military term for signals intelligence, as opposed to humint, which is human intelligence. Sigint is a polite term for reading someone else's mail. Sigint gets information from intercepting and often decrypting voice or electronic communications. In the United States, the Natonal Security Agency (NSA) does sigint and the Central Intelligence Agency (CIA) does humint. There is, of course, a great rivalry between the two agencies as to who can get it right. One former NSA director once scoffed, "The CIA is good at stealing a memo off a prime minister's desk. But they're not much good at anything else." See NSA.
To go through the process of beginning a working session between you, your data terminal or PC and a computer system.
The process of identifying oneself to a machine so as to gain access. In the case of an ACD system this process allows statistics to be kept for this person individually. It also allows for the movement of the person around the system while statistics are accumulated in one logical file.
An electrical wave used to convey information.
An acoustic device (e.g. a bell) or a visual device (e.g. a lamp) which calls attention. To transmit an information signal or alerting signal.
Bellcore defines signal as a state that is applied to operate and control the component groups of a telecommunications circuit to cause it to perform its intended function. Generally speaking, says Bellcore, there are five basic categories of "signals" commonly used in the telecommunications network. Included are supervisory signals, information signals, address signals, control signals, and alerting signals.
See Signal Booster and Beam Bender.
By FCC definition a signal booster is a low power relay or repeater.
Signal computing, as it has come to be, refers to the processing of analog signals for transmission over the worldwide telephone system. According to Analog Devices, the core of the Signal Computing concept is the ability to program an open, multi function chipset with easily upgraded software. The Signal Computing model gives non-traditional audio, video, speech, and communications technology providers opportunities to embrace PC channels. The term, signal computing, picked up steam in mid-1993 when Dialogic announced a new standard called SCSA (Signal Computing System Architecture). In Dialogic's words, SCSA is a comprehensive architecture that describes how both hardware and software building blocks work together. It focuses on "Signal Computing" devices, which refer to any devices that are required to transmit information over the telephone network. Information can be transmitted via data modems, fax, voice or even video. SCSA defines how all these devices work together.
Signal computing systems combine three major elements for call processing. Network interfaces provide for the input and output of signals transmitted and switched in telecommunications networks. Digital signal processors and software algorithms transform the signals through low-level manipulation. Application programs provide computer control of the processed signals to bring value to the end user.
SCSA is the common set of standards that telecommunication system manufacturers and computing system manufacturers can use to create computer telephony systems. No single company today can create the total solution for all customers. SCSA represents the common ground between the two fields so that manufacturers from each area can safely develop products that will work with other manufacturers.
SCSA's coverage extends from low-level bus and hardware interfaces, like the inter- board switching bus that enables boards from different suppliers to work together, to high- level application programming and software interfaces, so that software designed to work with one set of hardware products, will work with different hardware as well. SCSA has been defined with input from leading computer and switch manufacturers, call processing suppliers, and technology developers. In many cases, SCSA has drawn on existing standards, like the T.611 fax standard endorsed by the European Computer Manufacturers Association, and in other cases SCSA has extended standards to make them more useful for call processing suppliers and users.
SCSA is an open hardware and software architecture supported by over 240 companies for developing multi-technology computer telephony systems using standard interfaces. SCSA consists of two independent layers: The SCSA Hardware Model and the SCSA Telephony Application Objects (TAO) Framework. While designed for interoperability, these two layers may be implemented independently of one another. See Signal Computing.
The amplification and/or modification of electrical signals to make them more appropriate for transmission over a certain medium ” cable, microwave, etc.
SCP. Computers that hold databases in which customer- specific information used by the "advanced intelligent network" (AIN) to route calls is stored. The AIN refers to a specific architecture ” typically promulgated and created by a local or long distance phone company ” that provides core capabilities in which customer- specific information held in databases within the network is used to intelligently process calls. An example of an AIN service is an 800 service that routes calls based on where the calls are coming from. The routing information is stored in the SCP, which is typically tied into the Signaling System 7 network. See SCP. For a full explanation of the Advanced Intelligent Network, see AIN.
The equipment which changes the data signal into a form suitable for the transmission medium, or the reverse. The converter can also work with DC/AC current. The signal converter comprises a modulator and/or demodulator.
A test oscillator that can be adjusted to provide a test signal at some desired frequency, voltage, modulation, and waveform.
SGD. In RS-232-C signaling, Signal Ground establishes a common reference level for the voltages of all other signals (such as RXD/TXD), except Frame Ground.
The strength of a signal, generally expressed in either absolute units of voltage or power, or in units relative to the strength of the signal at its source.
Signal processing is a combination of computer telephony call control and media processing. Call control means moving telephone calls around ” answering them, hanging up on them, transferring them, conferencing them, etc. ” all the stuff you do on your office phone every day. Media processing means bringing computer power to bear on the media stream, the actual voice, video or data inside the phone call. You might save it to your hard disk. You might want to have your PC software listen for key words in what you saved, for example, the caller's phone number. You might even want your software to try transcribing the conversation into text you could use in your word processor. See Call Control, Digital Signal Processing, Media Processing and Native Signal Processing.
An SCSA definition. An atomic bundle of signal processing functionality which can be allocated to a single group. It can be capable of supporting the functionality of one or more resources or a simple coder .
An SCSA definition. That part of a Signal Processing Component which is associated with a single Resource.
A SCSA definition. This is a software component that supports a specific hardware package. This is typically an executable program and may control one or more instances of the vendor-specific hardware package. Each SPP may support several different types of signal processing functionality clustered into SPCs.
A signal repeater does nothing more than receive a signal and retransmit it. Repeaters are used where the original transmission is very weak, or the transmission is being sent over long distances.
A display on a cellular radio that lets you know before you call about the relative strength of the cellular transmitter in your immediate area. On most cellular radios, the signal strength indicator has five bars, with five the strongest. It's best to call when you have four or five. Three is marginal. Below three, forget it. Go elsewhere and try again.
SSP. See SSP. For a full explanation of the Advanced Intelligent Network, see AIN.
Often abbreviated as SNR or S/N. A measurement of the relative level of noise on a circuit and, therefore, the quality of a transmission, SNR is the ratio of the usable signal being transmitted to the noise or undesired signal. Human beings are fairly tolerant of noise, and within limits, can distinguish content from the "noise," but computer systems are not. If the level of extraneous noise is high in a data communications environment, data packets have to be re-sent. That not only slows down the data transfer, but also reduces the efficiency with which the circuit and network are used. SNR usually is measured in decibels (dB). See also dB.
The ratio between useful information and idle chatter to be found on an Internet Usenet newsgroup. bulletin board, or chat room. Often used derogatorily, for example: "The signal-to-noise ratio in this newsgroup is pretty low."
The packet switch in the Common Channel Interoffice Signaling (CCIS) system. The CCIS is a packet switched network operating at 4800 bits per second. CCIS replaces both SF (Single Frequency) and MF (Multi-frequency) by converting dialed digits to data messages. See SCP, STP and Signaling System 7. For a full explanation of the Advanced Intelligent Network, see AIN.
Signal being transmitted are information. They can be spoken words such as a telephone conversation, music, or even computer data. The simplest signal we can send is a sine wave. All sound waves are combinations of simpler sine waves at different amplitudes and frequencies to produce complicated wave forms. Similarly, computer data is a series of ones and zeros which electrically look like a square wave. Square waves, like all other types of waves, can be represented by a combination of sine waves with different frequencies and amplitudes. That a complex wave is the sum of simple sine waves was discovered by the French mathematician Jean Baptiste Joseph Fourier and is called Fourier's Theorem.
SIGINT. A federal government term. A category of intelligence information comprising, either individually or in combination, all communications intelligence, electronics intelligence, and foreign instrumentation signals intelligence, however transmitted. Signals intelligence is a polite term for reading someone else's mail. See NSA and SIGINT.
In any telephone system ” inside an office or across the country ” some form of signaling mechanism is required to set up and tear down the calls. When you call from your office desk across the country to someone else's desk, many forms of different signaling are used. There's the signaling between your office desk phone and your office phone system. There's the signaling between your office phone system and your local telephone company central office. And there's the signaling between your local central office and the central office you're trying to reach across the country. All forms of these signaling may be different. Simple examples of signalings are ringing of your phone (someone is calling), dial tone (it's OK to dial), ringing (hopefully someone will answer), etc.
Originally, telephone systems such as POTS (Plain Old Telephone Service) used in-band signaling to carry signals. With in-band signaling, signals such as DTMF tones (touchtones), are carried in the same circuit as the talk path. Newer signaling (i.e. most of it today) is carried as out-of-band signaling, which uses a separate data network. This is much more efficient. For example, voice circuits need not be allocated for calls that do not complete. Also, this approach allows additional quantities of information to be transferred to support advanced applications such as Caller ID, roaming in wireless systems, and 800 number routing. See Signaling System 7.
SCCP. Part of the SS7 protocol that provides communication between signaling nodes by adding circuit and routing information to the signaling message. The ISDN-UP (Integrated Services Digital Network User Part) and TCAP (Transaction Capabilities Application Part) use the SCCP (Signaling Connection Control Part) and the MTP (Message Transfer Part) to transport information. Definition from Bellcore in reference to its concept of the Advanced Intelligent Network.
SG. A software-based device that resolves interface issues between circuit-switched and packet-switched networks. See also MGCP and SCTP.
SIF. In SS7 (Signaling System 7) signaling messages, the SIF is a variable length field which contains all the signaling information. Also included is any routing information in the Routing Label, which the network uses to properly connect the call. Such signaling information might include the Calling Party Number (CPN) subfield, along with the Presentation Indicator (PI). The SIF contains 2-272 octets of data. See also Calling Party Number, Presentation Indicator, and SS7.
SLS. The part of a routing label that identifies the SS7 signaling link on which the message should be sent.
A node in a SS7 signaling network that either originates and receives signaling messages, or transfers signaling messages from one signaling link to another, or both. SPs are located at each switch in a Signaling System 7 network. They interface the switch with the Signal Transfer Points (STPs). See Signal Transfer Points and Signaling System 7.
A binary code uniquely identifying a SS7 signaling point in a signaling network. This code is used, according to its position in the label, either as destination point code or as originating point code.
SPOI. The demarcation point on the SS7 signaling link between a LEC network and a Wireless Services Provider (WSP) network. The point established the technical interface and can designate the test point and operational division of responsibility for the signaling.
SS1. A tone supervision system using a 500 Hertz tone modulated at a 20 Hertz rate to signal call requests between switchboards . International equivalent of Bell's 1000/20 manual ringdown signaling. Now obsolete.
SS2. A two-tone (600/750 Hertz) tone system for dial- pulsing selection information. Never used internationally. Closely akin to early Bell mobile radiotelephone dialing systems. Now obsolete.
SS3. A single-frequency (2280 Hertz) tone system used on one-way circuits only. Not intended for transit connections involving a third nation. A prime method through the late 1970s. Now obsolete.
SS4. A two-tone (2040 and 2400 Hertz) system for international transit and terminal traffic. The first truly global "direct dialing" signaling system. Now obsolete.
SS5. A two-tone (2400 and 2600 Hertz) system combined with multifrequency inter-register signaling for both terminal and transit traffic. Closest international equivalent to North American Bell "DDD trunks using SF supervision." Now obsolete.
SS6. A common digital data path between two switching machines to negotiate and oversee connection control on transmission facility trunks between the machines. International equivalent of Bell CCIS. Typically a 2400 bps data circuit.
SS7. SS7 typically employs a dedicated 64 kilobit data circuit to carry packetized machine language messages about each call connected between and among machines of a network to achieve connection control. International equivalent of Bell DNHR. Permits many ISDN services such as CNID or Random RCF. See below for more specific information:
All phone systems need signaling. According to James Harry Green, author of the Dow Jones-Irwin Handbook of Telecommunications, signals have three basic functions:
SUPERVISING. Monitoring the status of a line or circuit to see if it is busy, idle or requesting service. Supervision is a term derived from the job telephone operators perform in manually monitoring circuits on a switchboard. On switchboards, supervisory signals are shown by a lit lamp indicating a request for service on an incoming line or an on-hook condition of a switchboard cord circuit. In the network (i.e. the automated part of the network), supervisory signals are indicated by the voltage level on signaling leads, or the onhook/off-hook status of signaling tones or bits.
ALERTING. Indicates the arrival of an incoming call. Alerting signals are bells , buzzers, whoofers, tones, strobes and lights.
ADDRESSING. Transmitting routing and destination signals over the network. Addressing signals are in the form of dial pulses, tone pulses or data pulses over loops, trunks and signaling networks.
In the old days, signaling was mostly MF (multi-frequency) and SF (single frequency) and is inband. This means that it goes along and occupies the same circuits as those which carry voice conversations. There are two problems with this. First, about 35% of all toll calls are not completed because the phone doesn't answer or is busy, or there are equipment problems along the way. The circuit time used in signaling is substantial, expensive and wasteful . Second, inband signaling is vulnerable to fraud. So the idea of out-of-band signaling came about. It got the name of Common Channel Interoffice Signaling (CCIS) because it used a communications network totally separate from the switched voice network. In North America, CCIS started out as an AT&T packet switched network operating at 4800 bits per second. Each of the packet switches in this network (they are no longer exclusively AT&T's) are called Signal Transfer Points ” STPs. CCIS has the following advantages over SF/MF signaling:
Fraud is reduced. "Talk-off" is reduced. (Talk-off occurs when your voice contains enough 2600 Hz energy to activate the tone-detecting circuits in the central office.) Signaling is faster allowing circuits and conversations to be set up and torn down (i.e. disconnected) faster. Signals can be sent in both directions simultaneously and during voice conversation if necessary. Network management information is routed over the CCIS network. For example, when trunks fail, switching systems can be told with CCIS data messages to reroute traffic around problem areas.
The older CCIS signaling has been replaced with a newer out-of-band signaling system called ITU Signaling System 7. According to an AT&T technical paper delivered at the International Switching Symposium in Spring, 1987, ITU Signaling System 7 is being required by telecommunications administrations worldwide (i.e. all the local country- owned telephone companies) for their networks. AT&T continued with the introduction of digital switches and transmission equipment with 56 Kbps and 64 Kbps transmission rates, the International Telegraph and Telephone Consultative Committee (CCITT in French) in 1980 approved the ITU 7 recommendations optimized for digital networks. This new protocol uses destination routing, octet oriented fields, variable length messages and a maximum message length allowing for 256 bytes of data. Addition of flow control, connectionless services and Integrated Services Digital Network (ISDN) capabilities were approved by ITU in 1984. A major characteristic of ITU #7 is its layered functional structure. Its transport functions are divided into four levels, three of which constitute the Message Transfer Part (MTP). The fourth consists of a common Signaling Connection Control Part (SCCP).
The SS7 protocol consists of four basic sub-protocols:
Message Transfer Part (MTP), which provides functions for basic routing of signaling messages between signaling points.
Signaling Connection Control Part (SCCP), which provides additional routing and management functions for transfer of messages other than call setup between signaling points.
Integrated Services Digital Network User Part (ISUP), which provides for transfer of call setup signaling information between signaling points.
Transaction Capabilities Application Part (TCAP), which provides for transfer of non- circuit related information between signaling points. Signaling System 7 provides two major capabilities:
Fast call setup, via high-speed circuit-switched connections.
Transaction capabilities which deal with remote data base interactions. What this means in its simplest terms and in one simple application is that Signaling System 7 information can tell the called party who's calling and, more important, tell the called party's computer. A scenario: when you call a direct mail order business, Signaling System 7 will send a signal as to which phone is calling. The agent's CRT screen will pop the caller's name and perhaps the caller's most recent buying information. The agent may answer the phone "Good morning, Mr. Newton. Did you enjoy the three khaki pants we sent you last week?..." Signaling System 7 will be an integral part of ISDN. It will enable us to extend full PBX and Centrex-based services like call forwarding, call waiting, call screening, call transfer, etc. outside the switch to the full international network. In effect, with Signaling System 7, the entire network will acquire the "smarts" of today's smartest electronic digital PBX. See also Captain Crunch, ISUP, MTP, SCCP, Signaling System 7 Software Layers and TCAP.
MTP (Message Transfer Part) Layers 1 through 3: These layers provide complete lower level functionality at the Physical, Data Link and Network Level. They serve as a signaling transfer point, and support multiple congestion priority, message discrimination, distribution and routing.
ISUP (Integrated Services Digital Network User Part): This layer provides the network side protocol for the signaling functions required to support voice, data, text and video services in an Integrated Services Digital Network (ISDN). Specifically , ISUP supports the call control function for the control of analog or digital circuit switched network connections carrying voice or data traffic.
SCCP (Signaling Control Connection Part): This layer supports higher protocol layers (such as TCAP and IS-634) with an array of data transfer services including connection-less and connection orientated services. SCCP supports global title translation (routing based on directory number or application title rather than point codes), and ensures reliable data transfer independent of the underlying hardware.
TCAP (Transaction Capabilities Application Part): This layer provides the signaling function for communication with network databases. TCAP is an SS7 (and ISDN) application protocol which provides noncircuit transaction based information exchange between network entities. For example, TCAP enables transaction based service applications such as enhanced dial-800 which must exchange information between a pair of signaling nodes in an SS7 network to access remote databases, referred to as Service Control Points (SCPs). Important applications which use TCAP include:
800 number routing.
Automated credit card calling which queries the Line Information Database (LIDB) for calling card validation.
Advanced Intelligent Network call processing (referred to as AIN call "triggers"). TUP (Telephony User Part): This layer provides the telephone signaling function for national and international telephone call control. TUP is primarily used outside of the U.S. in Europe, China, parts of Asia and Latin America, and can control all the various types of national and international connections used worldwide.
Higher Level Application Parts: These layers are highly application specific, which each designed to serve a particular application type. Examples include:
GSM MAP (Mobile Application Part): This layer provides inter-system connectivity between wireless systems, and was specifically developed as part of the GSM standard.
IS-41: This layer provides similar functionality to GSM MAP. It provides inter-system connectivity between wireless systems and is typically deployed in North American wireless networks. For example, it is widely used to provide interconnection between the analog AMPS (Advanced Mobile Phone System) cellular systems in the U.S.
IS-634: This layer provides the interface for Mobile Switching Center (MSC) to base station communications for public 800 MHz cellular networks (i.e., for AMPS).
INAP (Intelligent Network Application Part): This layer runs on top of TCAP and provides similar functionality to MAP but for a fixed network. Note that INAP is primarily a European standard, developed by ETSI. INAP is part of the CS1, CS2 IN Capability Set, the European equivalent to the AIN specification. While the AIN and CS specifications are similar and can be deployed using SS7 for functions such as call routing, there are some differences which the standards organizations are working to converge.
1129/1129+/1129A: These protocols provide a direct connection between the SCP and IP and are variants of the Bellcore 1129 and AIN 0.2 standards. In some cases, SS7 may not be required to implement the direct SCP-IP connection; in other instances, SS7 is used. Using SS7 as the underlying protocol allows any SCP to communicate directly with any IP in the SS7 network. When SS7 is used, the 1129 application layer typically runs on top of TCAP. Thanks to Natural MicroSystems for an explanation of SS7 Software Layers. See also their white paper, "SS7 and Intelligent Networking Applications." It's on their web site, www.nmss.com
SS7 standards are defined in the ITU-TS documents as noted below:
Q.700-Q709 Messaging Transfer Part (MTP)
Q.710 PBX Application
Q.711-Q716 Signaling Connection Control Part (SCCP)
Q.721-Q.725 Telephone User Part (TUP)
Q.730 ISDN Supplementary Systems
Q.741 Data User Part (DUP)
Q.761-Q.766 ISDN User Part (ISUP)
Q.771-Q.775 Transaction Capabilities Application Part (TCAP)
Q.791-Q.795 Monitoring, Operations, and Maintenance
Q.780-Q.783 Test Specifications
International equivalent of Bell 2600 Hertz "SF signaling" used in North American DDD trunks. Largely used only in Third World nations.
carrier system signaling. Uses a tone of 3825 Hertz placed between voice channels of a carrier system. Used primarily in Europe.
STP. A signaling point with the function of transferring signaling messages from one signaling link to another and considered exclusively from the viewpoint of the transferrer.
A short text file that is automatically added to the end of your e-mail or Usenet posts. A signature file usually contains your name (or alias) and e- mail address, and some people like to add pithy quotes; whatever your signature file contains, remember to keep it short.
Any hour that influences the sizing of a trunk group.
Signaling Transport. The IETF (Internet Engineering Task Force) "Sigtran" WG (Working Group) is working on a Signaling and Transport protocol to enable over the Internet, or other IP-based network, the same reliability of signaling and control that the PSTN (Public Switched Telephone Network) enjoys. Sigtran is defined in RFC 2719 as "an architecture framework for transport of message-based signaling protocols over IP networks." The work includes definition of encapsulation methods, end-to-end protocol mechanisms, and use of IP's existing capabilities in support of the functional and performance requirements of signaling transport. The ultimate yield of Sigtran is intended to be a protocol stack for the transport of SCN (Switched Circuit Network) signaling over an IP transport protocol. The protocol stack will be implemented in Signaling Gateways (SGs), which serve as the points of interface between the two networks. An SG functions to relay, translate, or terminate SS7 signaling. See also SCTP (Stream Control Transmission Protocol) and www.ietf.org/html. charters /sigtran-charter.html
See Silence Suppression.
A term used in voice compression for transmission whereby silence in the voice conversation is filled with other transmissions ” e.g. data, video, imaging, etc. According to AT&T, the average voice conversation is 62% quiet and 38% not quiet (i.e. actual conversation). You can figure that for yourself: One person is speaking at a time. That's 50% of the circuit silent. The person who's speaking doesn't speak continuously. He pauses, takes a breath , thinks, etc. That's another 12%. Thus 62% in silence. A company like Micom in Simi Valley, CA makes a product called Marathon which uses the 62% silence between syllables, words and sentences to transmit data, fax and video. Micom tells me that the typical talk spurt sequence is 300 milliseconds. And it can use very small time (as short as 300 milliseconds) between talk spurts to stuff data, fax or video into and transmit.
A non-audible signal in a pager. Usually a vibrating motor that causes the pager to "shake" silently to alert you to a new message or an incoming call.
A Bluetooth term. A device that is in discoverable mode but cannot respond due to other baseband activity is said to be a silent device. The device could also be in non-discoverable mode and would also not respond to an inquiry.
Synonymous with Silent Participation.
This term covers all business solutions enabled by tagging, tracking, sensing and other technologies, including RFID, which make everyday objects intelligent and interactive. When combined with continuous and pervasive Internet connectivity, they form a new infrastructure that enables companies to collect data and deliver services without human interaction.
Many Japanese fax machine sport a "silent mode." People in Japan who have fax machines in their houses use it so they are not awaken in the middle of the night by incoming faxes. In silent mode, your fax machine simply answers incoming calls, grabs incoming faxes into memory, but makes no noise whatsoever. In the morning when you wake up, you see a message on the machine that says "Faxes received." You hit a button and the machine starts to print the faxes it received. According to my friend, Emiko Magoshi, the shortfall of the fax machine at her house is that its memory is limited to accepting only 10 pages.
A call center term. The process whereby a supervisor or other qualified person listens in to the calls of an agent from a specially designated room or place away from the agent's work area. The agent may or may not be aware that his call is being monitored. Often the calling user may hear an opening message "This call may be monitored for quality assurance purposes." Typically the supervisor can hear both sides of the conversation but cannot break in on the line and say anything.
A feature that allows a third party, such as an ACD agent supervisor, to join the call. The joining party can hear the entire conversation, but cannot be heard by either originating party. The feature, sometimes called Silent Intrusion or Silent Monitoring, may provide a tone to one or both devices to indicate that they are being monitored.
See CLLI Code.
A dark gray, hard, crystalline solid. Next to oxygen , the second most abundant element in the earth's surface. Transistor chips are made from silicon, and it is the basic material for most integrated circuits and semiconductor devices. Silicon, a neutral element, is found primarily in raw form as sand. See Semiconductor.
The area roughly corresponding to Chelsea, SOHO and NOHO in downtown Manhattan, New York. So called because so much of the web and Internet content is written by companies located in this area.
A fast-acting surge protector which features a narrow voltage clamping range.
In and around New Orleans, there are a growing number of a high- tech companies. They say their nw high-tech area is called Silicon Bayou. See the next few definitions.
The vast flat and marshy lands in and around Cambridge, England, the site of the prestigious university. According to the New York Times, Saturday January 4, 1998, "the area has become home to more than 1,000 high-technology companies that employ at least 30,000 people and produce more than $3 billion a year in revenues ."
Silicon Forest is the area of Portland/Beaverton/Hillsboro, where Intel has a large presence, as are Tektronix, Triquent, Lattice Semiconductors, Maximum Integrated Circuits, .. See also Silicon Bayou, Silicon Mudflats, Silicon Valley, Silicorn Valley and Sillywood.
Austin, Texas because of the concentration of high-tech companies that have located there. See the definitions above and below.
The part of the San Francisco area that is on the Oakland side of the bay and sits between San Francisco and Oakland. That area is home to a bunch of high- tech companies. See also Silicon Bayou, Silicon Forest, Silicon Valley, Silicorn Valley and Sillywood.
Silicon Valley in Santa Clara County, California, south of San Francisco Bay, is known for its microelectronics innovation. It is one of the two places (the other being Dallas, Texas) where the microchip was invented and produced. There are over 3,000 microelectronic hardware and software firms within a radius of about 30 miles. Silicon Valley owes its good fortune to:
The fact that W. Shockley, one of the three inventors of the transistor, being a native of Palo Alto, went there in 1955 after he left Bell Laboratories, to start his own industrial research center;
The proximity of technology universities, especially Stanford University;
A very active financial market in California and the enterprising attitude of capitalists willing to enter into "joint ventures ," often very profitable;
The West Coast orientation to Japan. The above information courtesy of Electronics, Computers and Telephone Switching by Robert J. Chapuis and Amos E Joel, Jr. See also Silicon Bayou, Silicon Forest, Silicon Mudflats, Silicorn Valley and Sillywood.
The Ottawa area in Canada is called Silicon Valley North by the local high-tech press. Local high-tech companies include Nortel Networks, Newbridge Networks, ObjectTime, Corel, Mitel, JDS Uniphase (formerly JDS Fitel) and Cognos. Others with with presence here include Cisco, Compaq and Siemens.
A part of Silicon Valley in Northern California around San Jose which headquarters America's flourishing pornographic industry, which makes the movies (for DVD, VCR, theater and satellite distribution) and web sites. Over 80% of the "actresses" who perform in pornographic movies have had their breasts enlarged. Thus the name, Silicone Valley.
Putting all the various components of a system into microprocessor chips. For example, in the fiber business many of the pieces are individual electronic components. Getting many of them converted of them into individual microprocessors is called "siliconize." Doing this saves time and money and improves the final reliability of the entire system.
A region in the state of Iowa that is fostering high-tech development. See also Silicon Bayou, Silicon Forest, Silicon Mudflats, Silicon Valley and Sillywood.
See CLLI Code.
A silly term for Silicon Valley in California.
The convergence of Silicon Valley and Hollywood.
A Standard being formulated for Interoperating LAN Security.
A panacea. THE solution. The one action that will solve all your problems.
A set of attitudes and prejudices that prevent older employees from rising to positions of power or responsibility in a workplace.
Once upon a time, phones came with cords that matched the color of the phone. This proved expensive and confusing to workers, who were color blind, who had to match the cord with the phone. So a manufacturer (we think it was AT&T) decided that the time was ripe for all phones to have a cord that matched every decor and every phone. In actuality, the color they settled upon ” silver satin ” matches no decor man or woman has ever created and certainly no phone has ever been produced in the silver satin color. However, the world is now stuck with every phone coming with one standard, ugly line cord, called silver satin. See also Touchtone.
Subscriber Identity Module. A 'smart' card installed or inserted into a mobile telephone containing all subscriber-related data. This facilitates a telephone call from any valid mobile telephone since the subscriber data is used to complete the call rather than the telephone internal serial number. See GSM and SIM Card for a better description.
Single Interface Module (SIM). An NEC term. - The minimum equipment configuration for the NEAX2400 IMS is the Single Interface Module. The SIM, says NEC, is a fully featured, totally non-blocking digital switch capable of supporting all NEAX2400 IMS feature package application programs. Typical stations installed range from only a few to 300 lines.
Subscriber Identity Module, also called Smart Cards. Every mobile phone that conforms to the GSM (global system for mobile communications) and including many PCS (personal communications services) handsets has something called a SIM card. GSM phones won't work without these cards. Each SIM card contains a microchip that houses a microprocessor with eight kilobytes of memory. The card stores a mathematical algorithm that encrypts voice and data transmissions and makes it nearly impossible to listen in on calls. The SIM card also identifies the caller to the mobile network as being a legitimate caller. PCS and GSM cards come in two basic varieties. Some handsets work with slot-in SIM cards that are the size of conventional credit cards. Others come with smaller cards already built into the handset. GSM is the standard mobile service for Europe and Australia and most countries outside the U.S. Some PCS operators in the U.S. have adopted the GSM standard. See GSM and SIM Toolkit.
Software that allows cellular operators to offer enhanced value-added services on the back of their short message services. These services can include e-mail, GPS (positioning services) home zone tariffs, and information services such as stock prices and news updates. See SIM Card.
Single Instruction Multiple Data is a type of parallel processing computer, which includes dozens of processors. Each processor runs the same instructions but on different data and one chip provides central coordination. See also MIMD and MMX.
Single In-line Memory Module. Used on Macs and PCs. A form of circuit board that holds a number of silicon chips. The connectors (i.e., leads, or pins) are attached to a stiff contact strip that permits a SIMM to be inserted into a slot like an expansion adapter. On PCs, SIMM-style RAM chips have virtually replaced the dual in-line package (DIP) chips, identifiable by two rows of protruding legs, that were popular in the 1980s. The most common SIMM is the 30-pin, 9-bit wide "1 by 9", which is the standard memory upgrade for PCs. See also DIP, PGA, SIMM Socket, and SIP.
The connector inside the Macintosh that holds the SIMM and connects it to the rest of the computer electronically.
SIP for Instant Messaging and Presence Leveraging Extensions (SIMPLE) is a developing enhancement to the SIP (Session Initiation Protocol) protocol. Developed by the SIMPLE working group of the IETF, SIMPLE adds instant messaging and presence. Presence allows you to determine if someone on your buddy list is on-line and available to communicate via instant messaging. See also SIP.
What the SEC said that financial documents should be written in. Simple English is what normal people are meant to be able to read. This means that lawyers , who write most of these documents, are meant to speak. Good luck, SEC.
SGCP is a protocol and an architecture that Bellcore has created to address the concept of a network that would combine voice and data on a single packet switched Internet Protocol (IP) network. SGCP largely operates at low level ” level 2 in the OSI. So it will probably be combined with higher level concepts such as IPDC (IP Device Control) and MGCP (Media Gateway Control Protocol). According to Bellcore, the philosophy behind the Simple Gateway Control Protocol (SGCP) is that the network is dumb, the "endpoint" is simple, and services are provided by intelligent Call Agents, not in the trunking gateway (TGW) or in the residential gateway (RGW). SGCP is simple to use and easy to program, according to Bellcore, but is powerful enough to support basic telephony services and enhanced telephony services like call waiting, call transfer, and conferencing. The protocol is also flexible enough to support future IP telephony services. The SGCP, according to Bellcore, is a simple UDP-based protocol, instead of TCP-based, that allows support for managing endpoints and the connections between the endpoints. The SGCP is scalable, has support for failovers, and processes information in real-time. There is a low CPU requirement and low memory requirement for the endpoint because the SGCP is handling a small set of simple transactions at a time. This means that the endpoint can then be mass-produced cheaply. And there is no need for expensive and resource-hungry parsers. The system is text-based, has an extensible protocol, and the connection descriptions are based on SDP. When new services are introduced by the call agent, there is no need to change or update the endpoint. SGCP controls the endpoint by hooking transactions, relying on DTMF input, and by playing tones. For full details see www.bellcore.com/SGCP/SGCPWhitePaper.rtf
SMTP. The TCP/IP protocol governing electronic mail transmissions and receptions. An application-level protocol which runs over TCP/IP, supporting text-oriented e-mail between devices supporting Message Handling Service (MHS). Multipurpose Internet Mail Extension (MIME) is a SMTP extension supporting compound mail, which is integrated mail, including perhaps e-mail, image, voice and video mail.
Simple MAPI is a subset of MAPI that lets developers easily create "mail-aware" applications capable of exchanging messages and data files with other network clients .
SMNP. The protocol governing network management and monitoring of network devices and their functions. SNMP came out of the TCP/IP environment.
A Versit term. A syntax for encoding the vCard in a clear-text encoding. Simplegrams are nominally, based on the ASCII, 7-bit character set.
Operating a channel in one direction only with no ability to operate in the other direction. For example one side of a telephone conversation is all that could be carried by a simplex line. Obviously a simplex line is not useful for a phone conversation. See Full Duplex.
A transmission path which is capable of transmitting in only one direction. The CCITT definition differs from this more common definition. CCITT simplex is a path which can operate in either direction, but only one direction at a time. This is commonly in North America called half-duplex.
In T-1, refers to the powering of the digital signal pairs that are simplex in nature (Tip or Ring) and that may have voltage applied to maintain the required 60 mA dc current to control repeater signal regeneration, loopbacks, keep alive signals and alarms.
The White Sands Missile Range used to maintain a giant collection of free and low-cost software of all kinds, which was "mirrored" to numerous other ftp sites on the Internet. In the fall of 1993, the Air Force decided it had better things to do than maintain a free software library and shut it down.
To broadcast simultaneously on two different channels (paths).
SPOOL. Temporarily storing programs, data or output on magnetic tape or in RAM for later output or execution. Many PCs use a small software spooling program which accepts material to be printed very quickly, stores it in a portion of RAM, then feeds that material to the printer at a speed the printer can handle. See Spooling.
A program in which a mathematical model represents an external system or process. For example, an engineer can simulate the forces that act on a building during an earthquake to find out how much damage is likely to be incurred.
A technique, often involving a computer, to guess the outcome of various events in the future. Where multitudes of complex events interact, simulation may well be the only way to deal with a given problem. Simulation is often used in traffic engineering instead of or in addition to the proven formula. Many people believe that simulation should NEVER be used when standard, proven formulas (such as Poisson, Erlang B and Erlang C) are appropriate. The difficulty with simulation is actually finding out what rules to use and then programming them correctly. Once this is done, it takes time, even on a fast computer, to run thousands of simulations to get a stable statistical estimate; a single run of simulation, like a single roll of the dice, is worse than useless. Simulators were built into hardware to predict the overall behavior of AT&T's No. 5 Crossbar switch when it was developed in the late 1940s; 1ESS behavior was simulated with software in the 1960s. These were major efforts involving many people and several years, but they dealt with problems far beyond the capabilities of standard traffic equations.
In ancient Rome, eating the flesh of a woodpecker was considered a sin.
A tax imposed by sincere politicians on anything that might remotely be fun. In the 1970s, the Rhode Island legislature proposed the enactment of a $2.00 tax for every act of sexual intercourse. Concerns about collecting said tax finally caused the legislature, in its infinite wisdom, to set aside the idea.
In ancient Rome, when a sculptor made a mistake while working on a statue ” chipped the nose, for instance ” he would artistically hide it with wax. The practice was so widespread that whenever someone ordered a statue, he would specify in the contract that it would be "sine cera"; that is "without wax." Hence the origin of the word "sincere."
In an AC (Alternating Current) electrical system, the polarity (+/-) is constantly reversing, and at precise intervals of time. For example, a 120-volt, 60-Hz electrical generator has a peak positive voltage (i.e., amplitude) of 169.7 volts (+169.7 volts) and a trough negative voltage of 169.7 volts (-169.7 volts ). The voltage value gradually rises to the peak positive voltage, and then gradually falls to the trough (i.e., peak negative voltage). This process takes place at a frequency of 60 times per second (60 Hz), which directly corresponds to the rotation of the electromagnet in the electrical generator which comprises the power source. Plotting the gradual rise and fall of the voltage level over time yields a curved waveform. The wave form is known as a "sine wave" because its shape is derived from plotting the sine of the angles of rotation from 0-360 degrees. The "phase" of the AC signal describes the relationship of the +/- signal to the zero-voltage crossing point, as the signal alternately increases to the peak and decreases to the trough.
Now to tackle the issue of 120 volts versus 169.7 volts. In consideration of resistance in a circuit, electrical engineering principles define the current flow in a circuit as the "root mean square" (RMS) voltage, which is equal to the peak value (169.7 volts) of the sine wave divided by the square root of 2, which is approximately 1.414. Note that 169.7 / 1.414 = 120. See also Analog, Frequency, Hertz, and Wavelength.
Military radios operating in the 30 to 80 MHz range. They were used during the second Iraq War in 2003.
An undesirable whistle or howl on a transmission circuit. Singing is usually caused by feedback, excessive gain, or unbalance of hybrid coils, or by some combination. Singing is the same effect observed when you increase the volume on a public address system until the system squeals or "sings."
The loss at which a circuit oscillates or sings at the extreme low and high ends of the voice band.
A message which is to be transmitted to only one specific terminal, as opposed to a broadcast or group message.
SAC. An FDDI (or CDDI) concentrator that connects to the network by being cascaded from an M (master) port of another FDDI(or CDDI) concentrator.
SAC. A concentrator that offers one S port for connection to one ring of the FDDI network and multiple M ports for attachment of devices such as workstations. A SAC provides less reliability than does a Dual Attachment Concentrator (DAC), although at lower cost, as it connects to only one, rather than, to both fiber rings of the FDDI dual counter-rotating ring architecture. See also Single Attachment Station, Dual Attachment Concentrator, Dual Attachment Station and FDDI.
SAS. A device such as a workstation which connects directly to only one of the FDDI dual counter-rotating rings, rather than attaching to both as does a Dual Attachment Station or gaining ring access through a Single or Dual Attachment Concentrator (DAC). See also Single Attachment Concentrator, Dual Attachment Concentrator, Dual Attachment Station and FDDI.