S

S Band The band of frequencies designated by the IEEE between 2 GHz and 4 GHz (15 cm to 7.5 cm). For a table, see IEEE Radar Band Designation.

S/MIME (Secure Multipurpose Internet Mail Extensions) - MIME is the standard format for attaching nontext files, such as graphics (JPG), spreadsheets (XLS), and formatted documents (DOC) to text-based e-mail messages. S/MIME enhances the MIME standard by encrypting or adding digital signatures to MIME-formatted messages. Digital signatures ensure the recipient that the message is from who it says and that it is private, thus preventing forgeries.

SAA (Supplemental Alert Adapter) - An AT&T term that is specific to the Merlin telephone system. It is the equivalent to a loud ringer.

SABM (Set Asynchronous Balanced Mode) - It is the command defined by the last three bits in the control byte of an unnumbered or “control” type frame in the X.25 protocol being 100. It is a code that an X.25 device sends when it has come into service and is ready to receive packets. It is also referred to as set or reset. This command resets all timers to zero and clears all buffers on all of the devices communicating on an X.25 link.

SABME - (Set Asynchronous Balanced Mode Extended) It is the extended version SABM command. It is defined by the last three bits in the control byte of an unnumbered or control-type frame in the X.25 protocol being “100.” It is a code that a device sends when it has come into service and is ready to receive frames. It is also referred to as set or reset. This command resets all timers to zero and clears all buffers on all of the devices communicating on an X.25 link.

SAC (Single Attached Concentrator) - A FDDI or CDDI concentrator that connects to the network by being cascaded from the master port of another FDDI or CDDI concentrator.

Safety Belt - Used by communications/power/construction personnel to harness themselves to telephone/power poles or tower structures. Also called a body belt and climbing belt.

Sag - If an outside plant engineer refers to sag, it is the amount that an aerial span dips down between telephone poles. Different cable needs to have a different sag, depending on the climate, the weight of the cable, the type of poles being used, etc.

SAP (Service Advertising Protocol) - A program within the Novell NetWare protocol stack that allows nodes on a network to notify devices on that network what services they are designed to deliver. Devices perform their advertising through SAP packets. The SAP packets communicate with files that reside in servers and routers that track which devices in a network provide required services. The routers and servers return SAP packets with requested information.

SARM (Set Asynchronous Response Mode) - An old (1970s) X.25 LAP-vintage command defined by the last three bits in the control byte of an unnumbered or control-type frame in the X.25 protocol. A device sends this command to notify that it is now ready to receive frames.

Satellite - A self-sustained electronic device/platform that orbits the earth at an altitude of about 22,000 miles. Communications satellites transmit and receive signals in the microwave range and are used for broadcast TV, telecommunications, global positioning, and many other applications.

Satellite Antenna - A reference to a parabolic dish that has an LNB (Low-Noise Block Converter) attached to the end of a protruding arm in front of the dish. The actual antenna element is very small and is inside the LNB. For a photo, see LNB Converter.

Satellite Link - A communications path that includes a satellite.

Satellite Receiver - The electronics that the output from a satellite antenna’s LNB converter feeds to. The satellite receiver demodulates the communications information into audio, video, and data. It is the equivalent of a tuner in a TV set or a radio. The satellite dish receives and sends a band of RF frequencies to the satellite receiver, which, in turn, “tunes” to a desired station.

SBC Communications - One of the RBOCs, formerly (but more commonly) known as Southwestern Bell.

SC Connector - A square-shaped snap-on fiber-optic plastic connector. SC connectors come in single or dual. For a photo of a single SC connector, see Fiber-Optic Connector.

Scattering - Attenuation of light in a fiber optic because of the light changing direction in the fiber.

SCC (Specialized Common Carrier) - An old term for an IXC (interexchange carrier) other than AT&T.

Schematic - A diagram of an electronic circuit. Schematics can be drawn at many different levels from block diagrams to the discrete component level.

Scotchlok - A family of splicing connectors that are manufactured by 3M. Scotchloks are used in splicing copper twisted pairs in outside and inside plant applications.

SCR (Silicon Controlled Rectifier) - An electronic component that works like a transistor, but much better in power switching applications. An SCR has three leads, one for the anode, gate, and cathode. When a negative bias pulse is applied to the gate, the SCR acts like a switch, turns on and stays on, even though the pulse is gone.

SCSI (Small Computer System Interface) - Pronounced as “scuzzy.” A parallel interface standard for linking internal computer components (such as hard drives) and peripheral devices (such as printers). The good thing about SCSI interfaces is that they are faster than others (such as IDE/ATA). The drawbacks are the higher cost and that many of the SCSI formats that are on the market are not compatible with each other. If you upgrade your PC, you might end up replacing the SCSI interface in your printer as well. Some examples of the SCSI formats and their transfer speeds are: Fast SCSI, 8-bit bus 10 Mbps; Fast Wide SCSI, 16-bit bus 20 Mbps; Ultra Wide SCSI, 16-bit bus 40 Mbps; and Wide Ultra2 SCSI, 16-bit bus 80 Mbps. See also IDE.

Scuzzy - See SCSI.

SDH (Synchronous Digital Hierarchy) - A European family of digital carrier rates. SDH defines a set of rate and format standards that are transmitted using optical signals over fiber. SDH is the term used by the ITU to refer to SONET OC rates referred to in the United States. Its basic building block is a rate of 155.52 Mbps, designated at STM-1 (OC-3). See also SONET and STM-1.

SDI (Serial Data Interface) - A connection designed for transmission of data over a media one bit at a time. The other type of transmission is parallel, which sends multiple bits at a time, over multiple wires. Many printers run in a parallel manner, modems work in a serial manner. For a diagram, see Serial Interface.

SDRAM (Synchronous Dynamic Random-Access Memory) - SDRAM is a newer type of RAM used in personal computers. It is capable of running at speeds greater than 100 MHz, and it synchronizes itself with the CPU clock. SDRAM was made obsolete by RDRAM (Rambus D RAM), which can run at speeds of 600 MHz.

SDLC (Synchronous Data-Link Control) - A revised revision of the IBM Bisync protocol that was submitted by its creator (IBM) to the ISO and ANSI in hopes that it would become a standard. Instead, it was evolved by the ISO into HDLC (High-level Data-Link Control) and evolved by the ANSI into ADCCP (Advanced Data Communication Control Procedure). The CCITT reviewed and modified HDLC and called it LAP (Link-Access Procedure), which became the basis for the frame or network layer of the X.25 standard in 1976. The LAP protocol was further modified by the CCITT to become LAPB (Link-Access Procedure Balanced mode) in 1978.

SDSL (Symmetrical Digital Subscriber Line) - A physical-layer telecommunications protocol that delivers high-speed data networking over a single pair of copper phone lines. SDSL is symmetrical, which means that upstream and downstream data-transfer rates are the same. Speeds range from 160 Kbps to 1.544 Mbps. The base transmission distance is 24,000 feet (about 4.5 miles), and it can be extended to greater than 30,000 feet with repeaters. SDSL can be extended to any distance over fiber optic. SDSL is ideal for business applications that require identical downstream and upstream speeds, such as video conferencing or collaborative computing, as well as similar applications that are appropriate for ADSL technology. SDSL uses the same kind of line-modulation technique used in ISDN, known as 2B1Q.

Second Dial Tone - The dial tone that you get after dialing 9 on a PBX system. When you first pick up the handset, you hear a dial tone, which is the PBX internal dial tone, then you dial 9 to get an outside dial tone.

Secondary Ring - The redundant and nontraffic carrying of the two rings making up an FDDI or CDDI ring. The secondary ring is usually reserved for use in the event of a failure of the primary ring, which is active and carries traffic.

Secondary Winding - A reference to the output of an electronic transformer. Transformers have at least one primary and at least one secondary winding. Transformers are made to work with AC voltages. If you connect a transformer to a DC voltage with no filtering electronics, the transformer will overheat and be destroyed. Transformers are used to “step-up” or “step-down” AC voltage levels. Transformers are rated with a ratio of the primary to secondary winding. A common transformer is a 10:1. This means that for every 10 windings of wire on the primary side of the transformer, only one winding is on the secondary side. Transformers have the same ratio to voltage as they do windings, so if a transformer with a 10:1 ratio that has 120 volts is applied to the primary winding, then 12 volts will be the output on the secondary winding.

Seed Router - A master router within an AppleTalk network that has the network number or cable range entered into its port descriptor. The seed router automatically responds to configuration queries from nonseed routers on its connected AppleTalk network, allowing those routers to confirm or modify their configurations accordingly. All AppleTalk networks need to have at least one seed router.

Segment - 1. A physical link in a network between two devices. 2. In dataencapsulation terminology, the name of a PDU (Packet Data Unit) when it reaches the transport layer in the OSI (Open Systems Interconnect). After becoming a data segment, the PDU becomes a packet at the network layer, and then a frame at the data-link layer.

Selective Ringing Module (SRM) - A device that is attached to each individual network interface for customers that are sharing a party line. The SRM contains electronics that can be configured to recognize different ringing formats using DIP switches. Some different ringing formats that an SRM would differentiate are ring voltage on the ring side, ring voltage on the tip side, ring voltage on the ring side with the tip side grounded, and ring on the tip side with the ring side grounded. See also Party Line.

Selectivity - The measure in dB of a radio receiver or tuner to select or pass a wanted signal carrier and reject all others. The higher the selectivity in dB, the better the receiver/transmitter/tuner. Selectivity is sometimes called the Q (quality) of a tuner, but the Q rating is usually used in reference to specific fixed-frequency filters.

Self Diagnostics - A feature of many telecommunications testing and transmitting equipment. PBX switches, microwave radio equipment, SONET equipment, and central-office switches are equipped with troubleshooting aids that indicate where trouble is. They are not always accurate, but they are of great assistance in the diagnosis of faulty equipment or transmission paths.

Self Test - The ability of telecommunications test, transmission equipment, or switching equipment to run a test on its hardware components and software. Most telecommunications equipment, as well as personal computer equipment, run a self test when they are first turned on. If there is a problem, then an error of some kind is displayed, which can be cross referenced in a user’s or administrator’s manual.

Semiconductor - Germanium, silicon, and carbon are all semiconductors. They are not great conductors (like copper wire) and they are not insulators (like plastic or rubber). They have special properties that allow a controlled amount of current to flow through them, given a certain amount of voltage, under certain conditions. Transistors, diodes, and other “active” components (devices that require power to do their job) are made from silicon or germanium. Passive devices (such as resistors) are made from carbon.

Sensitivity - A reference to the ability of a radio receiver or tuner to receive a tiny electronic signal from an antenna and amplify it. A sensitivity rating is given in microvolts (μV). If a sensitivity rating is better, the sensitivity for the same given output is lower.

SEPT (Signaling End-Point Translator) - The part of the SS7 (Signaling System 7) network that receives coded signals from another central office and translates those codes into a number plan or set of codes used in the central-office exchange. For more information, see Translations.

Sequenced Packet Exchange (SPX) - A part of the Novell NetWare protocol stack. SPX is used for very specific applications. SPX ensures complete delivery of messages. Applications that use SPX usually include interserver or other device communications, such as printing reports done by servers. An application that would use SPX is for the remote control/administration (RCONSOLE) of servers.

Serial Bus - A bus that transmits one bit at a time. Serial busses are usually one pair of wires: one used for transmit/receive and the other is ground (or common, for a balanced line). A modem line to your computer can be thought of as a kind of serial bus. See Parallel Bus.

Serial Data Interface - A connection designed for transmission of data over a media one bit at a time. The other type of transmission is parallel, which sends multiple bits at a time, over multiple wires. Many printers run in a parallel manner; modems work in a serial manner. For a diagram, see Serial Interface.

Serial Data Transmission - The transmission of data over a media one bit at a time. The other type of transmission is parallel, which sends multiple bits at a time, over multiple wires. Many printers run in a parallel manner, modems work in a serial manner. For a diagram, see Serial Interface.

Serial Interface - The transmission of data over a media, one bit at a time. The other type of transmission is parallel, which sends multiple bits at a time, over multiple wires. Many printers run in a parallel manner; modems work in a serial manner.

Serial Line Internet Protocol (SLIP) - A protocol that enables IP datagrams to be transmitted over dial-up telephone lines. The successor to SLIP is PPP, which provides error detection and automatic configuration.

Serial Port - A computer interface that is used to connect such devices as mice or modems. Serial port interfaces are commonly RS-232 (for modems), USB, or DIN (for keyboards).

Series Circuit - A circuit that has only one path for current through multiple loads. The other type of circuit is a parallel circuit, which has more than one path for current through multiple loads, or devices. For a diagram of a parallel and series circuit, see Parallel Circuit.

Server - A computer that is dedicated to providing services to other computers. File servers store common data for other computers to access via a LAN (Local-Area Network), and there are application servicers, which other computers access to run large or complicated tasks. The whole idea behind a LAN, or any other network, is to share information and/or processing power.

Service Access Code (SAC) - Service access codes are three-digit numbers that are used like an area code, but they are not an area code. These codes are used for special services, such as 800/888 or 900 numbers. Five SACs are in use at the time of this writing: 600, 700, 800, 888, and 900.

Service Advertising Protocol (SAP) - A program within the Novell NetWare protocol stack that allows nodes on a network to notify devices on that network what services they are designed to deliver. Devices perform their advertising through SAP packets. The SAP packets communicate with files that reside in servers and routers that track which devices in a network provide required services. The routers and servers return SAP packets with requested information.

Service Affecting - A reference to a problem that is critical and is interfering with the operation or ability of a network to meet its transmission objectives.

Service Area - The geographic area of a telecommunications service provider. The local service area for USWest is Washington, Oregon, Idaho, Montana, Wyoming, Utah, Arizona, New Mexico, Colorado, North Dakota, South Dakota, Nebraska, Iowa, and Minnesota.

Service Code - A three-digit code or shortened phone number that has a specific purpose, such as 911.

Service Entrance - Also called a building entrance. The place where communications cables enter a building.

Service Profile Identifier (SPID) - An ISDN (Integrated Services Digital Network) telephone number. The number that some telephone companies use to define the services to which an ISDN device subscribes. ISDN devices use SPID numbers when accessing the telephone company’s switch to identify the device it would like to be connected to. In the United States, SPID numbers can look like ordinary public-service telephone numbers with an extension, such as 972-555-1212 4455. There is one SPID for each B Channel. See also ISDN.

Session - A related set of communications transactions between two or more network devices.

Session Layer - A layer in a communications protocol model. In general, the session layer does the job of establishing and maintaining connection to the communications process of the lower layers. It also controls the direction of the data transfer. The latest model or guideline for communications protocols is the OSI (open systems interconnect). It is the best model so far because all of the layers or functions work independently of each other. For a diagram of the OSI and older proprietary communications models, see Open Systems Interconnection.

Set Asynchronous Balanced Mode (SABM) - It is the command defined by the last three bits in the control byte of an unnumbered or “control” type frame in the X.25 protocol being 100. It is a code that an X.25 device sends when it has come into service and is ready to receive packets. It is also referred to as set or reset. This command resets all timers to zero and clears all buffers on all of the devices communicating on an X.25 link.

Set Asynchronous Balanced Mode Extended (SABME) - It is the extended version SABM command. It is defined by the last three bits in the control byte of an unnumbered or control-type frame in the X.25 protocol being “100.” It is a code that a device sends when it has come into service and is ready to receive frames. It is also referred to as set or reset. This command resets all timers to zero and clears all buffers on all of the devices communicating on an X.25 link.

Set Asynchronous Response Mode (SARM) - An old (1970s) X.25 LAP-vintage command defined by the last three bits in the control byte of an unnumbered or control-type frame in the X.25 protocol. A device sends this command to notify that it is now ready to receive frames.

SF - 1. Single frequency, a method of in-band signaling in switched telephone networks. A single 2600-Hz frequency tone is used for signaling. 2. Superframe. A common framing type used on T1 circuits. SF consists of 12 frames of 192 bits each, with the 193rd bit providing clocking. SF is superseded by ESF, but is still widely used. SF is also called D4 framing. See also ESF.

SFC (Switch Fabric Controller) - An interface between the CPU/core and multiple networks of telecommunications switches.

SGRAM (Synchronous Graphics RAM) - A type of dynamic randomaccess memory used as a buffer/temporary storage in computers that enhances the performance of the graphics accelerator and video adapters.

SHARP (Self-Healing Alternate Route Protection) - A service offered from Local Telephone Companies over SONET networks. Sharp service is made possible by the SONET ring technology, which incorporates its network on a ring of fiber-optic cable. If the fiber is cut, all traffic is rerouted the other way around the ring. If you are talking on a telephone over a SONET sharp-based service and a fiber is cut, you might hear a very faint “click” sound. Other than that, you would never know there was a problem.

Shift Register - An electronic circuit used to temporarily store memory in a serial format. Shift registers are commonly used in the serial-to-parallel conversion for data transmission. Bits are clocked into the register one at a time, then clocked out to their destination when they are needed. Each memory segment of a register is typically an RS flip-flop. For a functional diagram, see Register.

Shiner - A common defect found in twisted-pair copper plant, where the plastic insulation on the copper conductors in terminals literally turns to dust and exposes the sheen of the copper conductor to other copper conductors and moisture.

Short Circuit - A circuit fault. A short is a “short circuit,” or an easier path to ground caused by a bad component, water, or other means for electricity to get to where it is not wanted. Many confuse an open with a short. An open is literally a “disconnection” in a circuit. For a diagram of open- and short-circuit faults, see Open Circuit.

Short-Haul Modem - Also called a “limited-distance modem” or “line driver.” Short-haul modems are commonly used to extend the distance of a printer or other DTE (Data-Termination Equipment) device from its host. One example is to extend the printer dedicated to printing callaccounting records from a PBX to an accountant’s office. For a network diagram and photo of a limited-distance modem, see Limited-Distance Modem.

Short-Tone DTMF - A reference to a telephone or other dialing equipment that sends a short pulse of touch-tone DTMF (100 to 300 ms), regardless of how long you hold the button down. Some telephony equipment cannot “hear” a tone that is that short, so equipment manufacturers have implemented adjustable short-tone lengths, and options to remove the short tone altogether.

Shortest-Path-First Algorithm (SPF) - SPF is also referred to as a link-state or Dijkstra’s Algorithm. A class of router-operating software that enables routers to build their own complex address routing tables that detail every router and node within their network. The routing table-building process is accomplished through information multicasts. The routing-table multicasts are referred to as LSPs (Link-State Packets) and they consume payload bandwidth to transmit this information. The process of sending and receiving LSPs is called the discovery process. Multicasts are only sent when there is a change in the network, such as a circuit connection going down, or a new router or connection being added. Link-state algorithms use tremendous amounts of router system memory (20 MB to 30 MB in a 30-node network), and consume significant processor resources within a router’s circuitry. During the startup of a link-start network, the discovery process can take hours. The great advantage to this complex operating method is that routing loops are not created. See also Distance Vector Routing Algorithm and Hybrid Routing Algorithm.

SI - The ASCII control-code abbreviation for shift in. The binary code is 1111000 and the hex is F0.

Sideband - A sideband is a harmonic radio frequency that is a result of modulation on an AM carrier, and is a transmission characteristic of an FM carrier. In AM radio transmissions, one sideband above the carrier frequency and one sideband below the carrier frequency are created. In FM, the modulation of the carrier itself is an infinite number of sidebands.

Side Tone - When you talk on a telephone, you can hear a little bit of your voice being sent back into the earpiece. This is called a sidetone and it lets you know that the line is live.

Signal Strength - Signal strength is measured in dB, dBrn, or DB.

Signal-to-Noise Ratio - Signal-to-noise ratio is the amount of desired signal, in comparison to the amount of unwanted signal, expressed as a ratio.

Signaling System 7 - A method of out-of-band inter-office signaling for telephone circuits. Simply stated, out of band means that a special separate line is used to carry signaling, such as dialed touch tones, ringing signals, busy tones, (everything, but the actual voices/conversation), etc.
Remember that the two different ways to send signals in telephone transmissions are: in band and out of band. Signals are digits that you dial, dial tone, the phone being off-hook, ringing, etc. An in-band telephone line is like the one in your home; the digits that you dial and the ringing are carried within the channel you talk on. Out-of-band signaling is a method that telephone companies and businesses use for larger PBX applications and data-transfer applications. An out-of-band signaled DS1 has 24 multiplexed channels. The 24th channel carries the signaling for the other 23 channels (phone lines). The advantage of out-of-band signaling is that each channel has an increased capacity to carry data (8Kb/s more) and the 23 channels are not used to find out if a line is busy (both directions, in and out). The off-hook sensing busy signaling and other signaling previously mentioned is done in the 24th channel. If your system receives thousands of calls per day, this can reduce traffic. SS7 makes it easy for long-distance companies to let us dial a phone number, get a busy signal, and not be billed for it because we are not really using a call channel to do this.

Silicon - The important thing to know about silicon is that it is an element used to make electronic components. It is used because it has special atomic properties that enable it to conduct or not conduct electricity, depending on the way it is doped. Doping is the implantation of impurities into the silicon, additional electrons to be specific. When a transistor, diode, or any other silicon active device is made, at least two types (two types of silicon doped differently) of silicon are used to form a junction. The first type of silicon is called a P-type (for positive) and the second type is called an N-type (for negative). The two (very small) pieces of silicon are placed together to form a P-N junction. A single PN junction is used to make a diode and three pieces of silicon are used to make a PNP or NPN junction transistor. Another element that is not as frequently used, but used in the same manner, is Germanium.

SIM (Single Interface Module) - An NEC trademark, this is a smaller PBX in the NEC telephone equipment family. Larger PBXs include the IMG and the MMG.

SIMM (Single-Inline Memory Module) - A small circuit board, about 1" by 3", that contains memory components for PCs and other memory-using devices. The edge of the SIMM circuit board has a single row of contacts so that it can be plugged into a socket or slot. The SIMM gets its name from the type of socket it plugs into. See also SDRAM.

Simple Mail-Transfer Protocol (SMTP) - A standard interchange format used by e-mail applications to exchange messages with each other. SMTP does not provide a user interface or method for a user to create a message. It only provides a way for the message to be transferred. For example, Lotus Notes can be configured to use SMTP when it sends an outgoing message to an Internet e-mail address. SMTP is used in conjunction with POP (Post Office Protocol) and MIME (Multipurpose Internet Mail Extensions) to provide TCP/IP Internet e-mail.

Simple Network-Management Protocol (SNMP) - A status and monitor subprogram that is used almost exclusively in TCP/IP networks. SNMP provides a means to monitor and control network devices, such as hosts and routers, on a LAN or WAN. It enables the user to troubleshoot, manage configurations, change/assign port addresses, collect statistics, performance, and security. In regard to SNMP, each device with an IP address on a TCP/IP network is called an agent. The station, host or terminal that an administrator uses to monitor the agents on the network is called the SNMP manager. Information and statistics gathered by SNMP include: the number of IP packets that have been sent and received, the number of errors encountered at the MAC layer, and the number of TCP retransmits.

Simplex Communications - in one direction. FM radio and broadcast TV are forms of simplex communication. Other methods are half duplex and full duplex.

Single-Frequency Signaling (SF) - Mostly referred to as single frequency, a method of in-band signaling in switched telephone networks. A single 2600-Hz frequency tone is used for signaling.

Single-Mode Fiber - The alternative to multi-mode fiber optic. Single-mode fiber optic has a smaller core, but is capable of longer-distance transmissions. It is used in the public network more often and is the choice for SONET applications. Multi-mode has a larger core, and therefore accepts more light and more frequencies of light. Multi-mode is used for shorterdistance applications, such as LANs. Multi-mode fiber optic is made with an orange-colored tube or jacket, and single-mode fiber is made with yellow.

Six Ones - Simple terminology for a “flag” in the X.25 protocol. Flags are bytes that are inserted and deleted by the frame layer (or network layer, if you refer to OSI terminology) in between each frame. The rules for the X.25 frame layer are defined by the LAPB (Link-Access Procedure Balanced mode) protocol. An X.25 flag bit is as follows: 01111110. See also Bit Stuffing.

Six-Pack Coax - A type of bundled coax that is used in STS/SONET environments. Bundled coax comes in many sizes, including 6 pack, 10 pack, 12 pack, and 24 pack. Bundled coax is generally used to interconnect SONET equipment, digital cross-connect systems, and routers. See also 12-Pack Coax.

Six-Pair Can - See 6-Pair Can.

Slamming - The illegal practice of changing a customer’s telecommunications carrier (long-distance or local) without their consent. To identify the primary long-distance carrier for a telephone circuit in the United States, dial 1-700-555-4141. To identify the local toll carrier for a circuit (line), dial 1 (the circuit area code) 700-4141.

SLC96 - Also known as Slick 96. A Lucent Technologies “pair-gain” system that multiplexes 96 telephone lines onto eight pairs of twistedpair wire. It is used extensively in the public telephone network to provide telephone service to areas that do not have enough twisted pairs to meet customer needs. The SLC 96 actually uses four T1 circuits (24 lines per T1) to achieve the 96-line transport. The SLC 96 is configured in a cabinet, one for inside rack-mount central-office use and the other (far end) as an outdoor cabinet. The circuit cards that are incorporated into the SLC 96 design are separate and redundant power cards, battery back-up for the remote end, common equipment (control) cards, and a separate card for every two lines that are multiplexed (48-line cards for a full system).

SLIP (Serial Line Internet Protocol) - A protocol that enables IP datagrams to be transmitted over dial-up telephone lines. The successor to SLIP is PPP, which provides error detection and automatic configuration.

Sloppy Floppy Copy - To copy data to a floppy disk, then load it onto another computer’s hard drive when you can’t get the LAN to work right or if you don’t have a LAN. Also called Sneaker Net.

Slot 1 - A “package” that CPUs for personal computers come in. Slot-1 packages provide users with easier interchangeability and a lower production cost to manufacturers, as opposed to the older Socket-7 packages. Slot-1 CPUs can only be installed in Slot-1 motherboards, which are equipped with the proper slot interface, which the CPU plugs into.

Slots - A reference to expansion capability of a PBX system, PC, or other electronic equipment. PBX manufacturers make extra slots for electronic circuit cards to plug into the backplane of a KSU or cabinet for future network expansion.

Slotted Ring - A LAN topology that is, for all practical purposes, a switched token ring.

Small Computer System Interface (SCSI) - Pronounced as “scuzzy.” A parallel interface standard for linking internal computer components (such as hard drives) and peripheral devices (such as printers). The good thing about SCSI interfaces is that they are faster than others (such as IDE/ATA). The drawbacks are the higher cost and that many of the SCSI formats that are on the market are not compatible with each other. If you upgrade your PC, you might end up replacing the SCSI interface in your printer as well. Some examples of the SCSI formats and their transfer speeds are: Fast SCSI, 8-bit bus 10 Mbps; Fast Wide SCSI, 16-bit bus 20 Mbps; Ultra Wide SCSI, 16-bit bus 40 Mbps; and Wide Ultra2 SCSI, 16-bit bus 80 Mbps. See also IDE.

Smart Card - A credit card that not only has a magnetic strip (ROM) like all traditional credit cards, but also has a RAM component. Smart cards are being implemented in places where it is inconvenient to carry cash, like on battleships at sea or in amusement parks. To buy something, you simply place your card into a machine, the machine deducts the balance from your account (which is directly on the card) and the transaction is completed.

Smart Jack - Also known as an RJ68. A smart jack is an RJ45 (8-pin modular jack) that has some simple electronic components inside it that enables it to be remotely placed in a loop-back mode for testing purposes.

SMDR (Station Message Detail Reporting) - Another term for call accounting. A call-accounting system is a computer (usually a dedicated PC) that connects to a PBX switch via a serial data port and monitors the details of every phone call made through that switch. The call details are stored as call records; with the appropriate software, they can be retrieved, sorted, processed, and queried to almost any specific nature that the call-accounting system administrator desires. These systems are used by hotels to track all the calls you make from your room so that they can bill you for them. They are also used by companies to do bill back reports for individual departments within the company.

SMDS (Switched Multimegabit Data Service) - A service offered by local telephone companies that is intended for the transport of large amounts of data at high speed from point to point over a switched type of network. Enter in the address or number that you would like your data to be sent and the SMDSU (SMDS Unit) packetizes the data and the SMDS network transports it. SMDS is a packet- or frame-type technology that is available in five transmission rates. Class 1 is 4Mb/s, Class 2 is 10Mb/s, Class 3 is 16Mb/s, Class 4 is 25Mb/s, and Class 5 is 44.7Mb/s.

SMSA (Standard Metropolitan Statistical Area) - An area that the FCC manages rights to provide cellular service. Most SMSAs have two cellular service providers.

SMTP (Simple Mail-Transfer Protocol) - A standard interchange format used by e-mail applications to exchange messages with each other. SMTP does not provide a user interface or method for a user to create a message. It only provides a way for the message to be transferred. For example, Lotus Notes can be configured to use SMTP when it sends an outgoing message to an Internet e-mail address. SMTP is used in conjunction with POP (Post Office Protocol) and MIME (Multipurpose Internet Mail Extensions) to provide TCP/IP Internet e-mail.

S/N Ratio (Signal-to-Noise Ratio) - The amount of desired transmission received in comparison to the amount of interference or distortion received with it. Expressed as a ratio.

SNA (Systems Network Architecture) - IBM protocol and architecture for mainframe/terminal computing environments.

SNADS (SNA, System Network Architecture, Distribution Services) - A data-transaction protocol that is capable of being encapsulated within frame relay and X.25. A software set of SNA programs that work together to provide asynchronous information transactions between end users. SNADS is one of three SNA transaction services. See also Distributed Data Management and Document Interchange Architecture.

Sneaker Net - See Sloppy Floppy Copy.

SNI (Standard Network Interface) - Also called TNI (Telephone Network Interface) and NI (Network Interface). It is a device used to terminate telephone service at the customer’s location and provide lightning protection. One side of the SNI is for telephone company use only and the other side provides a place for customers to access their telephone lines. For other photos of SNIs, see Standard Network Interface and Lightning Protector.

Snips - Scissors that telephone cable splicers and cable installation technicians use when installing/splicing cable. Snips have serrated blades, are very sturdy, and are capable of cutting copper that is as thick as a penny. For a photo, see Cable Knife.

SNMP (Simple Network Management Protocol) - A status and monitor subprogram that is used almost exclusively in TCP/IP networks. SNMP provides a means to monitor and control network devices, such as hosts and routers, on a LAN or WAN. It enables the user to troubleshoot, manage configurations, change/assign port addresses, collect statistics, performance, and security. In regard to SNMP, each device with an IP address on a TCP/IP network is called an agent. The station, host or terminal that an administrator uses to monitor the agents on the network is called the SNMP manager. Information and statistics gathered by SNMP include: the number of IP packets that have been sent and received, the number of errors encountered at the MAC layer, and the number of TCP retransmits.

Snowshoe - A device that is used to maintain a minimum bend radius for installed fiber-optic cable. The cable shown in the photo has a slack length to allow for future splicing. The slack is run along the strand and looped around snowshoes.

SO - The ASCII control-code abbreviation for shift out. The binary code is 1110000 and the hex is E0.

Socket - 1. In TCP/IP, a socket is a combination of a TCP port number and an IP address. Sockets uniquely identify all connections within an internet. 2. An AppleTalk socket is similar in concept to a TCP/IP port.

Socket 7 - A 321-pin ULSI (Ultra Large-Scale Integration) flat package that 586 CPUs for personal computers are manufactured in. Only Socket- 7 CPUs can be used on Socket-7 motherboards.

Socket 8 - Also called a zero insertion-force socket. A combination 387-pin package and matching socket for advanced 586 CPUs for personal computers. Socket-8 plugs (or sockets) have a lever that holds the CPU in place. Only Socket-8 CPUs can be used with Socket-8 motherboards. The Socket-8 architecture was outdated by the Slot-1 physical format.

Soft Call Forward - A type of call transfer where an incoming call is sent to another location after it has not been answered. A soft call forward is usually set by a voice-mail administrator or by a voice-mail user. In contrast, a hard call forward is a type of call transfer where an incoming call is immediately routed to an alternate destination with no ringing. A hard call forward is usually set on a phone or phone line by a user.

Software - Also referred to as application. Software is the programming instructions that are loaded into a computer’s memory that tells it how to function. Microsoft Word is a software application and so is Lotus Notes.

SOH - The ASCII control-code abbreviation for start of heading. The binary code is 0001000 and the hex is 10.

Solid State - The term solid state came about when the transistor was invented. Before the transistor, vacuum-tube amplifiers were in wide use. For a long time, many appliances you bought said “solid state” on them because they had been made with transistors and other silicon devices instead of tubes.

SONET (Synchronous Optical Network) - SONET is strictly a broadband transport system. It is implemented over fiber optic and is able to be configured in a ring, which allows it to reroute traffic with no interruption of service if a fiber is cut. CLECs are implementing SONET as the mainstay of their network construction. SONET is based on a hierarchy of STS (Synchronous Transport Signals), which is the electrical version of an OC-1 (Optical Carrier Level 1). An OC 1 has a transmission speed of 51.84 Mbs. The hierarchy of telephone communications services and their speeds is shown in the table. SONET permits a virtual tributary to be created from one node to another on a network. Virtual tributaries can be equal to a DS1, DS3, STS-1, or any of the OC levels. The important thing to know about a SONET network is that it simply replaces the older telecommunications technology copper twisted-pair outside plant with fiber optic and electronics.

Sound Card - An expansion board/card that is required by personal computers to process digital audio information and produce sound through speakers that are connected to it.

Source Routing Bridge - A type of network bridge that relies on routing information provided by an external sending system. See also Bridge.

Southwestern Bell Corp - Merged with SBC (Southern Bell Communications).

Spade Lug - A connector with two flat surfaces shaped like a two-prong fork that crimps onto a wire so that the wire can be mounted with screws.

SPAM (SPecialized Automated Mail) - The electronic version of “junk mail,” unrequested e-mail messages that advertise products to users that have Internet e-mail boxes.

Span - One section of aerial wire.

Spanning Tree - A term given to routing translation tables that are created automatically by network operating software algorithms.

Spark Gap - Two wires, one hot, and one ground that are separated by a gap of air. Spark gaps are used for lightning protection. If the hot lead, or anything connected to it, is struck by lightning, the lightning will arc across the spark gap because it is engineered to be the easiest path to ground.

Speakerphone - A feature of telephones. Speaker phone allows a user to talk on the phone as if it were an open intercom system in the room, without using a handset.

Spectrum Analyzer - A type of test equipment used to evaluate the status of a broadband transmission. Spectrum analyzers are commonly used by cable-TV head-end technicians to troubleshoot and isolate noise and other troubles on cable-TV networks.

Spectrum, Frequency - All electromagnetic radiation is categorized by its frequency in Hz. If some of the frequencies were vibrations, rather than electromagnetic waves, people could hear them. Some electromagnetic radiation (theoretically) is visible as light. See also IEEE Radar Band Designation.

Speed Dial - A feature of telephone sets that enables a user to input a frequently dialed telephone number and assign that number a speed-dial code. To initiate the speed dial, the user dials the code instead of the entire number.

Speed of Light - The approximate speed of light in a vacuum is 300,000,000 m/s.

SPF (Shortest Path First Algorithm) - SPF is also referred to as a linkstate or Dijkstra’s Algorithm. A class of router-operating software that enables routers to build their own complex address routing tables that detail every router and node within their network. The routing table-building process is accomplished through information multicasts. The routing-table multicasts are referred to as LSPs (Link-State Packets) and they consume payload bandwidth to transmit this information. The process of sending and receiving LSPs is called the discovery process. Multicasts are only sent when there is a change in the network, such as a circuit connection going down, or a new router or connection being added. Link-state algorithms use tremendous amounts of router system memory (20 MB to 30 MB in a 30-node network), and consume significant processor resources within a router’s circuitry. During the startup of a link-start network, the discovery process can take hours. The great advantage to this complex operating method is that routing loops are not created. See also Distance Vector Routing Algorithm and Hybrid Routing Algorithm.

SPID (Service Profile Identifier) - An ISDN (Integrated Services Digital Network) telephone number. The number that some telephone companies use to define the services to which an ISDN device subscribes. ISDN devices use SPID numbers when accessing the telephone company’s switch to identify the device it would like to be connected to. In the United States, SPID numbers can look like ordinary public-service telephone numbers with an extension, such as 972-555-1212 4455. There is one SPID for each B Channel. See also ISDN.

Splice - The connecting of two wires, cables, coax cables, or cable pairs together. A splice is shown on an engineering diagram as an arrow. The actual splices of twisted-pair telephone cable are done with modular-type splices, plain B wire connectors, or 3M Scotchloks. For photos, see Plain B Wire Connector, Modular Splice Tool, and Scotchlok. Fiber-optic cable is spliced via mechanical or fusion splicing, and coaxial cable is spliced with barrel connectors. For a photo of a barrel connector, see Barrel Connector.

Splice Tray - A place within a fiber-optic patch panel or other fiber-optic splice closure that holds fusion splices.

Split - The Lucent Technologies name for a queue. It was named so because it evenly “splits” incoming calls among agents logged into an ACD system. See Queue.

Split Horizon Update - A routing technique in which information about routes is prevented from exiting the router interface through which that information was received. Split-horizon updates are useful in preventing routing loops that count to infinity. They are incorporated into newer router operating systems, such as link-state, distance vector, and hybrid.

Split Pair - The use of one wire from two pairs to make a pair. Sometimes split pairs are done by mistake, but the majority of the time, it is done as a desperate measure to deliver a telephone service to a customer. If there are two bad pairs, but each pair has one good wire in it, the good wire is taken from each pair to make one good pair. Split pairs often cause inductive cross talk and pick up RFI. After RFI filters are placed on the split pair, it will work until new/more telephone wire can be installed or until the old wire can be fixed.

Splitter - Used to make a junction point or split a signal so that it will travel down multiple paths over coax. Also called an RF splitter and a UHF/ VHF Splitter.

Spoofing - 1. A method used by routers to cause a host to believe an interface is up and supporting a communications session. The router accomplishes this by responding to keep-alive messages sent from the host. This convinces the host that the communications session is still running. Spoofing is useful to routers in dial-on-demand environments, in which a router will disconnect a call when a transmission is complete, but keep its connection to a workstation active. By doing this, the router will know when the workstation needs to send packets again and initiate a call. This provides the ability to have effective routing and save on toll charges. 2. The illegal act of sending a data packet that claims to be from an address from which it was not actually sent. Spoofing is designed to foil network security mechanisms, such as filters and access lists.

Spread Spectrum - The radio type used in PCS cellular transmissions. Spread-spectrum radio transmits and receives carrier signals over a wide spectrum of frequencies (“channels”). Several technology platforms in wireless communications are considered to be spread spectrum. A spread-spectrum system is any system that occupies more bandwidth than the minimum required for data signal transfer. Two data formats transmitted on spread-spectrum platforms include CDMA (Code- Division Multiple Access) and TDMA (Time-Division Multiple Access).

SPS (Standard Positioning Service) - The GPS (Global-Positioning System) service that civilians get, but does not correct signal dithering.

Spud - A hand shovel especially made for digging holes for telephone poles.

Spudger - A device that is shaped and sized like a pencil that telephone technicians use to poke their way through telephone cable when they are looking for a certain pair of wires.

Spurs - What telecommunications and power company personnel wear to climb wooden telephone and power poles. The official name for these devices are lineman’s climbers. They are also called climbers, hooks, and gaffs. They consist of a steel shank that has straps on it so that it can be strapped to a person’s leg. On the inside of the shank is a spike that is used to stab into the pole. For a photo, see Climbers.

SPX (Sequenced Packet Exchange) - A part of the Novell NetWare protocol stack. SPX is used for very specific applications. Usually they include interserver or other device communications, such as printing reports, done by servers. An application that would use SPX is for remote control/administration (RCONSOLE) of servers.

SQL (Structured Query Language) - An international standard language for defining and accessing relational data bases.

Squelch - An electronic circuit or filter that is incorporated into microphone circuits that makes them have an adjustable sensitivity to the loudness of a sound the microphone will pick up. Squelch circuits are used in speakerphones to cut out background and transient noise.

SRAM (Static Random-Access Memory) - Electronic memory is available in two families, ROM (Read-Only Memory) and RAM (Random-Access Memory). Memory devices are made from two different technologies: bipolar (TTL) and MOS (Metal-Oxide Semi-conductor). Memory is stored by a technique called writing and retrieved by a technique called reading. ROM devices can only be read, and are programmed during manufacture. PROM devices (Programmable Read-Only Memory) can be programmed at a later date by an electronics reseller or electronic assembler for a special application using special equipment. Special ROM devices called EPROMs (Erasable Program-mable Read Only Memory) can be electronically erased and re-used. RAM has read and write capability. The term random access means that any memory address can be read in any order at any time. The two types of RAM are static and dynamic. Static RAM can hold its memory even when power is removed. Dynamic RAM needs constant power to refresh its memory. For a diagram that depicts the types of memory, see Memory.

SS7 (Signaling System 7) - A method of out-of-band interoffice signaling for telephone circuits. Simply stated, out of band means that there is a special separate line used to carry signaling, such as dialed touch tones, ringing signals, busy tones, (everything but the actual voices/conversation) etc. The two different ways to send signals in telephone transmissions are in band and out of band. Signals are digits that you dial, dial tone, the phone being off-hook, ringing, etc. An in-band telephone line is like the one in your home, the digits that you dial, and the ringing are carried within the channel you talk on. Out-of-band signaling is a method that telephone companies and businesses use for larger PBX applications and data-transfer applications. An out-of-band signaled DS1 has 24 multiplexed channels. The 24th channel carries the signaling for the other 23 channels or phone lines. The advantage of out-of-band signaling is that each channel has an increased capacity to carry data (8Kb/s more) and the 23 channels are not used to find out if a line is busy (both directions, in and out). The off-hook sensing, busy signaling, and other signaling previously mentioned is performed in the 24th channel. If your system receives thousands of calls per day, this can reduce traffic. SS7 makes it easy for long-distance companies to let us dial a phone number, get a busy signal, and not be billed for it because we are not really using a call channel.

ST Connector (Straight Tip Connector) - An older type of fiber-optic connector. The newer is the SC connector, which is constructed of plastic instead of metal. For a photo of an ST connector, See Fiber-Optic Connector.

Standard Network Interface (SNI) - The device used to terminate telephone service at the customer’s location and provide lightning protection. One side of the SNI is for telephone company use only, the other side provides a place for customers to access their telephone lines. For photos of other types of network interfaces, see Two-Line Network Interface.

Standby Processor - A second (redundant) CPU that takes over if the primary one fails.

Standing Wave - In radio transmission, a standing wave occurs when voltage and current form uneven points along a transmitter’s antenna or transmission line. This is caused by a mismatch of load (antenna) impedance to transmission-line impedance, and causes an inefficient transmission. The term relating to standing waves is the SWR (Standing-Wave Ratio), which is the ratio of maximum current points on the line to the minimum current points on the line. To picture a standing wave, imagine you make waves in a bathtub so that waves reflecting from the sides of the tub collide in perfect timing with new waves made from your hand. The waves would appear to stand still and thus be called standing waves.

Star LAN Network - See Star Topology.

Star Topology - A topology or type of LAN (Local-Area Network). The star topology is used in ethernet applications. Ethernet is one of the oldest communication protocols for personal computers. When a LAN is mentioned, the two things that should immediately come to mind are physical topology and the protocol that the LAN uses to manage communications between devices. Ethernet can be implemented in a bus or star physical topology. The alternative family of LAN protocols is the token-passing type, which is configured as a ring topology (see token ring). In an ethernet LAN, computers are given a means to communicate with each other called a protocol. A protocol is a set of rules and instructions for communicating. Within the protocol is a “logical topology.” Even though a network might be connected as a star, it can still “look” like a bus to the communications equipment because all of the computers/devices are connected to the same wire (in the star diagram, the hub is a device that connects all the wires together). Ethernet works similar to the way that people talk in a group. Instead of using wire to carry the binary coded information as ethernet does, people use air to carry sound information. When there is a silence, then one of the persons in the group is able to speak. When the people speak, they say “Johnny, do you know the answer for 5�5?” Even though all the people in the group hear this message, they know it is for Johnny because the message was “addressed” to him. Only Johnny will respond “10.” Then imagine Dawn and Vicki acknowledges a silence and try to speak at the same time. This is confusing and no one understands the information. Ethernet has the same problem and it is called a collision. Collision is the disadvantage of Ethernet. Because of the possibility of collisions (which happen very frequently), Ethernet is called a “contention-based” protocol because all of the connected devices are contending for use of the network. Manufacturers have come out with new ways to avoid collisions, called CSMA/CD and CSMA/CA. Ethernet has many different types of wiring to connect devices and many different NICs (Network Interface Cards) to select from that need to be installed in each computer or device on the network. The list shows Ethernet protocols and the type of wiring used for each.

Start of Heading (SOH) - The ASCII control code for start of heading. The binary code is 0001000 and the hex is 10.

Static RAM (SRAM, Static Random-Access Memory) - Electronic memory is available in two families, ROM (Read-Only Memory) and RAM (Random-Access Memory). Memory devices are made from two different technologies: bipolar (TTL) and MOS (Metal-Oxide Semi-conductor). Memory is stored by a technique called writing and retrieved by a technique called reading. ROM devices can only be read, and are programmed during manufacture. PROM devices (Programmable Read-Only Memory) can be programmed at a later date by an electronics reseller or electronic assembler for a special application using special equipment. Special ROM devices called EPROMs (Erasable Programmable Read Only Memory) can be electronically erased and re-used. RAM has read and write capability. The term random access means that any memory address can be read in any order at any time. The two types of RAM are static and dynamic. Static RAM can hold its memory even when power is removed. Dynamic RAM needs constant power to refresh its memory. For a diagram that depicts the types of memory, see Memory.

Static Route - In network routing, a path that is explicitly configured and entered into the routing table by a network administrator. Static routes take precedence over routes chosen by dynamic routing protocols.

Station Message-Detail Reporting (SMDR) - Another term for call accounting. A call-accounting system is a computer (usually a dedicated PC) that connects to a PBX switch via a serial data port and monitors the details of every phone call made through that switch. The call details are stored as call records. With the appropriate software, they can be retrieved, sorted, processed, and queried to almost any specific nature that the call-accounting system administrator desires. These systems are used by hotels to track all the calls that you make from your room so that you can be billed. They are also used by companies to bill back reports for individual departments within the company.

Statistical Time-Division Multiplexing - A multiplexing technology that gives users automatic adjustable bandwidth.

STDM (Statistical Time-Division Multiplexing) - A multiplexing technology that gives users automatic adjustable bandwidth.

Step-Down Transformer - A transformer that is wired in a fashion to receive an AC voltage on its primary winding and reduce that voltage through electromagnetic induction into the secondary winding. Reversing the way a transformer is wired changes it from a stepdown to a step-up and vice-versa.

Stepped-Index Fiber Optic - A fiber optic that has a core made of glass consisting of one refractive index. Stepped index fiber is available in multi-mode and single-mode. The alternative to stepped-index fiber optic is graded-index fiber optic. The core of graded-index fiber optic consists of many layers of glass with different refractive indexes that cause the light to gradually bend as it approaches the outside of the fiber. Graded-index fiber (like stepped index fiber) is available in multimode or single-mode, and it is more expensive.

Stepper Switch - Also called a crossbar switch. The old analog telephone switch had mechanical relays that connected telephone calls. This is where the term switch comes from. Old central-office switches contained literally thousands of mechanical switches.

STM (Synchronous Transfer Mode) - New technologies, such as SONET, ATM (Asynchronous Transfer Mode), and ISDN (Integrated- Services Digital Network), are leading up to STM. It is also referred to as BISDN (Broadband Integrated-Services Digital Network). It will enable the user to have a DS3 private line, a POTS line, or an ISDN BRI (Basic-Rate Interface) automatically, depending on the device they use to access the line, a high-definition TV set, a telephone, or a PC.

STM-1 - The basic bandwidth building block for SDH (Synchronous Digital Hierarchy). The STM-1 signal has a bandwidth of 155.52 Mbps. Furthermore, the STM-1 format is identical to the electrical STS-1 and the optical OC-1 formats. See also SDH and SONET.

Stop Bit - In serial data transmission, the stop bit is a logical one (1) after the transmission of each character (each character is seven or eight bits long).

Store and Forward - A packet-switching process in which frames are completely received and their headers read before they are forwarded out the appropriate port. This processing includes calculating the CRC (Cyclic Redundancy Check) and verifying the destination address. In addition, frames might be temporarily stored in memory until an available link (or channel) is available to carry the message. This method has advantages and disadvantages compared to cut-through packet switching.

STP (Shielded Twisted Pair) - The typical wire used in telephone networks and computer LANs. Shielded twisted pair is not as commonly used as UTP (Unshielded Twisted Pair). The physical makeup of twisted-pair wire is solid 24 AWG wires, twisted into pairs. Four pairs (two wires make one pair) is the most commonly used for new installations these days because it is only a penny or two more per foot than three pair. Twisted-pair wire also comes in different categories:

• Cat 3 for telephone

• Cat 4 for 10 base T LAN (local-area network) or telephone

• Cat 5 for 100 base T ethernet or token ring LAN

• Cat 7, (the newest) which is a little better than cat 5 for data, but a lot

more expensive.

Straight-Tip Connector - A type of round, metal fiber-optic connector, usually called an ST connector. The newer connector (and rapidly becoming more popular) is the SC connector, which is square in shape and made of plastic.

Strand Clamp - A pole-attachment device that is used to hold steel strand to utility poles.

Stranded Copper - See Stranded Wire.

Stranded Wire - A wire that is made up of many small wires, rather than one big solid one. Stranded wire is not used in telephony applications because it doesn’t stay connected to 66M150 or AT&T 110 termination blocks.

Strand, Steel - The support for telephone cable, cable-TV coax, and fiberoptic cable when installed in aerial applications. See also Pole Attachment.

Strap - An electrical connection (usually a wire or metal jumper) from one point to another. Strap is a common term used in reference to the configuration of rectifiers, power supplies, and circuit cards.

Stripe Pitch - A measurement (in millimeters) of the distance between dots along the vertical wires in a monitor that incorporates aperture grill technology. The smaller the stripe pitch, the higher the resolution capability of the monitor.

STS (Synchronous Transport Signal) - In SONET networks, the optical signal must be converted to electricity at one time so it can be de-multiplexed and further processed. This electrical version of the SONET OC-1 level signal is called a synchronous transport signal 1 (STS-1), and is transported from node to node or node to digital cross-connect system, or to DSX cross-connect panels via 50-ohm coax.

STS-1 (Synchronous Transport Signal 1) - See STS.

STS-3 (Synchronous Transport Signal 3) - Referred to by some as a level 2. The electrical equivalent of an OC-3 (Optical Carrier Level 3). 155Mbps.

STS-3c (Synchronous Transport Signal 3c) - A physical-layer transmission format that is known as an STM1 outside of the United States and Japan. The STS-3c is the electrical equivalent of the SONET OC-3. The transfer rate is 155 Mbps, including overhead and payload. The net payload on an STS-3c is 149.76 Mbps.

Studio-Transmitter Link (STL) - A studio-transmitter link is basically a remote control for a distant transmitter. It is a separate radio channel from the broadcast radio station itself and it is used to adjust the amount of power that the transmitter emits, performance monitoring, and provide remote access for testing and troubleshooting.

Stutter Dial Tone - A dial tone that blinks on and off when a telephone line initially goes into an off-hook state. A stutter dial tone is used to signal a user that a new voice message is in their voice mailbox, which is also known as voice-mail notification.

STX - The ASCII control-code abbreviation for start text. The binary code is 0010000 and the hex is 20.

SUB - The ASCII control-code abbreviation for substitute. The binary code is 1010001 and the hex is A1.

Subarea Network - A group of devices that communicate through the same control node on an SNA (IBM System Network Architecture) network. Two types of nodes are Type-4 communications controller nodes and Type-5 host nodes. All devices in a subarea share the same subarea address and have unique element addresses.

Subscriber - A telecommunications customer. This includes telephone, cable TV, and cellular (PCS and wireless).

Subscriber Loop - The pair of wires that runs from a telephone company central office (or from extended transmission equipment) to the customer’s network interface. A loop is a pair of wires.

Subscriber Loop Carrier (Another term for SLC 96) - See SLC 96.

Super Server - A server that has multiple microprocessors.

Superframe Format - A framing format for T1 that consists of 12 T1 frames, 193 bits each, transmitted in succession. The superframe format allows for maintenance and monitoring information to be sent along with the 24 DS0 channels. ESF (Extended Super Frame) is the newer version of T1 framing format.

Supervisory Signal - A way that telephone electronics communicates with each other to initiate a command. If you have call waiting on your home telephone, when you get another call (hear the beep or click indicating another call), you momentarily press the hook switch (flash button) to signal the central office to give you the other line. This is an example of a supervisory signal. It is called a supervisory signal because it relates to the connect and disconnect of a phone line. The general term for the ability for a central office or PBX switch to recognize that a telephone conversation has ended is disconnect supervision. When the telephone is “hung-up,” the central office or PBX recognizes the decrease in current flow and disconnects the call. PBX (Private Branch Exchange) phone systems have disconnect supervision, which means that when a call is ended, it recognizes a “hook-flash” from the central office and disconnects the call, or viceversa. If the PBX did not have this feature, it would not release (hang up) telephone calls.

Surface Mount - A reference to a modular jack that is shaped like a box, and can be fastened to the surface of a wall, baseboard, or anywhere else you do not have prewired outlets. Surface-mount jacks are also called biscuit jacks and baseboard jacks. 2. A reference to an electronic component package where the device is soldered to the surface of a PC board, rather than have leads that extend through the board.

Surge Protector - A power-filtering device. Most surge protectors come in the form of an extension cord with six to eight outlets box attached to the end. Not all surge protectors are created equal. Most surge protectors are more useful as an extension cord than any kind of protection from a voltage surge or spike. Some good surge protectors use fastswitching components to sense overvoltage and spikes on the power source. These good surge protectors cost about $50. If you are truly concerned about protection from all of the evil electrophysical characteristics of public power, a small UPS system is the best protection. A good UPS (Uninterrupted Power Supply) costs about $150.

SVC (Switched Virtual Circuit) - Any circuit that can be connected for a temporary amount of time with the use of electronic circuit switching equipment. This includes a plain-old telephone call. When the phone is on the hook and no one is using it, the telephone wire runs to the central office and ends. When you pick up the receiver and dial a number, the central office makes a connection through its electronics from one phone line to another that lasts only as long as the receivers are off hook. It is a “switched” circuit because it can be switched to any telephone with a number that you dial. It is virtual because the actual path through the electronics is multiplexed, as opposed to a physical pair of wires.

SVGA (Super Video Graphics Array) - The suggested monitor for the PC that is used for call-accounting applications, and other computertelephony integration applications. The SVGA monitor is capable of resolution to 1024 by 768 pixels (dots of light on the computer screen) per inch. SVGA is the newer version of VGA (Variable Graphics Array).

Switch - Another name for a PBX (phone system) or central office.

Switch Room - A room that is dedicated for switching equipment. Switch rooms are usually kept at a temperature of 65 degrees F and a humidity of 50% to reduce ESD.

Switched 56 - A service offered by local and long-distance telephone companies that works like a regular telephone line except, that it is intended for data/modem use. Switched 56K lines have 7-digit telephone numbers (plus area code) and they are available in digital or analog. When the telephone company installs the line, they condition the copper pair (remove bridge taps and coils) and install a DSU (Digital Service Unit), which is a line/signal amplifier. Connect it to your 56K modem; it will transmit at a rate of 56,000 bits per second as long as you are talking to another 56K modem on another 56K line.

Switched Ethernet - An efficiency enhancement to the original Ethernet specification. Switched Ethernet incorporates modified layer 2 (Data Link Layer) electronics in hubs and repeaters. This design provides an individual 100 Mbps (for fast Ethernet) to each far end segment.

Switched Multimegabit Digital Service (SMDS) - A service offered by local telephone companies that is intended for the transport of large amounts of data at high speed from point to point over a switched type of network. You enter in the address or number that you would like your data to be sent and the SMDSU (SMDS Unit) packetizes the data and the SMDS network transports it. SMDS is a packet- or frame-type technology that is available in five transmission rates. Class 1 is 4Mb/s, Class 2 is 10Mb/s, Class 3 is 16Mb/s, Class 4 is 25Mb/s, and Class 5 is 44.7Mb/s.

Switched Private Line - A reference to switched 56K service.

Switched Service - Basic voice telephone lines (POTS lines) are switched services.

Switched Virtual Circuit - A telephone line is a switched virtual circuit. The circuit only exists while the conversation is happening. After the conversation is over, the circuit, which acts like a pair of wires from point A to point B, is gone. Another form of a switched virtual circuit is like those in switched Ethernet or switched token-ring technology.

Switching Center - Another name for a telecommunications company’s central office. A location for switching equipment/electronics and transport equipment/electronics.

Switching Hub - Also called a concentrator. A LAN (Local-Area Network) element that links a device to a network with a specific amount of bandwidth or exchange rate of data, regardless of the number of users on the network. A switching hub performs the same function as a nonswitching hub, except that the nonswitching hub only connects many users into the same channel, where they all share the same bandwidth. For a photo of a switched Ethernet hub, see Switched Ethernet.

Symmetrical Digital Subscriber Line (SDSL) - A physical-layer telecommunications protocol that delivers high-speed data networking over a single pair of copper phone lines. SDSL is symmetrical, which means that upstream and downstream data-transfer rates are the same. Speeds range from 160 Kbps to 1.544 Mbps. The base transmission distance is 24,000 feet (about 4.5 miles), and it can be extended to greater than 30,000 feet with repeaters. SDSL can be extended to any distance over fiber optic. SDSL is ideal for business applications that require identical downstream and upstream speeds, such as video conferencing or collaborative computing, as well as similar applications that are appropriate for ADSL technology. SDSL uses the same kind of line-modulation technique used in ISDN, known as 2B1Q.

SYN - The ASCII control code abbreviation for synchronous idle. The binary code is 0110001 and the hex is 61.

Synchro Daemon - A background program or subroutine that is used for a timing reference in telecommunications platforms.

Synchronize - See Synchronous.

Synchronous - “With time.” A reference to communications equipment that is timed from a common timing source, such as a bits clock. SONET networks are synchronous and modem transmissions are asynchronous. Asynchronous means “without timing.” People talk asynchronously. Even though one person talks very fast and another very slowly, they both exchange information and process it in their brains.

Synchronous Data Link Control (SDLC) - A revised revision of the IBM Bisync protocol that was submitted by its creator (IBM) to the ISO and ANSI in hopes that it would become a standard. Instead, it was evolved by the ISO into HDLC (High-level Data-Link Control) and evolved by the ANSI into ADCCP (Advanced Data Communication Control Procedure). The CCITT reviewed and modified HDLC and called it LAP (Link-Access Procedure), which became the basis for the frame or network layer of the X.25 standard in 1976. The LAP protocol was further modified by the CCITT to become LAPB (Link-Access Procedure Balanced mode) in 1978.

Synchronous Digital Hierarchy (SDH) - A European family of digital carrier rates. SDH defines a set of rate and format standards that are transmitted using optical signals over fiber. SDH is the term used by the ITU to refer to SONET OC rates referred to in the United States. Its basic building block is a rate of 155.52 Mbps, designated at STM-1 (OC-3). See also SONET and STM-1.

Synchronous Graphics RAM (SGRAM) - A type of dynamic randomaccess memory used as a buffer/temporary storage in computers that enhances the performance of the graphics accelerator and video adapters.

Synchronous Transfer Mode (STM) - See STM.

Synchronous Transport Module Level-1 (STM-1) - The basic bandwidth building block for SDH (Synchronous Digital Hierarchy). The STM-1 signal has a bandwidth of 155.52 Mbps. Furthermore, the STM-1 format is identical to the electrical STS-1 and the optical OC-1 formats. See also SDH and SONET.

Synchronous Transport Signal (STS 1) - See STS 1.

Synchronous Transport Signal 3c (STS-3c) - A physical-layer transmission format that is known as an STM1 outside of the United States and Japan. The STS-3c is the electrical equivalent of the SONET OC-3. The transfer rate is 155 Mbps, including overhead and payload. The net payload on an STS-3c is 149.76 Mbps. See the diagram under STS-3c.

SyncLink Dynamic RAM (SLDRAM) - A class of random-access memory used for personal computers that is half as fast as RDRAM (Rambus Dynamic RAM) at 400 MHz, but less costly (at initial inception to the market). It is still faster than SDRAM, which exchanges data with central computer components at a rate of 100 MHz.

System Speed Dial - A feature of PBX (Private Branch Exchange) and key telephone systems. Unlike standard speed dial, where each individual user programs a speed dial under a button on their own phone, system speed dial programs a speed-dial number under a code. The telephone number programmed in the system speed dial can be dialed by entering the code from any telephone on the system (that has the feature). The Northern Telecom Meridian 1 PBX system is capable of having 1000 system speed-dial numbers.

Systems Network Architecture (SNA) - See SNA.