SA (Source Address) - The address from which the message or data originated.

SA (Source MAC Address) - A six octet value uniquely identifying an end point and which is sent in an IEEE LAN frame header to indicate source of frame.

SAAL (Signaling ATM Adaptation Layer) - The Signaling ATM Adaptation Layer resides between the ATM Layer and Q.2931. Its purpose is to provide reliable transport of Q.2931 messages between peer entities such as an ATM switch and an ATM host.

Safety Ground - Connection made to ground, as a protective measure, usually from the frame or chassis of a piece of equipment.

SAP (Service Access Point) - the point at which an entity of a layer provides services to its LM entity or to an entity of the next higher layer.

SAR (Segmentation And Reassembly) - the SAR accepts PDUs from the CS and divides them into very small segments (44 bytes long). If the CS-PDU is less than 44 bytes, it is padded to 44 with zeroes.

A two-byte header and trailer are added to this basic segment. The header identifies the message type (beginning, end, continuation, or single) and contains sequence numbering and message identification.

The trailer gives the SAR-PDU payload length, exclusive of pad, and contains a CRC check to ensure the SAR-PDU integrity. The result is a 48-byte PDU that fits into the payload field of an ATM cell.

Satellite Downlink - Microwave radio link from a satellite to a ground station on earth.

Satellite Office (Exchange) - A local end office (or exchange) on a low level of the telephone network hierarchy which is associated with another local office and which has no route switching functions except those towards the associated higher level local office. A satellite exchange normally has the capability to connect local subscribers' lines terminating in it without switching through to the higher level exchange.

Satellite Uplink - Microwave link from a ground station to a satellite.

SBus - hardware interface for add-in boards in later-version Sun 3 workstations.

SC (Structured Connectors or Cabling) - Designation for an Optical Connector featuring a 2.5 mm physically contacting ferrule with a push-pull mating design. Commonly referred to as Structured Cabling, Structured Connectors or Stick and Click.

SC (System Controller) - CellPath 300 System Controller; paired with the Extension Module (EM).

SCC (Stick-and-Click Connector) -Two fibers ganged side-by-side.

Scheduling - Defines when and in what order to service queues.

Schematic Diagram - A functional diagram of a circuit using conventional symbols for components.

Schottky Circuit - Circuit which takes advantage of the Schottky effect which occurs in junctions between metals and semiconductors and results in an increase in the operating speed of the device.

Scope - A scope defines the level of advertisement for an address. The level is a level of a peer group in the PNNI routing Hierarchy.

Scope - A cathode ray oscilloscope.

SCP (Switch Control Processor) - The main processor for an ASX switch.

SCR (Silicon-Controlled Rectifier) - Rectifier sometimes used in central office battery chargers which can be turned on by a control circuit.

SCR (Sustainable Cell Rate) - parameter defined by the ATM Forum for ATM traffic management. For VBR connections, SCR determines the long-term average cell rate that can be transmitted.

SCSI (Small Computer Systems Interface) - a standard for a controller bus that connects disk drives and other devices to their controllers on a computer bus. It is typically used in small systems.

SDLC (Synchronous Data Link Control) - IBM's data link protocol used in SNA networks.

SDU (Service Data Unit) - a unit of interface information whose identity is preserved from one end of a layer connection to the other.

SEAL (Simple and Efficient Adaptation Layer) - also called AAL 5, this ATM adaptation layer assumes that higher layer processes will provide error recovery, thereby simplifying the SAR portion of the adaptation layer.

Using this AAL type packs all 48 bytes of an ATM cell information field with data. It also assumes that only one message is crossing the UNI at a time. That is, multiple end-users at one location cannot interleave messages on the same VC, but must queue them for sequential transmission.

Seamless - In a LAN environment, transparent interaction between the user and the application accessed. The user doesn't perceive that he's on a network, i.e. his programs run as though they were running just on his personal computer.

SECAM - (Systeme En Coleur Avec Memoire) - Sequential and Memory Color Television - Started in France in the late 1960s, and used by other countries with a political affiliation.

The B-Y and R-Y signals are transmitted on alternate lines modulated on an FM subcarrier. The memory is a one line delay line in the receiver to make both color difference signals available at the same time on all lines. Due to FM, the signal is robust in difficult terrain.

Secondary Winding - Output winding of a transformer. It receives power by induction from the current flowing in the primary winding.

Segment - a single ATM link or group of interconnected ATM links of an ATM connection.

Seismic Zone - A geographic area designated by numerical value indicating the likelihood of seismic activity.

SEL (Selector) - A subfield carried in SETUP message part of ATM endpoint address Domain specific Part (DSP) defined by ISO 10589, not used for ATM network routing, used by ATM end systems only.

Selective Cell Discard - A network element in an impending congested state may discard CLP=1 cells from a CLP-significant VC.

Self-Diagnostics - Routines by which a phone system can alert you that there is something wrong with the system, usually via the operator console or through one of the data ports.

Self Test - The capability of a system to run test programs at regular intervals to test its own operation and to signal when failures have occurred or are about to occur without human intervention.

Semiconductor - Material which has a resistance to electricity somewhere between a conductor (e.g. a copper wire) and an insulator (e.g. plastic). Silicon and Germanium are the two most commonly used semiconductor materials. The flow of current in a semiconductor can be changed by light, or the presence or absence of an electric or magnetic field. < /P>

Semipermanent Connection - a connection established via a service order or via network management.

Sense - To detect the presence, absence or value of a signal.

Sensor - Detection device which is sensitive to changes in level or state.

Serial Port - An input/output port (plug) that transmits data out one bit at a time, in contrast to a parallel port, which transmits data out eight bits at a time.

Service Charge - The amount you pay each month to receive cellular service. This amount is fixed, and you pay the same fee each month regardless of how much or how little you use your cellular phone. It usually ranges from about $10 to $45 per month, depending on the carrier's tariffs and the particular plan of service you select. 

SES (Severely Errored Seconds) - a second during which more event errors have occurred than the SES threshold (normally 10^-3).

Session Layer - Layer 5 in the OSI model that is responsible for establishing and managing sessions between the application programs running in different nodes.

SF (Single Frequency) - A method of in-band signaling.

SF (Super Frame) - A term used to describe the repeating 12 D4 frame format that composes a standard (non-ESF) T1 service.

SGMP (Simple Gateway Management Protocol) - the predecessor to SNMP.

Shaping - The alteration of a traffic stream on a particular connection to increase network efficiency.

Shaping Descriptor - n ordered pairs of GCRA parameters (I,L) used to define the negotiated traffic shape of an APP connection. The traffic shape refers to the load-balancing of a network. In this context, load-balancing means configuring the data flows to maximize the efficiency of the network.

Shelf Life - The useful life of components when not in use, such as those stored as spare parts or in a warehouse awaiting shipment. Batteries tend to have the shortest shelf life of most elecommunications components.

Shielded Cable - Cable with metal tape shield wrapped around the insulated conductors.

Shielded Pair - Two insulated wires in a cable wrapped with metallic braid or foil to prevent interference and provide noise free transmission.

Short - A circuit impairment that exists when two conductors of the same pair, which normally make up on operating electrical circuit, are connected or touch.

Short Circuit - A near zero resistance connection between any two wires; where two pairs are involved, usually called a "cross." It disrupts transmission and may cause an excessive current flow.

Shortcut - An ATM VCC used to forward data packets in lieu of the default-routed path.

Shorted - A circuit prevented from operating normally because two or more conductors have provided a low resistance path, often in parallel with the device concerned, which stops operation.

Shunt - (1) A parallel and alternative path for current; and (2) a resistor of known value connected in parallel with a meter to enable the meter to be used to measure current values higher than those which would otherwise provide a full scale deflection for the meter.

SI (Status Indicator) - An option available on WECO coded plants for discrete or functional alarm connections developed as CSAC features to replace the older alarm transfer options when present (i.e. ATA, AT, ATC, etc.).

Signal - (1) An electrical wave used to convey information; (2) an alerting signal; and (3) an acoustic device such as a bell or a visual device such as a lamp which calls attention.

Signal Conditioning - The amplification and/or modification of electrical signals to make them more appropriate for transmission over a certain medium - cable, microwave, etc.

Silicon Diode - Silicon semiconductor used as a diode rectifier. It is on all of the time, unlike the SCR, which can be controlled.

Sine Wave - A symmetrical time varying wave in which the amplitude is proportional to the sine of an angle rotating at a constant rate through 360 degrees.

single mode fiber - Type of fiber optic cable with a smaller center core than multimode fiber. Single mode fiber can be used over relatively long distances.

Single Phase - A circuit or device energized by a single alternating voltage; one phase of a polyphase system.

Sinusoidal - Varying in proportion to the sine of an angle; the shape of a sine wave.

SIR (Sustained Information Rate) - In ATM this refers to the long-term average data transmission rate across the User-to-Network Interface. In SMDS this refers to the committed information rate (similar to CIR for Frame Relay Service).

SLIP (Serial Line IP) - A protocol used to run IP over serial lines, such as telephone circuits or RS-232 cables, interconnecting two systems.

S.M.A.R.T. ® (Sophisticated Monitoring And Reporting Teleview) - Indicative of a family of high quality, reliable, solid state remote monitoring systems covered by the Lorain Products S.M.A.R.T. ® trademark. Includes the S.M.A.R.T. ® Controller/Monitor, S.M.A.R.T. ® Monitor and S.M.A.R.T. ® Reporter.

Smart Buffers - Refers to buffers which are able to automatically support different classes of service while maintaining the Quality of Service (QoS) for each class.

SMDS (Switched Multimegabit Data Service) - a high-speed, datagram-based, public data network service expected to be widely used by telephone companies in their data networks.

SMF (Single Mode Fiber) - Fiber optic cable in which the signal or light propagates in a single mode or path. Since all light follows the same path or travels the same distance, a transmitted pulse is not dispersed and does not interfere with adjacent pulses. SMF fibers can support longer distances and are limited mainly by the amount of attenuation. Refer to MMF.

SMTP (Simple Mail Transfer Protocol) - the Internet electronic mail protocol used to transfer electronic mail between hosts.

SNA (Systems Network Architecture) - a proprietary networking architecture used by IBM and IBM-compatible mainframe computers.

SNAP (SubNetwork Access Protocol) - A specially reserved variant of IEEE 802.2 encoding SNAP indicates to look further into the packet where it will find a Type field.

SNI (Subscriber Network Interface) - The interface between an SMDS end user’s CPE and the network that directly serves the end user. It can be supported by either a DS1 or a DS-3 access arrangement.

SNMP (Simple Network Management Protocol) - the Internet standard protocol for managing nodes on an IP network.

snmpd - an SMNP agent for a given adapter card.

Software - The detailed instructions to operate a computer. The term was created to differentiate instructions (i.e. the program) from the hardware.

Solder - A lead or tin alloy which melts readily and is used in a wide variety of wire, terminal and component connecting applications.

Soldering - Process of joining metals by fusing them by means of a molten metal with a relatively low melting point.

Solderless Lug - Terminal which compresses and holds conductors by tightening a screw.

Solder Lug - Method of terminating a heavy stranded power conductor. The conductor is forced into one end of a short copper tube filled with molten solder. The other end of the tube is flattened and a hole drilled through it so the lug may be bolted to a power terminal.

Solid State - Any semiconductor device that controls electrons, electric fields and magnetic fields in a solid material and typically has no moving parts.

Solid State Circuit - A circuit composed of solid state devices. It contains no vacuum tubes. 

SONET (Synchronous Optical Network) - a new and growing body of standards that defines all aspects of transporting and managing digital traffic over optical facilities in the public network.

Source - Part of communications system which transmits information.

Source Route - A hierarchically complete source route.

Source Traffic Descriptor - a set of traffic parameters belonging to the ATM Traffic Descriptor used during the connection set-up to capture the intrinsic traffic characteristics of the connection requested by the source.

Spade Lug - A solder lug with an open-ended two-prong spade instead of a round hole which can be slipped under the head of a retaining screw or binding post terminal.

Spanning Tree Protocol - provides loop-free topology in a network environment where there are redundant paths.

SPANS (Simple Protocol for ATM Network Signaling) - Marconi's proprietary signaling protocol used for establishing SVCs between Marconi equipment.

SPARC (Scalable Processor Architecture Reduced instruction set Computer) - a powerful workstation similar to a reduced-instruction-set-computing (RISC) workstation.

SPE (Synchronous Payload Envelope) - the payload field plus a little overhead of a basic SONET signal.

Specific Gravity - Density. The ratio of the weight of a volume of a liquid or solid to the weight of the same volume of water, usually at 4°C.

Spikes - Electrical anomalies represented as short duration, instantaneous, very high voltage fluctuations on an electrical service.

Split System - A switching system that implements the functions of more than one logical node.

SPVC (Smart PVC) - a generic term for any communications medium which is permanently provisioned at the end points, but switched in the middle. In ATM, there are two kinds of SPVCs: smart permanent virtual path connections (SPVPCs) and smart permanent virtual channel connections (SPVCCs).

SS7 (Signaling System No. 7) - The SS7 protocol has been specified by ITU-T and is a protocol for interexchange signaling.

SSCF (Service Specific Coordination Function) - An SSCF maps the service of the SSCOP to the needs of the specific AAL SSCF user.

SSCOP (Service Specific Connection-Oriented Peer-to-Peer Protocol) - The SSCOP is used to transfer variable length SDUs between users and provides for recovery of lost or corrupt SDUs.

SSCS (Service Specific Convergence Sublayer) - The portion of the convergence sublayer that is dependent upon the type of traffic that is being converted. 

ST (Straight Tip) - A fiber-optic connector designed by AT&T which uses the bayonet style coupling rather than screw-on as the SMA uses. The ST is generally considered the eventual replacement for the SMA type connector.

Stability - Ability to remain stable in frequency, power level, etc.

Standby Power Generator - The engine/alternator facility present in a central office which provides AC power when utility power is not available.

Standby Time - The amount of time you can leave your fully charged cellular portable or transportable phone turned on before the phone will completely discharge the batteries.

Starting Battery - A source of reserve energy used for cranking the electric starting motor of an engine alternator set.

State - (1) Either of the two conditions of a bistable device, the "1" state or the "0" state; and (2) in specification and description language, the condition in which the action of a process is uspended and awaiting an input.

Statement of Compliance - A detailed list which has to be submitted with most international tenders indicating whether or not the equipment offered is fully compliant with the requirements in the specifications.

Static - Interference caused by natural electric disturbances in the atmosphere, in your office, in your home. Also, containing no vacuum tubes or motor generators.

Static Route - a route that is entered manually into the routing table.

Stationary Battery - Battery designed to be used in a fixed location.

Station Battery - A separate power source which provides the necessary DC power to drive a telephone system.

Statistical Multiplexing - a technique for allowing multiple channels and paths to share the same link, typified by the ability to give the bandwidth of a temporarily idle channel to another channel.

STC (Stick-and-Turn Connector (bayonet)) - A type of fiber optic connector.

Step-By-Step - An electromechanical type of central office, usually referred to by the initials SXS.

Step Down - Reduce the voltage.

Step-Down Transformer - Transformer producing a lower output, or secondary voltage, than its input, or primary voltage.

Step-Up Transformer - Transformer producing a higher output, or secondary voltage, than its input, or primary voltage.

STM (Synchronous Transfer Mode) - a transport and switching method that depends on information occurring in regular and fixed patterns with respect to a reference such as a frame pattern.

Storage Battery - A battery consisting of two or more storage cells electrically connected to produce electric energy. Common usage permits this designation to be applied also to a single storage cell used independently.

Storage Battery Tray - Lead or plastic tray placed under cells in a storage battery as a precaution against leakage.

Store-and-Forward - The technique of receiving a message, storing it until the proper outgoing line is available, then retransmitting it, with no direct connection between incoming and outgoing lines.

STP (Shielded Twisted Pair) - two or more insulated wires that are twisted together and then wrapped in a cable with metallic braid or foil to prevent interference and offer noise-free transmissions. 

Stray Capacitance - Unintended capacitance between wires and components which has a significant effect at high radio frequencies.

Stripping - Removal of the outer sheath from a cable prior to splicing or termination. 

STS (Synchronous Transport Signal) - a SONET electrical signal rate.

Subassembly - Functional unit of equipment.

Sublayer - a logical subdivision of a layer.

Substrate - The support of an integrated circuit, either a semiconductor or an insulator.

Subsystem - A functional unit of a system.

Summary Address - An address prefix that tells a node how to summarize reachability information.

Superimposed Ringing - A way of stopping party line phone users from hearing each other's ring by superimposing a DC voltage over the ringing signal and using it to alert a vacuum tube or semiconductor device in only the phone instrument for which the ring was intended.

Super User - a login ID that allows unlimited access to the full range of a device's functionality, including especially the ability to reconfigure the device and set passwords.

Surge Protector - A device which plugs between the phone system and the commercial AC power outlet to protect the system from high voltage spikes (also called surges) which might be damaging. When a surge occurs, the surge protector sends the overload to ground.

SVC (Switched Virtual Circuit [or Channel]) - a channel established on demand by network signaling, used for information transport between two locations and lasting only for the duration of the transfer; the datacom equivalent of a dialed telephone call.

SVCC (Switched Virtual Channel Connection) - A Switched VCC is one which is established and taken down dynamically through control signaling. A Virtual Channel Connection (VCC) is an ATM connection where switching is performed on the VPI/VCI fields of each cell.

SVPC (Switched Virtual Path Connection) - A Switched Virtual Path Connection is one which is established and taken down dynamically through control signaling. A Virtual Path Connection (VPC) is an ATM connection where switching is performed on the VPI field only of each cell.

Switch - Equipment used to interconnect lines and trunks.

Switched Connection - A connection established via signaling.

Switching System - A set of one or more systems that act together and appear as a single switch for the purposes of PNNI routing.

Symmetric Connection - a connection with the same bandwidth value specified for both directions.

Synchronous - signals that are sourced from the same timing reference and hence are identical in frequency.

Synthesized Voice - Human speech approximated by a computer device that concatenates basic speech parts (or phonemes) together.

System - An organized assembly of equipment, personnel, procedures, and other facilities designed to perform a specific function or set of functions.

System Build - The original manufacturer system building that occurs when the order is placed by the buyer with the vendor. The basic configuration is set up to reflect the user's needs at that point in time. Thereafter, if any changes occur to reflect changes in the operating environment, the manufacturer must reconfigure the system to reflect this change, and there is usually a reprogramming charge and delay associated with the change.