[S]

Satellite relay – Active or passive repeater in geosynchronous orbit which amplifies the signal it receives before transmitting it back to earth.

Scrolling – The vertical movement (up or down) of lines of data displayed on a CRT screen. Also see smooth scrolling and jump scrolling.

Secondary channel – Low-speed channel established on a four-wire circuit over which diagnostic or control information is passed. [User data is passed on the primary, high-speed channels of the circuit.]

Selective calling – Ability of a transmitting station to specify which of several stations is to receive a message through the use of assigned codes.

Service Delivery Improvement Project(SDIP) – From November 1996 through the end of 1997, ITD conducted a Service Delivery Improvement Project to reengineer the way it delivered basic telephone and data services to its customers across the Ann Arbor, Flint, and Dearborn campuses of the University of Michigan.

Service and equipment record – List of equipment billed to customer by type, quantity, monthly charge, location and billing dates.

Service group – One or more access lines (DAL or T1) used to terminate calls from one or more 800 service numbers; a group of lines built as one trunk group from a DMS-250 switch. [A call placed to an 800 number routed to that trunk group can be completed on any of the lines in that trunk group.]

Session – (1) Connection between two stations that allows them to communicate. (2) Meeting or period devoted to a particular activity.

Session layer – Layer 5 of the Open Systems Interconnection (OSI) model, responsible for binding and unbinding logical links between end users and maintaining an orderly dialog between them.

Severely errored second (SES) – One-second interval where the bit error ratio (BER) exceeds 10-3.
shielded pair – Two insulated wires in a cable wrapped with metallic braid or foil to prevent signal interferences and provide noise-free transmission.

Short haul – Circuit designed for use over distances of less than 200 miles.

Shoutdown line – A point-to-point circuit which permits one station to go off-hook and the conversation is automatically relayed to the distance point; used primarily between single-line telephones which are connected to speakers.

Sideband – Set of frequencies which are produced on either side of the carrier signal as a result of the modulation process. [Upper sidebands (USB) are higher in frequency than the carrier; lower sidebands (LSB) are below the frequency of the carrier. Various modulation techniques make use of one or both of the sidebands.]

Signal – An intentional introduction of energy onto a communications path, resulting in the transmission of information. Contrast with noise.

Signal-to-noise ratio – Relative power of the signal information to the noise in a specified bandwidth, usually expressed in decibels (dB). [As the ratio decreases on a line, it becomes more difficult to distinguish between information and non-information (noise).]

Signaling – (1) Use of signals for communication. (2) Method of conveying signals over a circuit. (3) The exchange of electrical information other than by speech. (4) Means of establishing and controlling connections in a communications network.

Signing Authority – Departmental Staff responsible for authorizing an expenditure.

Simple Network Management Protocol(SNMP) – A protocol used to manage devices on a network.

Simplex – One-way data transmission, with no capability for changing direction.

Singing – (1) An undesired, self-sustaining whistle or howl in an amplified telephone circuit. (2) An occurrence when the sum of the repeater gains exceeds the sum of the circuit losses.

Slope – (1) Difference in attenuation of the various frequencies in a band of frequencies; measured in decibels. (2) Measurement of the frequency response of a channel. See attenuation.

Smart terminal – (1) A display unit that can operate in either conversational or block mode and can support a full range of local editing capabilities. (2) A computer with communications capabilities.

Smooth scrolling - Continuous vertical movement (up or down) of lines of data displayed on a CRT screen, much in the same manner as a credit roll at the end of a movie. Contrast with jump scrolling.

Snapshot – (1) Extract or summary of data taken from a given system. (2) Extract passed to another system to complete processing.

Software – (1) Any of the routines, programs and instructions required to use computers. (2) A written statement of the procedures to be used and the format of the data at every step.

Source – Terminal or node at which data enters a network.

Speakerphone – Telephone equiped with a speaker and a microphone that allows hands-free conversation.

Special grade network trunk - A trunk conditioned to parameters, by providing amplitude and delay equalization for the purpose of handling special services such as medium-speed data (600 to 2400 bps).

Specialized carrier – A company that provides value-added communications facilities to limited geographical areas or for specific services.

Specialized common carrier (SCC) – A company that provides private line services, such as voice, teleprinter, data, facsimile transmission. Synonym : Other Common Carrier.

Speed number - A one-, three- or four-digit number that replaces a seven- or ten-digit telephone number. Numbers programmed into a PBX, the switch in the carrier’s office, or individual smart telephones.

Split screen – Capability of a CRT screen to be divided into two or more independent workspaces.

Standard Industrial Classification (SIC) – U.S. government code that categorizes commercial enterprises. [The first two digits place an organization in one of the 13 major groupings; two additional digits show the primary line of business and size.]

Star - A network topology in which each station is connected only to a central station by a point-to-point link; all stations communicate through the central station.

Star-lan – A local network design and specification within IEE 802.3 standards subcommittee; characterized by data transmission over two-pair twisted-pair wiring.

Start bit – A signal in asynchronous transmission used to signify the beginning of a character or a block of data.

Station – Any input or output points in a communications system capable of sending or receiving messages or calls.

Station message detail recording (SMDR) – A computer generated report showing internal usage on a telephone system; usually includes extension number, trunk number used, phone number dialed, time of call, duration and operator involvement.

Statistical multiplexing – A time-division interleaving technique in which timeslots are dynamically allocated on the basis of need or to equipment with data to be transmitted.

Stop bit – In asynchronous transmission, the bit that indicates the end of a block of data.

Store-and-forward – (1) Technique in which a message is received from the originator and held in storage until a circuit to the addressee becomes available. (2) Transmittal of complete network messages or packets into storage before sending them forward to the next center. (3) Capture of transaction data on magnetic media for subsequent batch input to a computer.

Stored program control (SPC) - A method whereby instructions are placed in the memory of a common controlled switching unit for use as a reference when processing calls. Instructions may include: class marks, code conversions, routing and trouble analysis.

Strap – Hard-wired connection link between two tags, terminals or items of equipment. [A strapping option is one implemented by changing wires.]

Subnet - A computer network composed of all devices whose IP addresses have the same prefix. Dividing a network into subnets is useful for both security and performance reasons.

Supergroup – In frequency division multiplexing (FDM), five channel banks, each containing 12 circuits, combined into a group bank to produce 60 voice channels.

Supermastergroup – In frequency division multiplexing (FDM), 10 group banks are combined to produce 600 voice channels.
supervisory signal – A signal, such as on- or off-hook, which indicates whether a circuit is in use.

Supported product - A product IT Communications Services has experience with and expects to have a reasonably long life cycle. ITD will typically be more efficient at engineering, acquiring, maintaining and repairing equipment in this category and this will be reflected in pricing.

Suspense file – An electronic file or folder in which records are kept until errors or problems are resolved.

Switch – An electronic device which opens or closes circuits, changes operating parameters or selects paths either on a space or time division basis.

Switched 56/64 kbps data transmission – Provides users with the end-to-end capability to transport high-speed data (up to 64 kbps) over the public network.

Switched line – One of a series of lines that can be interconnected to all other lines through a switching center; a line on the public telephone network. Contrast with leased line.

Switched message network – Any network service providing interconnection of message devices such as teletypewriters.

Switched network – A multipoint network with circuit switching capabilities.

Switching center - Location where an incoming call/message is automatically or manually directed to one or more outgoing circuits.

Switching office – Telephone company location housing a switch.

Sync character – Character or defined bit pattern used by a receiving terminal to adjust its clock and achieve synchronization with the master clocking device.

Synchronization – Process of adjusting a receiving terminal or switch clock to match the transmitting system’s master clock.

Synchronous – Having a constant time interval between successive bits, characters or events. [Synchronous transmission uses no redundant information (such as the start and stop bits in asynchronous transmission) to identify the beginning and end of characters; thus it is faster and more efficient than asynchronous transmission.]

Syntax – Rules governing structure in a programming language.

Syntax error – System response to a mistake in its instructions, such as a transposition of characters or an omission of a character or word.

System design – Specifications of the working relations between all the parts of a system in terms of their characteristic actions.

System reliability – Probability that a system will perform its specified task properly under stated conditions of environment.