It's a good time to pray for victims of September 11, 2001 terrorist activities!


S-100 bus 
    A group of 100 parallel common communications lines, each of which is able to carry one bit, or signal, through the entire computer.

    A type of video signal used in Hi8, S-VHS and some laserdisc formats. It transmits luminance and colour portions separately, using multiple wires. S-Video avoids composite video encoding, such as NTSC and the resulting loss of picture quality. Also known as Y-C Video.

    See access (SA)

    See systems application architecture (SAA)

    See Semi Automated Business Research Environment (SABRE)

SAC See single attachment concentrator.
single attachment concentrator (SAC)

SAER See service and equipment record.
service and equipment record (SAER)

SAL See special access line
special access line (SAL)

sample size The number of bits used to store the recorded sound's
amplitudes. It is also referred as Resolution. The sample size is
measured in bits and governs the difference in volume between the
softest sound and the loudest sound that can be recorded and played
back. The sample size of standard audio Cds is 16 bits, and the sample
size for standard broadcast radio is 8 bits. 16-bit audio allows 65,536
loudness levels, whereas, 8-bit audio allows 256 loudness levels.
Combined with sample rate, it provides a measure of how closely a sound
that is recorded and played back will match the original sound source.

sampling The process by which a random or representative set of
elements such as system file transfers or traffic volume is drawn from
the universe of those elements and analyzed to estimate characteristics
of the universal set.

Sampling Rate A measure of how often sound is converted from an analog
waveform to numbers. The sampling rate is measured in samples per
second and governs the highest and lowest frequencies of sound that can
be recorded and reproduced. Standard audio Cds use a sampling rate of
44kHz. The 44.1 kHz sampling rate captures 44,100 (amplitude samples)
picture of sound per second. Combined with sample size, sampling rate
provides a measure of how closely a sound that is recorded and played
back will match the original sound source.

SAP See service access point.
service access point (SAP)

SAPI See service access point identifier.
service access point identifier (SAPI)

SARTS See Switched Access Remote Test System.
Switched Access Remote Test System (SARTS)

SAS See single attachment station.
single attachment station (SAS)

SAT1 The submarine cable between Portugal and South Africa.

satellite communications The use of a satellite with a self-contained
energy source to transmit radio communications signals back to earth.

satellite office A local office or exchange on the low level of a
telephone network hierarchy that is associated with another local
office and has no route-switching functions except toward the
associated higher-level local office. See exchange.
exchange message interface

satellite relay An active or passive repeater, in geosynchronous orbit
around the Earth, that amplifies the signals it receives before
transmitting them back to earth.

saturation testing A program-testing technique that uses a large volume
of messages to expose errors that occur infrequently and can be
triggered by such rare coincidences as two different messages arriving
at the same time. Synonym: volume testing

saved-number redial A feature that allows a station to automatically
redial a previously dialed and saved number.

SC See signaling converter and switching center.
signaling converter (SC)
switching center (SC)

SCA short code address See abbreviated dialing.
abbreviated dialing (AD)

scalability The ability to add power and capability to an existing
system without significant expense or overhead. An "economy of scale"
exists when a small increase in load produces a less-than-linear
increase in overhead. A "dis-economy of scale" exists when a small
increase causes a more-than-linear increase in overhead.

scalable processor architecture reduced instruction set computer
(SPARC) A powerful workstation similar to a RISC workstation.

scalable video With respect to INDEO video, it is a playback format
that can determine the playback capabilities of the computer on which
it is playing. Using this information, allows video playback to
advantage of high performance computer capabilities, while retaining
the ability to play on a lower performance computer.

scattering The signal loss that occurs in fiber-optic transmission when
lightwaves strike molecules and imperfections in the core of the fiber.

SCE See service creation environment.
service creation environment (SCE)

scenario A set of one-or-more typical interaction dialogs between the
users of a system (people or other systems) and a proposed system.
Scenarios are developed during the analysis phase of system development
to assist in understanding business events, objects and interactions.
Scenarios document specific transaction sequences, transformations,
interfaces and information exchange. They represent cases that should
be included in the Software Quality Assurance Test Plan, and they may
be used for end-user training after the system is completed. Use case
scenarios facilitate communication between the people who request a
system, analysts, developers and testers. They are used to validate
understanding, and to identify normal and special use situations.
Scenarios clarify an evolving agreement between requesters and
development teams.

schematic A diagram that specifies the electrical components of a
circuit or system.

scientific visualization Scientific visualization is used to interpret
large amounts of numerical and physical data representing natural
events. It gives researchers visual options for understanding events
and processes. Depending on the dimensions of a project, researchers
choose an appropriate mode of representation, color, texture and other
elements. Synonym: computer modeling

SCOTICE The submarine cable between Scotland and Iceland.

SCP See service control point.
service control point (SCP)

SCPC See single channel per carrier.
single channel per carrier (SCPC)

scrambler A device that deliberately distorts transmitted signals to
make them unintelligible if the receiving end is not equipped with a
descrambling device.

screening The process of wrapping electrical conductors with metallic
foil or braid to insulate the conductors from interference. Synonym:
shielding See shielded twisted-pair.
shielded twisted-pair (STP)

script language Many term programs allow the user to write a program,
or script, which allows them to use the program without actually typing

SCSA See signal computing system architecture.
signal computing system architecture (SCSA)

SCSI See Small Computer System Interface.
Small Computer System Interface (SCSI)

SDA See source data automation.
source data automation

SDH See synchronous digital hierarchy.
synchronous digital hierarchy (SDH)

SDLC See synchronous data link control or Software Development Life
synchronous data link control (SDLC)

SDM See space-division multiplexing.
space-division multiplexing (SDM)

SDN See software-defined network.
software-defined network (SDN)

SDR See special drawing right.
special drawing right (SDR)

SDTM See Statistical Time Division Multiplexing.
statistical time division multiplexer (STDM)

SDU See service data unit.
service data unit (SDU)

SEACOM The submarine cable connecting Singapore, Malaysia, Hong Kong,
Papau New Guinea, and Australia.

seamless integration Refers to a situation in which a caller/user does
not experience any difficulties or interruptions when their call
entails an interconnection between different networks or systems.

SECAM See Sequential And Memory Color Television.
Sequential And Memory Color Television (SECAM)

SECAM Format 625 lines of resolution at 25 frames per second.

secondary channel A transmission channel having a lower rate than a
primary channel in a system where two channels share the same

secondary station A station on a network that has been selected to
receive a transmission from the primary station. The assignment of
secondary status is controlled by the primary station and normally
remains in force for the duration of the transmission.

secretarial intercept A private branch exchange (PBX) feature enabling
a secretary's telephone to accept all of an executive's calls.

section The smallest unit of a SONET service. It is the span between
regenerators and other section-terminating equipment.

sectional center A class 2 switching center. See class of office.
class of office

security Control mechanisms that prevent unauthorized use of resources.

segment A bus LAN term meaning an electrically continuous piece of the
bus. Segments can be joined together using repeaters or bridges.

selection Addressing a terminal or a component on a selective calling

selective calling The ability of a transmitting station to specify, by
the use of assigned codes, which of several stations is to receive a

selective ringing Ringing only the requested party on a party line.

self diagnostics A private branch exchange (PBX) feature allowing the
network to monitor itself for system failures, ensuring fault-free

self-learning bridge See smart bridge.
smart bridge

self-routing See spanning tree algorithm.
spanning tree algorithm (STA)

Semi Automated Business Research Environment (SABRE) An online flight
reservation system, the world's largest privately owned, real-time
computer network. Sabre provides ticket information and purchasing for
more than 600 airlines, 10,000 hotels, and 20 rental-car services
worldwide. See computer reservations system.

send-only codec A video codec able only to originate (transmit)
communications signals, for use at the sending location in
point-to-multipoint or broadcast applications when two-way codec
communication between locations is not possible or required.

sender Equipment that sends out the routing digits and the called

sensitivity The minimum power necessary on an incoming optical signal
for a receiver to be able to read the signal.

sequenced packet exchange (SPX) The Novell Xerox networking system
(XNS) implementation that provides the protocol guaranteed delivery
services which internetwork packet exchange (IPX) does not provide.

sequencing Dividing a data message into discrete units for
transmission. Each unit has its sequentially numbered place in the
whole to facilitate reassembly of the message.

sequential Events that occur in a particular time or code order.

sequential access The method for gaining entry to data through an
ordered succession. Contrast with random access

Sequential And Memory Color Television (SECAM) The television system
used in France and most Eastern European and Middle Eastern countries.
Also known as Systeme Electronique Couleur Avec Memoire (French)

sequential data set Data that is assembled on the basis of its
successive physical position.

serial The processing of successive items through a single facility.

serial access The consecutive transmission of data to or from storage.

serial call Feature that enables an attendant to program a call to
return to the attendant position after the extension to which it was
connected hangs up; the caller can then be connected to another
extension without redialing.

serial interface A mechanism that converts a parallel data arrangement
to a serial form to be used for data transmission.

serial line Internet protocol (SLIP) An Internet protocol (IP) for
connections over telephone lines, RS-232 cables, or other serial lines.
Point-to-point protocol (PPP) is replacing SLIP.

serial transmission A system in which character bits occur serially in
time over a single transmission channel.

server A combination of hardware and software capable of recognizing
and responding to client requests for services such as shared access to
a file system, a printer, or an electronic mail system, to local area
network (LAN) users or clients.

Server Message Block (SMB) A Microsoft - originated distributed system
which enables access to another computer's files and peripherals over
the network as if they were local.

service access point (SAP) The logical address of the specific service
entity to which data must be delivered when it arrives at its

service access point identifier (SAPI) Part of the layer 2 (LAPD)
address that identifies frames to/from a particular service.

service and equipment record (SAER) A list of equipment billed to
customer by type, quantity, monthly charge, location and billing dates.

service area The specific geographic area served by a
telecommunications provider.

service bureau A data processing center that does work such as
timesharing for subscribers.

service code A code, usually of the X11 series, such as 911 or 411 that
customers use to access telephone services.

service control point (SCP) A computer that enables carriers to offer
enhanced services by: 1) Acting on the format, content, code, protocol
or similar aspects of transmitted information. 2) Providing additional
or restructured information. 3) Involving subscriber interaction with
stored data, such as translating 800 numbers to a plain old telephone
service (POTS) number or a trunk group. SCPs connect to signalling
points, which connect to switches.

service creation environment (SCE) A graphical user interface (GUI)
software for entering complex enhanced service specifications.

service data unit (SDU) The unit of data transfer between a service
user and a service provider.

Service Management System (SMS) 1) An IBM interactive information
management system (IMS) that coordinates all national 800 numbers
across all U.S. telephone companies and carriers. It supports IBM 3270
terminal on-line access, batch processing for 800 basic service only,
and a mechanized interface. 2) A system outside of a network that
provides a support interface through which customer data and service
logic in service control points (SCP)s can be added to or managed.
Synonym: SMS/800

service order (SO and S/O) A request to provide communications

service organization Local independent companies or manufacturers that
contract to provide support for equipment supplied by different

service point IBM network management term for a system that allows
non-SNA equipment and network components to be incorporated into an SNA
management structure.

Service Provisioning Measurement Plan (SPMP) Based on monthly
interviews with approximately 20,000 customers who have initiated
orders for service (e.g., installation or repair) and the work has been
completed. Customers are asked if they were satisfied with access to
the Business Office/Customer Service Center, appointment convenience,
as well as employee courtesy, helpfulness, professionalism and
workmanship. Their reaction is one element in determining whether or
not Bell is meeting its quality of service standards.

service switching point A central office switching system with software
to recognize a variety of triggers within customer signals and, based
on these triggers, to generate queries to SCPs. Then they use
information from SCPs to process calls.

service terminal The equipment required to terminate a channel and
connect to the telephone equipment or customer terminal.

service type A classification of the service(s) requested on a service
order such as voice frequency (VF), digital data service (DDS), DS-1,
or DS-3.

services 1) A general term for resources made available by a server to
other nodes on the network. In Microsoft LAN Manager terminology, this
concept is broadened to include all main components of the LAN Manager
software. 2) A set of functions provided by one layer of an open
system, for use by a higher layer or sublayer entity or by management
entities. See open systems interconnection.
open systems interconnection (OSI)

serving translations scheme A method used in translating an 800 number
to a plain old telephone service (POTS) number or trunk group.

serving wire Telephone number or plain old telephone service (POTS)

serving wire center Designated area code/exchange (NPA/NXX). See
central office.

SES See severely errored second.
severely errored second (SES)

SESS See Scheduling Executor Server System.

session 1) A connection between two devices or stations that permits
them to communicate. 2) The time interval during which a terminal user
can communicate with an interactive system. 3) A logical network
connection between two workstations, such as a user station and a
server, for the exchange of data. It is possible to have more than one
session going between two devices simultaneously.

session layer The fifth layer in the open systems interconnection (OSI)
is responsible for binding and unbinding logical links between users.
It manages, maintains, and controls the dialogue between the users of
the service. See open systems interconnection.
open systems interconnection (OSI)

set computing An internal computing architecture in which processor
instructions are pared down so that most can be performed in a single
processor cycle.

severely errored second (SES) (DS1) A second which has an equivalent
error ratio greater than 1-in-1,000. In SF, a second with one or more
LOSs or frame sync losses, six or more framing bit errors, or 1,544 or
more BPVs. In ESF, a second with one or more LOSs or frame sync losses,
320 or more CRC-6 errors, or 1,544 or more BPVs. On unframed circuits,
a circuit with one or more LOSs, or 1,544 or more BPVs.

SF See super frame.
super frame (SF)

SF signaling See single-frequency signaling.
single-frequency signaling (SFS)

SFS See single-frequency signaling.
single-frequency signaling (SFS)

SG See supergroup.
supergroup (SG)

SGMP See Simple Gateway Monitoring Protocol.
Simple Gateway Monitoring Protocol (SGMP)

SGNT See special grade network trunk.
special grade network trunk (SGNT)

shannon equation A formula that uses signal-to-noise ratio and
bandwidth for determining the maximum rate of transmission.

shared network facilities agreements Agreements between the Bell
operating companies (BOCs) and AT&T for the sharing of facilities which
would be used for both interLATA and intraLATA service after
divestiture. The company that makes predominant use of the facilities,
the relevant BOC or AT&T, owns the facilities but shares them with the
other party.

shared tenant service (STS) The provision of private branch exchange
(PBX) services to multiple customers located in the same building,
campus or group of buildings. External calls can be placed and received
over common lines and intracompany calls can be made without the use of
outside telephone lines. State regulations frequently restrict the
provision of STS to protect local exchange carrier (LEC) interests.
This service is frequently provided by a landlord.

sharing The use, by two or more persons, of telecommunications services
jointly leased or purchased from a telecommunications carrier.

SharkMail A Windows mail client that was specifically developed for
Banyan VINES users as an alternative to the default VINES mail client.

sheath The outer jacket surrounding copper and fiber cables that
prevents water damage to the cables inside.

SHEFA The submarine cable between the Shetland Islands and the Faeroe

SHF See super high frequency.
super high frequency (SHF)

shielded pair See shielded twisted-pair.
shielded twisted-pair (STP)

shielded twisted-pair (STP) Twisted-pair cabling covered with an
additional protective metallic foil to help prevent data transmission
errors caused by electro-magnetic fields. Synonym: twisted-pair cable

short code address (SCA) See abbreviated dialing.
abbreviated dialing (AD)

short haul Circuits designed for use over distances of 10-200 miles.

short-haul facilities Facilities that stay within the digital serving
area. Can provide intrastate or interstate services with distances
typically less than 50 miles.

shout down See hoot-n-holler.

shutdown A complete termination of computer software and/or hardware.

sideband The frequency bands above and below the carrier frequency. The
frequencies of the wave produced by modulation fall within the

sidestream network management A method of controlling and diagnosing
networks that relies on modems and multiplexers to monitor components
in the analog portion of the network. Some can also check the digital

sidetone The equipment in a telephone handset that lets a user to hear
his or her own voice while talking on the telephone.

SIG See Special Interest Group.
Special Interest Group (SIG)

signal An event-oriented change in state, such as a tone, frequency
shift, binary value, alarm, or message.

signal computing system architecture (SCSA) An industry standard
architecture from Dialogic Corp. SCSA integrates multiple technologies
through an open, non-proprietary, specification for developing
integrated voice response (IVR) systems.

signal control See audible signal control.
audible signal control

signal element Each part of a digital signal, distinguished from others
by its duration, position, and/or sense. A signal element can be a
start, information, or stop element.

signal loss A received signal that has 125 plus or minus 25 consecutive
zeros. Or, the signal is of a received level less than 32 dB below the
DSX level.

Signal Quality Error (Test) (SQE(T)) A function of transceivers
immediately after its' attached computer has transmitted on to the LAN.
The transceiver sends a simple test signal over the AUI back to the
computer, ensuring the computer knows it has a working connection.
Because it acts as a confidence check and "pulses" down the line, it is
also called a heartbeat.

signal status The absence or presence of a signal.

signal-level 1 (STS-1) An electrical signal that is converted to or
from a SONET optically based signal. STS-1 is equivalent to the OC-1
signal of 51.84M bits per seconds.

signal-to-noise ratio (SNR) The ratio of signal power to noise power in
a specified bandwidth, usually expressed in decibels.

signaling The transmission of address and other switching information
between stations and central offices and between various central

signaling converter (SC) A device that transforms signals to different
types of electrical systems without changing the information. Signal
converters are used at the terminal of a trunk to convert equipment
signals to the system used on the trunk. For example, ringdown signals
are converted to Super Frame (SF) or E&M to signals are converted to

signaling equipment Devices that generate an audible signal, such as
tone generators, tone detection devices, and so forth.

Signaling System 7 (SS7) 1) International common-channel signalling
system recommendations established by the Consultative Committee for
International Telephone and Telegraph (CCITT). 2) An addressing
protocol that speeds up call processing by operating out of band.
Includes fraud detection, caller ID, store and forward, ring back,
concurrent data, and so forth.

Signaling Transfer Point (STP) A packet switch optimized for SS7
message handling.

Simple Gateway Monitoring Protocol (SGMP) A predecessor of SNMP.

simple mail transfer protocol (SMTP) The protocol in a transmission
control protocol/Internet protocol (TCP/IP) network that describes how
e-mail moves between hosts and users.

simplex One way transmission path, with no response of any kind.

simplex circuit A circuit using ground return and permitting
communications in either direction-one direction at a time. See

simplex signaling (SX) Signaling using two conductors for a single
channel. A center tapped coil or its equivalent is used at both ends
for this purpose.

SIMSCRIPT A programming language utilized for discrete simulation.

simulation A model that uses physical and mathematical quantities to
portray a real-life situation. For example, a computer model of a
chemical process.

Simultaneous Peripheral Operation On Line (SPOOL) A program or device
that controls the flow of data to an outputting device such as a
printer. Spooling means that a user can send data to a device which is
already occupied and can rest assured that the data will be passed onto
the desired destination as soon as possible. Spooling of printer output
is achieved on a LAN by means of a print server. It is also important
in WANs for providing a buffer for time non-critical applications such
as Electronic Mail and File Transfer.

simultaneous voice and data transmission The capability of a telephone
set to simultaneously transmit voice and data signals.

singing A continued whistle or howl in an amplified telephone circuit.
Singing occurs when the sum of the repeater gains exceeds the sum of
the circuit losses.

singing return loss (SRL) The difference in dB, between the level of
two separate composite-frequency signals sent into a circuit and the
level of the echo of that signal as it reaches the point of
application. The SRL-LO composite-frequency signal normally contains
spectral distributions between 260 Hz and 500 Hz at equal amplitudes.
The SRL-HI composite-frequency signal normally contains spectral
distributions between 2200 Hz and 34000 Hz at equal amplitudes.

single attachment concentrator (SAC) A concentrator that offers one
slave port for attachment to the fiber-distributed data interface
(FDDI) network and multiple-master ports for the attachment of stations
or other concentrators.

single attachment station (SAS) A fiber-distributed data interface
(FDDI) station that offers one slave port for attachment to the FDDI
network. An SAS is connected to the FDDI ring through a concentrator.

single channel per carrier (SCPC) A high-speed, satellite data
communications system using digital encoding and phase-shift keying
(PSK) to handle larger data volumes in narrower bandwidths than FM

single sideband radio (SSB) A form of amplitude modulation of a radio
signal in which only one of the two sidebands is transmitted. Either of
the two sidebands may be transmitted, and the carrier may be
transmitted, reduced, or suppressed.

single speed A CD-ROM drive that accesses data at a speed of 150kB per
second. This is the speed at which standard audio Cds can be read.
Single speed was the standard speed for CD-ROM drives. As of today,
speeds ranging up to 16 and above are common.

single threading The process of completing all programs or messages
before starting the next one.

single-digit dialing An accelerated version of speed dialing that
allows a preselected group of stations to be reached by dialing a
single digit.

single-ended testing A test equipment configuration used for
cooperative testing between test units at two points on the circuit.

Single-Frequency (SF) signaling A method of conveying dial-pulse and
supervision signals from one end of a trunk or line to the other. This
method uses the presence or absence of a single specified frequency
(usually 2600 Hz).

single-frequency signaling (SFS) A signaling system that uses a 2,600
Hz in-band signal on the voice path. The tone is on in the idle
condition, pulsed for dialing, and off when the circuit is in use.

single-mode fiber An optical waveguide that carries only the single
wavelength chosen for transmission.

single-point circuit A private line that has one interexchange carrier
(IEC) leg from one point of presence (POP) to another.

single-sideband transmission See single-sideband radio.
single sideband radio (SSB)

singlemode See single-mode fiber.
single-mode fiber

sink The portion of a communications system that receives or accepts
information from a transmission device.

SIR See Speaker Independent (Voice) Recognition.
Speaker Independent (Voice) Recognition (SIR)

SL-1 The trade name for a Northern Telecom private branch exchange
(PBX) system

slam The act of changing a customer's presubscribed primary interchange
carrier (PIC) without the customer's permission. Slamming is often the
result of using telemarketing salespeople to market long-distance
service to residential and small business subscribers. A regional Bell
operating company (RBOC) slam fee must be paid for each slam.

slamming dispute A situation in which a customer whose long distance
service has been changed without their knowledge or without their
authorization. The customer should call their preferred carrier who can
initiate a resolution of the disagreement on their behalf. The long
distance company that "slammed" the customer is assessed a "slamming
fee" if it is unable to produce appropriate authorization within 15
days following initiation of a dispute. See slam.

slave station In a data communications network, the station that is
selected and controlled by a master station. The slave station can
usually only call or be called by the master station.

SLCC See subscriber line carrier circuit.
subscriber line carrier circuit (SLCC)

SLCD A proprietary interface developed and used by Sony to connect Sony
CD-ROM drives to a PC.

sleeve A tubular covering, of lead, plastic, bronze, or copper, used
over splices, cables or outer contacts of switchboard plugs.

SLIP See serial line Internet protocol.
serial line Internet protocol (SLIP)

slotted ring A LAN architecture in which a constant number of fixed
length slots (packets) circulate continuously around the ring. A
full/empty indicator within the slot header indicates when a station
can place information into the slot.

slotting The process of assigning a circuit to available channel
capacity across the network during the circuit design process.

Small Computer System Interface (SCSI) An industry standard connection
for hardware devices.

smart bridge A bridge that reads the source address of received packets
and develops routing tables from those addresses.

smart hub A twisted-pair concentrator used in Ethernet or ARCnet
networks. A smart hub has built-in network management facilities that
allow a network manager to control and monitor the network performance,
as well as to plan network configuration.

smart terminal See intelligent workstation.
intelligent workstation

Smart Video Recorder Intel's PC Video single step compression,
real-time video capture card that uses Indeo software technology and an
Intel i750 processor.

Smart wiring hub A network concentrator enabling multiple media to be
supported and managed from a central location. When supporting
structured wiring systems, smart hubs provide port management.

SMARTEST A REACT option that enables testers to schedule automatic,
unattended testing.

smartjack An interface connector which provides T1 loopbacks at the
network interface. Used in place of or along with channel service units
at the customer's site.

SMAS See Switched Maintenance Access System.
Switched Maintenance Access System (SMAS)

SMB See Server Message Block.
Server Message Block (SMB)

SMDR See station message detail recording.
station message detail recording (SMDR)

SMDS See switched multi-megabit data services.
switched multi-megabit data services (SMDS)

SMG See supermastergroup.
supermastergroup (SMG)

SMPTE Society of Motion Picture and Television Engineers

SMS See Service Management System and responsible organization.
Service Management System (SMS)
responsible organization (RO and resporg)

SMS complete The date that the Service Management System (SMS) is
notified to activate an 800 number.

SMS customer record All the information related to one 800 number,
effective date and time, and so forth.

SMS FID See SMS field identifier.
SMS field identifier (SMS FID)

SMS field identifier (SMS FID) Specifies the type of information needed
in each field (variable) in a Service Management System (SMS) customer

SMS time The Service Management System (SMS) operates on the prevailing
U.S. Central Time: Central Standard Time (CST) in the winter and
Central Daylight Savings Time (CDT) in the summer. SMS users enter
local time and suffix their local zone, and SMS converts the local time
to Central time. When a user enters 10:00A/E for ten A.M. Eastern time
zone, SMS converts that time to 9:00A/C, or nine A.M. Central time

SMS/800 An IBM information management system (IMS) interactive computer
system that coordinates all national 800 numbers across all U.S.
telephone companies and carriers. It supports IBM 3270 terminal on-line
access, batch processing (for 800 basic service only), and a mechanized
interface. See Service Management System and responsible organization.
Service Management System (SMS)
responsible organization (RO and resporg)

SMT See station management.
station management (SMT)

SMTP See simple mail transfer protocol.
simple mail transfer protocol (SMTP)

SNA See Systems Network Architecture.
Systems Network Architecture (SNA)

SNA Distribution Services (SNADS) A standardized asynchronous
distribution service architecture for the transmission of files or jobs
around an IBM SNA network. It is implemented as a transaction service
of the SNA network.

SNA Network Interconnect (SNI) (In IBM SNA) The way in which autonomous
SNA networks can be connected, while still allowing them to be
independently managed.

SNADS See SNA Distribution Services.
SNA Distribution Services (SNADS)

SNFA See shared network facilities agreements.
shared network facilities agreements

SNI See SNA Network Interconnect or Subscriber-Network Interface.
SNA Network Interconnect (SNI)
Subscriber-Network Interface (SNI)

SNMP See simple network management protocol , WilView/Simple Network
Management Protocol, or Simple Network Management Protocol (SNMP)

SNMPv2 A combination of two proposed updates to SNMP: Secure SNMP and
Simple Management Protocol. Its 12 documents and 400 pages define
everything from SMI to a Manager-to-Manager MIB, plus much-needed
security improvements.

SNPA See subnetwork point of attachment.
subnetwork point of attachment (SNPA)

SNR See signal-to-noise ratio.
signal-to-noise ratio (SNR)

SO or S/O See service order or switching office.
service order (SO and S/O)
switching office (SO and S/O)

Society for Worldwide Interbank Financial Telecommunications (SWIFT) A
communications network that connects most of the banks and financial
institutions worldwide.

Socket A package of subroutines that provides access to transmission
control protocol/ Internet protocol (TCP/IP) on most systems.

software Computer programs, procedures, rules and any associated
documentation needed for the operation of a computer system.

software quality assurance (SQA) A formal approach to software
development, automated regression testing, configuration management,
versioning, profiling and release control with the goal of zero

software-defined network (SDN) A switched long-distance service for
very large users with multiple locations. Instead of putting together
their own network, large users can get special usage rates for calls
carried on regular switched long-distance lines. Synonym: virtual
private network

solid-state Pertaining to the use of semiconductors rather than
electromechanical relays and electron tubes.

SONET See synchronous optical network.
synchronous optical network (SONET)

sort To arrange in sequence by type, class, state, value, and so forth.

sound file In terms of the World Wide Web (WWW), a sound file is a
computer file containing digitised sound that can be retrieved by a Web
browser. These files can only be heard through player software
associated with the browser.

source address The part of a message, usually a collection of
characters or bits, that indicates the origination, or source, of the

source address filtering A feature of some bridges that always forwards
or always rejects messages from designated source addresses.

source code A collection of computer programming commands that defines
the behaviors (processes, operations, methods, functions) of computer
systems and applications.

source data automation A method for reusing recorded, coded data.

source routing A method used by a bridge for moving data between two
networks. Originally developed by IBM for Token-Ring networks, source
routing relies on information contained within the token to route the
packet between the two networks. For source routing to work, every
computer and every bridge on all networks must support this protocol.
See bridge. Compare with transparent routing.

source routing transparent (SRT) SRT is a Token-Ring bridging standard
jointly sponsored by the Institute of Electrical and Electronic
Engineers (IEEE) and IBM. It combines IBM Source Routing and
Transparent Bridging under IEEE 802.1 in the same unit. SRT provides
universal bridging of Token-Ring local area networks (LANs) supporting
IBM and all non-IBM LAN protocols. An SRT bridge examines each data
packet on the ring to discover whether the packet is using a source
routing or nonsource routing protocol. It then applies the appropriate
bridging method. See bridge, source routing, and transparent routing.
source routing
transparent routing

space 1) An impulse that, in a neutral circuit, causes the loop to open
or causes absence of signal. In a polar circuit, it causes the loop
current to flow in a direction opposite to that of a mark impulse. A
space impulse is equivalent to a binary 0. 2) In some codes, a space is
a character that causes a printer to leave a character width with no
printed symbol.

space segment In satellite communications, the free space, or
atmosphere, transmission media.

space-diversity A method of transmission and reception that reduces
signal fading by using two antennas, one below the other, on a signal

space-division multiplexing (SDM) The transmission of signals over
discrete voice paths.

space-division switching A switching method that uses a physically
separated set of matrix contacts to determine single transmission path
routing. The switching of inlets to outlets using space division

spanning tree A method of creating a loop-free logical topology on an
extended local area network (LAN). Formation of a spanning tree
topology for transmission of messages across bridges is based on the
spanning tree algorithm defined in the the Institute of Electrical and
Electronic Engineers (IEEE) 802.1d specification.

spanning tree algorithm (STA) The standard for bridge-to-bridge
communications, the Institute of Electrical and Electronic Engineers
(IEEE) 802.1, makes it possible to automatically update routes as an
organization adds or deletes bridges from a network. STA allows bridge
products from different vendors to communicate.

SPARC See scalable processor architecture reduced instruction set
scalable processor architecture reduced instruction set computer

spatial filtering In video compression, removal of redundant
information on a line by line basis by discarding diagonally-adjacent
pixels. Also known as field subsampling, loop filtering, H.261 usage.

SPC See stored program control.
stored program control (SPC)

Speaker Independent (Voice) Recognition (SIR) Technologies for the
automated conversion of speech to accurate and meaningful textual
information, typically ASCII. It typically accepts input from callers
to voice processors where callers are using rotary dial instead of DTMF
phones. SIR products have deliberately limited vocabularies, but are
increasing due to the vast installed base of non-DTMF phones.

speaker phone A telephone with a built in speaker and a microphone for
hands-free operation.

special access line (SAL) 1) A class of local exchange carrier (LEC)
service that provides the link from the customer's premises to an
interexchange carrier (IEC). Point of presence (POP) for non-switched,
dedicated circuits. 2) The private line local access, private line
entrance facilities, and other LEC-provided private line services.
Special access is used at the closed end of a circuit, such as a wide
area telecommunications service (WATS) line.

special character A character that is neither alphabetic nor numeric.

special drawing right (SDR) An international standard monetary unit
based on a basket of currencies. It is used in international
transactions such as settlement payments made between
telecommunications correspondents. The approximate value as of early
1993 was $1.38 per SDR.

special grade network trunk (SGNT) A trunk specially conditioned by
providing amplitude and delay equalization for the purpose of handling
special services such as medium-speed data in the range of 600 to 2400

Special Interest Group (SIG) This is similar to a message base but it
may also contain files.

special needs customer A person who may not have the ability to lift or
hold a telephone handset, to dial, to hear another person's voice and
the ringing telephone, or to speak at a level which can be heard

special temporary authority (STA) A temporary authorization issued by
the Federal Communications Commission (FCC), such as temporary
authority to operate a microwave transmitter. An STA is usually granted
after an application has been filed but before final approval has been

special-purpose computer A computer designed to manage only a certain
function or a specific range of problems.

specialized common carrier (SCC) See other common carrier.
other common carrier (OCC)

spectrum A continuous, wide range of frequencies, within which waves
have some specific, common characteristic.

speech circuit A circuit designed for analog or encoded speech
transmission at a bandwidth between 300 Hz and 3000 Hz. It can be used
for data or for telegraph transmission as well.

speech concatenation Voice processing term for economical digitized
speech playback. It uses independently recorded files of phrases or
file segments linked under application program control to produce a
customized response in natural sounding language. Examples could be
bank balances or bus schedules. It is done for speed and economy,
lending itself to limited, structured vocabularies that are best stored
in ram or readily accessible from disk.

speed dialing See abbreviated dialing.
abbreviated dialing (AD)

speed number A one-, three-, or four-digit number that replaces a
seven- or ten-digit telephone number. These numbers are programmed into
the switch in the carrier's office or in a private branch exchange

speed plus A technique used to combine voice and data on the same line
by assigning the top part of the normal voice bandwidth to data.

splash A method of transferring a call, by operator intervention, to
another carrier for billing purposes while the call is still being
carried on our network. Do not confuse splash with the redirect method.

split access to outgoing trunks Access using one trunk-access code, to
two separate groups of outward dialing trunks.

split-access testing Testing in either a loopback or single-end
configuration that disrupts the signal being tested.

splits See gate assignments.
gate assignments

splitter An analog device that divides one input signal into two output
signals or combines two input signals into one output signal. Splitting
is used in three topologies in community antenna television (CATV) or
broadband local area networks (LANs).

splitting A feature that allows an attendant to talk privately with one
party on a call without the other party hearing.

SPMP See Service Provisioning Measurement Plan.
Service Provisioning Measurement Plan (SPMP)

spoofing A method of fooling network end stations into believing that
keep-alive signals have come from and return to the host. Polls are
received and returned locally at either end of the network and are
transmitted only over the open network if there is a condition change.
The result is a non-time critical network with a minimum of keep-alive
traffic between deterministic end stations, while retaining the
opportunity to send flags should an end station alter its state. The
synchronous approach harks back to unreliable circuits and the need to
check end station existence at regular intervals. Now networks are more
reliable, spoofing by routers is an acceptable compromise.

SPOOL See Simultaneous Peripheral Operation On Line.
Simultaneous Peripheral Operation On Line (SPOOL)

spooling A technique in which output to slow devices, such as printers,
is placed in a RAM storage queue to await transmission and processing,
giving the user access to the system while waiting for the data to be

spot beam antenna A satellite antenna able to concentrate on a limited
portion of the earth's surface.

spread spectrum A method of modulating or changing a data signal so
that it occupies more of the radio band than it needs to transmit the
information. This spreading of the data makes the signal secure from
eavesdropping and protects it from outside interference. Another
spread-spectrum benefit is that it uses portions of the electromagnetic
spectrum known as the industrial/scientific/medical (ISM) bands. The
ISM bands cover the frequencies of 902 MHz to 928 MHZ and 2.4GHz to
2.484GH, and they do not require an FCC license. See shannon equation.
shannon equation

SPX See sequenced packet exchange.
sequenced packet exchange (SPX)

SQA See software quality assurance.
software quality assurance (SQA)

SQCIF See Sub-Quarter Common Intermediate Format.
Sub-Quarter Common Intermediate Format (SQCIF)

SQE(T) See Signal Quality Error (Test).
Signal Quality Error (Test) (SQE(T))

SQL See structured query language.
structured query language (SQL)

SRAM See static random access memory.
static random access memory

SRL See singing return loss.
singing return loss (SRL)

SRT See source routing transparent.
source routing transparent (SRT)

SS See supervisory signals.
supervisory signals (SS)

SS7 See Signaling System 7.
Signaling System 7 (SS7)

SSB See single sideband radio.
single sideband radio (SSB)

SSCP See systems service control point.
systems services control point (SSCP)

SSN See switched service network.
switched service network (SSN)

SSP See service switching point.
service switching point

ST connector One type of connector used for terminating optical fibers.

ST-II See stream protocol 2.
stream protocol 2 (ST-II)

STA See special temporary authority.
special temporary authority (STA)

stable state In a trigger circuit, the state in which the circuit
remains until the application of a suitable pulse.

stand alone Any device that functions independently.

standalone server In LAN Manager terminology, a server that maintains
its own user accounts database and does not participate in logon

star A network topology in which each station connects only to a
central station (hub) by a point-to-point link and communicates with
all other stations through the central station. If the hub fails, the
entire network fails. In a local area network (LAN), the hub is likely
to be a workstation; in larger, multiport networks, the hub is more
likely to be a multiplexer.

star network See star topology.
star topology

star topology A network interconnection scheme in which one central
node, or hub, has links to all the other nodes, which have no direct
connections to each other.

StarLAN The AT&T local area network that transmits data at l Mbits per
second over unshielded twisted-pair wires.

start bit See start element.
start element

start element The first element of a character in certain serial
transmissions; it allows for synchronization. In Baudot teletypewriter
operation, it is one space bit.

start/stop transmission Asynchronous transmission in which each byte or
character is preceded by a start signal and followed by a stop signal.
See asynchronous transmission.
asynchronous transmission

state One of the 50 states, a territory or a possession of the United
States of America or the District of Columbia.

state tax A collection of tax types that each state is allowed to
charge. Tax jurisdiction is the state's authority to charge tax for a
call. Tax jurisdiction is based on the two-out-of-three rule: where the
call originates, where it terminates, and where it is being billed. If
two match, that state charges the tax.

static random access memory Random access memory that retains recorded
information after main power is switched off by using a battery that
supplies the minimum current necessary to refresh the system.

static routing A routing method in which the network manager
permanently configures the routing table; the paths on the network do
not change.

station 1) An addressable logical and physical node on a
fiber-distributed data interface (FDDI) ring capable of transmitting,
repeating, and receiving information. A station has one instance of
station management (SMT), at least one instance of physical layer
protocol (PHY) and physical-layer media-dependent (PMD), and an
optional media access control (MAC) entity. 2) Any customer location on
a network capable of sending or receiving messages or calls. 3) A
terminal for originating or receiving communications, such as a

station address A group of alphanumeric characters that uniquely
identifies a station on a network. Data transmitted to a station uses
the station address as a destination address, while a message
transmitted from a station uses the station address as the source

station busy lamp See busy lamp field.
busy lamp field (BLF)

station busy-out See attendant station busy-out.
attendant station busy-out

station camp-on A telephone that can queue onto a busy line; it signals
the busy station that there is a call waiting.

station equipment The telephone equipment and services provided to

station hunting A method of routing calls to an idle station in a
prearranged group when the dialed station is busy.

station line A line between an individual extension and a private
branch exchange (PBX) or key system. It may also refer to an internal
circuit that can be connected to a PBX switchboard.

station loop The wiring between a station and the switching device, for
example, between a telephone set and a PBX.

station management (SMT) Software and hardware in the fiber-distributed
data interface (FDDI) specification that provide control at the station
level to manage processes to ensure that the station may work
cooperatively on a network.

station message detail recording (SMDR) A computer generated report
showing internal usage on a telephone system or private branch exchange
(PBX). SMDRs usually includes extension number, trunk number used,
telephone number dialed, time of call, duration and operator
involvement. In contrast to automatic identified outward dialing
(AIOD), it can also track local and toll-free calls. Synonyms:
automatic message accounting and call detail recording 2) The
definition is changing to refer to the RS-232-C port on the back of
most modern PBXs.

station message registers Counting devices that centrally record each
station's outgoing calls.

station override security A security feature that shields specific
telephones from executive override.

station rearrangement and change A feature that permits a user to move
telephones, alter features, or restrictions to certain stations or to
initiate other features.

station release See automatic station release.
automatic station release

station tone ringing An electronic, rather than mechanical bell, on a

station transfer security A feature that automatically routes an
unanswered, transferred call to the attendant.

station-busy override A telephone with the ability to override a busy
signal and break into a conversation.

station-to-station 1) A normal long-distance telephone call that is
billed if anyone answers. 2) The rate charged when the caller will
speak to anyone at the number being called.

station-to-station camp-on See camp-on.

station-to-station dialing Any directly dialed telephone call.

statistical multiplexer A device which combines a number of
time-varying bit streams into a single bit stream for transmission. In
DBS, may dynamically allocate bandwidth through control signals to
MPEG2 video codecs.

statistical multiplexing A technique for multiplexing a channel to
simultaneously process multiple data communications transmissions; a
channel is assigned to a communications device only if it actually has
data to send or receive.

statistical time division multiplexer (STDM) A variable allocation
system that allows several terminal devices to share the resources of
the digital high-speed link on an as-needed basis. STDMs operate on the
premise that communications links between computers and terminals are
rarely used 100 percent of the time. STDMs use real-time statistics to
allocate capacity on the high-speed link only to those terminals that
are actively sending information.

statmux See statistical time division multiplexer.
statistical time division multiplexer (STDM)

status code Object, class, or instance-state codes that have an
enumerated list of possible values.

status indication See line status indication.
line status indication

STD See subscriber trunk dialing.
subscriber trunk dialing

STDM See statistical time division multiplexer.
statistical time division multiplexer (STDM)

Stentor (Canada) The Stentor Alliance was formed in 1992 by Canada's
leading telecommunications services providers. The Alliance works with
customers across Canada to economically deliver leading-edge local,
national and international telecommunications services. These companies
maintain the world's longest, fully digital, fiber optic network. This
network forms the backbone of a Canadian information highway which the
Alliance is committed to completing by the year 2005 under the Beacon
initiative. The members of the Alliance are: Alberta Government
Telephones (AGT); Bell Canada; British Columbia Telephone Company (B.C.
Tel); The Island Telephone Company Limited; Manitoba Telephone System
(MTS); Maritime Telegraph and Telephone Company Limited (MT&T);
Newfoundland Telephone Company Limited; New Brunswick Telephone Company
Limited (NBTel); and SaskTel. Québec Téléphone and NorthwesTel are
associate members of the Stentor Alliance.

step call A feature that allows a caller to transfer a call to a busy
number to a nearby idle telephone by dialing an additional digit.

step index A characteristic of fiber-optic cable in which the
refractive index of the core material is uniform. A sudden change, or
step, of the refractive index exists at the core-cladding boundary.

step-by-step exchange (SXS) An electromechanical type of central office
that uses switching steps working one after another, independently of
the state of the following steps.

stochastic network See nondeterministic network.
nondeterministic network

stop bit See stop element.
stop element

stop element The last element of a character in an asynchronous serial
transmission; it is used to ensure recognition of the next start
element. In Baudot teletypewriter operation, it is 1.42 mark bits.

storage A term used to describe any device (generally electronic or
magnetic) capable of retaining information.

storage protection Limiting access to a storage device to prevent files
from being written over or destroyed.

store-and-forward The technique of receiving a message, storing it
until an outgoing line is available, then retransmitting it, with no
direct connection between incoming and outgoing lines. Synonyms: line
switching and message switching

stored program control (SPC) A technique that programs the memory of a
common controlled switching unit to provide processing instructions
relating to class marks, code conversions, routing, and trouble

STP See shielded twisted-pair or Signaling Transfer Point.
shielded twisted-pair (STP)
Signaling Transfer Point (STP)

straightaway test Tests in which the transmitter and receiver are
connected to physically different points of a circuit under test,
usually in different offices. The transmitter originates tests on the
circuit, and the receiver displays the results. This differs from
loopback testing, in which the transmitter and the receiver are at the
same point.

straightforward outward A feature that allows an attendant to place an
outgoing call completion for a station user without requiring the
station user to hang up and redial the operator.

stream protocol 2 (ST-II) A revised protocol built on top of IP for
audio-visual and reserved-resource applications and services.

streaming Nonstop transmission of signals down a data line, from a
defective piece of equipment, such as a modem. Streaming equipment ties
up a multipoint circuit with false signals and prevents other equipment
from using the circuit.

StreetTalk The VINES naming system that identifies every user and
component of a network. A StreetTalk name consists of three parts, each
separated by an at sign (@). The three parts are Item Name, Group Name,
and Organization Name.

stress test A data test pattern used to determine a circuit's ability
to accurately carry digital signals with a "low ones density."

structured query language (SQL) 1) A standard language for database
access. It is evolving as a database standard for client/server
computing. 2) The relational database management system (RDBMS)
interface language. Major commands of SQL are: insert, select, update,
delete, and so forth. Object-oriented database management systems
(ODBMSs) use some form of object-oriented structured query language

STS See shared tenant service, synchronous transport signals, or
serving translations scheme.
shared tenant service (STS)
synchronous transport signal (STS)
serving translations scheme

stuck beacon The condition in token-passing networks where a station is
locked into sending continuous beacon frames.

stunt box A device used to control the nonprinting functions of a
teletypewriter terminal, such as carriage return and line feed.

Sub-Area Network The original hierarchical approach used in the
construction of IBM SNA backbone networks. The structure of a Sub-Area
Network is predefined. The relationship between the components of the
network and the links is generated into the software in the host
systems involved. The network can, however, be modified without having
to re-build the definition of the entire network. A new node can de
added by defining it in the adjacent nodes to which it is directly
attached. Such a network is constructed around a backbone of
communications controllers to which the host systems are attached.

Sub-Quarter Common Intermediate Format (SQCIF) Describes a subset of
the type of coded video signals transmitted when using ITU-T Rec. H.261
and H.263 coding methods. See CIF.

subchannel The result of subdividing a communications channel into
narrower bandwidth channels. See bandsplit.

subclass A group of similar objects that is derived from a superclass.

subcomponent A part of an assembly or a system.

subnet A portion of a network partitioned by a router.

subnet address An extension of an Internet protocol (IP) address that
allows a network to be autonomous by itself and still be a subsection
of a larger user network.

subnetwork point of attachment (SNPA) The address where the subnetwork
routes data units through the subnetwork and delivers them to the
intended DTE.

subprogram A program that is implemented by another program.

subrate digital multiplexer A unit in the hub office that combines
several data streams at or below some basic rate (2.4, 4.8, 9.6, or 56
kbps) into a single 64-kbps (DS0B) signal.

subrate frame slip A slip that occurs when a subrate framing bit is
lost or duplicated, but the framing pattern integrity is otherwise

subrate framing errors Incorrect framing bits from the DS0B signal
under test.

subscriber The customer of a local telephone company or interexchange
carrier. Synonyms: end user, customer, and local user

subscriber line The telephone line that connects a local telephone
company to the subscriber's telephone system or medium.

subscriber line carrier circuit (SLCC) A system that allows one pair of
copper wires to carry multiple conversations. SLCC is used between
central offices and areas that have outgrown the original cable serving
the area.

subscriber loop A circuit, usually a pair of wires, that links a
central office (CO) to a demarcation point on a customer's property.

subscriber trunk dialing A non-American term for direct distance

Subscriber-Network Interface (SNI) User-to-Network Interface (UNI)
defined specifically for SMDS. Based on the the Institute of Electrical
and Electronic Engineers (IEEE) 802.6 access protocol, present Layer 1
speeds are subrate (N X 64 kbps), DS1 (1.544 Mbps), and DS3 (44.736
Mbps). Interfaces for the future are expected to follow the
Broadband-ISDN access rates of 155 Mbps.

subsynchronous orbit satellite A satellite in orbit at a lower altitude
than the 35,880 kilometers (22,300 miles) required for a synchronous
equatorial orbit.

subsystem A secondary system able to work independently or
asynchronously with the primary system.

subvoice-grade channel A channel of narrow bandwidth, unable to manage
voice communications, that is used for slow data communications and

super frame (SF) A data transmission format comprised of 12 frames of
192 bits each. A single 193rd bit is used for link control and error
checking. As an industry standard, D4, also known as SF, has been
superseded by the ESF format. However, because ESF is not backward
compatible and a large installed base of channel banks and DS-1
Multiplexers that are based on D4 is still in use, it is still the
default private line formatting technique. See D-4.

super high frequency (SHF) Frequencies ranging from 3 GHz to 30 GHz.

superclass A grouping of similar class definitions.

supergroup (SG) 60 circuits processed as a unit in a carrier system,
occupying adjacent bands in the spectrum, for simultaneous modulation
or demodulation.

supermastergroup (SMG) 600 circuits processed as a unit in a carrier

superservers Based on the Intel i486 microprocessor chip and RISC
architecture, these servers provide exceptional error detection
capabilities. They are equipped with multiple processors and a
mainframe-like I/O structure that eliminates the bottlenecks associated
with traditional file servers.

supervision See answer supervision.
answer supervision (AS)

supervisory control Signals that automatically drive equipment or
indicators at a remote terminal.

supervisory lamp See busy lamp field.
busy lamp field (BLF)

supervisory signals (SS) A signal, such as on-hook or off-hook, that
indicates whether a circuit or line is in use.

surcharge An additional charge added to a base rate. See property
imposed fee.
property imposed fee (PIF)

SVC See switched virtual connection, switched virtual circuit, or
switched virtual call.
switched virtual circuit (SVC)
switched virtual connection (SVC)
switched virtual call (SVC)

SWIFT See Society for Worldwide Interbank Financial Telecommunications.
Society for Worldwide Interbank Financial Telecommunications (SWIFT)

switch 1) A device that can be controlled to interconnect two circuits.
2) A device, similar to a DMS-250 or a private branch exchange (PBX),
that responds to originator signals and dynamically accepts, routes,
and places or forwards a call or other transmission; includes LEC
central office switches, IXC switches and PBXs. switch hook See

switch over The manual or automatic activation of an alternative system
such as a file unit, a communications line, or a computer when an
equipment failure occurs.

switch site A location that supports dynamic communications path

switchboard Originally, the manually operated equipment that performed
switching functions; now, the attendant position for a PBX.

switched 56Kbps A dial up digital data service (DDS).

switched access (SA) 1) The connection between a caller's telephone
system and the switch of the caller's chosen long-distance carrier when
a regular long-distance call is made using regular local lines. 2) The
connection between the switch of a caller's long-distance carrier in
the distant city and the telephone being called.

Switched Access Remote Test System (SARTS) An AT&T operations support
system that permits remote testing of end offices. The SARTS system
communicates with these end offices through the public data packet

switched access service A class of telephone service that provides the
link from the customer's premises to the interexchange carrier's
(IEC's). Point of presence (POP) for switched circuits.

switched attachment The IBM term for linking devices to host computers
through a PBX capable of handling data switching.

switched circuit A communications path that allows the originator to
specify a desired destination for each call.

switched DAL See switched dedicated access (egress) line.
switched dedicated access (egress) line

switched dedicated access (egress) line A dedicated trunk group (T1)
circuit used to access (1+) or egress (800) through normal network
switching facilities.

switched line A communications link for which the physical path may
vary with each use, for example, the dial-up telephone network.

switched loop operation Each call needing attendant assistance is
automatically switched to one of several switched loops on an attendant

Switched Maintenance Access System (SMAS) An AT&T system that provides
remote circuit testing for intermediate and end offices. It allows a
tester to access and test a circuit without the aid of another tester
in a distant office.

switched multi-megabit data services (SMDS) 1) A broadband
communications standard for the public network that does not require
predefinition of a specific path. 2) A fast packet-switching service
using uniform-sized cells to transmit information. SMDS operates at
speeds of 1.544 Mbps to 45 Mbps. SMDS is designed to take advantage of
evolving MAN standards and technology that telephone companies can
deploy to provide cross-premises communications services.

switched network See public switched telephone.
public switched telephone network (PSTN)

switched resellers Resellers that utilize their own switching hardware,
and sometimes their own lines, and the lines of other IXCs to provide
long-distance service to their subscribers. They also provide their own
billing and service.

switched service network (SSN) A private-line network that uses scan or
common control switching.

switched services All dial up long-distance services, including
conventional residential services and wide area telecommunications
services (WATS). Most have incremental use charges.

switched virtual call (SVC) A call established only for the duration of
a session.

switched virtual circuit (SVC) A logical connection across a packet
switched network. An SVC is established on an as-needed basis and can
provide a connection to any other switched user in the network.

switched virtual connection (SVC) A virtual connection established for
a short period of time, such as for a dial-up telephone call, using
signaling techniques to generate, capture, and accommodate the
connection and provisioning request.

switches reseller A reseller of long-distance services across lines and
switching equipment owned by an interexchange carrier (IXC). The
reseller usually bills the subscriber directly.

switching The operations involved in interconnecting circuits in order
to establish communications.

switching center (SC) A location at which telephone traffic, either
local or toll, is switched or connected from one circuit or line to
another. A SC is usually a part of a central office (CO). Computers
provide the communications functions of routing, priority processing,
code and speed conversion, and transmission in addition to their other

switching entity A single switching machine. One or more switching
units constitutes a switching center.

switching fee A per-line fee imposed by the local telephone company for
reprogramming their switching system to change a subscriber's default
carrier. Subscribers must usually pay this fee when switching to a
reseller. Some resellers will reimburse the subscribers for this fee.

switching matrix In a space division exchange, a group of crosspoints
that operates as a traffic switch. See matrix.

switching office (SO and S/O) A telephone company office that contains
a switch.

switching unit See switching entity.
switching entity

SX See simplex signaling.
simplex signaling (SX)

SXS See step-by-step exchange.
step-by-step exchange (SXS)

symbol The smallest signaling element used by the media access control
(MAC) sublayer. The symbol set consists of 16 data symbols and 16
nondata symbols. Each symbol corresponds to a specific sequence of code
bits to be transmitted by the physical layer.

symbolic language A language written in a humanly understandable form;
other than a machine language.

synch character A character transmitted to fix the character
synchronization in synchronous communications.

synchronization A technique of regulating the corresponding significant
instants of two signals to obtain the desired phase relationship
between these instants.

synchronization lost seconds Seconds of lost DS1 synchronization.

synchronous 1) Having a constant time interval between successive bits,
characters, or vents. Most mainframes use synchronous communications.
2) A form of communications transmission with a direct timing
relationship between input and output signals. The transmitter and
receiver are synchronized and signals are sent at a fixed rate.
Information is sent in multibyte packets. Synchronous transmission is
faster than asynchronous character transmission since start and stop
bits are not required. It is used for mainframe-to-mainframe and faster
workstation transmission. 3) A class of data transmission service in
which each requester is preallocated a maximum bandwidth and is
guaranteed a response time that will not exceed a specific delay.

synchronous communications A transmission technique that transfers
serial binary data between computer systems or between systems and

synchronous data link control (SDLC) An IBM communications protocol for
the transfer of data between stations in a point-to-point, multipoint,
or loop arrangement, using synchronous data transmission techniques.

synchronous data switching A facility for transmitting synchronous data
using a synchronous data adapter; data transmission in which the
transmitter and receiver have a fixed time relationship.

synchronous digital hierarchy (SDH) The Consultative Committee on
International Telephone and Telegraph (CCITT) version of synchronous
optical network (SONET).

synchronous error measurement A measurement that, after an error
occurs, measures any further errors in that synchronous second. After
one second from the original event, the second is marked as a
synchronous errored second, and a new measurement begins.

synchronous network A network in which all communications connections
are synchronized to a shared clock.

synchronous optical network (SONET) A 1984 American National Standards
Institute (ANSI) standard, developed by the Exchange Carriers Standards
Association (ECSA), for optical fiber transmission on the public
network. The speed is 52Mbps to 13.22Gbps. Effective for integrated
services digital network (ISDN) services, including asynchronous
transfer mode (ATM). See optical carrier.
optical carrier (OC)

synchronous optical networking standard A high-speed transport network
standard for optical media. The protocol is hierarchical in structure.
The speed is between 45 Mbps to 1.5 Gbps.

synchronous satellite orbit The path followed by a communications
satellite that is at such a distance above the earth (about 35,880
kilometers or 22,300 miles) that the satellite keeps pace with the
earth's rotation and thus hovers above a particular point on the earth.

synchronous transmission A more sophisticated, faster transmission
method than asynchronous whereby there is a constant, or fixed,
interval between the transmitted bits, eliminating the need for stop
and start bits. However, the method demands that the two computers
involved in the interchange be synchronized. This synchronization is
achieved by the use of a clock in both devices and by sending control
information with the transmission.

synchronous transport See synchronous transmission.
synchronous transmission

synchronous transport signal (STS) The signal carried over a SONET OC
unit of capacity. STS-1 corresponds to OC-1 at 51.84 Mbps, STS-24
corresponds to OC-24, and so forth.

syndrome A code transmitted along with data to enable correction of
transmission- induced errors in the received data. See Forward Error
Correction. Compare with Checksum .
forward error correction

syntax error An error caused by incorrect programrning statements in
the context of the language being used.

synthesized audio Audio output from a synthesizer.

synthesizer An electronic musical device that generates sound.

Sysop Short for SYStems OPerator. Person who is in charge of a BBS.
Usually the person who paid for the BBS equipment and pays for the
phone line.

system 1) An organization of equipment, personnel, and facilities,
designed to perform a set of functions, and governed by a set of
procedures. 2) The equipment connected to a fiber pair to enable it to
transmit, regenerate, and receive light pulse signals. For example, a
cable with three pairs of fiber in service would be said to have three
systems in place. A system is usually designated by its speed in Mbps
or Gbps.

system administration The configuration and operation of the system.

system controller node The location of the REACT system controller
equipment and the system console. The system console node allows
maintenance of the REACT software. Maintenance tasks include
installing, updating, modifying, and backing up the REACT software and
circuit databases.

system integrator A vendor that offers design, connection,
implementation and management services for diverse network resources.

system log A file or data set in which job-related and operational
information, descriptions of unusual happenings, commands, and messages
to or from the operator may be stored.

system management Initial and ongoing maintenance of a computer's

system reliability The probability that equipment will perform
accurately under normal operating conditions.

Systeme Electronique Couleur Avec Memoire (SECAM) The 625 line color
television standard used in France and the former Soviet Union.

systems application architecture (SAA) Comprehensive IBM specifications
describing the evolving integration of disparate IBM hardware
platforms, communications devices, and system software products.

Systems Network Architecture (SNA) The proprietary architecture
developed by IBM for mini and mainframe computers. SNA can be viewed as
three distinct byte-related entities: a specification, a plan for
constructing a network, and a set of products. SNA is a specification
governing the design of products for an SNA network. It is called an
architecture because it specifies the operating relationships of those
products. SNA provides a structure that allows users to establish and
manage their networks and, in response to new requirements and
technologies, to change or expand them. SNA can be viewed as a set of
products: hardware and programs designed to the SNA specifications.

systems services control point (SSCP) An element of a network based on
the IBM System Network Architecture that provides overall network
control. The SSCP is usually a mainframe.

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