Glossary S0-A | B | C-Cn | Co-Cz | D | E | F-G | H-I | J-L | M | N-O | P-Q | R | S | T | U-Z
0-A | B | C-Cn | Co-Cz | D | E | F-G | H-I | J-L | M | N-O | P-Q | R | S | T | U-Z
- SAA: See System Application Architecture
- Scattering: A
property of glass which causes light to deflect from the fiber & contributes to
- SCSI: See Small Computer System
- SD: See Send Data
See Synchronous Data Link Control
Management: Protects a network from invalid accesses. It is one of the
management categories defined by the ISO.
- SEF: See Source Explicit Forwarding
- Segment: One portion of
the bus of an Ethernet LAN, consisting of standard Ethernet coaxial cable up to
500 meters or thinnet (RG58) coaxial cable up to 185
- Segmentation: The division of breaking larger segments (ring)
into multiple small segments (rings)
- Semaphore: A method with which
multiple applications can coordinate related operations using
- Send Data: (SD) A signal in the RS232-C
DTE-DCE interface. This signal is used by the DTE to send Data..
- Sequenced Packet Protocol: (SPP) XNS (Xerox Network Systems) protocol governing
- Sequential Packet Exchange: (SPX)
Novell's implementation of SPP.
Transmission: The most common transmission mode; information bits are sent
sequentially on a single data channel.
- Server: A computer that
provides shared resources, such as files & printers, to the
- Session: An active communications connection between nodes
- Session Establishment: The process of starting a
Session. It is a part of the Initial Handshaking. (see Initial
- Session Layer: Layer 5 of the OSI (Open Systems
Interconnection) model; it defines protocols governing communications between
- Shared memory: Portion of memory accessible to multiple
- Shield: A tape, screen or braid of metal, usually copper,
aluminum, or other conductive material placed around or between electric
circuits or cables or their components, to prevent signal leakage or
- Shielded: Wiring protected from electromagnetic & radio
frequency interference by metal-backed mylar foil & plastic or PVC.
- Shielded Twisted Pairs: (STP) General term for cabling
systems that are designed specifically for data transmission, & where the
cables are shielded.
- Shielding: Protective cable covering that
eliminates electromagnetic & radio frequency interference.
(Short-Haul Modem) See line
- Short-Haul Modem: (SHM) See line Driver
- Shrink Tubing: Tubing which
has been extruded, cross-linked & mechanically expanded, which when reheated
will return to its original diameter.
- Signal: Any visible or audible
indication which can convey information. Also, the information conveyed through
a communication system.
- Signal Distortion: The discrepancy of the
signal at the output point from the signal transmitted at the point of
- Signal Ground: One of the signals in the RS232-C DTE-DCE
interface. The signal performs as the electrical reference point for other
signals in the interface.
- Signal Quality Error:
(SQE) A signal quality error message sent by transceivers to the Ethernet
controller card when there are network faults or collisions on the
- Signal to Noise Ratio: (SNR) Commonly
used interchangeably with ACR
- Silicone: A material made from silicone
& oxygen. Can be in thermosetting elastomer or liquid form. The thermosetting
elastomer form is noted for high heat resistance.
- Simple Mail Transfer Protocol: (SMTP) TCP/IP protocol
governing electronic mail transmissions.
- Simple Terminal: A terminal
device with little or not computing power.
- Simultaneous Peripheral
Operation On-Line: (SPOOL) See Print
- Sine Wave: The basic signal waveform. In analog data
communications, the carrier signal on the telephone line is a type of sine
- Singlemode: Describing an optical waveguide that is designed to
propagate light of only a single wavelength & perhaps a single phase;
essentially, an optical fiber that allows the transmission of only one light
beam, or data carrying lightwave channel, & is optimized for a particular
lightwave frequency, compared with multimode. Single Mode Fiber: An optical
fiber that will allow only one mode to propagate; this fiber is a step index
- Skew Rays: A ray that does not intersect the fiber axis.
Generally, a light ray that enters the fiber core at a very high
- Skin Effect: The tendency of alternating current to travel
only on the surface of a conductor as its frequency increases.
- Small Computer System Interface: (SCSI) An interface type
for computer adapters & controller boards.
Office/Home Office: (SOHO) Small scale equipment (4 port hubs and so
- SMTP: See Simple Mail Transfer
- SNA: Systems Network Architecture
- SNMP: Simple
Network Management Protocol.
- SNR: See Signal to Noise
- Sockets: An API (Application Program Interface) for
communications between Unix & TCP/IP.
- Software: Binary information
the computer understands to perform certain tasks.
- SOH: See Start of Header
- SOHO: See Small
- Source: the device( usually LED or laser) used
to convert an electrical information-carrying signal into a corresponding
optical signal for transmission by an optical wave guide.
- Source Explicit Forwarding: (SEF) Security feature that
allows transmissions only from specified stations to be forwarded by
- Space: Absence of signal. In telegraph communications, a
space represents the open condition or no current flowing. A space impulse is
equivalent to a binary 0.
- Spanning Tree Algorithm:
(STA) An IEEE 802.1 standard algorithm used by bridges to automatically compute
a set of routes between all bridges in the network to avoid loops. It is
required in a bridge network if redundant links are needed for backup
- Spectral Bandwidth: The difference between wavelengths at
which the radiant intensity of illumination is half its peak
- Spectrum: Frequencies that exists in a continuous range &
have a common characteristic. A spectrum may be inclusive of many
- Spike: See Transient
- SPOOL: (Simultaneous
Peripheral Operation On-Line) See Print
- SPP: See Sequenced Packet
- SPX: See Sequential Packet
- SQE: See Signal Quality
- SQL: See Structured Query
- STA: See Spanning Tree
- Standing Wave: The stationary pattern of waves produced
by two waves of the same frequency traveling in opposite directions on the same
transmission line. The existence of voltage & current maxima & minima along a
transmission line is a result of reflected energy from an impedance
- Standing Wave Ratio: A ratio of the maximum amplitude to
the minimum amplitude of a standing wave slated in current or voltage
- Star: A LAN topology in which all the nodes are connected
to one central point or hub.
- Star Coupler: Optical components which
allows emulation of a bus topology in fiber optic systems.
Topology: A network topology in which nodes are connected to a common
device such as a hub or concentrator.
- StarLAN: A local area network
design & specification, within the IEEE standards, characterized by 1 Mbps
baseband data transmission over two twisted-pair wiring.
- Start Bit:
The first bit in a character in asynchronous transmission to indicate the
beginning of a character. By convention, the Start bit is a Zero ("Space"
condition on the line).
- Start of Header: (SOH) SOH
is a Data Link Control character. SOH precedes the main message & contains
auxiliary information related to a message. STX ends the SOH function.
- Start of Text: (STX) A control character used to indicate
the beginning of a message; it immediately follows the header in transmission
- Start-Stop: A technique used in asynchronous transmission so
that a group of bits representing a character is preceded by a Start Bit &
ended with a Stop Bit.
- Start-Stop Protocol: A commonly-used term for
Data Link Control Procedures used by terminals (DTE's) using Start-Stop
- Static Charge: An electrical charge that is bound to an
object. An unmoving electrical charge.
- Station: Any DTE that receives
or transmits messages on a data link, including network nodes & user
- Station Activation: A sequence in the data transfer between
two DTE's. It is the reverse of station activation. Upon completion of this
sequence, the DTE's become non-operational.
- Statistical Multiplexing:
A multiplexing technique: Bandwidth is dynamically allocated on the basis of
- Stay Cord: A component of a cable, usually of high tensile
strength, used to anchor the cable ends at their points of termination & keep
any pull on the cable from being transferred to the electrical
- Step-Index Fiber: A fiber in which the core is of a
uniform refractive index, & there's a sharp decrease in the index of refraction
at the cladding.
- Stop Bit: The last bit in a character in
asynchronous transmission to indicate the ending of the character. By
conversion, the Stop Bit is a One ("Mark" condition on the line). Some
equipment us4es 1.5 or 2 bits for stop.
- Storage Device: A device for
holding (strong) programs or data. Storage devices may be temporary (memory
with the computer) or permanent (disk storage).
- Storage Media:
Usually refers to devices, such as, magnetic disks, magnetic tapes, LSI memory
chips, for storing programs or data.
- Store-and-Forward: A message
switching technique in which messages are temporarily stored at intermediate
points before being retransmitted to the next destination.
Procedures: Compiled code residing on an intelligent database server that
reduces the processing burden on the client.
- STP: See Shielded Twisted Pairs
- Strain Gauge: A device for
determining the amount of strain (change in dimensions) when a stress is
- StreetTalk: (Virtual Network
Software) protocol for discovering & maintaining network resource
information distributed among different servers.
- String: A process
consisting of a series of threads or a series of characters.
Return Loss: Backward reflected energies from uneven parts of the cable
structure are termed structural return loss.
- Structured Networking: A
new design of the network fabric in which physical connections are decoupled
from logical associations in the network, & a network center serves as a
centralized location for hubs & servers. Structured networking allows networks
to be created to organizations structure rather than the building
- Structured Query Language: (SQL) A
widely used programming language for manipulating database
- STX: See Start of
- Sublayer: A portion of an OSI model layer. For
- Subnet: A network that has been connected to larger & more
powerful network system. Subnets are connected to a larger net to by a bridge
- Suite: A related group of protocols, such as the TCP/IP
protocol suite. The TCP/IP protocol suite includes IP,ARP,ICMP, TCP, UDP,
Telnet, FTP, SMTP, & others.
- Surge: An oversupply of voltage from the
power company, lasting as long as several seconds. A strong surge can damage
- Sweep Test: A method to determine the frequency
response of cable by generating an RF voltage whose frequency is varied at a
rapid constant rate over a given range.
- Swell: A persistent voltage
surplus. The overvoltage is not enough to cause a surge but can damage
- Switch: Multiport LAN device designed to
increase network performance by allowing only essential traffic on the attached
individual LAN segment. Packets are filtered or forwarded based upon their
source & destination addresses.
- Switched LAN: A term which
encompasses all switched approaches to providing LAN information transport,
including frame switching, hybrid switching & cell switching.
Line: A communications link for which the physical path may vary with each
usage, such as the public telephone network.
- Synchronous: Data
transmission where characters & bits are transmitted at a fixed rate with the
transmitter & receiver synchronized.
- Synchronous Data
Link Control: (SDLC) an IBM standard protocol, superseding bisynchronous
- Synchronous Transmission: Transmission in which data bits are
sent at a fixed rate, with the transmitter & receiver synchronized.
Synchronized transmission eliminates the need for start & stop bits. See also
- System Application
Architecture: (SAA) An IBM developed set of standards that provides
identical user interfaces for applications running on PCs, minicomputers, &