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
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
- Scattering: A property of glass which
causes light to deflect from the fiber & contributes to losses.
See Small Computer System Interface
- SD: See Send Data
- SDLC: See Synchronous Data
- Security Management: Protects a network from invalid
accesses. It is one of the management categories defined by the
- 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 meters.
- Segmentation: The division of
breaking larger segments (ring) into multiple small segments
- Semaphore: A method with which multiple applications can
coordinate related operations using messages.
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 sequenced data.
- Sequential Packet
Exchange: (SPX) Novell's implementation of SPP.
- Serial Transmission: The most common
transmission mode; information bits are sent sequentially on a single data
- Server: A computer that provides shared resources, such as
files & printers, to the network.
- Session: An active communications
connection between nodes or applications.
- Session Establishment: The
process of starting a Session. It is a part of the Initial Handshaking. (see
- 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
- Shrink Tubing: Tubing which has been extruded,
cross-linked & mechanically expanded, which when reheated will return to its
- Signal: Any visible or audible indication which
can convey information. Also, the information conveyed through a communication
- Signal Distortion: The discrepancy of the signal at the
output point from the signal transmitted at the point of origin.
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
- 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 network.
- Signal to Noise Ratio: (SNR) Commonly used interchangeably
- 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
- Simple Terminal: A terminal device with little or not
- Simultaneous Peripheral Operation On-Line: (SPOOL)
See Print Spooler.
- Sine Wave: The basic
signal waveform. In analog data communications, the carrier signal on the
telephone line is a type of sine wave.
- Single Mode Fiber: An optical
fiber that will allow only one mode to propagate; this fiber is a step index
- 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.
- Skew Rays: A ray that
does not intersect the fiber axis. Generally, a light ray that enters the fiber
core at a very high angle.
- Skin Effect: The tendency of alternating
current to travel only on the surface of a conductor as its frequency
- Small Computer System Interface: (SCSI)
An interface type for computer adapters & controller boards.
- Small Office/Home Office: (SOHO) Small scale equipment (4
port hubs and so forth).
- SMTP: See Simple Mail
- SNA: Systems Network
- SNMP: Simple Network Management Protocol.
See Signal to Noise Ratio
- Sockets: An API
(Application Program Interface) for communications between Unix &
- Software: Binary information the computer understands to
perform certain tasks.
- SOH: See Start of
- SOHO: See Small Office/Home
- 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.
Explicit Forwarding: (SEF) Security feature that allows transmissions only
from specified stations to be forwarded by bridges.
- 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 purposes.
- Spectral Bandwidth:
The difference between wavelengths at which the radiant intensity of
illumination is half its peak intensity.
- Spectrum: Frequencies that
exists in a continuous range & have a common characteristic. A spectrum may be
inclusive of many spectrums.
- Spike: See Transient
(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 like a switch or hub.
- Star Coupler: Optical
components which allows emulation of a bus topology in fiber optic
- Star Topology: A network topology in which nodes are
connected to a common device such as a switch, hub or
- 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.
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 of data that uses a
clock signal to synchronize the transmitter and receiver. Synchronized
transmission eliminates the need for start & stop bits. See also asynchronous transmission.
- System Application Architecture: (SAA) An IBM developed set
of standards that provides identical user interfaces for applications running
on PCs, minicomputers, & mainframes.