| Term
| Definition |
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S & T Reference Point
|
In Integrated Service Digital Network technology the connection
point for ISDN type terminals.
|
|
S Interface
|
System interface - separates user terminal equipment from network
related functions within ISDN.
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S/N
|
Signal to Noise.
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SAA
|
Systems Application Architecture.
|
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SAAL
|
Signaling AAL - Service specific parts of the AAL protocol
responsible for signaling. Its specifications, were adopted from
N-ISDN.
|
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Sampling Rate
|
The number of samples per unit time.
|
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SAP
|
Service Access Point - Reference point between the networking stack
and applications within an end system.
|
|
SAR
|
Segmentation and Reassembly - Method of partitioning TDM frames into
ATM cells, and reassembling the TDM frames at the destination.
|
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SAR-PDU
|
Segmentation And Reassembly Protocol Data Unit - The 48 octet PDU
that the SAR sublayer exchanged with the ATM layer. It is comprised
of the SAR-PDU payload and any control information that the SAR
sublayer might add.
|
|
Satellite
|
A receiver/transmitter orbiting the earth and used to relay signals
over great distances.
|
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Satellite Relay
|
An active or passive satellite repeater which transfers signals from
one earth station to another.
|
|
SAW
|
Surface Acoustic Wave
|
|
SBA
|
Semiconductor Business Association.
|
|
SCART
|
Societe de Constructeurs des Appareils Radio Television.
|
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Scattering
|
The diffusion of a light beam within an optical fiber medium caused
by minor variations in the material. The result is signal loss.
|
|
Scatternet
|
Two or more piconets co-located in the same area (with or without
inter-piconet communication).
|
|
SCDMA
|
Synchronous Code Division Multiplex Access.
|
|
SDH
|
Synchronous digital hierarchy - An ITU standard for transmitting
data over optical fiber.
|
|
SDLC
|
Synchronous Data Link Control.
|
|
SDSL
|
Symmetric digital subscriber line - provides dedicated Internet
access. Operates at speeds that can reach 1.544 megabits per second
(Mbps). Data upload speeds equal download speeds.
|
|
SDTV
|
Standard Definition Television - Digitally transmitted SDTV includes
480 line resolution in both interlaced and progressively scanned
formats. It offers significant improvement over today's conventional
NTSC picture resolution, and is similar to DVD or DBS quality
because the digital transmission eliminates snow and ghosts, which
can be common with the current NTSC TV format. Also, thanks to
digital compression technology, several programs can be transmitted
simultaneously within the same channel.
|
|
SEAL
|
Simple Efficient Adaptation Layer - ATM AAL5 was originally defined
as SEAL, providing adaptation with no additional cell payload
overhead for data traffic.
|
|
SECAM
|
Sequential Color and Memory.
|
|
Segment
|
In a bus based local area network, a single piece of transmission
medium. Segments are normally connected together using repeaters.
|
|
Segmentation
|
The process whereby the transport layer (in an ISO/OSI layered
architecture) breaks down the sequential data stream from the
session layer buffer into numbered messages for transmission through
a packet switched (or other) network.
|
|
Segmented Encoding Law
|
An encoding law which an approximation to a smooth law is obtained
by a number of linear segments.
|
|
SEMI
|
Semiconductor Equipment and Materials Institute.
|
|
Sequencing
|
The process of dividing long messages into shorter blocks or packets
and appending to each an identifying number.
|
|
Serial Interface
|
The electronic interface between a transmitting (or receiving)
device and a single transmission channel.
|
|
Serial Transmission
|
The process whereby binary bits are transmitted one at time. Used
heavily in data communications applications. Parallel transmission
is normally only used between the computer and closely situated high
speed peripherals.
|
|
Set-Top Box
|
A transmission/reception device that acts as an interface typically
to a television or other video output display device. In addition to
ADSL, SDSL, HDSL, and VDSL interfaces, settop units are increasingly
modular and other interfaces can include Ethernet, MMDS, coaxial
cable, V.34 modem, and ISDN, among others.
|
|
SHF
|
Super High Frequency.
|
|
Shielding
|
The process of surrounding a transmission medium with materials
which are designed to reduce or eliminate the effects of radiated
electromagnetic transmission from, or reception by, on the medium.
|
|
Short Circuit
|
The condition wherein conductor which are supposed to be insulated
from one another come in direct electrical contact.
|
|
Side Tone
|
The portion of the signal from the handset microphone fed back to
the handset speaker.
|
|
SIF
|
Sound Intermediate Frequency.
|
|
Signal Conditioning
|
The modification of a signal (by amplification or transformation)
which is done to make it more suitable for transmission across a
specific medium.
|
|
Signal Reflection
|
When a signal is transmitted through a medium if it encounters a
sudden change in electrical impedance a portion of the signal will
be reflected back the way it came. Particularly problematic if
multiple reflections occur in the same medium.
|
|
Signal Regeneration
|
The process whereby a signal is modified to ensure that it meets
it's original specification.
|
|
Signal to Noise Ratio
|
A measure of the quality of a transmission defined as the ratio
produced by dividing the transmitted signal strength by the strength
of the induced noise.
|
|
Signal Transformation
|
The action of modifying one or more characteristics of a signal,
such as it's maximum value, shape, or timing.
|
|
Signaling
|
The exchange of electrical information (other than by speech)
specifically concerned with establishment and control of
connections, and management, in a communication network. May be
transmitted by independent link, designed timeslots, designated bit
positions in a timeslot or by "bit stealing" specific speech bit
positions in the PCM code-word.
|
|
Signaling Timeslot
|
A timeslot starting at a particular phase in each frame and
allocated to the transmission of signaling.
|
|
Single Chip CODEC
|
A single integrated circuit capable of performing all CODEC
functions and in some cases providing an auxiliary signaling
interface. It may be anything from single channel up to quad and
above.
|
|
Skew
|
The time delay between any two transmitted signals.
|
|
SLIC
|
Subscriber Line Interface Circuit.
|
|
SLIP
|
Serial Link Internet Protocol - An Internet protocol for host
dial-up connection. SLIP frames are encapsulated IP datagrames in
which SLIP adds just a few bytes of control data.
|
|
Slotted Ring
|
A LAN medium access control method whereby available time slots are
routed around a ring and used by transmitting devices based on the
network's defined set of rules.
|
|
SMA Connector
|
A threaded type fiber optic connector.
|
|
Small Area Network
|
A network, generally limited to tens of meters, which uses
specialized communications methods and is applied in such areas as
process control and other specific real time computer applications.
|
|
SMATV
|
Satellite master antenna television - Transmission of television
programming to a Satellite Master Antenna installed on top of an
apartment building, a hotel, or at another central location from
where it serves a private group of viewers. The transmission is
usually done in C-band to 1.5 or 2 meter dishes.
|
|
SMDS
|
Switched Multimegabit Data Service - A connectionless, fast packet
switching B-ISDN service, based on 53 byte packets. It originally
targeted the interconnection of different LANs into a switched
public network. It is used also to interconnect WANs and MANs at
speeds up to 45 Mbps.
|
|
SNAP
|
Sub Network Access Protocol - A SNAP header consists of 5 bytes,
three bytes of OUI (Organizationally Unique Identifier) and 2 bytes
of PID (Protocol IDentifier). The OUI defines which organization
administers the PID that follows. The value of 000000h in the OUI
means that the PID is defined as an EtherType.
|
|
SOHO
|
Small Office/Home Office.
|
|
SONET
|
Synchronous Optical Network - a physical layer specification for
high-speed synchronous transmission of packets or cells over
fiber-optic cabling. Both ATM and packet-based networks can be based
on SONET.
|
|
Space Division Multiplexing
|
A method whereby a number of entities use a single service
capability by having amounts of physical space within the service
facility dedicated for their individual use. A simple example is the
way in which a number of office employees share the common facility
by having individual desks within the office "space". A data
communications example is the sharing of a single conduit between
floors of a building by providing individual, wire based, physical
circuits for each user.
|
|
Speech Digit Signaling
|
Sometimes called Bit Stealing or Robbed-bit Signaling. Signaling in
which digit time-slots primarily used for the transmission of
encoded speech are periodically used for signaling.
|
|
SPICE
|
Simulation Program with Integrated Circuit Emphasis.
|
|
Spine Network
|
A interconnection network which users access through another (access
network) network. The term is often used in place of "backbone
network".
|
|
Splitter
|
A device which separates a single transmission medium into two or
more identical channels.
|
|
Spot Beam
|
A narrow beam satellite transmission method.
|
|
Spread Spectrum
|
A modulation technique in which the information content is spread
over a wider bandwidth than the frequency range of the original
signal.
|
|
SRAM
|
Static Random Access Memory - Type of RAM that retains its contents
for as long as power is supplied. SRAM does not require constant
refreshing, like DRAM.
|
|
SSTV
|
Slow Scan Television.
|
|
Subnet Mask
|
Subnetting allocates a portion of the host part of a Class A, B or C
Internet address for use as a subnet. A subnet mask is a 32-bit
value used to distinguish the combined network and subnet parts of
the Internet address from the remaining host part. Bits in a subnet
mask set to 1 correspond to the bits in the network portion of the
Internet address. Bits in a subnet mask set to 0 correspond to the
bits in the host portion of the Internet address. A subnet mask may
be specified when a server is initially started up.
|
|
Supertrunk
|
A cable that carries several video channels between the facilities
of a cable television company.
|
|
SVC
|
Switched Virtual Circuit - A logical ATM connection established via
signaling. End systems transmit their UNI 3.
|
|
SVD
|
Simultaneous Voice and Data.
|
|
S-VHS
|
Super Video Home System.
|
|
S-Video
|
Separated video - An encoded video signal which separates the
brightness from color data. S-video can greatly improve the picture
when connecting TVs to any high quality video source such as digital
broadcast satellite (DBS) and DVDs.
|
|
Switch
|
A switch is a multi-port bridge. Each port on the switch is in its
own collision domain.
|
|
Switching
|
The process whereby a connection is transferred from one circuit to
another by interconnecting the two circuits.
|
|
Symmetric
|
A network configuration that enables the same bandwidth to be used
to send data downstream (from the Internet to the user) as upstream
(from the user to the Internet).
|
|
Symmetric Digital Subscriber Line
|
This technology provides the same bandwidth in both directions,
upstream and downstream. That means whether you're uploading or
downloading information, you have the same high-quality performance.
SDSL provides transmission speeds within a T1/E1 range, of up to 1.5
Mbps at a maximum range of 12,000 - 18,000 feet from a central
office, over a single-pair copper wire. This option is ideal for
small and medium sized businesses that have an equal need to
download and upload data over the Internet.
|
|
Synchronization bits
|
Bits transmitted from source to destination for the purpose of "time
clock" synchronization of the transmitting and receiving devices.
|
|
Synchronous
|
A mode of transmission in which the sending and receiving terminal
equipment are operating continually at the same rate and are
maintained in a desired phase relationship by an appropriate means.
|
|
Synchronous Time Division Multiplexing
|
A time division multiplexing method whereby devices have fixed time
period access to a high speed transmission medium independent of
likely load.
|
|
Synchronous Transmission
|
The movement of binary bits across a transmission medium where the
transmitter and receiver have synchronized clocks. Synchronization
is accomplished either by the transmission of special synchronizing
bits or by taking timing from the transmitted message. During
synchronous transmission it is normal to place controlling
information (framing) around complete messages.
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