Glossary
dB
Decibels: A ratio of one quantity to another using a logarithmic
scale, to give results related to human aural or visual perception. dB
is a ratio of two quantities. dBm, for example, is an absolute power
level, quoted as a ratio to a fixed power of 1 mW (0 dBm), typically
terminated into 50 Ω (RF) or 600 Ω (audio). 0 dBmV is 1 mV across
75 Ω.
DCE
Data Communications Equipment: Typically a modem. It
establishes, maintains and terminates a session on a network but in
itself is not the source (originator) or destination (end receiving unit)
of signals (e.g. a computer, see DTE). A DCE device may also
convert signals to comply with the transmission path (network)
format.
DCT
Discrete Cosine Transform: A technique for expressing a waveform
as a weighted sum of cosines. Raw video data is not readily
compressible. DCT is not in itself a compression technique but is
used to process the video data so that it is compressible by an
encoder. DCT processes the picture on an 8x8-pixel block basis,
converting the data from an uncompressible X Y form (as displayed
by an oscilloscope) to a compressible frequency domain form (as
displayed by a spectrum analyzer). Can be forward DCT or inverse
DCT.
DDS
Direct Digital Synthesiser.
Decoder
The unit containing the electronic circuitry necessary to decode
encrypted signals. Some Decoders are separate from the receiver
but in satellite TV broadcasting, the term is often used
interchangeably as a name for an Integrated Receiver Decoder
(IRD). The term IRD, or IRD / Decoder, is usually associated with
satellite TV broadcasting while Cable systems are based on
Converters or on Set-Top Boxes / Converters.
Decoding Time
stamp
A field that may be present in a PES packet header that indicates
the time that an access unit is to be decoded in the system target
Decoder.
DENG
Digital Electronic News Gathering
DID
Data Identifier.
Differential Coding
Method of coding using the difference between the value of a
sample and a predicted value.
DiffServ
Differentiated Services. A mechanism used on layer 3 - e.g. the IP
layer - to differentiate between traffic of various types. DiffServ is
based on the ToS field and provides a mechanism for the network to
give e.g. video traffic higher priority than other traffic (for example
Internet traffic).
DIL
Dual In Line: The most common type of package for small and
medium scale integrated circuits. The pins hang vertically from the
two long sides of the rectangular package, spaced at intervals of 0.1
inch.
DIN
Deutsches Institut für Normung: German Standards Institute.
Downlink
The part of the satellite communications circuit that extends from the
satellite to an Earth station.
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