Ericsson SVP 2000, Справочное руководство, Страница: 159 / 196

Glossary
CRC Cyclic Redundancy Check: A mathematical algorithm that computes
a numerical value based on the bits in a block of data. This number
is transmitted with the data and the receiver uses this information
and the same algorithm to ensure the accurate delivery of data by
comparing the results of algorithm and the number received. If a
mismatch occurs, an error in transmission is presumed.
CVBS Color Video Black Sync Signal
DASH see MPEG-DASH
dB Decibels: A ratio of one quantity to another using logarithmic scales
to give results related to human aural or visual perception. dB is a
ratio whereas dBm, for example, is an absolute value, quoted as a
ratio to a fixed point of 0 dBm. 0 dBm is 1 mW at 1 kHz terminated
in 600
Ω . 0 dBmV is 1 mV terminated in 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).
EN/LZT 790 0046/1 R1A A-5