Annex A

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

A field that may be present in a PES packet header that indicates

stamp

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.

Downconvert

The process by which the frequency of a broadcast transport stream

 

is shifted to a lower frequency range.

DPCM

Differential Pulse Code Modulation: An audio digitization technique

 

that codes the difference between samples rather than coding an

 

absolute measurement at each sample point.

EN/LZT 790 0005 R1A

A-5