Annex A

GUI

Graphical User Interface: The use of pictures rather than just words

 

to represent the input and output of a program. A program with a

 

GUI runs under a windowing system and has a screen interface

 

capable of displaying graphics in the form of icons, drop-down

 

menus and a movable pointer. The on-screen information is usually

 

controlled / manipulated by a mouse or keyboard.

HDTV

High Definition Television.

HPA

High Power Amplifier: Used in the signal path to amplify the

 

modulated and up-converted broadcast signal for feeding to the

 

uplink antenna.

HSYNC

Horizontal (line) SYNCs.

HTTP

HyperText Transfer Protocol. The fundamental protocol used on the

 

Internet for transmission of WEB pages and other data between

 

servers and PCs

HU

Height Unit

Hub

A device in a multi-point network at which branch nodes

 

interconnect.

ICAM

Integrated Conditional Access Module: Embedded in the IRD and

 

responsible for descrambling, plus packet filtering and reception. It

 

also contains the physical interface to the subscriber’s viewing card.

ICMP

Internet Control Message Protocol. ICMP messages, delivered in IP

 

packets, are used for out-of-band messages related to network

 

operation or mis-operation

IGMP

Internet Group Management Protocol. IGMP is a protocol used to

 

manage multicasts on the Internet. For a host (receiver unit) to

 

receive a multicast, it needs to transmit IGMP "join" messages on

 

the right format. Three versions exist. IGMPv2 is common today but

 

IGMPv3 is the next step.

IDU

Indoor unit

IEC

International Electrotechnical Committee.

IF

Intermediate Frequency: Usually refers to the 70 MHz or 140 MHz

 

output of the Modulator in cable, satellite and terrestrial transmission

 

applications.

Interframe Coding

Compression coding involving consecutive frames. When

 

consecutive frames are compared, temporal redundancy is used to

 

remove common elements (information) and arrive at difference

 

information. MPEG-2 uses B and P frames, but since they are

 

individually incomplete and relate to other adjacent frames, they

 

cannot be edited independently.

Intraframe Coding

Compression coding involving a single frame. Redundant

 

information is removed on a per frame basis. All other frames are

 

ignored. Coding of a macroblock or picture that uses information

 

only from that macroblock or picture. Exploits spatial redundancy by

 

using DCT to produce I frames; these are independent frames and

 

can be edited.

A-8

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