TANDBERG M2/TT1220CIF/D, Инструкция по эксплуатации

Страница: 64 / 114

Glossary
Page A-6 Instruction Manual: Professional Decoder
ST.TM.TT1220.1
NIT (Network Information
Table) Part of the service information data. The NIT provides information about the physical organisation of each transport
stream multiplex, and the characteristics of the network itself (such as the actual frequencies and modulation being
used).
nm Nano metres (10 -9 metres).
NTSC (National Television
Systems Committee) The group which develops standards used in television broadcast systems in the United States. Also adopted in other
countries (e.g. Mexico, Canada, Japan). This system uses 525 picture lines and a 60 Hz field frequency.
NVOD (Near Video On
Demand) A method of offering multiple showings of movies or events. The showings are timed to start at set intervals,
determined by the broadcaster. Each showing of a movie or event can be sold to subscribers separately.
NVRAM (Non-volatile
Random Access Memory) Memory devices which, although permitting random read/write access, will not lose their information when power is
removed. Stores the default configuration parameters set by the user.
OFDM Orthogonal Frequency Division Multiplexing.
OSD (On-screen display) Messages and graphics, typically originating from the SMS, and displayed on the subscriber’s TV screen by the IRD,
to inform the subscriber of problems or instruct the subscriber to contact the SMS.
Packet A unit of data transmitted over a packet-switching network. A packet consists of a header followed by a number of
contiguous bytes from an elementary data stream.
PAL (Phase Alternation by
Line) A colour television broadcasting system developed in Europe that uses 625 picture lines and a 50 Hz field frequency.
PAT (Program Association
Table) Part of the service information data. For each service in the multiplex, the PAT carries the basic mapping of all the
data in the transport stream, associating each programme with a Program Map Table.
PCM (Pulse Code
Modulation) A process in which a signal is sampled, each sample is quantised independently of other samples, and the resulting
succession of quantised values is encoded into a digital signal.
PCR (Program Clock
Reference) A time-stamp in the transport stream from which the decoder timing is derived.
Pel (Picture Element) Also known as a pixel.
PES (Packetised
Elementary Stream) A sequential stream of data bytes that has been converted from original elementary streams of audio and video
access units and transported as packets. Each PES packet consists of a header and a payload of variable length and
subject to a maximum of 64 kBytes. A time-stamp is provided by the MPEG-2 systems layer to ensure correct
synchronisation between related elementary streams at the decoder.
PID
Packet Identifier: the header on a packet in an elementary data stream which identifies that data stream. An MPEG-
2/DVB standard.
Also: Project Initiation Document, Programme ID.
PIN (Personal Identification
Number) A password used to control access to programming and to set purchase limits. Each subscriber household can
activate several PINs and may use them to set individual parental rating or spending limits for each family member.
Pixel; Picture Element The digital representation of the smallest area of a television picture capable of being delineated by the bit-stream.
pk-pk Peak to peak.
PLL Phase-Locked Loop.
PMT (Program Map Table) Part of the Service Information data. Each programme has a PMT which lists the component parts (the elementary
streams of video, audio, etc.) for the various programmes being transmitted.
P-picture/P-frame
A picture/frame produced using forward prediction. It contains predictions from either previous I frames or previous P
frames. The P frame is used as a reference for future P or B frames.
ppm Parts per million.
PPV (Pay Per View) A system of payment for viewing services based on a usage/event basis rather than on on-going subscription.
Subscribers must purchase viewing rights for each PPV event that they wish to view. PPV events may be purchased
as IPPV or OPPV (q.v.).
Program A sequence of instructions for a computer.
A concept having a precise definition within ISO 13818-1 (MPEG-2). For a transport stream, the time base is defined
by the PCR. The use of the PCR for timing information creates a virtual channel within the stream.
Programme A linking of one or more events under the control of a broadcaster. For example, football match, news show, film
show. In the MPEG-2 concept, the collection of elementary streams comprising the programme have a common start
and end time. A series of programmes are referred to as events.
PROM (Programmable
Read-Only Memory) A device which may be written once with data for permanent storage, and then read whenever required. Special
types of PROM permit the erasure of all data by Ultra Violet light (EPROM) or by application of an electronic signal
(EEPROM).
PS (Program Stream) A combination of one or more PESs with a common timebase.