Wegener Communications UNITY 4600 - Manual (Page 19)

Unity 4600 User’s Manual
www.wegener.com 11 800032-01 Rev. F
MPEG Moving Picture Experts Group - refers to the method of video compression established by this group.
(The Unity 4600 utilizes the MPEG2 format for video.)
Network Protection
Mode A non-volatile setup parameter whose value is “Shared” or “Protected” (or “not Shared”). Similarly,
each network control stream has a “Share” status field as part of the COMPEL packet framing. A
network control stream is considered “invalid” to the U4600 if the network ID in the stream differs
from that of the IRD and if either the network stream or the U4600 are set to be “Protected”. For test
purposes only, there is a generic network ID that the COMPEL system may transmit which is always
considered to be “valid” by all IRDs.
NTSC National Television System Committee. The composite color video standard used domestically (and
in a few countries outside US) based on 525-line 59.97 Hz field rate (with 2:1 interlace).
PAL Phase-Alternating-Line. A set of composite color video standards used worldwide (outside US)
which implements a line-by-line reversal of phase of one of the orthogonal color components. For
our use, all PAL signals are assumed to be 625-line 50 Hz field-rate systems with varying chroma
and luma bandwidths and color subcarrier frequencies.
PAT Program Allocation Table. A PSI table within an MPEG transport stream which cross-references all
available programs to a PID for its PMT. This table is always present in legal transport streams and
must always be in the clear (not scrambled) even when Conditional Access scrambling is used.
PCR Program Clock Reference. A time-base signal used to synchronize the IRDs internal timing to the
same timing in the MPEG encoder for the received program. Multiple programs may share a PCR,
depending on the multiplexer used to create the final transport stream.
PES Stream Packetized Elementary Stream. The MPEG designation for a compressed component of a Program
(such as audio or video) which includes the timing information necessary for synchronization (e.g. -
synchronizing audio to video).
PID (or Packet ID) The unique transport stream packet identifier assigned to each constituent data stream within the
transport stream. Also, in this document, “PID” is used to designate the stream itself.
PMT Program Map Table. A PSI table within an MPEG transport stream which cross-references a
program (or programs) against all the PIDs that bear its component streams (such as audios, video,
DPI, PCR, etc.). IRDs need this table to decode the compressed components of that program.
Presets Table A non-volatile table of unit presets. This table is used for either automatic recoveries or as a
shorthand method to quickly reconfigure the unit. The presets table may be programmed at the
factory and edited by the customer, either locally or via network control.
Program A single media stream (combination of audio, video, data, etc.) tied to a common time base.
Program Number A numerical code representing a program.
PSI Tables A group of information-bearing tables, each borne by well-known PIDs, regularly transmitted in the
transport stream. See also “PAT” and “PMT”. Also, ISO 13818-1 gives a thorough description of
these and other Tables.
PTS Presentation Time Stamp. A marker signal associated with audio and video streams within a
program conveyed in MPEG transport stream. This signal allows the audio and video to be
presented in synchronism to each other.
RAM Random access memory. A general term for all volatile memory types out of which application
software executes and into which its variables, state information, and messages are stored. RAM is
also used to designate the volatile storage used by the Transport Demux and decompression
devices.
RF Radio frequency
Table 1.3: Glossary of Terms
Term Definition