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The Master Guide table lists summary information for all other PSIP and data broadcasting tables in an ATSC transport stream, with the exception of the System Time table.

packetization characteristics maximums

The purpose of the Master Guide Table (MGT) can be stated simply: the MGT lists summary data on PSIP (or ATSC announcement, if a station is engaged in data broadcasting) table section typess in an ATSC transport stream. There is an exception: the MGT does not list the System Time table.

Many accounts state incorrectly that the Master Guide Table must be used or is used to discover the location of certain PSIP table sections in the transport stream. Anyone who has ever written an MPEG-2 packet demultiplexer knows the falsity of this statement; it is quite easy to extract MPEG-2 Program Specific Information and PSIP table sections from a transport stream before ever encountering a Master Guide Table section in the same stream, and only a fool would wait for the occurrence of a Master Guide Table before making use of previously-discovered table sections.

That said, the Master Guide table provides the information necessary to know (see table_type_version number, below) if a particular table type has been updated, and the number_bytes field provides a double-check to establish that a receiver has processed all the table sections of a certain type that are present in the transport stream.

The MGT, per ATSC A/65, must be injected onto the transport stream at least once per any 150 ms period. This maximum repetition cycle is the shortest for any PSIP table, and is only 'bested' by the ATSC-compliant Program Association Table (PAT) which has a maximum repetition cycle of 100 ms.

Master Guide tables may carry optonal descriptors for any table section type (see the descriptor() field just after table_type_descriptors_length) and for the Master Guide Table section itself (see the descriptor() field just after descriptors_length). The former descriptor location has no descriptors defined for this purpose when a PSIP table is listed, but if a private section (user-defined) is listed, an MPEG-2 registration descriptor shall be present with a format_identifier that identifies the entry with the SMPTE registration authority that applies to the particular type of table.

Master Guide table syntax

syntax	bit index	# of bits	mnemonic
table_id	0	8	199 / 0xC7
section_syntax_indicator	8	1	'1'
private_indicator	9	1	'1'
reserved	10	2	'11'
section_length	12	12	uimsbf
table_id_extension	24	16	0 / 0x0000
reserved	40	2	bslbf
version_number	42	5	uimsbf
current_next_indicator	47	1	'1'
section_number	48	8	0 / 0x00
last_section_number	56	8	0 / 0x00
ATSC_protocol_version	64	8	0 / 0x00
tables_defined	72	16	uimsbf
for i = 0 to tables_defined-1
table_type	88	16	uimsbf
reserved	104	3	'111'
table_type_pid	107	13	uimsbf
reserved	120	3	'111'
table_type_version_number	123	5	uimsbf
number_bytes	128	32	uimsbf
reserved	160	4	'1111'
table_type_descriptors_length	164	12	uimsbf
descriptor()	176	varA	uimsbf
next
reserved	176+varA	4	'1111'
descriptors_length	180+varA	12	uimsbf
descriptor()	192+varA	varB	uimsbf
CRC_32	192+varA+varB	32	rpchof
Table section legend
Note: bit index is only indicated for a single iteration of any loop.

Semantics changed via ATSC A/81, Section 9.9.4

Note: This page was changed on August 3, 2009 to add explanatory text, and to add the previously omitted descriptor field for individual table types in the Master Guide Table, and the 'reserved', descriptor_length and descriptor field just before the CRC-32 field.

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