ETSI
inal draft ETSI EN 300 468 V1.6.1 (2004
6)
6
Value Description
0x7E discontinuity_information_section
0x7F selection_information_section
0x80 to 0xFE user defined
0xFF reserved
5.1.4 Repetition rates and random access
In systems where random access is a consideration, it is recommended to re-transmit SI sections specified within the
present document several times, even when changes do not occur in the configuration.
For SI specified within the present document the minimum time interval between the arrival of the last byte of a section
to the first byte of the next transmitted section with the same PID, table_id and table_id_extension and with the same or
different section_number shall be 25 ms. This limit applies for TSs with a total data rate of up to 100 Mbit/s.
5.1.5 Scrambling
With the exception of the EIT carrying schedule information, all tables specified in the present document shall not be
scrambled. One method for scrambling the EIT schedule table is given in annex D, Bibliography. If a scrambling
method operating over TS packets is used, it may be necessary to use a stuffing mechanism to fill from the end of a
section to the end of a packet so that any transitions between scrambled and unscrambled data occur at packet
boundaries.
In order to identify the CA streams which control the descrambling of the EIT data, a scrambled EIT schedule table
shall be identified in the PSI. Service_id value 0xFFFF is allocated to identifying a scrambled EIT, and the program
map section for this service shall describe the EIT as a private stream and shall include one or more CA_descriptors
(defined in ISO/IEC 13818-1 [1]) which give the PID values and optionally, other private data to identify the associated
CA streams. Service_id value 0xFFFF shall not be used for any other service.
5.2 Table definitions
The following clauses describe the syntax and semantics of the different types of table.
NOTE: The symbols and abbreviations, and the method of describing syntax used in the present document are the
same as those defined in clauses 2.2 and 2.3 of ISO/IEC 13818-1 [1].
5.2.1 Network Information Table (NIT)
The NIT (see table 3) conveys information relating to the physical organization of the multiplexes/TSs carried via a
given network, and the characteristics of the network itself. The combination of original_network_id and
transport_stream_id allow each TS to be uniquely identified throughout the ETS application area. Networks are
assigned individual network_id values, which serve as unique identification codes for networks. The allocation of these
codes may be found in ETR 162 [6]. In the case that the NIT is transmitted on the network on which the TS was
originated, the network_id and the original_network_id shall take the same value.
Guidelines for the processing of SI at transitions between delivery media boundaries, e.g. from satellite to cable or
SMATV systems, can be found in TR 101 211 [7].
IRDs may be able to store the NIT information in non-volatile memory in order to minimize the access time when
switching between channels ("channel hopping"). It is also possible to transmit a NIT for other networks in addition to
the actual network. Differentiation between the NIT for the actual network and the NIT for other networks is achieved
using different table_id values (see table 2).
The NIT shall be segmented into network_information_sections using the syntax of table 3. Any sections forming part
of an NIT shall be transmitted in TS packets with a PID value of 0x0010. Any sections of the NIT which describe the
actual network (that is, the network of which the TS containing the NIT is a part) shall have the table_id 0x40 with the
same table_id_extension (network_id). The network_id field takes the value assigned to the actual network in
ETR 162 [6]. Any sections of an NIT which refer to a network other than the actual network shall take a table_id value
of 0x41 and the network_id shall take the value allocated to the other network in ETR 162 [6].