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S7200 TV Signal Analyzer Operation Manual
During the transmission, all tables in the MPEG-2 transport stream, whether they
are PSI tables or other private tables according to DVB (SI tables) or according to
ATSC (PSIP tables), are protected by a CRC checksum. It is 32 bits long and
transmitted at the end of each sector. Each sector, which can be composed of
many transport stream packets, is thus additionally protected. A CRC error has
occurred if these checksums don't match the content of the actual section of the
respective table. The MPEG-2 decoder must then discard this table content and
wait for this section to be repeated.
A CRC_error occurs when
• A table (PAT, PMT, CAT, NIT,...) in a section has a wrong checksum which doesn't
match its content.
(3) PCR_repetition_error
The PCRs are used to re-generate the local 27 MHz system clock. If the PCRs are
not transmitted with sufficient regularity, then this clock may jitter or drift. The
receiver/decoder may even go out of lock. In DVB, a repetition period of not more
than 100 ms is permitted, previously a maximum of 40ms was recommended.
A PCR_error occurs when
• The difference between two successive PCR values of a program is greater than
100 ms, and no discontinuity is indicated in the adaptation field or Header
Optional adaptation field, or
• The time interval between two packets with PCR values of a program is more
than 40 ms.
(4) PCR_discontinity_indicator_error
The PCR_discontinuity_indicator_error is set in the case that a discontinuity of the
PCR values occured and has not been signalled appropriately by the discontinuity
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