protocol_version [ATSC Semantics]
To permit later backwards-compatible table syntax definitions, the ATSC has established that the first field in PSIP table sections after the MPEG-2 generic table header is ATSC_protocol_version.
ATSC_protocol_version is an 8-bit value that, until further notice, the value in this field is always zero.
Appears in the header of the Event Information table sections
Appears in the header of the Channel Extended Text table and Event Extended Text table section
Note also ATSC_protocol_version.