Parental Ratings

As with most other DTV systems, ATSC service information includes information about parental ratings. This can either be applied to a complete channel, or to a single event. Parental ratings are partly controlled by an SI table called the Rating Region Table. This can be used to define parental ratings for several geographical regions, in those cases where ratings may not be the same across the areas that the content is broadcast (this may be more of an issue for satellite broadcasts than for terrestrial or cable broadcasts). Right now, the only geographical regions that are supported are the USA and Canada as one region, and Taiwan as another.

Each RRT can define several rating dimensions. A rating dimension defines one way of rating content: for instance the MPAA rating system is one rating dimension, while the TV Parental Guidelines ratings could be included as another rating dimension. The advantage of this approach is that it allows several different rating systems to be used simultaneously. An event can be given different ratings values in different systems - for instance, a movie rated R using the MPAA rating system can also be given a more detailed rating under other systems. The RRT table looks like this:

Format of the Rating Region Table. Source: ATSC A/65b (PSIP Specification)
Syntax No. of bits Format
rating_region_table_section () {
table_id 8 0xCA
section_syntax_indicator 1 '1'
private_indicator 1 '1'
reserved 2 '11'
section_length 12 uimsbf
table_id_extension {
reserved 8 0xFF
rating_region 8 uimsbf
}
reserved 2 '11'
version_number 5 uimsbf
current_next_indicator 1 '1'
section_number 8 uimsbf
last_section_number 8 uimsbf
protocol_version 8 uimsbf
rating_region_name_length 8 uimsbf
rating_region_name_text() var  
dimensions_defined 8 uimsbf
for (i = 0; i < dimensions_defined; i++) {
dimension_name_length 8 uimsbf
dimension_name_text() var  
reserved 3 '111'
graduated_scale 1 bslbf
values_defined 4 uimsbf
for (j = 0; j < values_defined; j++) {

abbrev_rating_value_length

8 uimsbf
abbrev_rating_value_text() var  
rating_value_length 8 uimsbf
rating_value_text() var  
}
}
reserved 6 uimsbf
descriptors_length 8 uimsbf
for (i = 0; i < N; i++) {
descriptor
}
CRC_32 32 rpchof
}

This shows how the various rating systems are sent to the receiver, but it doesn't tell us how these ratings are applied to a channel of event. To do this, ATSC uses the Content Advisory Descriptor. This descriptor can either be carried in the event loop of the AEIT to give a rating for a single event, or it can be carried in the VCT to give a rating for an entire channel.

The descriptor has the following format:

Format of the Content Advisory Descriptor. Source: ATSC A/65b (PSIP Specification)
Syntax No. of bits Format
content_advisory_descriptor () {
descriptor_tag 8 0x87
descriptor_length 8 uimsbf
reserved 2 '11'
rating_region_count 6  
for (i = 0; i < rating_region_count; i++) {
rating_region 8 uimsbf
rated_dimensions 8 uimsbf
for (j = 0; j < rated_dimensions; j++) {
rating_dimension_j 8 uimsbf
reserved 4 '1111'
rating_value 4 uimsbf
}
rating_description_length 8 uimsbf
rating_description_text() var  
}
}

As you can see, this allows any show to be rated on several dimensions at the same time, in several regions. In practice this is not completely used at the moment, but that may change depending on how ATSC standards are adopted in the rest of the world. In addition to a set of ratings in the various dimensions, it can also carry a text description that provides more detail, for instance saying why that rating was given (e.g. sex, violence or bad language).

The RRT is always broadcast on the same PID - number 0x1FFB. This is the same PID that is used for the VCT, and means that the receiver can process both tables more efficiently.