==== CA_service_descriptor

Defined by ARIB in <<ARIB-B25>>.

[source,xml]
----
<CA_service_descriptor
    CA_system_id="uint16, required"
    ca_broadcaster_group_id="uint8, required"
    message_control="uint8, required">

  <!-- One per service -->
  <service id="uint16, required"/>

</CA_service_descriptor>
----
