Conditional Access

Conditional Access

Introduction

Conditional access (CA) is a technology used to control access to digital television services to authorized users by encrypting the transmitted programming. The content scrambling algorithm is used to encrypt content. The algorithm operates on the payload of a Transport Stream (TS) packet in the case of TS-level scrambling. A structuring of PES packets is used to implement PES-level scrambling with the same scrambling algorithm. Icareus server allows configuring the following PSI/SI tables parameters to define scrambled content.
CA_descriptor: The conditional access (CA) descriptor is used to specify both system-wide conditional access management information such as EMMs and elementary stream-specific information such as ECMs.

free_CA_mode field: This 1-bit field, when set to "0" indicates that all the component streams of the service are not scrambled. When set to "1" it indicates that access to one or more streams may be controlled by a CA system.

CA_identifier_descriptor: The CA identifier descriptor indicates whether a particular bouquet, service or event is associated with a conditional access system and identifies the CA system type by means of the CA_system_id.

2. CONFIGURATION

2.1. BOUQUET ASSOCIATION TABLE (BAT)

It is possible to add a CA_identifier_descriptor to a BAT and specify CA_system_id for the descriptor.

  • Select PSI/SI->Edit BAT...->'Bouquet Descriptors' menu item
  • Bouquet Information Table dialog should appear
  • Right-click 'Bouquet descriptors' node and select 'Add descriptor' menu item
  • Choose 'CA Identifier descriptor' in a drop-down list and press OK button
  • Expand 'CA identifier descriptor' node
  • Right-click CA_system_ids node and select 'Add CA_system_id' menu item
  • Expand CA_system_id node
  • Double-click CA_system_id field to update its value
  • Press OK to save the changes and close the dialog

2.2. PROGRAM MAP TABLE (PMT)

It is possible to add one or more CA_descriptor to a particular service in PMT.

  • Select PSI/SI->Edit PMT...->'Service Name' menu item
  • Program Map Table dialog should appear for the selected service
  • Right-click 'PMT common descriptors' node and select 'Add descriptor' menu item
  • Choose 'CA descriptor' in a drop-down list and press OK button
  • Expand 'CA descriptor' node
  • Double-click any descriptor's field to update its value
  • Press OK to save the changes and close the dialog

2.3. SERVICE DESCRIPTION TABLE (SDT)

It is possible to add a CA_identifier_descriptor to a particular service and specify CA_system_id for the descriptor. These parameters can be specified for a newly created service.

Select 'Scrambled content' option to set free_CA_mode flag to 1 for a service. Once the option is selected, it is possible to specify a set of CA system ids for the service. A CA identifier descriptor will be added to the service with the list of CA system ids defined in this dialog.

The same options are available for updating using 'Edit service' scenario.

Another approach to add CA identifier descriptor to a service is editing SDT descriptors directly.

  • Select PSI/SI->Edit SDT...->'Service Name' menu item
  • Service Description Table dialog should appear for the selected service
  • Right-click 'Service descriptors' node and select 'Add descriptor' menu item
  • Choose 'CA identifier descriptor' in a drop-down list and press OK button
  • Expand 'CA identifier descriptor' node
  • Right-click CA_system_ids node and select 'Add CA_system_id' menu item
  • Expand CA_system_id node
  • Double-click CA_system_id field to update its value
  • Press OK to save the changes and close the dialog

2.4. EVENT INFORMATION TABLE (EIT)

free_CA_mode field is automatically set to 1 for a particular event if the event is defined for a service that is declared as one that has scrambled content. Otherwise, it is set to 0.

3. APPENDIX

Conditional Access identifier descriptor sample (XML format)
<!DOCTYPE data PUBLIC "" "si.dtd">
<data>
    <descriptor name="CA identifier descriptor">
        <field bitcount="8" name="descriptor_tag" type="ulong" value="53" visible="false"/>
        <length bitcount="8" target="total"/>
        <list item="CA_system_id" name="CA_system_ids">
            <listitem name="CA_syctem_id">
                <field bitcount="16" name="CA_system_id" type="ulong" value="508" visible="true"/>
            </listitem>
        </list>
    </descriptor>
</data>


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