DVB-SI

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The standard DVB-SI ( D igital V ideo B road casting - S ervice I nformation ) specifies the processing of additional data within the Digital Video Broadcasting (DVB) and has been approved by the European Telecommunications Standards Institute defines (ETSI) in the standard ETS 300 468th It enables u. a. the localization and decoding of the contents of an MPEG transport stream . These data are processed by the recipient and either displayed automatically or they can be called up by the viewer in various menu pages. The information is transmitted within a transport stream in the user data of packets intended for this purpose.

Table overview

The following SI ( Service Information ) are defined for viewer information :

  • BAT: Bouquet Allocation Table (optional)
    • Contains information about the bouquet of programs from a provider, even if they are broadcast via different broadcasting channels.
  • SDT: Service Description Table
    • Contains the programs offered.
    • Contains e.g. B. References to the broadcasters.
  • TDT: Time and Date Table
    • Contains the current time in UTC format
  • TOT: Time Offset Table
    • contains both the time in UTC and the offset to the local time zone
  • RST: Running Status Table (optional)
    • Indicates whether a certain program is currently running, not yet running or will start in the immediate future and thus enables the control of video recorders, among other things
  • EIT: Event Information Table (information for timed recording control)
    • Contains program boards similar to those in program guides.
    • Contains the identifier of the "content_descriptor" (that is the respective program type, or category, or classification).
    • Contains a classification of the programs with regard to their suitability for viewers of certain age groups.
  • NIT: Network Information Table
    • In addition to the name and type of the transmission system (Astra, satellite) it also contains technical parameters such as frequency and error protection

In addition to this "service information", parameters for the technical implementation of the PSI ( program-specific information ) transmission are also defined:

  • PAT: Program Association Table
    • Contains the program number and the packet identifier (PID) for each program on which the PMT is transmitted.
  • PMT: Program Map Table
    • Contains, for each program, information about the elementary streams (video, audio, teletext, etc.) needed to decode them.
  • TSDT: Transport Stream Description Table (optional)
  • CAT: Conditional Access Table (optional)
    • Contains information required to decrypt Encrypted Programs ( Pay TV ), e.g. B. which system is used.

Transmission format

Representation of a decoded TS packet with PAT

The tables are made up of at least one, but usually several, sections. The data volume of a single section consists of a maximum of one kilobyte, with some tables up to four kilobytes. Since the data of a section is often larger than the amount of user data of a single transport stream packet, the content of a section is distributed to the user data of several packets with the same packet identifier (PID). To find the beginning of a section, you must first wait for a package in which the Payload_unit_start_indicator field is set. In this case at least one section begins in the payload of this packet. The first byte of the user data contains the Pointer_field , the number of bytes that have to be skipped to find the first byte of the new section. This value is often "0", so that the section begins immediately after the Pointer_field . If the end of the section is not at the same time the end of the payload of a package and no further section immediately follows, the rest of the payload must be filled with 0xFF.

Each section begins with a byte that contains the Table_id (the value 0xFF is forbidden), followed by four bits and a 12-bit length specification of the bytes that follow in this section. A 32-bit CRC (cyclical redundancy check) checksum forms the end to detect transmission errors. When collecting the section data distributed over several packets, attention must be paid to lost packets or packets sent twice, this is made possible by the Continuity_counter field of the respective packets.

The content is then interpreted according to the syntax diagrams of the individual tables.

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