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Common Interface scheme
DVB-Receiver with Common Interface module

Digital Video Broadcasting – Common Interface (or DVB-CI), is a defined standard, to enable the addition of a conditional access module, CAM, in a DTV Receiver, to adapt it to different kinds of cryptography. Indeed, one of DVB's main strengths is the option of implementing the required conditional access capability on the Common Interface.

This allows broadcasters to use modules containing solutions from different suppliers in the same broadcast system, thus increasing their choice and anti-piracy options.

Contents

Technical

A DVB receiver may have one or two slots implementing the Common Interface (CI). The CI uses the PCMCIA connector and conforms to the Common Scrambling Algorithm (CSA), the normative that specifies that such a receiver must be able to accept DES (Data Encryption Standard) keys in intervals of some milliseconds, and use them to decode private channels according to a specific algorithm.

Those algorithms are proprietary to individual suppliers. Each one uses their own algorithms and there is no defined standard for them.

As the full MPEG-2 transport data stream comes out of the demodulator, and error correction units, the DTV Receiver sends it through the card plugged into the Common Interface, before it is processed by the MPEG demultiplexer in the receiver. If several CI cards are present, the MPEG transport data stream will be passed sequentially through all these cards.

An embedded CAM may not physically exist, as it may be in CPU software. In such a case, only the ISO card reader normally in the CAM is fitted and not the PCMCIA type CI slots.

Even if the Common Interface has been created to resolve cryptography issues, it can have other functions using other types of modules such as Web Browser, iDTV (Interactive Television), and so forth.

In Europe, DVB-CI is obligatory in all iDTV terminals.

Standard

The normative DVB-CI standard EN 50221 was defined in 1997 by CENELEC, the European Committee for Electrotechnical Standardization.

According to the Common Interface scheme:

  • host : A device where module(s) can be connected; for example, an Integrated receiver/decoder (IRD), a VCR, a PC ...
  • module : A small device, not working by itself, designed to run specialised tasks in association with a host; for example, a conditional access sub system, an electronic program guide application module, or to provide resources required by an application but not provided directly by the host.

The specification only defines two aspects, two logical interfaces to be included on the same physical interface. The first interface is the MPEG-2 Transport Stream. The link and physical layers are defined in this specification and the higher layers are defined in the MPEG-2 specifications. The second interface, the command interface, carries commands between the host (receiver) and the module.

The specification does not define the operation or functionality of a conditional access system application on the module. The applications that may be performed by a module communicating across the interface are not limited to conditional access or to those described in this specification. More than one module may be supported concurrently.

See also

References

External links

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