2. Cont. on demand
3. Deferred TV
Business models for interactive services can based on the direct billing of multimedia contents. This applies primarily to television and VoD. However, other data which incurs fees is also conceivable. The contents must be transmitted in encrypted format in this case. Only authorised viewers with the respective access codes can use the contents.


Embedded Conditional Access (CA) systems

Embedded CA systems are predominantly used in digital television. These are based on three concepts:

  1. New CA data is sent together with the encrypted moving image at regular intervals (e.g. every minute) in the so-called Entitlement Control Messages (ECM).
  2. The personalised access code is located on a card (smart card) which is inserted into the receiver unit.
  3. The actual decryption algorithm is a component of the receiver device software.
Data, access codes and algorithms allow decryption in real-time.


Conditional Access Module (CAM)

Access with the aid of such modules functions in a similar way to that with embedded CA systems. However, the smart card is first plugged into a hardware module, which is then connected with the receiver unit via the so-called Common Interface (CI).

The advantage of using a CAM is the possibility to quickly change the encryption system. The coverage of interactive services which incur fees could expand. CI-interfaces are lacking in many receiver devices due to the high hardware costs.


Software-based systems for digital rights (DRM)

In principle, DRM systems, which are familiar from computers, can also run on iTV devices. Connection takes place with the aid of a software key and a licence which is requested via the return channel. This method appears simple and flexible for use with the contents of iTV applications. Dispensing with a smart card does unfortunately make this system less secure.



Harald Molina-Tillmann

Introduction to interactive television

4. Return channel
5. Encryption

5. Encryption

6. Further technology
7. Runtime environm.
1. TV transmission
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8. Programming
9. API