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Chapter 3The DVB/DAVIC protocol pEuropean cable operators. The final EuroModem specification [36] was published afterapproval by the ECLs in May 1999.Two different types of EuroModem devices have been defined. The class “A”EuroModem is the basic version and is used mainly for high-speed Internet access. Thishas functionality similar to that of a DOCSIS 1.0 compliant modem. Using a class AEuroModem a secure data transmission is possible due to the defined encryptiontechnique. The class “B” EuroModem is the enhanced version supporting someadditional features. For instance, it is possible to deliver high-quality telephony servicesor Integrated Services Digital Network (ISDN) connections and also IP telephony(VoIP) with a guaranteed Quality-of-Service (QoS) level. A common telephonyinterface allows connection of a telephone device directly to the class B EuroModem.This modem has functionality similar to that of the DOCSIS 1.1 compliant cablemodem. For a further comparison of these three protocol specifications the readers arereferred to [84] and [109].3.4 DVB/DAVIC reference modelThe system reference model for interactive services for the DVB/DAVIC protocolspecification is shown in Figure 3.1. In the system model there are two channelsestablished between the service provider and the user.Broadcast ChannelBroadcastServiceProviderBroadcastNetworkAdaptorBroadcastDeliveryMediaBCSet Top Box (STB)/EuroModemBIMInteractive ChannelsIIMSTUInteractiveServiceProviderInteractiveNetworkAdaptorInteractionNetworkNIUEndUserInteractive ChannelNetwork IndependentNetwork DependentFigure 3.1 – DVB system reference model.Network Independent3-3