DOWNLOAD MY Ph.D Thesis - UNAM

Chapter 3The DVB/DAVIC protocol pThey are the Broadcast Channel (BC) and the Interaction Channel (IC). The BC is aunidirectional broadband broadcast channel including video, audio and data. The IC is abi-directional interaction channel, which is established between the service provider andthe user for interaction purposes. It is formed by the following paths:• Return interaction path (also referred to as upstream channel): from the user to theservice provider. It is used to make requests to the service provider, transmit userdata or to answer questions.• Forward interaction path (also referred to as downstream channel): from the serviceprovider to the user. It is used to provide information generated by the serviceprovider for the user and any other required communication for interaction serviceprovision.Data connectivity is achieved via STB or EuroModem, which contain a NetworkInterface Unit (NIU) for interfacing with the cable network. The NIU consists of theBroadcast Interface Module (BIM) and the Interactive Interface Module (IIM). The userterminal provides an interface for both the broadcast and interaction channels. Theinterface between the user terminal and the interaction network is via the IIM.In the upstream channel, a 64-byte (upstream) slot structure is used and in thedownstream channel, the packet structure is based on 188-byte MPEG2 TS frames.Appendix B presents a description of packet formats, PDU structures, signallingmethods and protocol configurations.3.5 DVB/DAVIC MAC operationOne downstream channel can manage up to eight upstream channels by using MACcontrol information (referred here as MCI, see Figure B.4). This MCI field plays a vitalrole in the operation of this communication system, because it contains synchronisationinformation of the upstream slots. Its main functionality is to co-ordinate the usage,assign access modes, and indicate if reception of contention-based slots was successful.Each slot is assigned one of the following four classifications from the INA: ranging(for synchronisation and calibration purposes), contention (for light traffic load and3-4