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Chapter 3The DVB/DAVIC protocol pMAC control message transmissions), reservation (for bursty or high traffic load) orfixed slots (for constant bit rate traffic).These MPEG2 frames with MCI information are transmitted in the downstream channel(at least) once every 3 ms when the upstream data rate is 6.176 Mbps [grade D], 3.088Mbps [grade C] or 1.544 Mbps [grade B], and every 6 ms for 256 kbps [grade A]). TheMCI field describes up to 36, 18, 9 and 3 upstream slots for grades D, C, B, and A,respectively. The limits between access regions allow the EuroModem (which is alsoreferred to as EM, NIU or station) to know when to send data on contention at a timethat risk of collision with data of reservation or fixed-rate regions does not exist.Previously in [101] and also in [34] the authors have reported that several functions areperformed by the MAC protocol for connection control and data transmission asdepicted in Figure 3.2. On power-on or reset, the initialisation and provisioningprocedure makes sure that an NIU is capable of tuning to the correct channel in theupstream and downstream directions and that it can receive the basic networkparameters.Initialisation and R egistration ProcessIN A / H eadendN IU / EuroM odemProvisioning Channel M essageD efault Configuration M essageInitialisation andprovisioning signallingSign-on M essageSign-on R esponse M essageR anging and Pow er Calibration M essageRanging and Power CalibrationResponse M essageInitialisation Com plete M essageSign-on, ranging andcalibration signallingC onnect M essageConnect Response M essageConnect ConfirmConnection signallingFigure 3.2 – DVB/DAVIC initialisation and registration process.3-5