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Chapter 3The DVB/DAVIC protocol pThe ‘Feedback Collision Number’ is equal to 0xFF or 0xFE for idle and successfultransmission, respectively.All other values of the ‘Collision Number’ are numbered as collisions and used to selectthe retransmission minislots. The NIU should retransmit in a minislot having an‘Allocation Collision Number’ equal to ‘Collision Number’. The retransmission of thecollided request takes place in a minislot that is randomly selected from among thegroup of three minislots with the corresponding ‘Allocation Collision Number’3.5.4 Upstream slot structureIn Section 3.4, we have stated that the upstream channel is divided into discrete basicslots called upstream slots. A fixed number of upstream slots are grouped to form asignalling frame. A generic slot structure is shown in Figure 3.6 (for a 3.088 Mbpsupstream channel), where the INA determines the slot structure format (and reservationcapacity) by setting the number of ranging, contention, reservation and fixed slots ineach signalling frame, an example of which is depicted in Figure 3.6a. They are used forthe following purposes:• Ranging slots: These slots are used in the sign-on, ranging and calibrationsignalling process to measure and adjust the time delay and the power.Signalling Slot Structure3 milisecond periodSlot Configuration Field 1 Slot Configuration Field 2a)b)c)1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18Ranging slotContention slotReservation slotFixed slotMinislotFigure 3.6 – Slot structure.3-11