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Chapter 3The DVB/DAVIC protocol pThe reservation-access mode uses the following ‘Contention-Resolution-Grant Cycle’,(CRGC) for data transmissions, as shown in Figure 3.3:1) Wait until a ‘Reservation_ID’ has been received (which allows an NIU to send areservation request).2) When a packet arrives, send a reservation request message, using theReservation_ID assigned, in a contention-based slot.3) Wait until the INA sends the following MPEG2 frame with signalling information(MCI) and check in the reception indicator field whether the reservation wasreceived successfully.4) If the request resulted in a collision, use the CRA selected (exponential backoffalgorithm or the splitting tree algorithm) to retransmit the reservation request aslong as collisions are resolved.T im e fo r n e x tM P E G 2 F ra m ew ith M C I & G ra n tIn fo rm a tio nT im e fo r n e x tM P E G 2 F ra m ew ith M C I & G ra n tIn fo rm a tio nIN A (H E )R e s e rv a tio n _ IDA s s ig n m e n tM P E G 2 F ra m e(M C I)R e s e rv a tio nR e q u e s tM P E G 2 F ra m e(M C I/ R e s e rv a ito n G ra n t/F e e d b a c k )D a ta P a c k e t T ra n s m is s io nD a ta s lo t 1D a ta s lo t 2D a ta s lo t 3N IU (E M )P a c k e tA rriv e sT im e u n tilc o n te n tio n s lo tT im e u n til s u c c -fu l re q u e s t (in c a -s e o f c o llis io n s )T im e u n tilre q u e s t isg ra n te d& p a c k e tre c e iv e dWaiting delay Contention delay Grant delayD a ta s lo t nFigure 3.3 – Contention-Resolution-Grant Cycle.3-7