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Chapter 6Optimisation of CRA using adaptive CSAs pThis effect can be appreciated in Figure 6.20, which presents in detail the collision ofthree NIUs. For this analysis the period begin when three stations collide and ends whenthe NIUs transmit their data message successfully.In Figure 6.20 each line shows the use of the 18 slots described in each signalling frame(MCI). For the exponential backoff algorithm, stations 43, 25 and 8 transmit areservation request at MCI 1, using the same contention slot. Then, the stations shouldwait until the headend sends back the acknowledgements of these reservation requests,which is at MCI 3. At this point, the stations detect the collision. Station 43 backs offfor 10 CSs, and stations 8 and 25 transmit in CS 0 and 1, respectively.3a) a) Exponential Backoff Algorithmb) Splitting Spliting Tree Algorithmtime (ms) 691215 18212427⌨30333639 42 45 4860Successful requestslot/minislotCollidedslot/minislotEmptyslot/minislotRersed Reserved data data slot slotFigure 6.20 – Upstream slot usage. Exponential backoff vs. splitting tree algorithmfor IP traffic with 49 stations. Sequence captured at 30 seconds of simulation.6-27