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Chapter 8Final conclusions pfocused on the optimisation of the initial and truncated backoff bounds (or backoffwindow Bw[i-t]) for the exponential backoff algorithm. Results for mixed traffic at 41.7kbps per station revealed that an increase in system performance is achieved with Bw[4-6]. With this backoff window, up to 75% of all data packets are transmitted in less than100 ms.A good system performance can also be obtained with Bw[3-4], Bw[2-4], Bw[3-6], andBw[3-5]. From this analysis it was seen that defining short values for the initial backoffexponent, such as Bw[2-3], results in a poor system performance. This is becausebacklogged stations are forced to transmit in the next 2 i = 4 contention slots, whichincreases considerably the risk of collision with new incoming packets. A similarperformance degradation is obtained with a large backoff window (e.g. Bw[5-7]). Theconsequence of this is because backlogged stations are now forced to wait a relativelylong period of time before they can compete again for contention access. With Bw[2-3]and Bw[5-7] only up to ≈ 33% of all packets generated are transmitted in less that 100ms.We also found the backoff window that provided optimal performance when only VoIPtraffic (9.7 kbps) is transmitted. They were Bw[5-7] and Bw[4-8]. If we compare therange of the optimum backoff window for mixed traffic and VoIP streams, we can seethat larger backoff windows are needed when only VoIP traffic is transmitted. This is tobe expected since the data rate of VoIP stream is lower than the data rate for mixedtraffic, thus the number of streams (or stations) can be increased. This in turn increasesthe probability of collisions, and indicates that larger backoff windows should beconsidered to reduce this probability. An important point here is that the maximumsystem throughput is reduced from ≈ 45% when mixed traffic is transmitted to ≈ 32%when only VoIP is delivered. This reduction is attributed to the increased number ofstreams supported, which requires more bandwidth to resolve collisions, and the higherprotocol overhead involved when delivering VoIP traffic.Similarly, the second performance optimisation focused on the Entry spreading (Es)factor of the splitting tree algorithm. In this analysis it was found that there is not muchdifference from selecting different Es values. Simulations results suggested that for8-10