Th`ese de Doctorat de l'université Paris VI Pierre et Marie Curie Mlle ...

Table 8.1: Average performance gain achieved by IBA (Ideal Bandwidth Allocation) with respect to
OBA (Optimum Bandwidth Allocation)
Network Scenarios Average increase Average increase
in accepted load in network revenue
Single-Bottleneck 17% 31%
Simple Core Network 24% 34%
Multi-Bottleneck 24% 32%
Complex Core Network 27% 44%
8.2 Discussion
Note that, when Exponential sources are always active (the right points in all the graphs),
the performance of OBA almost overlaps that of IBA, especially in the last three network
scenarios. When the Off time of Exponential sources is greater than zero, the difference
between IBA and OBA is more evident.
Two main factors impact on the performance of our proposed heuristic bandwidth
allocation algorithms: traffic prediction and bandwidth allocation granularity. Let us recall
that in the bandwidth allocation process Non-greedy sources are allocated the quantity
min{2 · b n−1
k ,srk}, thus leading to a potential bandwidth wastage. On the other hand,
since bandwidth allocation is performed only every Tu seconds, traffic variations can be
tracked only with such granularity, leading again to potential inefficiency in bandwidth
allocation.
The behavior observed in these scenarios shows that the impact of traffic prediction is
less remarkable with respect to that of the update interval Tu. In effect, when all sources
are always active, no traffic changes occur, and Tu has no impact on the performance of the
allocation algorithms. Moreover, since in this case the gap between IBA and the heuristic
algorithms is negligible, the bandwidth wasted due to the traffic predictor has little impact
on the algorithms performance.
Since in these scenarios traffic prediction has even lower impact when sources are not
77