An Investigation into Transport Protocols and Data Transport ...

9.2. Preferential Flow Handling Using DiffServ 219
1000
AF
BE
800
Throughput (mbit/sec)
600
400
200
0
0 50 100 150 200 250 300
Time (seconds)
Figure 9.19: Dynamic switching of BE:AF bandwidth allocations every 60 seconds
from 90:10, 70:30, 50:50, 30:70 and 10:90.
and 10:90 between the AF class and BE classes.
The results show that the bandwidth scheduler works well as the allocations
are changed approximately every minute. The peaks and drops of
throughput at each change are a result of the dynamic switching whereby
the bandwidth scheduler is over providing the AF flow.
9.2.2 Results
Figure 9.20 shows the measurement of QEF for the different allocations of
AF:BE ratios. Compared to the results of Figure 9.3, where in the absence of
differentiated traffic, Standard TCP performs very poorly, the improvement
in goodput of single TCP flows when the TCP flow is protected is dramatic
- utilising at least 95% of the pipe allocation (so at 90% AF Standard TCP
is able to achieve approximately 85.5% of the pipe).
Surprisingly, however, is that the other algorithms perform relatively
badly with large AF allocations with ScalableTCP showing the lowest utilisation
of its AF pipe. At the lowest AF allocations, all algorithms perform
identically.
The dynamic bandwidth allocations between the AF and BE classes is