An Investigation into Transport Protocols and Data Transport ...

8.3. Results 169
This is due to the adaptive back-off (See Figure 6.1.3) whereby upon sudden
changes in bandwidth at congestion, a more conservative back-off of 0.5 is
utilised. This is aided by the short congestion epoch time as a result of its
polynomial increase. Even with a RTT of 324ms, two H-TCP flows converge
to 80% throughput ratio within approximately half a minute under all tested
conditions; this is about four times faster than BicTCP or HSTCP.
The low convergence times of Standard TCP for the latencies of 162ms
were found to be caused by the second Standard TCP flow’s cwnd to grow
beyond the of the first flow as a consequence of slow start; which causes
immediate convergence between the two competing flows.
8.3.2 Asymmetric Network
The interaction between New-TCP flows of different latencies was investigated.
This was accomplished by keeping the initial flow at a latency of
162ms and varying the latency of the second flow from 16ms to 162ms.
In order to determine the effects of buffering upon the competing flows,
two values were use for the queue-size 20% of the BDP of the short latency
flow (small queue-size) and that of 20% of the long latency flow (large queuesize).
Small Queue-size
Figure 8.22 shows the aggregate throughput of both flows under asymmetric
network conditions with a queue size buffer set to 20% BDP of the smallest
latency flow which is marked on the abscissa.
Similar to the results shown in Figure 8.10, ScalableTCP and BicTCP
managed to achieve the highest throughput out of all the New-TCP algo-