An Investigation into Transport Protocols and Data Transport ...

8.3. Results 176
2000
HTCP 1
HTCP 2
2000
HTCP 1
HTCP 2
1500
1500
cwnd (packets)
1000
cwnd (packets)
1000
500
500
0
100 150 200 250 300 350 400
Time (seconds)
(a) 36 packets (20% of 16ms BDP)
0
100 150 200 250 300 350 400
Time (seconds)
(b) 270 packets (20% of 162ms BDP)
Figure 8.30: H-TCP under asymmetric network conditions (100Mbit/sec capacity,
with Flow 1 experiencing 162ms RTT and Flow 2 experiencing 22ms RTT.
Bottleneck queue size at 20% BDP of the 162ms flow).
8.3.3 Friendliness
Figure 8.31 shows the aggregate throughput between a Standard TCP flow
and a New-TCP flow under symmetric network conditions.
As the New-TCP algorithms are more aggressive, especially in high BDP
environments, the question is by what ratio the goodput is shared between
the legacy TCP flow and the New-TCP flow. Figure 8.32 shows the friendliness
of New-TCP algorithms against Standard TCP under identical network
conditions across a range of different network environments.
The aggressiveness of a ScalableTCP flow against Standard TCP can be
seen in Figure 8.33. Even under environments where Standard TCP is still
capable of high throughput, the cwnd dynamic of ScalableTCP forces the
goodput of Standard TCP to well below fair sharing of the link. It can be
seen that all loss-based congestion algorithms predictably become less fair to
Standard TCP as the bottleneck capacity increases. At 10Mbit/sec, however,
ScalableTCP and FAST are still more aggressive to the Standard TCP flow
and impose an unfairness of approximately 1:5.