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An Investigation into Transport Protocols and Data Transport ...

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8.3. Results 162<br />

2000<br />

ScalableTCP 1<br />

ScalableTCP 2<br />

100<br />

ScalableTCP 1<br />

ScalableTCP 2<br />

1500<br />

80<br />

cwnd (packets)<br />

1000<br />

500<br />

Goodput (mbit/sec)<br />

60<br />

40<br />

20<br />

0<br />

0 100 200 300 400 500 600<br />

Time (seconds)<br />

0<br />

0 100 200 300 400 500 600<br />

Time (seconds)<br />

(a) Congestion Window<br />

(b) Goodput<br />

Figure 8.13: Unfairness between ScalableTCP flows (Symmetric network,<br />

100Mbit/sec, 162ms RTT, queuesize 20% BDP).<br />

30<br />

25<br />

ScalableTCP 1<br />

ScalableTCP 2<br />

High-Speed Threshold<br />

10<br />

8<br />

ScalableTCP 1<br />

ScalableTCP 2<br />

cwnd (packets)<br />

20<br />

15<br />

10<br />

Goodput (mbit/sec)<br />

6<br />

4<br />

5<br />

2<br />

0<br />

100 200 300 400 500 600<br />

Time (seconds)<br />

0<br />

100 200 300 400 500 600<br />

Time (seconds)<br />

(a) Congestion Window<br />

(b) Goodput<br />

Figure 8.14: Unfairness between ScalableTCP flows (Symmetric network,<br />

10Mbit/sec, 22ms RTT, queuesize 20% BDP).<br />

of the unfairness experienced by ScalableTCP is shown in Figure 8.13. Similar<br />

to the effects of having large queue size provisions, it can be seen that<br />

the unfairness between the two ScalableTCP flows is caused by very slow<br />

convergence. Similar results were gathered for all cases where ScalableTCP<br />

showed unfairness.<br />

ScalableTCP also demonstrates unfairness at 22ms <strong>and</strong> 42ms under the<br />

10Mbit/sec environment. This was found to be due to its low/high speed<br />

mode switch when cwnd is equal to or more than 16 packets <strong>and</strong> the vastly<br />

different cwnd update algorithms as shown in Figure 8.14.

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