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An Investigation into Transport Protocols and Data Transport ...

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8.3. Results 179<br />

1000<br />

St<strong>and</strong>ard TCP<br />

FAST<br />

100<br />

St<strong>and</strong>ardTCP<br />

FAST<br />

800<br />

80<br />

cwnd (packets)<br />

600<br />

400<br />

Goodput (mbit/sec)<br />

60<br />

40<br />

200<br />

20<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 8.34: St<strong>and</strong>ard TCP competing against FAST under symmetric network<br />

conditions (100Mbit/sec capacity, 82ms RTT, 20% BDP queuesize).<br />

1400<br />

St<strong>and</strong>ard TCP<br />

FAST<br />

250<br />

St<strong>and</strong>ard TCP<br />

FAST<br />

1200<br />

200<br />

cwnd (packets)<br />

1000<br />

800<br />

600<br />

400<br />

200<br />

Goodput (mbit/sec)<br />

150<br />

100<br />

50<br />

0<br />

100 150 200 250 300<br />

Time (seconds)<br />

0<br />

100 150 200 250 300<br />

Time (seconds)<br />

(a) Congestion Window<br />

(b) Goodput<br />

Figure 8.35: St<strong>and</strong>ard TCP competing against FAST under asymmetric network<br />

conditions (250Mbit/sec capacity, 42ms RTT, 20% BDP queuesize).<br />

The failure of the FAST dynamic upon insufficiently provisioned queuesizes<br />

is shown in Figure 8.35. In contrast to the dynamic as shown in Figure<br />

8.34, FAST continually induces an aggressive ramp up without being able<br />

to stabilise <strong>into</strong> its congestion control algorithm. The result is unfairness between<br />

the St<strong>and</strong>ard TCP flow <strong>and</strong> the FAST flow that is actually more aggressive<br />

than that of ScalableTCP. The utilisation under such environments<br />

is also lower than that of just two St<strong>and</strong>ard TCP flows, due primarily to<br />

flooding of packets <strong>into</strong> the network by the FAST flow at 250Mbit/sec.<br />

Conversely to the other loss-based algorithms, H-TCP at high speeds

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