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An Investigation into Transport Protocols and Data Transport ...

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8.3. Results 165<br />

Fraction Bytes Retransmitted per Mbit/sec<br />

1<br />

0.1<br />

0.01<br />

0.001<br />

1e-04<br />

1e-05<br />

1e-06<br />

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

1e-07 BicTCP<br />

FAST<br />

1e-08<br />

HSTCP<br />

HTCP<br />

ScalableTCP<br />

1e-09<br />

10 100<br />

RTT (msec)<br />

(a) 10Mbit/sec Bottleneck Capacity<br />

Fraction Bytes Retransmitted per Mbit/sec<br />

1<br />

0.1<br />

0.01<br />

0.001<br />

1e-04<br />

1e-05<br />

1e-06<br />

1e-07<br />

1e-08<br />

1e-09<br />

10 100<br />

RTT (msec)<br />

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

BicTCP<br />

FAST<br />

HSTCP<br />

HTCP<br />

ScalableTCP<br />

(b) 100Mbit/sec Bottleneck Capacity<br />

Fraction Bytes Retransmitted per Mbit/sec<br />

0.01<br />

0.001<br />

1e-04<br />

1e-05<br />

1e-06<br />

1e-07<br />

1e-08<br />

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

BicTCP<br />

FAST<br />

HSTCP<br />

HTCP<br />

ScalableTCP<br />

1e-09<br />

10 100<br />

RTT (msec)<br />

(c) 250Mbit/sec Bottleneck Capacity<br />

Figure 8.18: Overhead of New-TCP algorithms with two competing TCP flows<br />

with symmetric network conditions (Bottleneck Queuesize set to 20% BDP).<br />

actually quite poor in relation to the other algorithms. This was found to<br />

be due to FAST requiring sufficiently provisioned bottleneck queue sizes in<br />

order to provide the multi-bit network information for FAST to be able to<br />

settle <strong>into</strong> a constant value of cwnd. Otherwise, FAST has to resort to an<br />

aggressive probing of b<strong>and</strong>width with large values of α, which induces loss<br />

<strong>and</strong> hence decreases efficiency. This is confirmed by [KRB05] which states<br />

that the queue has to be sized to enable the bursts of packets caused by this<br />

increase.<br />

The cwnd dynamic of FAST is shown in Figure 8.19. Under the lower<br />

latency network of 42ms, it can be seen that FAST is continuously attempting

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