An Investigation into Transport Protocols and Data Transport ...

10.2. New-TCP Suitability Study 251
be possible to manually set the intermittent devices queuesize to facilitate
FAST TCP usage.
The ability for the TCP flows to quickly ‘grab’ available throughput on
such empty pipes is also important. Section 9.3 demonstrates that FAST, H-
TCP and BicTCP are able to maintain high throughput by virtue of having
aggressive throughput gradients on the Internet - which is also applicable on
dedicated circuits. ScalableTCP, on the other hand, has a very slow growth
rate when throughputs are relatively small - as demonstrated in Figure 9.34.
H-TCP also implements an adaptive backoff algorithm whereby the measured
latency can be used to provide maximal utilisation of the network
path.
10.2.4 Area 4
In this application area, the sharing dedicated circuits will require that New-
TCP algorithms are both fair and have quick convergence times to maximise
utilisation.
Both FAST and H-TCP is able to quickly converge to fairness between
competing flows, whilst ScalableTCP has undesirable properties of very long
convergence times and hence is also transiently unfair. The issue of RTT
unfairness will also seriously limit the rate at which sites further away from
their parent Tiers can transfer data. It is therefore preferable for each site
to sustain equal goodput; irrelevant of the geographical distance. As such,
ScalableTCP, BicTCP and HSTCP are not recommended.
Similar to the arguments for Area 3, as long as there is sufficient buffering
for the FAST flows, FAST is able to maintain very good properties for high
thoughput and fairness. Under insufficient buffering, the loss-based nature of