An Investigation into Transport Protocols and Data Transport ...

9.3. Internet Transfers 234
Fraction Bytes Retransmitted per Mbit/sec
10 −4
10 −6
10 −8
10 −10
10 −12
Standard TCP HSTCP ScalableTCP HTCP FAST BicTCP
New−TCP
Figure 9.29: Overhead from CERN to Stanford.
H-TCP and BicTCP have a high number of outliers which cause very unstable
results. However, BicTCP has a lower median and inter-quartile range,
suggesting generally better stability when compared to H-TCP.
Whilst ScalableTCP does not have the large number of outliers, it has
the largest inter-quartile range of results. FAST also maintains a large range
of values, but has a very narrow inter-quartile range; making it the most
consistent TCP protocol, bar Standard TCP.
Standard TCP demonstrates low coefficient of variance due to the slow
growth of cwnd which over this long latency path is unable to frequently
induce packet loss and hence multiplicative decrease.
Overhead
The overhead inefficiency is shown in Figure 9.29. It shows that all New-
TCP algorithms perform similarly (although note the log scale), with approximately
a magnitude greater overhead compared to Standard TCP. It is
arguable that ScalableTCP has the highest overhead. However, BicTCP also
maintains many outlying points, with as much range as that of ScalableTCP.