An Investigation into Transport Protocols and Data Transport ...

8.3. Results 173
800
700
600
StandardTCP 1
StandardTCP 2
100
80
StandardTCP 1
StandardTCP 2
cwnd (packets)
500
400
300
200
100
Goodput (mbit/sec)
60
40
20
0
100 150 200 250 300 350 400
Time (seconds)
0
100 150 200 250 300 350 400
Time (seconds)
(a) Congestion Window
(b) Goodput
Figure 8.26: Standard TCP under asymmetric network conditions (100Mbit/sec
capacity, with Flow 1 experiencing 162ms RTT and Flow 2 experiencing 42ms
RTT, queuesize 20% BDP of 42ms).
magnitude more unfair than Standard TCP in identical test environments.
HSTCP, BicTCP and FAST have similar unfairness properties at across the
board.
Out of all the algorithms, only H-TCP shows fairness across the
range of RTT ratios that is more than that of Standard TCP. This suggests
that on a long distance link, H-TCP flows will not be starved of throughput
by shorter latency H-TCP flows, whilst the other New-TCP algorithms are
likely to cause lock-up of the competing New-TCP flow.
Large Queuesize
The effect of a larger queue size clearly shows an almost full utilisation of
the network capacity for all algorithms as shown in Figure 8.27. However,
Standard TCP still suffers from reduced goodput with long latencies. This
effect was also observed with HSTCP (although not as much), and is expected
as it only gradually deviates from that of Standard TCP with larger BDP at
such low cwnd values.
The fairness between the flows is shown in Figure 8.28.
The effect of
differing queue sizes upon the fairness between two asymmetric ScalableTCP