An Investigation into Transport Protocols and Data Transport ...

8.3. Results 163
cwnd (packets)
1200
1000
800
600
400
200
HSTCP 1
HSTCP 2
α
20
15
10
5
HSTCP 1 α
HSTCP 1 β
HSTCP 2 α
HSTCP 2 β
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
β
0
50 100 150 200 250 300 350
Time (seconds)
(a) Congestion Window
0
0
50 100 150 200 250 300 350
Time (seconds)
(b) AIMD Parameters
Figure 8.15: Unfairness between HSTCP flows (Symmetric network, 250Mbit/sec,
42ms RTT, queuesize 20% BDP).
2500
2000
HSTCP 1
HSTCP 2
20
15
HSTCP 1 α
HSTCP 1 β
HSTCP 2 α
HSTCP 2 β
1
0.9
0.8
0.7
cwnd (packets)
1500
1000
500
α
10
5
0.6
0.5
0.4
0.3
0.2
β
0.1
0
100 200 300 400 500 600
Time (seconds)
(a) Congestion Window
0
0
50 100 150 200 250 300 350
Time (seconds)
(b) AIMD Parameters
Figure 8.16: Unfairness between HSTCP flows (Symmetric network, 250Mbit/sec,
82ms RTT, queuesize 20% BDP).
There are also fairness problems with HSTCP at certain latencies, caused
by the regions of mode switching between the different α and β regimes.
This is visible at 82ms with 10Mbit/sec, 42ms at 100Mbit/sec and 42ms
at 100Mbit/sec. An example of this cwnd and AIMD dynamic is shown in
Figures 8.15 and 8.16 and shows that the unfairness appears to be caused
by the quantisation of HSTCP’s AIMD parameters of the two flows. This is
caused by the implementation of the look-up table as defined in [Flo03] with
discrete values of AIMD for the various operating regions of HSTCP.
In Figure 8.12(a), it can be seen that BicTCP appears to have prob-