An Investigation into Transport Protocols and Data Transport ...

8.3. Results 180
600
500
Standard TCP
HTCP
4500
4000
3500
Standard TCP
HTCP
cwnd (packets)
400
300
200
cwnd (packets)
3000
2500
2000
1500
100
1000
500
0
100 150 200 250 300
Time (seconds)
0
100 150 200 250 300
Time (seconds)
(a) 22ms
(b) 162ms
Figure 8.36: Standard TCP competing against H-TCP under asymmetric network
conditions (250Mbit/sec capacity, 20% BDP queuesize).
shares its goodput very fairly in low latency environments, and becomes
more aggressive as the RTT increases; utilising more of the path capacity
in environments where Standard TCP would be incapable of high transport.
This is shown in Figure 8.36. This dynamic is due to the time based adaptive
congestion control that becomes more aggressive as the congestion epoch time
becomes larger, and indicates that Standard TCP is incapable of utilising the
network resources. However, the use of a polynomial increase function results
in a very aggressive algorithm that results in less friendliness to Standard
TCP compared to that of HSTCP and BicTCP in high bandwidth delay
product environments.
It was observed that the friendliness of BicTCP and HSTCP follow similar
trends to each other. Figure 8.37 shows the interaction between BicTCP and
Standard TCP for 22ms and 162ms with a bottleneck capacity of 250Mbit/sec.
It can be seen that the plateau’ing of BicTCP’s cwnd facilitates the growth
of Standard TCP’s cwnd and hence improves fairness upon long latency environments
- whilst still maintaining a high value of cwnd to enable high
utilisation of the network capacity. However, under short latency environ-