An Investigation into Transport Protocols and Data Transport ...

8.2. Test Calibration 157
1000
FAST 1
FAST 2
1000
FAST 1
FAST 2
800
800
cwnd (packets)
600
400
cwnd (packets)
600
400
200
200
0
100 200 300 400 500 600
Time (seconds)
(a) Congestion Window at 10% BDP Queuesize
0
100 200 300 400 500 600
Time (seconds)
(b) Congestion Window at 80% BDP
Queuesize
200000
FAST 1
FAST 2
200000
FAST 1
FAST 2
Retransmitted (bytes)
150000
100000
50000
Retransmitted (bytes)
150000
100000
50000
0
100 150 200 250 300 350 400
Time (seconds)
(c) Data Retransmissions per 100ms at 10%
BDP Queuesize
0
100 150 200 250 300 350 400
Time (seconds)
(d) Data Retransmissions per 100ms at 80%
BDP Queuesize
Figure 8.8: cwnd and retransmissions dynamic of FAST at various queue size provisions
under symmetric network conditions (100Mbit/sec, 82ms RTT, Queuesize
as shown).
upon network bursts. This is shown in Figure 8.6(c). It was observed that all
New-TCP algorithms achieve higher throughput at the expense of increased
fractional losses. However, even at large queue provisions, all of the New-
TCP algorithms induce much more packet loss, with no obvious benefit in
extra goodput. This is demonstrated by the differences between the overhead
of Standard TCP and nearly all of the New-TCP algorithms. The exception
to both points is FAST, which manages to avoid excessive losses, but only
when sufficiently large queue-sizes of > 30% of BDP are provisioned.
Figure 8.8 shows the number of bytes retransmitted for the experiments.