Ack loss, throughput decrease

[muellert@ifn.et.tu-dresden.de (Torsten Mueller)]

Hi,

I have made a simple simulation with the TCP/SACK1, dropping ACK packets
with a certain probability (without delayed Ack).
The strange behavior is, that at about p_loss = 0.5, there is a
drop in goodput:

p_loss	  goodput (Mbit/s)
---------------------------
0.1      5.0020800000000003
0.2      5.0020800000000003
0.3      5.00176
0.45     5.0015999999999998
0.5      5.0014399999999997
0.51     5.0014399999999997
0.52     5.0014399999999997
0.53     5.0014399999999997
0.54     0.01184
0.55     0.01184
0.6      0.01136
0.7      0.0022399999999999998
0.8      0.00064000000000000005


The results are similar also with other TCP versions.
With delayed Ack the goodput drop starts earlier and  is more smootly.

Does anybody know, why this happens?


Thanks,
Torsten