I'm doing test on test plateform and I try some QoS policies. I'm testing my netwok with WFQ algorithm as scheduling algorithm. I do FTP transmission across my network and I overload my network with trafic created by a IXIA traffic generator.
I use shapping on my FastEthernet Interface to limit the output bandwidth and so that output trafic be schedule by WFQ algorithm.
I became to limit speed to 2Mbps, and I start my ftp transfert. My ftp transfert use all the available bandwidth. I overload my network with 12 Mbps flux created by the IXIA trafic generator. The result is as predicted, i.e,the two flows share among them the available bandwith
(1 Mbps for ftp transfert and 1Mbps for IXIA flux)
I restart the test with a shapping values of 4Mbps , 6Mbps and 8Mbps. the results are as predicted.
The problem begin when I do my test with 10Mbps value shapping. The result is completely unexpected. The IXIA flux use 9Mbps of available bandwith and FTP flux fall to 1Mbps.
I obtain exactly the same result when I use a 10Mbps FastEthernet Interface with fair-queuing enable.
I can't explain this behaviour of FTP traffic. Does the problem come from cisco router and WFQ algorithme???Does the problem come from FTP software, TCP stack???
Has someone already seen this strange behaviour?
Thank you very much for your help.
PS:I join sreenshoot of my test result (wireshark graph)