Changing bandwidth during a simulation...

[ardo80]

Hi everybody!... I'm doing some simulations (using Iperf) to obtain throughputs values of a link between two gigabit ethernet cards for different delays and different drop probability (using netem) .... Now I have to do a 3minute long simulation in which during the first minute the bandwidth is 1000Mbit/s, 500Mbit/s during the second minute and 1000Mbit/s during the third one....
Does anybody know how can i do this type simulation?
Thank you and sorry for my english....

[Rubberman]

There is the ethtool command which is supposed to be able to change the speed of an ethernet port. You can try that.

[ardo80]

There is the ethtool command which is supposed to be able to change the speed of an ethernet port. You can try that.

Thank you. I tried to use ethtool, but it only allows to switch 10, 100, 1000, 2500 or 10000Mbps and I need to set an arbitral bandwidth ( 500Mbps in this specific case)....

[Rubberman]

Well, run ethtool ethN where ethN is the ethernet device, such as eth0, and it will tell you what speeds the device actually supports which you can set with ethtool. In my case, the two ports on my system support 10/100/1000mbps in half or full duplex. I would expect that 500mbps would not be supported on any device since it is a non-standard ethernet speed. In that case, you might have to do some kernel mods to be able to arbitrarily throttle the apparent speed of the device. Good luck in that!

[ardo80]

Hi! I need to simulate a 500Mbps link with a 100ms delay and a loss probability of 0.0001% on an ethernet link between two gigabit ethernet cards...
I tryed to use these commands:

# tc qdisc add dev lo root handle 1:0 netem delay 100ms loss 0.0001
# tc qdisc add dev lo parent 1:1 handle 10: tbf rate 500Mbit buffer XXXX limit YYYYY

But during some simulation throughputs are very low ( 190Kbps....210Kbps....) for different values of XXXX and YYYY.... (I don't want that the loss probability is caused by the buffer and the limit value but only by the loss probability setted on netem...)
What's the problem?
Does anybody know what commands should I use for my purpose?
Thanks.