Networking :: Simulate A 500Mbps Link On A 1000Mbps?

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...)