Thank you all, iproute was what I was looking for so long. just with this I reduce a little my outgoing bandwidth, but interactivity is greatly increased as well as my ping and DL bandwidth !
# tc qdisc add dev ppp0 root tbf rate 240kbit latency 30ms burst 1700 Raising the burst (=bucket) increases the outgoing bandwidth to the depends of interactivity. Also possible to do this by increasing the priority of the small packets. Guillaume
