If you have something like 
traffic from Host A - queue A - pipe 1
traffic from Host B - queue B - pipe 1
traffic from Host C - queue C - pipe 1

then you assign weight to each queue. This controls the bandwidth in a
relative manner - if A has weight 20,  B has weight 40 then B should
get twice the bandwidth available.

see http://m0n0.ch/wall/list/?action=show_msg&actionargs%5B%5D=49&actionargs%5B%5D=99
for  good, detailed info