hello,everyone,i want to add a monitor queue to ns,but it works not well,what's wrong with it? the tcl is: set qf [open qwf.tr w] set qt [$ns trace-queue $n0 $n2 $qf] set qm [$ns monitor-queue $n0 $n2 $qt] #the up three works well,but the next is wrong: puts [$qm pdrops_]//here i want to account the drop packets