cisco router bandwidth limit between fms and live publisher

I put a cisco router between fms and a live publisher(the publisher also play a stream from fms).

I print the Kb/s of the publish netStream, It's OK when unlimit bandwidth(both publish and play).

when I limit bandwidth to 20KB/s on upload and 20KB/s on download, the Kb/s of the publishing netStream is down to 2KB/s, (but play side is OK,can reach 20Kb/s).

and I caculate the upload bandwidth to fms is 20KB/s. Can router packet droping cause this problem?

Why that happend??????  Can't I limit bandwidth with router????? What can I do ????

Any one help! Thx!!!!!! .