Before i tried zeroshell, i was using monowall.
In their forums some one asked the question: “whats the use for the downstream shaper?”
I answered then, and i will explain now:
when a server has more upload then you have download, the server sends packages at the max speed it can, but your ISP system does not allow you to get them at that speed, they simply hold the packages there. This causes lag in your downstream.
Since the server wont send more packages until your client sends the message saying that he got the last packages, it will reduce the stress on the ISP.
If you have a shaper with a lower limit then your ISP, then, its your shaper that causes the lag, but in that case, you have a chance to chose what lags and what does not.
So downstream QOS wont add QOS to the package passing, but it will add QOS in the next packages, because of the delay on that one.