Manual:Queues - PCQ
PCQ was introduce to optimize massive QoS systems where most of the queues was exactly the same only for different sub-streams. For example a sub-stream can be download or upload for one particular client (IP) of connection to server.
PCQ algorithm is very simple - at first it uses selected classifiers to distinguish one sub-stream from another, then applies individual FIFO queue size and limitation on every sub-stream (witch is exactly the same for every sub-stream), then group all sub-streams together and apply global FIFO queue size and limitation
So instead of having 100 queues with 1000kbps limitation for download we can have one PCQ queue with 100 sub-streams