Packets received by the BS and destined to the DL are sorted by the packet classifier and buffered into one of the per-class queues in the BS, according to the class of service they belong to. In the queues, packets wait for transmission over the air toward a given SS. Queues are managed by the scheduler on a frame basis.
The main task of the classifier is to match the CID of the incoming packets with the traffic class they belong to, and to queue such packets in their relevant buffers. Only the service received by rtPS, nrtPS, and BE queues will be analyzed, because flows belonging to the UGS and ertPS service classes are assumed to receive a constant reserved amount of bandwidth frame-by-frame and not need to be scheduled. This choice allows high demanding (UGS and ertPS) flows to save up the time required for the BR process.
Another important task of the classifier is to timestamp each incoming packet according to its arrival time. This information is exploited by the buffer manager to recognize when a queued packet’s timeout expires, i.e., when its elapsed waiting time exceeds the maximum tolerated latency.
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