3.10.3 CoS Mapping Function

The CoS mapping functionality determines the send queue based on the CoS value determined by either user priority mapping or priority determination for flow control.

<Structure of this section>

(1) Mapping CoS to Port Outbound Queues

There are eight queues per port for MAC address learned unicast frames (UC queue), and four queues for MAC address not learned unicast frames, multicast frames, broadcast frames, and mirrored frames (MC queue). The following table shows how CoS are mapped to port-egress queues:

Table 3-15: Mapping CoS to Port Send Queues (UC Queues)
CoS value	Queue number for sending
CoS value	Transmit queue length 2880	Transmit queue length 24272
0	1	2
1	2	2
2	4	2
3	5	2
4	6	2
5	8	2
6	10	2
7	12	4

Table 3-16 Mapping CoS to Port Send Queues (MC Queues)
CoS value	Queue number for sending
CoS value	Transmit queue length 2880	Transmit queue length 24272
0	3	1
1	3	1
2	3	1
3	3	1
4	7	1
5	7	1
6	9	1
7	11	3

(2) Mapping CoS to CPU Send Queues

Unlike the port's transmit queue, the transmit queue for CPU destinations has eight transmit queues that are shared by all frame types. The following tables show how CoS are mapped to CPU send queues.

Table 3-17 Mapping CoS to CPU Send Queues
CoS value	Queue number for sending
0	1
1	2
2	3
3	4
4	5
5	6
6	7
7	8