I'm trying to understand the expected behavior of a L2 switch with enabled QoS and 802.1p mapping, i.e. cos 0 is mapped to queue 0, cos 1 to queue 1 and so on.
Consider example: 1G ports, pump traffic from port1 to port3 and from port2 to port3 at a maximum rate, as a result port3 is unable to sustain it; in such case enabling priority mapping will prioritize one type of traffic over another, does this mean that I will see high priority frames leaving the egress port first, and then only low-priority packets, i.e. I will observe packets re-ordering at the egress side?
To backup my reasoning, here is the example -- L2 switch with 4 queues (0 has the highest priority), maps COS values in such way:
p1 has cos7 -> q3 p2 has cos5 -> q2 p3 has cos3 -> q1 p4 has cos0 -> q0
p1,p2,p3,p4 --->[L2 switch with 802.1p mapping] -----> p4,p3,p2,p1
I believe this is correct when strict priority queuing is enabled. Is my understanding of the priority mapping and switch's behavior correct?
Thanks in advance for comments !