2.2.1 User Priority Mapping

User priority mapping functionality determines priority based on the user priority in the VLAN tags of received frames. The Switch always operates user priority mapping and determines the priority for unicast frames. Since user priority mapping is not performed for broadcast frames and multicast frames, CoS determined by priority determination is used.

CoS values that indicate the priority on the Switch are used as priority values. The user priority value of the received frame is mapped to a CoS value, and the send queue is determined based on the CoS value. For the correspondence between CoS and send queues, see "3.10.3 CoS Mapping Function".

The user priority is the three highest-order bits of the Tag Control field (VLAN tag header information). Note that CoS value 3 is always used for frames without a VLAN tag.

When running, priority determination by flow control has priority over user priority mapping.

Table 2-2: Mapping of user priorities and CoS

Frame type		Mapped CoS values
VLAN tag	User priority value
Without VLAN tag	-	3
VLAN Tag available*	0	0
	1	1
	2	2
	3	3
	4	4
	5	5
	6	6
	7	7