Alloy Computer Products 16-PORT GIGABIT WEB SMART SWITCH GSS-16T2SFP - Manual (Page 35)

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4-2-8. Quality of Service Configuration
The switch offers powerful QoS functions including: VLAN tagged priority for 8
levels, TOS field IP header (equal DSCP low 3 bits) on Layer 3 network framework,
6 types of layer 4 network transmission events, and IP DiffServe QoS services.
In the Quality of Service (QoS) Configuration there is an option named ”Default
Class”. Once you have selected one of the four QoS methods, this Default Class is
used to group packets that do not match any of the QoS rules defined for the
particular QoS method selected. For instance, if you set the QoS function as VLAN
Tag Priority mode, and then choose Default Class as High, the priority of the
packets with no tags will be considered as High priority precedence. The initial
value of the Default Class is High.
Fig. 4-13
Function name:
VLAN Tag Priority
Function description:
VLAN tags have 3 bits that belonging to a priority flag. These 3 bits can define 8
traffic classifications. These classifications can then be mapped to High priority
or Low priority queues. Packets tagged as High priority will be forwarded over
packets with a low priority when the destination port is in a congested state.