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4-2-8. Quality of Service Configuration
The switch offers powerful QoS function. This function supports VLAN-tagged
priority that can make precedence of 8 priorities, TOS field of IP header (equal
DSCP High 3 bits) on Layer 3 of network framework, 6 kinds of special network
transmission events on Layer 4 and IP DiffServe QoS service.
In Quality of Service (QoS) Configuration, there is one option named” Default
Class”. As you had selected one of the four QoS functions, then some packets that
did not belong to this QoS would be viewed as Default Class. For instance, if you
set QoS function as VLAN Tag Priority mode, and then choose Default Class as
High, finally, the priority of the packets with no tag will be considered as High priority
precedence. The initial value of the Default Class is High.
Fig. 4-13
Functi on name:
VLAN Tag Priority
Functi on description:
In vlan tag, there are 3 bits belonging to priority. According to these 3 bits, we
could arrange 8 traffics –0 0 0, 0 0 1, 0 1 0, 0 1 0, 1 0 0, 1 0 1, 1 1 0, 1 1 1. We
can set High priority or Low priority for each traffic class. For instance, if we let
VLAN-tagged priority 0 0 0 be high priority and VLAN-tagged priority 0 0 1 be
Low Priority, and then make port 1, 2, 3 be in the vlan 2. We sent in the
packets that have vlan-tagged Field appears 0 0 0 and VID equals 2 from the
port 2 and the packets that have vlan-tagged Field appears 0 0 1 and VID
equals 2 from the port 3. We let the two kinds of packets be transmitted for
port 1 until the port results in congestion. The result is that the packets will be
dropped partially from the port 3 because the packets that belong to Low
Priority. For the use of VLAN Tag Priority function, please press Configure at
the right section for setting in advance.
Publication date: January, 2005
Revision A1
65