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C
ONFIGURING THE
QOS Settings
QoS (Quality of Service) is a mechanism which is used to prioritize certain
traffic as it is moves through the switch. Traffic can be classified as High or
Normal priority and, when the switch is heavily loaded, it is the Normal
priority packets that are dropped first. You can select how traffic is
prioritized by using one of the four QoS modes which is selected using the
QoS Mode drop-down list.
Note:
QoS Disabled
QoS is turned off and all packets have equal priority.
802.1p
Packets are prioritzed using the content of the VLAN-tag. The 802.1p field
is held within the VLAN-tag of a packet. The field is three bits long so can
hold eight values; 0 - 7 inclusive. When QoS Mode is set to 802.1p, the
802.1p Configuration table appears which allows a priority (normal or
high) to be set for each of the eight values.
You can use the Prioritize Traffic drop-down list to quickly set the values
in the 802.1p Configuration table. Select All Normal Priority to set all
values to normal priority or select All High Priority to set all values to high
priority. Use Custom if you want to set each value individually.
Note: Because end-stations, like PCs, are not usually VLAN aware, they do
not create VLAN-tagged frames. As a result, this method of prioritization
is not ideal when there are a lot of PCs connected to the Switch.
5-32
S
WITCH
Figure 5-22 VLAN Settings
Only one QoS mode can be active at one time. It is not possible,
for example, to prioritise traffic using the IP Port number and
802.1p tag.
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