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Psion Teklogix 9160 G2 Wireless Gateway User Manual 189
Chapter 19: Quality of Service (QoS)
802.1p And DSCP Tags
The 802.1p header includes a three-bit field for prioritization, which allows packets
to be grouped into various traffic classes. Eight priority levels are defined. The
highest priority is seven, which might go to network-critical traffic (voice). Higher
priority packets are always transmitted first. Lower priority packets are not transmit-
ted if higher priority packets are still in transmission, rather they are held in a queue
until the higher packets have been successfully transmitted.The lowest priority level
is zero, this is used as a best-effort default, it is invoked automatically when no other
value has been set.
Note: It is important to note that 802.1p will not work unless QoS and WMM are
enabled. WMM must be enabled on both the AP and on the client connect-
ing to the AP.
The flow diagram in Figure 19.2 outlines the way in which tags are retrieved and
traffic prioritized on a network.
Figure 19.2 Prioritization Of Network Traffic
START
Is VLAN tag?
NO
YES
Take Priority from
DSCP
Is VLAN priority tag
(VLAN id = 0)
Take priority from tag
Is priority tag = 0
NO
NO
YES
Take priority from tag
YES
Take Priority from
DSCP