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348 Configuring quality of service
NN47250-500 (320657-F Version 02.01)
Session-based Call Admission Control (CAC) is also supported. You can use CAC with either QoS mode to
ensure bandwidth availability by limiting the number of active sessions a radio can have.
The static CoS option enables you to easily set CoS for all traffic on an SSID by marking all the SSID’s traffic
with the same CoS value.
You can use ACLs to override CoS markings or set CoS for non-WMM traffic.
The following sections describe each of these options.
WMM QoS mode
WSSs and APs each provide classification and marking for WMM QoS:
• WSSs classify and mark traffic based on 802.1p tag value (for tagged traffic) or Differentiated Services
Code Point (DSCP) value.
• APs classify ingress traffic from wireless clients based on the service type value in the 802.11 header, and
mark the DSCP value in the IP tunnel on which the AP forwards the user traffic to the WSS.
APs place traffic from a WSS to a wireless client in a forwarding queue based on the DSCP
value in the tunnel carrying the traffic, then forward the traffic based on the queue’s priority.
Figure 1 on page 349 shows how WSSs classify ingress traffic. Figure 2 on page 350 shows how WSSs mark
egress traffic. Figure 3 on page 351 and Figure 4 on page 352 show how APs classify ingress traffic and mark
egress traffic. The figures show the default mappings between DSCP and CoS. (For information about
changing CoS mappings, see “Changing CoS mappings” (page 360).)