420 Configuring quality of service

NN47250-500 (Version 03.01)

End-to-End QoS

WSS and APs each perform classification on ingress to determine a CoS value for the packet. This CoS value
is used to mark the packet at the egress interface and to determine priority treatment on egress from the AP.
CoS values range from 0 to 7. Differentiated Services Code Point (DSCP) is a 6-bit value in IP-TOS with a
range from 0 to 63.
WSS and MP access points each provide classification and marking for QoS:
WSS switches and APs classify wired traffic based on the 802.1p tag value (for tagged VLAN traffic) or
DSCP value. Tunnel packets are classified using the DSCP of the tunnel header (TH), other packets with
the inner or 'client' DSCP.
APs classify ingress traffic from wireless clients based on the user priority value in the 802.11 header. If
the use-client-dscp option is enabled for a service profile, WMM QoS is ignored, and the QoS level is
classified based on the DSCP value. 802.11 data packets without WMM are classified as QoS level 0
unless static CoS is enabled or the use-client-dscp option is enabled.
WSSs and APs mark CoS for wired traffic in 802.1p and TH DSCP.
APs place traffic to a wireless client in a forwarding queue, based on the CoS value, and mark user
priority for WMM clients. The traffic is then forwarded based on the queue priority.

QoS Mapping

The mapping between DSCP and CoS values is configurable. An ingress map determines how DSCP values
are classified into CoS values. An egress map determines how CoS values are marked in the TH DSCP. The
WSS and associated APs share the same set of maps.
Mapping from 802.1p, WMM user priority to CoS is static. Also, mapping from CoS to access category (AC)
on the APs is static.
Table 24 shows how WMM priority information is mapped across the network.
Note. It is recommended to configure the same ingress and egress maps across the
mobility domain.
Note. It is also recommended that any CoS va lue mapped to a DSCP value and
then mapped back to CoS results in the same CoS value.