Cisco Cisco Catalyst 6000 Multilayer Switch Feature Card MSFC2 Bulletins
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Wireless LAN Controllers Supported: Cisco 4400 Series wireless LAN controllers; Cisco WiSM
Access Points Supported: Not applicable
Management Interfaces Supported: Cisco WCS, controller web user interface, command line interface
Layer 3 QoS Packet Marking Enhancements
This feature adds support for Layer 3 IP Differentiated Services Code Point (DSCP) marking of packets sent by wireless LAN controllers and
lightweight access points. It also enhances how access points use this Layer 3 information to ensure that packets receive the correct over-the-air
prioritization from the access point to the wireless client.
In the centralized wireless LAN architecture, wireless LAN data is tunneled between the access point and the wireless LAN controller via LWAPP.
In order to maintain the original QoS classification across this tunnel, the QoS settings of the encapsulated data packet must be appropriately mapped
to the Layer 2 (802.1p) and Layer 3 (IP DSCP) fields of the outer tunnel packet. See Figure 10.
Figure 10. Mapping of QoS Packet Markings
For example, when 802.11e traffic is sent by a WLAN client, it will have a User Priority (UP) classification in its frame. The access point needs to
map this 802.11e classification into a DSCP value for the LWAPP packet carrying the frame to ensure that the packet is given the appropriate
priority on its way to the wireless LAN controller. A similar process needs to occur on the wireless LAN controller for LWAPP packets going to the
access point. Also needed is a mechanism to classify traffic on both the access point and the wireless LAN controller for non-802.11e clients, so that
their LWAPP packets can also be given the appropriate priority.