result, packets transmitted over a WLAN will also lose Layer 2 QoS information. Since it is vital to use the Layer 3 DSCP information to provide QoS in the absence of Layer 2 QoS information, a solution is needed. Cisco WLAN controllers using software version 3.2 or later ensure that packets receive proper QoS handling end-to-end during transmission. WLAN controllers ensure that the packet maintains the QoS information while the packet traverses the network using RF wireless IEEE 802.1e markings or WMM mappings, as appropriate. Figure depicts how to overcome this challenge using LWAPP to encapsulate and tunnel packets from the access point to the controller. In this way, end-to-end QoS implementation requires mapping between Layer 2 802.1p or Layer 3 DSCP and wireless RF using 802.11e or WMM. The lightweight access point WLAN solution enhances the way access points use Layer 3 information to ensure that packets receive the correct over-the-air prioritization when the packets are transmitted from the access point to the wireless client.
Content 6.1 Implementing WLAN QoS 6.1.6 WLAN QoS Implementation When voice or video uses a WLAN, the service must integrate with the wired network and Voice over IP (VoIP) systems to deliver consistent, high quality end-to-end service. QoS protocols used on the WLAN and wired network media must be mapped to one another while traffic transits the boundary between the two media. In particular, WLAN 802.11e packets must be mapped to LAN 802.1p packets and vice versa. Figure [1] provides a brief overview of how to implement QoS on a WLAN. When a WLAN client sends 802.11e traffic, it will have a User Priority (UP) classification in its frame (802.1p or 802.11e). 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. Figure shows how traffic that originated in the wired network passes through a LAN switch to a controller, through LWAPP tunnels to an access point, and then to a wireless client. The bottom of the diagram shows the process from the wireless client to the wired LAN. There are four steps in the process: Step 1 The traffic travels from the Ethernet switch to the controller. Step 2 The traffic travels from the access point to the wireless client. Step 3 The traffic travels from the client to the access point. Step 4 The traffic travels from the controller to the Ethernet switch. This series of subtopics gives details on the steps of QoS implementation: WLAN QoS Implementation Step 1: From Ethernet Switch to Controller and LWAPP Tunnel
When a LAN controller forwards an LWAPP packet to an access point, it must contain the QoS information from the original Ethernet packet coming from the Ethernet switch. The WLAN controller puts this information into the outer header in an LWAPP packet. Figure shows how the controller encapsulates the incoming Ethernet packet retaining the original DSCP value and payload. The controller also translates the DSCP value of the incoming packet to the appropriate 802.1p priority value. These values are placed in the outer header of the LWAPP frame. LWAPP control packets are always tagged with an 802.1p value of 7, while the encapsulated LWAPP data packets derive the DSCP and 802.1p value from the original packet. QoS Packet Marking Translations
Default mapping between DSCP, 802.1p, and 802.11e exist as shown in the table in Figure . The following are notes on Layer 3 QoS packet marking enhancements: There are benefits of Layer 3 QoS packet marking enhancements: The following are notes on network control (IP DSCP 56, Cisco Unified Communications 802.1p 7, and IEEE 802.1e 7): WLAN QoS Implementation Step 2: Out of the Tunnel and Through the Access Point to the Wireless Client
When a packet goes from an access point to the client, the DSCP value from the incoming LWAPP packet is mapped to the 802.11e priority value as shown in Figure . For a WMM client, the access point translates the DSCP value of the incoming LWAPP packet to the 802.11e priority value. The access point polices the value to ensure that the value does not exceed the maximum value allowed, based on the WLAN QoS policy assigned to that client. Then the access point places the packet in the 802.11e transmit queue that is appropriate for that WMM access category or 802.11e priority level. For a regular (non-WMM) client, the access point places the packet in the default 802.11e or WMM transmit queue based on the WLAN QoS policy that is assigned to that client. WLAN QoS Implementation Step 3: From Client to Access Point and Into the Tunnel
When a packet is sent from the client to the access point, the 802.11e priority value is mapped to the DSCP value on the access point. Figure shows this process. When the access point receives an 802.11 frame from a WMM client, the access point polices the 802.11e priority value to ensure that the value does not exceed the maximum value that is allowed for the QoS policy assigned to that client and then maps the 802.11e priority value to the DSCP value.

When the access point receives a frame from a regular (non-WMM) client, the access point uses the default 802.11e priority or WMM value for the QoS policy that is assigned to that client or WLAN ID and translates the value to the DSCP value. Mapping Traffic from Access Point to Controller
When packets from an access point go to the controller, the access point translates a DSCP value based on the incoming 802.11e value as shown in Figure . The access point does not send tagged packets because doing so causes a problem with Cisco switches that are not configured for trunking from the access point. Because the access point is not trunked, the access point does not copy the 802.11e incoming value to an 802.1p (outer) packet. WLAN QoS Implementation Step 4: Out of the Tunnel Through the Controller to Ethernet Switch
The controller uses the incoming outer DSCP value from an LWAPP packet to generate an 802.1p priority value in the packets, which are sent to the Ethernet switch by the controllers as shown in Figure . When the controller receives an LWAPP packet, the controller generates the IEEE 802.1p priority value for the wired side using the incoming DSCP (outer) value.
Content 6.1 Implementing WLAN QoS 6.1.7 Packet Tagging There are two situations to consider: tagged and untagged packets.