IEEE 802.11e is an extension to the WLAN standards that incorporates quality-of-service (QoS) functions. An access point operating this standard can assign a user priority to each wireless client associated with it. By prioritizing wireless data packets, the access point can provide preferred handling for voice over IP clients, for example. On the LAN side, access points are commonly connected with a switch, and different LAN segments are often separated by VLANs. The wired LAN uses other mechanisms for the prioritization of data packets.
The following example application illustrates this:
- A wireless client (e.g. VoIP phone) is connected to an access point, QoS is enabled on the WLAN, the data between the phone and access point is not VLAN tagged.
- On the Ethernet side, the access point is connected to a VLAN-capable switch, and the data between AP and switch is VLAN tagged.
The access point is the interface between wired LAN and wireless LAN, and it converts the different prioritization information accordingly:
- When an access point receives data for transfer to a WLAN client, it determines the priority of each data packet either from the VLAN tag or the ToS/DSCP field in the IP header. The access point sends the packets to the client with this priority.
- However, data packets transferred from the WLAN client to the access point do not have a VLAN tag. What's more, in this direction the access point does not inspect the IP header. Instead, the access point takes the user priority of the WLAN packet and translates this into the appropriate VLAN tag to be attached to outgoing data packets on their way to the switch.
