Users Guide

WMM Access Category Description 802.1p Tag
Voice Highest priority 7, 6
Video Prioritize video traffic above other data traffic 5, 4
Best Effort Traffic from legacy devices or traffic from applications or
devices that do not support QoS
0, 3
Background Low priority traffic (file downloads, print jobs) 2, 1
Table 212: WMM Access Categories and 802.1p Tags
While the WMM ACs designate specific types of traffic, you can determine the priority of the ACs. For example,
you can choose to give video traffic the highest priority. With WMM, applications assign data packets to an AC.
In the client, the data packets are then added to one of the transmit queues for voice, video, best effort, or
background.
WMM is an extension to the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol’s
Distributed Coordination Function (DCF). The collision resolution algorithm responsible for traffic prioritization
depends on the following configurable parameters for each AC:
l arbitrary inter-frame space number (AIFSN)
l minimum and maximum contention window (CW) size
For each AC, the backoff time is the sum of the AIFSN and a random value between 0 and the CW value. The AC
with the lowest backoff time is granted the opportunity to transmit (TXOP). Frames with the highest-priority AC
are more likely to get TXOP, because they tend to have the lowest backoff times (a result of having smaller
AIFSN and CW parameter values). The value of the CW varies through time as the CW doubles after each
collision up to the maximum CW. The CW is reset to the minimum value after successful transmission. In
addition, you can configure the TXOP duration for each AC.
On the controller, you configure the AC priorities in the WLAN EDCA parameters profile. There are two sets of
EDCA profiles you can configure:
l AP parameters affecting traffic from the AP to the client.
l STA parameters affecting traffic from the client to the AP.
Using the WebUI to configure EDCA parameters
Use the following procedure to define an Enhanced Distributed Channel Access (EDCA) profile for APs or for
clients (stations).
1. Navigate to the Configuration > AP Configuration page. Select either the AP Group tab or AP Specific
tab:
l If you selected AP Group, click Edit for the AP group name for which you want to configure EDCA
parameters.
l If you selected AP Specific, select the name of the AP for which you want to configure EDCA
parameters.
2. Under Profiles, select the Wireless LAN, then Virtual AP. In the Virtual AP list, select the appropriate
virtual AP.
3. Expand the SSID profile. Select the EDCA Parameters Station or EDCA Parameters AP profile.
Dell Networking W-Series ArubaOS 6.4.x | User Guide Voice and Video |
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