Users Guide

Dell PowerConnect W-Series ArubaOS 6.1 | User Guide Voice and Video | 693
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:
 arbitrary inter-frame space number (AIFSN)
 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 as 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:
 AP parameters affect traffic from the AP to the client.
 STA parameters affect 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.
 If you selected AP Group, click Edit for the AP group name for which you want to configure EDCA
parameters.
 If you selected AP Specific, select the name of the AP for which you want to configure EDCA parameters.
2. Under Profiles, expand the Wireless LAN menu, then select 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.
4. Configure your desired EDCA Profile Parameters. Table 157 describes the parameters you can configure in
this profile.
Table 157 EDCA Parameters Station and EDCA Parameters AP Profile Settings
Parameter Description
Best Effort Set the following parameters to define the best effort queue.
 aifsn: Arbitrary inter-frame space number. Possible values are 1-15.
 ecw-max: The exponential (n) value of the maximum contention window size, as expressed by 2
n
-1.
A value of 4 computes to 2
4
-1 = 15. Possible values are 1-15.
 ecw-min: The exponential (n) value of the minimum contention window size, as expressed by 2
n
-1.
A value of 4 computes to 2
4
-1 = 15. Possible values are 0-15.
 txop: Transmission opportunity, in units of 32 microseconds. Divide the desired transmission
duration by 32 to determine the value to configure. For example, for a transmission duration of 3008
microseconds, enter 94 (3008/32). Possible values are 0-2047.
 acm: This parameter specifies mandatory admission control. With a value of 1, the client reserves
the access category through traffic specification (TSPEC) signaling. A value of 0 disables this
option.