Brocade Mobility RFS Controller CLI Reference Guide (Supporting software release 5.5.0.0 and later) - Manual (Page 1194)

1186 Brocade Mobility RFS Controller CLI Reference Guide
53-1003098-01
22
WMM’s prioritization capabilities are based on the four access categories (background, best-effort,
video, and voice). Higher the Access Category (AC) higher is the transmission probability over the
controller managed WLAN. ACs correspond to the 802.1d priorities, facilitating interoperability with
QoS policy management mechanisms. WMM enabled controllers coexist with legacy devices (not
WMM-enabled).
Packets not assigned to a specific access category are categorized as best effort by default.
Applications assign each data packet to a given access category. Categorized packets are added to
one of four independent transmit queues (one per access category). The client has an internal
collision resolution mechanism to address collision among different queues, which selects the
frames with the highest priority to transmit.
The same mechanism deals with external collision, to determine which client should be granted the
Opportunity to Transmit (TXOP). The collision resolution algorithm responsible for traffic
prioritization is probabilistic and depends on two timing parameters that vary for each access
category. These parameters are:
• The minimum interframe space, or Arbitrary Inter-Frame Space Number (AIFSN)
• The contention window, sometimes referred to as the random back off wait
Both values are smaller for high-priority traffic. The value of the contention window varies through
time. Initially the contention window is set to a value that depends on the AC. As frames with the
highest AC tend to have the lowest back off values, they are more likely to get a TXOP.
After each collision the contention window is doubled until a maximum value (also dependent on
the AC) is reached. After successful transmission, the contention window is reset to its initial, AC
dependant value. The AC with the lowest back off value gets the TXOP.
Supported in the following platforms:
• Access Points — Brocade Mobility 650 Access Point, Brocade Mobility 6511 Access Point,
Brocade Mobility 1220 Access Point, Brocade Mobility 71XX Access Point, Brocade
Mobility 1240 Access Point
• Wireless Controllers — Brocade Mobility RFS4000, Brocade Mobility RFS6000, Brocade
Mobility RFS7000
• Service Platforms — Brocade Mobility RFS9510
Syntax:
wmm [background|best-effort|power-save|qbss-load-element|video|voice]
wmm [power-save|qbss-load-element]
wmm [background|best-effort|video|voice] [aifsn <2-15>|cw-max <0-15>|cw-min
<0-15>|
txop-limit <0-65535>]
Parameters
wmm [power-save|qbss-load-element]
wmm Configures 802.11e/wireless multimedia parameters
power-save Enables support for the WMM-Powersave mechanism. This mechanism, also known as Unscheduled
Automatic Power Save Delivery (U-APSD), is specifically designed for WMM voice devices.
qbss-load-element Enables support for the QOS Basic Service Set (QBSS) load information element in beacons and probe
response packets advertised by access packets. This feature is enabled by default.