Brocade Mobility RFS7000-GR Controller System Reference Guide (Supporting software release 4.1.0.0-040GR and later) - Manual (Page 28)

14 Brocade Mobility RFS7000-GR Controller System Reference Guide
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Software overview
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1. When a new AP is adopted, it scans each channel. However, the switch does not forward traffic
at this time.
2. The switch then selects the least crowded channel based on the noise and traffic detected on
each channel.
3. The algorithm used is a simplified maximum entropy algorithm for each radio, where the signal
strength from adjoining AP's/MU's associated to adjoining AP's is minimized.
4. The algorithm ensures adjoining AP's are as far away from each other as possible (in terms of
channel assignment).
NOTE
Individual radios can be configured to perform automatic channel selection.
WMM-unscheduled APSD
This feature is also known as WMM Power Save or WMM-UPSD (Unscheduled Power Save Delivery).
WMM-UPSD defines an unscheduled service period, which are contiguous periods of time during
which the switch is expected to be awake. If the switch establishes a downlink flow and specifies
UPSD power management, it requests (and the AP delivers) buffered frames associated with that
flow during an unscheduled service period. The switch initiates an unscheduled service period by
transmitting a trigger frame. A trigger frame is defined as a data frame (e.g. an uplink voice frame)
associated with an uplink flow with UPSD enabled. After the AP acknowledges the trigger frame, it
transmits the frames in its UPSD power save buffer addressed to the triggering switch.
UPSD is well suited to support bi-directional frame exchanges between a voice STA and its AP.
Multiple VLANs per WLAN
The switch permits the mapping of a WLAN to more than one VLAN. When a MU associates with a
WLAN, the MU is assigned a VLAN by means of load balance distribution. The VLAN is picked from a
pool assigned to the WLAN. The switch tracks the number of MUs per VLAN, and assigns the least
used/loaded VLAN to the MU. This number is tracked on a per-WLAN basis.
A broadcast key, unique to the VLAN, encrypts packets coming from the VLAN. If two or more MUs
are on two different VLANs, they both hear the broadcast packet, but only one can decrypt it. The
switch provides each MU a unique VLAN broadcast key as part of the WPA2 handshake or group
key update message of a WPA handshake.
Limiting users per VLAN
Not all VLANs within a single WLAN must have the same DHCP pool size. Assign a user limit to each
VLAN to allow the mapping of different pool sizes.
Specify the VLAN user limit. This specifies the maximum number of MUs associated with a VLAN
(for a particular WLAN). When the maximum MU limit is reached, no more MUs can be assigned to
that VLAN.
Packet flows
There are four packet flows supported when the switch is configured to operate with multiple VLAN
per WLAN: