Operating Modes - Motorola AP-51XX Product Reference Manual

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AP-51xx Access Point Product Reference Guide
• Signal strength between the and MU
• Number of MUs currently associated with the access point
• MUs encryption and authentication capabilities
• MUs supported data rate
MUs perform pre-emptive roaming by intermittently scanning for 's and associating with the best
available access point. Before roaming and associating, MUs perform full or partial scans to collect
statistics and determine the direct-sequence channel used by the access point.
Scanning is a periodic process where the MU sends out probe messages on all channels defined by
the country code. The statistics enable an MU to reassociate by synchronizing its channel to the
access point. The MU continues communicating with that until it needs to switch cells or roam.
MUs perform partial scans at programmed intervals, when missing expected beacons or after
excessive transmission retries. In a partial scan, the MU scans 's classified as proximate on the
access point table. For each channel, the MU tests for Clear Channel Assessment (CCA). The MU
broadcasts a probe with the ESSID and broadcast BSS_ID when the channel is transmission-free. It
sends an ACK to a directed probe response from the and updates the table.
An MU can roam within a coverage area by switching access points. Roaming occurs when:
• Unassociated MU attempts to associate or reassociate with an available access point
• Supported rate changes or the MU finds a better transmit rate with another access point
• RSSI (received signal strength indicator) of a potential access point exceeds the current
access point
• Ratio of good-transmitted packets to attempted-transmitted packets falls below a threshold.
An MU selects the best available access point and adjusts itself to the access point direct-sequence
channel to begin association. Once associated, the access point begins forwarding frames addressed
to the target MU. Each frame contains fields for the current direct-sequence channel. The MU uses
these fields to resynchronize to the access point.
The scanning and association process continues for active MUs. This process allows the MUs to find
new access point's and discard out-of-range or deactivated access point's. By testing the airwaves,
the MUs can choose the best network connection available.

1.3.6 Operating Modes

The access point can operate in a couple of configurations.

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Ap-51 seriesAp-5131Ap-5181

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