Introduction
Spectrum24 AP-4111 DS Access Point Product Reference Guide
19
1.3.6
MU Association Process
APs recognize MUs as they associate with the AP. The AP keeps a list of the
MUs it services. MUs associate with an AP based on the following conditions:
•
the signal strength between the AP and MU
•
the MU data rate (1 Mbps, 2 Mbps, 5.5 Mbps or 11 Mbps).
MUs perform preemptive roaming by intermittently scanning for APs and
associating with the best available AP. Before roaming and associating with
APs, MUs perform full or partial scans to collect AP statistics and determine
the direct-sequence channel used by the AP.
Scanning is a periodic process where the MU sends out probe messages on
all frequencies defined by the country code. The statistics enable an MU to
reassociate by synchronizing its frequency to the AP. The MU continues
communicating with that AP until it needs to switch cells or roam.
MUs perform full scans at start-up. In a full scan, an MU uses a sequential set
of channels as the scan range. For each channel in range, the MU tests for
CCA (Clear Channel Assessment)
. When a transmission-free channel
becomes available, the MU broadcasts a probe with the Net_ID (ESS) and
the broadcast BSS_ID. An AP-directed probe response generates an MU ACK
(Mobile Unit Acknowledgment) and the addition of the AP to the AP table
with a proximity classification. An unsuccessful AP packet transmission
generates another MU probe on the same channel. If the MU fails to receive
a response within the time limit, it repeats the probe on the next channel in
the sequence. This process continues through all channels in the range.
MUs perform partial scans at programmed intervals, when missing expected
beacons or after excessive transmission retries. In a partial scan, the MU
scans APs classified as proximate on the AP table. For each channel, the MU
tests for CCA. The MU broadcasts a probe with the Net_ID (ESS) and
broadcast BSS_ID when the channel is transmission-free. It sends an ACK to
a directed probe response from the AP, and updates the AP table. An
Summary of Contents for AP-4111 DS
Page 112: ...Monitoring Statistics 104 Spectrum24 AP 4111 DS Access Point Product Reference Guide ...
Page 120: ...Hardware Installation 112 Spectrum24 AP 4111 DS Access Point Product Reference Guide ...
Page 124: ...A 4 Spectrum24 Access Point AP 3020 Product Reference Guide ...
Page 126: ...B 2 Spectrum24 Access Point AP 3020 Product Reference Guide ...