Symbol Technologies AP-4131 manual Introduction

Introduction

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 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 unsuccessful AP packet transmission causes the MU to broadcast another probe on the same channel. The MU classifies an AP as out-of-range in the AP table if it fails to receive a probe response within the time limits. This process continues through all APs classified as proximate on the AP table.

20 AP-4131 Access Point Product Reference Guide