Preferred AP List Description
The Preferred AP List is comprised of up to 16 APs to which the SM sequentially attempts registration. The order of this list signifies the preference of registration for APs in range (i.e. the first AP is the highest preferred, the second AP is the second-most preferred, and so on). For each AP SSID configured, configure applicable Wireless Security parameters (EAP-TTLS, WPA2, or Open) and WPA2 Pre-shared Key (if using WPA2 authentication at the AP). Once SM network entry is complete, the SM will not rescan APs in range until the active link is disconnected. When the Preferred AP List is populated, the SM will not attempt network entry for APs omitted from the Preferred AP List.
SM Network Entry Behavior with an Empty Preferred AP List
If the Preferred AP List is empty, the SM scans and registers to the AP with the best signal (based on RSSI and CINR measurements). In this case, the SM scans all of the channels configured in its Scan List and records the SSID, RSSI, and CINR of the APs within range. Next, the SM attempts registration to the AP with the highest RSSI measurement. If two or more AP candidates have similar RSSI readings, the SM attempts registration with the AP exhibiting the highest CINR (and RSSI). Successful SM network entry is always dependent on matching AP and SM configurations of security parameters (EAP-TTLS, WPA2, and corresponding pre-shared keys).
Sector Considerations when Configuring the Preferred AP List
In a network deployment utilizing frequency re-use, it is important to configure the Preferred AP List such that SMs register to their assigned sector’s AP only. If a co-located, co-channel AP in an opposite sector is also included in the SM’s Preferred AP List and the SM cannot register to its first-choice AP (in the sector), the SM will attempt registration to the opposite sector AP (only when configured in the Preferred AP List). This registration may introduce extra system self-interference, especially if automatic transmit power control is configured for the SMs. Please note that the SM will not attempt to re-register to its first-choice AP until the link is terminated manually or lost.