User's Manual

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Wireless LAN Mode
AT+i Programmer‘s Manual Version 8.32 15-9
15.8 Roaming Mode
When set to operate in Roaming mode, iChip can roam seamlessly among Access Points
(APs) sharing the same SSID and the same security configuration without interrupting its
IP connectivity. iChip also has a monitoring mechanism that is sensitive to drops in AP
signal strength. When iChip detects such a drop, it automatically starts searching for APs
in its vicinity that have a stronger signal, while remaining connected to the current AP.
The following parameters are required to set iChip to Roaming mode:
WROM Enables Roaming mode.
WPSI Sets the time interval between consecutive scans that iChip performs for
APs in its vicinity.
WSRL Sets a low SNR threshold for iChip in Roaming mode.
WSRH Sets a high SNR threshold for iChip in Roaming mode.
In addition, two reports provide useful information pertaining to the Roaming feature:
AT+i!RP10 Returns a report of the current WLAN connection.
AT+iRP20 Returns a list of all APs and Ad-Hoc networks available in the vicinity.
15.8.1 iChip Behavior Following a Hardware or Software Reset
After power-up, hardware or software reset, iChip starts scanning for APs in its vicinity
at intervals set by the WPSI parameter. iChip reads the value set in the WLSI parameter
and acts accordingly:
If WLSI refers to an AP, iChip scans for all APs in its vicinity. iChip attempts to
connect to an AP whose SSID is listed first in the WSIn parameter. If several APs
having that same SSID exist, iChip attempts to connect to the one having the
strongest signal. If association succeeds, iChip stops scanning and activates its DHCP
client. It then monitors the SNR level of the AP it is associated with.
If WLSI refers to an Ad-Hoc network, iChip scans for all Ad-Hoc networks in its
vicinity. iChip attempts to join an Ad-Hoc network whose SSID is listed first in the
WSIn parameter. If no such network is found, iChip creates its own network and
stops scanning.
If WLSI is set to (*), iChip stops scanning and remains disconnected.
15.8.2 iChip Behavior when AP Signal Becomes Weak
When the beacon signal of the AP with which iChip is associated becomes weak (SNR
drops below the level set by the WSRL parameter), iChip starts its periodic scan for APs
having SNR above the threshold set by the WSRH parameter.
iChip attempts to connect to the AP that appears first on the list of SSIDs specified in the
WSIn parameter, while remaining connected to the current AP. If association with the
new AP fails, iChip continues scanning until it succeeds connecting to an AP with a
stronger signal.