Technical information

Chapter 2: AT+i Commands Reference
May 31, 2008 AT+i Commands Reference Manual 2-45
• WROM - Enables Roaming mode.
• WPSI - Sets the time interval between consecutive scans that W24 performs for APs in its
vicinity.
• WSRL - Sets a low SNR threshold for W24 in Roaming mode.
• WSRH - Sets a high SNR threshold for W24 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.
W24 Behavior Following a Hardware or Software Reset
After power-up, hardware or software reset, W24 starts scanning for APs in its vicinity at
intervals set by the WPSI parameter. W24 reads the value set in the WLSI parameter and acts
accordingly:
• If WLSI refers to an AP, W24 scans for all APs in its vicinity. W24 attempts to connect to an
AP whose SSID is listed first in the WSIn parameter. If several APs having that same SSID
exist, W24 attempts to connect to the one having the strongest signal. If association succeeds,
W24 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, W24 scans for all ad-hoc networks in its vicinity. W24
attempts to join an ad-hoc network whose SSID is listed first in the WSIn parameter. If no
such network is found, W24 creates its own network and stops scanning.
• If WLSI is set to (*), W24 stops scanning and remains disconnected.
W24 Behavior when AP Signal Becomes Weak
When the beacon signal of the AP with which W24 is associated becomes weak (SNR drops
below the level set by the WSRL parameter), W24 starts its periodic scan for APs having SNR
above the threshold set by the WSRH parameter.
W24 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,
W24 continues scanning until it succeeds connecting to an AP with a stronger signal.
When in Roaming mode, W24 does not restart its DHCP client process for new connections.
When W24 is not in Roaming mode, W24 remains connected to an AP as long as it has an open
active socket, or until triggered by a Link Lost event. When not in Roaming mode, W24 ignores
any decrease in AP signal strength while having open active sockets.
When W24 is not in Roaming mode and no active sockets are open, W24 starts periodic scanning
for APs having an SNR level above the WSRH threshold. W24 attempts to connect to the AP that
has the highest priority. After associating with an AP, W24 starts its DHCP client and monitors
the SNR level of the AP it is associated with.
W24 Behavior in the Event of a Lost Link
If the connection is not active, W24 starts periodic scanning for APs and attempts to connect to an
AP having the highest priority. After associating to an AP, W24 starts its DHCP client and
monitors the SNR level of the AP it is associated with.