Weidmuller WI-MOD-945-E: 900Mhz Wireless Ethernet & Device Server v2.16 - Manual (Page 52)

Weidmuller Wireless Ethernet Modem & Device Server WI-MOD-945-E User Manual
Page 52 www.weidmuller.com Rev 2.136
Roam check Interval If a better AP is not found, the background scan is repeated every Roam
Check Interval while the signal strength to the currently connected AP is
below the Roam Scan Threshold.
Channel Width Channel Width setting will apply only when there are no entries in the Scan
List. Selects channel width bands for background scan. If 5MHz is selected
then only 5MHz channels will be scanned during the background scan.
Default is Auto, which means all channels will be scanned.
Save Changes Save changes to non-volatile memory. Changes will not take effect until
module is reset.
Save Changes and Reset Save changes to non-volatile memory and reset module
When Fast Roaming is enabled the Client goes off-channel and periodically performs a background scan to identify
available AP’s. When AP’s are identified the RSSI is recorded as a potential connection. It takes 50msec to scan each
channel, with a 1 second delay between each scanned channel. So scanning 10 channels will take 10 second, during
which time latency of up to 50msec will occur and any throughput traffic is essentially paused and buffered for
retransmission when complete. It is therefore recommended the scan list is used to limit the number of channels the client
needs to scan thus reducing the overall scan time.
During the background scan a client will scan all of the channels in the Scan List to identify better AP's. If no channels are
configured it will scan all channels.
The above configuration shows that the Client will start scanning when the RSSI of its current connection to the Access
Point falls below -90dBm. When this happens it will scan the list of Access Points configured in the Roaming Scan List (in
this case channels 6, 15, 16 &26) and if any of the RSSI levels are greater than -84dBm it will change to this Access
Point, i.e.6dB (Roam Changeover Threshold) better than -90dBm (Roam Scan Threshold).
Figure 32 - Scan List