Weidmuller WI-MOD-945-E: 900Mhz Wireless Ethernet & Device Server v2.16 - Manual (Page 51)

Weidmuller Wireless Ethernet Modem & Device Server WI-MOD-945-E User Manual
Page 51 www.weidmuller.com Rev 2.136
Response Timeout Enter the timeout (in milliseconds) to wait for a response to the specified
transaction.
Comm Fail Register Enter the onboard I/O Register number to store the communication
status of the specified transaction. The Specified register will be set to 0
if communications is successful, 0xFFFF if there is no connection to the
specified server, or 0xFFxx where xx is the Modbus Exception Code
3.15 - Roaming
In certain cases a Client may be in a mobile situation and require a method of roaming to another Access Point.
Normal network communications provides only basic roaming behaviour which means as the client moves further from the
AP it will go through a period of poor communication followed by a complete disconnection of the radio link.
It is at this point that the Client will scan for Access Points and if one is in range it could take up to 10 seconds for the
client to establish a connection.
Fast Roaming will significantly reduce the time taken for a client to roam from Access Point to Access Point. Also the
discovery of AP’s is done before the existing radio link deteriorates therefore eliminating the periods of poor performance
during transition to the next AP.
The following settings/thresholds can be configured to fine tune the fast roaming process.
Fast Roaming Fast Roaming allows a client (station) to roam to an AP with a stronger
signal strength without disrupting communications. Or roam seamlessly
between multiple Access Points based on configuration parameters such as
RSSI threshold.
Passive Scanning (STA
only) Selecting this item stops a Client device from sending “probe request”
messages when it is searching for an access point to connect to. Instead,
the client waits for a beacon transmission from the access point.
Passive Scanning should be disabled when Fast Roaming is enabled.
Roam Scan Threshold Background Scan will be initiated when the RSSI to the currently connected
AP drops below this threshold and Fast Roaming (above) is enabled. Default
is -90dBm
Roam changeover
Threshold This is the RSSI value above the Roam Scan Threshold that is required for
the Client to change to the new Access Point. In the example shown above
the Access Point RSSI would need to be above -84dB before it would
changeover.
In general, the Roam Changeover Threshold should be at least 6dB,
otherwise changeovers could occur too frequently.
Figure 31 - Roaming