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Cooper Bussmann 945U-E Wireless Ethernet Modem & Device Server User Manual
49
Rev Version 2.14
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 provide only basic roaming behavior, which means as the client moves further
from the access point 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.
In addition, the discovery of access points is completed before the existing radio link deteriorates, therefore
eliminating the periods of poor performance during transition to the next access point.
Figure 43 Roaming
The following settings and thresholds can be configured to fine tune the fast roaming process.
Fast Roaming
Fast roaming allows a client (station) to roam to an access point 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 checkbox 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 -90 dBm.
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 -84 dB before it would change over. In general, the roam
changeover threshold should be at least 6 dB, otherwise changeovers could occur
too frequently.
Roam Check Interval
If a better access point 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.