Weidmuller Wireless Ethernet Modem & Device Server WI-MOD-E-G/A User Manual
Rev.
2.16
www.weidmuller.com
18
CHAPTER 3 - OPERATION
3.0 - Start-up
“Access Point” Start-up (WI-MOD-E-G)
When an Access Point (AP) unit starts up it checks to see if the Channel selection is set to “Auto” and if so will scan all
available channels, pick the quietest then begin transmitting periodic messages, called beacons, if it is configured with a
fixed channel it will immediately begin sending beacons, on the configured channel.
Beacons include information that a Client may examine in order to identify if the Access Point is suitable for link
establishment. Clients will only attempt to establish a link with an Access Point whose beacon indicates a matching SSID.
Access Points do not initiate link establishment.
“Access Point” Start-up (WI-MOD-E-A)
If the modem is configured to use “DFS” then it will behave slightly different, as it needs to comply with DFS regulations.
When an Access Point starts up it will scan all available channels from the selected groups and then select the quietest
similar to the WI-MOD-E-G. It will then go into a scan mode for 60 seconds where it listens for any Radar signals.
If a radar signal is detected it will flag the channel as being unavailable (Channel will stay unavailable for 30 minutes) and
then pick another random channel and go through the same scanning process until a radar free channel becomes
available.
“Client” Start-up
When a Client powers up, it scans for beacons from Access Points. While a link is not established, the Client cyclically
scans all available channels for a suitable Access Point. The Client will attempt to establish a link with an Access Point
only if it has matching SSID, Encryption method, etc. and other compatible capabilities as indicated by the beacon. If more
than one suitable Access Point is discovered, the client will attempt to establish a link with the Access Point that has the
strongest radio signal.
Link Establishment
Once a Client identifies a suitable Access Point for link establishment it attempts to establish a link using a two-step
process – “Authentication” and “Association”. During Authentication the Client and Access Point check if their
configurations permit them to establish a link. Once the Client has been authenticated, it will then request an Association
to establish a link.
Status of the wireless link is indicated via the TX/LINK LED. For an Access Point, the TX/LINK LED will be OFF while no
links have been established. Once one or more links have been established, the TX/LINK LED is on GREEN. For a Client,
the Link LED will reflect the connection status to an Access Point. Link status is also displayed on the “Connectivity” page
of the web interface.
After the link is established, data may be transferred in both directions. The Access Point will act as a master-unit and will
control the flow of data to the Clients linked to it. Clients can only transmit data to the AP to which they are connected.
When a Client transfers data to another Client, it first transmits the data to the AP, which then forwards the data to the
destined Client.
Presence of a “link” does not mean that the connected unit is authorized to communicate over radio. If
the encryption keys are incorrect between units in the same system, or a dissimilar encryption scheme
is configured, the LINK led will light, however data cannot be passed over the wireless network.
A maximum of 127 Clients may be linked to an Access Point.
