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245U-E Wireless Ethernet Modem User Manual
Rev Version 2.24
Chapter 3 - OPERATION
3.0 Startup
Access Point Startup (245U-E-G)
When an access point unit starts up, it checks if the channel selection is set to “Auto.” If it is, the access
point will scan all available channels, pick the quietest then begin transmitting periodic messages, called
beacons. If the access point 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 Startup (245U-E-A)
If the modem is configured to use Dynamic Frequency Selection (DFS), it will behave slightly differently than
the 245U-E-G because 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 245U-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 (the channel will stay unavailable for 30 minutes) and then
pick another random channel and repeat the same scanning process until a radar-free channel becomes
available.
Client Startup
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 and encryption method, 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
access point to which they are connected. When a client transfers data to another client, it first transmits
the data to the access point, which then forwards the data to the destined client. A maximum of 127 clients
may be linked to an access point.
NOTE The 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
