www.cooperbussmann.com/wirelessresources
Cooper Bussmann 945U-E Wireless Ethernet Modem & Device Server User Manual
19
Rev Version 2.14
C
hapTEr
3 - OpEraTION
3.0 Startup
Access Point Startup
When an access point (AP) unit starts up, it will immediately begin transmitting periodic messages (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.
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, 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 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 as
long as 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 encryption
scheme is configured, the Link LED turns on, but data cannot be passed over the wireless network.
How a Link Connection Is Lost
The access point refreshes the link status with a client every time a message is received from that client. If nothing
is received from a client for a period of 120 seconds, the access point sends a “link-check” message. If there is no
response to the link check a de-authenticate message is sent and the link is dropped.
A client monitors beacon messages from an access point to determine whether the link is still present. If the client
can no longer receive beacons from the access point it assumes the access point is out of range and the link is
dropped. Whenever a Client is not connected to an access point, it will cyclically scan all available channels for a
suitable access point.
Roaming Clients
Clients can roam within a system, but if the link to the access point fails or the radio signal level becomes too weak
it will scan for beacons and connect to an access point (provided the SSID and any encryption methods, keys are
compatible). If there are multiple access points, it selects the connection with the best signal level. This functionality
permits a client to have mobility while maintaining a link with the most suitable access point.
