Weidmuller Wireless Ethernet Modem and Device Server User Manual
17
Rev Version 1.1
Chapter
3 - OPERATION
This chapter describes the normal operation of the WI-MOD-xxx-E-5W Ethernet modem. The modem allows
transparent communications between different Ethernet devices, and also allows some connectivity with RS-232
and RS-485 serial devices. All configuration and diagnostics is performed by accessing the embedded Web
Server, which is described in Chapter 4.
3.1 Startup
Access Point Startup
Normal module startup time is approximately 1 minute and 20 seconds from when the module is powered on to
when you can connect to the IP address. After the access point (AP) completes its startup process, it immediately
begins broadcasting periodic messages (beacons) on the configured channel using the default beacon interval time
of 15 seconds.
Beacons include information that a client may examine in order to identify whether 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 service set identifier (SSID). Access points do not initiate link establishment.
Client Startup
Normal module startup time is approximately 1 minute and 20 seconds from when powered on to when you can
connect to the IP address. After a client completes its startup process, it begins scanning its configured frequency
for a suitable access point. The client will attempt to establish a link with an access point only if the access point
has a matching SSID, encryption method, and the correct password. If more than one suitable access point is
discovered, the client attempts 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 link using a two-step
process
— authentication, and association. During authentication, the client and access point check whether
their configurations permit them to establish a link. Once the client is authenticated it requests an association to
establish a link.
The status of the wireless link is indicated by the TX/LINK LED. For an access point, the TX/LINK LED is off as
long as no links are established. Once one or more links are established the TX/LINK LED appears on and green.
For a client, the Link LED reflects the connection status to an access point. Link status is also displayed on the
Connectivity page of the Web interface (see
“5.2 Connectivity” on page 70).
After the link is established, data may be transferred in both directions. The access point acts as a master unit and
controls 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
the 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, however data cannot be passed over the wireless network.
How a Link Connection is Lost
A client monitors beacon messages from an access point to determine whether the link is still present. If the client
can no longer hear the access point beacons it waits seven beacon times (7 x 15 seconds) and then sends a link
check message. If the client still does not receive an acknowledgment, it will drop the link and clear its connectivity
list. If an access point is connected to a single client and the client fails or is turned off, the access point will wait
five minutes before dropping the link and clearing the connectivity list.
