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Weidmuller Wireless Ethernet Modem & Device Server WI-MOD-E-G/A User Manual
3.6 - Compatibility
3 Address (Layer 3 Bridge) & 4 Address Mode
What Addresses are in a wireless Ethernet data frame?
There are two different Wi-Fi communication "modes", 3 Address and 4 Address Modes. Each mode has a slightly
different way that it addresses the data frames to other devices on the network.
In 3 Address Mode the addressing is made up of a Destination Address (DA), a Source Address (SA), and a BSSID (MAC
Address of the Access Point)
In 4 Address Mode the addressing is made of a Destination Address (DA), a Source Address (SA), a Radio Transmit
Address (RTA), and a Radio Receive Address (RRA).
Packets between AP and Client
Communications between Access Points and Client is generally done using 3 Address Mode because there are only 3
addresses within the communication path as indicated in the path from the Laptop to Station #1 in the diagram below.
If the Laptop wishes to communicate to Station #1 the DA will be Station #1, the SA will be the Laptop and the BSSID will
be the AP's MAC Address hence the 3 Address Mode.
The example shows the Laptop may need to communicate to the Ethernet Device connected to Station #2.
You can see that there is now a fourth address that cannot be addressed using the 3 Address Mode of communications.
i.e. Laptop, AP, Station #2 and Ethernet Device.
The example shows the Access Point and the Station as both being WI-MOD-E modules which will happily communicate
as both support 4 Address Mode.
However, there are some instances where a third Party Access Point may not be able to communicate using 4 Address
Mode to a Client (Sta).
There are only a couple of ways around this sort of situation.
Changing Station #2 to a Router, however this may mean that Station #2 and the Ethernet Device will use a different
network address scheme which may be inconvenient and will require more setup.
Configure the Access Point to communicate 4 Address Mode
If choosing the later this will only be possible if the Station and the AP support 4 Address Mode, some third Party AP's do
not.
WI-MOD-E-100 Compatibility
WI-MOD-E-G modules can communicate with WI-MOD-E-100 Ethernet
modems however only in certain modes. The following table shows
compatible configurations.
If communicating with WI-MOD-E-100 Ethernet modems the WI-MOD-E-
100's need to be configured with WDS (4 address mode), not the default "3-
address mode" and the WI-MOD-E-100 AP's cannot be auto connect to any
WDS AP.
WI-MOD-E-G
AP
WI-MOD-E-G AP
Y
WI-MOD-E-G Sta
Y
Notes:
1. Notes: Connection only if the WI-MOD-E-G is configured with a virtual Station (Client) which in turn connects to
the WI-MOD-E-100 Access Point.
Rev. 2.16
WI-MOD-E-G
WI-MOD-E-
Sta
100 AP
(4Add)
Y
Y (Note 1)
Y
Y
www.weidmuller.com
Access
Point
Laptop #1
Figure 21 - Compatibility
WI-MOD-
WI-MOD-E-
E-100 CL
100 AP
(4Add)
(3Add)
Y
N
N/A
N (Note 2)
Station #1
Station #2
Ethernet
Device
WI-MOD-E-
100 CL
(3Add)
Y
N/A
31
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