Entry type: FAQ, Entry ID: 23584230, Entry date: 10/22/2014
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How do you set up a WDS connection between SCALANCE W modules?

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Description
WDS stands for "Wireless Distribution System" and is the wireless connection of multiple access points (APs) with each other in order to extend the range of a radio network without having to connect the extension access points via Ethernet.
See the following example:


Fig. 01

The APs are connected with the previous access point and possibly with the following access point and permit additional wireless access for clients located in their radio cells.
A fundamental disadvantage here is that the usable bandwidth is halved by each additional AP, because each data package has to be transferred double. If the usable bandwidth shrinks too much, you can use a Dual Access Point (e.g. SCALANCE W 788-2) to help out. The type of Dual Access Point mentioned has two WLAN interfaces that can operate on different radio bandwidths. In this way you can use one interface for WDS and the second interface for connecting clients.

Requirements and Restrictions
The following conditions must be met.

  • All APs connected via WDS must use the same frequency channel (menu item "Interfaces > WLAN"). "Auto Channel Select" cannot be used with WDS.


    Fig. 02
     
  • WDS can only be configured when the SCALANCE W788 is being operated in Access Point mode. If the SCALANCE W788 is configured as client, you cannot set up a WDS connection.


    Fig. 03
  • You cannot configure WDS if the Access Point is using iPCF ("industrial Point Coordination Function") for controlling data traffic in its radio cell (this only applies to SCALANCE W788-1RR and SCALANCE W788-2RR).
  • You can also connect other manufacturers' access points as long as they support WDS. However, this connection only works using the MAC address. In this case a WDS connection via the "System Name" is not possible.
  • It is not permitted to use IEEE 802.11h for WDS segments.
  • Both APs have a unique IP address and can be reached separately without a network connection (in order to avoid any loop formation).

Configuration Instructions
WDS can be implemented both unencrypted and encrypted with WEP (40 or 104 bits) or AES (128 bits) encryption. We recommend using one of the two security settings described below.
In order to meet current security directives we will consider only the encrypted options in the following.

Proceed as follows to configure a WDS.
   

Step no. Procedure
1 Select the "Security > Keys" menu item of the AP concerned and create a Private Key with 128 bits (for this you need 16 ASCII or 32 HEX characters). Press "Set Values" and the key appears with its length as Private Key in the key list.


Fig. 04

Then you must restart the AP.

2

Switch to the "Security > Basic WLAN" menu item.

Version "WEP"
Select the "Shared Key" authentication type and from the public keys you select a "Default WEP Key" corresponding to the encryption depth.

Version "WPA"
Select the "WPA PSK" authentication type and the "AES" cipher. Specify the key to be used twice identically under Pass phrase and Pass phrase confirmation.


Fig. 05

Then you must restart the AP.

3 Switch to the "Bridge > WDS" item of the SCALANCE W concerned.

Here you must select a line for each AP connected. Click the "Sel" selection box in each case.
Under MAC / sysName you enter the "System > System name" of the WDS partner to be connected. In the case of an AP that is not from the SCALANCE series you must enter the MAC address here.
Click the "Enc" selection box in each case.
Finally you use the drop-down menu to select the key to be used as defined in Step 2. The keys must be identical on both communication partners.

Acknowledge the settings with "Set Values".

4 If both stations are configured correctly, a green light appears under the Link display after "Set Values".


Fig. 06

More information

  • To implement PROFINET IO with WDS you must use Dual Access Points. This is the only way to ensure adequate bandwidth for the PN IO communication. Note here the conditions described in the document "IWLAN: Configuring a Wireless LAN in the industrial environment" in Entry ID 22681042.
  • Use the C-PLUG. This saves reconfiguration if there are hardware defects. However, if there is WDS connection via MAC addresses here, you have to reconfigure the APs connected.
  • An alternative to the C-PLUG is to save the configuration via HTTP or TFTP via the menu item "System > Load&Save" on a PC.
  • For this refer to the notes on WDS given for the Firmware Update V3.0.37 for SCALANCE W-700 (Download: 23522136)