First we must switch the mode to Wifi. Do so by selecting Wifi from the list and wait for the page to quickly reload.
Now you have a selection of protocols available for you. Depending on whether the Access Point that you intend to connect to runs a DHCP server or not, you will have to choose DHCP or Static (AP runs a DHCP server – DHCP; Does not run - Static). When you’ve configured your protocol settings press Save and wait until the settings are applied.
Next, go to the Network -> Wireless page and wait until it loads (For the first time an automatic Site Survey will be initiated). You should now see a list of available, local Access Points. Choose one and click Join Network.
Should you be asked enter the secret Encryption Key and click Submit.
Now you should be transported to the Wireless Station page.
Click Save and wait until all the settings are applied.
The configuration is complete and you should now be able to access the internet.
Please note that if you're willing to WiFi as WAN, you will not be able to use Access Points coming out of RUT500 at the same time.