WEP encryption:
-is part of the IEEE 802.11b standard
-however defining the WEP keys in client software is not at all same
-there is not yet standardized way to change keys

IPSEC/VPN:
-IPSEC/VPN solutions can be used to provide additional security for encrypting the radio way

Vendor specific solutions:
-Lucent ”closed network” very insecure
-is based on the network id (essid), the WLAN devices must know this to be able to connect
-Bugtraq announced recently that this was buggy and it was possible to find out the essid from the radio traffic without connecting to the network
-WEP encryption with ”closed network” setting may provide additional security but in author’s humble opinion it’s not enough

MAC address based access filtering in access point
-The WLAN access point filters from the device which MAC address is not in its access list or verifiable from access database / authentication server via for example Radius server
-Access Point may have this kind of limited firewall capability
-However the access point may let the device to associate to the WLAN cell so that the device is able to eavesdrop traffic
-this feature exists only in few vendors’ access point products