Which wireless encryption protocol uses a 24-bit initialization vector?

Wired Equivalent Privacy (WEP) uses either 40- or 104-bit encryption; it also uses a 24-bit initialization vector (IV) to randomize each session. The encryption and IV combined, WEP advertises encryption strength of 64-bit or 128-bit. All Protected Access (WPA) variants use a variety of other mechanisms, but they do not use initialization vectors.