At last I am able to configure dot1x authentication for wireless devices. My requirement is that if any user come on wireless he should be authenticated from microsoft active directory(ad) database. For implementing dot1x I have installed a microsoft active directory server with radius & dhcp. A switch was connected to server and wireless device. When ever the laptop or any pc request to connect the wireless network a logon windows screen prompt which asks for the username & passowrd with domain. On successful authentication user gets the ip address if it fails no ip is given.