Abstract: In a wireless communication system, a method of authenticating a mobile station is claimed. A first CHAP challenge message is transmitted. A first CHAP response message is received in response to the first CHAP message. An IMSI message corresponding to the received CHAP message is transmited. A plurality of parameters is received in response to the transmitted IMSI message. at least one parameter is then transmitted. A second CHAP response message is received in response to the transmitted parameter. The second CHAP response message is then compared to one of said plurality of parameters.