Patent ID: 7016326

Claim:
A method of effecting handoff of a mobile station from a first base station in a first cellular communications system controlled by a first mobile switching control station to a second base station in a second, different cellular system controlled by a second mobile switching control station, the method comprising: generating at the second cellular communication system an authentication code as the result of applying an algorithm to a private key assigned to the mobile station for the second cellular communications system and a random number generated by the second cellular communications system; generating at the first cellular communication system an authentication code as the result of applying an algorithm to the private key and the random number; transmitting the authentication code generated at the first cellular communication system to a mobile station in a data packet; transmitting from the mobile station to the second cellular communication system the authentication code generated at the first cellular communication system; and comparing the authentication code generated at the first cellular communications system with the authentication code generated at the second cellular communications system.