Both computer and telecommunication networks have developed rapidly and become much more popular recently. On the basis of the characteristics of the two networks, we can see that they are complementary. If we can integrate the most popular technologies of these two kinds of networks, the integration will result in a new, attractive network access method. From the viewpoints of both the user and the service provider, the advantages of the integration include increased profits and better support for services. However, the integration of the two heterogeneous networks still presents many problems, the most critical of which concern authentication and billing. In this paper, we propose a practical, efficient, and secure authentication, authorization, and accounting mechanism within the interworking architecture proposed by Third Generation Partnership Project (3GPP). Copyright © 2013 John Wiley & Sons, Ltd.