The traditional multicast model has some problems, such as access control, address allocation and protocol extensibility. To solve these problems, we provide a new group communication model named MixCast, which is suitable for large-scale heterogeneous networks. MixCast uses unicast between different access networks and use multicast in the same access network; at the same time, MixCast uses IEEE 802.1X protocol to provide user access control and billing scheme for carriers. We also analysis the cost of MixCast communication in the network equipments.