AbstractIn recent years, VPN (Virtual Private Network) has become an important subject not only in the Internet, but also on intranets and extranets. The VPN enables us to communicate safely by using public networks. A number of researchers have studied DVPN (department VPNs). Furthermore, multicasting has been attracting attention as a means to increase the volume of voice data and multimedia data on the Internet. However, a multicast router is needed to deliver data with multicasting on the default network. Although it is possible that the IP multicast function will be added to all new routers in the future, it is not realistic to convert all default routers in use to multicast routers at this moment. Systems which make use of multicast servers without using multicast routers have been proposed. However, many problems arise in the conventional model, such as excess load on the multicast server, and traffic on its domain when data with multicasting are sent or received over the DVPN. In this paper, we propose an effective method of multicast communication over the DVPN in order to establish a secure DVPN for multicast applications such as video conferencing. In the proposed method, the relay function for multicast communication is added to the DVPN terminals themselves, which leads to easy use compared to the conventional method with multicast server. We propose two packet delivery system models, the daisy chain model and the extended daisy chain model. The daisy chain model is made up of a group of DVPN hosts, which have the copy function. In the extended daisy chain model, a branch division function is added to the daisy chain model. We present a network model for numerical calculation to show the efficiency of our proposed models. We investigate the effects of load variance, network traffic, and delay time on the performance of the two proposed models compared to the conventional model, and show that the two proposed models are superior to the conventional model. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 84(7): 45–56, 2001