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Group applications like the audioconference require a minimum level of quality of service for the adequate transmission of voice packets and the improvement of the signaling processes for joining, maintaining and leaving multicast groups. Traditionally, SIP servers have dealed with unicast signaling and have also been supported by IP multicast facilities described within the SDP payload information for the multicast distribution. As a consequence, the same existing drawbacks of IP multicast affect the performance of multicast conferences based on SIP requests. This work proposes a new multicast architecture based on SIP extensions and a group management system. Such architecture supports both overlay multicast and IP multicast together in data and control plane. The group management functions are executed inside a conference manager, for the calculus of the optimal multicast structure and also for the correct visualization of groups. The results regarding QoS show that joining and leaving durations in SIP multicast for group members might be shorter in comparison with the IP multicast approach in some scenarios and reliability also increases. Future research will give quantitative results at great scale with the proposed architecture.