The efficient support of the IP Integrated Services architecture (IIS) in ATM networks is nowadays a challenging research topic in the internetworking area. The integration of the two architectures needs the overcoming of the inconsistencies existing between their service models, in particular when considering multicast communications. The IIS architecture is based on the Resource Reservation Protocol (RSVP). IP multicast and RSVP rely on a receiver- oriented mode, where a receiver is not only capable of deciding whether to join or leave a multicast sessions, but it is also allowed to choose the associated QoS independently from the other participants. On the other hand, the ATM service model is sender-oriented: the originating node of a multipoint session is the only entity allowed to add or delete leaf nodes. In addition, the originating node sets the QoS of a session, which is unique for all the receivers. The IETF standard for IP multicast over ATM is the MARS model. Nevertheless this approach has been developed for best effort connections only. In this paper we present an extension to the MARS protocol n order to be integrated with the RSVP protocol for supporting QoS management. Within a logical IP Subnet, a Multicast Integration Server (MIS) is entitled of IP multicast address to ATM addressees resolution using the MARS protocol, and of QoS management using RSVP. In addition to the functionalities foreseen by the MARS specification, the MARS server within the MIS uses anew set of messages to inform the sender to a group about the QoS chosen by each receiver. An RSVP entity within the MIS is used to distribute RSVP messages within the LIS and to provide to the MARS the translation of the QoS level form IIS to ATM.