There is no effective method to support IP level Internet wide multisource multicast sessions, that can be easily used from almost every ISP There are several protocols implementing the necessary functionality, but the penetration of them is really low recently. The most obvious work all-round is using SSM – Source Specific Multicasting, in which, the IP multicast session is identified by the multicast group address and the source’s unicast IP address. SSM allows using all the SSM address range for every source IP addresses and limits the address allocation problem inside the host of the source; however, its significant drawback is that the SSM has no native support to create multicast sessions with more than one source; it uses separate source specific distribution trees for every single source therefore it needs more resources on the router side. The alternative solution for supporting multisource multicast session is the ASM – Any Source Multicasting. However, its significant drawback is the lack of Internet wide dynamic address allocation. To address the recent problems of the Internet wide multisource multicast session a novel IP multicast service model, the Responsible Source Multicasting - RSM is introduced in this paper. RSM uses shared distribution trees like ASM; however, builds a reverse path tree towards an appropriate well-known unicast IP address like SSM. The paper demonstrates that this novel multicast routing protocol handles Internet wide multisource multicast sessions. The paper also shortly presents the DAMA – Dynamic Address Allocation of Multicast Addresses protocol for dynamic multicast IP address allocation, which works in a strong collaboration with the RSM.