Cisco Systems Multicast-VPN feature is based on the multicast domain solution described in section 2 of draft-rosen-vpn-mcast, "Multicast in MPLS/BGP VPN," which you can find at http://www.ietf.org. Multicast domains allow a service provider to offer mVPN services to their customers by using native multicasting techniques in the core. Native multicast is a mature technology on Cisco IOS; therefore, stability of the P-network is protected because no new features or software upgrades need to be performed on the P routers.
Scalability of the solution is ensured because the P-network has no visibility into the customer's multicast network. All mVPN traffic is carried inside a single multicast tunnel for that VPN. The number of multicast tunnels in the provider network is predictable and is significantly lower than the number of potential multicast groups in all VPNs.
From the end customer's point of view, no changes need to be made in the network to connect to a mVPN service. The service provider can support all customer modes, including PIM SM, PIM DM, PIM SSM, and any type of customer rendezvous point topology.
Routing optimality is improved in the P-network via the use of special tunnels for high-bandwidth sources that ensure that enterprise multicast traffic is delivered only to PE routers that have an interested receiver.