The LSP tunnels that carry unicast or multicast traffic for the same customer are separated due to their completely different characteristics. A tunnel that is carrying multicast traffic will not affect the same customer’s unicast traffic, even if the tunnel is down.
As shown in Multicast routing protocol that uses PIM, iBGP is used for route distribution. Multicast route information within the multicast VPN is exchanged between PEs. Such information, which is denoted as a source and group pair (S, G), is learned from the CEs through the Protocol Independent Multicast (PIM) interface.
PIM is the multicast routing protocol that is used in the IP network. “C-S, C-G” means “Customer-Source, Customer-Group.” “Provider-S, Provider-Group” would exist if PIM were used in the core network.