This application discloses a communications system, a communication method, and an apparatus thereof. The system includes: a multicast session management network element, an access and mobility management network element and a user plane function network element. The multicast session management network element sends a first multicast session request carrying a multicast session context to the access and mobility management network element to request to establish a multicast session based on the multicast session context; and sends a second multicast session request to the user plane function network element, where the second multicast session request carries user plane forwarding-related information indicating a user plane forwarding rule of the multicast session. The access and mobility management network element sends the first multicast session request to an access network node. The user plane function network element sets, based on the user plane forwarding-related information, the user plane forwarding rule of the multicast session.