A communications system, comprising: a multicast session management network element, an access and mobility management network element and a user plane function network element, wherein the multicast session management network element is configured to: send a first multicast session request to the access and mobility management network element, wherein the first multicast session request carries a multicast session context and an access network node side user plane multicast receiving address, and the first multicast session request is used to request to establish a multicast session based on the multicast session context; and send a second multicast session request to the user plane function network element, wherein the second multicast session request carries user plane forwarding-related information, and the user plane forwarding-related information is used to indicate a user plane forwarding rule of the multicast session; the access and mobility management network element is configured to: receive the first multicast session request, and send the first multicast session request to an access network node; and the user plane function network element is configured to: receive the second multicast session request, and set, based on the user plane forwarding-related information, the user plane forwarding rule of the multicast session; wherein the communications system further comprises: the access network node, wherein the access network node supports multicast and is configured to: join a multicast group based on the access network node side user plane multicast receiving address in the first multicast session request. the multicast session management network element is configured to: send a first multicast session request to the access and mobility management network element, wherein the first multicast session request carries a multicast session context and an access network node side user plane multicast receiving address, and the first multicast session request is used to request to establish a multicast session based on the multicast session context; and send a second multicast session request to the user plane function network element, wherein the second multicast session request carries user plane forwarding-related information, and the user plane forwarding-related information is used to indicate a user plane forwarding rule of the multicast session; the access and mobility management network element is configured to: receive the first multicast session request, and send the first multicast session request to an access network node; and the user plane function network element is configured to: receive the second multicast session request, and set, based on the user plane forwarding-related information, the user plane forwarding rule of the multicast session; wherein the communications system further comprises: the access network node, wherein the access network node supports multicast and is configured to: the access network node, wherein the access network node supports multicast and is configured to: join a multicast group based on the access network node side user plane multicast receiving address in the first multicast session request.