Network access control method, SDF, CP, UP and network system

The embodiment of the invention discloses a network access control method, an SDF, a CP, UPs and a network system. The SDF obtains a CGN resource pool through CGN resources reported to the SDF by a plurality of UPs, the CGN resources comprise CGN service load conditions of each UP in the plurality of UPs, so when user equipment is online, the CP sends a CGN instance acquisition request to the SDF to allocate a CGN instance for the user equipment; the SDF allocates a first CGN instance to the user equipment according to the CGN resource pool, the first CGN instance indicates a first UP with available CGN resources, the first UP is one of a plurality of UPs, and finally the SDF sends the first CGN instance to the CP, so the CP can enable the first UP with the CGN resources to bear the flow of the user equipment according to the first CGN instance and provide CGN business service for the user equipment. Therefore, the UP with the available CGN resources can be allocated to the user equipment in a traffic path pl