A method for Protocol Data Unit, PDU, session management, the method comprising: - receiving, at an Access and Mobility Management function entity, AMF, a registration request message transmitted by a user equipment, UE, characterized in that the registration request message comprises information indicating that one or more PDU sessions require user plane, UP, resources and identifying each of the PDU sessions that require UP resources, wherein the information comprises one or more bits, each of the one or more bits indicating that uplink data needs to be transmitted for a corresponding PDU session of the one or more PDU sessions and that the UP resources are required for the corresponding PDU session, wherein one or more PDU sessions require UP resources because the UE has UP data to transmit in the one or more PDU sessions; and wherein the method comprises: - in response to receiving the registration request message and if the registration request message indicates that one or more PDU sessions require UP resources, the AMF transmitting to a session management function, SMF, a UP resource request message for requesting the SMF to establish UP resources for at least one of the PDU sessions that requires UP resources. - receiving, at an Access and Mobility Management function entity, AMF, a registration request message transmitted by a user equipment, UE, characterized in that the registration request message comprises information indicating that one or more PDU sessions require user plane, UP, resources and identifying each of the PDU sessions that require UP resources, wherein the information comprises one or more bits, each of the one or more bits indicating that uplink data needs to be transmitted for a corresponding PDU session of the one or more PDU sessions and that the UP resources are required for the corresponding PDU session, wherein one or more PDU sessions require UP resources because the UE has UP data to transmit in the one or more PDU sessions; and wherein the method comprises: - in response to receiving the registration request message and if the registration request message indicates that one or more PDU sessions require UP resources, the AMF transmitting to a session management function, SMF, a UP resource request message for requesting the SMF to establish UP resources for at least one of the PDU sessions that requires UP resources. the registration request message comprises information indicating that one or more PDU sessions require user plane, UP, resources and identifying each of the PDU sessions that require UP resources, wherein the information comprises one or more bits, each of the one or more bits indicating that uplink data needs to be transmitted for a corresponding PDU session of the one or more PDU sessions and that the UP resources are required for the corresponding PDU session, wherein one or more PDU sessions require UP resources because the UE has UP data to transmit in the one or more PDU sessions; and wherein the method comprises: - in response to receiving the registration request message and if the registration request message indicates that one or more PDU sessions require UP resources, the AMF transmitting to a session management function, SMF, a UP resource request message for requesting the SMF to establish UP resources for at least one of the PDU sessions that requires UP resources. - in response to receiving the registration request message and if the registration request message indicates that one or more PDU sessions require UP resources, the AMF transmitting to a session management function, SMF, a UP resource request message for requesting the SMF to establish UP resources for at least one of the PDU sessions that requires UP resources.