This disclosure involves enabling a terminal device to connect to a core network and move in a communication system in which multiple core networks are overlaid. In some embodiments, a core network device can receive a tracking area update request message from a base station device. The core network device can transmit, to the base station device, a signaling message after receiving the tracking area update request message. The signaling message can contain information indicating a second core network, where the first core network and the second core network exist within an identical PLMN.