In an optional embodiment, S210 includes operations as follows. The remote terminal device determines the state information based on quality information on a link between the remote terminal device and the network device within the coverage of the network, and/or based on quality information on a link between the remote terminal device and a relay terminal device having the subscription relationship and/or the connection relationship with the remote terminal device. Therefore, the state information includes identification information of the network where the remote terminal device is located, and quality information on a link between the remote terminal device and a network device corresponding to the identification information of the network, and/or, the state information includes identification information of the relay terminal device having the subscription relationship and/or the connection relationship with the remote terminal device, and the quality information on a link between the remote terminal device and the relay terminal device.