Method for performing registration with network in wireless communication system and device therefor

1. A method performed by a user equipment (UE) in a wireless communication system, the method comprising:

transmitting, to a first core network, a registration request message via a cell connected to the first core network and a second core network;

receiving, from the first core network, a registration reject message via the cell, wherein the registration reject message comprises a cause value related to a rejection of registration and wherein the cause value is set to inform that a registration to the second core network is required; and

performing a procedure for registration in the second core network based on identifying the cause value.

2. The method of claim 1 , further comprising:

receiving information indicating that the cell is connected to the first core network and the second core network from the first core network.

3. The method of claim 1 , further comprising:

receiving information indicating the second core network is allowed from the first core network.

4. The method of claim 3 , wherein the information indicating the second core network is allowed is received during a radio resource control (RRC) connection release procedure.

5. The method of claim 1 , further comprising:

upon receiving the registration reject message, disabling access to the first core network.

6. The method of claim 1 , wherein

the cause value indicates that the first core network is not allowed and redirection to the second core network is required.

7. The method of claim 1 , wherein

unless the UE supports the second core network, the UE regards the first cell as forbidden.

8. The method of claim 1 , wherein

the UE puts on hold an attempt to perform the procedure for registration in the second core network until a predetermined criterion is met.

9. The method of claim 1 , further comprising:

unless the UE supports the second core network, performing a procedure for registration in the first core network on a different cell other than the cell.

10. The method of claim 1 , wherein

when a base station of the UE is able to connect to both the first core network and the second core network, the base station of the UE is regarded as a first type of radio access network when connected with the first core network and as a second type of radio access network when connected with the second core network.

11. The method of claim 1 , further comprising:

determining whether a signal strength of the cell is a predetermined level or more based on the cause value.

12. The method of claim 11 , wherein

when the signal strength of the cell is the predetermined level or more, a procedure for registration in the second core network supported on the cell is performed.

13. The method of claim 11 , further comprising:

unless the signal strength of the cell is the predetermined level or more, selecting a different cell other than the cell.

14. A user equipment (UE) in a wireless communication system, the UE comprising:

a transceiver for transmitting or receiving a wireless signal; and

a processor controlling the transceiver, wherein the processor is configured to:

transmit, to a first core network, a registration request message via a cell connected to the first core network and a second core network;

receive, from the first core network, a registration reject message via the cell, wherein the registration reject message comprises a cause value related to a rejection of registration and wherein the cause value is set to inform that a registration to the second core network is required; and

perform a procedure for registration in the second core network based on identifying the cause value.