Managing alternate-network slice in multi-SIM UE

1 . A method performed by a multi-universal subscriber identity module (MUSIM) user equipment (UE) for managing alternate-network slice, the method comprising:

storing slice mapping information in a network slice database, wherein the slice mapping information comprises a mapping relationship among a first candidate network slice of the first SIM, a second candidate network slice of the first SIM, and a candidate network slice of a second SIM, wherein the slice mapping information indicates that the candidate network slice of the second SIM has a higher priority than the second candidate network slice of the first SIM as the alternate-network slice;

transmitting, to a first network operator associated with the first SIM, a registration request message for the first candidate network slice of the first SIM;

receiving, from the first network operator, a registration response message rejecting the first candidate network slice in response to the registration request message;

determining the candidate network slice of the second SIM based on the stored slice mapping information in the network slice database in response to receiving the registration response message rejecting the first candidate network slice; and

transmitting, to a second network operator associated with the second SIM, a registration request message for the candidate network slice of the second SIM.

2 . The method of claim 1 , wherein the determining of the candidate network slice of the second SIM comprises:

determining the candidate network slice of the second SIM based on the stored slice mapping information in the network slice database according to the first candidate network slice of the first SIM being unavailable in response to receiving the registration response message.

3 . The method of claim 1 , wherein the transmitting of the registration request message for the candidate network slice of the second SIM comprises:

switching a data connection from the first SIM to the second SIM based on the candidate network slice of the second SIM being available;

transmitting the registration request message to the second network operator associated with the second SIM; and

receiving a registration accept message from the second network operator.

4 . The method of claim 3 , wherein the registration request message transmitted to the first network operator comprises single network slice selection assistance information (S-NSSAI) about the first candidate network slice of the first SIM.

5 . The method of claim 1 , wherein the registration request message transmitted to the second network operator comprises S-NSSAI about the candidate network slice of the second SIM same as S-NSSAI about the first candidate network slice of the first SIM.

6 . The method of claim 1 , wherein storing the slice mapping information in the network slice database comprises:

receiving, from the first network operator, information on a plurality of network slices supported by the first network operator and receiving, from the second network operator, information on a plurality of network slices supported by the second network operator;

determining the first candidate network slice and the second candidate network slice supported by the first network operator and the candidate network slice supported by the second network operator;

creating the slice mapping information based on priorities of the first candidate network slice, the second candidate network slice, and the candidate network slice; and

storing the created slice mapping information in the network slice database.

7 . The method of claim 1 , further comprising:

updating that the first candidate network slice of the first SIM is unavailable in the network slice database based on the first candidate network slice of the first SIM being unavailable or upon receiving the registration response message from the first network operator associated with the first SIM.

8 . The method of claim 1 , wherein determining the candidate network slice of the second SIM comprises:

checking the slice mapping information stored in the network slice database to determine the candidate network slice of the second SIM of a plurality of SIMs based on the first candidate network slice of the first SIM being unavailable.

9 . The method of claim 1 , further comprising:

determining at least one critical candidate network slice based on received information on a plurality of network slices supported by the first network operator associated with the first SIM and information on a plurality of network slices supported by the second network operator associated with the second SIM;

prioritizing the at least one critical candidate network slice in the network slice database based on the at least one critical candidate network slice;

checking the network slice database whether the at least one critical candidate network slice of the first SIM is available based on the prioritization;

transmitting the registration request message to the first network operator based on the at least one critical candidate network slice of the first SIM being available;

transmitting the registration request message to the second network operator based on the at least one critical candidate network slice of the first SIM being unavailable.

10 . A multi-universal subscriber identity module (MUSIM) user equipment (UE) configured to manage an alternate-network slice, wherein the MUSIM UE comprises:

memory; and

at least one processor coupled to the memory, wherein the at least one processor is configured to:

store slice mapping information in the network slice database, wherein the slice mapping information comprises a mapping relationship among a first candidate network slice of a first SIM, a second candidate network slice of the first SIM, and a candidate network slice of the second SIM, wherein the slice mapping information indicates that the candidate network slice of the second SIM has a higher priority than the second candidate network slice of the first SIM as the alternate-network slice;

transmit, to a first network operator associated with a first SIM, a registration request message for the first candidate network slice of the first SIM;

receive, from the first network operator, a registration response message rejecting the first candidate network slice in response to the registration request message;

determine the candidate network slice of the second SIM based on the stored slice mapping information in the network slice database in response to receiving the registration response message rejecting the first candidate network slice; and

transmit, to a second network operator associated with the second SIM, a registration request message for the candidate network slice of the second SIM.

11 . The MUSIM UE of claim 10 , wherein the at least one processor is configured to:

switch a data connection from the first SIM to the second SIM based on the candidate network slice of the second SIM being available;

transmit the registration request message to the second network operator associated with the second SIM; and

receive a registration accept message from the second network operator.

12 . The MUSIM UE of claim 11 , wherein the registration request message transmitted to the first network operator comprises single network slice selection assistance information (S-NSSAI) about the first candidate network slice of the first SIM.

13 . The MUSIM UE of claim 10 , wherein the registration request message transmitted to the second network operator comprises S-NSSAI about the candidate network slice of the second SIM same as S-NSSAI about the first candidate network slice of the first SIM.

14 . The MUSIM UE of claim 10 , wherein the at least one processor is configured to:

receive, from the first network operator, information on a plurality of network slices supported by the first network operator and receive, from the second network operator, information on a plurality of network slices supported by the second network operator;

determine the first candidate network slice and the second candidate network slice supported by the first network operator and the candidate network slice supported by the second network operator;

create the slice mapping information based on priorities of the first candidate network slice, the second candidate network slice, and the candidate network slice; and

store the created slice mapping information in the network slice database.

15 . The MUSIM UE of claim 10 , wherein the at least one processor is configured to update that the first candidate network slice of the first SIM is unavailable in the network slice database based on the first candidate network slice of the first SIM being unavailable or upon receiving the registration response message from the first network operator associated with the first SIM.

16 . The MUSIM UE of claim 10 , wherein the at least one processor is configured to check the slice mapping information stored in the network slice database to determine the candidate network slice of the second SIM of a plurality of SIMs based on the first candidate network slice of the first SIM being unavailable.

17 . The MUSIM UE of claim 10 , wherein the at least one processor is configured to:

determine at least one critical candidate network slice based on received information on a plurality of network slices supported by the first network operator associated with the first SIM and information on a plurality of network slices supported by the second network operator associated with the second SIM;

prioritize the at least one critical candidate network slice in the network slice database based on the at least one critical candidate network slice;

check the network slice database to determine whether the at least one critical candidate network slice of the first SIM is available based on the prioritization;

transmit the registration request message to the first network operator based on the at least one critical candidate network slice of the first SIM being available;

transmit the registration request message to the second network operator based on the at least one critical candidate network slice of the first SIM being unavailable.

18 . A non-transitory computer-readable storage medium storing one or more programs, wherein the one or more programs comprise instructions, wherein the instructions, when executed by at least one processor of a multi-universal subscriber identity module (MUSIM) user equipment (UE), cause the MUSIM UE to:

store slice mapping information in the network slice database, wherein the slice mapping information comprises a mapping relationship among a first candidate network slice of a first SIM, a second candidate network slice of the first SIM, and a candidate network slice of a second SIM, wherein the slice mapping information indicates that the candidate network slice of the second SIM has a higher priority than the second candidate network slice of the first SIM as the alternate-network slice:

transmit, to a first network operator associated with a first SIM, a registration request message for the first candidate network slice of the first SIM;

receive, from the first network operator, a registration response message rejecting the first candidate network slice in response to the registration request message;

determine the candidate network slice of the second SIM based on the stored slice mapping information in the network slice database based in response to receiving the registration response message rejecting the first candidate network slice; and

transmit, to a second network operator associated with the second SIM, registration request message for the candidate network slice of the second SIM.