Methods and related devices for multi-connectivity

1. A User Equipment (UE) for multi-connectivity, comprising:

one or more non-transitory computer-readable media having computer-executable instructions embodied thereon; and

at least one processor coupled to the one or more non-transitory computer-readable media, and configured to execute the computer-executable instructions to:

receive a first Radio Resource Control (RRC) message comprising at least one Secondary Cell Group (SCG) Data Radio Bearer (DRB) configuration from a Master Cell Group (MCG);

start a first timer upon receiving the first RRC message;

report failure information to the MCG via an SCG Failure Information message when the first timer expires, the failure information comprising an SCG failure cause value and at least one first cell identity (ID) indicating at least one suitable cell determined by the UE, the SCG failure cause value indicating a reconfiguration failure of the first RRC message; and

stop the first timer when at least one of the following conditions is satisfied:

initiating an RRC reestablishment procedure by sending an RRC reestablishment request message to the MCG;

sending the SCG Failure Information message to the MCG before the first timer expires; and

successfully adding the SCG DRB configuration.

2. The UE according to claim 1 , wherein the at least one SCG DRB configuration comprises a first SCG DRB configuration and a second SCG DRB configuration, and the at least one processor is further configured to execute the computer-executable instructions to:

set the first timer for the first SCG DRB configuration; and

set a second first timer for the second SCG DRB configuration.

3. The UE according to claim 2 , wherein the first timer and the second timer have different values.

4. The UE according to claim 1 , wherein the at least one processor is further configured to execute the computer-executable instructions to:

perform at least one of a plurality of procedures after reporting the failure information, the plurality of procedures comprising:

performing measurements configured by the MCG; and

establishing an MCG DRB to the MCG.

5. A method performed by a User Equipment (UE) for multi-connectivity, comprising:

receiving a first Radio Resource Control (RRC) message comprising at least one Secondary Cell Group (SCG) Data Radio Bearer (DRB) configuration from a Master Cell Group (MCG);

starting a first timer upon receiving the first RRC message;

reporting failure information to the MCG via an SCG Failure Information message when the first timer expires, the failure information comprising an SCG failure cause value and at least one first cell identity (ID) indicating at least one suitable cell determined by the UE, the SCG failure cause value indicating a reconfiguration failure of the first RRC message; and

stopping the first timer when at least one of the following conditions is satisfied:

initiating an RRC reestablishment procedure by sending an RRC reestablishment request message to the MCG;

sending the SCG Failure Information message to the MCG before the first timer expires; and

successfully adding the SCG DRB configuration.

6. The method according to claim 5 , wherein the at least one SCG DRB configuration comprises a first SCG DRB configuration and a second SCG DRB configuration, and the method further comprises:

setting, by the UE, the first timer for the first SCG DRB configuration; and

setting, by the UE, a second timer for the second SCG DRB configuration.

7. The method according to claim 6 , wherein the first timer and the second timer have different values.

8. The method according to claim 5 , further comprising:

performing at least one of a plurality of procedures after reporting the failure information, the plurality of procedures comprising:

performing measurements configured by the MCG; and

establishing an MCG DRB to the MCG.

9. A base station for multi-connectivity, comprising:

one or more non-transitory computer-readable media having computer-executable instructions embodied thereon; and

at least one processor coupled to the one or more non-transitory computer-readable media, and configured to execute the computer-executable instructions to:

transmit a first Radio Resource Control (RRC) message comprising a timer and at least one Secondary Cell Group (SCG) Data Radio Bearer (DRB) configuration to a User Equipment (UE), the timer being configured to be started by the UE when the UE receives the first RRC message; and

receive failure information from the UE via an SCG Failure Information message after the timer expires, the failure information comprising an SCG failure cause value and at least one first cell identity (ID) indicating at least one suitable cell determined by the UE, the SCG failure cause value indicating a reconfiguration failure of the first RRC message, wherein the timer is configured to be stopped by the UE when at least one of the following conditions is satisfied:

initiating an RRC reestablishment procedure by sending an RRC reestablishment request message to the MCG;

sending the SCG Failure Information message to the MCG before the timer expires; and

successfully adding the SCG DRB configuration.

10. The base station according to claim 9 , wherein the at least one processor is further configured to execute the computer-executable instructions to:

perform at least one of a plurality of procedures in response to the failure information, the plurality of procedures comprising:

transmitting a measurement configuration to the UE;

adding an SCG for the UE; and

establishing an MCG DRB to the UE.