Device and method of handling a dual connectivity with base stations

1. A communication device for handling a dual connectivity (DC) with a first base station (BS) and a second BS, comprising:

at least one storage device; and

at least one processing circuit, coupled to the at least one storage device, wherein the at least one storage device stores, and the at least one processing circuit is configured to execute instructions of:

configuring a first signalling radio bearer (SRB) for communicating a first plurality of radio resource control (RRC) messages with the first BS;

receiving a first measurement configuration on the first SRB from the first BS;

transmitting a first measurement report associated to the first measurement configuration, on the first SRB to the first BS;

receiving a first RRC message on the first SRB from the first BS, wherein the first RRC message configures the second BS as a secondary node (SN) such that the communication device is in the DC with the first BS and the second BS;

configuring a second SRB for communicating a second plurality of RRC messages with the second BS in the DC;

receiving a second measurement configuration on the second SRB from the second BS in the DC;

transmitting a second measurement report associated to the second measurement configuration on the second SRB to the second BS in the DC;

detecting a failure on a connection with the second BS;

maintaining the second measurement configuration and the second SRB, in response to the failure;

maintaining a data radio bearer (DRB) configuration in response to the failure, wherein the DRB configuration configures a secondary cell group (SCG) bearer or a split bearer;

transmitting a SCG Failure Information message to the first BS in response to the failure, wherein the SCG Failure Information message comprises a measurement result; and

releasing the measurement result in response to the SCG Failure Information message.

2. The communication device of claim 1 , wherein the communication device maintains at least one of a measurement gap configuration and a SCG configuration in response to the failure.

3. The communication device of claim 1 , wherein the failure is a radio link failure, a transmission failure, an integrity check failure or a reconfiguration failure.

4. The communication device of claim 1 , wherein the instructions further comprise:

maintaining the first measurement configuration in response to the failure.

5. The communication device of claim 1 , wherein the first measurement configuration configures the communication device to measure a first carrier, and the second measurement configuration configures the communication device to measure a second carrier.

6. The communication device of claim 1 , wherein the instructions further comprise:

transmitting a first RRC response message to the first BS on the first SRB or to the second BS via the first BS on the first SRB, in response to the first RRC message.

7. A method for handling a dual connectivity (DC) with a first base station (BS) and a second BS of a communication device, comprising:

configuring a first signalling radio bearer (SRB) for communicating a first plurality of radio resource control (RRC) messages with the first BS;

receiving a first measurement configuration on the first SRB from the first BS;

transmitting a first measurement report associated to the first measurement configuration, on the first SRB to the first BS;

receiving a first RRC message on the first SRB from the first BS, wherein the first RRC message configures the second BS as a secondary node (SN) such that the communication device is in the DC with the first BS and the second BS;

configuring a second SRB for communicating a second plurality of RRC messages with the second BS in the DC;

receiving a second measurement configuration on the second SRB from the second BS in the DC;

transmitting a second measurement report associated to the second measurement configuration on the second SRB to the second BS in the DC;

detecting a failure on a connection with the second BS;

maintaining the second measurement configuration and the second SRB, in response to the failure;

maintaining a data radio bearer (DRB) configuration in response to the failure, wherein the DRB configuration configures a secondary cell group (SCG) bearer or a split bearer;

transmitting a SCG Failure Information message to the first BS in response to the failure, wherein the SCG Failure Information message comprises a measurement result; and

releasing the measurement result in response to the SCG Failure Information message.

8. The method of claim 7 , wherein the communication device maintains at least one of a measurement gap configuration and a SCG configuration in response to the failure.

9. The method of claim 7 , wherein the failure is a radio link failure, a transmission failure, an integrity check failure or a reconfiguration failure.

10. The method of claim 7 , further comprising:

maintaining the first measurement configuration in response to the failure.

11. The method of claim 7 , wherein the first measurement configuration configures the communication device to measure a first carrier, and the second measurement configuration configures the communication device to measure a second carrier.

12. The method of claim 7 , further comprising:

transmitting a first RRC response message to the first BS on the first SRB or to the second BS via the first BS on the first SRB, in response to the first RRC message.