Device and method of handling data transmission

1. A communication device of handling data transmission, comprising:

a storage device, for storing instructions of:

configuring a first bearer and a second bearer according to at least one bearer configuration received from a network;

encrypting a first packet of a first flow into a first encrypted packet according to an encryption key and a first bearer identity of the first bearer;

receiving a first radio resource control (RRC) message from the network before transmitting the first encrypted packet to the network successfully, wherein the first RRC message configures the communication device to transmit at least one packet of the first flow via the second bearer to the network;

transmitting the first encrypted packet to the network via the first bearer, after receiving the first RRC message;

encrypting a second packet of the first flow into a second encrypted packet according to the encryption key and a second bearer identity of the second bearer in response to the first RRC message; and

transmitting the second encrypted packet to the network via the second bearer; and

a processing circuit, coupled to the storage device, configured to execute the instructions stored in the storage device.

2. The communication device of claim 1 , wherein the instruction of receiving the first RRC message from the network before transmitting the first encrypted packet to the network successfully comprises:

receiving the first RRC message from the network, before transmitting the first encrypted packet to the network; or

receiving the first RRC message from the network, after transmitting the first encrypted packet to the network but not receiving an acknowledgment of the first encrypted packet from the network.

3. The communication device of claim 1 , wherein the storage device further stores an instruction of:

receiving at least one second RRC message from the network, wherein the at least one second RRC message comprises the at least one bearer configuration, wherein one of the at least one second RRC message indicates that the first flow is mapped to the first bearer.

4. The communication device of claim 1 , wherein the storage device further stores an instruction of:

encrypting a plurality of packets of the first flow into a plurality of encrypted packets and transmitting the plurality of encrypted packets to the network via the first bearer, when the communication device configures the first bearer according to one of the at least one bearer configuration.

5. The communication device of claim 1 , wherein the storage device further stores an instruction of:

receiving a plurality of encrypted packets of the first flow from the network via the first bearer and decrypting the plurality of encrypted packets of the first flow to a plurality of packets, when the communication device configures the first bearer according to one of the at least one bearer configuration.

6. The communication device of claim 3 , wherein one of the at least one second RRC message or the first RRC message indicates that a second flow is mapped to the first bearer or the second bearer.

7. The communication device of claim 1 , wherein the first bearer is a default data radio bearer (DRB) with a first quality of service (QoS) configuration, and the second bearer is a dedicated DRB with a second QoS configuration different from the first QoS configuration.

8. A network of handling data transmission, comprising:

a storage device, for storing instructions of:

transmitting at least one bearer configuration configuring a first bearer and a second bearer to a communication device;

encrypting a first packet of a first flow into a first encrypted packet according to an encryption key and a first bearer identity of the first bearer;

transmitting a first radio resource control (RRC) message to the communication device before transmitting the first encrypted packet to the communication device successfully, wherein the first RRC message configures the communication device to transmit at least one packet of the first flow to the network via the second bearer;

transmitting the first encrypted packet to the communication device via the first bearer, after transmitting the first RRC message;

encrypting a second packet of the first flow into a second encrypted packet according to the encrypted key and a second bearer identity of the second bearer in response to the first RRC message; and

transmitting the second encrypted packet to the communication device via the second bearer; and

a processing circuit, coupled to the storage device, configured to execute the instructions stored in the storage device.

9. The network of claim 8 , wherein the instruction of transmitting the first RRC message to the communication device before transmitting the first encrypted packet to the communication device successfully comprises:

transmitting the first RRC message to the communication device, before transmitting the first encrypted packet to the network to the communication device.

10. The network of claim 8 , wherein the instruction of transmitting the first RRC message to the communication device before transmitting the first encrypted packet to the communication device successfully comprises:

transmitting the first RRC message to the communication device, after transmitting the first encrypted packet to the communication device but not receiving an acknowledgment of the first encrypted packet from the communication device.

11. The network of claim 8 , wherein the storage device further stores an instruction of:

transmitting at least one second RRC message to the communication device, wherein the at least one second RRC message comprises the at least one bearer configuration, wherein one of the at least one second RRC message indicates that the first flow is mapped to the first bearer or the second bearer.

12. The network of claim 8 , wherein the storage device further stores an instruction of:

encrypting a plurality of packets of the first flow into a plurality of encrypted packets and transmitting the plurality of encrypted packets to the communication device via the first bearer, when the network configures the first bearer to the communication device.

13. The network of claim 8 , wherein the storage device further stores an instruction of:

receiving a plurality of encrypted packets of the first flow from the communication device via the first bearer and decrypting the plurality of encrypted packets of the first flow to a plurality of packets, when the network configures the first bearer to the communication device.

14. The network of claim 11 , wherein one of the at least one second RRC message or the first RRC message indicates that a second flow is mapped to the first bearer or the second bearer.

15. The network of claim 8 , wherein the first bearer is a default data radio bearer (DRB) with a first quality of service (QoS) configuration, and the second bearer is a dedicated DRB with a second QoS configuration different from the first QoS configuration.