Enhanced handling on QoS flow description

1. A method of performing a Quality of Service (QoS) Operation in a mobile communication network, comprising:

receiving a Protocol data unit (PDU) session modification command message by a user equipment (UE) for performing the QoS operation associated with a PDU session based at least on one of a QoS rules information element (IE) and a QoS flow descriptions IE in the mobile communication network;

determining that a QoS rule associated with a QoS flow having a specific QoS flow ID (QFI) has no corresponding QoS flow description, wherein the specific QFI indicates a guaranteed bit rate (GBR) QoS flow; and

deleting the QoS rule after completing the QoS operation if the QoS rules IE contains another valid QoS rule, or rejecting the PDU session modification command message if the QoS rules IE does not contain another valid QoS rule, wherein the QoS rule is not a default QoS rule.

2. The method of claim 1 , wherein the UE releases the PDU session when the QoS rule is the default QoS rule.

3. The method of claim 1 , wherein a mapping between a 5QI value and a QoS flow resource type of GBR or non-GBR is predefined in the network, and wherein the 5QI value is used as the specific QFI of the QoS flow.

4. The method of claim 3 , wherein the QoS operation is for “creating new QoS rule”, and wherein the UE does not receive any QoS flow description for the specific QFI of the QoS rule.

5. The method of claim 1 , wherein the specific QFI has a QoS flow description before the QoS operation, and wherein the QoS flow description indicates the QoS flow is a GBR QoS flow.

6. The method of claim 5 , wherein the QoS operation is for “deleting existing QoS flow description”, and wherein the QoS flow description associated with the QFI of the QoS rule will be deleted after the QoS operation.

7. The method of claim 1 , wherein the QoS operation is for “modify existing QoS rule”, and wherein the QoS rule will be associated with the specific QFI having no QoS flow description after the QoS operation.

8. The method of claim 1 , wherein the UE rejects the modification command message with a 5GSM cause value indicating a QoS operation error.

9. A User Equipment (UE), comprising:

a receiver that receives a Protocol data unit (PDU) session modification command message for performing a Quality of Service (QoS) operation associated with a PDU session based at least on one of a QoS rules information element (IE) and a QoS flow descriptions IE in a mobile communication network;

a QoS rule and flow management circuit determines that a QoS rule associated with a QoS flow having a specific QoS flow ID (QFI) has no corresponding QoS flow description, wherein the specific QFI indicates a guaranteed bit rate (GBR) QoS flow; and

a PDU session handling circuit that deletes the QoS rule after completing the QoS operation if the QoS rules IE contains another valid QoS rule, or rejects the PDU session modification command message if the QoS rules IE does not contain another valid QoS rule, wherein the QoS rule is not a default QoS rule.

10. The UE of claim 9 , wherein the UE releases the PDU session when the QoS rule is the default QoS rule.

11. The UE of claim 9 , wherein a mapping between a 5QI value and a QoS flow resource type of GBR or non-GBR is predefined in the network, and wherein the 5QI value is used as the specific QFI of the QoS flow.

12. The UE of claim 11 , wherein the QoS operation is for “creating new QoS rule”, and wherein the UE does not receive any QoS flow description for the specific QFI of the QoS rule.

13. The UE of claim 9 , wherein the QoS flow of the specific QFI has a QoS flow description before the QoS operation, and wherein the QoS flow description indicates the QoS flow is a GBR QoS flow.

14. The UE of claim 13 , wherein the QoS operation is for “deleting existing QoS flow description”, and wherein the QoS flow description associated with the QFI of the QoS rule will be deleted after the QoS operation.

15. The UE of claim 9 , wherein the QoS operation is for “modify existing QoS rule”, and wherein the QoS rule will be associated with the specific QFI having no QoS flow description after the QoS operation.

16. The UE of claim 9 , wherein the UE rejects the modification command message with a 5GSM cause value indicating a QoS operation error.

17. A method of performing a Quality of Service Operation (QoS) in a mobile communication network, comprising:

receiving a Protocol data unit (PDU) session establishment accept message by a user equipment (UE) for performing the QoS operation associated with a PDU session based at least on one of a QoS rules information element (IE) and a QoS flow descriptions IE in a mobile communication network;

determining that a QoS rule associated with a QoS flow having a specific QoS flow ID (QFI) has no corresponding QoS flow description after the QoS operation;

determining that the specific QFI indicates a guaranteed bit rate (GBR) QoS flow; and

deleting the QoS rule if the QoS rule is not a default QoS rule and releasing the PDU session if the QoS rule is the default QoS rule.

18. The method of claim 17 , wherein a mapping between a 5QI value and a QoS flow resource type of GBR or non-GBR is predefined in the network, and wherein the 5QI value is used as the specific QFI of the QoS flow.

19. The method of claim 17 , wherein the QoS operation is for “creating new QoS rule”, and wherein the UE does not receive any QoS flow description for the QFI of the QoS rule.

20. The method of claim 17 , wherein the UE deletes the QoS rule by sending a PDU session modification request message to the network with a 5GSM cause value indicating a QoS operation error.