Method for processing exceptional case of establishing default bearer in mobile communication system and device therefor

1. A method for processing an exceptional case of establishing a default bearer in a mobility management entity (MME) of a mobile communication system, comprising:

receiving a network attachment request from a user equipment as part of a network attachment procedure;

transmitting a network attachment acceptance with an activation request of the default bearer to the user equipment in response to the network attachment request; and

cancelling, by the MME, the network attachment procedure when a completion response to the activation request of the default bearer is not received from the user equipment within a predetermined time.

2. The method of claim 1 , wherein cancelling the network attachment procedure includes determining whether or not the predetermined time elapses by using a timer.

3. The method of claim 2 , wherein cancelling the network attachment procedure further includes retransmitting the network attachment acceptance to the user equipment when the timer is expired while the completion response to the activation request of the default bearer is not received.

4. The method of claim 3 , wherein:

the network attachment acceptance is retransmitted until the timer is expired at the n-1-th times (n is a natural number equal to or larger than 2), and

cancelling the network attachment procedure includes cancelling the network attachment procedure when the complete response to the activation request of the default bearer is not received until the timer is expired at the n-th times.

5. The method of claim 4 , wherein the n is 5.

6. The method of claim 1 , wherein:

the mobility management entity includes a session management layer and a mobility management layer, and

wherein transmitting the network attachment acceptance includes,

allowing the session management layer to transmit the activation request of the default bearer to the mobility management layer; and

allowing the mobility management layer to transmit the network attachment acceptance with the default bearer activation request to the user equipment.

7. The method of claim 1 , wherein:

the mobility management entity includes the session management layer and the mobility management layer, and,

cancelling the network attachment procedure further includes,

allowing the session management layer to notify a failure in establishing the default bearer to the mobility management layer.

8. The method of claim 1 , wherein cancelling the network attachment procedure includes releasing an allocated resource for establishing the default bearer.

9. The method of claim 1 , wherein when a time taken to activate the default bearer is longer than the predetermined time, the mobility management entity determines the failure in establishing the default bearer through an expiration frequency of a timer.

10. The method of claim 1 , wherein the cancelling comprises cancelling a resource allocated for establishing the default bearer when the completion response to the activation request of the default bearer is not received from the user equipment within the predetermined time.

11. A device for processing an exceptional case of establishing a default bearer in a mobile communication system, comprising:

a communication unit that communicates with a user equipment; and

a control unit, including at least one processing device, that transmits a network attachment acceptance with an activation request of the default bearer in response to the network attachment request of the user equipment to the user equipment and cancels the network attachment procedure when a complete response to the activation request of the default bearer is not received from the user equipment within a predetermined time.

12. The device of claim 11 , further comprising a timer for determining whether or not the predetermined time elapses.

13. The device of claim 12 , wherein the control unit retransmits a message of the network attachment acceptance to the user equipment when the timer is expired while the complete response to the activation request of the default bearer is not received within the predetermined time.

14. The device of claim 13 , wherein:

the control unit retransmits the network attachment acceptance until the timer is expired at the n-1-th (n is a natural number equal to or larger than 2) times, and

cancels the network attachment procedure when the complete response to the activation request of the default bearer is not received until the timer is expired at the n-th times.

15. The device of claim 14 , wherein the n is 5.

16. The device of claim 12 , wherein:

the control unit includes an evolved session management (ESM) control unit and an evolved mobility management (EMM) control unit, and

wherein when the ESM control unit transmits the activation request of the default bearer to the EMM control unit, the EMM control unit the network attachment acceptance with the activation request of the default bearer to the user equipment.

17. The device of claim 16 , wherein when the complete response to the activation request of the default bearer is not received from the user equipment within a predetermined time, the ESM control unit notifies a failure in establishing the default bearer to the EMM control unit.

18. The device of claim 11 , wherein the control unit releases an allocated resource for establishing the default bearer and cancels the network attachment procedure when a complete response to the activation request of the default bearer is not received from the user equipment within a predetermined time.

19. A method for processing an exceptional case of establishing a default bearer in a mobility management entity (MME) of a mobile communication system, comprising:

receiving a network attachment request from a user equipment as part of a network attachment procedure;

transmitting a network attachment acceptance with an activation request of the default bearer to the user equipment in response to the network attachment request; and

cancelling, by the MME, the network attachment procedure when a complete response to the activation request of the default bearer is not received from the user equipment until a timer is expired at the predetermined times.

20. The method of claim 19 , wherein cancelling the network attachment procedure further includes retransmitting the network attachment acceptance to the user equipment whenever the timer is expired and restarting the timer.