Method and apparatus for sequential forwarding considering multi-flow in dual connectivity system

1. A method for user equipment receiving multi-flow data with respect to one evolved packet system (EPS) bearer through a macro base station (macro eNB) and a small base station (small eNB) serving a single cell in a wireless communication system supporting dual connectivity, the method comprising:

configuring a first radio bearer (RB) and a second RB;

receiving packet data convergence protocol (PDCP) packet data units (PDUs) through the macro base station through the first RB and the small base station through the second RB;

obtaining PDCP service data units (SDUs) corresponding to the PDCP PDUs;

receiving from the macro base station information related to an in-sequence timer for the PDCP SDUs through a radio resource control (RRC) message over the first RB; and

confirming the respective PDCP sequence numbers (SNs) of the obtained PDCP SDUs and performing in-sequence delivery of the PDCP SDUs to an upper layer from a PDCP entity according to the PDCP SN,

wherein the PDCP SDUs are indicated by a predefined PDCP sequence number (SN).

2. The method of claim 1 , further comprising:

confirming whether there is a PDCP SDU of PDCP SN #n−1 which is missed in spite of obtaining a PDCP SDU of PDCP SN #n; and

driving the in-sequence timer with respect to the PDCP SDU of PDCP SN#n when there is the PDCP SDU of PDCP SN#n−1 which is missed.

3. The method of claim 2 , wherein when the in-sequence timer for the PDCP SDU of PDCP SN#n has expired, the PDCP SDU of PDCP SN#n is exceptionally delivered to the upper layer of the PDCP entity even though there is no PDCP SDU of PDCP SN #n−1.

4. The method of claim 2 , wherein before the in-sequence timer for the PDCP SDU of PDCP SN#n has expired, when the PDCP SDU of PDCP SN#n−1 is obtained, the PDCP SDU of PDCP SN#n−1 and the PDCP SDU of PDCP SN#n are delivered to the upper layer according to the order of the PDCP SN.

5. The method of claim 2 , wherein:

the RRC message includes a PDCP-configuration information element (IE), and

the PDCP-configuration IE includes a field indicating a value of the in-sequence timer.

6. A method for transmitting multi-flow data for one evolved packet system (EPS) bearer to user equipment (UE) from a macro base station through the macro base station and a small base station serving a single cell in a wireless communication system supporting dual connectivity, the method comprising:

configuring a first radio bearer (RB) and a second RB;

generating packet data convergence protocol (PDCP) packet data units (PDUs) in a PDCP entity with respect to packets received by the macro base station according to a PDCP sequence number (SN) of a PDCP service data unit (SDU);

distributing the PDCP PDUs to radio link control (RLC) entities of the macro base station and RLC entities of the small base station according to a predetermined rule and transmitting the distributed PDCP PDUs to the UE through the first RB and second RB;

transmitting to the UE a radio resource control (RRC) message including information related to an in-sequence timer for the PDCP SDUs through the first RB; and

receiving confirmation of the respective PDCP sequence numbers (SNs) of the transmitted PDCP SDUs and in-sequence delivery of the PDCP SDUs to an upper layer from a PDCP entity according to the PDCP SN.

7. The method of claim 6 , wherein the RRC message including the information related to the in-sequence timer is an RRC connection reconfiguration message.

8. The method of claim 6 , wherein:

the RRC connection reconfiguration message includes a PDCP-configuration information element (IE), and

the PDCP-configuration IE includes a field indicating a value of the in-sequence timer.

9. A user equipment (UE) for receiving multi-flow data with respect to one evolved packet system (EPS) bearer through a macro base station (macro eNB) and a small base station (small eNB) serving a single cell in a wireless communication system supporting dual connectivity, the UE comprising:

a transmitting unit and receiving unit configuring a first radio bearer (RB) and a second RB;

the receiving unit receiving packet data convergence protocol (PDCP) packet data units (PDUs) through the macro base station through the first RB and the small base station through the second RB and receiving from the macro base station information related to an in-sequence timer for the PDCP SDUs through a radio resource control (RRC) message over the first RB; and

a processor obtaining PDCP service data units (SDUs) corresponding to the PDCP PDUs,

wherein the PDCP SDUs are indicated by a predefined PDCP sequence number (SN), and

wherein the processor confirms the respective PDCP sequence numbers (SNs) of the obtained PDCP SDUs and performs in-sequence delivery of the PDCP SDUs to an upper layer from a PDCP entity according to the PDCP SN.

10. The UE of claim 9 , wherein the processor confirms whether there is a PDCP SDU of PDCP SN #n−1 which is missed in spite of obtaining a PDCP SDU of PDCP SN #n and drives the in-sequence timer with respect to the PDCP SDU of PDCP SN#n when there is the PDCP SDU of PDCP SN#n−1 which is missed.

11. The UE of claim 10 , wherein the processor exceptionally delivers, when the in-sequence timer for the PDCP SDU of PDCP SN#n has expired, the PDCP SDU of PDCP SN#n to the upper layer of the PDCP entity even though there is no PDCP SDU of PDCP SN #n−1.

12. The UE of claim 10 , wherein the processor delivers, before the in-sequence timer for the PDCP SDU of PDCP SN#n has expired, when the PDCP SDU of PDCP SN#n−1 is obtained, the PDCP SDU of PDCP SN#n−1 and the PDCP SDU of PDCP SN#n to the upper layer according to the order of the PDCP SN.

13. The UE of claim 10 , wherein:

the RRC message includes a PDCP-configuration information element (IE), and

the processor determines the value of the in-sequence timer based on the PDCP-configuration information element (IE).