Early data transmission in CU-DU split

1. A method performed by a distributed unit (DU) of a network node adapted to operate in a wireless communication system, the method comprising:

transmitting a radio resource control (RRC) resume request message to a central unit (CU) control plane (CP) of the network node;

upon a determination by the CU-CP to perform early data transmission (EDT) based on the RRC resume request message, transmitting uplink (UL) data to a CU-user plane (UP) of the network node;

receiving information informing that downlink (DL) data exists from the CU-CP;

receiving the DL data from the CU-UP;

transmitting the DL data to a wireless device in response to the information, upon receiving the DL data; and

releasing transmission resources after transmitting the DL data,

wherein the DU is a logical node hosting radio link control (RLC), media access control (MAC) and physical layers of the network node,

wherein the CU-CP is a logical node hosting radio resource control (RRC) and a control plane part of a packet data convergence protocol (PDCP) of the network node, and

wherein the CU-UP is a logical node hosting a user plane part of the PDCP of the network node.

2. The method of claim 1 , wherein the information is received with an RRC message.

3. The method of claim 2 , wherein the RRC message informs to release the transmission resources.

4. The method of claim 2 , wherein the transmitting the DL data includes multiplexing the DL data with the RRC message.

5. The method of claim 1 , wherein the information informs the DU of waiting for releasing the transmission resources until reception of the DL data.

6. The method of claim 1 , wherein the UL data is forwarded to a core network upon successful resume of a bearer context of the wireless device.

7. The method of claim 1 , wherein the wireless device communicates with at least one of a mobile terminal, a network or autonomous vehicles other than the wireless device.

8. A distributed unit (DU) of a network node adapted to operate in a wireless communication system, the DU comprising:

a memory;

a transceiver; and

a processor, operably coupled to the memory and the transceiver, and configured to:

control the transceiver to transmit a radio resource control (RRC) resume request message to a CU) control plane (CP) of the network node;

upon a determination by the CU-CP to perform early data transmission (EDT) based on the RRC resume request message, control the transceiver to transmit uplink (UL) data to a CU-user plane (UP) of the network node;

control the transceiver to receive information informing that downlink (DL) data exists from the CU-CP;

control the transceiver to receive the DL data from the CU-UP;

control the transceiver to transmit the DL data to a wireless device in response to the information, upon receiving the DL data; and

release transmission resources after transmitting the DL data,

wherein the DU is a logical node hosting radio link control (RLC), media access control (MAC) and physical layers of the network node,

wherein the CU-CP is a logical node hosting radio resource control (RRC) and a control plane part of a packet data convergence protocol (PDCP) of the network node, and

wherein the CU-UP is a logical node hosting a user plane part of the PDCP of the network node.

9. The DU of claim 8 , wherein the information is received with an RRC message.

10. The DU of claim 9 , wherein the RRC message informs to release the transmission resources.

11. The DU of claim 9 , wherein the transmitting the DL data includes multiplexing the DL data with the RRC message.

12. The DU of claim 8 , wherein the information informs the DU of waiting for releasing the transmission resources until reception of the DL data.

13. The DU of claim 8 , wherein the UL data is forwarded to a core network upon successful resume of a bearer context of the wireless device.