Method and apparatus for triggering uplink buffer status report in a wireless communication system

1. A method for a first wireless transmit/receive unit (WTRU), comprising:

receiving a second buffer status report (BSR) from a second WTRU, wherein the second WTRU is a child node of the first WTRU;

triggering a first BSR due to reception of the second BSR, wherein the first BSR indicates an estimated amount of data expected to arrive but not data already available for uplink transmission,

wherein the first WTRU derives the estimated amount of data expected to arrive based on the second BSR without taking into account data received from the second WTRU after the reception of the second BSR; and

transmitting the first BSR to a third WTRU, wherein the third WTRU is a parent node of the first WTRU.

2. The method of claim 1 , wherein the estimated amount of data expected to arrive indicated by the first BSR includes data expected to arrive from the second WTRU.

3. The method of claim 2 , wherein user plane data and control plane signaling is considered in the estimated amount of data expected to arrive from the second WTRU.

4. The method of claim 2 , wherein the data expected to arrive from the second WTRU is data that has not been received from the second WTRU.

5. The method of claim 1 , wherein the first BSR is a BSR for Integrated Access and Backhaul (IAB), which has the same characteristics as an ordinary Regular BSR, including triggering Scheduling Request (SR) and re-triggering itself.

6. The method of claim 1 , wherein the estimated amount of data expected to arrive is for a logical channel group.

7. The method of claim 1 , wherein the first BSR and/or the second BSR is reported in BSR Medium Access Control (MAC) Control Element (CE).

8. The method of claim 1 , wherein the first WTRU is an Integrated access and backhaul-node (IAB-node), the second WTRU is an IAB-node or a User Equipment (UE), and the third WTRU is an IAB-node or an IAB-donor.

9. A first wireless transmit/receive unit (WTRU), comprising:

a processor; and

a memory operatively coupled to the processor, wherein the processor is configured to execute a program code to:

receive a second buffer status report (BSR) from a second WTRU, wherein the second WTRU is a child node of the first WTRU;

trigger a first BSR due to the reception of the second BSR, wherein the first BSR indicates an estimated amount of data expected to arrive but not data already available for uplink transmission,

wherein the first WTRU derives the estimated amount of data expected to arrive based on the second BSR without taking into account data received from the second WTRU after the reception of the second BSR; and

transmit the first BSR to a third WTRU, wherein the third WTRU is a parent node of the first WTRU.

10. The first WTRU of claim 9 , wherein the estimated amount of data expected to arrive indicated by the first BSR includes data expected to arrive from the second WTRU.

11. The first WTRU of claim 10 , wherein user plane data and control plane signaling is considered in the estimated amount of data expected to arrive from the second WTRU.

12. The first WTRU of claim 10 , wherein the data expected to arrive from the second WTRU is the data that has not been received from the second WTRU.

13. The first WTRU of claim 9 , wherein the first BSR is a BSR for Integrated Access and Backhaul (IAB), which has same characteristics as an ordinary Regular BSR, including triggering Scheduling Request (SR) and re-triggering itself.

14. The first WTRU of claim 9 , wherein the estimated amount of data expected to arrive is for a logical channel group.

15. The first WTRU of claim 9 , wherein the first BSR and/or the second BSR is reported in BSR Medium Access Control (MAC) Control Element (CE).

16. The first WTRU of claim 9 , wherein the first WTRU is an Integrated access and backhaul-node (IAB-node), the second WTRU is an IAB-node or a User Equipment (UE), and the third WTRU is an IAB-node or an IAB-donor.