Section: 4.7.3.2 Flow and Congestion Control
Content: Flow and congestion control can be supported in both upstream and downstream directions in order to avoid congestion-related packet drops on IAB-nodes and IAB-donor-DU: - In upstream direction, UL scheduling on MAC layer can support flow control on each hop; - In downstream direction, the NR user plane protocol (TS 38.425[ NG-RAN; NR user plane protocol ]  [33]) supports flow and congestion control between the IAB-node and the IAB-donor-CU for UE bearers that terminate at this IAB-node. Further, flow control is supported on BAP sublayer, where the IAB-node can send feedback information on the available buffer size for an ingress BH RLC channel or BAP routing ID to its parent node. The feedback can be sent proactively, e.g., when the buffer load exceeds a certain threshold, or based on polling by the parent node.