Question: In which direction does the NR user plane protocol support flow and congestion control between the IAB-node and the IAB-donor-CU for UE bearers that terminate at this IAB-node?
Option 1: Downstream
Option 2: Upstream
Option 3: Both upstream and downstream
Option 4: Neither upstream nor downstream
Explanation: The NR user plane protocol supports flow and congestion control in the downstream direction, specifically between the IAB-node and the IAB-donor-CU for UE bearers that terminate at this IAB-node. This is important to prevent congestion-related packet drops on IAB-nodes and IAB-donor-DUs.