ng advantage of flexible and low-cost backhauling. The economic necessity of wireless backhauling using 5G mmWaves was instrumental when 3GPP defined the scope of the initial IAB feature set in Release-16: Focus was set on stationary infrastructure relays. Support for relay mobility was consid- ered less important and therefore left for later releases. 5.2 Wireless Relaying in 5G Multi-hop backhauling and topological redundancy were considered essential for deploy- ments in convoluted urban environments. Plug-and-play network integration and dynamic topology adaptation were included to lower deployment cost of a densified network and to ensure robustness to changes in propagation environment and load distribution. Compliance with the relevant 5G architecture deployment scenarios, in particular opera- tion with EPC and 5GC, was considered critical. It was also desirable to support network connectivity via IAB for Release-15 UEs. Finally, efforts were made to retain high spectral efficiency through integration of access and backhaul links at the radio frame and enabling TDM operation among access and backhaul links. At the time of writing, the normative specification of Release-16 IAB had not been finalized. The following description may therefore lack some details or differ in some minor aspects with respect to the final Release-16 specification. 5.2.3 Functional Description 5.2.3.1 IAB Architecture The IAB architecture introduces the IAB node as the 5G relay and the IAB donor gNB as the anchor point to the wireline network (Figure 5.2.3). The IAB node provides access to UEs, and it wirelessly backhauls the access traffic to/from the IAB donor gNB. It also for- wards backhaul traffic via peer nodes. While typical deployments are expected to require only a few backhaul hops the architecture does not pose any limitation to the achievable hop count. The IAB donor holds gNB functionality and includes additional features for the Figure 5.2.3 IAB topology. IAB donor gNB Wireless backhaul link IAB-node IAB-node Wireless 