ent trade-offs. In one scheme, which is used for the first IAB release (Release-16), the frame boundaries are aligned for downlink transmissions of all IAB nodes. This makes the entire IAB topology appear to the UE like a time-aligned small-cell system (Figure 5.2.11). Since the uplink transmission by an MT occurs earlier to account for the propagation delay, it cannot be time-aligned with the downlink transmission of the collocated DU. This mismatch leads to slight, but tolerable inefficiency for TDM-based resource partitioning between upstream and downstream links. SDM, however, cannot take advantage of common Fast-Fourier-Transform processing for upstream and downstream transmissions or receptions under such conditions. Other time-alignment schemes allow for an efficient SDM operation, but they lead to mis- alignment of downlink transmissions across the IAB topology, which may limit the tolerable hop count. These schemes may be considered for later releases of IAB. 5 NG-RAN Evolution 5.2.3.4 Plug-and-Play Network Integration To enable lower-cost rollout of IAB nodes, the integration of IAB nodes has to follow a fully automated procedure. This procedure should ensure interoperability, where IAB nodes of one vendor connect with IAB donors and neighbor IAB nodes of other vendors (assuming proper interoperability testing has been performed). The integrating IAB node should fur- ther enjoy OAM connectivity to allow for vendor-specific configuration and optimization. Network integration needs to include the following tasks: Bootstrapping of IAB node MT and DU functions; Discovery of network, including discovery of suitable parent nodes and IAB donor CU; Authentication to the network and authorization of IAB operation by network; Support of OAM connectivity; Establishment of signaling and data connectivity for backhauling. To reduce specification efforts, IAB node integration leverages the existing procedures. It includes the following sequence of steps (Figure 5.2.12): 1. The IAB node launches the MT function and co