 part in the IAB node, with the radio connection being the normal NR Uu interface, as for the UEs connected to the IAB node(s) and to the IAB donor gNB. This is shown in Figure 15.6. When there are further IAB nodes in the chain, the F1* is then established between the IAB donor and each IAB node. The IAB nodes in the middle simply route the traf- fic to the correct IAB node (based on the adaptation layer routing information). The UE is not seen whether it is connected to IAB node or to a regular base station, nor if there is more than a single hop in place. Multiple hops naturally add to the extra delay budget for the connection, depending on the parameters in use (scheduling interval) and connection quality (number of retransmissions occurring) as well as on the load of the connection(s) due to the scheduling delay experienced. An example IAB config- uration is shown in Figure 15.7 with a vertical beam used between lamppost-installed nodes and a downward beam for serving UEs. Additional considerations for the IAB link configuration and installation are needed due to the interference between nodes. IAB beam 5G UE IAB gNB Donor gNB with fiber conectivity Figure 15.7 Example IAB configuration. 15.2 3GPP Release 16 Timing and Key Themes 15.2.5 Mobility Enhancements The work on the mobility enhancements aims to reduce the interruption time caused when handover takes place or when the Secondary Cell Group (SCG) needs to be changed. Also, the reliability of the handover process is intended to be improved. The identified approaches under investigation include those for interruption time reduction: Simultaneous connectivity with the source and target cells during handover, in line with the dual connectivity operation. This allows the ping-pong between different cells to be reduced. Establishing a connection to the target cell before dropping the connection from the source cell (make-before-break), with the source dropped only once the RACH trans- mission for the target actually starts. This avoids the need for dual conn