st up to two SDAP pro- tocol entities for each PDU session, one for MN and the other one for SN. The UE is configured with one SDAP protocol entity per PDU session [4]. In MR-DC, the SN is not required to broadcast SI other than for radio frame timing and SFN. The SI for initial configuration is provided to the UE by dedicated RRC signaling via the MN. The UE acquires radio frame timing and SFN of SCG from the LTE primary and secondary synchronization signals and MIB (if the SN is an eNB) and from the NR primary and secondary synchronization signals and MIB (if the SN is a gNB) of the PSCell. Moreover, upon change of the relevant SI of a configured SCell, the network releases and subsequently adds the corresponding SCell (with updated SI), via one or more RRC recon- figuration messages sent on SRB1 or SRB3. If the measurement is configured for the UE in preparation for the secondary node addition procedure, the MN may configure the measure- ment for the UE. In the case of the intra-secondary node mobility, the SN may configure the measurement for the UE in coordination with the MN [4]. 280 Chapter 2 The secondary node change procedure can be triggered by both MN (only for inter- frequency secondary node change) and SN. For secondary node changes triggered by the SN, the RRM measurement configuration is maintained by the SN which also processes the measurement reporting, without providing the measurement results to the MN. Measurements can be configured independently by the MN and by the SN (intra-RAT mea- surements on serving and non-serving frequencies). The MN indicates the maximum num- ber of frequency layers and measurement identities that can be used in the SN to ensure that UE capabilities are not exceeded. If MN and SN both configure measurements on the same carrier frequency then those configurations must be consistent. Each node (MN or SN) can independently configure a threshold for the SpCell quality. When the PCell quality is above the threshold configured by the MN, the UE is still required to per- fo