ed by the MN via the direct path and via the SN. The split SRB utilizes the NR PDCP. The NR Rel-15 specifications do not sup- port duplication of RRC PDUs generated by the SN via the MN and SN paths. In EN-DC, the SCG configuration is maintained in the UE during suspension. The UE releases the SCG configuration (but not the radio bearer configuration) during resumption initiation (see Fig. 2.24). In MR-DC with 5GC, the UE stores the PDCP/SDAP configuration when mov- ing to RRC_INACTIVE state, but it releases the SCG configuration [4]. There are three bearer types in MR-DC from a UE perspective: MCG bearer, SCG bearer, and split bearer. For EN-DC, the network can configure either LTE PDCP or NR PDCP for the MN-terminated MCG bearers, while NR PDCP is always used for all other bearers. In MR-DC with 5GC, NR PDCP is always used for all bearer types. In NGEN-DC, LTE RLC/ MAC is used in the MN, while NR RLC/MAC is used in the SN. In EN-DC, NR RLC/MAC is used in the MN while LTE RLC/MAC is used in the SN. In NR-DC, NR RLC/MAC is used in both MN and SN. From the network perspective, each bearer (MCG, SCG, and split bearer) can be terminated either in MN or in SN. If only SCG bearers are configured for UE, for SRB1 and SRB2, the logical channels are always configured at least in the MCG, that is, this is still an MR-DC configuration and a PCell always exists. If only MCG bearers are configured for a UE, that is, there is no SCG, this is still considered an MR-DC configura- tion, if at least one of the bearers is terminated in the SN [4]. In MR-DC, two or more component carriers may be aggregated over two cell groups. A UE may simultaneously receive or transmit on multiple component carriers depending on its capabilities. The maximum number of configured component carriers for a UE is 32 for New Radio Access Layer 2/3 Aspects and System Operation 279 downlink and uplink. Depending on UE's capabilities, up to 31 component carriers can be configured for an LTE cell group when the NR cell group is configured. For the NR cell