Section: 6.10.1.2 Dual Connectivity protocol architecture for MR-DC with 5GC
Content: The dual connectivity protocol architecture for MR-DC with 5GC is shown in figure 6.10.1.2-1. The TS 37.340[ Evolved Universal Terrestrial Radio Access (E-UTRA) and NR; Multi-connectivity; Overall Description; Stage-2 ]  [51] is to be referred for further details of the architecture illustrating MCG, SCG, and Split bearers for both SRBs and DRBs. The architecture has the following variants: - NG-RAN E-UTRA-NR Dual Connectivity (NGEN-DC) is the variant when the UE is connected to one ng-eNB that acts as a Master Node (MN) and one gNB that acts as a Secondary Node (SN). The ng-eNB is connected to the 5GC and the gNB is connected to the ng-eNB via Xn interface. - NR-E-UTRA Dual Connectivity (NE-DC) is the variant when the UE is connected to one gNB that acts as a MN and one ng-eNB that acts as a SN. The MN (i.e., gNB) is connected to 5GC and the ng-eNB (i.e., SN) is connected to the gNB via Xn interface. - NR-NR Dual Connectivity (NR-DC) is the variant when the UE is connected to one gNB that acts as a MN and one gNB that acts as a SN. The MN is connected to 5GC while the SN is connected to MN via Xn interface. Figure 6.10.1.2-1 Multi-Radio dual connectivity (MR-DC) protocol architecture. When the MN establishes security context between an SN and the UE for the first time for a given AS security context shared between the MN and the UE, the MN generates the KSN for the SN and sends it to the SN over the Xn-C. To generate the KSN, the MN associates a counter, called an SN Counter, with the current AS security context. The SN Counter is used as freshness input into KSN derivations as described in the clause 6.10.3.2. The MN sends the value of the SN Counter to the UE over the RRC signalling path when it is required to generate a new KSN. The KSN is used to derive further RRC and UP keys that are used between the UE and SN.