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Content for  TS 37.340  Word version:  18.2.0

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4.3 Network interfaces  4.3.1 Control Plane  4.3.1.1 Common MR-DC principles  4.3.1.2 MR-DC with EPC  4.3.1.3 MR-DC with 5GC  4.3.2 User Plane  4.3.2.1 Common MR-DC principles  4.3.2.2 MR-DC with EPC  4.3.2.3 MR-DC with 5GC 
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4.3  Network interfaces  p. 14

4.3.1  Control Plane  p. 14

4.3.1.1  Common MR-DC principles  p. 14

In MR-DC, there is an interface between the MN and the SN for control plane signalling and coordination. For each MR-DC UE, there is also one control plane connection between the MN and a corresponding CN entity. The MN and the SN involved in MR-DC for a certain UE control their radio resources and are primarily responsible for allocating radio resources of their cells.
Figure 4.3.1.1-1 shows C-plane connectivity of MN and SN involved in MR-DC for a certain UE.
Reproduction of 3GPP TS 37.340, Fig. 4.3.1.1-1: C-Plane connectivity for EN-DC (left) and MR-DC with 5GC (right)
Figure 4.3.1.1-1: C-Plane connectivity for EN-DC (left) and MR-DC with 5GC (right)
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4.3.1.2  MR-DC with EPC  p. 15

In MR-DC with EPC (EN-DC), the involved core network entity is the MME. S1-MME is terminated in MN and the MN and the SN are interconnected via X2-C.

4.3.1.3  MR-DC with 5GC  p. 15

In MR-DC with 5GC (NGEN-DC, NE-DC and NR-DC), the involved core network entity is the AMF. NG-C is terminated in the MN and the MN and the SN are interconnected via Xn-C.

4.3.2  User Plane  p. 15

4.3.2.1  Common MR-DC principles  p. 15

There are different U-plane connectivity options of the MN and SN involved in MR-DC for a certain UE, as shown in Figure 4.3.2.1-1. The U-plane connectivity depends on the bearer option configured:
  • For MN terminated bearers, the user plane connection to the CN entity is terminated in the MN;
  • For SN terminated bearers, the user plane connection to the CN entity is terminated in the SN;
  • The transport of user plane data over the Uu either involves MCG or SCG radio resources or both:
    • For MCG bearers, only MCG radio resources are involved;
    • For SCG bearers, only SCG radio resources are involved;
    • For split bearers, both MCG and SCG radio resources are involved.
  • For split bearers, MN terminated SCG bearers and SN terminated MCG bearers, PDCP data is transferred between the MN and the SN via the MN-SN user plane interface.
Reproduction of 3GPP TS 37.340, Fig. 4.3.2.1-1: U-Plane connectivity for EN-DC (left) and MR-DC with 5GC (right)
Figure 4.3.2.1-1: U-Plane connectivity for EN-DC (left) and MR-DC with 5GC (right)
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4.3.2.2  MR-DC with EPC  p. 16

For MR-DC with EPC (EN-DC), X2-U interface is the user plane interface between MN and SN, and S1-U is the user plane interface between the MN, the SN or both and the S-GW.

4.3.2.3  MR-DC with 5GC  p. 16

For MR-DC with 5GC (NGEN-DC, NE-DC and inter-gNB NR-DC), Xn-U interface is the user plane interface between MN and SN, and NG-U is the user plane interface between the MN, the SN or both and the UPF.

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