Content for TS 37.340 Word version: 17.3.0

1… 4… 4.2… 4.3… 5… 7… 8… 9 10… 10.2… 10.2.2… 10.3… 10.3.2 10.4… 10.5… 10.5.2 10.6 10.7… 10.8… 10.9… 10.10… 10.11… 10.12… 10.12.2 10.13… 10.14… 10.15 10.16… 10.17… 10.18… 10.19… 11… A B…

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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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.

Copy of original 3GPP image for 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)
(⇒ copy of original 3GPP image)

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.

Copy of original 3GPP image for 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)
(⇒ copy of original 3GPP image)

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.