5.49.1.1 Principles and functional entities

Mobile gNB with Wireless Access Backhauling (MWAB) provides an NR access link to UEs in proximity and connects to the 5GC serving the UE through an IP/Ethernet connectivity provided by a Backhaul PDU session(s), as illustrated in figure 5.49.1.1-1. The MWAB consists of a gNB component (MWAB-gNB) and a UE component (MWAB-UE). The MWAB-gNB is based on the gNB functionality specified in TS 38.300 [27] and TS 38.401 [42]. The MWAB may be mounted on a moving vehicle and may serve UEs inside or outside the vehicle.

The MWAB-UE establishes the IP/Ethernet connectivity for the backhaul links for the MWAB-gNB, via NR Uu, using the existing registration procedure and PDU session establishment procedure. The backhaul links are between the MWAB-gNB and entities of the network (e.g. AMF, UPF, other gNBs and OAM server) that a MWAB-gNB cell serves. The IP/Ethernet connectivity provided by the MWAB-UE may be either via the same PLMN/SNPN that the MWAB-gNB serves or a different PLMN/SNPN, depending on the MWAB-UE PLMN selection mechanism as specified in TS 23.122 [17]. Different possible deployment scenarios are presented in Annex S.

NOTE 1: It is assumed that there is no address translation affecting the IP layer of the backhauling interfaces. The entity allocating the IP address (either the BH-SMF or the BH-UPF or an external server) ensures that the IP address is visible on the N6 reference point to the MWAB Broadcasted PLMN, i.e. no NAT is used on the BH-UPF based on the dedicated S-NSSAI(s) and DNN(s) for MWAB operation to make sure the IP address is routable on N6 (e.g. using public IP address).

MWAB operation supports both PLMN and SNPN cases. When the MWAB-gNB is serving a PLMN, the UEs served by MWAB may be non-roaming or roaming in the MWAB Broadcasted PLMN. In case the MWAB-gNB is serving a SNPN, the subscribed SNPN of the UEs may be different from the MWAB Announced SNPN. The UEs served by the MWAB are not aware of the network serving the MWAB-UE.

NOTE 2: In this Release, the CU/DU split of the MWAB-gNB is not supported.

NOTE 3: The interface between MWAB-UE and MWAB-gNB is implementation based and not in scope of this specification.

MWAB-UE has a single NR Uu hop to the BH NG-RAN, using either TN or NTN access technology. The NR Uu access link between the MWAB-gNB and the served UE(s) does not use NTN access technology. 5G MOCN can be supported by the MWAB-gNB.

The details of the MWAB configuration/provisioning process are described in clause 5.49.2.

In order to operate as MWAB, the MWAB-gNB component and MWAB-UE component are authorized and controlled separately. The detailed procedures for the authorization of MWAB are described in clause 5.49.3.

When UE(s) are served by MWAB, the MWAB-gNB provides Additional User Location Information to the 5GC as described in clause 5.49.4.

Service continuity for the UE(s) served by the MWAB-gNB is supported when the MWAB moves. The UE(s) move or do not move together with the MWAB. The detailed procedures for the support of mobility are described in clause 5.49.5.

The MWAB shall be able to serve UE(s) without any MWAB-specific enhancements. For some operations, the MWAB may be configured to provide access only to certain UEs. Existing access control mechanisms, e.g. CAG control, can be used to manage the UE(s)'s access to the MWAB-gNB. The details of the access control for the UEs served by MWAB are described in clause 5.49.6.

The LCS framework as defined in TS 23.273 [87] is used for providing the location service to the UE(s) served by MWAB. When the AMF determines the UE is served by a MWAB cell based on e.g. the Additional ULI, the AMF selects the LMF that can support the MWAB handling and sends MWAB indication and Additional ULI (if available) to the LMF as defined in clause 8.3.2.2 of TS 23.273 [87]. Details on supporting the LCS over MWAB are described in clause 5.49.7.

Regulatory services (e.g. emergency services, priority services) can be supported by the MWAB and the details are provided in clause 5.49.8.

Details on MWAB-gNB's Xn connection, N2 connection and N3 connection are specified in TS 38.401 [42].

The support of PWS functionality with MWAB is described in TS 23.041 [46].