8.11 Support of Network Sharing with multiple cell-ID broadcast
38.4013GPPArchitecture descriptionNG-RANRelease 17TS
8.11.1 General
This clause describes necessary additions as compared to the case where network sharing with multiple cell-ID broadcast is not applied.
The signalling flows in the subsequent clauses assuming 2 sharing operators, A and B. The F1-C signalling transport deployment used is indicated within the subsequent clauses.
8.11.2 Initial Registration – separate PLMN signalling
The signalling flow for Initial Registration for network sharing with multiple cell-ID broadcast with separate per-PLMN signalling is shown in Figure 8.11.2-1.
In this example message flow
– the UE is assumed to not provide an ue-Identity from which the DU is able to deduce the PLMN ID.
– each F1-C interface instance uses a separate signalling transport or share signalling transport with other F1-C interface instances.
– the gNB-DUA/B entity shown in Figure 8.11.2-1 is a simplified representation of the gNB-DUA of PLMN A, the gNB DUB of PLMN B and respective radio resources of the shared cell.
Figure 8.11.2-1: UE Initial Access procedure and network sharing with multiple cell-ID broadcast
NOTE: Steps 1-5 are defined in clause 8.1. Note, that the selectedPLMN-Identity is provided in step 5.
6. The gNB-DUA sends the F1AP UE CONTEXT RELEASE REQUEST message to the gNB-CUA. including a Cause set to "PLMN not served by the CU".
7. The gNB-DUB sends the F1AP INITIAL UL RRC MESSAGE to the gNB-CUB. including the NR CGI associated with PLMNB, the C-RNTI indicated by the gNB-DUA at step 2, and the RRC-Container IE and the RRC-Container-RRCSetupComplete IE with the RRC message received in step1 and step 5 respectively. The RRC-Container-RRCSetupComplete IE are included in the INITIAL UL RRC MESSAGE TRANSFER for the case of network sharing and shall contain the RRC messages received via the RRC UL-DCCH-Message IE from the UE, but never previously sent to the gNB-CUB.
8. The gNB-CUA sends the UE CONTEXT RELEASE COMMAND message to the gNB-DU.
9. The gNB-DU sends the UE CONTEXT RELEASE COMPLETE message to the gNB-CUA.
NOTE: Initiating procedures from gNB-DUA towards gNB-CUA and from gNB-DUB to gNB-CUB in parallel is not precluded.
8.11.3 RRC Connection Reestablishment – separate PLMN signalling
The signalling flow for RRC Connection Reestablishment for network sharing with multiple cell-ID broadcast with separate per-PLMN signalling is shown in Figure 8.11.3-1.
In this example message flow
– each F1-C/Xn-C interface instance uses either a separate signalling transport or a share signalling transport with other interface instances.
– the New gNB-DUA/B entity shown in Figure 8.11.3-1 is a simplified representation of the New gNB-DUA of PLMN A, the New gNB DUB of PLMN B and respective radio resources of the shared cell.
Figure 8.11.3-1: RRC Connection Reestablishment and network sharing with multiple cell-ID broadcast
1. The UE sends the RRCReestablishmentRequest.
2A-5A. Depicts the case where the UE context could not be retrieved by the new gNB-CUA. In step 2A, the NR CGI associated to PLMNA is indicated. In step 5A, the gNB-CUA would prepare the possibility to revert back to normal RRC Connection Establishment, indicating that the UE Context was not retrieveable and may include the re-directed RRC message as received in step 1. After step 5A, the gNB-DUA may redirect the UE towards the PLMN indicated in DL RRC MESSAGE TRANSFER message, if the PLMN assistance information is provided by the gNB-CUA. If the New gNB-DUA/B was not able to deduce the RRC message from step 1, this indicator triggers step 2B. The New gNB-DUA is supposed to trigger the release the UE-associated signalling connection (not shown).
2B-5B. Depicts the case where the UE context was retrieveable by the New gNB-CUB. In step 2B, the NR CGI associated to PLMNB is indicated. Step 2B also includes the C-RNTI allocated at reception of step 1.
6-8. The RRC Connection Reestablishment continues with the New gNB-CUB.
NOTE: If all gNB-CUs indicate that the UE context is not retrievable, the RRC connection reestablishment falls back to RRC Connection setup, as described in clause 8.11.2.
NOTE: Initiating procedures from gNB-DUA towards gNB-CUA and from gNB-DUB to gNB-CUB in parallel is not precluded.
8.11.4 Support of shared signalling transport
This clause specifies for F1-C, Xn-C and, in case of EN-DC, for X2-C, how an interface instance is identified in case of network sharing with multiple cell ID broadcast with shared signalling transport.
For UE associated signalling, the interface instance is identified by assigning on F1-C appropriate UE F1AP IDs, on Xn-C appropriate UE XnAP IDs and on X2-C appropriate UE X2AP IDs.
For non-UE associated signalling, the interface instance is identified on F1-C by the assigning an appropriate value to the Transaction ID, on Xn-C and X2-C by including the Interface Instance Indication in the respective message and assigning an appropriate value to it.