Content for TS 38.401 Word version: 18.3.0
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8.22 Overall procedures for multi-path support
8.22.1 Inter-DU direct path addition on top of indirect path
8.22.2 Inter-DU indirect path addition on top of direct path
8.22.3 Intra-DU direct path addition on top of indirect path
8.22.4 Intra-DU indirect path addition on top of direct path
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8.22 Overall procedures for multi-path support |R18| p. 138
8.22.1 Inter-DU direct path addition on top of indirect path p. 138
The signalling flow for inter-DU direct path addition is shown in Figure 8.22.1-1. This procedure is only applicable to the MP Remote UE using PC5 link.
Step 1.
The Uu measurement configuration and measurement report signalling are performed between MP Remote UE and the gNB-CU to evaluate both relay link measurement and Uu link measurement. The MP Remote UE may report Uu measurement results of neighboring cells and a list of MP Relay UE L2 ID and cell ID of one or multiple candidate MP Relay UE(s).
Step 2.
The gNB-CU decides to add the direct path to MP Remote UE under a different gNB-DU (i.e., gNB-DU1).
Step 3.
The gNB-CU sends the UE CONTEXT SETUP REQUEST message for the MP Remote UE to the gNB-DU1, which contains at least the HandoverPreparationInformation IE and the serving cell ID on the direct path.
Step 4.
The gNB-DU1 responds to the gNB-CU with a UE CONTEXT SETUP RESPONSE message.
Step 5.
The gNB-CU sends an RRCReconfiguration message to the MP Relay UE to update the indirect path configuration if necessary.
Step 5a.
The gNB-CU may send an UE CONTEXT MODIFICATION REQUEST message to the gNB-DU2 to query the latest configuration if the configuration of the MP Remote UE on the indirect path is updated.
Step 5b.
The gNB-DU2 responds with an UE CONTEXT MODIFICATION RESPONSE message that includes the configuration information.
Step 6.
The gNB-CU sends the UE CONTEXT MODIFICATION REQUEST message for MP Remote UE by including the direct path addition information and the RRCReconfiguration message to the gNB-DU2. The gNB-DU2 may update the stored UE context for MP Remote UE. The contents in the RRCReconfiguration message may include at least direct path addition configuration, RLC channel configuration, bearer mapping and the associated radio bearer(s).
Step 7.
The gNB-DU2 sends the RRCReconfiguration message to the MP Remote UE via the MP Relay UE.
Step 8.
The gNB-DU2 sends the UE CONTEXT MODIFICATION RESPONSE message to the gNB-CU.
Step 9.
The MP Remote UE performs random access procedure at the gNB-DU1.
Step 10.
The MP Remote UE sends the RRCReconfigurationComplete message to the gNB-DU1 via direct path in order to complete the direct path addition procedure.
Step 10a.
In case the SRB1 with duplication is configured, the MP Remote UE also sends the RRCReconfigurationComplete message to the gNB-DU2 via indirect path.
Step 11.
The gNB-DU1 sends the UL RRC MESSAGE TRANSFER message including the RRCReconfigurationComplete message received in step 10, to gNB-CU.
Step 11a.
In case the SRB1 with duplication is configured, the gNB-DU2 also sends the UL RRC MESSAGE TRANSFER message including the RRCReconfigurationComplete message received in step 10a, to gNB-CU.
Step 12.
The MP Remote UE performs data transmission and reception by using both the direct path and the indirect path served by a MP Relay UE.
8.22.2 Inter-DU indirect path addition on top of direct path p. 140
The signalling flow for inter-DU indirect path addition is shown in Figure 8.22.2-1.
Step 1.
The Uu measurement configuration and measurement report signalling are performed between MP Remote UE and the gNB-CU to evaluate relay link measurement and/or Uu link measurement.
In case that the MP Remote UE is connected with the MP Relay UE using PC5 link, the MP Remote UE may report Uu measurement results of neighboring cells and a list of MP Relay UE L2 ID and cell ID of one or multiple candidate MP Relay UE(s).
In case that the MP Remote UE is connected with the MP Relay UE using N3C link and the MP Relay UE is in RRC_CONNECTED state, the MP Remote UE reports at least the list of the C-RNTI and the cell ID of one or multiple candidate MP Relay UE(s).
Step 2.
The gNB-CU decides to add the indirect path via MP Relay UE to MP Remote UE under a different gNB-DU (i.e., gNB-DU2).
Step 3.
The reconfiguration to MP Relay UE is performed among MP Relay UE, the gNB-DU2 and the gNB-CU if MP Relay UE is in RRC_CONNECTED state. The gNB-CU sends an RRCReconfiguration message to the MP Relay UE. If the MP Relay UE is in RRC_IDLE/INACTIVE state, this step is skipped and the configuration to the target MP Relay UE is performed in Step 9/9a.
Step 4.
The gNB-CU sends the UE CONTEXT SETUP REQUEST message for the MP Remote UE to the gNB-DU2, which contains the indirect path addition configuration at least.
Step 5.
The gNB-DU2 responds to the gNB-CU with a UE CONTEXT SETUP RESPONSE message.
Step 5a.
The gNB-CU may send an UE CONTEXT MODIFICATION REQUEST message to the gNB-DU1 to query the latest configuration if the configuration of the MP Remote UE on the direct path is updated.
Step 5b.
The gNB-DU1 responds with an UE CONTEXT MODIFICATION RESPONSE message that includes the configuration information.
Step 6.
The gNB-CU sends the DL RRC MESSAGE TRANSFER message for MP Remote UE by including the RRCReconfiguration message to gNB-DU1. If the MP Remote UE is connected with the MP Relay UE using the PC5 link, the contents in the RRCReconfiguration message may include at least indirect path addition configuration, PC5 Relay RLC channel configuration for relay traffic, bearer mapping and the associated radio bearer(s). If the MP Remote UE is using N3C link, the contents in the RRCReconfiguration message may include at least indirect path addition configuration, bearer mapping and the associated radio bearer(s).
Step 7.
The gNB-DU1 sends the RRCReconfiguration message to the MP Remote UE.
Step 8.
If the MP Remote UE is using the PC5 link, the MP Remote UE establishes PC5 connection with the target MP Relay UE.
If the MP Remote UE is connected with the MP Relay UE using N3C link, this step is skipped.
Step 9.
The MP Remote UE sends the RRCReconfigurationComplete message to the gNB-DU1 via direct path in order to complete the indirect path addition procedure.
Step 9a.
In case the SRB1 with duplication is configured, the MP Remote UE also sends the RRCReconfigurationComplete message to the gNB-DU2 via indirect path.
Step 10.
The gNB-DU1 sends the UL RRC MESSAGE TRANSFER message to gNB-CU by including the RRCReconfigurationComplete message received in step 9.
Step 10a.
In case the SRB1 with duplication is configured, the gNB-DU2 also sends the UL RRC MESSAGE TRANSFER message to gNB-CU by including the RRCReconfigurationComplete message received in step 9a.
Step 11.
The MP Remote UE performs data transmission and reception by using both the direct path and the indirect path served by a MP Relay UE.
8.22.3 Intra-DU direct path addition on top of indirect path p. 142
The signaling flow for intra-DU direct path addition is shown in Figure 8.22.3-1. This procedure is only applicable to the MP Remote UE using PC5 link.
Step 1.
The Uu measurement configuration and measurement report signalling are performed between MP Remote UE and gNB-CU to evaluate both relay link measurement and Uu link measurement. The MP Remote UE may report Uu measurement results of neighboring cells and a list of MP Relay UE L2 ID and cell ID of one or multiple candidate MP Relay UE(s).
Step 2.
The gNB-CU decides to add the direct path to MP Remote UE under the same gNB-DU.
Step 3.
The gNB-CU sends the UE CONTEXT MODIFICATION REQUEST message for the MP Remote UE to the gNB-DU, which contains at least the HandoverPreparationInformation IE and the serving cell ID on the direct path.
Step 4.
The gNB-DU responds to the gNB-CU with a UE CONTEXT MODIFICATION RESPONSE message.
Step 5.
The gNB-CU sends an RRCReconfiguration message to the MP Relay UE to update the indirect path configuration if necessary.
Step 6.
The gNB-CU sends the DL RRC MESSAGE TRANSFER message for MP Remote UE by including the RRCReconfiguration message to the gNB-DU. The contents in the RRCReconfiguration message may include at least direct path addition configuration, RLC channel configuration, bearer mapping and the associated radio bearer(s).
Step 7.
The gNB-DU sends the RRCReconfiguration message to the MP Remote UE.
Step 8.
The MP Remote UE performs random access procedure at the gNB-DU.
Step 9.
The MP Remote UE sends the RRCReconfigurationComplete message to the gNB-DU via direct path in order to complete the direct path addition procedure.
Step 9a.
In case the SRB1 with duplication is configured, the RRCReconfigurationComplete message is also sent to the gNB-DU via indirect path.
Step 10/10a.
The gNB-DU sends the UL RRC MESSAGE TRANSFER message to gNB-CU by including the RRCReconfigurationComplete message.
Step 11.
The MP Remote UE performs data transmission and reception by using both the direct path and the indirect path served by a MP Relay UE.
8.22.4 Intra-DU indirect path addition on top of direct path p. 144
The signaling flow for intra-DU indirect path addition is shown in Figure 8.22.4-1.
Step 1.
The Uu measurement configuration and measurement report signalling are performed between MP Remote UE and gNB-CU to evaluate relay link measurement and/or Uu link measurement.
In case that the MP Remote UE is connected with the MP Relay UE using PC5 link, the MP Remote UE may report Uu measurement results of neighboring cells and a list of MP Relay UE L2 ID and cell ID of one or multiple candidate MP Relay UE(s).
In case that the MP Remote UE is connected with the MP Relay UE using N3C link and the MP Relay UE is in RRC_CONNECTED state, the MP Remote UE reports at least the list of the C-RNTI and the cell ID of one or multiple candidate MP Relay UE(s).
Step 2.
The gNB-CU decides to add the indirect path via MP Relay UE to MP Remote UE under the same gNB-DU.
Step 3.
The reconfiguration to MP Relay UE is performed among MP Relay UE, gNB-DU and gNB-CU if MP Relay UE is in RRC_CONNECTED state. The gNB-CU sends an RRCReconfiguration message to the MP Relay UE. If the MP Relay UE is in RRC_IDLE/INACTIVE state, this step is skipped and the configuration to the target MP Relay UE is performed in Step 9/9a.
Step 4.
The gNB-CU sends the UE CONTEXT MODIFICATION REQUEST message for the MP Remote UE to the gNB-DU, which contains the indirect path addition configuration at least.
Step 5.
The gNB-DU responds to the gNB-CU with a UE CONTEXT MODIFICATION RESPONSE message.
Step 6.
The gNB-CU sends the DL RRC MESSAGE TRANSFER message for MP Remote UE by including the RRCReconfiguration message to gNB-DU. If the MP Remote UE is connected with the MP Relay UE using the PC5 link, the contents in the RRCReconfiguration message may include at least indirect path addition configuration, PC5 Relay RLC channel configuration for relay traffic, bearer mapping and the associated radio bearer(s). If the MP Remote UE is using N3C link, the contents in the RRCReconfiguration message may include at least indirect path addition configuration, bearer mapping and the associated radio bearer(s).
Step 7.
The gNB-DU sends the RRCReconfiguration message to the MP Remote UE.
Step 8.
If the MP Remote UE is using the PC5 link, the MP Remote UE establishes PC5 connection with the target MP Relay UE.
If the MP Remote UE is using N3C link, this step is skipped.
Step 9.
The MP Remote UE sends the RRCReconfigurationComplete message to the gNB-DU via direct path to complete the indirect path addition procedure.
Step 9a.
In case the SRB1 with duplication is configured, the RRCReconfigurationComplete message is also sent to the gNB-DU via indirect path.
Step 10/10a.
The gNB-DU sends the UL RRC MESSAGE TRANSFER message to gNB-CU by including the RRCReconfigurationComplete message.
Step 11.
The MP Remote UE performs data transmission and reception by using both the direct path and the indirect path served by a MP Relay UE.
