8.9.6 RRC State transition

38.4013GPPArchitecture descriptionNG-RANRelease 17TS

8.9.6.1 RRC Connected to RRC Inactive

The procedure for changing the UE state from RRC-connected to RRC-inactive is shown in Figure 8.9.6.1-1.

Figure 8.9.6.1-1: RRC Connected to RRC Inactive state transition.

1. The gNB-CU-CP sends BEARER CONTEXT SETUP REQUEST message with UE/PDU session/DRB level inactivity timer.

2. The gNB-CU-UP sends BEARER CONTEXT SETUP RESPONSE message.

3. The gNB-CU-UP sends BEARER CONTEXT INACTIVITY NOTIFICATION message with inactivity monitoring results.

4. The gNB-CU-CP determines that the UE should enter RRC-inactive (e.g., after receiving Bearer Context Inactivity Notification procedure).

5. The gNB-CU-CP sends BEARER CONTEXT MODIFICATION REQUEST message with a Bearer Context Status Change to the gNB-CU-UP, which indicates that the UE is entering RRC-inactive state. The gNB-CU-CP keeps the F1 UL TEIDs.

6. The gNB-CU-UP sends the BEARER CONTEXT MODIFICATION RESPONSE message including the PDCP UL and DL status that may be needed for e.g., data volume reporting. The gNB-CU-UP keeps the Bearer Context, the UE-associated logical E1-connection, the NG-U related resource (e.g., NG-U DL TEIDs) and the F1 UL TEIDs.

7. The gNB-CU-CP sends the UE CONTEXT RELEASE COMMAND message to the gNB-DU serving the UE, together with the RRCRelease message to be sent to the UE.

NOTE: step 5 and step 7 can be performed at the same time.

8. The gNB-DU sends the RRCRelease message to the UE.

9. The gNB-DU sends the UE CONTEXT RELEASE COMPLETE message to the gNB-CU-CP.

8.9.6.2 RRC Inactive to other states

The procedure for changing the UE state from RRC-inactive to RRC-connected is shown in Figure 8.9.6.2-1.

Figure 8.9.6.2-1: RRC Inactive to RRC Connected state transition.

0. The gNB-CU-UP receives DL data on NG-U interface.

1. The gNB-CU-UP sends DL DATA NOTIFICATION message to the gNB-CU-CP.

2. The gNB-CU-CP sends PAGING message to the gNB-DU.

3. The gNB-DU sends the Paging message to the UE.

NOTE: steps 0-3 are needed only in case of DL data.

4. The UE sends RRCResumeRequest message either upon RAN paging or UL data arrival.

5. The gNB-DU sends the INITIAL UL RRC MESSAGE TRANSFER message to the gNB-CU-CP.

6. The gNB-CU-CP sends UE CONTEXT SETUP REQUEST message including the stored F1 UL TEIDs to create the UE context in the gNB-DU.

7. The gNB-DU responds with the UE CONTEXT SETUP RESPONSE message including the F1 DL TEIDs allocated for the DRBs.

8. The gNB-CU-CP and the UE perform the RRC-Resume procedure via the gNB-DU.

9. The gNB-CU-CP sends BEARER CONTEXT MODIFICATION REQUEST message with a RRC Resume indication, which indicates that the UE is resuming from RRC-inactive state. The gNB-CU-CP also includes the F1 DL TEIDs received from the gNB-DU in step 7.

10. The gNB-CU-UP responds with theBEARER CONTEXT MODIFICATION RESPONSE message.

NOTE steps 8 and 9 can be performed in parallel.