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Content for  TS 38.401  Word version:  17.2.0

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8.9  Overall procedures involving E1 and F1p. 58

The following clauses describe the overall procedures involving E1 and F1.

8.9.1  UE Initial Accessp. 58

The signalling flow for UE Initial access involving E1 and F1 is shown in Figure 8.9.1-1.
Reproduction of 3GPP TS 38.401, Fig. 8.9.1-1: UE Initial Access procedure involving E1 and F1
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Step 1-8.
Steps 1-8 are defined in clause 8.1.
Step 9.
The gNB-CU-CP sends the BEARER CONTEXT SETUP REQUEST message to establish the bearer context in the gNB-CU-UP.
Step 10.
The gNB-CU-UP sends the BEARER CONTEXT SETUP RESPONSE message to the gNB-CU-CP, including F1-U UL TEID and transport layer address allocated by the gNB-CU-UP.
Step 11-13.
Steps 11-13 are defined in clause 8.1.
Step 14.
The gNB-CU-CP sends the BEARER CONTEXT MODIFICATION REQUEST message to the gNB-CU-UP, including F1-U DL TEID and transport layer address allocated by the gNB-DU.
Step 15.
The gNB-CU-UP sends the BEARER CONTEXT MODIFICATION RESPONSE message to the gNB-CU-CP.
Step 16-22.
Steps 16-22 are defined in clause 8.1.
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8.9.2  Bearer context setup over F1-Up. 59

Figure 8.9.2-1 shows the procedure used to setup the bearer context in the gNB-CU-UP.
Reproduction of 3GPP TS 38.401, Fig. 8.9.2-1: Bearer context setup over F1-U
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Step 0.
Bearer context setup (e.g., following an SGNB ADDITION REQUEST message from the MeNB) is triggered in gNB-CU-CP.
Step 1.
The gNB-CU-CP sends a BEARER CONTEXT SETUP REQUEST message containing UL TNL address information for S1-U or NG-U, and if required, DL TNL address information for X2-U to setup the bearer context in the gNB-CU-UP. For NG-RAN, the gNB-CU-CP decides flow-to-DRB mapping and sends the generated SDAP and PDCP configuration to the gNB-CU-UP.
Step 2.
The gNB-CU-UP responds with a BEARER CONTEXT SETUP RESPONSE message containing the UL TNL address information for F1-U, and DL TNL address information for S1-U or NG-U, and if required, UL TNL address information for X2-U or Xn-U.
Step 3.
F1 UE context setup procedure is performed to setup one or more bearers in the gNB-DU.
Step 4.
The gNB-CU-CP sends a BEARER CONTEXT MODIFICATION REQUEST message containing the DL TNL address information for F1-U and PDCP status.
Step 5.
The gNB-CU-UP responds with a BEARER CONTEXT MODIFICATION RESPONSE message.
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8.9.3  Bearer context release over F1-Up. 60

8.9.3.1  gNB-CU-CP initiated bearer context releasep. 60

Figure 8.9.3.1-1 shows the procedure used to release the bearer context in the gNB-CU-UP initiated by the gNB-CU-CP.
Reproduction of 3GPP TS 38.401, Fig. 8.9.3.1-1: Bearer context release over F1-U - gNB-CU-CP initiated
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Step 0.
Bearer context release (e.g., following an SGNB RELEASE REQUEST message from the MeNB) is triggered in gNB-CU-CP.
Step 1.
The gNB-CU-CP sends a BEARER CONTEXT MODIFICATION REQUEST message to the gNB-CU-UP.
Step 2.
The gNB-CU-UP responds with a BEARER CONTEXT MODIFICATION RESPONSE carrying the PDCP UL/DL status.
Step 3.
F1 UE context modification procedure is performed to stop the data transmission for the UE. It is up to gNB-DU implementation when to stop the UE scheduling.
Step 4.
The gNB-CU-CP may receive the UE CONTEXT RELEASE message from the MeNB in EN-DC operation as described in clause 8.4.2.1.
Step 5-7.
Bearer context release procedure is performed.
Step 6.
F1 UE context release procedure is performed to release the UE context in the gNB-DU.
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8.9.3.2  gNB-CU-UP initiated bearer context releasep. 61

Figure 8.9.3.2-1 shows the procedure used to release the bearer context in the gNB-CU-UP initiated by the gNB-CU-UP.
Reproduction of 3GPP TS 38.401, Fig. 8.9.3.2-1: Bearer context release over F1-U - gNB-CU-UP initiated
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Step 0.
Bearer context release is triggered in gNB-CU-UP e.g., due to local failure.
Step 1.
The gNB-CU-UP sends a BEARER CONTEXT RELEASE REQUEST message to request the release of the bearer context in the gNB-CU-UP. This message may contain the PDCP status.
Step 2-5.
If the PDCP status needs to be preserved, the E1 Bearer Context Modification and the F1 UE Context Modification procedures are performed. The E1 Bearer Context Modification procedure is used to convey data forwarding information to the gNB-CU-UP. The gNB-CU-CP may receive the UE Context Release from the MeNB.
Step 6.
The gNB-CU-CP sends a BEARER CONTEXT RELEASE COMMAND message to release the bearer context in the gNB-CU-UP.
Step 7.
The gNB-CU-UP responds with a BEARER CONTEXT RELEASE COMPLETE to confirm the release of the bearer context including also data forwarding information.
Step 8.
F1 UE context release procedure may be performed to release the UE context in the gNB-DU.
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