8.7.7 SgNB initiated SgNB Modification

36.4233GPPEvolved Universal Terrestrial Radio Access Network (E-UTRAN)Release 17TSX2 Application Protocol (X2AP)

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

8.7.7.1 General

This procedure is used by the en-gNB to modify the UE context in the en-gNB.

The procedure uses UE-associated signalling.

8.7.7.2 Successful Operation

Figure 8.7.7.2-1: SgNB initiated SgNB Modification, successful operation.

The en-gNB initiates the procedure by sending the SGNB MODIFICATION REQUIRED message to the MeNB. When the en-gNB sends the SGNB MODIFICATION REQUIRED message, it shall start the timer T_DCoverall.

The SGNB MODIFICATION REQUIRED message may contain

– the PDCP Change Indication IE;

– the SgNB to MeNB Container IE.

– E-RABs to be modified within the E-RABs To Be Modified Item IE;

– E-RABs to be released within the E-RABs To Be Released Item IE;

– the SgNB Resource Coordination Information IE.

For the SN terminated split bearers, the en-gNB may include in the SGNB MODIFICATION REQUIRED message the UL Configuration IE to indicate that the MCG UL configuration of the UE has changed.

The en-gNB may include for each bearer in the E-RABs to Be Modified List IE in the SGNB MODIFICATION REQUIRED message the New DRB ID Request IE to request the MeNB to assign a new DRB ID for that bearer.

If the MeNB is able to perform the change requested by the en-gNB, the MeNB shall send the SGNB MODIFICATION CONFIRM message to the en-gNB. The SGNB MODIFICATION CONFIRM message may contain the MeNB to SgNB Container IE.

If the SGNB MODIFICATION REQUIRED message contains the SgNB Resource Coordination Information IE, the MeNB may use it for the purpose of resource coordination with the en-gNB. The MeNB shall consider the received UL Coordination Information IE value valid until reception of a new update of the IE for the same UE. The MeNB shall consider the received DL Coordination Information IE value valid until reception of a new update of the IE for the same UE. If the SgNB Coordination Assistance Information IE is contained in the SgNB Resource Coordination Information IE, the MeNB shall, if supported, use the information to determine further coordination of resource utilisation between the en-gNB and the MeNB.

If the en-gNB applied a full configuration or delta configuration, e.g. as part of a mobility procedure involving a change of DU, the en-gNB shall inform the MeNB by including the RRC config indication IE in the SGNB MODIFICATION REQUIRED message.

For each E-RAB successfully modified as requested by the en-gNB, the MeNB shall inform the en-gNB, in the SGNB MODIFICATION CONFIRM message, the same value in the EN-DC Resource Configuration IE as received in the SGNB MODIFICATION REQUIRED message.

If the SCG resources IE in the EN-DC Resource Configuration IE in the SGNB MODIFICATION REQUIRED message for all the E-RABs of the UE are set to “not present”, the MeNB shall, if supported, deduce that the SCG resources are removed.

Upon reception of the SGNB MODIFICATION CONFIRM message the en-gNB shall stop the timer T_DCoverall.

If the SGNB MODIFICATION CONFIRM message contains the MeNB Resource Coordination Information IE, the en-gNB should forward it to lower layers and it may use it for the purpose of resource coordination with the MeNB, or to coordinate with sidelink resources used in the MeNB. The en-gNB shall consider the received UL Coordination Information IE value valid until reception of a new update of the IE for the same UE. The en-gNB shall consider the received DL Coordination Information IE value valid until reception of a new update of the IE for the same UE. If the MeNB Coordination Assistance Information IE is contained in the MeNB Resource Coordination Information IE, the en-gNB shall, if supported, use the information to determine further coordination of resource utilisation between the en-gNB and the MeNB.

If the MeNB receives for an E-RAB for which the PDCP entiy is allocated at the MeNB the Secondary SgNB DL GTP Tunnel Endpoint at SCG IE in the SGNB MODIFICATION REQUIRED message, it shall provide the Secondary MeNB UL GTP Tunnel Endpoint at PDCP IE to the en-gNB in the SGNB MODIFICATION CONFIRM message. If the LCID IE is included in the SGNB MODIFICATION REQUIRED message, the MeNB should take it into account.

If the SGNB MODIFICATION REQUIRED message contains the RLC Status IE, the MeNB shall assume that RLC has been reestablished at the en-gNB and may trigger PDCP data recovery.

If the RLC Mode IE is included for an E-RAB within the E-RABs To Be Released List IE (for E-RABs hosted at the en-gNB) in the SGNB MODIFICATION REQUIRED message, it indicates the mode that the en-gNB used for the E-RAB when it was hosted at the en-gNB.

The MeNB shall include only E-RABs with the following IE in E-RABs Admitted To Be Modified List IE:

– the Secondary MeNB UL GTP Tunnel Endpoint at PDCP IE.

If the Location Information at SgNB IE is included in the SGNB MODIFICATION REQUIRED, the MeNB shall store the included information so that it may be transferred towards the MME.

For each requested E-RAB configured as MN-terminated split bearer/SCG bearer, if the QoS Mapping Information IE is included in the GTP Tunnel Endpoint IE in the SGNB MODIFICATION REQUIRED message, the MeNB shall, if supported, use it to set DSCP and/or flow label fields for the downlink IP packets which are transmitted from MeNB to SgNB through the GTP tunnels indicated by the GTP Tunnel Endpoint IE.

If the SGNB MODIFICATION REQUIRED message includes the SCG UE History Information IE, the MeNB shall, if supported, use the information to update the UE History Information with PSCell history.

If the SCG Activation Request IE is included in the SGNB MODIFICATION REQUIRED message, the MeNB shall, if supported, consider that the en-gNB node is about to reconfigure the SCG resources as specified in TS 37.340 [32].

If the CPAC Information Required IE is included in the SGNB MODIFICATION REQUIRED message, the MeNB shall, if supported, consider that the request provides the configuration update for the list of PSCells prepared at the target en-gNB, as described in TS 37.340 [32].

If the CG-CandidateList is included in the SgNB to MeNB Container IE in the SGNB MODIFICATION REQUIRED message, the MeNB shall, if supported, use it for the purpose of CPAC.

If the SCG Reconfiguration Notification IE is included in the SGNB MODIFICATION REQUIRED message and set to "executed", the MeNB shall, if supported, consider that a prepared SN-initiated intra-SN CPC procedure or a reconfiguration with sync of the SCG using SRB3 has been executed, as specificed in TS 37.340 [32]. If the SgNB to MeNB Container IE is also included in the SGNB MODIFICATION REQUIRED message, the MeNB shall, if supported, consider that the received SCG configuration has already been applied in the UE and should not be forwarded to the UE.

Interaction with the MeNB initiated SgNB Modification Preparation procedure:

If applicable, as specified in TS 37.340 [32], the en-gNB may receive, after having initiated the SgNB initiated SgNB Modification procedure, the SGNB MODIFICATION REQUEST message including the DL Forwarding GTP Tunnel Endpoint IE and the UL Forwarding GTP Tunnel Endpoint IE within the E-RABs To Be Released List IE.

If applicable, as specified in TS 37.340 [32], the en-gNB may receive, after having initiated the SgNB initiated SgNB Modification procedure, the SGNB MODIFICATION REQUEST message including the SgNB Security Key IE within the UE Context Information IE.

If applicable, as specified in TS 37.340 [32], the en-gNB may receive, after having initiated the SgNB initiated SgNB Modification procedure, the SGNB MODIFICATION REQUEST message including the measGapConfig IE as defined in TS 38.331 [31] within the MeNB to SgNB Container IE.

The en-gNB may receive, after having initiated the SgNB initiated SgNB modification procedure including the New DRB ID Request IE for an SN terminated bearer within the E-RABs To Be Modified List IE, the SGNB MODIFICATION REQUEST message to release and add the same bearer with a new DRB ID or with the same DRB ID but together with the SgNB Security Key IE within the UE Context Information IE.

The en-gNB may receive, after having initiated the SgNB initiated SgNB modification procedure, the SGNB MODIFICATION REQUEST message including the SN triggered IE.

8.7.7.3 Unsuccessful Operation

Figure 8.7.7.3-1: SgNB initiated SgNB Modification, unsuccessful operation.

In case the requested modification cannot be performed successfully the MeNB shall respond with the SGNB MODIFICATION REFUSE message to the en-gNB with an appropriate cause value in the Cause IE.

The MeNB may also provide configuration information in the MeNB to SgNB Container IE.

8.7.7.4 Abnormal Conditions

If the timer T_DCoverall expires before the en-gNB has received the SGNB MODIFICATION CONFIRM or the SGNB MODIFICATION REFUSE message, the en-gNB shall regard the requested modification as failed and may take further actions like triggering the SgNB initiated SgNB Release procedure to release all en-gNB resources allocated for the UE.

If the value received in the E-RAB ID IE of any of the E-RABs To Be Released Items IE is not known at the MeNB, the MeNB shall regard the procedure as failed and may take appropriate actions like triggering the MeNB initiated SgNB Release procedure.

If the en-gNB does not receives for an E-RAB for which the PDCP entiy is allocated at the MeNB the Secondary MeNB UL GTP Tunnel Endpoint at PDCP IE to the en-gNB in the SGNB MODIFICATION CONFIRM message although the Secondary SgNB DL GTP Tunnel Endpoint at SCG IE was provided to the MeNB in the SGNB MODIFICATION REQUIRED message, it shall assume the setup of the secondary X2-U bearer as being failed.

Interaction with the MeNB initiated SgNB Modification Preparation procedure:

If the en-gNB, after having initiated the SgNB initiated SgNB Modification procedure, receives the SGNB MODIFICATION REQUEST message including other IEs than an applicable SgNB Security Key IE and/or applicable forwarding addresses or applicable measurement gap pattern or information applicable to release and add the same bearer with different DRB ID and/or the SN triggered IE set to "True", the en-gNB shall

– regard the SgNB initiated SgNB Modification Procedure as being failed;

– stop the T_DCoverall, which was started to supervise the SgNB initiated SgNB Modification procedure;

– be prepared to receive the SGNB MODIFICATION REFUSE message from the MeNB and;

– continue with the MeNB initiated SgNB Modification Preparation procedure as specified in section 8.7.6.

Interaction with the MeNB initiated handover procedure:

If the MeNB, after having initiated the handover procedure, receives the SGNB MODIFICATION REQUIRED message, the MeNB shall refuse the SgNB modification procedure with an appropriate cause value in the Cause IE.