8.3.4 S-NG-RAN node initiated S-NG-RAN node Modification

38.4233GPPNG-RANRelease 17TSXn Application Protocol (XnAP)

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

8.3.4.1 General

This procedure is used by the S-NG-RAN node to modify the UE context in the S-NG-RAN node.

The procedure uses UE-associated signalling.

8.3.4.2 Successful Operation

Figure 8.3.4.2-1: S-NG-RAN node initiated S-NG-RAN node Modification, successful operation.

The S-NG-RAN node initiates the procedure by sending the S-NODE MODIFICATION REQUIRED message to the M-NG-RAN node.

When the S-NG-RAN node sends the S-NODE MODIFICATION REQUIRED message, it shall start the timer TXn_DCoverall.

The S-NODE MODIFICATION REQUIRED message may contain

– the S-NG-RAN node to M-NG-RAN node Container IE.

– PDU session resources to be modified within the PDU Session Resources To Be Modified Item IE;

– PDU session resources to be released within the PDU Session Resources To Be Released Item IE;

– the PDCP Change Indication IE;

– the Spare DRB IDs IE;

– the Required Number of DRB IDs IE;

– the QoS Flow Mapping Indication IE;

– the MR-DC Resource Coordination Information IE.

If the M-NG-RAN node receives a S-NODE MODIFICATION REQUIRED message containing the PDCP Change Indication IE, the M-NG-RAN node shall act as specified in TS 37.340 [8].

If the S-NODE MODIFICATION REQUIRED message contains the MR-DC Resource Coordination Information IE, the M-NG-RAN node may use it for the purpose of resource coordination with the S-NG-RAN node. The M-NG-RAN node shall consider the value of the received UL Coordination Information IE valid until reception of a new update of the IE for the same UE. The M-NG-RAN node shall consider the value of the received DL Coordination Information IE valid until reception of a new update of the IE for the same UE. If the E-UTRA Coordination Assistance Information IE or the NR Coordination Assistance Information IE is contained in the MR-DC Resource Coordination Information IE, the M-NG-RAN node shall, if supported, use the information to determine further coordination of resource utilisation between the M-NG-RAN node and the S-NG-RAN node.

If the M-NG-RAN node receives an S-NODE MODIFICATION REQUIRED message containing the Spare DRB IDs IE, the M-NG-RAN node may take those into consideration to be used for MN-terminated bearers.

If the M-NG-RAN node receives an S-NODE MODIFICATION REQUIRED message containing the Required Number of DRB IDs IE, the M-NG-RAN node shall provide new DRB IDs to be used by the S-NG-RAN node for SN-terminated bearers , if such DRB IDs are available, in the Additional DRB IDs IE included in the S-NODE MODIFICATION CONFIRM message.

If the M-NG-RAN node is able to perform the modifications requested by the S-NG-RAN node, the M-NG-RAN node shall send the S-NODE MODIFICATION CONFIRM message to the S-NG-RAN node. The S-NODE MODIFICATION CONFIRM message may contain the M-NG-RAN node to S-NG-RAN node Container IE.

If the PDCP Duplication Configuration IE in the PDU Session Resource Modification Required Info – SN terminated IE is contained in the S-NODE MODIFICATION REQUIRED message and set to "configured", the M-NG-RAN node shall, if supported, add the RLC entity of secondary path and the RLC entity of all additional path(s) for the indicated DRB. And if the S-NODE MODIFICATION REQUIRED message contains the Duplication Activation IE, the M-NG-RAN node shall, if supported, store this information and use it for the purpose of PDCP duplication.

If the S-NODE MODIFICATION REQUIRED message contains the RLC Duplication Information IE, the S-NG-RAN node shall, if supported, store this information and use it for the purpose of PDCP duplication for the indicated DRB with more than two RLC entities.

The S-NG-RAN node may include for each DRB in the DRBs To Be Modified List IE in the S-NODE MODIFICATION REQUIRED message the RLC Status IE to indicate that RLC has been reestablished at the S-NG-RAN node and the M-NG-RAN node may trigger PDCP data recovery.

If the S-NODE MODIFICATION REQUIRED message contains the QoS flows To Be Released List within the PDU Session Resource Modification Info – SN terminated IE, the S-NG-RAN node may also propose to apply forwarding of UL data for which in-order delivery is requested by including the UL Forwarding Proposal IE in the Data Forwarding and Offloading Info from source NG-RAN node IE within the PDU Session Resource Modification Required Info – SN terminated IE of the S-NODE MODIFICATION REQUIRED message. The M-NG-RAN node may include the PDU Session Level UL Data Forwarding UP TNL Information IE in the Data Forwarding Info from target NG-RAN node IE within the PDU Session Resource Modification Confirm Info – SN terminated IE of the S-NODE MODIFICATION CONFIRM message to indicate that it accepts the proposed forwarding.

Upon reception of the S-NODE MODIFICATION CONFIRM message the S-NG-RAN node shall stop the timer TXn_DCoverall.

If the S-NODE MODIFICATION CONFIRM message contains the MR-DC Resource Coordination Information IE, the S-NG-RAN node should forward it to lower layers and it may use it for the purpose of resource coordination with the M-NG-RAN node, or to coordinate with sidelink resources used in the M-NG-RAN node. The S-NG-RAN node shall consider the value of the received UL Coordination Information IE valid until reception of a new update of the IE for the same UE. The S-NG-RAN node shall consider the value of the received DL Coordination Information IE valid until reception of a new update of the IE for the same UE. If the E-UTRA Coordination Assistance Information IE or the NR Coordination Assistance Information IE is contained in the MR-DC Resource Coordination Information IE, the S-NG-RAN node shall, if supported, use the information to determine further coordination of resource utilisation between the S-NG-RAN node and the M-NG-RAN node.

If the S-NODE MODIFICATION REQUIRED message contains a PDU session resource to be released which is configured with the SCG bearer option within the PDU sessions to be released List – SN terminated IE, the S-NG-RAN node shall include the RLC Mode IE within the DRBs To Be Released List IE in the PDU Session to be released List – SN terminated IE in the S-NODE MODIFICATION REQUIRED message. The RLC Mode IE indicates the RLC mode used in the S-NG-RAN node for the DRB.

If the Location Information at S-NODE IE is included in the S-NODE MODIFICATION REQUIRED, the M-NG-RAN node shall store the included information so that it may be transferred towards the AMF.

If the QoS Flows Mapped To DRB List IE is included in the S-NODE MODIFICATION REQUIRED message for a DRB to be modified, the M-NG-RAN node shall replace any existing QoS flow mapping for that DRB with the one received.

If the S-NG-RAN node applied a full configuration or delta configuration, e.g., as part of mobility procedure involving a change of DU, the S-NG-RAN node shall inform the M-NG-RAN node by including the RRC config indication IE in the S-NODE MODIFICATION REQUIRED message.

If the S-NODE MODIFICATION CONFIRM message includes the DRB IDs taken into use IE, the S-NG-RAN node shall, if applicable, act as specified in TS 37.340 [8]

If the SCG Indicator IE is contained in the S-NODE MODIFICATION REQUIRED message and it is set to "released", the M-NG-RAN node shall, if supported, deduce that the SCG is removed.

For each DRB configured as MN-terminated split bearer/SCG bearer, if the QoS Mapping Information IE is included in the DRBs To Be Modified List IE in the PDU Session Resource Modification Required Info – MN terminated IE of the S-NODE MODIFICATION REQUIRED message, the M-NG-RAN node shall, if supported, use it to set DSCP and/or IPv6 flow label fields for the downlink IP packets which are transmitted from M-NG-RAN node to S-NG-RAN node through the GTP tunnels indicated by the UP Transport Layer Information IE.

For each DRB configured as SN-terminated split bearer/MCG bearer, if the QoS Mapping Information IE is included in the DRBs Admitted to be Setup or Modified List IE in the PDU Session Resource Modification Confirm Info – SN terminated IE of the S-NODE MODIFICATION CONFIRM message, the S-NG-RAN node shall, if supported, use it to set DSCP and/or IPv6 flow label fields for the downlink IP packets which are transmitted from S-NG-RAN node to M-NG-RAN node through the GTP tunnels indicated by the UP Transport Layer Information IE.

If the S-NG-RAN node receives in the S-NODE MODIFICATION CONFIRM message within the PDU Session Resource Modification Confirm Info – SN terminated IE a DRBs Admitted to be Setup or Modified Item IE with DRB ID(s) that it has not requested to be setup or modified, the S-NG-RAN node shall ignore the contained information.

If the S-NODE MODIFICATION REQUIRED message includes the SCG UE History Information IE, the M-NG-RAN node shall, if supported, use the information to update UE History Information with PSCell history.

If the SCG Activation Request IE is included in the S-NODE MODIFICATION REQUIRED message, the M-NG-RAN node shall consider that the S-NG-RAN node is about to reconfigure the SCG resources as specified in TS 37.340 [8].

If the Management Based MDT PLMN Modification List IE is contained in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall, if supported, overwrite any previously stored Management Based MDT PLMN List information in the UE context and use the received information to determine subsequent selection of the UE for management based MDT defined in TS 32.422 [23].

If the CPAC Information Required IE is included in the S-NODE MODIFICATION REQUIRED message, the M-NG-RAN node shall, if supported, consider that the request provides the configuration update for the list of PSCells prepared at the target SN, as described in TS 37.340 [8].

If the CG-CandidateList is included in the S-NG-RAN node to M-NG-RAN node Container IE in the S-NODE MODIFICATION REQUIRED message, the M-NG-RAN node shall, if supported, use it for the purpose of CPAC.

If the SCG Reconfiguration Notification IE is included in the S-NODE MODIFICATION REQUIRED message and set to "executed", the M-NG-RAN node 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 specified in TS 37.340 [8]. If the S-NG-RAN node to M-NG-RAN node Container IE is also included in the S-NODE MODIFICATION REQUIRED message, the M-NG-RAN node 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 M-NG-RAN node initiated S-NG-RAN node Modification Preparation procedure:

If applicable, as specified in TS 37.340 [8], the S-NG-RAN node may receive, after having initiated the S-NG-RAN node initiated S-NG-RAN node Modification procedure, the S-NODE MODIFICATION REQUEST message including the measGapConfig IE as defined in TS 38.331 [10] within the M-NG-RAN node to S-NG-RAN node Container IE.

If applicable, the S-NG-RAN node may receive, after having initiated the S-NG-RAN node initiated S-NG-RAN node Modification procedure, the S-NODE MODIFICATION REQUEST message including the SN triggered IE.

8.3.4.3 Unsuccessful Operation

Figure 8.3.4.3-1: S-NG-RAN node initiated S-NG-RAN node Modification, unsuccessful operation.

In case the requested modification cannot be performed successfully the M-NG-RAN node shall respond with the S-NODE MODIFICATION REFUSE message to the S-NG-RAN node with an appropriate cause value in the Cause IE.

In case that the Required Number of DRB IDs IE was included in the S-NODE MODIFICATION REQUIRED message and if the M-NG-RAN node is not able to provide additional DRB IDs, the M-NG-RAN node shall respond with the S-NODE MODIFICATION REFUSE with an appropriate cause value in the Cause IE.

The M-NG-RAN node may also provide configuration information in the M-NG-RAN node to S-NG-RAN node Container IE.

8.3.4.4 Abnormal Conditions

If the M-NG-RAN node receives an S-NODE MODIFICATION REQUIRED message including a PDU Session Resources To Be Modified Item IE, containing neither the PDU Session Resource Modification Required Info – SN terminated IE nor the PDU Session Resource Modification Required Info – MN terminated IE, the M-NG-RAN node shall fail the S-NG-RAN node initiated S-NG-RAN node Modification procedure indicating an appropriate cause.

If the timer TXn_DCoverall expires before the S-NG-RAN node has received the S-NODE MODIFICATION CONFIRM or the S-NODE MODIFICATION REFUSE message, the S-NG-RAN node shall regard the requested modification as failed and may take further actions like triggering the S-NG-RAN node initiated S-NG-RAN node Release procedure to release all S-NG-RAN node resources allocated for the UE.

If the value received in the PDU Session ID IE of any of the PDU Sessions Resources To Be Released Items IE is not known at the M-NG-RAN node, the M-NG-RAN node shall regard the procedure as failed and may take appropriate actions like triggering the M-NG-RAN node initiated S-NG-RAN node Release procedure.

Interaction with the S-NG-RAN node initiated S-NG-RAN node Release procedure:

If the S-NG-RAN node receives an S-NODE MODIFICATION CONFIRM message including a PDU Session Resources Admitted To Be Modified Item IE, containing neither the PDU Session Resource Modification Confirm Info – SN terminated IE nor the PDU Session Resource Modification Confirm Info – MN terminated IE, the S-NG-RAN node shall trigger the S-NG-RAN node initiated S-NG-RAN node Release procedure indicating an appropriate cause.

Interaction with the M-NG-RAN node initiated S-NG-RAN node Modification Preparation procedure:

If the S-NG-RAN node, after having initiated the S-NG-RAN node initiated S-NG-RAN node Modification procedure, receives the S-NODE MODIFICATION REQUEST message including other IEs than an applicable S-NG-RAN node Security Key IE and/or LCID applicable for PDCP duplication and/or the SN triggered IE set to "TRUE", the S-NG-RAN node shall

– regard the S-NG-RAN node initiated S-NG-RAN node Modification Procedure as being failed;

– stop the TXn_DCoverall, which was started to supervise the S-NG-RAN node initiated S-NG-RAN node Modification procedure;

– be prepared to receive the S-NODE MODIFICATION REFUSE message from the M-NG-RAN node and;

– continue with the M-NG-RAN node initiated S-NG-RAN node Modification Preparation procedure as specified in section 8.3.

Interaction with the M-NG-RAN node initiated handover procedure:

If the M-NG-RAN node, after having initiated the handover procedure, receives the S-NODE MODIFICATION REQUIRED message, the M-NG-RAN node shall refuse the S-NG-RAN node modification procedure with an appropriate cause value in the Cause IE.