8.3.3 M-NG-RAN node initiated S-NG-RAN node Modification Preparation

38.4233GPPNG-RANRelease 17TSXn Application Protocol (XnAP)

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

8.3.3.1 General

This procedure is used to enable an M-NG-RAN node to request an S-NG-RAN node to either modify the UE context at the S-NG-RAN node or to query the current SCG configuration for supporting delta signalling in M-NG-RAN node initiated S-NG-RAN node change, or to provide the S-RLF-related information to the S-NG-RAN node.

The procedure uses UE-associated signalling.

8.3.3.2 Successful Operation

Figure 8.3.3.2-1: M-NG-RAN node initiated S-NG-RAN node Modification Preparation, successful operation

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

When the M-NG-RAN node sends the S-NODE MODIFICATION REQUEST message, it shall start the timer TXn_DCprep.

The S-NODE MODIFICATION REQUEST message may contain

– within the UE Context Information IE;

– PDU session resources to be added within the PDU Session Resources To Be Added Item 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 S-NG-RAN node Security Key IE;

– the S-NG-RAN node UE Aggregate Maximum Bit Rate IE;

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

– the PDCP Change Indication IE;

– the SCG Configuration Query IE;

– the Requested split SRBs IE;

– the Requested split SRBs release IE;

– the Requested fast MCG recovery via SRB3 IE;

– the Requested fast MCG recovery via SRB3 Release IE;

– the Additional DRB IDs IE;

– the MR-DC Resource Coordination Information IE.

If the S-NODE MODIFICATION REQUEST message contains the Selected PLMN IE, the S-NG-RAN node may use it for RRM purposes.

If the S-NODE MODIFICATION REQUEST message contains the Mobility Restriction List IE, the S-NG-RAN node shall

– replace the previously provided Mobility Restriction List by the received Mobility Restriction List in the UE context;

– use this information to select an appropriate SCG.

If the S-NG-RAN node UE Aggregate Maximum Bit Rate IE is included in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall:

– replace the previously provided S-NG-RAN node UE Aggregate Maximum Bit Rate by the received S-NG-RAN node UE Aggregate Maximum Bit Rate in the UE context;

– use the received S-NG-RAN node UE Aggregate Maximum Bit Rate for Non-GBR Bearers for the concerned UE as defined in TS 37.340 [8].

If the S-NG-RAN node UE Slice Maximum Bit Rate IE is included in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall, if supported:

– store and replace the previously provided S-NG-RAN node UE Slice Maximum Bit Rate, if any, by the received S-NG-RAN node UE Slice Maximum Bit Rate for each S-NSSAI for the concerned UE;

– use the received S-NG-RAN node UE Slice Maximum Bit Rate for all PDU sessions associated with the S-NSSAI for the concerned UE as defined in TS 23.501 [7].

If the S-NODE MODIFICATION REQUEST message contains the Index to RAT/Frequency Selection Priority IE, the S-NG-RAN node may use it for RRM purposes.

If the S-NODE MODIFICATION REQUEST message contains the S-NG-RAN node PDU Session Aggregate Maximum Bit Rate IE, the S-NG-RAN node may use it for RRM purposes.

If the S-NODE MODIFICATION REQUEST 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 REQUEST message contains the NE-DC TDM Pattern IE, the S-NG-RAN node should forward it to lower layers and use it for the purpose of single uplink transmission. The S-NG-RAN node shall consider the value of the received NE-DC TDM Pattern IE valid until reception of a new update of the IE for the same UE.

The allocation of resources according to the values of the Allocation and Retention Priority IE included in the QoS Flow Level QoS Parameters IE for each QoS flow shall follow the principles specified for the PDU Session Resource Setup procedure in TS 38.413 [5].

If the Additional QoS Flow Information IE is included for a QoS flow in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall behave the same as the NG-RAN node in the PDU Session Resource Setup procedure, specified in TS 38.413 [5].

For each GBR QoS flow, if the Alternative QoS Parameters Sets IE is included in the GBR QoS Flow Information IE, the S-NG-RAN node shall, if supported, behave the same as the NG-RAN node in the PDU Session Resource Setup procedure specified in TS 38.413 [5].

If the TSC Traffic Characteristics IE is included for a QoS flow in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall behave the same as the NG-RAN node in the PDU Session Resource Setup procedure, specified in TS 38.413 [5].

For each PDU session, if the Network Instance IE is included in the PDU Session Resource Setup Info – SN terminated IE and in the PDU Session Resource Modification Info – SN terminated IE and the Common Network Instance IE is not present, the S-NG-RAN node shall, if supported, use it when selecting transport network resource as specified in TS 23.501 [7].

For each PDU session, if the Common Network Instance IE is included in the PDU Session Resource Setup Info – SN terminated IE and in the PDU Session Resource Modification Info – SN terminated IE, the S-NG-RAN node shall, if supported, use it when selecting transport network resource as specified in TS 23.501 [7].

For each GBR QoS flow, if the Offered GBR QoS Flow Information IE is included in the QoS Flows To Be Setup List IE contained in the PDU Session Resource Setup Info – SN terminated IE, the S-NG-RAN node may request the M-NG-RAN node to configure the DRB to which that QoS flow is mapped with MCG resources.

For each PDU session, if the Non-GBR Resources Offered IE is included in the PDU Session Resource Modification Info – SN terminated IE contained in the PDU Session Resources To Be Added List IE and set to "true", the S-NG-RAN node may request the M-NG-RAN node to configure the DRBs to which non-GBR QoS flows of the PDU session are mapped with MCG resources.

If at least one of the requested modifications is admitted by the S-NG-RAN node, the S-NG-RAN node shall modify the related part of the UE context accordingly and send the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message back to the M-NG-RAN node.

The M-NG-RAN node shall include RLC Mode IE for each bearer offloaded from M-NG-RAN node to S-NG-RAN node in the DRBs to QoS Flow Mapping List IE within the PDU Session Resource Setup Info – SN terminated IE of the S-NODE MODIFICATION REQUEST message, and the RLC Mode IE indicates the mode that the M-NG-RAN used for the DRB when it was hosted at the M-NG-RAN node.

The S-NG-RAN node shall include the PDU sessions for which resources have been either added or modified or released at the S-NG-RAN node either in the PDU Session Resources Admitted To Be Added List IE or the PDU Session Resources Admitted To Be Modified List IE or the PDU Session Resources Admitted To Be Released List IE. The S-NG-RAN node shall include the PDU sessions that have not been admitted in the PDU Session Resources Not Admitted List IE with an appropriate cause value.

If the M-NG-RAN node requests transfer of the PDCP hosting from the S-NG-RAN node to the M-NG-RAN node for a PDU session, in which case the S-NODE MODIFICATION REQUEST message contains an PDU session resource to be released which is configured with the SCG bearer option within the PDU Session Resources To Be Released List IE, the S-NG-RAN node shall include the RLC Mode IE within the DRBs To Be Released List IE in the PDU Session Resources admitted to be released List – SN terminated IE in the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message. The the RLC Mode IE indicates the RLC mode that the S-NG-RAN node uses for the DRB.

If the QoS Flow Mapping Indication IE is included in the S-NODE MODIFICATION REQUEST message for a QoS flow to be modified, the S-NG-RAN node may replace and take it into account that only the uplink or downlink QoS flow is mapped to the DRB.

If the S-NODE MODIFICATION REQUEST message contains for a PDU session resource to be modified which is configured with the SN terminated bearer option, the UL NG-U UP TNL Information at UPF IE the S-NG-RAN node shall use it as the new UL NG-U address.

If the S-NODE MODIFICATION REQUEST message contains for a PDU session resource to be modified which is configured with the MN terminated bearer option, the MN UL PDCP UP TNL Information IE the S-NG-RAN node shall use it as the new UL Xn-U address.

Redundant transmission:

– If the S-NODE MODIFICATION REQUEST message contains for a PDU session resource to be modified which is configured with the SN terminated bearer option, the Redundant UL NG-U UP TNL Information at UPF IE, the S-NG-RAN node shall, if supported, use it as the new UL NG-U address for the redundant transmission as specified in TS 23.501 [7].

– For each PDU session, if the Redundant Common Network Instance IE is included in the PDU Session Resource Setup Info – SN terminated IE or in the PDU Session Resource Modification Info – SN terminated IE, the S-NG-RAN node shall, if supported, use it when selecting transport network resource for the redundant transmission as specified in TS 23.501 [7].

– For each PDU session, if the Redundant QoS Flow Indicator IE is set to false for all QoS flows, the S-NG-RAN node shall, if supported, stop the redundant transmission and release the redundant tunnel for the concerned PDU Session as specified in TS 23.501 [7].

– For each PDU session for which the Redundant QoS Flow Indicator IE is included in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall, if supported, store and use it as specified in TS 23.501 [7].

– For each PDU session, if the Redundant PDU Session Information IE is included in the PDU Session Resource Setup Info – SN terminated IE in the S-NODE MODIFICATION REQUEST message, the S-NODE-RAN node shall, if supported, store the received information in the UE context and setup the redundant user plane for the concerned PDU session, as specified in TS 23.501 [7]. If the PDU Session Pair ID IE is included in the Redundant PDU Session Information IE, the S-NG-RAN node may store and use it to identify the paired PDU sessions.

– For each PDU session resource successfully setup for which the Redundant PDU Session Information IE is included in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall, if supported, include the Used RSN Information IE in the PDU Session Resource Setup Response Info – SN terminated IE in the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message.

If the S-NODE MODIFICATION REQUEST 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 propose to apply forwarding of UL data for the QoS flows 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 Response Info – SN terminated IE of the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message.

For a PDU session resource to be modified which is configured with the SN terminated bearer option the S-NG-RAN node may include in the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message the DL NG-U UP TNL Information at NG-RAN IE.

For a PDU session resource to be modified which is configured with the MN terminated bearer option the S-NG-RAN node may include in the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message the SN DL SCG UP TNL Information IE.

If the PDCP Change Indication IE is included in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall act as specified in TS 37.340 [8].

Upon reception of the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message the M-NG-RAN node shall stop the timer TXn_DCprep. If the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message has included the S-NG-RAN node to M-NG-RAN node Container IE, the M-NG-RAN node is then defined to have a Prepared S-NG-RAN node Modification for that Xn UE-associated signalling.

If the SCG Configuration Query IE is included in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall provide corresponding radio configuration information within the S-NG-RAN node to M-NG-RAN node Container IE and may provide the corresponding data forwarding related information within the PDU Session Resources with Data Forwarding List IE as specified in TS 37.340 [8].

For each bearer for which allocation of the PDCP entity is requested at the S-NG-RAN node:

– if applicable, the M-NG-RAN node may propose to apply forwarding of downlink data by including the DL Forwarding IE within the PDU Session Resource Setup Info – SN terminated IE of the S-NODE MODIFICATION REQUEST message. For each bearer that it has decided to admit, the S-NG-RAN node may include the DL Forwarding GTP Tunnel Endpoint IE within the PDU Session Resource Setup Response Info – SN terminated IE of the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message to indicate that it accepts the proposed forwarding of downlink data for this bearer.

– the S-NG-RAN node may include for each bearer in the PDU Session Resource Setup Response Info – SN terminated IE the UL Forwarding GTP Tunnel Endpoint IE to indicate it requests data forwarding of uplink packets to be performed for that bearer.

The M-NG-RAN node may propose to apply forwarding of UL data when offloading QoS flows 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 Setup Info – SN terminated IE or PDU Session Resource Modification Info – SN terminated IE of the S-NODE MODIFICATION REQUEST message. The S-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 Setup Response Info – SN terminated IE or PDU Session Resource Modification Response Info – SN terminated IE of the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message to indicate that it accepts the proposed forwarding.

If the S-NODE MODIFICATION REQUEST message contains the Requested Split SRBs IE, the S-NG-RAN node may use it to add split SRBs. If the S-NODE MODIFICATION REQUEST message contains the Requested Split SRBs release IE, the S-NG-RAN node may use it to release split SRBs.

If the Requested Fast MCG recovery via SRB3 IE set to "true" is included in the S-NODE MODIFICATION REQUEST message and the S-NG-RAN decides to configure fast MCG link recovery via SRB3 as specified in TS 37.340 [8], the S-NG-RAN node shall, if supported, include the Available fast MCG recovery via SRB3 IE set to "true" in the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message. If the Requested Fast MCG recovery via SRB3 Release IE set to "true" is included in the S-NODE MODIFICATION REQUEST message and the S-NG-RAN decides to release fast MCG link recovery via SRB3, the S-NG-RAN node shall, if supported, include the Release fast MCG recovery via SRB3 IE set to "true" in the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message.

If the Lower Layer presence status change IE set to "release lower layers" is included in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall act as specified in TS 37.340 [8].

If the Lower Layer presence status change IE set to "re-establish lower layers" is included in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall act as specified in TS 37.340 [8].

If the Lower Layer presence status change IE set to "suspend lower layers" is included in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall act as specified in TS 37.340 [8].

If the Lower Layer presence status change IE set to "resume lower layers" is included in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall act as specified in TS 37.340 [8].

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

If the S-NODE MODIFICATION REQUEST message contains the PDCP SN Length IE in the DRBs To Be Setup List IE, the S-NG-RAN node shall, if supported, store this information and use it for lower layer configuration of the concerned MN terminated bearer.

If the PDCP Duplication Configuration IE in the PDU Session Resource Modification Info – MN terminated IE is contained in the S-NODE MODIFICATION REQUEST message and set to "configured", the S-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 REQUEST message contains the Duplication Activation IE, the S-NG-RAN node shall, if supported, store this information and use it for the purpose of PDCP duplication.

If the S-NODE MODIFICATION REQUEST message contains 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 bearer in the DRBs To Be Setup List IE in the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message the PDCP SN Length IE to indicate the PDCP SN length for that DRB.

The S-NG-RAN node may include the QoS Flow Mapping Indication IE for a QoS flow in the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message to indicate that only the uplink or downlink QoS flow is mapped to the DRB.

If the Additional DRB IDs IE is included in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall store this information and use it together with previously provided DRB IDs if any, for SN terminated bearers.

If the S-NODE MODIFICATION REQUEST message contains the S-NG-RAN node Maximum Integrity Protected Data Rate Uplink IE or the S-NG-RAN node Maximum Integrity Protected Data Rate Downlink IE, the S-NG-RAN node shall use the received information when enforcing the maximum integrity protected data rate for the UE.

If the Security Indication IE is included in the PDU Session Resource Setup Info – SN terminated IE of the S-NODE MODIFICATION REQUEST message, the behaviour of the S-NG-RAN node shall be the same as specified for the same IE in the PDU Session Resources To Be Setup List IE in the Handover Preparation procedure, for the concerned PDU session, and the S-NG-RAN node shall include the Security Result IE in the PDU Session Resource Setup Response Info – SN terminated IE.

If the Security Result IE is included in the PDU Session Resource Setup Info – SN terminated IE of the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node may take the information into account when deciding whether to perform user plane integrity protection or ciphering for the DRBs that it establishes for the concerned PDU session, except if the Split Session Indicator IE is included in the PDU Session Resource Setup Info – SN terminated IE and set to "split", in which case it shall perform user plane integrity protection or ciphering according to the information in the Security Result IE. If the S-NG-RAN node is an ng-eNB, it shall reject all PDU sessions for which the Integrity Protection Indication IE is set to "required" as specified in TS 33.501 [28]. If either the S-NG-RAN node or the M-NG-RAN node is an ng-eNB, the S-NG-RAN node shall behave according to clause 6.10.4 of TS 33.501 [28] for PDU sessions for which the Integrity Protection Indication IE is set to "preferred".

The S-NG-RAN node may include the Location Information at S-NODE IE in the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message, if respective information is available at the S-NG-RAN node.

If the Location Information at S-NODE Reporting IE set to "pscell" is included in the S-NODE MODIFICATION REQUEST, the S-NG-RAN node shall start providing information about the current location of the UE. If the Location Information at S-NODE IE is included in the S-NODE MODIFICATION REQUEST ACKNOWLEDGE, the M-NG-RAN node shall store the included information so that it may be transferred towards the AMF.

If the S-NSSAI IE is included in the PDU Session Resources To Be Modified List IE in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall replace the previously S-NSSAI IE by the received S-NSSAI IE.

If the S-NODE MODIFICATION REQUEST ACKNOWLEDGE 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 S-NODE MODIFICATION REQUEST message contains the PCell ID IE, the S-NG-RAN node may search for the target cell among the neighbour cells of the PCell indicated, as specified in the TS 37.340 [8].

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 REQUEST ACKNOWLEDGE message.

If the Default DRB Allowed IE is included in the PDU Session Resource Setup Info – SN terminated IE or PDU Session Resource Modification Info – SN terminated IE of the S-NODE MODIFICATION REQUEST message and set to "true", the S-NG-RAN node may configure the default DRB for the PDU session.

If the Default DRB Allowed IE is included in the PDU Session Resource Setup Info – SN terminated IE or PDU Session Resource Modification Info – SN terminated IE of the S-NODE MODIFICATION REQUEST message and set to "false", the S-NG-RAN node shall not configure the default DRB for the PDU session and the S-NG-RAN node shall reconfigure the default DRB into a normal DRB if it has configured the default DRB before.

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

If the QoS Monitoring Request IE is included in the QoS Flow Level QoS Parameters IE for a QoS flow contained in the DRBs To Be Setup List IE or the DRBs To Be Modified List IE within the PDU Session Resource Setup Info – MN terminated IE or the PDU Session Resource Modification Info – MN terminated IE, the S-NG-RAN node shall, if supported, use it to configure lower layers for the purpose of delay measurement and QoS monitoring as specified in TS 23.501 [7]. If the QoS Monitoring Reporting Frequency IE is included in the QoS Flow Level QoS Parameters IE for a QoS flow contained in the DRBs To Be Setup List IE or the DRBs To Be Modified List IE within the PDU Session Resource Setup Info – MN terminated IE or the PDU Session Resource Modification Info – MN terminated IE, the S-NG-RAN node shall, if supported, use it for RAN part delay reporting.

For each QoS flow which has been successfully added or modified in the S-NG-RAN node, if the QoS Monitoring Request IE was included in the QoS Flow Level QoS Parameters IE contained in the PDU Session Resource Setup Info – SN terminated IE or the PDU Session Resource Modification Info – SN terminated IE, the S-NG-RAN node shall store this information, and shall, if supported, perform delay measurement and QoS monitoring as specified in TS 23.501 [7]. If the QoS Monitoring Reporting Frequency IE was included in the QoS Flow Level QoS Parameters IE contained in the PDU Session Resource Setup Info – SN terminated IE or the PDU Session Resource Modification Info – SN terminated IE, the S-NG-RAN node shall store this information, and shall, if supported, use it for RAN part delay reporting. In case such a QoS flow is included in the DRBs To Be Setup List IE or the DRBs To Be Modified List IE within the PDU Session Resource Setup Response Info – SN terminated IE or the PDU Session Resource Modification Response Info – SN terminated IE, the M-NG-RAN node shall, if supported, use it to configure lower layers for the purpose of delay measurement and QoS monitoring. If the QoS Monitoring Reporting Frequency IE is included in the DRBs To Be Setup List IE or the DRBs To Be Modified List IE within the PDU Session Resource Setup Response Info – SN terminated IE or the PDU Session Resource Modification Response Info – SN terminated IE, the M-NG-RAN node shall, if supported, use it for RAN part delay reporting.

If the PDU Session Expected UE Activity Behaviour IE is included in the PDU Session Resources To Be Added List IE or the PDU Session Resources To Be Modified List IE of the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall, if supported, use it for the concerned PDU session as specified in TS 23.501 [7].

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

For each DRB configured as MN-terminated split bearer/SCG bearer, if the QoS Mapping Information IE is included in the DRBs Admitted List IE in the PDU Session Resource Setup Response Info – MN terminated IE of the S-NODE MODIFICATION REQUEST ACKNOWLEDGE 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 MN-terminated split bearer/SCG 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 Response Info – MN terminated IE of the S-NODE MODIFICATION REQUEST ACKNOWLEDGE 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 To Be Modified List IE in the PDU Session Resource Modification Info – SN terminated IE of the S-NODE MODIFICATION REQUEST 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 Security Indication IE is included in the PDU Session Resource Modification Info – SN terminated IE of the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall, if supported, replace any existing security indication, and enable/disable ciphering or integrity protection as specified in TS 38.331 [10], for the concerned PDU session, and the S-NG-RAN node shall include the Security Result IE in the PDU Session Resource Modification Response Info – SN terminated IE.

If the Target Node ID IE is included in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall, if supported, include the Direct Forwarding Path Availability IE in the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message if the direct forwarding path is available between the S-NG-RAN node and the indicated target node.

If the PSCell History Information Retrieve IE is included in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall, if supported, use this information as specified in TS 37.340 [8].

If the UE History Information from the UE IE is included in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall, if supported, store this information.

If the CHO Information SN Modification IE is included in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall consider that the M-NG-RAN node initiated S-NG-RAN node Modification Preparation procedure has been triggered as part of a conditional handover. If the Estimated Arrival Probability IE is contained in the CHO Information SN Modification IE included in the S-NODE MODIFICATION REQUEST message, then the S-NG-RAN node may use the information to allocate necessary resources for the UE.

If the SCG Activation Request IE is included in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node may use it to configure SCG resources as specified in TS 37.340 [8], and shall, if supported, include the SCG Activation Status IE in the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message.

If the Conditional PSCell Change Information Update IE is included in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall, if supported, consider that the request provides the list of PSCells prepared at the target S-NG-RAN node, as described in TS 37.340 [8].

If the Conditional PSCell Addition Information Modification Request IE is included in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall, if supported, consider that the request concerns an update of the previous CPAC preparation, as described in TS 37.340 [8]. Accordingly, the S-NG-RAN shall, if supported, include the Conditional PSCell Addition Information Modification Acknowledge IE in the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message.

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

If the Estimated Arrival Probability IE is contained in the Conditional PSCell Addition Information Modification Request IE included in the S-NODE MODIFICATION REQUEST message, then the candidate target S-NG-RAN node may use the information to allocate necessary resources for the incoming CPAC procedure.

If for a given QoS Flow the Source DL Forwarding IP Address IE is included within the Data Forwarding and Offloading Info from source NG-RAN node IE in the PDU Session Resource Setup Info – SN terminated IE and/or in the PDU Session Resource Modification Info – SN terminated IE contained in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall, if supported, store this information and use it as part of its ACL functionality configuration actions, if such ACL functionality is deployed.

If for a given QoS Flow the Source DL Forwarding IP Address IE is included within the QoS Flows Mapped To DRB List IE in the PDU Session Resource Setup Response Info – SN terminated IE and/or in the PDU Session Resource Modification Response Info – SN terminated IE contained in the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message, the M-NG-RAN node shall, if supported, store this information and use it as part of its ACL functionality to identify source TNL address for data forwarding in case of subsequent handover preparation, if such ACL functionality is deployed.

Interactions with the S-NG-RAN node Reconfiguration Completion procedure:

If the S-NG-RAN node admits a modification of the UE context requiring the M-NG-RAN node to report about the success of the RRC connection reconfiguration procedure, the S-NG-RAN node shall start the timer TXn_DCoverall when sending the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message to the M-NG-RAN node except for a request for conditional configuration. The reception of the S-NG-RAN node RECONFIGURATION COMPLETE message shall stop the timer TXn_DCoverall if TXn_DCoverall is running.

Interaction with the Activity Notification procedure

Upon receiving an S-NODE MODIFICATION REQUEST message containing the Desired Activity Notification Level IE, the S-NG-RAN node shall, if supported, use this information to decide whether to trigger subsequent Activity Notification procedures, or stop or modify ongoing triggering of these procedures due to a previous request.

Interaction with the Xn-U Address Indication procedure

For QoS flow mapped to DRBs configured with an SN terminated bearer option and removed from the SDAP in the S-NG-RAN node the S-NG-RAN node may provides data forwarding related information in the S-NODE MODIFICATION REQUEST ACKNOWLEDGE within the Data Forwarding and offloading Info from source NG-RAN node IE, in which case the M-NG-RAN node may decide to provide data forwarding addresses to the S-NG-RAN node and trigger the Xn-U Address Indication procedure as specified in TS 37.340 [8].

For QoS flow offloading from the S-NG-RAN node to the M-NG-RAN, the S-NG-RAN node may provide the data forwarding related information in the S-NODE MODIFICATION REQUEST ACKNOWLEDGE within the Data Forwarding and offloading Info from source NG-RAN node IE, in which case the M-NG-RAN node may decide to provide data forwarding addresses to the S-NG-RAN node and trigger the Xn-U Address Indication procedure as specified in TS 37.340 [8].

Interactions with the S-NG-RAN node initiated S-NG-RAN node Modification:

If the SN triggered IE set to "TRUE" is included in the S-NODE MODIFICATION REQUEST message, the S-NG-RAN node shall consider that the procedure has been initiated in response to the previously initiated S-NG-RAN node initiated S-NG-RAN node Modification procedure.

8.3.3.3 Unsuccessful Operation

Figure 8.3.3.3-1: M-NG-RAN node initiated S-NG-RAN node Modification Preparation, unsuccessful operation

If the S-NG-RAN node does not admit any modification requested by the M-NG-RAN node, or a failure occurs during the M-NG-RAN node initiated S-NG-RAN node Modification Preparation, the S-NG-RAN node shall send the S-NODE MODIFICATION REQUEST REJECT message to the M-NG-RAN node. The message shall contain the Cause IE with an appropriate value.

If the S-NG-RAN node receives a S-NODE MODIFICATION REQUEST message containing the M-NG-RAN node to S-NG-RAN node Container IE that does not include required information as specified in TS 37.340 [8], the S-NG-RAN node shall send the S-NODE MODIFICATION REQUEST REJECT message to the M-NG-RAN node.

8.3.3.4 Abnormal Conditions

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

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

If the S-NG-RAN node receives an S-NODE MODIFICATION REQUEST message containing multiple PDU Session ID IEs (in the PDU Session Resources To Be Released List IE) set to the same value, the S-NG-RAN node shall initiate the release of one corresponding PDU Session and ignore the duplication of the instances of the selected corresponding PDU Sessions.

If the supported algorithms for encryption defined in the NR Encryption Algorithms IE in the NR UE Security Capabilities IE in the UE Context Information IE, plus the mandated support of NEA0 in all UEs (TS 33.501 [58]), do not match any algorithms defined in the configured list of allowed encryption algorithms in the S-NG-RAN node (TS 33.501 [28]), the S-NG-RAN node shall reject the procedure using the S-NODE MODIFICATION REQUEST REJECT message.

If the supported algorithms for integrity defined in the NR Integrity Protection Algorithms IE in the NR UE Security Capabilities IE in the UE Context Information IE do not match any algorithms defined in the configured list of allowed integrity protection algorithms in the S-NG-RAN node (TS 33.501 [28]), the S-NG-RAN node shall reject the procedure using the S-NODE MODIFICATION REQUEST REJECT message.

If the timer TXn_DCprep expires before the M-NG-RAN node has received the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message, the M-NG-RAN node shall regard the M-NG-RAN node initiated S-NG-RAN node Modification Preparation procedure as being failed and shall release the UE Context at the S-NG-RAN node.

If the Lower Layer presence status change IE set to "re-establish lower layers" is included in the S-NODE MODIFICATION REQUEST message and was not set to "release lower layers" before, the S-NG-RAN node shall ignore the IE.

If the S-NG-RAN node receives an S-NODE MODIFICATION REQUEST message containing, for a PDU session, a PDU Session Resource Setup Info – SN terminated IE for which the Split Session Indicator IE is included and set to "split", the Security Result IE is not included, and either the Integrity Protection Indication IE or the Confidentiality Protection Indication IE is set to "preferred", it shall reject the PDU session.

Interactions with the S-NG-RAN node Reconfiguration Completion and S-NG-RAN node initiated S-NG-RAN node Release procedure:

If the timer TXn_DCoverall expires before the S-NG-RAN node has received the S-NODE RECONFIGURATION COMPLETE or the S-NODE RELEASE REQUEST message, the S-NG-RAN node shall regard the requested modification RRC connection reconfiguration as being not applied by the UE and shall trigger the S-NG-RAN node initiated S-NG-RAN node Release procedure.

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

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

If the M-NG-RAN node has a Prepared S-NG-RAN node Modification and receives the S-NODE MODIFICATION REQUIRED message, 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.

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

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

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

If the timer TXn_DCprep expires before the M-NG-RAN node has received the S-NODE MODIFICATION REQUEST ACKNOWLEDGE message, the M-NG-RAN node shall regard the S-NG-RAN node Modification Preparation procedure as being failed and may trigger the M-NG-RAN node initiated S-NG-RAN node Release procedure.