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Content for  TS 38.423  Word version:  16.3.0

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8.2.3  Handover Cancel

8.2.3.1  General

The Handover Cancel procedure is used to enable a source NG-RAN node to cancel an ongoing handover preparation or an already prepared handover.
The procedure uses UE-associated signalling.

8.2.3.2  Successful Operation

Reproduction of 3GPP TS 38.423, Figure 8.2.3.2-1: Handover Cancel, successful operation
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The source NG-RAN node initiates the procedure by sending the HANDOVER CANCEL message to the target NG-RAN node. The source NG-RAN node shall indicate the reason for cancelling the handover by means of an appropriate cause value.
If the Candidate Cells To Be Cancelled List IE is included in the HANDOVER CANCEL message, the target NG-RAN node shall consider that the source NG-RAN node is cancelling only the handover associated to the candidate cells identified by the included NG-RAN CGI and associated to the same UE-associated signaling connection identified by the Source NG-RAN node UE XnAP ID IE and, if included, also by the Target NG-RAN node UE XnAP ID IE.
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8.2.3.3  Unsuccessful Operation

Not applicable.

8.2.3.4  Abnormal ConditionsWord‑p. 28
If the HANDOVER CANCEL message refers to a context that does not exist, the target NG-RAN node shall ignore the message.
If the Candidate Cells To Be Cancelled List IE is included in the HANDOVER CANCEL message and the handover is not associated to a conditional handover, the target NG-RAN node shall ignore the Candidate Cells To Be Cancelled List IE.
If one or more candidate cells in the Candidate Cells To Be Cancelled List IE included in the HANDOVER CANCEL message were not prepared using the same UE-associated signaling connection, the target NG-RAN node shall ignore those non-associated candidate cells.
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8.2.4  Retrieve UE Context

8.2.4.1  General

The purpose of the Retrieve UE Context procedure is to either retrieve the UE context from the old NG-RAN node and transfer it to the NG-RAN node where the UE RRC Connection has been requested to be established, or to enable the old NG-RAN node to forward an RRC message to the UE via the new NG-RAN node without context transfer.
The procedure uses UE-associated signalling.

8.2.4.2  Successful Operation

Reproduction of 3GPP TS 38.423, Figure 8.2.4.2-1: Retrieve UE Context, successful operation
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The new NG-RAN node initiates the procedure by sending the RETRIEVE UE CONTEXT REQUEST message to the old NG-RAN node.
If the old NG-RAN node is able to identify the UE context by means of the UE Context ID, and to successfully verify the UE by means of the integrity protection contained in the RETRIEVE UE CONTEXT REQUEST message, and decides to provide the UE context to the new NG-RAN node, it shall respond to the new NG-RAN node with the RETRIEVE UE CONTEXT RESPONSE message.
If the Index to RAT/Frequency Selection Priority IE is contained in the RETRIEVE UE CONTEXT RESPONSE message, the new NG-RAN node shall store this information and use it as defined in TS 23.501.
If the Location Reporting Information IE is included in the RETRIEVE UE CONTEXT RESPONSE message, then the new NG-RAN node should initiate the requested location reporting functionality as defined in TS 38.413.
If the Trace Activation IE is included in the RETRIEVE UE CONTEXT RESPONSE message which includes
  • the MDT Activation IE set to "Immediate MDT and Trace", then the target NG-RAN node shall if supported, initiate the requested trace session and MDT session as described in TS 32.422.
  • the MDT Activation IE set to "Immediate MDT Only" or "Logged MDT only", the target NG-RAN node shall, if supported, initiate the requested MDT session as described in TS 32.422 and the target NG-RAN node shall ignore the Interfaces To Trace IE, and the Trace Depth IE.
  • the MDT Location Information IE, within the MDT Configuration IE, the target NG-RAN node shall, if supported, store this information and take it into account in the requested MDT session.
  • the MDT Activation IE set to "Immediate MDT Only" or "Logged MDT only", and if the Signalling based MDT PLMN List IE is included in the MDT Configuration IE, the target NG-RAN node may use it to propagate the MDT Configuration as described in TS 37.320.
  • the Bluetooth Measurement Configuration IE, within the MDT Configuration IE, the target NG-RAN node shall, if supported, take it into account for MDT Configuration as described in TS 37.320.
  • the WLAN Measurement Configuration IE, within the MDT Configuration IE, the target NG-RAN node shall, if supported, take it into account for MDT Configuration as described in TS 37.320.
  • the Sensor Measurement Configuration IE, within the MDT Configuration IE, take it into account for MDT Configuration as described in TS 37.320.
  • the MDT Configuration IE and if the target NG-RAN Node is a gNB at least the MDT Configuration-NR IE shall be present, while if the target NG-RAN Node is an ng-eNB at least the MDT Configuration-EUTRA IE shall be present.
For each QoS flow in the RETRIEVE UE CONTEXT RESPONSE message, if the QoS Monitoring Request IE is included in the QoS Flow Level QoS Parameters IE in the PDU Session Resources To Be Setup List IE, the new NG-RAN node shall store this information, and, if supported, perform delay measurement and QoS monitoring, as specified in TS 23.501.
If the 5GC Mobility Restriction List Container IE is included in the RETRIEVE UE CONTEXT RESPONSE message, the new NG-RAN node shall, if supported, store this information in the UE context and use it as specified in TS 38.300.
V2X:
  • If the NR V2X Services Authorized IE is included in the RETRIEVE UE CONTEXT RESPONSE message and it contains one or more IEs set to "authorized", the new NG-RAN node shall, if supported, consider that the UE is authorized for the relevant service(s).
  • If the LTE V2X Services Authorized IE is included in the RETRIEVE UE CONTEXT RESPONSE message and it contains one or more IEs set to "authorized", the new NG-RAN node shall, if supported, consider that the UE is authorized for the relevant service(s).
  • If the NR UE Sidelink Aggregate Maximum Bit Rate IE is included in the UE Context Information Retrieve UE Context Response IE in the RETRIEVE UE CONTEXT RESPONSE message, the new NG-RAN node shall, if supported, use the received value for the concerned UE's sidelink communication in network scheduled mode for NR V2X services.
  • If the LTE UE Sidelink Aggregate Maximum Bit Rate IE is included in the UE Context Information Retrieve UE Context Response IE in the RETRIEVE UE CONTEXT RESPONSE message, the new NG-RAN node shall, if supported, use the received value for the concerned UE's sidelink communication in network scheduled mode for LTE V2X services.
If the PC5 QoS Parameters IE is included in the RETRIEVE UE CONTEXT RESPONSE message, the target NG-RAN node shall, if supported, use it as defined in TS 23.287.
In case of RRC Re-establishment, the old NG-RAN may include the UE History Information IE or the UE History Information from the UE IE in the RETRIEVE UE CONTEXT RESPONSE message. Upon reception of the UE History Information IE or the UE History Information from the UE IE in the RETRIEVE UE CONTEXT RESPONSE message, the new NG-RAN node shall, if supported, store the collected information and use it for future handover preparations.
If the UE Radio Capability ID IE is contained in the RETRIEVE UE CONTEXT RESPONSE message, the new NG- RAN node shall, if supported store this information in the UE context and use it as defined in TS 23.501 and TS 23.502.
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8.2.4.3  Unsuccessful OperationWord‑p. 30
Reproduction of 3GPP TS 38.423, Figure 8.2.4.3-1: Retrieve UE Context, unsuccessful operation
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If the old NG-RAN node is not able to identify the UE context by means of the UE Context ID, or if the integrity protection contained in the RETRIEVE UE CONTEXT REQUEST message is not valid, or, if it decides not to provide the UE context to the new NG-RAN node, it shall respond to the new NG-RAN node with the RETRIEVE UE CONTEXT FAILURE message.
If the old NG-RAN node decides to keep the UE context in case of periodic RNAU, it shall store the Allocated C-RNTI IE and the Access PCI IE in the UE Context ID IE, as described in TS 38.300.
If the Old NG-RAN node to New NG-RAN node Resume Container IE is included in the RETRIEVE UE CONTEXT FAILURE message, the new NG-RAN node should transparently forward the content of this IE to the UE as described in TS 38.300.
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8.2.4.4  Abnormal Conditions

Void.

8.2.5  RAN Paging

8.2.5.1  General

The purpose of the RAN Paging procedure is to enable the NG-RAN node1 to request paging of a UE in the NG-RAN node2.
The procedure uses non UE-associated signalling.

8.2.5.2  Successful operation

Reproduction of 3GPP TS 38.423, Figure 8.2.5.2-1: RAN Paging: successful operation
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The RAN Paging procedure is triggered by the NG-RAN node1 by sending the RAN PAGING message to the NG-RAN node2, in which the necessary information e.g. UE RAN Paging Identity should be provided.
If the Paging Priority IE is included in the RAN PAGING message, the NG-RAN node2 may use it to prioritize paging.
If the Assistance Data for RAN Paging IE is included in the RAN PAGING message, the NG-RAN node2 may use it according to TS 38.300.
If the UE Radio Capability for Paging IE is included in the RAN PAGING message, the NG-RAN node2 may use it to apply specific paging schemes.
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8.2.5.3  Unsuccessful OperationWord‑p. 31
Not applicable.

8.2.5.4  Abnormal Condition

Void.

8.2.6  XN-U Address Indication

8.2.6.1  General

For the retrieval of a UE context, the Xn-U Address Indication procedure is used to provide forwarding addresses from the new NG-RAN node to the old NG-RAN node for all PDU session resources successfully established at the new NG-RAN node for which forwarding was requested.
For MR-DC with 5GC, the Xn-UAddress Indication procedure is used to provide forwarding addresses and Xn-U bearer address information for completion of setup of SN terminated bearers from the M-NG-RAN node to the S-NG-RAN node as specified in TS 37.340,
The procedure uses UE-associated signalling.
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8.2.6.2  Successful Operation

Reproduction of 3GPP TS 38.423, Figure 8.2.6.2-1: Xn-U Address Indication, successful operation for UE context retrieval
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Reproduction of 3GPP TS 38.423, Figure 8.2.6.2-2: Xn-U Address Indication, successful operation for MR-DC with 5GC
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UE Context Retrieval
The Xn-U Address Indication procedure is initiated by the new NG-RAN node. Sending the XN-U ADDRESS INDICATION message, the new NG-RAN node informs the old NG-RAN node of successfully established PDU Session Resource contexts to which user data pending at the old NG-RAN node can be forwarded.
The new NG-RAN node may include Secondary Data Forwarding Info from target NG-RAN node List IE for an additional Xn-U tunnel for data forwarding.
Upon reception of the XN-U ADDRESS INDICATION message, the old NG-RAN node should forward pending user data to the indicated TNL addresses.
MR-DC with 5GC
The Xn-U Address Indication procedure is initiated by the M-NG-RAN node.
Upon reception of the XN-U ADDRESS INDICATION message, in case of data forwarding, the S-NG-RAN node should forward pending DL user data to the indicated TNL addresses; in case of completion of Xn-U bearer establishment for SN terminated bearers, the S-NG-RAN node may start delivery of user data to the indicated TNL address.
If the XN-U ADDRESS INDICATION message includes the DRB IDs taken into use IE, the S-NG-RAN node shall, if applicable, act as specified in TS 37.340.
If the XN-U ADDRESS INDICATION message includes the CHO MR-DC Indicator IE, the S-NG-RAN node shall, if supported, consider that the XN-U ADDRESS INDICATION message concerns a Conditional Handover, and act as specified in TS 37.340.
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8.2.6.3  Unsuccessful OperationWord‑p. 32
Not applicable.

8.2.6.4  Abnormal Conditions

Void.

8.2.7  UE Context Release

8.2.7.1  General

For handover, the UE Context Release procedure is initiated by the target NG-RAN node to indicate to the source NG-RAN node that radio and control plane resources for the associated UE context are allowed to be released.
For dual connectivity, the UE Context Release procedure is initiated by the M-NG-RAN node to initiate the release the UE context at the S-NG-RAN node. For dual connectivity specific mobility scenarios specified in TS 37.340, where SCG radio resources in the S-NG-RAN node are kept, only resources related to the UE-associated signalling connection between the M-NG-RAN node and the S-NG-RAN node are released.
For UE context retrieval, the UE Context Release procedure is initiated by the new NG-RAN node to indicate to the old NG-RAN node that radio and control plane resources for the associated UE context are allowed to be released.
The procedure uses UE-associated signalling.
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8.2.7.2  Successful OperationWord‑p. 33
Reproduction of 3GPP TS 38.423, Figure 8.2.7.2-1: UE Context Release, successful operation for handover
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Reproduction of 3GPP TS 38.423, Figure 8.2.7.2-2: UE Context Release, successful operation for dual connectivity
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Reproduction of 3GPP TS 38.423, Figure 8.2.7.2-3: UE Context Release, successful operation for UE context retrieval
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Handover
The UE Context Release procedure is initiated by the target NG-RAN node. By sending the UE CONTEXT RELEASE message the target NG-RAN node informs the source NG-RAN node of Handover success and triggers the release of resources.
Upon reception of the UE CONTEXT RELEASE message, the source NG-RAN node may release radio and control plane related resources associated to the UE context. If data forwarding has been performed, the source NG-RAN node should continue forwarding of user plane data as long as packets are received at the source NG-RAN node.
Dual Connectivity
The UE Context Release procedure is initiated by the M-NG-RAN node. By sending the UE CONTEXT RELEASE message the M-NG-RAN node informs the S-NG-RAN node that the UE Context can be removed.
Upon reception of the UE CONTEXT RELEASE message, the S-NG-RAN node may release radio and control plane related resources associated to the UE context. If data forwarding has been performed, the S-NG-RAN node should continue forwarding of user plane data as long as packets are received at the S-NG-RAN node.
UE Context Retrieval
The UE Context Release procedure is initiated by the new NG-RAN node. By sending the UE CONTEXT RELEASE message the new NG-RAN node informs the old NG-RAN node of RRC connection reestablishment success or RRC connection resumption success and triggers the release of resources.
Interaction with the M-NG-RAN node initiated S-NG-RAN node Release procedure:
The S-NG-RAN node may receive the S-NODE RELEASE REQUEST message including the UE Context Kept Indicator IE set to "True", upon which the S-NG-RAN node shall, if supported, only release the resources related to the UE-associated signalling connection between the M-NG-RAN node and the S-NG-RAN node, as specified in TS 37.340.
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8.2.7.3  Unsuccessful OperationWord‑p. 34
Not applicable.

8.2.7.4  Abnormal Conditions

If the UE Context Release procedure is not initiated towards the source NG-RAN node from any prepared NG-RAN node before the expiry of the timer TXnRELOCoverall, the source NG-RAN node shall request the AMF to release the UE context.
If the UE returns to source NG-RAN node before the reception of the UE CONTEXT RELEASE message or the expiry of the timer TXnRELOCoverall, the source NG-RAN node shall stop the TXnRELOCoverall and continue to serve the UE.

8.2.8  Handover Success |R16|

8.2.8.1  General

The Handover Success procedure is used during a conditional handover or a DAPS handover to enable a target NG-RAN node to inform the source NG-RAN node that the UE has successfully accessed the target NG-RAN node.
The procedure uses UE-associated signalling.

8.2.8.2  Successful Operation

Reproduction of 3GPP TS 38.423, Figure 8.2.8.2-1: Handover Success, successful operation
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The target NG-RAN node initiates the procedure by sending the HANDOVER SUCCESS message to the source NG-RAN node.
If late data forwarding was configured for this UE, the source NG-RAN node shall start data forwarding using the tunnel information related to the global target cell ID provided in the HANDOVER SUCCESS message.
When the source NG-RAN node receives the HANDOVER SUCCESS message, it shall consider all other CHO preparations accepted for this UE under the same UE-associated signalling connection in the target NG-RAN node as cancelled.
Interactions with other procedures
If a CONDITIONAL HANDOVER CANCEL message was received for this UE prior the reception of the HANDOVER SUCCESS message, the source NG-RAN node shall consider that the UE successfully executed the handover.
The source NG-RAN node may initiate Handover Cancel procedure towards the other signalling connections or other candidate target NG-RAN nodes for this UE, if any.
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8.2.8.3  Unsuccessful OperationWord‑p. 35
Not applicable.

8.2.8.4  Abnormal Conditions

If the HANDOVER SUCCESS message refers to a context that does not exist, the source NG-RAN node shall ignore the message.

8.2.9  Conditional Handover Cancel |R16|

8.2.9.1  General

The Conditional Handover Cancel procedure is used to enable a target NG-RAN node to cancel an already prepared conditional handover.
The procedure uses UE-associated signalling.

8.2.9.2  Successful Operation

Reproduction of 3GPP TS 38.423, Figure 8.2.9.2-1: Conditional Handover Cancel, successful operation
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The target NG-RAN node initiates the procedure by sending the CONDITIONAL HANDOVER CANCEL message to the source NG-RAN node. The target NG-RAN node shall indicate the reason for cancelling the conditional handover by means of an appropriate cause value.
At the reception of the CONDITIONAL HANDOVER CANCEL message, the source NG-RAN node shall consider that the target NG-RAN node is about to remove any reference to, and release any resources previously reserved for candidate cells associated to the UE-associated signalling identified by the Source NG-RAN node UE XnAP ID IE and the Target NG-RAN node UE XnAP ID IE. If the Candidate Cells To Be Cancelled List IE is included in CONDITIONAL HANDOVER CANCEL message, the source NG-RAN node shall consider that only the resources reserved for the cells identified by the included NG-RAN CGI are about to be released.
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8.2.9.3  Unsuccessful Operation

Not applicable.

8.2.9.4  Abnormal ConditionsWord‑p. 36
If the CONDITIONAL HANDOVER CANCEL message refers to a context that does not exist, the source NG-RAN node shall ignore the message.
If one or more candidate cells in the Candidate Cells To Be Cancelled List IE included in the CONDITIONAL HANDOVER CANCEL message were not prepared using the same UE-associated signaling connection, the source NG-RAN node shall ignore those non-associated candidate cells.

8.2.10  Early Status Transfer |R16|

8.2.10.1  General

The purpose of the Early Status Transfer procedure is to transfer the COUNT of the first downlink SDU that the source NG-RAN node forwards to the target NG-RAN node or the COUNT for discarding of already forwarded downlink SDUs for respective DRB during DAPS Handover or Conditional Handover.
The procedure uses UE-associated signalling.

8.2.10.2  Successful Operation

Reproduction of 3GPP TS 38.423, Figure 8.2.10.2-1: Early Status Transfer during DAPS Handover or Conditional Handover, successful operation
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Reproduction of 3GPP TS 38.423, Figure 8.2.10.2-2: Early Status Transfer during Conditional Handover in MR-DC operation, successful operation
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Between source NG-RAN node and target NG-RAN node
The DRBs Subject To Early Status Transfer List IE included in the EARLY STATUS TRANSFER message contains the DRB ID(s) corresponding to the DRB(s) subject to be simultaneously served by the source and the target NG-RAN nodes during DAPS Handover or the DRB(s) transferred during Conditional Handover.
For each DRB in the DRBs Subject To Early Status Transfer List IE, the target NG-RAN node shall use the value of the FIRST DL COUNT Value IE as the COUNT of the first downlink SDU that the source NG-RAN node forwards to the target NG-RAN node.
For each DRB in the DRBs Subject To Early Status Transfer List IE for which the DISCARD DL COUNT Value IE is received in the EARLY STATUS TRANSFER message, the target NG-RAN node does not transmit forwarded downlink SDUs to the UE whose COUNT is less than the provided and discards them if transmission has not been attempted.
Between source S-NG-RAN node and source M-NG-RAN node (MR-DC with 5GC)
The DRBs Subject To Early Status Transfer List IE included in the EARLY STATUS TRANSFER message contains the DRB ID(s) corresponding to the DRB(s) transferred during Conditional Handover.
For each DRB in the DRBs Subject To Early Status Transfer List IE, the source M-NG-RAN node shall forward to the target, the value of the received FIRST DL COUNT Value IE or DISCARD DL COUNT Value IE.
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8.2.10.3  Unsuccessful OperationWord‑p. 37
Not applicable.

8.2.10.4  Abnormal Conditions

If the target NG-RAN node receives this message for a UE for which no prepared DAPS Handover or Conditional Handover exists at the target NG-RAN node, the target NG-RAN node shall ignore the message.

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