8 W1AP procedures

37.4733GPPApplication Protocol (W1AP)Release 17TSW1 interface

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

8.1 List of W1AP Elementary procedures

In the following tables, all EPs are divided into Class 1 and Class 2 EPs:

Table 8.1-1: Class 1 procedures

Elementary Procedure	Initiating Message	Successful Outcome	Unsuccessful Outcome
Elementary Procedure	Initiating Message	Response message	Response message
Reset	RESET	RESET ACKNOWLEDGE
W1 Setup	W1 SETUP REQUEST	W1 SETUP RESPONSE	W1 SETUP FAILURE
ng-eNB-DU Configuration Update	NG-ENB-DU CONFIGURATION UPDATE	NG-ENB-DU CONFIGURATION UPDATE ACKNOWLEDGE	NG-ENB-DU CONFIGURATION UPDATE FAILURE
ng-eNB-CU Configuration Update	NG-ENB-CU CONFIGURATION UPDATE	NG-ENB-CU CONFIGURATION UPDATE ACKNOWLEDGE	NG-ENB-CU CONFIGURATION UPDATE FAILURE
UE Context Setup	UE CONTEXT SETUP REQUEST	UE CONTEXT SETUP RESPONSE	UE CONTEXT SETUP FAILURE
UE Context Release (ng-eNB-CU initiated)	UE CONTEXT RELEASE COMMAND	UE CONTEXT RELEASE COMPLETE
UE Context Modification (ng-eNB-CU initiated)	UE CONTEXT MODIFICATION REQUEST	UE CONTEXT MODIFICATION RESPONSE	UE CONTEXT MODIFICATION FAILURE
UE Context Modification Required (ng-eNB-DU initiated)	UE CONTEXT MODIFICATION REQUIRED	UE CONTEXT MODIFICATION CONFIRM	UE CONTEXT MODIFICATION REFUSE
Write-Replace Warning	WRITE-REPLACE WARNING REQUEST	WRITE-REPLACE WARNING RESPONSE
PWS Cancel	PWS CANCEL REQUEST	PWS CANCEL RESPONSE
NG-ENB-DU RESOURCE COORDINATION	NG-ENB-DU RESOURCE COORDINATION REQUEST	NG-ENB-DU RESOURCE COORDINATION RESPONSE

Table 8.2-2: Class 2 procedures

Elementary Procedure	Message
Error Indication	ERROR INDICATION
UE Context Release Request (ng-eNB-DU initiated)	UE CONTEXT RELEASE REQUEST
Initial UL RRC Message Transfer	INITIAL UL RRC MESSAGE TRANSFER
DL RRC Message Transfer	DL RRC MESSAGE TRANSFER
UL RRC Message Transfer	UL RRC MESSAGE TRANSFER
UE Inactivity Notification	UE INACTIVITY NOTIFICATION
System Information Delivery	SYSTEM INFORMATION DELIVERY COMMAND
Paging	PAGING
Notify	NOTIFY
PWS Restart Indication	PWS RESTART INDICATION
PWS Failure Indication	PWS FAILURE INDICATION
ng-eNB-DU Status Indication	NG-ENB-DU STATUS INDICATION
RRC Delivery Report	RRC DELIVERY REPORT

8.2 Interface Management procedures

8.2.1 Reset

8.2.1.1 General

The purpose of the Reset procedure is to initialise or re-initialise the W1AP UE-related contexts, in the event of a failure in the ng-eNB-CU or ng-eNB-DU. This procedure does not affect the application level configuration data exchanged during, e.g., the W1 Setup procedure.

The procedure uses non-UE associated signalling.

8.2.1.2 Successful Operation

8.2.1.2.1 Reset Procedure Initiated from the ng-eNB-CU

Figure 8.2.1.2.1-1: Reset procedure initiated from the ng-eNB-CU. Successful operation

In the event of a failure at the ng-eNB-CU, which has resulted in the loss of some or all transaction reference information, a RESET message shall be sent to the ng-eNB-DU.

At reception of the RESET message the ng-eNB-DU shall release all allocated resources on W1 and radio resources related to the UE association(s) indicated explicitly or implicitly in the RESET message and remove the indicated UE contexts including W1AP ID.

After the ng-eNB-DU has released all assigned W1 resources and the UE W1AP IDs for all indicated UE associations which can be used for new UE-associated logical W1-connections over the W1 interface, the ng-eNB-DU shall respond with the RESET ACKNOWLEDGE message. The ng-eNB-DU does not need to wait for the release of radio resources to be completed before returning the RESET ACKNOWLEDGE message.

If the RESET message contains the UE-associated logical W1-connection list IE, then:

– The ng-eNB-DU shall use the ng-eNB-CU UE W1AP ID IE and/or the ng-eNB-DU UE W1AP ID IE to explicitly identify the UE association(s) to be reset.

– The ng-eNB-DU shall include in the RESET ACKNOWLEDGE message, for each UE association to be reset, the UE-associated logical W1-connection Item IE in the UE-associated logical W1-connection list IE. The UE-associated logical W1-connection Item IEs shall be in the same order as received in the RESET message and shall include also unknown UE-associated logical W1-connections. Empty UE-associated logical W1-connection Item IEs, received in the RESET message, may be omitted in the RESET ACKNOWLEDGE message.

– If the ng-eNB-CU UE W1AP ID IE is included in the UE-associated logical W1-connection Item IE for a UE association, the ng-eNB-DU shall include the ng-eNB-CU UE W1AP ID IE in the corresponding UE-associated logical W1-connection Item IE in the RESET ACKNOWLEDGE message.

– If the ng-eNB-DU UE W1AP ID IE is included in the UE-associated logical W1-connection Item IE for a UE association, the ng-eNB-DU shall include the ng-eNB-DU UE W1AP ID IE in the corresponding UE-associated logical W1-connection Item IE in the RESET ACKNOWLEDGE message.

Interactions with other procedures:

If the RESET message is received, any other ongoing procedure (except for another Reset procedure) on the same W1 interface related to a UE association, indicated explicitly or implicitly in the RESET message, shall be aborted.

8.2.1.2.2 Reset Procedure Initiated from the ng-eNB-DU

Figure 8.2.1.2.2-1: Reset procedure initiated from the ng-eNB-DU. Successful operation

In the event of a failure at the ng-eNB-DU, which has resulted in the loss of some or all transaction reference information, a RESET message shall be sent to the ng-eNB-CU.

At reception of the RESET message the ng-eNB-CU shall release all allocated resources on W1 related to the UE association(s) indicated explicitly or implicitly in the RESET message and remove the W1AP ID for the indicated UE associations.

After the ng-eNB-CU has released all assigned W1 resources and the UE W1AP IDs for all indicated UE associations which can be used for new UE-associated logical W1-connections over the W1 interface, the ng-eNB-CU shall respond with the RESET ACKNOWLEDGE message.

If the RESET message contains the UE-associated logical W1-connection list IE, then:

– The ng-eNB-CU shall use the ng-eNB-CU UE W1AP ID IE and/or the ng-eNB-DU UE W1AP ID IE to explicitly identify the UE association(s) to be reset.

– The ng-eNB-CU shall in the RESET ACKNOWLEDGE message include, for each UE association to be reset, the UE-associated logical W1-connection Item IE in the UE-associated logical W1-connection list IE. The UE-associated logical W1-connection Item IEs shall be in the same order as received in the RESET message and shall include also unknown UE-associated logical W1-connections. Empty UE-associated logical W1-connection Item IEs, received in the RESET message, may be omitted in the RESET ACKNOWLEDGE message.

– If the ng-eNB-CU UE W1AP ID IE is included in the UE-associated logical W1-connection Item IE for a UE association, the ng-eNB-CU shall include the ng-eNB-CU UE W1AP ID IE in the corresponding UE-associated logical W1-connection Item IE in the RESET ACKNOWLEDGE message.

– If the ng-eNB-DU UE W1AP ID IE is included in a UE-associated logical W1-connection Item IE for a UE association, the ng-eNB-CU shall include the ng-eNB-DU UE W1AP ID IE in the corresponding UE-associated logical W1-connection Item IE in the RESET ACKNOWLEDGE message.

Interactions with other procedures:

8.2.1.3 Abnormal Conditions

Not applicable.

8.2.2 Error Indication

8.2.2.1 General

The Error Indication procedure is initiated by a node in order to report detected errors in one incoming message, provided they cannot be reported by an appropriate failure message.

If the error situation arises due to reception of a message utilising UE associated signalling, then the Error Indication procedure uses UE associated signalling. Otherwise the procedure uses non-UE associated signalling.

8.2.2.2 Successful Operation

Figure 8.2.2.2-1: Error Indication procedure, ng-eNB-CU originated. Successful operation

Figure 8.2.2.2-2: Error Indication procedure, ng-eNB-DU originated. Successful operation

When the conditions defined in clause 10 are fulfilled, the Error Indication procedure is initiated by an ERROR INDICATION message sent from the receiving node.

The ERROR INDICATION message shall contain at least the Cause IE. In case the Error Indication procedure is triggered by utilising UE associated signalling the ng-eNB-CU UE W1AP ID IE and ng-eNB-DU UE W1AP ID IE shall be included in the ERROR INDICATION message. If one or both of the ng-eNB-CU UE W1AP ID IE and the ng-eNB-DU UE W1AP ID IE are not correct, the cause shall be set to appropriate value, e.g., "Unknown or already allocated ng-eNB-CU UE W1AP ID", "Unknown or already allocated ng-eNB-DU UE W1AP ID" or "Unknown or inconsistent pair of UE W1AP ID".

8.2.2.3 Abnormal Conditions

Not applicable.

8.2.3 W1 Setup

8.2.3.1 General

The purpose of the W1 Setup procedure is to exchange application level data needed for the ng-eNB-DU and the ng-eNB-CU to correctly interoperate on the W1 interface. The procedure uses non-UE associated signalling. This procedure shall be the first W1AP procedure triggered for the W1-C interface instance after a TNL association has become operational.

The procedure uses non-UE associated signalling.

This procedure erases any existing application level configuration data in the two nodes and replaces it by the one received. This procedure also re-initialises the W1AP UE-related contexts (if any) and erases all related signalling connections in the two nodes like a Reset procedure would do.

8.2.3.2 Successful Operation

Figure 8.2.3.2-1: W1 Setup procedure: Successful Operation

The ng-eNB-DU initiates the procedure by sending a W1 SETUP REQUEST message including the appropriate data to the ng-eNB-CU. The ng-eNB-CU responds with a W1 SETUP RESPONSE message including the appropriate data.

The exchanged data shall be stored in respective node and used as long as there is an operational TNL association. When this procedure is finished, the W1 interface is operational and other W1 messages may be exchanged.

If the W1 SETUP REQUEST message contains the ng-eNB-DU Served Cells List IE, the ng-eNB-CU shall take into account as specified in TS 38.401 [4].

If ng-eNB-DU System Information IE is included in the W1 SETUP REQUEST message, the ng-eNB-CU shall take into account, and the ng-eNB-CU may include the ng-eNB-CU System Information IE in the W1 SETUP RESPONSE message. The ng-eNB-DU shall include the TAI Slice Support List IE in the W1 SETUP REQUEST message.

The ng-eNB-CU may include the Cells to be Activated List IE in the W1 SETUP RESPONSE message. The Cells to be Activated List IE includes a list of cells that the ng-eNB-CU requests the ng-eNB-DU to activate. The ng-eNB-DU shall activate the cells included in the Cells to be Activated List IE and reconfigure the physical cell identity for cells for which the E-UTRAN PCI IE is included.

If the RAN Area Code IE is included in the W1 SETUP REQUEST message, the ng-eNB-CU may use it according to TS 38.300 [6].

The ng-eNB-CU may include Available PLMN List IE, and optionally also Extended Available PLMN List IE, if the available PLMN(s) are different from what ng-eNB-DU has provided in W1 SETUP REQUEST message, ng-eNB-DU shall take this into account and only broadcast the PLMN(s) included in the received Available PLMN list(s).

8.2.3.3 Unsuccessful Operation

Figure 8.2.3.3-1: W1 Setup procedure: Unsuccessful Operation

If the ng-eNB-CU cannot accept the setup, it should respond with a W1 SETUP FAILURE and appropriate cause value.

8.2.3.4 Abnormal Conditions

Not applicable.

8.2.4 ng-eNB-DU Configuration Update

8.2.4.1 General

The purpose of the ng-eNB-DU Configuration Update procedure is to update application level configuration data needed for the ng-eNB-DU and the ng-eNB-CU to interoperate correctly on the W1 interface. This procedure does not affect existing UE-related contexts, if any. The procedure uses non-UE associated signalling.

8.2.4.2 Successful Operation

Figure 8.2.4.2-1: ng-eNB-DU Configuration Update procedure: Successful Operation

The ng-eNB-DU initiates the procedure by sending an ng-eNB-DU CONFIGURATION UPDATE message to the ng-eNB-CU including an appropriate set of updated configuration data that it has just taken into operational use. The ng-eNB-CU responds with NG-ENB-DU CONFIGURATION UPDATE ACKNOWLEDGE message to acknowledge that it successfully updated the configuration data. If an information element is not included in the NG-ENB-DU CONFIGURATION UPDATE message, the ng-eNB-CU shall interpret that the corresponding configuration data is not changed and shall continue to operate the W1-C interface with the existing related configuration data.

The updated configuration data shall be stored in both nodes and used as long as there is an operational TNL association or until any further update is performed.

If Served Cells To Add Item IE is contained in the NG-ENB-DU CONFIGURATION UPDATE message, the ng-eNB-CU shall add cell information according to the information in the Served Cell Information IE. If the ng-eNB-DU System Information IE is contained in the NG-ENB-DU CONFIGURATION UPDATE message, the ng-eNB-CU shall store and replace any previously provided system info if any, and may include the ng-eNB-CU System Information IE in the NG-ENB-DU CONFIGURATION UPDATE ACKNOWLEDGE message. The SIB type to Be Updated List IE shall contain the full list of SIBs to be broadcast.

If Served Cells To Modify Item IE is contained in the NG-ENB-DU CONFIGURATION UPDATE message, the ng-eNB-CU shall modify information of cell indicated by Old E-UTRAN CGI IE according to the information in the Served Cell Information IE and overwrite the served cell information for the affected served cell. Further, if the ng-eNB-DU System Information IE is present the ng-eNB-CU shall store and replace any previous information received.

If Served Cells To Delete Item IE is contained in the NG-ENB-DU CONFIGURATION UPDATE message, the ng-eNB-CU shall delete information of cell indicated by Old E-UTRAN CGI IE.

If Cells Status Item IE is contained in the NG-ENB-DU CONFIGURATION UPDATE message, the ng-eNB-CU shall update the information about the cells, as described in TS 38.401 [4].

If Cells to be Activated List Item IE is contained in the NG-ENB-DU CONFIGURATION UPDATE ACKNOWLEDGE message, the ng-eNB-DU shall activate the cell indicated by E-UTRAN CGI IE and reconfigure the physical cell identity for cells for which the E-UTRAN PCI IE is included.

If Cells to be Activated List Item IE is contained in the NG-ENB-DU CONFIGURATION UPDATE ACKNOWLEDGE message and the indicated cells are already activated, the ng-eNB-DU shall update the cell information received in Cells to be Activated List Item IE.

If Cells to be Deactivated List Item IE is contained in the NG-ENB-DU CONFIGURATION UPDATE ACKNOWLEDGE message, the ng-eNB-DU shall deactivate all the cells with E-UTRAN CGI listed in the IE.

If the RAN Area Code IE in contained in the NG-ENB-DU CONFIGURATION UPDATE message, the ng-eNB-CU shall store and replace any previously provided RAN Area Code IE by the received RAN Area Code IE.

If Available PLMN List IE, and optionally also Extended Available PLMN List IE, is contained in NG-ENB-DU CONFIGURATION UPDATE ACKNOWLEDGE message, the ng-eNB-DU shall overwrite the whole available PLMN list and update the corresponding system information.

8.2.4.3 Unsuccessful Operation

Figure 8.2.4.3-1: ng-eNB-DU Configuration Update procedure: Unsuccessful Operation

If the ng-eNB-CU cannot accept the update, it shall respond with an ng-eNB-DU CONFIGURATION UPDATE FAILURE message and appropriate cause value.

8.2.4.4 Abnormal Conditions

Not applicable.

8.2.5 ng-eNB-CU Configuration Update

8.2.5.1 General

The purpose of the ng-eNB-CU Configuration Update procedure is to update application level configuration data needed for the ng-eNB-DU and ng-eNB-CU to interoperate correctly on the W1 interface. This procedure does not affect existing UE-related contexts, if any. The procedure uses non-UE associated signalling.

8.2.5.2 Successful Operation

Figure 8.2.5.2-1: ng-eNB-CU Configuration Update procedure: Successful Operation

The ng-eNB-CU initiates the procedure by sending an ng-eNB-CU CONFIGURATION UPDATE message including the appropriate updated configuration data to the ng-eNB-DU. The ng-eNB-DU responds with an ng-eNB-CU CONFIGURATION UPDATE ACKNOWLEDGE message to acknowledge that it successfully updated the configuration data. If an information element is not included in the NG-ENB-CU CONFIGURATION UPDATE message, the ng-eNB-DU shall interpret that the corresponding configuration data is not changed and shall continue to operate the W1-C interface with the existing related configuration data.

The updated configuration data shall be stored in the respective node and used as long as there is an operational TNL association or until any further update is performed.

If Cells to be Activated List Item IE is contained in the NG-ENB-CU CONFIGURATION UPDATE message, the ng-eNB-DU shall activate the cell indicated by E-UTRAN CGI IE and reconfigure the physical cell identity for which the E-UTRAN PCI IE is included.

If Cells to be Deactivated List Item IE is contained in the NG-ENB-CU CONFIGURATION UPDATE message, the ng-eNB-DU shall deactivate the cell indicated by E-UTRAN CGI IE.

If Cells to be Activated List Item IE is contained in the NG-ENB-CU CONFIGURATION UPDATE message and the indicated cells are already activated, the ng-eNB-DU shall update the cell information received in Cells to be Activated List Item IE.

If the ng-eNB-CU System Information IE is contained in the NG-ENB-CU CONFIGURATION UPDATE message, the ng-eNB-DU shall store and replace any previously provided system info if any. The SIB type to Be Updated List IE shall contain the full list of SIBs to be broadcast.

If Available PLMN List IE, and optionally also Extended Available PLMN List IE, is contained in NG-ENB-CU CONFIGURATION UPDATE message, the ng-eNB-DU shall overwrite the whole available PLMN list and update the corresponding system information.

If Cells Failed to be Activated Item IE is contained in the NG-ENB-CU CONFIGURATION UPDATE ACKNOWLEDGE message, the ng-eNB-CU shall consider that the indicated cells are out-of-service as defined in TS 38.401 [4].

8.2.5.3 Unsuccessful Operation

Figure 8.2.5.3-1: ng-eNB-CU Configuration Update: Unsuccessful Operation

If the ng-eNB-DU cannot accept the update, it shall respond with an ng-eNB-CU CONFIGURATION UPDATE FAILURE message and appropriate cause value.

8.2.5.4 Abnormal Conditions

Not applicable.

8.2.6 ng-eNB-DU Resource Coordination

8.2.6.1 General

The purpose of the ng-eNB-DU Resource Coordination procedure is to enable coordination of radio resource allocation between an ng-eNB-CU and an ng-eNB-DU for the purpose of spectrum sharing between E-UTRA and NR. This procedure is to be used only for the purpose of spectrum sharing between E-UTRA and NR.

The procedure uses non-UE-associated signalling.

8.2.6.2 Successful Operation

Figure 8.2.6.2-1: ng-eNB-DU Resource Coordination, successful operation

An ng-eNB-CU initiates the procedure by sending the NG-ENB-DU RESOURCE COORDINATION REQUEST message to an ng-eNB-DU over the W1 interface.

The ng-eNB-DU extracts the E-UTRA – NR Cell Resource Coordination Request Container IE and it replies by sending the NG-ENB-DU RESOURCE COORDINATION RESPONSE message.

In case of NR-initiated ng-eNB-DU Resource Coordination procedure, the Ignore Coordination Request Container IE shall be present and set to "yes" and the E-UTRA – NR Cell Resource Coordination Request Container IE in the NG-ENB-DU RESOURCE COORDINATION REQUEST message shall be ignored.

8.2.7 ng-eNB-DU Status Indication

8.2.7.1 General

The purpose of the ng-eNB-DU Status Indication procedure is informing the ng-eNB-CU that the ng-eNB-DU is overloaded so that overload reduction actions can be applied. The procedure uses non-UE associated signalling.

8.2.7.2 Successful Operation

Figure 8.2.7.2-1: ng-eNB-DU Status Indication procedure

If the ng-eNB-DU Overload Information IE in the NG-ENB-DU STATUS INDICATION message indicates that the ng-eNB-DU is overloaded, the ng-eNB-CU shall apply overload reduction actions until informed, with a new NG-ENB-DU STATUS INDICATION message, that the overload situation has ceased.

The detailed overload reduction policy is up to ng-eNB-CU implementation.

8.2.7.3 Abnormal Conditions

Void.

8.3 UE Context Management procedures

8.3.1 UE Context Setup

8.3.1.1 General

The purpose of the UE Context Setup procedure is to establish the UE Context including, among others, SRB, and DRB configuration. The procedure uses UE-associated signalling.

8.3.1.2 Successful Operation

Figure 8.3.1.2-1: UE Context Setup Request procedure: Successful Operation

The ng-eNB-CU initiates the procedure by sending UE CONTEXT SETUP REQUEST message to the ng-eNB-DU. If the ng-eNB-DU succeeds to establish the UE context, it replies to the ng-eNB-CU with UE CONTEXT SETUP RESPONSE. If no UE-associated logical W1-connection exists, the UE-associated logical W1-connection shall be established as part of the procedure.

If the SCell To Be Setup List IE is included in the UE CONTEXT SETUP REQUEST message, the ng-eNB-DU shall act as specified in TS 38.401 [4].

If the DRX Cycle IE is contained in the UE CONTEXT SETUP REQUEST message, the ng-eNB-DU shall use the provided value from the ng-eNB-CU.

If the SRB To Be Setup List IE is contained in the UE CONTEXT SETUP REQUEST message, the ng-eNB-DU shall act as specified in TS 38.401 [4].

If the DRB To Be Setup List IE is contained in the UE CONTEXT SETUP REQUEST message, the ng-eNB-DU shall act as specified in TS 38.401 [4].

The ng-eNB-DU shall report to the ng-eNB-CU, in the UE CONTEXT SETUP RESPONSE message, the result for all the requested DRBs and SRBs in the following way:

– A list of DRBs which are successfully established shall be included in the DRB Setup List IE;

– A list of DRBs which failed to be established shall be included in the DRB Failed to Setup List IE;

– A list of SRBs which failed to be established shall be included in the SRB Failed to Setup List IE.

When the ng-eNB-DU reports the unsuccessful establishment of a DRB or SRB, the cause value should be precise enough to enable the ng-eNB-CU to know the reason for the unsuccessful establishment.

The ng-eNB-CU shall include in the UE CONTEXT SETUP REQUEST the DRB Information IE.

If the SCell Failed To Setup List IE is contained in the UE CONTEXT SETUP RESPONSE message, the ng-eNB-CU shall regard the corresponding SCell(s) failed to be established with an appropriate cause value for each SCell failed to setup.

If the C-RNTI IE is included in the UE CONTEXT SETUP RESPONSE, the ng-eNB-CU shall consider that the C-RNTI has been allocated by the ng-eNB-DU for this UE context.

The UE Context Setup Procedure is not used to configure SRB0.

If the UE CONTEXT SETUP REQUEST message contains the RRC-Container IE, the ng-eNB-DU shall send the corresponding RRC message to the UE via SRB1.

If the UL PDU Session Aggregate Maximum Bit Rate IE is included in the QoS Flow Level QoS Parameters IE contained in the UE CONTEXT SETUP REQUEST message, the ng-eNB-DU shall store the received UL PDU Session Aggregate Maximum Bit Rate and use it when enforcing uplink traffic policing for non-GBR Bearers for the concerned UE as specified in TS 23.501 [8].

The ng-eNB-DU shall store the received ng-eNB-DU UE Aggregate Maximum Bit Rate Uplink and use it for non-GBR Bearers for the concerned UE.

If the PDCP Terminating Node DL Transport Layer Address IE is included in the QoS Flow Level QoS Parameters IE contained in the UE CONTEXT SETUP REQUEST message, then the ng-eNB-DU shall, if supported, use it as part of its ACL functionality configuration actions, if such ACL functionality is deployed.

8.3.1.3 Unsuccessful Operation

Figure 8.3.1.3-1: UE Context Setup Request procedure: unsuccessful Operation

If the ng-eNB-DU is not able to establish a W1 UE context, or cannot even establish one bearer it shall consider the procedure as failed and reply with the UE CONTEXT SETUP FAILURE message.

If the ng-eNB-DU is not able to accept the SpCell ID IE in UE CONTEXT SETUP REQUEST message, it shall reply with the UE CONTEXT SETUP FAILURE message with an appropriate cause value. Further, if the Candidate SpCell List IE is included in the UE CONTEXT SETUP REQUEST message and the ng-eNB-DU is not able to accept the SpCell ID IE, the ng-eNB-DU shall, if supported, include the Potential SpCell List IE in the UE CONTEXT SETUP FAILURE message and the ng-eNB-CU should take this into account for selection of an opportune SpCell. The ng-eNB-DU shall include the cells in the Potential SpCell List IE in a priority order, where the first cell in the list is the one most desired and the last one is the one least desired (e.g., based on load conditions). If the Potential SpCell List IE is present but no Potential SpCell Item IE is present, the ng-eNB-CU should assume that none of the cells in the Candidate SpCell List IE are acceptable for the ng-eNB-DU.

8.3.1.4 Abnormal Conditions

Not applicable.

8.3.2 UE Context Release Request (ng-eNB-DU initiated)

8.3.2.1 General

The purpose of the UE Context Release Request procedure is to enable the ng-eNB-DU to request the ng-eNB-CU to release the UE-associated logical W1-connection. The procedure uses UE-associated signalling.

8.3.2.2 Successful Operation

Figure 8.3.2.2-1: UE Context Release (ng-eNB-DU initiated) procedure. Successful operation

The ng-eNB-DU controlling a UE-associated logical W1-connection initiates the procedure by generating a UE CONTEXT RELEASE REQUEST message towards the affected ng-eNB-CU node.

The UE CONTEXT RELEASE REQUEST message shall indicate the appropriate cause value.

Interactions with UE Context Release procedure:

The UE Context Release procedure may be initiated upon reception of a UE CONTEXT RELEASE REQUEST message.

8.3.2.3 Abnormal Conditions

Not applicable.

8.3.3 UE Context Release (ng-eNB-CU initiated)

8.3.3.1 General

The purpose of the UE Context Release procedure is to enable the ng-eNB-CU to order the release of the UE-associated logical connection. The procedure uses UE-associated signalling.

8.3.3.2 Successful Operation

Figure 8.3.3.2-1: UE Context Release (ng-eNB-CU initiated) procedure. Successful operation

The ng-eNB-CU initiates the procedure by sending the UE CONTEXT RELEASE COMMAND message to the ng-eNB-DU.

Upon reception of the UE CONTEXT RELEASE COMMAND message, the ng-eNB-DU shall release all related signalling and user data transport resources and reply with the UE CONTEXT RELEASE COMPLETE message.

If the old ng-eNB-DU UE W1AP ID IE is included in the UE CONTEXT RELEASE COMMAND message, the ng-eNB-DU shall additionally release the UE context associated with the old ng-eNB-DU UE W1AP ID.

Interactions with UE Context Setup procedure:

The UE Context Release procedure may be performed before the UE Context Setup procedure to release an existing UE-associated logical W1-connection and related resources in the ng-eNB-DU, e.g. when ng-eNB-CU rejects UE access it shall trigger UE Context Release procedure with the cause value of UE rejection.

8.3.3.4 Abnormal Conditions

Not applicable.

8.3.4 UE Context Modification (ng-eNB-CU initiated)

8.3.4.1 General

The purpose of the UE Context Modification procedure is to modify the established UE Context, e.g., establishing, modifying and releasing radio resources. This procedure is also used to command the ng-eNB-DU to stop data transmission for the UE for mobility (see TS 38.401 [4]). The procedure uses UE-associated signalling.

8.3.4.2 Successful Operation

Figure 8.3.4.2-1: UE Context Modification procedure. Successful operation

The UE CONTEXT MODIFICATION REQUEST message is initiated by the ng-eNB-CU.

Upon reception of the UE CONTEXT MODIFICATION REQUEST message, the ng-eNB-DU shall perform the modifications, and if successful reports the update in the UE CONTEXT MODIFICATION RESPONSE message.

If the SpCell ID IE is included in the UE CONTEXT MODIFICATION REQUEST message, the ng-eNB-DU shall replace any previously received value and regard it as a reconfiguration with sync as defined in TS 36.331 [2]. If the ServCellIndex IE is included in the UE CONTEXT MODIFICATION REQUEST message, the ng-eNB-DU shall take this into account for the indicated SpCell.

If the SCell To Be Setup List IE or SCell To Be Removed List IE is included in the UE CONTEXT MODIFICATION REQUEST message, the ng-eNB-DU shall act as specified in TS 38.401 [4]. If the SCell To Be Setup List IE is included in the UE CONTEXT MODIFICATION REQUEST message and the indicated SCell(s) are already setup, the ng-eNB-DU shall replace any previously received value.

If the DRX Cycle IE is contained in the UE CONTEXT MODIFICATION REQUEST message, the ng-eNB-DU shall use the provided value from the ng-eNB-CU.

If the SRB To Be Setup List IE is contained in the UE CONTEXT MODIFICATION REQUEST message, the ng-eNB-DU shall act as specified in the TS 38.401 [4], and replace any previously received value.

If the DRB To Be Setup List IE is contained in the UE CONTEXT MODIFICATION REQUEST message, the ng-eNB-DU shall act as specified in the TS 38.401 [4].

If the UE CONTEXT MODIFICATION REQUEST message contains the RRC-Container IE, the ng-eNB-DU shall send the corresponding RRC message to the UE.

The ng-eNB-CU shall include the DRB Information IE in the UE CONTEXT MODIFICATION REQUEST message.

The ng-eNB-DU shall report to the ng-eNB-CU, in the UE CONTEXT MODIFICATION RESPONSE message, the result for all the requested or modified DRBs and SRBs in the following way:

– A list of DRBs which are successfully established shall be included in the DRB Setup List IE;

– A list of DRBs which failed to be established shall be included in the DRB Failed to be Setup List IE;

– A list of DRBs which are successfully modified shall be included in the DRB Modified List IE;

– A list of DRBs which failed to be modified shall be included in the DRB Failed to be Modified List IE;

– A list of SRBs which failed to be established shall be included in the SRB Failed to be Setup List IE.

When the ng-eNB-DU reports the unsuccessful establishment of a DRB or SRB, the cause value should be precise enough to enable the ng-eNB-CU to know the reason for the unsuccessful establishment.

If the SCell Failed To Setup List IE is contained in the UE CONTEXT MODIFICATION RESPONSE message, the ng-eNB-CU shall regard the corresponding SCell(s) failed to be established with an appropriate cause value for each SCell failed to setup.

If the C-RNTI IE is included in the UE CONTEXT MODIFICATION RESPONSE, the ng-eNB-CU shall consider that the C-RNTI has been allocated by the ng-eNB-DU for this UE context.

The UE Context Modify Procedure is not used to configure SRB0.

If the UL PDU Session Aggregate Maximum Bit Rate IE is included in the QoS Flow Level QoS Parameters IE contained in the UE CONTEXT MODIFICATION REQUEST message, the ng-eNB-DU shall replace the received UL PDU Session Aggregate Maximum Bit Rate and use it as specified in TS 23.501 [8].

If the ng-eNB-DU UE Aggregate Maximum Bit Rate Uplink IE is included in the UE CONTEXT MODIFICATION REQUEST message, the ng-eNB-DU shall:

– replace the previously provided ng-eNB-DU UE Aggregate Maximum Bit Rate Uplink with the new received ng-eNB-DU UE Aggregate Maximum Bit Rate Uplink;

– use the received ng-eNB-DU UE Aggregate Maximum Bit Rate Uplink for non-GBR Bearers for the concerned UE.

The UL PDU Session Aggregate Maximum Bit Rate IE shall be sent if DRB to Be Setup List IE is included and the ng-eNB-CU has not previously sent it. The ng-eNB-DU shall store and use the received ng-eNB-DU UE Aggregate Maximum Bit Rate Uplink.

For MN in NGEN-DC, if the SCG Indicator IE is included in the UE CONTEXT MODIFICATION REQUEST message and it is set to “released”, the ng-eNB-DU shall, if applicable, consider the SCG is removed.

If the Source Transport Layer Address IE is included in the QoS Flow Level QoS Parameters IE contained in the UE CONTEXT MODIFICATION REQUEST message, then the ng-eNB-DU shall, if supported, use it as part of its ACL functionality configuration actions, if such ACL functionality is deployed.

8.3.4.3 Unsuccessful Operation

Figure 8.3.4.3-1: UE Context Modification procedure. Unsuccessful operation

In case none of the requested modifications of the UE context can be successfully performed, the ng-eNB-DU shall respond with the UE CONTEXT MODIFICATION FAILURE message with an appropriate cause value.

If the ng-eNB-DU is not able to accept the SpCell ID IE in UE CONTEXT MODIFICATION REQUEST message, it shall reply with the UE CONTEXT MODIFICATION FAILURE message.

8.3.4.4 Abnormal Conditions

Not applicable.

8.3.5 UE Context Modification Required (ng-eNB-DU initiated)

8.3.5.1 General

The purpose of the UE Context Modification Required procedure is to modify the established UE Context, e.g., modifying and releasing radio bearer resources. The procedure uses UE-associated signalling.

8.3.5.2 Successful Operation

Figure 8.3.5.2-1: UE Context Modification Required procedure. Successful operation

The W1AP UE CONTEXT MODIFICATION REQUIRED message is initiated by the ng-eNB-DU.

The ng-eNB-CU reports the successful update of the UE context in the UE CONTEXT MODIFICATION CONFIRM message.

8.3.5.3 Unsuccessful Operation

Figure 8.3.5.2A-1: UE Context Modification Required procedure. Unsuccessful operation.

In case none of the requested modifications of the UE context can be successfully performed, the ng-eNB-CU shall respond with the UE CONTEXT MODIFICATION REFUSE message with an appropriate cause value.

8.3.5.4 Abnormal Conditions

Not applicable.

8.3.6 UE Inactivity Notification

8.3.6.1 General

This procedure is initiated by the ng-eNB-DU to indicate the UE activity event.

The procedure uses UE-associated signalling.

8.3.6.2 Successful Operation

Figure 8.3.6.2-1: UE Inactivity Notification procedure.

The ng-eNB-DU initiates the procedure by sending the UE INACTIVITY NOTIFICATION message to the ng-eNB-CU.

If the DRB ID IE is included in the DRB Activity Item IE in the UE INACTIVITY NOTIFICATION message, the DRB Activity IE shall also be included

8.3.6.3 Abnormal Conditions

Not applicable.

8.3.7 Notify

8.3.7.1 General

The purpose of the Notify procedure is to enable the ng-eNB-DU to inform the ng-eNB-CU that the QoS of an already established GBR DRB cannot by fulfilled any longer or that it can be fulfilled again. The procedure uses UE-associated signalling.

8.3.7.2 Successful Operation

Figure 8.3.7.2-1: Notify procedure. Successful operation.

The ng-eNB-DU initiates the procedure by sending a NOTIFY message.

The NOTIFY message shall contain the list of the GBR DRBs associated with notification control for which the QoS is not fulfilled anymore or for which the QoS is fulfilled again by the ng-eNB-DU.

Upon reception of the NOTIFY message, the ng-eNB-CU may identify which are the affected PDU sessions and QoS flows. The ng-eNB-CU may inform the 5GC that the QoS for these PDU sessions or QoS flows is not fulfilled any longer or it is fulfilled again.

8.3.7.3 Abnormal Conditions

Not applicable.

8.4 RRC Message Transfer procedures

8.4.1 Initial UL RRC Message Transfer

8.4.1.1 General

The purpose of the Initial UL RRC Message Transfer procedure is to transfer the initial RRC message to the ng-eNB-CU. The procedure uses non-UE-associated signaling.

8.4.1.2 Successful operation

Figure 8.4.1.2-1: Initial UL RRC Message Transfer procedure

The establishment of the UE-associated logical W1-connection shall be initiated as part of the procedure.

8.4.1.3 Abnormal Conditions

Not applicable.

8.4.2 DL RRC Message Transfer

8.4.2.1 General

The purpose of the DL RRC Message Transfer procedure is to transfer an RRC message. The procedure uses UE-associated signalling.

8.4.2.2 Successful operation

Figure 8.4.2.2-1: DL RRC Message Transfer procedure

If a UE-associated logical W1-connection exists, the DL RRC MESSAGE TRANSFER message shall contain the ng-eNB-DU UE W1AP ID IE, which should be used by ng-eNB-DU to lookup the stored UE context. If no UE-associated logical W1-connection exists, the UE-associated logical W1-connection shall be established at reception of the DL RRC MESSAGE TRANSFER message.

The DL RRC MESSAGE TRANSFER message shall include, if available, the old ng-eNB-DU UE W1AP ID IE so that the ng-eNB-DU can retrieve the existing UE context in RRC connection reestablishment procedure, as defined in TS 38.401 [4].

If the ng-eNB-DU identifies the UE-associated logical W1-connection by the ng-eNB-DU UE W1AP ID IE in the DL RRC MESSAGE TRANSFER message and the old ng-eNB-DU UE W1AP ID IE is included, it shall release the old ng-eNB-DU UE W1AP ID and the related configurations associated with the old ng-eNB-DU UE W1AP ID.

8.4.2.3 Abnormal Conditions

Not applicable.

8.4.3 UL RRC Message Transfer

8.4.3.1 General

The purpose of the UL RRC Message Transfer procedure is to transfer an uplink RRC message as UL RLC SDU to the ng-eNB-CU. The procedure uses UE-associated signalling.

8.4.3.2 Successful operation

Figure 8.4.3.2-1: UL RRC Message Transfer procedure

When the ng-eNB-DU has received from the radio interface an RRC message to which a UE-associated logical W1-connection for the UE exists, the ng-eNB-DU shall send the UL RRC MESSAGE TRANSFER message to the ng-eNB-CU including the RRC message as a RRC-Container IE.

8.4.3.3 Abnormal Conditions

Not applicable.

8.4.4 RRC Delivery Report

Void

8.5 Warning Message Transmission Procedures

8.5.1 Write-Replace Warning

8.5.1.1 General

The purpose of Write-Replace Warning procedure is to start or overwrite the broadcasting of warning messages. The procedure uses non UE-associated signalling.

8.5.1.2 Successful Operation

Figure 8.5.1.2-1: Write-Replace Warning procedure: successful operation

The ng-eNB-CU initiates the procedure by sending a WRITE-REPLACE WARNING REQUEST message to the ng-eNB-DU.

Upon receipt of the WRITE-REPLACE WARNING REQUEST message, the ng-eNB-DU shall prioritise its resources to process the warning message.

The ng-eNB-DU acknowledges the WRITE-REPLACE WARNING REQUEST message by sending a WRITE-REPLACE WARNING RESPONSE message to the ng-eNB-CU.

If the Notification Information IE is included in the PWS System Information IE in the WRITE-REPLACE WARNING REQUEST message, the ng-eNB-DU shall use this information to avoid that duplications trigger new broadcast or replace existing broadcast.

If the ng-eNB-DU receives a WRITE-REPLACE WARNING REQUEST message with the Notification Information IE in the PWS System Information IE which are different from those of ongoing broadcast warning messages, and if the SIB Type IE is set to "12", the ng-eNB-DU shall broadcast the received warning message concurrently with other ongoing messages.

If the ng-eNB-DU receives a WRITE-REPLACE WARNING REQUEST message with the Notification Information IE in the PWS System Information IE which are different from those of ongoing broadcast warning messages, and if the SIB Type IE is set to the value other than "12", the ng-eNB-DU shall use the newly received one to replace the ongoing broadcast warning message with the same value of SIB Type IE.

If the SIB Type IE in the PWS System Information IE in the WRITE-REPLACE WARNING REQUEST message is set to "12" and if a value "0" is received in the Number of Broadcast Requested IE and if the Repetition Period IE is different from "0", the ng-eNB-DU shall broadcast the received warning message indefinitely.

If Additional SIB Message List IE is included in PWS System Information IE, the ng-eNB-DU shall store all SIB message(s) in PWS System Information IE, and consider that the first segment of public warning message is included in SIB message IE, and the remaining segments are listed in Additional SIB Message List IE in segmentation sequence order.

8.5.1.3 Unsuccessful Operation

Not applicable.

8.5.1.4 Abnormal Conditions

Not applicable.

8.5.2 PWS Cancel

8.5.2.1 General

The purpose of the PWS Cancel procedure is to cancel an already ongoing broadcast of a warning message. The procedure uses non UE-associated signalling.

8.5.2.2 Successful Operation

Figure 8.5.2.2-1: PWS Cancel procedure: successful operation

The ng-eNB-CU initiates the procedure by sending a PWS CANCEL REQUEST message to the ng-eNB-DU.

The ng-eNB-DU shall acknowledge the PWS CANCEL REQUEST message by sending the PWS CANCEL RESPONSE message.

If the Cancel-All Warning Messages Indicator IE is present in the PWS CANCEL REQUEST message, then the ng-eNB-DU shall stop broadcasting and discard all warning messages for the area as indicated in the Cell Broadcast To Be Cancelled List IE or in all the cells of the ng-eNB-DU if the Cell Broadcast To Be Cancelled List IE is not included. The ng-eNB-DU shall acknowledge the PWS CANCEL REQUEST message by sending the PWS CANCEL RESPONSE message, and shall, if there is area to report where an ongoing broadcast was stopped successfully, include the Cell Broadcast Cancelled List IE with the Number of Broadcasts IE set to 0.

If the Cell Broadcast To Be Cancelled List IE is not included in the PWS CANCEL REQUEST message, the ng-eNB-DU shall stop broadcasting and discard the warning message identified by the Message Identifier IE and the Serial Number IE in the Notification Information IE in all of the cells in the ng-eNB-DU.

If an area included in the Cell Broadcast To Be Cancelled List IE in the PWS CANCEL REQUEST message does not appear in the Cell Broadcast Cancelled List IE in the PWS CANCEL RESPONSE, the ng-eNB-CU shall consider that the ng-eNB-DU had no ongoing broadcast to stop for the public warning message identified, if present, by the Notification Information IE in that area.

If the Cell Broadcast Cancelled List IE is not included in the PWS CANCEL RESPONSE message, the ng-eNB-CU shall consider that the ng-eNB-DU had no ongoing broadcast to stop for the public warning message identified by the Notification Information IE.

8.5.2.3 Unsuccessful Operation

Not applicable.

8.5.2.4 Abnormal Conditions

Not applicable.

8.5.3 PWS Restart Indication

8.5.3.1 General

The purpose of PWS Restart Indication procedure is to inform the ng-eNB-CU that PWS information for some or all cells of the ng-eNB-DU are available for reloading from the CBC if needed. The procedure uses non UE-associated signalling.

8.5.3.2 Successful Operation

Figure 8.5.3.2-1: PWS restart indication

The ng-eNB-DU initiates the procedure by sending a PWS RESTART INDICATION message to the ng-eNB-CU.

8.5.3.3 Abnormal Conditions

Not applicable.

8.5.4 PWS Failure Indication

8.5.4.1 General

The purpose of the PWS Failure Indication procedure is to inform the ng-eNB-CU that ongoing PWS operation for one or more cells of the ng-eNB-DU has failed. The procedure uses non UE-associated signalling.

8.5.4.2 Successful Operation

Figure 8.5.4.2-1: PWS failure indication

The ng-eNB-DU initiates the procedure by sending a PWS FAILURE INDICATION message to the ng-eNB-CU.

8.5.4.3 Abnormal Conditions

Not applicable.

8.6 Paging procedures

8.6.1 Paging

8.6.1.1 General

The purpose of the Paging procedure is used to provide the paging information to enable the ng-eNB-DU to page a UE. The procedure uses non-UE associated signalling.

8.6.1.2 Successful Operation

Figure 8.6.1.2-1: Paging procedure. Successful operation.

The ng-eNB-CU initiates the procedure by sending a PAGING message.

The Paging DRX IE may be included in the PAGING message, and if present the ng-eNB-DU may use it to determine the final paging cycle for the UE.

At the reception of the PAGING message, the ng-eNB-DU shall perform paging of the UE in cells which belong to cells as indicated in the Paging Cell List IE.

The Paging Origin IE may be included in the PAGING message, and if present the ng-eNB-DU shall transfer it to the UE.

8.6.1.3 Abnormal Conditions

Not applicable.