8.7.2 EN-DC Configuration Update

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

8.7.2.1 General

The purpose of the EN-DC Configuration Update procedure is to update application level configuration data needed for eNB and en-gNB to interoperate correctly over the X2 interface.

NOTE: Update of application level configuration data also applies between eNB and en-gNB in case the SN (i.e. the en-gNB) does not broadcast system information other than for radio frame timing and SFN, as specified in the TS 37.340 [32]. How to use this information when this option is used is not explicitly specified.

The procedure uses non UE-associated signalling.

8.7.2.2 Successful Operation

Figure 8.7.2.2-1: eNB Initiated EN-DC Configuration Update, successful operation

Figure 8.7.2.2-2: en-gNB Initiated EN-DC Configuration Update, successful operation

If case of network sharing with multiple cell ID broadcast with shared X2-C signalling transport, as specified in TS 36.300 [15], the EN-DC CONFIGURATION UPDATE message and the EN-DC CONFIGURATION UPDATE ACKNOWLEDGE message shall include the Interface Instance Indication IE to identify the corresponding interface instance.

If the SFN Offset IE is included in the EN-DC CONFIGURATION UPDATE or EN-DC CONFIGURATION UPDATE ACKNOWLEDGE message, the receiving node shall, if supported, use this information to update the SFN0 time offset of the reported cell.

eNB initiated EN-DC Configuration Update:

An eNB initiates the procedure by sending an EN-DC CONFIGURATION UPDATE message to a peer en-gNB.

After successful update of requested information, en-gNB shall reply with the EN-DC CONFIGURATION UPDATE ACKNOWLEDGE message to inform the initiating eNB that the requested update of application data was performed successfully.

If the Cell Assistance Information IE is present, the en-gNB shall, if supported, use it to generate the List of Served NR Cells IE and include the list in the EN-DC CONFIGURATION UPDATE ACKNOWLEDGE message.

If the EN-DC CONFIGURATION UPDATE REQUEST message contains the Protected E-UTRA Resource Indication IE, the receiving en-gNB should take this into account for cell-level resource coordination with the eNB. The en-gNB shall consider the received Protected E-UTRA Resource Indication IE content valid until reception of a new update of the IE for the same eNB. The protected resource pattern indicated in the Protected E-UTRA Resource Indication IE is not valid in subframes indicated by the Reserved Subframes IE, as well as in the non-control region of the MBSFN subframes i.e. it is valid only in the control region therein. The size of the control region of MBSFN subframes is indicated in the Protected E-UTRA Resource Indication IE.

The eNB may initiate a further EN-DC Configuration Update procedure only after a previous EN-DC Configuration Update procedure has been completed.

If Supplementary Uplink is configured at the en-gNB, the en-gNB shall include in the EN-DC CONFIGURATION UPDATE ACKNOWLEDGE message the SUL Information IE and the Supported SUL band List IE for each cell added in the Served NR Cells To Add IE and in the Served NR Cells To Modify IE.

If the EN-DC CONFIGURATION UPDATE message contains the TNL Transport Layer Address info IE, the receiving en-gNB shall, if supported, take this into account for IPSEC tunnel establishment.

If the EN-DC CONFIGURATION UPDATE ACKNOWLEDGE message contains the TNL Transport Layer Address info IE, the receiving eNB shall, if supported, take this into account for IPSEC tunnel establishment.

If the NR Cell PRACH Configuration IE is included in the Served NR Cell Information IE contained in the EN-DC CONFIGURATION UPDATE ACKNOWLEDGE message, the eNB may update the information.

If the CSI-RS Transmission Indication IE is contained in the EN-DC CONFIGURATION UPDATE message, the en-gNB may use this information for neighbour NR cell’s CSI-RS measurement.

If the Additional Measurement Timing Configuration List IE is contained in the EN-DC CONFIGURATION UPDATE message, the en-gNB may use this information for neighbour NR cell’s CSI-RS measurement.

If the Served Cell Specific Info Request IE is included in the EN-DC CONFIGURATION UPDATE message, the en-gNB shall, if supported, include the Additional Measurement Timing Configuration List IE for the requested NR cells in the EN-DC CONFIGURATION UPDATE ACKNOWLEDGE message.

If the Intended TDD DL-UL Configuration NR IE is contained in the NR Neighbour Information IE in the EN-DC CONFIGURATION UPDATE message, en-gNB should take this information into account for cross-link interference management. The en-gNB shall consider the received Intended TDD DL-UL Configuration NR IE content valid until reception of an update of the IE for the same cell(s).

Interaction with the eNB Configuration Update procedure:

The receiving eNB may forward the Intended TDD DL-UL Configuration NR IE received in the Served NR Cell Information IE in the EN-DC CONFIGURATION UPDATE ACKNOWLEDGE message to neighbouring eNBs by triggering the eNB Configuration Update procedure.

Interaction with the EN-DC Configuration Update procedure:

The receiving eNB may forward the Intended TDD DL-UL Configuration NR IE received in the Served NR Cell Information IE in the EN-DC CONFIGURATION UPDATE ACKNOWLEDGE message to neighbouring en-gNBs by triggering the EN-DC Configuration Update procedure.

en-gNB initiated EN-DC Configuration Update:

An en-gNB initiates the procedure by sending an EN-DC CONFIGURATION UPDATE message to an eNB.

If Supplementary Uplink is configured at the en-gNB, the en-gNB shall include in the EN-DC CONFIGURATION UPDATE message the SUL Information IE and the Supported SUL band List IE for each served cell added in the Served NR Cells To Add IE and in the Served NR Cells To Modify IE.

If the Deactivation Indication IE is contained in the Served NR Cells To Modify IE, it indicates that the concerned NR cell was switched off to lower energy consumption, and is available for activation on request from the eNB, as described in TS 36.300 [15].

After successful update of requested information, eNB shall reply with the EN-DC CONFIGURATION UPDATE ACKNOWLEDGE message to inform the initiating en-gNB that the requested update of application data was performed successfully. In case the eNB receives an EN-DC CONFIGURATION UPDATE without any IE except for Message Type IE it shall reply with EN-DC CONFIGURATION UPDATE ACKNOWLEDGE message without performing any updates to the existing configuration.

Upon reception of an EN-DC CONFIGURATION UPDATE message, eNB shall update the information for en-gNB as follows:

Update of Served NR Cell Information:

– If Served NR Cells To Add IE is contained in the EN-DC CONFIGURATION UPDATE message, eNB shall add cell information according to the information in the Served NR Cell Information IE.

– If Served NR Cells To Modify IE is contained in the EN-DC CONFIGURATION UPDATE message, eNB shall modify information of cell indicated by Old NR-CGI IE according to the information in the Served NR Cell Information IE.

– If Served NR Cells To Delete IE is contained in the EN-DC CONFIGURATION UPDATE message, eNB shall delete information of cell indicated by Old NR-CGI IE.

The en-gNB may initiate a further EN-DC Configuration Update procedure only after a previous EN-DC Configuration Update procedure has been completed.

If the EN-DC CONFIGURATION UPDATE message contains the TNL Transport Layer Address info IE, the receiving eNB shall, if supported, take this into account for IPSEC tunnel establishment.

If the EN-DC CONFIGURATION UPDATE ACKNOWLEDGE message contains the TNL Transport Layer Address info IE, the receiving en-gNB shall, if supported, take this into account for IPSEC tunnel establishment.

If the NR Cell PRACH Configuration IE is included in the Served NR Cell Information IE contained in the EN-DC CONFIGURATION UPDATE message, the eNB may update the information.

If the CSI-RS Transmission Indication IE is contained in the EN-DC CONFIGURATION UPDATE message, the eNB should take it into account when forwarding neighbour NR cell’s CSI-RS configuration.

If the Additional Measurement Timing Configuration List IE is contained in the EN-DC CONFIGURATION UPDATE message, the eNB should take it into account when forwarding neighbour NR cell’s CSI-RS configuration.

Update of SCTP associations:

If the TNL Association to Add List IE is included in the EN-DC CONFIGURATION UPDATE message, the receiving eNB shall, if supported, use it to establish the TNL association(s) with the en-gNB. The eNB shall report to the en-gNB, in the EN-DC CONFIGURATION UPDATE ACKNOWLEDGE message, the successful establishment of the TNL association(s) with the en-gNB as follows:

– A list of successfully established TNL associations shall be included in the TNL Association Setup List IE;

– A list of TNL associations that failed to be established shall be included in the TNL Association Failed to Setup List IE.

If the TNL Association to Remove List IE is included in the EN-DC CONFIGURATION UPDATE message, the receiving eNB shall, if supported, initiate removal of the TNL association(s) indicated by the received Transport Layer information towards the en-gNB.

If the TNL Association to Update List IE is included in the EN-DC CONFIGURATION UPDATE message the receiving eNB shall, if supported, update the TNL association(s) indicated by the received Transport Layer information towards the en-gNB.

If the Intended TDD DL-UL Configuration NR IE is contained in the NR Neighbour Information IE in the EN-DC CONFIGURATION UPDATE ACKNOWLEDGE message, en-gNB should take this information into account for cross-link interference management. The en-gNB shall consider the received Intended TDD DL-UL Configuration NR IE content valid until reception of an update of the IE for the same cell(s).

Interaction with the eNB Configuration Update procedure:

The receiving eNB may forward the Intended TDD DL-UL Configuration NR IE received in the Served NR Cell Information IE in the EN-DC CONFIGURATION UPDATE message to neighbouring eNBs by triggering the eNB Configuration Update procedure.

Interaction with the EN-DC Configuration Update procedure:

The receiving eNB may forward the Intended TDD DL-UL Configuration NR IE received in the Served NR Cell Information IE in the EN-DC CONFIGURATION UPDATE message to neighbouring en-gNBs by triggering the EN-DC Configuration Update procedure.

8.7.2.3 Unsuccessful Operation

Figure 8.7.2.3-1: eNB Initiated EN-DC Configuration Update, unsuccessful operation

Figure 8.7.2.3-2: en-gNB Initiated EN-DC Configuration Update, unsuccessful operation

If the candidate receving node can not accept the update it shall respond with an EN-DC CONFIGURATION UPDATE FAILURE message and appropriate cause value.

If the EN-DC CONFIGURATION UPDATE FAILURE message includes the Time To Wait IE the initiating node shall wait at least for the indicated time before reinitiating the EN-DC Configuration Update procedure towards the same peer node. Both nodes shall continue to operate the X2 with their existing configuration data.

If case of network sharing with multiple cell ID broadcast with shared X2-C signalling transport, as specified in TS 36.300 [15], the EN-DC CONFIGURATION UPDATE message and the EN-DC CONFIGURATION UPDATE FAILURE message shall include the Interface Instance Indication IE to identify the corresponding interface instance.

8.7.2.4 Abnormal Conditions

If the initiating node after initiating EN-DC Configuration Update procedure receives neither EN-DC CONFIGURATION UPDATE ACKNOWLEDGE message nor EN-DC CONFIGURATION UPDATE FAILURE message, the initiating node may reinitiate the EN-DC Configuration Update procedure towards the same candidate receving node, provided that the content of the EN-DC CONFIGURATION UPDATE message is identical to the content of the previously unacknowledged EN-DC CONFIGURATION UPDATE message.