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Content for  TS 37.340  Word version:  18.1.0

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7  RRC related aspectsp. 18

7.1  System information handlingp. 18

In MR-DC, the SN is not required to broadcast system information other than for radio frame timing and SFN. System information for initial configuration is provided to the UE by dedicated RRC signalling via the MN. The UE acquires, at least, radio frame timing and SFN of SCG from the PSS/SSS and MIB (if the SN is an eNB) / NR-PSS/SSS and PBCH (if the SN is a gNB) of the PSCell. In EN-DC, SN may broadcast system information to allow only IAB-MT to access the SN.
Additionally, upon change of the relevant system information of a configured SCell, the network releases and subsequently adds the concerned SCell (with updated system information), via one or more RRC reconfiguration messages sent on SRB1 or SRB3, if configured.
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7.2  Measurementsp. 18

If the measurement is configured to the UE in preparation for the Secondary Node Addition procedure described in clause 10.2, the Master node should configure the measurement to the UE.
In case of the intra-secondary node mobility described in clause 10.3, the SN should configure the measurement to the UE in coordination with the MN, if required.
The Secondary Node Change procedure described in clause 10.5 can be triggered by both the MN (only for inter-frequency secondary node change) and the SN. For secondary node changes triggered by the SN, the RRM measurement configuration is maintained by the SN which also processes the measurement reporting, without providing the measurement results to the MN.
Measurements can be configured independently by the MN and by the SN (intra-RAT measurements on serving and non-serving frequencies). The MN indicates the maximum number of frequency layers and measurement identities of intra-frequency and inter-frequency measurement that can be used in the SN to ensure that UE capabilities are not exceeded. In MR-DC, to assist MN to identify the measurement type, the SN indicates to the MN the list of SCG serving frequencies. In NR-DC, to assist SN to identify the measurement type, the MN indicates also to SN the list of MCG serving frequencies. The SN can also request the MN for new maximum values of the number of measurement identities that it can configure, and it is up to the MN whether to accommodate the SN request, based on the capability coordination principles as described in 7.3. If the SN receives from the MN a new value for the maximum number of measurement identities, is SN responsibility to ensure that its configured measurement identities to comply with the new limit.
If MN and SN both configure measurements on the same carrier frequency then the configurations need to be consistent (if the network wants to ensure these are considered as a single measurement layer). Each node (MN and SN) can configure independently a threshold for the SpCell quality. In (NG)EN-DC scenario, when the PCell quality is above the threshold configured by the MN, the UE is still required to perform inter-RAT measurements configured by the MN on the SN RAT (while it's not required to perform intra-RAT measurements); when the PSCell quality is above the threshold configured by the SN, the UE is not required to perform measurements configured by the SN. In NR-DC or NE-DC scenario, when the PCell quality is above the threshold configured by the MN, the UE is not required to perform measurements configured by the MN; when the PSCell quality is above the threshold configured by the SN, the UE is not required to perform measurements configured by the SN.
In MR-DC, both the MN and the SN can configure CGI reporting. The MN can configure CGI reporting for intra-RAT and inter-RAT cells but the SN can only configure CGI reporting of intra-RAT cells. At any point in time, the UE can be configured with at most one CGI reporting configuration. For CGI reporting coordination, the SN sends the CGI measurement request and the embedded CGI reporting configuration to the MN. Optionally, the SN sends the unknown cell information to the MN. If there is no ongoing CGI reporting measurement on UE side, the MN forwards the SN CGI measurement configuration to UE. Otherwise the MN rejects the request by sending X2/Xn reject message. In case the SN indicates the unknown cell information, and the CGI information of the requested cell is already available in the MN, the MN can also reject the request, and sends the CGI information of the requested cell to the SN. The SN cannot configure the CGI measurement using the SRB3.
Both MN-configured and SN-configured RRM measurements are supported while the SCG is deactivated. The PSCell measurement cycle when in deactivated SCG state is configured by RRC.
When SRB3 is not configured or the SCG is deactivated, reports for measurements configured by the SN are sent on SRB1. When SRB3 is configured and SCG transmission of radio bearers is not suspended and the SCG is not deactivated, reports for measurements configured by the SN are sent on SRB3.
Measurement results related to the target SN can be provided by MN to target SN at MN initiated SN change procedure. Measurement results of target SN can be forwarded from source SN to target SN via MN at SN initiated SN change procedure. Measurement results related to the target SN can be provided by source MN to target MN at Inter-MN handover with/without SN change procedure.
Measurement results according to measurement configuration from the MN are encoded according to SN RRC when they are provided by MN to SN in SgNB Addition Request message / SN Addition Request message. During SN initiated SN change procedure, measurement results according to measurement configuration from SN are encoded according to SN RRC when they are provided by MN to SN in SgNB Addition Request message / SN Addition Request message.
Per-UE or per-FR measurement gaps can be configured, depending on UE capability to support independent FR measurement and network preference. Per-UE gap applies to both FR1 (E-UTRA, UTRA-FDD and NR) and FR2 (NR) frequencies. For per-FR gap, two independent gap patterns (i.e. FR1 gap and FR2 gap) are configured for FR1 and FR2 respectively. The UE may also be configured with a per-UE gap sharing configuration (applying to per-UE gap) or with two separate gap sharing configurations (applying to FR1 and FR2 measurement gaps respectively) [8].
A measurement gap configuration is always provided:
  • In EN-DC, NGEN-DC and NE-DC, for UEs configured with E-UTRA inter-frequency measurements as described in Table 9.1.2-2 in TS 38.133;
  • In EN-DC and NGEN-DC, for UEs configured with UTRAN and GERAN measurements as described in Table 9.1.2-2 in TS 38.133;
  • In NR-DC, for UEs configured with E-UTRAN measurements as described in Table 9.1.2-3 in TS 38.133;
  • In NR-DC, NE-DC, for UEs configured with UTRAN measurements as described in Table 9.4.6.3-1 and 9.4.6.3-2 in TS 38.133;
  • In MR-DC, for UEs that support either per-UE or per-FR gaps, when the conditions to measure SSB based inter-frequency measurement or SSB based intra-frequency measurement as described in clause 9.2.4 in TS 38.300 are met;
If per-UE gap is used, the MN decides the gap pattern and the related gap sharing configuration. If per-FR gap is used, in EN-DC and NGEN-DC, the MN decides the FR1 gap pattern and the related gap sharing configuration for FR1, while the SN decides the FR2 gap pattern and the related gap sharing configuration for FR2; in NE-DC and NR-DC, the MN decides both the FR1 and FR2 gap patterns and the related gap sharing configurations.
In EN-DC and NGEN-DC, the measurement gap configuration from the MN to the UE indicates if the configuration from the MN is a per-UE gap or an FR1 gap configuration. The MN also indicates the configured per-UE or FR1 measurement gap pattern and the gap purpose (per-UE or per-FR1) to the SN. Measurement gap configuration assistance information can be exchanged between the MN and the SN. For the case of per-UE gap, the SN indicates to the MN the list of SN configured frequencies in FR1 and FR2 measured by the UE. For the per-FR gap case, the SN indicates to the MN the list of SN configured frequencies in FR1 measured by the UE and the MN indicates to the SN the list of MN configured frequencies in FR2 measured by the UE.
In NE-DC, the MN indicates the configured per-UE or FR1 measurement gap pattern to the SN. The SN can provide a gap request to the MN, without indicating any list of frequencies.
In NR-DC, the MN indicates the configured per-UE, FR1 or FR2 measurement gap pattern and the gap purpose to the SN. The SN can indicate to the MN the list of SN configured frequencies in FR1 and FR2 measured by the UE.
In (NG)EN-DC and NR-DC, SMTC can be used for PSCell addition/PSCell change to assist the UE in finding the SSB in the target PSCell. In case the SMTC of the target PSCell is provided by both MN and SN it is up to UE implementation which one to use.
CLI measurements can be configured for NR cells in all MR-DC options. In EN-DC and NGEN-DC, only the SN can configure CLI measurements. In NE-DC, only the MN can configure CLI measurements. In NR-DC, both the MN and the SN can configure CLI measurements, and the MN informs the SN about the maximum number of CLI measurement resources that can be configured by the SN to ensure that the total number of CLI measurement resources does not exceed the UE capabilities.
For MUSIM operation, when the UE is configured to operate in NR-DC in Network A (as described in TS 38.300), the MN indicates the per-UE MUSIM gap configuration to the SN.
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7.3  UE capability coordinationp. 20

In (NG)EN-DC and NE-DC, the capabilities of a UE supporting MR-DC are carried by different capability containers. Some MR-DC related capabilities are in the MR-DC container e.g. MR-DC band combinations, while other MR-DC related capabilities are contained in the E-UTRA and NR capability containers e.g. feature sets as described in TS 38.300. The MR-DC capabilities in the MR-DC container need to be visible to both MN and SN, while the capabilities in the E-UTRA and NR containers only need to be visible to the node of the concerned RAT.
In NR-DC, all NR-DC related capabilities are in the NR capability container and are visible to both MN and SN.
When retrieving MR-DC related capabilities, the MN shall provide an MR-DC filter that affects the MR-DC related capabilities in MR-DC, E-UTRA and NR capability containers. When using different UE capability enquiry messages to retrieve the different containers, the MN shall employ the same MR-DC filter in all enquiry messages. In the E-UTRA RRC UE capability enquiry, the MR-DC filter is also used for retrieval of NR capabilities i.e. there is in fact one MR-DC/NR filter (while there is a separate filter for E-UTRA capabilities). Furthermore, the MN stores the retrieved capabilities and the corresponding filter, used to retrieve those capabilities, in the core network for later use.
For the UE capabilities requiring coordination between E-UTRA and NR (i.e. band combinations, feature sets and the maximum power for FR1 the UE can use in SCG) or between NR MN and NR SN (i.e. band combinations, feature sets and the maximum power for FR1 and FR2), it is up to the MN to decide on how to resolve the dependency between MN and SN configurations. The MN then provides the resulting UE capabilities usable for SCG configuration to the SN, including the list of allowed MR-DC band combinations and feature sets, and the SN indicates the selected band combination and feature set to the MN. When subsequently reconfiguring the SCG, the SN should inform the MN whenever the band combination and/or feature set it selected for the SCG changes (i.e. even if the selection concerns a band combination and feature set that is allowed). As part of an SN initiated SN modification, the SN may also indicate the desired UE capabilities usable for SCG configuration (e.g. a band combination and a feature set) outside those allowed by the MN (i.e. it may re-negotiate the UE capabilities for SCG configuration), and it is up to the MN to make the final decision whether to accept or reject the request. If the MN accepts the request, the MN may provide the resulting UE capabilities e.g. by indicating the allowed band combinations and feature sets. If MN accepts but does not provide resulting UE capabilities, SN assumes the UE capabilities usable for SCG configuration are updated in accordance with the modification it requested. Otherwise, the MN rejects the request by sending X2/Xn refuse message.
In EN-DC and MR-DC with 5GC, the MN may provide the UE radio capability ID to the SN. For EN-DC, the SN may retrieve the UE Radio Capability information associated to a UE radio capability ID from the MN. For MR-DC with 5GC, the SN may retrieve the UE radio capability information associated to a UE radio capability ID from the 5GC.
For MUSIM operation, when the UE is configured to operate in NR-DC in Network A (as described in TS 38.300), the MN may indicate the temporary capability restriction to the SN based on the temporary capability restrictions indicated by the UE.
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7.4  Handling of combined MN/SN RRC messagesp. 21

When both MCG and SCG reconfiguration is required due to the need for coordination with the MN, the SN RRC reconfiguration message is encapsulated in an MN RRC message that also carries the corresponding MCG reconfiguration that ensures that the combined configuration can be jointly processed by the UE. If the MN terminates a bearer using NR PDCP, the NR PDCP configuration is generated by the MN itself. If the SN terminates the bearer, the SN generates the NR PDCP configuration and sends it to the MN as a separate container.
The UE uses a joint success/failure procedure for messages in an encapsulating MN RRC message. A failure of the MN RRC messages, including one encapsulated SN RRC message with or without any MCG reconfiguration fields, triggers a re-establishment procedure. Each SN RRC reconfiguration message should have its own RRC response message even when the SN RRC message is encapsulated in an MN RRC message. The SN RRC response message is forwarded over X2/Xn to the SN. If a SN RRC reconfiguration message is contained in a MN RRC message, the UE sends a MN RRC response message that encapsulates the SN RRC response message.
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7.5  SRB3p. 21

SRB3 is supported in EN-DC, NGEN-DC and NR-DC, but not in NE-DC.
The decision to establish SRB3 is taken by the SN, which provides the SRB3 configuration using an SN RRC message. SRB3 establishment and release can be done at Secondary Node Addition and Secondary Node Change. SRB3 reconfiguration can be done at Secondary Node Modification procedure.
SRB3 may be used to send SN RRC Reconfiguration, SN RRC Reconfiguration Complete, SN Measurement Report, SN Failure Information (i.e., in case of failure for an SCG RLC bearer), SN UE Assistance Information message and SN IABOtherInformation, only in procedures where the MN is not involved. SN RRC Reconfiguration Complete messages are mapped to the same SRB as the message initiating the procedure. SN Measurement Report messages are mapped to SRB3, if configured, regardless of whether the configuration is received directly from the SN or via the MN. No MN RRC messages are mapped to SRB3.
If split SRB1 is not configured, SRB3 may be used by the UE to transmit to the MN an encapsulated MCG Failure Information message in the ULInformationTransferMRDC message and receive in response an encapsulated RRC reconfiguration message, MobilityFromNRCommand message, MobilityFromEUTRACommand message or RRC release message in the DLInformationTransferMRDC message.
SRB3 is modelled as one of the SRBs defined in TS 38.331 and uses the NR-DCCH logical channel type. RRC PDUs on SRB3 are ciphered and integrity protected using NR PDCP, with security keys derived from S-KgNB. The SN selects ciphering and integrity protection algorithms for the SRB3 and provides them to the MN within the SCG Configuration for transmission to the UE.
SRB3 is of higher scheduling priority than all DRBs. The default scheduling priorities of split SRB1 and SRB3 are the same.
There is no requirement on the UE to perform any reordering of RRC messages between SRB1 and SRB3.
When SCG is released, SRB3 is released.
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7.6  Split SRBp. 22

Split SRB is supported for both SRB1 and SRB2 (split SRB is not supported for SRB0, SRB3, SRB4 and SRB5) in all MR-DC cases. RRC PDUs on split SRB are ciphered and integrity protected using NR PDCP.
Split SRB can be configured by the MN in Secondary Node Addition and/or Modification procedure, with SN configuration part provided by the SN. A UE can be configured with both split SRB and SRB3 simultaneously. SRB3 and the SCG leg of split SRB can be independently configured.
For the split SRB, the selection of transmission path in downlink depends on network implementation. For uplink, the UE is configured via MN RRC signalling whether to use MCG path or duplicate the transmission on both MCG and SCG.
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7.7  SCG/MCG failure handlingp. 22

RLF is declared separately for the MCG and for the SCG.
If radio link failure is detected for MCG, fast MCG link recovery is configured and the SCG is not deactivated, the UE triggers fast MCG link recovery. Otherwise, the UE initiates the RRC connection re-establishment procedure. During the execution of PSCell addition or PSCell change, if radio link failure is detected for MCG, the UE initiates the RRC connection re-establishment procedure.
During fast MCG link recovery, the UE suspends MCG transmissions for all radio bearers, except SRB0, and, if any, BH RLC channels and reports the failure with MCGFailureInformation message to the MN via the SCG, using the SCG leg of split SRB1 or SRB3.
The UE includes in the MCGFailureInformation message the measurement results available according to current measurement configuration of both the MN and the SN. Once the fast MCG link recovery is triggered, the UE maintains the current measurement configurations from both the MN and the SN, and continues measurements based on configuration from the MN and the SN, if possible. The UE initiates the RRC connection re-establishment procedure if it does not receive an RRCConnectionReconfiguration message, RRCReconfiguration message, MobilityFromNRCommand message, MobilityFromEUTRACommand message, RRCConnectionRelease message or RRCRelease message within a certain time after fast MCG link recovery was initiated.
Upon reception of the MCGFailureInformation message, the MN can send RRCConnectionReconfiguration message, RRCReconfiguration message, MobilityFromNRCommand message, MobilityFromEUTRACommand message, RRCConnectionRelease message or RRCRelease message to the UE, using the SCG leg of split SRB1 or SRB3. Upon receiving an RRCConnectionReconfiguration message, RRCReconfiguration message, MobilityFromNRCommand message or MobilityFromEUTRACommand message, the UE resumes MCG transmissions for all radio bearers. Upon receiving an RRCConnectionRelease message or RRCRelease message, the UE releases all the radio bearers and configurations.
The following SCG failure cases are supported:
  • SCG RLF;
  • SCG beam failure while the SCG is deactivated;
  • SN addition/change failure;
  • For EN-DC, NGEN-DC and NR-DC, SCG configuration failure or CPC configuration failure (only for messages on SRB3);
  • For EN-DC, NGEN-DC and NR-DC, SCG RRC integrity check failure (on SRB3);
  • For EN-DC, NGEN-DC and NR-DC, consistent UL LBT failure on PSCell;
  • For IAB-MT, reception of a BH RLF indication from SCG;
  • CPA/CPC or subsequent CPAC execution failure;
  • SCG LTM cell switch failure.
Upon SCG failure, if MCG transmissions of radio bearers are not suspended, the UE suspends SCG transmissions for all radio bearers and, if any, BH RLC channels, if the SCG failure is not triggered by SCG beam failure, and reports the SCGFailureInformation to the MN, instead of triggering re-establishment. If SCG failure is detected while MCG transmissions for all radio bearers are suspended, the UE initiates the RRC connection re-establishment procedure.
SCG/MCG failure handling by UE also applies to IAB MT.
In all SCG failure cases, the UE maintains the current measurement configurations from both the MN and the SN and the UE continues measurements based on configuration from the MN and the SN if possible. The SN measurements configured to be routed via the MN will continue to be reported after the SCG failure.
The UE includes in the SCGFailureInformation message the measurement results available according to current measurement configuration of both the MN and the SN. The MN handles the SCGFailureInformation message and may decide to keep, change, or release the SN/SCG. In all the cases, the measurement results according to the SN configuration and the SCG failure type may be forwarded to the old SN and/or to the new SN.
In case of CPA/CPC, upon transmission of the SCGFailureInformation message to the MN, the UE stops evaluating the CPA/CPC execution condition. In case of subsequent CPAC, upon transmission of the SCGFailureInformation message to the MN or upon transmission of the MCGFailureInformation message to the SN, the UE stops evaluating the subsequent CPAC execution condition. The UE is not required to continue measurements for candidate PSCell(s) for execution condition upon transmission of the SCGFailureInformation message to the MN.
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7.8  UE identitiesp. 23

In MR-DC, two C-RNTIs are independently allocated to the UE: one for MCG, and one for SCG.

7.9  Inter-node Resource Coordinationp. 23

For MR-DC operations, MN and SN may coordinate their UL and DL radio resources in semi-static manner via UE associated signalling. The MN may coordinate its sidelink radio resources with the SN using the same UE associated signalling.
In EN-DC, CSI-RS based SgNB change between neighbour en-gNBs is supported by enabling that neighbour en-gNBs can exchange their own CSI-RS configurations and on/off status via the MeNB.
In NGEN-DC and NR-DC, CSI-RS based SN change between neighbour gNBs is supported by enabling that neighbour gNBs can exchange their own CSI-RS configurations and on/off status via the MN.
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7.10  UE assistance information |R16|p. 23

In MR-DC, the UE can be configured to report MCG specific UE assistance information if the MN is a gNB and/or SCG specific UE assistance information if the SN is a gNB, if it prefers an adjustment on the connected mode DRX parameters, the maximum aggregated bandwidth, the maximum number of secondary component carriers, the maximum number of MIMO layers, whether the UE prefers the SCG to be deactivated, the minimum scheduling offset for cross-slot scheduling cycle length, whether the UE is applying RLM/BFD measurements relaxation for power saving, and/or whether the UE is experiencing IDC problems as described in TS 36.300 and TS 38.300. In these cases, it is up to the network whether to accommodate the preference or how to use the relaxation status indications or how to solve the IDC problems. SCG specific UE assistance information for power saving or IDC can be configured by the network via SRB1 or SRB3. SCG specific UE assistance information for power saving or IDC is directly transmitted to the SN via SRB3, if SRB3 is configured and the SCG is activated, otherwise UE transmits SCG specific UE assistance information for power saving or IDC in a transparent container to the MN. When network simultaneously configures the UE to perform radio link monitoring on the SCG and beam failure detection on the SCG while the SCG is deactivated, UE assistance information for the relaxation state report of RLM/BFD measurements for SCG is reported over MCG. UE can implicitly indicate a preference for NR SCG release by indicating zero number of carriers and zero aggregated maximum bandwidth in both FR1 and FR2.
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7.11  F1-C transfer over E-UTRA |R16|p. 24

In EN-DC, the F1-AP message encapsulated in SCTP/IP or F1-C related (SCTP/)IP packet can be transferred between IAB-donor and IAB-node via E-UTRA, if configured by IAB-donor, as specified in TS 38.331. When both E-UTRA and NR are configured to transfer the F1-AP message encapsulated in SCTP/IP or F1-C related (SCTP/)IP packet, it is up to the IAB implementation when to select the E-UTRA. SRB2 is used for transporting the F1-AP message encapsulated in SCTP/IP or F1-C related (SCTP/)IP packet between IAB-MT and MN [10], and the F1-AP message encapsulated in SCTP/IP or F1-C related (SCTP/)IP packet is transferred as a container via X2-AP between MN and SN, see TS 36.423.
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7.12  F1-C transfer in NR-DC |R17|p. 24

In NR-DC, the F1-AP message encapsulated in SCTP/IP or F1-C related (SCTP/)IP packet can be transferred via BAP sublayer or via SRB between the IAB-node and F1-terminating IAB-donor (as specified in TS 38.401), as specified in TS 38.331. When both MCG and SCG are configured to transfer the F1-AP message encapsulated in SCTP/IP or F1-C related (SCTP/)IP packet, it is up to the IAB-node implementation for path selection. Two scenarios are supported, as shown in Figure 7.12-1.
Reproduction of 3GPP TS 37.340, Fig. 7.12-1: F1-C transfer in NR-DC; a) Scenario 1; b) Scenario 2
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Scenario 1:
IAB-node exchanges F1-AP message encapsulated in SCTP/IP or F1-C related (SCTP/)IP packet with the SN (F1-terminating IAB-donor as specified in TS 38.401) using NR access link via MN (non-F1-terminating IAB-donor), and exchanges F1-U traffic using backhaul link(s) with SN. SRB2 is used for transporting the F1-AP message encapsulated in SCTP/IP or F1-C related (SCTP/)IP packet between IAB-MT and MN (see TS 38.331), and the F1-AP message encapsulated in SCTP/IP or F1-C related (SCTP/)IP packet is transferred in a container via XnAP between MN and SN, see TS 38.423.
Scenario 2:
IAB-node exchanges F1-AP message encapsulated in SCTP/IP or F1-C related (SCTP/)IP packet with the MN (F1-terminating IAB-donor) using NR access link via SN (non-F1-terminating IAB-donor), and exchanges F1-U traffic using backhaul link(s) with MN. Split SRB2 is used for transporting the F1-AP message encapsulated in SCTP/IP or F1-C related (SCTP/)IP packet between IAB-MT and SN (see TS 38.331), and the F1-AP message encapsulated in SCTP/IP or F1-C related (SCTP/)IP packet is transferred in a container via XnAP between SN and MN, see TS 38.423.
The F1-AP message encapsulated in SCTP/IP or the F1-C related (SCTP/)IP packet can be transferred either over BAP sublayer or over SRB, but the two mechanisms cannot be supported simultaneously on the same parent link. The F1-AP message encapsulated in SCTP/IP or the F1-C related (SCTP/)IP packet is transferred over BAP sublayer, if the BH RLC channel used for transferring the F1-C traffic is configured on the cell group indicated for F1-C traffic transfer according to TS 38.331.
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7.13  Activation and Deactivation of SCG |R17|p. 24

To enable reasonable UE battery consumption while having fast usage of SCG when (NG)EN-DC or NR-DC is configured, an activation/deactivation mechanism of SCG is supported. While the SCG is deactivated, there is no transmission via SCG RLC bearers. Only the NR SCG can be deactivated, and all SCG SCell(s) are in deactivated state while the SCG is deactivated.
Upon SCG deactivation and while the SCG is deactivated, the network ensures that there is no uplink control PDU transmission to the deactivated SCG (e.g. the network releases statusReportRequired from PDCP entities of SCG bearers if configured, the network does not perform QoS flow remapping from a DRB associated to the deactivated SCG to another DRB). The network ensures the SCG is activated while PDCP duplication is activated for SCG RLC entities associated with a PDCP entity.
While the SCG is deactivated, the UE will not transmit PUSCH, SRS and CSI report on SCG, and the UE is not required to monitor PDCCH or receive DL-SCH on SCG. If configured by the network, the UE performs radio link monitoring on the SCG and beam failure detection on the SCG while SCG is deactivated. In case of SCG activation without performing random access, the network can indicate TCI states to UE for PDCCH/PDSCH reception on PSCell, if not provided, the UE uses the previously activated TCI states.
The MN can configure the SCG as activated or deactivated upon e.g. PSCell addition, PSCell change, RRC Resume or handover. In case the SCG is configured as deactivated, the UE does not perform random access towards the PSCell. The network can trigger SCG RRC reconfiguration (e.g. PSCell change, configuration update) when deactivating the SCG and while the SCG is in deactivated state.
SCG activation can be requested by the MN, by the SN and by the UE. SCG deactivation can be requested by the MN and by the SN. For UL data arrival on SCG bearer(s) while the SCG is deactivated, the UE indicates to the MN that it has UL data to transmit over SCG bearer. During handover procedure, the target MN can indicate the SCG state in the RRC reconfiguration message sent to the UE by the source MN.
Network can configure whether the UE is allowed to indicate a preference for SCG deactivation to the MN.
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7.14  RLM/BFD relaxation |R17|p. 25

For RLM and BFD relaxation, network may configure low mobility criterion in the NR PCell for the case of NE-DC/NR-DC, and in the NR PSCell for the case of EN-DC and NGEN-DC. MN informs SN when low mobility criterion has been configured in the NR PCell for NR-DC.
For RLM relaxation, network may configure good serving cell criterion in the NR PCell for the case of NE-DC/NR-DC, and in the NR PSCell for the case of EN-DC, NGEN-DC and NR-DC.
For BFD relaxation, network may configure good serving cell criterion in the NR PCell and/or SCell(s) for the case of NE-DC/NR-DC, and in the NR PSCell and/or SCell(s) for the case of EN-DC, NGEN-DC and NR-DC.
For RLM/BFD relaxation, network may simultaneously configure the UE to perform radio link monitoring on the SCG and beam failure detection on the SCG while SCG is deactivated. In such case, UE initiates UE assistance information for the relaxation state report of RLM/BFD measurements for SCG.
For RLM/BFD relaxation, network may simultaneously configure the UE not to perform radio link monitoring on the SCG and beam failure detection on the SCG while SCG is deactivated. In such case, UE assistance information for the relaxation state report of RLM/BFD measurements for SCG will not be initiated.
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