ages to be sent directly between the UE and the SN. RRC Reconfiguration messages generated by the SN can only be transported directly to the UE if the reconfiguration does not require any coor- dination with the MN. Additionally, measurement-reporting messages for mobility within the SN can be transmitted directly from the UE to the SN, if SRB3 is configured. The dual connectivity functionality provided by MR-DC can also be applied to the SRBs. The split SRB option, supported for all MR-DC options, allows the duplication of RRC mes- sages generated by the MN, via the direct path and via the SN. However, duplication of RRC 4 NG-RAN Architecture messages generated by the SN is not possible. In other words, split SRB is supported for both SRB1 and SRB2, but not for SRB3. For downlink, duplication of RRC messages over split SRB is up to network implementation. For uplink, the UE uses the MCG path or the SCG path depending on configuration from the MN. For full details of network functions defined for MR-DC refer to 3GPP TS 36.423, sub-clause 9.1.4, for X2-based MR-DC options, and 3GPP TS 38.423, sub-clause 9.1.2, for Xn-based MR-DC options. 4.3.4.1.1 UE Capability Coordination A UE configured with MR-DC needs to share its baseband and RF capabilities between the two connections to the network. As a consequence, the network needs to know and then coordinate the capabilities that can be used over the two links. More specifically, the capa- bilities of a UE supporting MR-DC are included in different containers. The capabilities that need to be visible to both MN and SN are carried in a specific MR-DC container, including for instance the supported MR-DC band combinations. Other capabilities that only need to be visible to the node of the concerned RAT are then contained in two separate E-UTRA and NR capability containers. When the MN needs to retrieve the MR-DC related capabilities, the MN transmits an RRC UE Capability Enquiry message to the UE, providing an MR-DC filter to retrieve the corresponding MR-DC-related capa