Tunnel Endpoint IE if data forwarding is configured. When the source SN receives the SgNB Change Confirm message it stops providing user data to the UE and, if applicable, starts data forwarding. 7. If the RRC connection reconfiguration procedure was successful, the MN then sends the X2-AP SgNB Reconfiguration Complete message to the target SN, which may con- tain the MeNB to SgNB Container IE carrying the encoded NR RRC response message for the target SN, if received from the UE. 8. The UE performs the random access procedure to synchronize to the new PSCell in the target SN. 9. For SN terminated bearers using RLC AM, the source SN sends the X2-AP SN Status Transfer message with the PDCP SN and HFN status, which the MN sends then to the target SN in a separate X2-AP message. 10. Data forwarding from the source SN takes place either at this step or as early as step 6, if configured. 11. For source SN terminated bearers, the MN then triggers the update of the user-plane path toward the EPC using the S1-AP Path Switch procedure. 12. The MN also sends the X2-AP UE Context Release message to the source SN, upon which the SN releases all the resource associated to the UE context. 4.3.5 Further Reading Readers interested in further details about various options of MR-DC, should start from the general stage 2 description in 3GPP TS 37.340. Note that while the overall stage 2 RAN specification is normally provided in the 300 series, that is, 3GPP TS 36.300 for LTE and 3GPP TS 38.300 for NR, MR-DC is described separately. Once a reader has familiarized himself with the high-level aspects, readers interested in the RAN aspects of MR-DC operation should familiarize themselves with the X2-AP control-plane protocol (3GPP TS 36.423) and the similar but somewhat different Xn-AP control-plane protocol (3GPP TS 38.423). References Network interface user-plane details can be found in 3GPP TS 36.424 and TS 36.425 for EN-DC, and 3GPP TS 38.424 and TS 38.425 for MR-DC with 5GC. While the present chapter and the specifications mention