Once RRC Reconfiguration is sent to UE via source DU :

1. Trigger RACH Indication with dedicated RA preamble index from PHY stub to target DU
2. At SCH, Allocate PDCCH and PDSCH resources to send RAR 
3. At SCH, Allocate PUCCH resource for any further SR request (No resource allocated for MSG3 since this is contention-free RA)
4. Create RAR PDU at MAC and send to PHY
5. Trigger RRC Reconfiguration complete from PHY stub to target DU