Foreword1 Scope2 References3 Definitions and abbreviations4 Architecture5 Optimal routeing for basic mobile-to-mobile calls: message flows6 Optimal routeing for conditional call forwarding: message flows7 Interactions between optimal routeing and supplementary services8 Interactions between optimal routeing and other network features9 Functional requirements of entities performing optimal routeing9.1 Charging requirements for optimal routeing9.2 Functional behaviour of VMSCA9.3 Functional behaviour of VLRA9.4 Functional behaviour of GMSC9.4 Functional behaviour of GMSC9.4.1 Procedure OR_Set_ORA_Parameters9.4.2 Procedure OR_Handle_RCH9.4.3 Procedure Route_Permitted9.4.4 Procedure OR_Handle_SRI_Negative_Response9.5 Functional behaviour of HLR9.6 Functional behaviour of VLRB9.7 Functional behaviour of VMSCB10 Contents of messages 9.4.3 Procedure Route_Permitted 23.0793GPPRelease 17Support of Optimal Routeing (SOR)Technical realizationTS Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM