Foreword1 Scope2 References3 Definitions, symbols and abbreviations4 IP multimedia subsystem concepts4.0 General4.1 Relationship to CS domain and the IP-Connectivity Access Network4.2 IMS services concepts4.3 Naming and addressing concepts4.4 Signalling concepts4.5 Mobility related concepts4.6 Roles of Session Control Functions4.7 Multimedia Resource Function4.7a Media Resource Broker4.8 Security Concepts4.9 Charging Concepts4.10 IMS group management concepts4.11 Relationship to 3GPP Generic User Profile (GUP)4.12 Network Address Translation traversal in access network4.13 Identification of IMS communication Services4.14 Border Control concepts4.15 IMS in transit network scenarios4.15a Roaming Architecture for Voice over IMS with Local Breakout4.15b Roaming Architecture for Voice over IMS with home routed traffic4.16 Support of multimedia telephony4.17 Support of short message service4.18 Support of Number portability4.19 Support of Preferred Circuit Carrier Access and Per Call Circuit Carrier Selection4.20 Support of IMS Service Centralization and Continuity4.21 Support of Overlap Signalling4.22 Support of Explicit Congestion Notification (ECN)4.23 Support of Load Balancing4.24 Support of Restoration Procedures4.25 Support of Overload Control4.26 Support for Business Trunking5 IP multimedia subsystem procedures5.0 General5.0a Session-unrelated procedures5.1 CSCF related procedures5.2 Application level registration procedures5.3 Application level de-registration procedures5.4 Procedures for IP multi-media sessions5.4a Overview of session flow procedures5.5 Serving‑CSCF/MGCF to serving‑CSCF/MGCF procedures5.6 Origination procedures5.7 Termination procedures5.7a Procedures for the establishment of sessions without preconditions5.8 Procedures related to routing information interrogation5.9 Routing of mid-session signalling5.10 Session release procedures5.11 Procedures to enable enhanced multimedia services5.11.1 Session Hold and Resume Procedures5.11.2 Procedures for anonymous session establishment5.11.3 Procedures for codec and media characteristics flow negotiations5.11.4 Procedures for providing or blocking identity5.11.5 Session Redirection Procedures5.11.6 Session Transfer Procedures5.12 Mobile Terminating call procedures to unregistered Public User Identities5.13 IMS Emergency Sessions5.14 Interactions involving the MRFC/MRFP5.15 Mobile Terminating session procedure for unknown user5.16 IMS messaging concepts and procedures5.17 Refreshing sessions5.18 Void5.19 Support for Transit scenarios in IMS5.20 Procedures for Assigning, Using, and Processing GRUUs5.21 IMS Multimedia Priority Services Procedures5.22 Support of Overload ControlE.0 GeneralE.1 Mobility related conceptsE.2 QoS related conceptsE.3 Address and identity management conceptsE.4 VoidE.5 IP version interworking in IMSE.6 Usage of NAT in GPRS/EPSE.7 Retrieval of Network Provided Location Information in GPRS/EPSE.8 Geographical IdentifierE.9 Support for Paging policy differentiation for IMS servicesE.10 Support of RAN Assisted Codec AdaptationG.1 GeneralG.2 Reference modelsG.3 Network elements for employing the IMS-ALG and IMS Access GatewayG.4 Procedures for employing the IMS-ALG and IMS Access GatewayG.5 Network elements for employing NAT Traversal for ICE and OutboundG.6 Procedures for employing ICE and OutboundI.1 GeneralI.2 Overall architectureI.3 Border Control FunctionsJ.1 GeneralJ.2 Representative ASJ.3 Dynamic assignment of AS by S‑CSCF cachingK.1 GeneralK.2 Overall architectureL.1 GeneralL.2 DefinitionsL.3 Mobility related concepts when using 3GPP2 Packet Data SubsystemL.4 QoS related concepts when using 3GPP2 Packet Data SubsystemL.5 IP version support in IMS when using 3GPP2 Packet Data SubsystemL.6 Address and identity management conceptsL.7 Relationship to 3GPP Generic User Profile (GUP)M.1 P‑CSCF located in visited networkM.2 P‑CSCF located in home networkM.3 P-CSCF located in visited network and with VPLMN loopback possibilityN.1 Origination proceduresN.2 Termination proceduresN.3 Geographical IdentifierP.1 GeneralQ.1 GeneralQ.2 Procedures and flowsQ.3 ChargingR.1 GeneralR.2 Session Establishment/Modification at Mobile Origination - Location Info in RequestR.3 Session Establishment/Modification at Mobile Origination - Location Info in ResponseR.4 Session Establishment/Modification at Mobile TerminationR.5 Session Establishment/Modification - Location Information Distributed by IMS ASR.6 Session ReleaseS.1 GeneralS.2 IP‑PBXs using static mode Business TrunkingT.0 GeneralT.1 Retrieval of Network Provided Location Information in TWAN accessU.1 OverviewU.2 ProceduresV.1 GeneralV.2 UE Provided Access Information in Untrusted WLAN accessW.1 GeneralW.2 ArchitectureW.3 VoidW.4 Procedures related to PLMN ID changeX.1 GeneralX.2 UE BehaviourX.3 Network BehaviourY.0 GeneralY.1 Mobility related conceptsY.2 QoS related conceptsY.3 Address and identity management conceptsY.4 IP version interworking in IMSY.5 Usage of NAT in 5GSY.6 Retrieval of Network Provided Location Information in 5GSY.7 Geographical IdentifierY.8 Support for Paging policy differentiation for IMS servicesY.9 Support of IMS Services for roaming usersY.10 Support of RAN Assisted Codec AdaptationY.11 VoidY.12 P-CSCF Registration in NRFY.13 Subscription to EPS Fallback EventZ.1 GeneralZ.2 ArchitectureZ.3 IMS Registration to access RLOSZ.4 IMS-based RLOS Session InitiationAA.1 GeneralAA.2 IMS SBA ServicesAA.3 SBI Capable HSS Discovery and SelectionAB.1 IMS in SNPN 5.18 Void 23.2283GPPIP Multimedia Subsystem (IMS)Release 18Stage 2TS Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM