Description
The IP Multimedia Subsystem (IMS) is a fundamental, access-agnostic core network subsystem within the 3GPP architecture. It is not a single node but a complete framework of logical functions and reference points designed to establish, modify, and terminate multimedia sessions using the Session Initiation Protocol (SIP) as its primary signaling protocol. IMS decouples service delivery from the underlying transport layer (e.g., GSM, UMTS, LTE, 5G NR, WiFi, fixed broadband), enabling convergence and consistent service experience across diverse access networks. Its architecture is organized into three main layers: the Transport Layer (providing IP connectivity), the Control Layer (the IMS core itself), and the Application/Services Layer.
The core of the IMS control layer consists of Call Session Control Functions (CSCFs): the Proxy-CSCF (P-CSCF), Serving-CSCF (S-CSCF), and Interrogating-CSCF (I-CSCF). The P-CSCF is the first contact point for the User Equipment (UE), handling SIP message forwarding, security, and policy enforcement. The I-CSCF acts as the entry point to an operator's network, selecting an appropriate S-CSCF and hiding network topology. The S-CSCF is the central brain; it performs user registration, session routing, and interacts with the Home Subscriber Server (HSS) for authentication and user profile retrieval. Other critical functions include the HSS (master user database), Breakout Gateway Control Function (BGCF) for routing to circuit-switched networks, and Media Resource Functions (MRF) for conferencing and tones.
A session begins with UE registration. The UE discovers the P-CSCF, then sends a SIP REGISTER request. The S-CSCF authenticates the user (using credentials from HSS) via the IMS Authentication and Key Agreement (AKA) protocol. Once registered, the UE can initiate a session (e.g., a VoLTE call) by sending a SIP INVITE. The S-CSCF routes the request based on initial Filter Criteria (iFC) downloaded from the HSS, which may trigger services on Application Servers (AS). IMS also integrates policy and charging control via the Rx interface to the Policy and Charging Rules Function (PCRF), ensuring appropriate Quality of Service (QoS) and billing for the media flows. Media itself typically flows directly between endpoints (UEs) over IP, using protocols like RTP, under the control established by SIP signaling.
Purpose & Motivation
IMS was conceived to address the limitations of traditional mobile networks, which were built around circuit-switched technology optimized primarily for voice. As the internet grew, demand for integrated data and multimedia services (like video calling, instant messaging, and presence) increased. Pre-IMS attempts to offer these services were often vertical 'silos' – proprietary, access-dependent, and difficult to integrate, leading to poor user experience and high operator costs for development and maintenance.
The primary motivation for IMS was to create a horizontal, standardized service delivery platform. By basing it on Internet Engineering Task Force (IETF) protocols like SIP and Diameter, 3GPP aimed to leverage internet technology while adding the necessary capabilities for carrier-grade telephony: robust security, guaranteed quality of service, lawful interception, and sophisticated charging models (prepaid, postpaid, event-based). This allowed operators to rapidly deploy and blend services (voice, video, text, file transfer) into rich communication suites, competing with Over-The-Top (OTT) internet players.
Furthermore, IMS was designed to be access-agnostic from its inception in 3GPP Release 5. This future-proofed the architecture, allowing it to serve not just 3G UMTS, but also subsequent technologies like LTE (where it became the foundation for VoLTE), 5G (for Voice over New Radio), WiFi (via VoWiFi), and fixed networks (leading to Fixed-Mobile Convergence). It solved the problem of service fragmentation, enabling a user to have the same phone number, identity, and service features whether connected via cellular, office WiFi, or home broadband. IMS thus became the cornerstone for the evolution of mobile networks towards All-IP networks, enabling the retirement of legacy circuit-switched cores.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (225 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, IMS was enhanced to operate over the new 5G System (5GS) and to support supplementary services like Communication HOLD (HOLD) and Message Waiting Indication (MWI) using the IP Multimedia Core Network subsystem. The release also introduced procedures for retrieving migration credentials for IMS access and updated the IMS registration process for UEs in Dual Registration mode. Furthermore, it provided enhancements for UE location description for IMS charging when connected over WLAN.
- Retrieval of migration credentials for access to SIP core / IMS of a partner MC system TS 23.280CR0066
- IMS multimedia telephony communication service and supplementary services TS 24.173CR0122
- Message Waiting Indication (MWI) using IP Multimedia (IM) Core Network (CN) subsystem TS 24.606CR0020
- Terminating Identification Presentation (TIP) and Terminating Identification Restriction (TIR) using IP Multimedia (IM) Core Network (CN) subsystem TS 24.608CR0029
- Communication HOLD (HOLD) using IP Multimedia (IM) Core Network (CN) subsystem TS 24.610CR0043
- Communication Waiting (CW) using IP Multimedia (IM) Core Network (CN) subsystem TS 24.615CR0073
+ 20 more changes
In Release 16, the IMS was enhanced to support new procedures for the P-CSCF, including restoration, handling session timers, and support for SIP forking and RTCP flows. Furthermore, IMS integration with the 5G core network was deepened by enabling the P-CSCF to use the NRF for discovery and allowing IMS to interact with the PCF via the N5 interface. The release also introduced updates for emergency services, charging with a new service-based interface, and support for providing the Network Identifier (NID) to the P-CSCF.
- Support for RLOS in IMS TS 23.228CR1193
- eIMS P-CSCF use of NRF TS 23.228CR1199
- SBA HSS Services for IMS TS 23.228CR1200
- Allowing SMF to perform P-CSCF Discovery using NRF TS 23.228CR1202
- Allowing IMS to use N5 interface to interact with PCF TS 23.228CR1203
- Additional corrections for allowing IMS to use N5 interface to interact with PCF TS 23.228CR1204
+ 34 more changes
In Release 17, key IMS enhancements included the introduction of IMS Credentials (IMC) to support terminals accessing IMS via a Standalone Non-Public Network (SNPN), along with specific support for IMS emergency services and multiple independent IMS providers within SNPNs. The release also added IMS authentication using the AKAv2-SHA-256 digest AKA algorithm and introduced an IMS data channel media feature tag for the Accept-Contact header. Furthermore, improvements were made to converged charging architecture and the ability to upgrade a non-MPS session to an MPS session.
- Upgrade IMS non-MPS session to an IMS MPS session. TS 23.228CR1238
- Support for Attestation for IMS priority sessions TS 23.228CR1241
- SNPN configuration in IMS MO TS 24.167CR0225
- IMS data channel media feature tag in Accept-Contact header TS 24.173CR0147
- Failed P-CSCF TS 29.228CR0697
- Failed P-CSCF TS 29.229CR0298
+ 27 more changes
In Release 18, the IMS introduced comprehensive support for the IMS Data Channel service, including new capabilities for its establishment, capability discovery, and negotiation. Key additions encompassed UE-triggered setup, duration-based charging principles, and roaming support for this feature. The release also brought updates to IMS Application Server services within a Service-Based Architecture and clarified procedures for cross-border mobility with home-routed IMS calls.
- Architecture of IMS supporting data channel TS 23.228CR1263
- IMS SBA Services TS 23.228CR1264
- IMS DC capability discovery TS 23.228CR1268
- The requirement of the IMS AS during registration TS 24.186CR0001
- Adding 3gpp-req-app attribute to SDP negotiation of IMS data channels TS 26.114CR0551
- Add charging principle of duration-based charging for IMS data channel TS 32.260CR0431
+ 35 more changes
In Release 19, key IMS enhancements included the introduction of a standalone IMS Data Channel feature and a framework for network-initiated data channels, alongside new procedures for adding a data channel to an existing IMS session. The release also expanded support for UE-to-UE satellite communication within IMS, defining specific call setup and mobility procedures, including ground fallback. Furthermore, it added support for MPS priority for IMS messaging and for conveying third-party user identity information.
- Support of IMS data channel interworking between DCMTSI UE and MTSI UE TS 23.228CR1418
- Support of MPS priority for IMS Immediate Messaging and IMS Session-based Messaging TS 23.228CR1419
- KI#6: Support of Standalone IMS Data Channel feature TS 23.228CR1422
- Supporting of network initiated IMS Data Channel TS 23.228CR1425
- KI#1: IMS Subscribe/Notify Framework Architecture TS 23.228CR1409
- Support of UE-Satellite-UE communication in IMS - Functionality TS 23.228CR1428
+ 79 more changes
Explore further
Broader topics and technologies where IMS plays a role.
Defining Specifications
3GPP specifications that define or reference IMS, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 21.905 vj00 | 3GPP Technical Terms and Definitions | Rel-19 |
| TS 22.234 vd10 | 3GPP-WLAN Interworking Index Specification | Rel-13 |
| TS 22.240 vj00 | 3GPP Generic User Profile Requirements | Rel-19 |
| TS 22.250 vj00 | IMS Group Management Requirements | Rel-19 |
| TS 22.273 v1700 | IMS Multimedia Telephony with PSTN/ISDN Simulation | Rel-7 |
| TS 22.340 vj00 | IMS Messaging Stage 1 Requirements | Rel-19 |
| TS 22.401 v1800 | Videotelephony Service Requirements for NGN | Rel-8 |
| TS 22.495 v1700 | NGN Requirements for IMS Services | Rel-7 |
| TS 22.519 vj00 | NGN Business Communication Requirements | Rel-19 |
| TR 22.940 vj00 | IMS Messaging Requirements Analysis | Rel-19 |
| TR 22.944 vj00 | UE Functionality Split Scenarios and Requirements | Rel-19 |
| TR 22.949 vj00 | Privacy Requirements Study for 3GPP Services | Rel-19 |
| TR 22.977 vj00 | Speech Enabled Services and Multimodal Framework | Rel-19 |
| TR 22.980 vj00 | Network Composition Feasibility Study | Rel-19 |
| TS 23.125 v1700 | Flow Based Charging Architecture | Rel-7 |
| TS 23.127 v1600 | Virtual Home Environment Stage 2 Specification | Rel-6 |
| TS 23.141 vj00 | Presence Service Stage 2 Architecture | Rel-19 |
| TS 23.179 vd50 | MCPTT Functional Architecture | Rel-13 |
| TS 23.198 v1900 | Open Service Access (OSA); Stage 2 | Rel-9 |
| TS 23.207 vj00 | End-to-End QoS Framework for GPRS | Rel-19 |
| TS 23.218 vj00 | IMS Call Model Specification | Rel-19 |
| TS 23.221 vj00 | 3GPP System Architectural Requirements | Rel-19 |
| TS 23.228 vj50 | IMS Stage-2 Service Description | Rel-19 |
| TS 23.271 vj00 | LCS Stage 2 Specification | Rel-19 |
| TS 23.280 vk10 | Common Architecture for Mission Critical Services | Rel-20 |
| TS 23.281 vk10 | MCVideo Functional Architecture and Flows | Rel-20 |
| TS 23.379 vk00 | MCPTT Functional Architecture | Rel-20 |
| TS 23.392 vj20 | MMTel Application Enablement | Rel-19 |
| TS 23.417 v1700 | IMS Core Component for NGN Architecture | Rel-7 |
| TS 23.517 v1800 | IMS Core Component for NGN Architecture | Rel-8 |
| TS 23.700 vk00 | XR Services Application Enablement Layer | Rel-20 |
| TS 23.701 vc00 | WebRTC Access to IMS Architecture Study | Rel-12 |
| TS 23.719 ve00 | Study on Service Domain Centralization (SeDoC) | Rel-14 |
| TR 23.794 vh00 | Study on enhanced IMS to 5GC integration | Rel-17 |
| TS 23.802 v1700 | Enhanced End-to-End QoS Architecture | Rel-7 |
| TS 23.806 v1700 | Voice Call Continuity between CS and IMS | Rel-7 |
| TS 23.815 v1500 | IMS Charging Implications | Rel-5 |
| TS 23.844 vc00 | IMS P2P Content Distribution Services Study | Rel-12 |
| TR 23.976 vj00 | Push Service Requirements Analysis | Rel-19 |
| TR 23.979 vj00 | PoC over 3GPP Systems Architectural Requirements | Rel-19 |
| TR 23.981 vj00 | IPv4 IMS Interworking and Migration Study | Rel-19 |
| TS 24.103 vj00 | Telepresence Protocol for IMS | Rel-19 |
| TS 24.147 vj00 | IMS Conferencing Protocol Details | Rel-19 |
| TS 24.166 vj00 | IMS Conferencing Management Object | Rel-19 |
| TS 24.167 vj00 | 3GPP IMS Management Object Specification | Rel-19 |
| TS 24.173 vj00 | Multimedia Telephony Service and Supplementary Services in IMS | Rel-19 |
| TS 24.186 vj60 | IMS Data Channel applications | Rel-19 |
| TS 24.196 vj00 | Enhanced Calling Name (eCNAM) Stage 3 Protocol | Rel-19 |
| TS 24.216 vj00 | Communication Continuity Management Object | Rel-19 |
| TS 24.229 vj50 | IMS call control protocol based on SIP and SDP | Rel-19 |
| TS 24.247 vj10 | IMS Messaging Service Protocol Details | Rel-19 |
| TS 24.259 vj00 | Personal Network Management (PNM) Protocol Details | Rel-19 |
| TS 24.286 vj00 | 3GPP TS 24.286: ICS Management Object | Rel-19 |
| TS 24.305 vj00 | Selective Disabling of 3GPP UE Capabilities | Rel-19 |
| TS 24.322 vj00 | IMS Tunneling over Restrictive Networks | Rel-19 |
| TS 24.323 vj00 | IMS Service Level Tracing Management Object | Rel-19 |
| TS 24.390 vj00 | USSD over IMS Procedures | Rel-19 |
| TS 24.391 vj00 | USSD over IMS Management Object Specification | Rel-19 |
| TS 24.404 v1700 | Communication Diversion Services (CDIV) | Rel-7 |
| TS 24.405 v1700 | Conference Service Protocol Description | Rel-7 |
| TS 24.406 v810 | Message Waiting Indication (MWI) Protocol | Rel-8 |
| TS 24.407 v830 | OIP and OIR Simulation Services Protocol | Rel-8 |
| TS 24.408 v1700 | TIP/TIR Services Protocol Specification | Rel-7 |
| TS 24.410 v810 | Protocol Description of HOLD Services | Rel-8 |
| TS 24.416 v1700 | Malicious Call Identification Service | Rel-7 |
| TS 24.428 v1700 | Common Basic Communication Procedures | Rel-7 |
| TS 24.447 v800 | Advice Of Charge (AOC) Service Protocol | Rel-8 |
| TS 24.454 v840 | Closed User Group (CUG) Protocol Specification | Rel-8 |
| TS 24.504 v8m0 | Communication Diversion Services Stage 3 | Rel-8 |
| TS 24.505 v810 | Protocol Description of the Conference Service | Rel-8 |
| TS 24.508 v820 | TIP and TIR Service Protocol Description | Rel-8 |
| TS 24.516 v830 | MCID Protocol Specification for NGN | Rel-8 |
| TS 24.523 vj00 | NGCN-NGN Interconnection Scenarios | Rel-19 |
| TS 24.524 vj00 | Hosted Enterprise Services Architecture | Rel-19 |
| TS 24.526 vj30 | UE Policies for 5GS; Stage 3 | Rel-19 |
| TS 24.528 v830 | Common Basic Communication Procedures for IMS Services | Rel-8 |
| TS 24.604 vj00 | Communications Diversion (CDIV) Protocol Spec | Rel-19 |
| TS 24.605 vj00 | 3GPP CONF Service Protocol Specification | Rel-19 |
| TS 24.606 vj00 | MWI Service Protocol Description | Rel-19 |
| TS 24.607 vj10 | OIP and OIR Supplementary Services Stage 3 | Rel-19 |
| TS 24.608 vj00 | 3GPP TS 24608: TIP/TIR Services Protocol | Rel-19 |
| TS 24.610 vj00 | Communication Hold (HOLD) Service Protocol | Rel-19 |
| TS 24.615 vj00 | Communication Waiting (CW) Service Protocol | Rel-19 |
| TS 24.616 vj00 | Malicious Call Identification (MCID) Protocol | Rel-19 |
| TS 24.623 vj00 | XCAP Protocol for Supplementary Services | Rel-19 |
| TS 24.628 vj00 | Common Basic Communication Procedures in IMS | Rel-19 |
| TS 24.642 vj00 | CCBS/CCNR/CCNL SIP Protocol Specification | Rel-19 |
| TS 24.647 vj00 | Advice of Charge (AOC) service protocol | Rel-19 |
| TS 24.654 vj00 | Closed User Group (CUG) supplementary service | Rel-19 |
| TS 24.803 vc00 | Telepresence using IMS - Study | Rel-12 |
| TS 24.819 v1700 | IMS Services via Fixed Broadband Access | Rel-7 |
| TR 24.930 vj00 | IMS Session Setup Signalling Flows | Rel-19 |
| TS 26.114 vj10 | IMS Multimedia Telephony Media Handling | Rel-19 |
| TS 26.131 vj00 | Terminal Acoustic Performance Requirements | Rel-19 |
| TS 26.132 vj00 | Terminal Acoustic Test Methods | Rel-19 |
| TS 26.141 vj00 | IMS Messaging & Presence Media Formats | Rel-19 |
| TS 26.237 vj00 | IMS for PSS and MBMS Control | Rel-19 |
| TS 26.238 vj00 | Framework for Live Uplink Streaming (FLUS) | Rel-19 |
| TS 26.264 vj20 | IMS-based AR Real-Time Communication | Rel-19 |
| TS 26.506 vj20 | Real-Time Media Communication Architecture for 5G | Rel-19 |
| TS 26.567 vj00 | IMS-based Split Rendering | Rel-19 |
| TS 26.804 vj10 | 5G Media Streaming Extensions Study | Rel-19 |
| TS 26.822 vj20 | 5G RTP Configurations Study Phase 2 | Rel-19 |
| TR 26.862 vh00 | Immersive Teleconferencing & Telepresence for Remote Terminals | Rel-17 |
| TR 26.902 vj00 | Video Codec Performance for 3GPP Packet Services | Rel-19 |
| TR 26.905 vj00 | Study on Mobile 3D Video Services | Rel-19 |
| TR 26.914 vj00 | Multimedia Telephony over IP Optimization | Rel-19 |
| TR 26.927 vj00 | AI/ML in 5G Media Services Study | Rel-19 |
| TR 26.944 vj00 | QoE, ESQoS and SQoS metrics for 3G multimedia services | Rel-19 |
| TR 26.948 vj00 | Video enhancements for 3GPP Multimedia Services | Rel-19 |
| TR 26.982 vj00 | Multiparty Real-Time Text Protocol Details | Rel-19 |
| TR 26.998 vj00 | 5G AR/MR Glasses Integration Study | Rel-19 |
| TS 27.060 vj00 | TE-MT Interworking for Packet Domain | Rel-19 |
| TS 28.701 vj00 | Core Network NRM IRP Requirements | Rel-19 |
| TS 28.702 vj00 | Core Network NRM IRP Information Service | Rel-19 |
| TS 28.704 vj00 | IMS NRM IRP Requirements | Rel-19 |
| TS 28.705 vj00 | IMS NRM IRP Information Service | Rel-19 |
| TS 28.706 vj00 | IMS NRM IRP Solution Set definitions | Rel-19 |
| TR 28.840 vi10 | Technical Report | Rel-18 |
| TS 29.061 vj00 | Packet Domain Interworking for PLMN | Rel-19 |
| TS 29.172 vj00 | EPC LCS Protocol (ELP) specification | Rel-19 |
| TS 29.176 vj40 | Nmf Service Based Interface for Media Function | Rel-19 |
| TS 29.199 v1900 | Multimedia Messaging Web Services | Rel-9 |
| TS 29.228 vj20 | Cx and Dx Interface Signaling Flows | Rel-19 |
| TS 29.229 vj10 | Diameter Protocol for Cx/Dx Interfaces | Rel-19 |
| TS 29.234 vb20 | WLAN-3GPP Interworking Stage-3 Protocol | Rel-11 |
| TS 29.278 vj00 | CAMEL Application Part (CAP) for IMS Phase 4 | Rel-19 |
| TS 29.328 vj20 | Sh and Dh Interfaces: HSS-AS Interactions | Rel-19 |
| TS 29.329 vj10 | Diameter Protocol for Sh Interface | Rel-19 |
| TS 29.330 vj00 | Diameter-based Sc Interface Specification | Rel-19 |
| TS 29.332 vj00 | MGCF-IM-MGW Interface Protocol (Mn) | Rel-19 |
| TS 29.412 v1810 | Trunking Gateway Control Procedures | Rel-8 |
| TS 29.421 v810 | IMS Interworking with External IP Networks | Rel-8 |
| TS 29.424 v801 | H.248 Profile for Trunking Media Gateways | Rel-8 |
| TS 29.458 v850 | SIP Transfer of Tariff Info for Charging | Rel-8 |
| TS 29.514 vj40 | 5G System; Policy Authorization Service; Stage 3 | Rel-19 |
| TS 29.562 vj40 | HSS Services for IMS & GBA Interworking | Rel-19 |
| TS 29.658 vj00 | SIP Transfer of Tariff Information | Rel-19 |
| TS 29.866 vj00 | IMS Disaster Prevention & Restoration Enhancement | Rel-19 |
| TR 29.949 vj00 | VoLTE IMS Roaming Architecture & Procedures | Rel-19 |
| TS 31.103 vj00 | ISIM Application Specification | Rel-19 |
| TS 31.829 vd00 | ISIM Conformance Requirements Technical Report | Rel-13 |
| TS 32.102 vj00 | Telecom Management Physical Architecture Framework | Rel-19 |
| TS 32.140 vj00 | Subscription Management (SuM) requirements | Rel-19 |
| TS 32.141 vj00 | Subscription Management (SuM) Architecture | Rel-19 |
| TS 32.182 vj00 | UDC Common Baseline Information Model (CBIM) | Rel-19 |
| TS 32.240 vj40 | Charging Management Architecture & Principles | Rel-19 |
| TS 32.250 vj00 | Circuit Switched Offline Charging | Rel-19 |
| TS 32.260 vj10 | IMS Charging Management | Rel-19 |
| TS 32.270 vj00 | MMS Charging Management Specification | Rel-19 |
| TS 32.271 vj20 | 3GPP LCS Charging Management Spec | Rel-19 |
| TS 32.272 vj00 | Charging for Push-to-Talk over Cellular (PoC) | Rel-19 |
| TS 32.277 vj20 | Charging Management for Proximity Services (ProSe) | Rel-19 |
| TS 32.291 vj40 | Charging Management: Service-Based Interface Protocol | Rel-19 |
| TS 32.296 vj00 | Online Charging System (OCS) Architecture | Rel-19 |
| TS 32.297 vj00 | Charging Data Record File Transfer | Rel-19 |
| TS 32.298 vj30 | Charging Data Record (CDR) Parameter Specification | Rel-19 |
| TS 32.299 vj00 | Diameter Charging Applications for 3GPP | Rel-19 |
| TS 32.409 vj00 | IMS Performance Management Measurements | Rel-19 |
| TS 32.410 vj00 | 3GPP TS 32.410: Key Performance Indicators (KPI) | Rel-19 |
| TS 32.454 vj00 | IMS Key Performance Indicators (KPIs) | Rel-19 |
| TS 32.631 vb00 | Core Network Resources IRP Requirements | Rel-11 |
| TS 32.632 vb00 | Core Network Resources IRP: Network Resource Model | Rel-11 |
| TS 32.731 vb00 | IMS Network Resource Model IRP Requirements | Rel-11 |
| TS 32.732 vb00 | IMS Network Resource Model IRP: Information Service | Rel-11 |
| TS 32.735 v1910 | IMS NRM IRP Bulk CM XML Format | Rel-9 |
| TS 32.736 vb00 | IMS NRM IRP Solution Set Definitions | Rel-11 |
| TS 32.808 v1800 | Common User Profile Storage Framework | Rel-8 |
| TS 32.833 vb00 | Converged OSS End-to-End Management Study | Rel-11 |
| TR 32.901 vj00 | UDC Application Data Models Study | Rel-19 |
| TS 33.107 vj00 | Lawful Interception Architecture & Functions | Rel-19 |
| TS 33.108 vj00 | LI Handover Interface Specification | Rel-19 |
| TS 33.141 vj00 | Security for Presence Service (Ut reference point) | Rel-19 |
| TS 33.203 vj10 | IMS Security Specification | Rel-19 |
| TS 33.310 vj50 | 3GPP Authentication Framework for Network Nodes | Rel-19 |
| TS 33.328 vj10 | IMS Media Plane Security Specification | Rel-19 |
| TS 33.790 vj10 | Security for Next-Gen Real-Time Communication Phase 2 | Rel-19 |
| TS 33.804 vc00 | Non-UICC SSO using SIP Digest credentials | Rel-12 |
| TS 33.856 vg10 | Security for 5G to 3G Voice Continuity | Rel-16 |
| TR 33.978 v1800 | Interim Security for Early IMS | Rel-8 |
| TS 43.129 vj00 | PS Handover in GERAN A/Gb and GAN Modes | Rel-19 |
| TR 43.901 vj00 | Generic Access to A/Gb Interface Feasibility Study | Rel-19 |
| TR 45.902 vj00 | Flexible Layer One (FLO) for GERAN | Rel-19 |