IP Multimedia Subsystem (IMS) Architecture and Protocols

Did you know that operators deploying IMS-based services have achieved milestones like Telia Finland’s commercial VoLTE launch after rigorous end-to-end IMS testing, VoWiFi-driven savings of 1 cent per minute per subscriber that can deliver over $2.2 billion in TCO reduction in five years, and flexible 5G integration models that extend existing IMS investments into VoNR and converged 5G voice architectures?

Course Overview

The IP Multimedia Subsystem (IMS) Architecture and Protocols course by Rcademy is designed to equip core network engineers, protocol engineers, service engineers, technical managers, and system integrators with comprehensive understanding of IMS architecture, functional entities, reference points, and protocols as defined by 3GPP standards for 4G, 5G, and converged networks. Participants gain expert-level knowledge of Session Initiation Protocol (SIP), Diameter, Session Description Protocol (SDP), IMS registration and session establishment procedures, Policy and Charging Control, security mechanisms, and VoLTE/VoWiFi architectures.​

Without specialized IMS training, professionals may struggle to analyze end-to-end VoLTE signaling traces, troubleshoot registration failures, validate IMS infrastructure configurations, or plan VoNR deployments that protect legacy investments, limiting their ability to support critical voice service deployments and operational excellence. This comprehensive course provides a structured path to mastery across IMS protocols, call flows, interworking scenarios, and 5G integration strategies, preparing attendees to lead IMS deployment, operations, and optimization initiatives.​

The IP Multimedia Subsystem (IMS) Architecture and Protocols course covers IMS fundamentals and evolution, IMS architecture overview, core network functions, interworking functions, reference points and interfaces, SIP fundamentals, Session Description Protocol, Diameter protocol in IMS, IMS identities and addressing, registration procedures, session establishment and termination, Policy and Charging Control, security architecture, VoLTE architecture and procedures, VoWiFi architecture and procedures, IMS services and applications, service provisioning and triggering, roaming and interconnection, signaling analysis and troubleshooting, performance and optimization, and IMS in 5G networks. Participants learn to apply IMS call flow analysis, design PCC and QoS architectures, architect security mechanisms, execute interworking with circuit-switched networks, and troubleshoot signaling issues using protocol analyzers.​

Real-world cases show how Telia Finland achieved VoLTE implementation in Q3 2017 through systematic testing that validated fundamental VoLTE functionality, voice continuity, data-voice compatibility, and roaming scenarios, requiring careful UE configuration with XML patches for APNS-CONF, CARRIER-CONFIG, and vendor parameters including codec specifications (AMR-WB, EVS) and IPsec authentication (IKEv1/IKEv2, DPD intervals, SA lifetimes).

Studies also show that VoWiFi implementation across mobile networks can save operators 1 cent per minute per subscriber on voice calls, with one modeled operator achieving $2.2 billion in total cost of ownership savings over five years (88% operational expense savings) by offloading voice traffic from expensive RANs to Wi-Fi via ePDG/TWAG, extending coverage indoors, and deploying in approximately three months.

Take charge of your IMS expertise. Enroll now in the Rcademy IP Multimedia Subsystem (IMS) Architecture and Protocols course to master the protocol knowledge and signaling analysis skills that drive successful voice service deployments.

Who Should Attend?

The IP Multimedia Subsystem (IMS) Architecture and Protocols course by Rcademy is ideal for:

• Core network engineers and architects
• Service engineers and IP engineers
• Radio and packet core engineers
• Protocol engineers and signaling specialists
• Technical managers and project managers
• Product managers overseeing IMS projects
• Network planning and optimization engineers
• System integrators and consultants
• Solutions architects designing converged networks
• Software and systems engineers developing IMS applications
• VoLTE and VoWiFi deployment engineers
• SIP/Diameter protocol analysts
• Network operations center (NOC) engineers
• Quality assurance engineers for IMS testing
• Anyone seeking comprehensive IMS certification

What are the Training Goals?

The main objectives of the IP Multimedia Subsystem (IMS) Architecture and Protocols course are to enable professionals to:

• Master comprehensive IMS architecture, functional entities, reference points, and protocols as defined by 3GPP standards for 4G, 5G, and converged networks.
• Develop expert-level knowledge of Session Initiation Protocol (SIP), Diameter, and Session Description Protocol (SDP) in IMS context.
• Understand IMS-based services including VoLTE, VoWiFi, video calling, messaging, conferencing, and multimedia applications.
• Apply IMS registration, session establishment, and routing procedures through detailed call flow analysis and signaling traces.
• Design and implement Policy and Charging Control (PCC), Quality of Service (QoS), and charging architectures in IMS networks.
• Architect security mechanisms including authentication, encryption, and privacy protection in IMS deployments.
• Execute IMS interworking with circuit-switched networks, PSTN breakout, and roaming scenarios.
• Troubleshoot IMS signaling issues using protocol analyzers and trace analysis tools for operational excellence.

How Will This Training Course Be Presented?

At Rcademy, the extensive focus is laid on the relevance of the training content to the audience. Thus, content is reviewed and customised as per the professional backgrounds of the audience.

The training framework includes:

• Expert-led lectures by senior IMS and core network professionals using audio-visual sessions
• Hands-on protocol analysis with Wireshark and signaling trace tools
• Interactive workshops for SIP/Diameter message analysis and call flow debugging
• Case studies covering Finnish VoLTE deployment, VoWiFi economics, and 5G VoNR strategies
• Practical exercises analyzing registration, session establishment, and troubleshooting scenarios

The theoretical part of training is delivered by an experienced professional from the relevant domain, using audio-visual presentations. This protocol-focused approach ensures IMS professionals translate theory into practical workflows through signaling trace analysis, call flow validation, and systematic troubleshooting methodologies.​

This comprehensive certification model ensures participants gain both architectural knowledge and hands-on proficiency to immediately apply IMS protocol expertise in deployment, operations, and optimization roles.​

Register now to experience a rigorous, hands-on learning journey designed to equip you for leading IMS deployment, troubleshooting, and 5G voice integration projects.

Course Syllabus

Module 1: IMS Fundamentals and Evolution

• Telecom evolution from circuit-switched to all-IP packet-switched networks.​
• IMS definition, purpose, and role in Next Generation Networks (NGN).​
• IMS as a service delivery platform: convergence of voice, video, and data.​
• IMS standardization: 3GPP, 3GPP2, ETSI TISPAN, and CableLabs PacketCable.​
• IMS market opportunities and business drivers for operators.​
• Benefits of IMS: service creation, interoperability, and cost-effective delivery.​

Module 2: IMS Architecture Overview

• IMS reference architecture and functional layers: application, control, media, and transport.​
• IMS as a service-oriented architecture (SOA) and separation of control/user planes.​
• IMS support for multiple IP Connectivity Access Networks (IP-CANs): 3G, 4G, 5G, Wi-Fi, fixed broadband.​
• IMS deployment models: centralized, distributed, and cloud-native architectures.​
• IMS roaming architecture: home and visited network responsibilities.​

Module 3: IMS Core Network Functions

• Call Session Control Functions (CSCF): P-CSCF, I-CSCF, S-CSCF roles and responsibilities.​
• Home Subscriber Server (HSS): subscriber data management and authentication.​
• Subscription Locator Function (SLF) for distributed HSS architectures.​
• Application Servers (AS): SIP AS, OSA-SCS, IM-SSF for service logic execution.​
• Media Resource Function (MRF): MRFC and MRFP for media processing and conferencing.​
• Media Resource Broker (MRB) for media resource allocation.​

Module 4: IMS Interworking Functions

• Breakout Gateway Control Function (BGCF) for PSTN call routing.​
• Media Gateway Control Function (MGCF) for circuit-switched interworking.​
• Media Gateway (MGW) for media conversion between IP and circuit-switched networks.​
• Signaling Gateway (SGW) for SS7 signaling interworking.​
• IMS-Application Layer Gateway (IMS-ALG) and Translation Gateway (TrGW).​
• Interconnection Border Control Function (IBCF) for carrier-to-carrier interconnection.​

Module 5: IMS Reference Points and Interfaces

• User-to-network interfaces: Gm (UE to P-CSCF) interface and signaling flows.​
• Control layer interfaces: Mw (CSCF to CSCF), ISC (S-CSCF to AS), Cx/Dx (CSCF to HSS).​
• Media control interfaces: Mr/Mr’ (S-CSCF to MRFC), Mg (MGCF to MGW).​
• Policy and charging interfaces: Rx (P-CSCF to PCRF), Gx (PGW to PCRF).​
• Charging interfaces: Rf (offline charging), Ro (online charging).​
• Utility interfaces: Sh/Dh (AS to HSS for user data), Ut (UE to AS for configuration).​

Module 6: Session Initiation Protocol (SIP) Fundamentals

• SIP architecture, components, and role in IMS session control.​
• SIP methods: REGISTER, INVITE, ACK, BYE, CANCEL, UPDATE, PRACK, and others.​
• SIP responses: provisional (1xx), success (2xx), redirection (3xx), client error (4xx), server error (5xx).​
• SIP message structure: request line, headers, and message body.​
• SIP transactions, dialogs, and sessions: lifecycle management.​
• SIP extensions for IMS: P-headers, preconditions, and IMS-specific requirements.​

Module 7: Session Description Protocol (SDP)

• SDP purpose and role in multimedia session negotiation.​
• SDP message structure: session-level and media-level descriptions.​
• Media types, formats, transport protocols, and codec negotiation.​
• SDP offer/answer model in SIP-based session establishment.​
• Bandwidth, quality parameters, and media attributes in SDP.​

Module 8: Diameter Protocol in IMS

• Diameter protocol architecture and role in IMS for AAA and policy.​
• Diameter message format: commands, Attribute-Value Pairs (AVPs), and sessions.​
• Diameter applications in IMS: Cx/Dx, Sh/Dh, Rx, Gx, Rf, Ro interfaces.​
• Diameter routing, peer discovery, and transport security.​
• Diameter vs. RADIUS: protocol comparison and migration considerations.​

Module 9: IMS Identities and Addressing

• IMS Public User Identity (IMPU): SIP URI and Tel URI formats.​
• IMS Private User Identity (IMPI): authentication and subscription identification.​
• Relationship between IMPU, IMPI, and device identities (IMEI).​
• Public Service Identity (PSI) for application and service identification.​
• Wildcarded Public User Identity for scalable provisioning.​

Module 10: IMS Registration Procedures

• IMS registration architecture and flows: UE, P-CSCF, I-CSCF, S-CSCF, HSS.​
• Registration state machines and timers.​
• Constructing the SIP REGISTER request: headers, authentication, and security.​
• Authentication and key agreement (AKA) in IMS using Diameter Cx interface.​
• Re-registration, de-registration, and subscription refresh mechanisms.​
• Emergency registration procedures for public safety calls.​

Module 11: IMS Session Establishment and Termination

• IMS session setup: originating and terminating call flows.​
• Constructing the SIP INVITE request: routing headers, SDP offer, and preconditions.​
• Session routing through P-CSCF, S-CSCF, and Application Servers.​
• Media negotiation and codec selection using SDP offer/answer.​
• Resource reservation and QoS establishment using preconditions.​
• Session modification: re-INVITE and UPDATE procedures.​
• Session release: BYE request and session teardown flows.​

Module 12: Policy and Charging Control (PCC) in IMS

• PCC architecture: PCRF, PCEF, BBERF, TDF, and their roles.​
• Policy Control Function (PCF) in 5G Core integration with IMS.​
• QoS management: QoS Class Identifier (QCI) in LTE and 5QI in 5G.​
• Dynamic policy rules and service data flow detection.​
• Charging architectures: online (OCS) and offline (OFCS) charging systems.​
• Rx interface: AF (P-CSCF) to PCRF communication for session-based policies.​
• Gx interface: PCEF to PCRF for bearer establishment and policy enforcement.​

Module 13: IMS Security Architecture

• IMS security domains: access security, network domain security, and application security.​
• Authentication and Key Agreement (AKA): IMS-AKA procedures.​
• IPsec tunnel establishment between UE and P-CSCF for signaling protection.​
• Security Association (SA) management and integrity protection.​
• Encryption of SIP signaling and media streams (SRTP).​
• Network domain security: hop-by-hop security using TLS and IPsec/IKEv2.​
• Privacy and identity protection: P-Asserted-Identity and anonymization.​

Module 14: VoLTE (Voice over LTE) Architecture and Procedures

• VoLTE service architecture and IMS integration with LTE/EPS.​
• LTE bearer establishment: default and dedicated bearers for VoLTE.​
• VoLTE registration and IMS PDN connection setup.​
• VoLTE call establishment: mobile-originated and mobile-terminated flows.​
• Quality of Service (QoS) for VoLTE: guaranteed bit rate and latency requirements.​
• VoLTE supplementary services: call forwarding, call waiting, conference calling.​
• Circuit-Switched Fallback (CSFB) and Single Radio Voice Call Continuity (SRVCC).​

Module 15: Voice over WiFi (VoWiFi) Architecture and Procedures

• VoWiFi architecture: trusted and untrusted non-3GPP access.​
• Evolved Packet Data Gateway (ePDG) for secure VoWiFi connectivity.​
• IKEv2 and IPsec tunnel establishment for untrusted WiFi access.​
• VoWiFi registration and PDN connection procedures.​
• VoWiFi call flows and media stream handling.​
• Mobility between WiFi and LTE: handover procedures and ANDSF role.​
• VoWiFi optimization: QoS, WMM, and 802.11e for voice quality.​

Module 16: IMS Services and Applications

• IMS Multimedia Telephony Service (MMTel) and supplementary services.​
• Rich Communication Services (RCS) and Advanced Messaging.​
• Video calling and video conferencing over IMS.​
• Messaging services: native IMS messaging, SMS over IMS, and MMS.​
• Push-to-Talk over Cellular (PoC) and group communication.​
• Presence and instant messaging services.​
• Location-based services and emergency services (E911/E112).​

Module 17: IMS Service Provisioning and Triggering

• Service profiles and initial Filter Criteria (iFC) in HSS.​
• Service triggering: matching criteria and AS invocation.​
• Application Server (AS) selection and service chaining.​
• Service continuity and user experience management.​

Module 18: IMS Roaming and Interconnection

• IMS roaming scenarios: home routing and visited network services.​
• Service-oriented Interconnection (SoIx) and Connectivity-oriented Interconnection (CoIx).​
• Interconnection Border Control Function (IBCF) and IPX network integration.​
• Roaming charging and settlement considerations.​

Module 19: IMS Signaling Analysis and Troubleshooting

• Protocol analyzer tools: Wireshark, NetScout, and vendor-specific platforms.​
• Capturing and analyzing SIP traces in IMS networks.​
• Diameter message analysis on Cx, Sh, Rx, and Gx interfaces.​
• Common IMS signaling issues: registration failures, call setup failures, media problems.​
• Root cause analysis and troubleshooting methodology.​

Module 20: IMS Performance and Optimization

• IMS Key Performance Indicators (KPIs): registration success rate, call setup success rate, latency.​
• Capacity planning and dimensioning for IMS networks.​
• Load balancing across CSCF and AS instances.​
• Voice quality optimization: codec selection, jitter, packet loss mitigation.​
• End-to-end Quality of Experience (QoE) monitoring and improvement.​

Module 21: IMS in 5G Networks

• IMS evolution for 5G: integration with 5G Core (5GC).​
• Voice over 5G NR (Vo5G/VoNR) architecture and procedures.​
• Network slicing and IMS: dedicated slices for voice and multimedia services.​
• Service-Based Architecture (SBA) and IMS northbound interfaces.

Training Impact

The impact of IP Multimedia Subsystem (IMS) Architecture and Protocols training is visible in how operators achieve rapid VoLTE rollout through rigorous testing, deliver multi-billion dollar TCO savings via VoWiFi offloading, and flexibly integrate IMS with 5G Core using multiple deployment strategies.​

Telia Finland – Systematic IMS and VoLTE Implementation with Rigorous Testing

Implementation: Telia Finland, along with DNA and Elisa, deployed IMS-based network infrastructure to introduce VoLTE, VoWiFi, and SMS over IP to the Finnish public, with Telia achieving VoLTE implementation in Q3 2017. The deployment required careful configuration of VoLTE-capable devices with three separate XML patches (APNS-CONF, CARRIER-CONFIG, and vendor patches) based on detailed network operator requirements, including UE options to turn VoLTE on/off, set VoLTE as default calling mode, specify emergency call preferences, define codec specifications (AMR-WB, EVS), and configure IPsec parameters for authentication including IKEv1/IKEv2, DPD intervals, and SA lifetimes. Telia’s general requirements dictated that UE should have options to turn on/off VoLTE, set VoLTE instead of CSFB as default calling mode, use VoLTE calling even when mobile data is disabled, specify emergency call preference as VoLTE-CS-other, include location info in both normal and emergency calls, define VoLTE codec specifications, set VoLTE as primary option for voice, and set IP as primary option for SMS. The configuration specified IPSec protocol usage with Ikev1 and Ikev2 RCT algorithms, SA lifetime, and DPD interval parameters to ensure secure, reliable VoLTE sessions.​

Results: Telia’s systematic testing approach validated fundamental VoLTE functionality, voice continuity in changing network environments, data-voice compatibility in simultaneous use cases, and VoLTE compatibility during roaming, ensuring reliability, performance, and service maturity before commercial availability. Quality control procedures required cross-examination between Telia-Elisa and Telia-DNA USIM for all call sessions, five to ten times repetition for voice quality monitoring test cases, and verification of priority one test cases for each firmware or IMS network update. The comprehensive testing covered UE attach, IMS registration, session establishment, and end-to-end signaling, demonstrating how rigorous IMS verification is crucial to successful VoLTE rollout and directly reflects the protocol analysis, call flow mastery, and troubleshooting skills taught in comprehensive IMS certification courses. DNA became the first operator to launch VoLTE and VoWiFi services in Finland, followed by Elisa and Telia, with all three operators viewing IMS service not as a revenue generation opportunity but as a complimentary service offered to IMS-enabled UEs to improve customer experience.​

Major US Operators – VoWiFi Delivering $2.2B TCO Savings and Expanded Coverage

Implementation: ACG Research analyzed VoWiFi deployment economics for a major operator and found that implementing VoWiFi across the mobile network can save 1 cent per minute per subscriber on voice calls, resulting in $2.2 billion in total cost of ownership savings over five years, with operational expenses accounting for 88% of total savings. The analysis modeled a subscriber base starting at 5–7% VoWiFi penetration and growing to 25–27%, showing that offloading voice traffic from RANs to Wi-Fi access networks via ePDG (for untrusted WiFi) and TWAG (for trusted WiFi) dramatically reduces capital expenditure on expensive RAN buildouts and spectrum while solving indoor coverage problems and protecting against customer churn. Major US carriers including AT&T, Verizon, T-Mobile, and Sprint deployed VoWiFi, leveraging the existing IMS core used for VoLTE and adding only WiFi access gateways (ePDG/TWAG) to enable seamless handover between WiFi and LTE, maintain consistent policy enforcement and charging, and support service continuity regardless of user location.​

Results: For subscribers, VoWiFi offers improved indoor wireless coverage, better call quality and security over Wi-Fi, and service continuity and seamless handover as subscribers roam or move indoors/outdoors. For operators, VoWiFi offers a cost-effective way to offload RAN traffic, increased capacity and coverage without investing in expensive RAN buildouts or additional wireless spectrum, higher customer satisfaction and loyalty, and new revenue generation opportunities through additional Wi-Fi services including strategic alliances with MSOs or MVNOs, location-based services for increased access to goods and services, replacing landlines in households to increase service portfolio, and increasing number of calls at lower cost per call to increase network efficiencies and marginal revenue. The approximately three-month deployment time for VoWiFi compared to lengthy RAN buildouts, combined with dramatic TCO savings and coverage extension, demonstrates the compelling economics and strategic value of IMS-based VoWiFi implementations.​

Be inspired by how Telia, US carriers, and 5G providers deliver seamless voice and save billions. Join the Rcademy IP Multimedia Subsystem (IMS) Architecture and Protocols course to gain the skills that drive successful voice networks.