This course presents the handling multimedia telephony service in 5G and related interworking procedures with 4G, as specified in the current R16 3GPP standards.

The course focuses on the voice/multimedia telephony service under IMS control for networks with 5G deployed. It presents the UE and network features and definitions that guarantee establishment, handling, and service continuity for the telephony service within the 5G ecosystem, including the interworking between 4G and 5G to support the device mobility and service continuity in a multi-access environment.


Technical knowledge of the voice service handling in mobile telecom networks is crucial.

Understanding the technical solutions for the handling of the voice service in 5G requires a good grasp of voice handling in 4G (VoLTE, with IMS control) and the general 5G network architecture. Attending Apis “VoLTE Overview” and “5G System Overview” courses, or having the equivalent knowledge will allow the participants to benefit fully from the course.

Note: This course is under development and the content may be subject to changes.

Network Architecture

  • Brief overview of the 4G and 5G System architecture.
  • Overview of deployment options for 4G and 5G core networks.
  • Overview of deployment options for connecting 4G/5G radio to 4G/5G core networks.
  • Brief overview of the IMS functionalities.
  • Protocol used for communication on various interfaces within 4G/5G core networks, towards RAN, and to/inside IMS network elements.
  • Overview of idle and connected mode mobility procedures for UEs moving between 2G/3G/4G/5G radio and core network.
  • Overview of various possibilities to handle IMS signaling and media between 4G/5G RAN and core network.

IMS Voice over PS: 4G versus 5G

  • IMS usage of PDN Connections and EPS Bearers in 4G.
  • IMS usage of PDU Sessions and QoS Flows in 5G.
  • Selected details of IMS procedures and IMS related procedures in 5G.
  • Subscription data synchronization for IMS.
  • Requesting the multimedia service: setting up telephony-specific behavior and resources at 5G Registration, PDU Session Establishment, IMS Registration and IMS Session Setup.
  • Protocol stack for IMS media transport over NR, E-UTRA, and in Dual Connectivity scenarios.
  • Signaling and media flow for various roaming scenarios.
  • Single or dual IMS registration for UE.
  • SMS transport options over 4G, 5G, and IMS over 4G or 5G.

5GS Support for Telephony

  • UE Capabilities related to IMS voice support and IMS related network procedures.
  • Handling of UE related capabilities and IMS related subscription parameters between 5G core network functions.
  • IMS PDU Session attributes.
  • PS Data Off service exemptions for IMS service handling.
  • ANDSP and URSP for IMS services.
  • P-CSCF discovery procedure.

IMS Support for telephony

  • Deployment options for HSS/UDM/UDR.
  • HTTP-based comunication for IMS service handling; mapping of Diameter messages to HTTP service requests and responses.
  • UE and network features to be supported according to GSM Association “IMS Profile for Voice, Video and Messaging over 5GS”.
  • UE inputs for Originating Access Domain Selection for MO IMS calls.
  • Media codecs and media transport.
  • Role of Telephony Application Server.
  • Selected SIP message parameters for multimedia telephony.

Interworking: Core Network

  • UE idle mode mobility procedures between 2G, 3G, 4G, and 5G.
  • UE connected mode mobility procedures between 2G, 3G, 4G, and 5G.
  • Handling of data connections in idle/connected mode mobility procedures.
  • PDN Connection/PDU Session establishment aspects: CN domain selection, redirection, etc.
  • Single and dual registration mode UEs.
  • Interworking with and without N26 interfaces between 4G and 5G core networks.
  • RAT Fallback and EPS Fallback for IMS sessions.
  • Handling of Terminating Access Domain Selection for MT IMS calls.

Interworking: Access Network

  • 5G Access Network options: NR, E-UTRA, WiFi, Fixed Access.
  • Various intra-/inter-RAT Dual Connectivity options.
  • System Information parameters and UE radio capabilities related to IMS and 4G/5G interworking.
  • RAN bases Dual Connectivity procedures.
  • CN-based and RAN-based User Plane splitting options.
  • Session transfer procedures between 3GPP and non-3GPP access, e.g. Wi-Fi to/from 5G NR.
  • RAN procedures for Dual Connectivity handling: Secondary Node handling, handover procedures.
  • Unified Access Control in 5G and IMS related options for UAC.

Duration: 2 days

We offer substantial discounts for group bookings, and we have corporate rates with most of the operators and equipment suppliers in the world.

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