IP Multimedia Subsystem (IMS) Call Flows

The sequence diagrams were generated using EventStudio System Designer.

Analyzing a live SIP/VoLTE capture instead of a modeled flow? VisualEther renders a Wireshark IMS PCAP as a sequence diagram like these, and Claude Code can explain a failed registration, codec negotiation, or call setup.

IP Multimedia Subsystem (IMS) Sequence Diagrams

IMS Registration

An IMS terminal accesses the home IMS via a visited IMS. Unauthenticated registration followed by authenticated registration is covered here.

IMS to IMS Call Flow

Call flow for an IMS subscriber to another IMS subscriber is covered here.

PSTN to IMS Call

A ISUP to IMS call flow is described here. Megaco/H.248 interactions and ISUP-SIP interworking are covered in detail.

IMS to PSTN Call

Here we explore an IMS to PSTN terminating call. The call flow covers the IMS-ISUP interworking and Megaco/H.248 interactions between the MGCF and IM-MGW. Call routing via the BGCF is also illustrated.

SDP Codec Selection and QoS Signaling in an IMS call

An IMS call is analyzed with a focus on the SDP interactions involved in codec selection and QoS.

IMS Presence Subscription and Notification

IP Multimedia Subsystem (IMS) provides a framework for building advanced telecom services. One such service is network wide publication and subscription of presence information.

IMS Presence Resource List Subscription and Notification

This scenario describes how a user can subscribe to a predefined list of subscribers via a Resource List Server. The RLS handles the interactions needed for presence subscription for individual users on that list.

IMS Conference Call

Setup of an IMS conference call with REFER based invitation to other subscribers.

IMS Push-to-talk Sequence Diagram - Pre-established Session

Push-to-talk communication between IMS users that have pre-established a session.