IP Multimedia Subsystem - PSTN to IMS Call

This flow covers a PSTN-to-IMS call with ISUP–SIP interworking on the originating side. To analyze SIP/RTP signaling in your own capture, VisualEther renders the Wireshark PCAP as a sequence diagram and Claude Code reads the call leg by leg.

This call flow covers the handling of a CS network originated call with ISUP. In the diagram the MGCF requests seizure of the IM CN subsystem side termination and CS network side bearer termination. When the MGCF receives an answer indication, it requests the IM-MGW to both-way through-connect the terminations. Originating and terminating end initiated call releases are also covered.

The following call flows analyze the PSTN to IMS call flow from different points of view:

• PSTN to IMS Call Flow
• PSTN to IMS Call Flow Poster (11x17)
• PSTN to IMS Call Overview
• High Level Flow (PSTN-IMS-Called UE)
• High Level Flow (With CSCF Details)
• IM-MGW Call Flow
• IM-MGW Context Diagram
• MGCF Call Flow
• MGCF Context Diagram
• I-CSCF Call Flow
• I-CSCF Collaboration Diagram
• Terminating S-CSCF Call Flow
• Terminating S-CSCF Context Diagram