IMS Subscriber to IMS Subscriber Call Flow

The diagrams below trace a call between two IMS subscribers.

• The calling IMS subscriber is currently roaming outside the home network.
• The called user is registered in the home network.
• The caller and the called user require resource reservation before the call can be set up.

The major steps in the call flow are:

• IMS routing of the initial SIP INVITE.
• IMS routing of the first response to the INVITE.
• Resource allocation via PDP context activation.

The following diagrams slice and dice the IMS to IMS call flow:

• IMS to IMS Call Flow
• IMS to IMS Call Flow Poster (11x17)
• IMS to IMS Call Flow Overview
• IMS to IMS call flow with focus on UE and Network Interactions
• IMS to IMS Call Flow that focuses on interactions between the UE, the visited and the home IMS networks.
• Originating UE Role Sequence Diagram
• Originating UE Role Collaboration Diagram
• Originating P-CSCF Role Sequence Diagram
• Originating P-CSCF Role Collaboration Diagram
• Originating S-CSCF Role Sequence Diagram
• Originating S-CSCF Role Collaboration Diagram
• Terminating I-CSCF Role Sequence Diagram
• Terminating I-CSCF Role Collaboration Diagram
• Terminating S-CSCF Role Sequence Diagram
• Terminating S-CSCF Role Collaboration Diagram
• Terminating P-CSCF Role Sequence Diagram
• Terminating P-CSCF Role Collaboration Diagram
• Terminating UE Role Sequence Diagram
• Terminating UE Role Collaboration Diagram