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IMS Registration Sequence Diagrams

This sequence diagram details the message interactions involved in IMS registration. IMS registration from a visited IMS network is covered. The interactions covered are:

  • Terminal attaching to the GPRS Network.
  • Terminal activates a PDP context.
  • An unauthenticated IMS registration is attempted.
  • IPSec security association is established between the User terminal and the P-CSCF.
  • Finally the terminal performs an IPSec protected registration that completes the authentication of the network and the terminal.

IMS Registration pdf                                 IMS Registration Poster (11x17) pdf
The diagrams on this page were generated with EventStudio System Designer 4.0. You can download the FDL source for these diagrams by clicking the button on the left.

Different aspects of this registration are discussed in the following diagrams:

IMS Registration Overview
The following diagram provides a single sheet overview of the message interactions involved in IMS registration. Interaction details and remarks are omitted from the diagram.

 IMS Registration Overview pdf

IMS Registration (High Level Diagram)
The visited network first performs an unauthenticated registration with the home network. This is followed up with an authenticated registration.

 Registration Interactions between Visited and Home IMS Networks pdf

IMS Registration (Interactions between UE, Visited and Home Networks)
The following diagram adds more details. Interactions between the UE, Visited and Home network are covered. The diagram also shows the message exchanges involving subscriber and the subscriber database HSS (represented as the Home Core Network).

 Registration Interactions between User Equipment, the  Visited Network and the Home IMS Network pdf

User Equipment (UE) Role
UE is the initiator of the registration sequence It performs the following steps:
  • Attach and PDP context activation
  • Unauthenticated registration attempt.
  • IPSec Security Association establishment
  • Authenticated registration

UE Role Sequence Diagram pdf                                        UE Role Collaboration Diagram pdf

P-CSCF Role
The P-CSCF resides in the visited network. It acts as the UE's gateway into the UE's home network. The P-CSCF is responsible for:
  • Identifying the home IMS network.
  • Routing traffic to and from the home IMS network.
  • Establishing the IPSec security association

P-CSCF Role Sequence Diagram pdf                           P-CSCF Role Collaboration Diagram pdf

I-CSCF Role
The I-CSCF resides in the home network. It acts as the front-end of the Home IMS network. The I-CSCF is responsible for:
  • Interfacing with the P-CSCF in the visited network.
  • Selecting the S-CSCF by querying the HSS.

I-CSCF Role Sequence Diagram pdf                           I-CSCF Role Collaboration Diagram pdf

S-CSCF Role
The S-CSCF resides in the home network. The S-CSCF is responsible for:
  • Handling the registration request from the I-CSCF.
  • Pulling the authentication vectors from the HSS
  • Passing the authentication vectors to the P-CSCF via the I-CSCF.
  • Authenticate the user in the second registration attempt.

S-CSCF Role Sequence Diagram pdf                       S-CSCF Role Collaboration Diagram pdf

Role Wise Summary
Role wise summary of all the components involved in IMS registration.

IMS Registration Role Wise Summary
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