1. Internet Telephony 1 Reference Architecture of R00

2. Internet Telephony 2 Support of Roaming Subscribers via the service platform in the Home Network via an external service platform

3. Internet Telephony 3 UE Accessing IM Subsystem Services In the visited network

4. Internet Telephony 4 Public and Private Identities One or more private user identities IMSI within a NAI is not used for routing of SIP messages One or more public user identities

5. Internet Telephony 5 Relationship of Private and Public User Identities

6. Internet Telephony 6 Roles of CSCF Call State Control Function SIP proxy servers Proxy CSCF The first contact point within the IM subsystem Forward the SIP register requests from the UE to an I-CSCF Forward the SIP messages from the UE to the S- CSCF CDR Authorisation of bearer resources and QoS management. For details see TS 23.207

7. Internet Telephony 7 Interrogating CSCF The contact point within an operator ’ s network Assign an S-CSCF to a user performing SIP Reg Route a SIP request received from another network towards the S ‑ CSCF Obtain from HSS the address of the S-CSCF Forward the SIP request or response to the S ‑ CSCF determined by the step above CDR

8. Internet Telephony 8 Serving CSCF A registrar Session control for the registered endpoint's sessions. Interaction with Services Platforms On behalf of an originating endpoint On behalf of an destination endpoint CDR Authenticate the UEs

9. Internet Telephony 9 Registration Information Flow

10. Internet Telephony 10 Re-Registration

11. Internet Telephony 11 NodeBefore RegistrationDuring RegistrationAfter Registration UE - in local networkCredentials Home Domain Proxy Name/Address Same as before registrationCredentials Home Domain Proxy Name/Address Proxy ‑ CSCF - in Home or Visited network Routing FunctionInitial Network Entry point UE Address Public and Private User IDs Final Network Entry point UE Address Public and Private User IDs Interrogating ‑ CSCF - in Home network HSS or SLF Address Serving ‑ CSCF address/name P ‑ CSCF Network ID Home Network contact Information No State Information HSSUser Service Profile P ‑ CSCF Network IDServing ‑ CSCF address/name\ Serving ‑ CSCF (Home) No state informationHSS Address/name User profile (limited – as per network scenario) Proxy address/name P ‑ CSCF Network ID Public/Private User ID UE IP Address May have session state Information Same as during registration

12. Internet Telephony 12 De-registration

13. Internet Telephony 13 Call flow

14. Internet Telephony 14

15. Internet Telephony 15 Different Kinds of CSCFs P-SCSF Visited B S-CSCF Home A 1 2 7 10 1112 13 15 17 P-CSCF Visited A 18 AB GGSN SGSN Radio Access Network GGSN SGSN Radio Access Network S-CSCF Home B 8 I-CSCF HSS 9 14 6 34 I-CSCF HSS 5 16

16. Internet Telephony 16 PSTN origination procedure

17. Internet Telephony 17 PSTN origination procedure

18. Internet Telephony 18 PSTN termination procedure

19. Internet Telephony 19 PSTN termination procedure