IP Multimedia Subsystem & W-CSCF Speaker: Meng-Ta Hsu

Outline IP Multimedia Subsystem concepts Role of Cx interface Application level registration procedures Procedures for IP multimedia sessions W-CSCF Summary

IP Multimedia Subsystem Introduced in the 3GPP Release 5 Based on the 3G GPRS Core Network Enables IP multimedia services for the mobile users Support interworking with PSTN

3GPP Architecture PSTN CSCF HSS Internet RNC SGSN GGSN MGCF MGW MGW Legacy mobile signaling network Signaling (SS7 or IP based) Circuit Packet (user traffic and/or signaling) R-SGW Cx CSCF HSS Internet RNC Iu_PS SGSN GGSN Node B MGCF MS Iu_CS (user traffic) Node B PSTN MS MGW MGW Iu_CS (control part) MAP MAP MSC Server GMSC Server T-SGW

Call Session Control Function (CSCF) A SIP Proxy Performs session initiation, modification, deletion control Interacting with HSS to receive user subscription information Supports session routing and address mapping Interacting with service platform to support advanced services

CSCF

Proxy-CSCF (P-CSCF) The first contact point within the IMS A SIP proxy to redirect SIP messages toward MS’s home network Its address is discovered by MS following PDP context activation procedure P-CSCF discovery Use DHCP/DNS procedure Use PDP context activation message

Interrogating-CSCF (I-CSCF) Assign a S-CSCF to the MS Route a SIP message from another network towards the S-CSCF A SIP Proxy

Serving-CSCF (S-CSCF) Control the session state Download user profile from HSS Interact with Service Platforms A SIP Proxy, Registrar

IMS Architecture for Service Provision

Role of Cx interface Procedure related to Support information transfer between CSCF and HSS Procedure related to Location management procedures User data handling procedures User authentication procedures Cx interface is implemented by DIAMETER protocol

Location management procedures – User registration status query Used between the I-CSCF and the HSS during SIP registration Diameter command: User-Authorization-Request/Answer (UAR/UAA) To authorize the registration of the user To obtain the user registration status UAR I - CSCF HSS UAA

Location management procedures – S-CSCF registration/deregistration notification Used between the S-CSCF and the HSS during SIP registration Diameter command: Server-Assignment-Request/Answer (SAR/SAA) To assign and S-CSCF to a MS To download user profile from HSS SAR S - CSCF HSS SAA

Location management procedures – User location query To obtain the name of the S-CSCF where a MS is registered Diameter command: Location-Info-Request/Answer (LIR/LIA) LIA LIR I - CSCF HSS

Authentication procedures Used between the S-CSCF and the HSS to exchange authentication information To retrieve authentication vectors from the HSS Diameter command: Multimedia-Auth-Request/MAA MAA MAR S - CSCF HSS

First Time Registration UAR: User-Authorization-Request UAA: User-Authorization-Answer MAR: Multimedia-Authentication-Request MAA: Multimedia-Authentication-Answer SAR: Server-Assignment-Request SAA: Server-Assignment-Answer

Re-Registration procedures UAR: User-Authorization-Request UAA: User-Authorization-Answer SAR: Server-Assignment-Request SAA: Server-Assignment-Answer

Session Initiation Flow S-CSCF P-CSCF GGSN SGSN Radio Access Network I-CSCF HSS App. Server 3 1 2 Originating Home Network Visited/Home Network 5 6 7 8 Terminating Home Network 4 10 9 Originating Terminating

Authorize QoS Resources iFC iFC Authorize QoS Resources 183Session Progress (SDP) Authorize QoS Resources PRACK Resource Reservation 200 OK Resource Reservation UPDATE (SDP) 200 OK(SDP) Approval of QoS Commit Approval of QoS Commit

WCSCF Architecture

UE Registration

Session Initiation

GPRS Authentication

IMS Authentication

W-CSCF Authentication

Summary Cx interface supports information transfer between HSS and CSCF IMS is based on SIP protocol QoS management is important for real-time & non real-time services W-CSCF reduces SIP signaling messages and user authentication time