Service routing in 3GPP IP Multimedia Subsystem

1. Service routing in 3GPP IP Multimedia Subsystem Teemu Jalava Supervisor: Raimo Kantola Instructor: M.Sc. Markus Isomäki, Nokia Research Center

2. Agenda • Introduction to 3GPP • Introduction to SIP • IP Multimedia Subsystem • Service Routing in IMS • Implementation • Conclusions

3. 3rd Generation Partnership Project (3GPP) • The 3rd Generation Partnership Project (3GPP) is a collaboration agreement that brings together a number oftelecommunications standards bodies and telecommunications companies. • Release ’99 was renamed Release 3 • Release 4 was out March 2001 • - IP network • Release 5 should be ready in summer 2002 • - IP multimedia • Release 6 • - All IP network

4. 3GPP Network Architecture AS

5. Session Initiation Protocol (SIP) • Creation, modification and termination of multimedia sessions • RCF 2543 -> RCF 3261 • Request - Reply based transactions • Easy to make new extensions • ASCII based, clear text, similar to HTTP • Uses UDP or TCP • URL addressing • sip:teemu.jalava@nokia.com Client 1 Proxy Client 2 INVITE INVITE 100 Trying 180 Ringing 180 Ringing 200 OK 200 OK ACK ACK Media streams BYE BYE 200 OK 200 OK

6. SIP sample packet

7. SIP Routing • SIP proxy takes care of user location resolving • teemu.jalava@nokia.com -> user1@130.233.20.40 • using registrar, DNS (ENUM in case of tel URL) or other means • DNS Service Resource Records (SRV RR) can be used to locate a SIP proxy in an other domain • via header is needed to ensure packets route the same way back • record-route header is needed is sertain proxies need to be in the routing path

8. IP Multimedia Subsystem (IMS) Call State Control Function (CSCF) Interrogating-CSCF • Accesspoint to domain • Hides topology and configuration (User Agent) Serving-CSCF Proxy-CSCF • Session control services • Registration, AS usage, charging, etc • First contact point • Provides provicy control and QoS authorization • Local services, like emergency calls and local numbering

9. IMS Session overview

10. Application servers • Using: • Call Processing Lanquage (CPL) • SIP Common Gateway Interface (CGI) • SIP Servets • What: • Presence • Instant Messaging • Group services Roles: • SIP proxy • redirect server • Back-to-back-user-agent (B2BUA) • User Agent How: • Forking • SUBSCRIBE - NOTIFY • MESSAGE • Third party call control

11. Application example: Presence • Presence enables user to express willingness and availability to communicate • Can be used with phonebook to make a "buddy list" • Presence updates with REGISTER method • Presence download with SUBSCRIBE - NOTIFY

12. Example of service routing Example of service routing

13. S-CSCF routing decisions • Based of Filter Criteria downloaded from Home Subscriber Server (HSS) at user registration • User profile • Filter Criteria • Address of the Application Server to be contacted. • Priority • Trigger Points (method, presence or apsence of any header, header content, etc) • Default Handling • Optional Service Information

14. Implementation • Proof of concept work • S-CSCF from a SIP proxy • Adding filtering • Integrated user profile • Configuring user profile • Testing with network containing Presence AS, redirection AS and SIP-SMSGW

15. Conclusions • SIP based services are easy to make and integrate to the IMS network • Configuration is easy • Scalable sollution, AS and S-CSCF duplication • Release 5 has been delayed from jan 2002 to june 2002, some features have been postponed to Release 6 • Some pressure from 3GPP to IETF to finalize new SIP RFC and SIP compression • These might have some impact to service routing issues

16. Thank you! • Questions?