Service routing in 3 GPP IP Multimedia Subsystem

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

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

3 rd Generation Partnership Project (3 GPP) • The 3 rd Generation Partnership Project (3 GPP) is a collaboration agreement that brings together a number of telecommunications 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

3 GPP Network Architecture AS

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

SIP sample packet

SIP Routing • SIP proxy takes care of user location resolving • teemu. jalava@nokia. com -> user 1@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

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

IMS Session overview

Application servers Roles: • SIP proxy • redirect server • Back-to-back-useragent (B 2 BUA) Using: • Call Processing Lanquage (CPL) • SIP Common Gateway Interface • (CGI) SIP Servets • User Agent How: • Forking • SUBSCRIBE NOTIFY • MESSAGE • Third party call control What: • Presence • Instant Messaging • Group services

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

Example of service routing

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

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

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 3 GPP to IETF to finalize new SIP RFC and SIP compression These might have some impact to service routing issues

• Questions?