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

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

3 rd Generation Partnership Project (3GPP) The 3rd Generation Partnership Project (3GPP) 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 IP network Release 5 should be ready in summer IP multimedia Release 6 - All IP network

3GPP Network Architecture AS

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

SIP sample packet

SIP Routing SIP proxy takes care of user location resolving -> 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) First contact point Provides provicy control and QoS authorization Local services, like emergency calls and local numbering Proxy-CSCF Accesspoint to domain Hides topology and configuration Interrogating-CSCF Session control services Registration, AS usage, charging, etc Serving-CSCF (User Agent)

IMS Session overview

Application servers Roles: SIP proxy redirect server Back-to-back-user- agent (B2BUA) User Agent How: Forking SUBSCRIBE - NOTIFY MESSAGE Third party call control Using: Call Processing Lanquage (CPL) SIP Common Gateway Interface (CGI) SIP Servets 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 3GPP to IETF to finalize new SIP RFC and SIP compression These might have some impact to service routing issues

Questions?