SIP and the application of SIP as used in 3GPP Keith Drage - Lucent Technologies

Overview of the 3GPP IM CN subsystem architecture Independent of the access mechanism Mobility provided by underlying access mechanism Functional entities use IPv6 Functionality apportioned between visited network and home network Home network control of services

Overall 3GPP architecture GPRS IM CN subsystem

GPRS - user plane versus transport plane –User and transport planes are completely independent, i.e. the transport plane can run on a different IP version than the user plane –UTRAN and Core Network transport can also run on different IP versions UTRAN Core Network User IPv6 Transport IPv6 Application Server GGSN Terminal

GPRS - Transport of user IP packets in UMTS Application Server GGSN Terminal SGSNUTRAN GTP-U User IPv6 (PDP type IPv6) Radio Bearer IP packets to/from the terminal are tunneled through the UMTS network, they are not routed directly at the IP level.

3GPP requires multiple outbound proxies UAP- CSCF I- CSCF S- CSCF REG 200 OK User equipment Visited network Home network Home network P-CSCF - Proxy CSCF (Call Session Control Function). The terminals point of contact in the visited network after registration. Point where network places constraint on the bearer. I-CSCF - Interrogating-CSCF. Responsible for finding the S-CSCF at registration. May also perform hiding of the S-CSCF network architecture. S-CSCF - Serving-CSCF. Responsible for identifying user’s service privileges. Responsible for selecting access to home network application server (service platform) and for providing access to that server.

Example allocation of functional entities - mobile to mobile P-CSCF I-CSCF A’s visited network User A User B B’s visited network A’s home network S-CSCF I-CSCF S-CSCF I-CSCF P-CSCF B’s home network Optional Required on registration, optional on sessiion establish GPRS

Example allocation of functional entities - PSTN to mobile User B B’s visited network MGW MGCF S-CSCF I-CSCF P-CSCF B’s home network Required on registration, optional on sessiion establish GPRS

Example allocation of functional entities - mobile to PSTN P-CSCF I-CSCF A’s visited network User A A’s home network S-CSCF BGCF MGCF SGW Breakout network Required on registration, optional on sessiion establish GPRS MGW

Provision of services SIP Application Server CAMEL Service Environment ISC OSA API Cx IM SSF ISC OSA Application Server S-CSCF OSA Service Capability Server (SCS) HSS ISC CAP MAP Sh ISC interface runs the SIP protocol

Summary of architecture UA P-CSCFI-CSCFS-CSCF BCGFMGCF Gm Mw SLF Dx Cx HSSAS Cx MGW Mc Mg

Key 3GPP documents and their location on 3GPP servers TS : "3rd GPP; Technical Specification Group Services and System Aspects; IP Multimedia (IM) Subsystem - Stage 2". TS : "3rd GPP; Technical Specification Group Core Network; Signalling flows for the IP multimedia call control based on SIP and SDP". TS : "3rd GPP; Technical Specification Group Core Network; IP Multimedia Call Control Protocol based on SIP and SDP". TS : "3rd GPP; Technical Specification Group Core Network; IP Multimedia (IM) Session Handling; IP Multimedia (IM) call model” These drafts can be found at the 3gpp web site either at: ftp://ftp.3gpp.org/Specs/Latest_drafts/ ftp://ftp.3gpp.org/Specs/ /Rel-5 depending on the status of the document

Issues for SIP

Multiple outbound proxies - path UAP- CSCF I- CSCF S- CSCF REG 200 OK Insert P-CSCF address Add I-CSCF address Store P-CSCF and I-CSCF addresses Add S-CSCF address Store S-CSCF and I-CSCF addresses

Compression Efficient use of bandwidth is required on the radio interface. Will be applied to both the media streams (header compression or removal) and to the signalling bearers. Compression / decompression of SIP will be performed by the UE and the P-CSCF. These entities will also perform integrity protection on the signalling bearer.

Other issues still in discussion at requirements level Emergency calls, and support of location based services, requires the transfer of location information (needs GEOPRIV to complete). Interworking with external SIP environments requires transcoding support. Default codec for 3GPP is the AMR codec. There are functional entities which have not been shown in these slides which will require SIP support, e.g. MRF.

Questions