Content Forschungszentrum Telekommunikation Wien ! IMS Basics ! Standardization ! IMS Components and Interfaces ! IMS Services IMS ! Conclusion The IP Multimedia Subsystem Part 1: Peter Eichinger, Joachim Fabini © ftw. 2005 FTW IMS member tutorial IMS Fundamentals IMS Overlay Network Coverage ! What is IMS? - IP Multimedia Subsystem - Architectural framework AAA, Security - Overlay network for existing PS and CS networks Mobile access User Data Fixed access network network • Support for IP-based interactive multimedia (QoS) Mobile MM device • Mandatory support of IPV6 (Standard: IPV4 optional) • Signaling based on IETF-Protocols: SIP, Diameter, COPS MM Terminal 2 • Core and Access • Integration with PSTN IP core - Access agnostic MM Terminal 1 IMS • Wireless (UMTS, WLAN, WiMax) • Wired MM Server 1 MM Server 2 © ftw. 2005 FTW IMS member tutorial © ftw. 2005 FTW IMS member tutorial IMS Standardisation Why do we need IMS? (Santa Claus wish list) ! Involved parties ! Worldwide Interoperability required - Operators, Users, Content Providers, Legal Authorities, … - Metcalfe‘s law: "The usefulness, or utility, of a network ! All-IP network equals the square of the number of users.“ - Interactive Multimedia - QoS guarantee - Access transparency, seamless handover ! 3GPP (3rd Generation Partnership Protocol) - AAA - http://www.3gpp.org/ - Billing, Charging - TS (Technical specifications, TSpecs) ! Services and Service Aggregation - 3rd party Application Servers - 3GPP Release 4/5/6/7 - Services: No preferential treatement of voice - Voice (VoIP) is just one service, positioned at same level like ! IETF (Internet Engineering Task Force) any other services ! Communication security in IP networks - http://www.ietf.org/ - Signaling and Media - IETF Drafts, RFCs - Access and Core - Regulatory requirements (lawful interception, …) © ftw. 2005 FTW IMS member tutorial © ftw. 2005 FTW IMS member tutorial Requirements context for UMTS IMS Requirements operators ! Want more service flexibility and differentiation than GSM ! 3GPP TS 22.228 ! UMTS operator controls value chain - Requirements that shall be enforced by 3GPP IMS standards ! Move towards Internet economics (but not willing to compromise on many of their service and operational ! High-level requirements objectives) - Negotiable QoS for IP multimedia applications ! Require “plug and play” interop achieved with GSM • At session establishment and during session - 100% compatibility between terminals and networks - End-to-end QoS for voice - International roaming • Equal to or better than quality of mobile CS voice call ! Strong security based on smart-card - Roaming • Inter-operator QoS negotiation ! Roaming to CS-domain and PSTN interworking • Use services provided by home- and by serving network ! International roaming - Mandatory default set of media types to ensure interop • Codec (audio: AMR, video: H.263), header compression - Access independence (GPRS, fixed, LAN) - Support for session-oriented non-3GPP Internet apps © ftw. 2005 FTW IMS member tutorial © ftw. 2005 FTW IMS member tutorial Standardised service capabilities Vertical Service Architecture ! Do not standardise multimedia applications - Standardise interfaces, capabilites ! Base IMS application concept on Internet - Flexible architectural framework Service 1 Service 2 Service 3 Service Service 1 Service - IP multimedia applications, no special requirements 1 Service 2 Service 3 Service 2 Service 3 Service - Standardised storage and retrieval of user data (GUP) - Mechanisms that enable applications to detect mobile Terminal Network Terminal limitations and to take appropriate actions - Improve/extend APIs of CAMEL, OSA, etc. to support IP multimedia applications ! Topics ! Service interaction - Application complexity Applications - Security - To be considered, research topic Common Functions ! Vertical vs. Horizontal Service Architecture - Roaming Network/Routing Functions © ftw. 2005 FTW IMS member tutorial © ftw. 2005 FTW IMS member tutorial Horizontal Service Architecture 3GPP Release History ! … ! Release 99 - March 2000 Pre-IMS Releases Service 1 Service 2 Service Service 1 Service 1 Service 2 Service 3 Service Service 2 Service 3 Service Service 3 Service ! Release 4 } - March 2001 ! Release 5 Terminal Network Terminal - March-June 2002 ! Release 6 ! Topics: - Content/Feature freeze initially scheduled for 2003 - Generic architecture Applications - Scheduled for December 2004 – March (May) 2005 - Specific applications ! Release 7 Common Functions Network/Routing Functions © ftw. 2005 FTW IMS member tutorial © ftw. 2005 FTW IMS member tutorial 3 GPP Release 6 topics The IP multimedia subsystem ! IMS Phase 2 Intranet/Intranet/ • Interworking with H323 and H324/M endpoints PS-Domain InternetInternet • Interworking with Internet SIP endpoints “session” • SIP/SDP/RTP compression SGSN GGSN • Real-Time Services over IP IP Backbone • Relationship of IMS to HTML and other non-SIP CSCF IM Subsystem applications ! Push Services & Presence SCP HLRHSS??? ! WLAN Interworking MGCF IP based CS-Domain ! MBMS (Multimedia Broadcast/Multicast MSC GMSC Service) MSC “call” GMSC Server Server PSTN ! Network Sharing MGW TDM, ATM or IP MGW ! Priority Service ! Evolution of GTP and PS-domain mobility New subsystem overlays existing architecture © ftw. 2005 FTW IMS member tutorial © ftw. 2005 FTW IMS member tutorial 3GPP R4 & R5 Architecture Applications Legacy Mobile Protocols in IMS and Services* Signalling Network R5 IMS elements SCP CSCF (IP Multimedia Subsystem) Mh R-SGW* Mw Other Ms CSE(SCP) SIP Application OSA Application SGSN Home IMS Servers Server PLMN Mm Multi-Media CAP HSS* Cx CSCF Network GGSN IP Networks ISC Mg Si Gn OSA-SCS Gp Gr Mr IM-SSF Gi Gi Sh Gc ISC ISC SIP MRF EIR Cx RUm HSS TE MT GERAN Diameter Cx Gb Gf Gi MGCF T-SGW* Mi BGCF IP A SGSN GGSN TDM Gn Mc Mw Mw SS7 Gi Iu P-CSCF Mr S-CSCF I-CSCF RUu Iu1 PSTN/ TE MT UTRAN MGW MGW Nb Legacy/External Mg Iu2 Mc Gi MRF Mw Mc Legend Nc MGCF T-SGW MSC Server GMSC Server T-SGW* MGW Gi Signalling interface ISUP/BICC Signalling and data transfer interface GGSN * Elements duplicated Applications MAP MAP (for illustrative purposes only) & Services* HSS* R-SGW* Mh Home Access Iu1 = Iucs (RTP, AAL2) Network Visited IMS 2 Iu = Iu (RANAP) Network P-CSCF CSCF Call State Control Function EIR Equipment Identity Register PSTN PLMN HSS Home Subscriber Server R-SGW Registered Signalling Gateway T-SGW Transport Signalling Gateway MGW Media Gateway Internet GGSN Visited Access IP networks Network MRF Media Resource Function © ftw. 2005 FTW IMS member tutorial © ftw. 2005 FTW IMS member tutorial IMS Architecture: Components • The HSS stores the Serving CSCF name to assist in the routeing of multimedia SIP Registration sessions ! CSCF - 3GPP: Call Session Control Function • The I-CSCF allocates a Serving CSCF based on the requested services (provided by the HSS) 2. HSS 6. The HSS may perform subscription checking at - Sometimes found as “Call State Control Function” 3. 5. this stage Home Network 4. Register ! Three flavours of CSCF I-CSCF 7. - Proxy CSCF (P-CSCF) From External HSS S-CSCF PDN - Interrogating CSCF (I-CSCF) BG I-CSCF - Serving CSCF (S-CSCF). • The S-CSCF requests the service S-CSCF 1. Register profile from the HSS. Security checks may be performed. Home Network Visited Network 8. • The S-CSCF stores the address(es) for BG contacting the UE, for any future To External routeing terminating sessions P-CSCF Visited Network PDN SGSN GGSN P-CSCF • Proxy uses a DNS a query on the destination address (in the SGSN GGSN Request URI) to determine routeing for I-CSCF. © ftw. 2005 FTW IMS member tutorial © ftw. 2005 FTW IMS member tutorial End-to-End SIP Session Home Subscriber Server Requirements Originating Mobile’s Network Interactions Terminating Mobile’s Network Interactions HSS The HSS acts as a Location S-CSCF routes the SIP Invite The I-CSCF acts as a SIP Server to assist in locating to the called party’s home Proxy forwarding the HLR ??? MAP the S-CSCF domain. The S-CSCF may SIP Invite to the users invoke services current S-CSCF IM Cx The HSS acts as a Location Subsystem Server to assist in locating S-CSCF HSS the S-CSCF HSS BG GPRS P-CSCF I-CSCF S-CSCF Home Network BG Home Network SIP Access SIP SIP SIP I- S-CSCF (Originating) I-CSCF Call State Control Function (CSCF) CSCF S-CSCF S-CSCF potentially BG The I-CSCF BG invokes service profile but P-CSCF routes the SIP proxies the SIP normally forwards the SIP ! HSS model incorporates 3G-HLR (MAP) and IM Subsystem functions (Cx) Invite to the user’s home Invite to the Invite to the P-CSCF domain (I-CSCF) users serving S- ! “One-touch” subscriber administration across domains BG Potentially filters off BG CSCF ! Large profiles will mean similar capacity dynamics as HLR emergency calls and local - Overload control will be key free phone numbers Visited Network Visited Network C-plane (Originating) (Terminating) - Platform must be fully scalable to retain focus on value oriented features P-CSCF P-CSCF BG BG ! Support open protocols/APIs for OAM, provisioning and applications access SGSN GGSN GGSN SGSN Bearer established directly between U-plane user client following successfully CC signalling © ftw. 2005 FTW IMS member tutorial © ftw. 2005 FTW IMS member tutorial HSS Background HSS: Home Subscriber Server ! Open interface Cx enables multi-vendor solution HSS - Operators see a clear functional separation between HSS and CSCFs (as Cx Cx with HLRs and MSCs, and therefore potential for multi-vendor solutions). I-CSCF S-CSCF Mw (SIP) Mw (SIP) Mw