IMS IP Multimedia Subsystem Rev A Limited Internal
IMS IP Multimedia Subsystem Rev A Limited Internal 1 ETH/RKC Sarolta Dibuz +36 -1 -4377625
IMS is… § § § IP Multimedia Subsystem (IMS) is an architecture for offering multimedia services on the packet domain. IMS is access agnostic, hence it is not just for UMTS or GPRS, but also supports WLAN, fixed line, LTE etc. IMS is not a service, but a service enabler § IMS gives Service control by introducing service signalling § All IMS services can be done without IMS but without IMS, service creation can be complex, and expensive to the operator and the user § IMS gives Convergence of all media communications on to the packet network. Rev A Limited Internal 2 ETH/RKC Sarolta Dibuz +36 -1 -4377625
Service interoperability non-IMS Service 2 Service 1 Operator 3 Operator 1 Service 2 Service 1 Operator 2 Rev A Limited Internal 3 ETH/RKC Sarolta Dibuz +36 -1 -4377625
Service interoperability IMS Service 2 Service 1 Operator 3 Operator 1 Service 2 Service 1 Operator 2 Rev A Limited Internal 4 ETH/RKC Sarolta Dibuz +36 -1 -4377625
IMS architecture SIP Application Servers HSS SIP Application Servers IMS I-CSCF MRF P-CSCF MGCF CDMA 2000 S-CSCF MGW MSC(Server) RNC Corporate SGSN GGSN BSC CN UMTS/GPRS MGW WLAN Rev A Limited Internal 6 ETH/RKC Sarolta Dibuz +36 -1 -4377625
Architecture Elements Database Elements • HSS (Home Subscriber Server) • SLF (Subscription Locator Function) IMS Control Elements (Call Session Control Function) • • • S-CSCF P-CSCF I-CSCF • • Rev A MGCF - Media Gateway Control Function BGCF - Breakout Gateway Control Function SGW - Signaling Gateway Limited Internal 7 SIP Application Servers OSA Application Server OSA-SCS IM-SSF HSS P-CSCF Control Plane Interworking Elements • CSE(SCP) S-CSCF I-CSCF MRF MGCF BGFC SGW MGW ETH/RKC Sarolta Dibuz +36 -1 -4377625
Other Elements IMS Service Elements • AS (Application Server) CSE(SCP) SIP Application Servers OSA-SCS IM-SSF External Service and Service Interworking Elements • • • OSA SCS OSA Framework OSA Application Server • CAMEL elements - IM-SSF (IP Multimedia HSS P-CSCF S-CSCF I-CSCF Switching Service Function) Resource Elements • MRF Media Resources Function (MRF) MGCF BGCF Media Interworking Elements • MGW (Media Gateway) Rev A Limited Internal OSA Application Server SGW MGW 8 ETH/RKC Sarolta Dibuz +36 -1 -4377625
Proxy-CSCF (P-CSCF) Home IMS Network CSE(SCP) • Entry point to IMS from any access network • Local outbound stateful proxy for all SIP requests/responses, ensuring all signalling is sent via the home network HSS • Includes a Policy Decision Function (PDF) that authorizes bearer resources • The P-CSCF and the GGSN are located in the same network, that is, either both in the visited PLMN or both in the home PLMN. Rev A Limited Internal 9 OSA Application Server OSA-SCS IM-SSF P-CSCF I-CSCF S-CSCF • Performs compression/decompression for efficient use of the radio interface • Performs integrity protection mechanisms using IPsec SIP Application Servers MRF MGCF SGW MGW GGSN Home Access Network Visited IMS Network P-CSCF PSTN PLMN Internet IP networks ETH/RKC Sarolta Dibuz +36 -1 -4377625 GGSN Visited Access Network
PDF • Performs policy control and media authorisation based on the policy of the access network and based on the session parameters carried in the SIP signalling Home IMS Network CSE(SCP) HSS SIP Application Servers OSA Application Server OSA-SCS IM-SSF P-CSCF S-CSCF I-CSCF MRF MGCF SGW MGW GGSN Home Access Network P-CSCF PDF Rev A Limited Internal 10 ETH/RKC Sarolta Dibuz +36 -1 -4377625
Interrogating-CSCF (I-CSCF) • First point of contact in the home network from a visited NW • Acts as a SIP proxy located at the edge of a network. • Queries the HSS to help in selecting a SCSCF for a user. Home IMS Network CSE(SCP) HSS SIP Application Servers OSA Application Server OSA-SCS IM-SSF P-CSCF I-CSCF S-CSCF MRF MGCF SGW MGW GGSN Home Access Network Visited IMS Network P-CSCF PSTN PLMN Internet IP networks Rev A Limited Internal 11 ETH/RKC Sarolta Dibuz +36 -1 -4377625 GGSN Visited Access Network
Serving-CSCF (S-CSCF) • Stateful SIP server providing session control. • Acts as a SIP registrar Home IMS Network CSE(SCP) HSS SIP Application Servers OSA Application Server OSA-SCS IM-SSF • Always located in the home network. • Central point for control of operator provided services. P-CSCF I-CSCF S-CSCF MRF • Performs authentication. MGCF SGW MGW GGSN Home Access Network Visited IMS Network P-CSCF PSTN PLMN Internet IP networks Rev A Limited Internal 12 ETH/RKC Sarolta Dibuz +36 -1 -4377625 GGSN Visited Access Network
HSS and SLF Home IMS Network Home Subscriber Server (HSS) CSE(SCP) • An evolution of the HLR • HLR (subscriber and authentication data for CS and PS domains) + the new IMS functionality • Location Register • IMS subscriber records • IMS service profile processing • IMS authentication data HSS SIP Application Servers OSA Application Server OSA-SCS IM-SSF P-CSCF I-CSCF S-CSCF MRF MGCF SGW MGW GGSN Home Access Network Visited IMS Network P-CSCF PSTN PLMN Subscription Locator Function (SLF) • A look-up function that can be used in networks where several HSS exist. Rev A Limited Internal 13 ETH/RKC Sarolta Dibuz +36 -1 -4377625 Internet IP networks GGSN Visited Access Network
Breakout Gateway Control Function (BGCF) • Selects the appropriate PSTN/CS domain break out point for the session. • Selects the network in which the interworking with the PSTN/CS Domain is to occur. If the interworking is in another network, then the BGCF will forward the SIP signalling to the BGCF of that network. If the interworking is in another network and network hiding is required by the operator, the BGCF will forward the SIP signalling via an I-CSCF toward the BGCF of the other network. Home Network S-CSCF BGCF MGCF Limited Internal 14 BGCF MGCF GGSN MGW Home GSM/UMTS CS Network • Selects the MGCF in the network in which the interworking with PSTN/CS domain is to occur and forwards the SIP signalling to that MGCF. Rev A External Network ETH/RKC Sarolta Dibuz +36 -1 -4377625 MGW External Network
Multimedia Resource Function (MRF) Home IMS Network CSE(SCP) The media resource function provides the additional media resources complementary or fundamental for services. The functions to be applied will be: HSS • Conference management such as, a floor control mechanism to allow some members of a conference to control the conference. SIP Application Servers IM-SSF OSA-SCS P-CSCF S-CSCF • To provide additional media streams to the session, such as media fade-in for rich calls. I-CSCF MRF • Play announcements and tones MGCF MGW GGSN The MRF is split in to two functional parts : Home Access Network • Multimedia Resource Function Controller (MRFC) MRF • Multimedia Resource Function Processor (MRFP) MRFC Mp MRFP Rev A Limited Internal 15 OSA Application Server ETH/RKC Sarolta Dibuz +36 -1 -4377625 SGW
IMS service environment There are three different types of application servers, depending on the application hosted: Home IMS Network CSE(SCP) HSS • SIP AS (Application Server): IMS native applications • IM-SSF (IP Multimedia Switching Service Function) Legacy applications • OSA-SCS (Service Capability Server): Service frameworks (e. g. OSA) SIP Application Servers OSA Application Server OSA-SCS IM-SSF S-CSCF P-CSCF I-CSCF MRF MGCF SGW MGW GGSN Home Access Network Visited IMS Network P-CSCF PSTN PLMN Internet IP networks Rev A Limited Internal 16 ETH/RKC Sarolta Dibuz +36 -1 -4377625 GGSN Visited Access Network
SIP Application Server Home IMS Network • Accept requests and responses. It will be able to control, finish or initiate a new SIP transaction • Route the session towards another user or network • Interact with other service platforms for the support of services • Communicate with the HSS in order to obtain information about subscriptions and services CSE(SCP) HSS P-CSCF S-CSCF 17 I-CSCF MRF MGCF MGW Home Access Network Limited Internal OSA Application Server OSA-SCS IM-SSF GGSN Rev A SIP Application Servers ETH/RKC Sarolta Dibuz +36 -1 -4377625 SGW
Registration to the network UE GSN HLR 1. Bearer Level Registration: GPRS 2. PDP Context Activation 3. CSCF Discovery 4. Application Level Registration Rev A Limited Internal 18 ETH/RKC Sarolta Dibuz +36 -1 -4377625 IMS
Session establishment model Steps: Home B AS 11 HSS 8 10 7 9 I-CSCF 16 1) Route signalling to A’s home network 4 3 S-CSCF I-CSCF 17 18 15 19 Visited B P-CSCF 13 5 6 S-CSCF 12 Home A AS Visited A 14 P-CSCF 20 GGSN SGSN Radio Access Network User plane (RTP) 2 1 2) Route signalling to B’s home network 3) Route signalling to B terminal
Application level Registration (I) Home A I-CSCF Subscriber P-CSCF SIP-AS HSS The I-CSCF finds the A UES-CSCF P-CSCF initiates finds a SIP the. SI contacts downloads allocated to this -CSCF Registration the including help the challenges HSSwith to find the S-of userpublic authentication orserving selects vector a new DNS his userthis ID and CSCF subscriber S-CSCF for this subscriber foruser this user. his private ID subscriber. from the HSS 7 3 4 6 5. REGISTER I-CSCF S-CSCF 8. Unauthorized 2. REGISTER 9. Unauthorized Visited A P-CSCF 1. REGISTER 10. Unauthorized GGSN SGSN Radio Access Network A Rev A Limited Internal 20 ETH/RKC Sarolta Dibuz +36 -1 -4377625
Application level Registration (II) Home A P-CSCF S-CSCF I-CSCF Subscriber SIP-AS HSS 17 14 13 18. REGISTER 19. OK 15. REGISTER I-CSCF S-CSCF 20. OK 16 S-CSCF I-CSCF finds informs the The UE P-CSCF calculates finds the. SI contacts other allocated that Application this to S-S-of -CSCF credentials with and the help the authorizes HSS to the find the Servers this user is about serving the DNS reinitiates the SIP CSCF registration serving and this subscriber. user's registration HSS Registration informs the The subscriber sends the S-CSCF the service profile 12. REGISTER 21. OK Visited A P-CSCF 11. REGISTER 22. OK GGSN SGSN Radio Access Network A Rev A Limited Internal 21 ETH/RKC Sarolta Dibuz +36 -1 -4377625
Session Establishment Home A Home B SIP-AS I-CSCF 6 7. INVITE 4. INVITE S-CSCF 14. OK 2. INVITE SIP-AS HSS 5 3. INVITE I-CSCF HSS P-CSCF Subscriber I-CSCF 13. OK S-CSCF 12. OK 15. OK Visited B P-CSCF 1. INVITE P-CSCF 16. OK 10. OK 9. INVITE GGSN SGSN Radio Access Network A Calls B A Rev A 8. INVITE 11. OK Visited A S-CSCF in Home Subscriber P-CSCF A routes isinitiates the first the The I-CSCF HSS returns fetches the B A performs service message point a SIP of invitation contact tothe in the from address the of HSS the S-CSCF invocation for originating IMS including for the S-CSCF subscriber. SIP URI address serving subscriber ofthe S-CSCF B subscriber B. B. A. It. INVITE The SIt forwards of subscriber the that is serving forwards CSCF finds INVITE entryto request tothe I-CSCF subscriber Bthe P-CSCF point in Home and B UE Limited Internal 22 B ETH/RKC Sarolta Dibuz +36 -1 -4377625
IMS-CS interworking MG MGCF S-CSCF/DNS Subscriber BGCF Home A BGCF DNS 4 5 7. INVITE 6. INVITE 15. OK 3. INVITE I-CSCF 14. OK S-CSCF 11. IAM 8. INVITE BGCF 16. OK 2. INVITE Subscriber The MG performs S-CSCF BGCF home MGCF BGCF selects performs Aqueries detects: initiates the bearer a No selects the SIP DNS MGCF signalling invitation interworking URL another for inthe assigned thetel between including to URL. breakout BGCF, interworking the. DNS E. 164 perhaps RTP/IP network the returns number. between E. 164 in and a the bearer number The negative another SIP and call the of network ismatch. routed used subscriber into the a PSTN network B. home BICC/ISUP BGCF. in PSTN IMS Gateway MGCF 12. ANM 13. OK 17. OK 9. ADD 10. RESP Visited A P-CSCF 1. INVITE MG 18. OK GGSN SGSN Radio Access Network A Rev A A Calls B (CS Subscriber) Limited Internal 23 ETH/RKC Sarolta Dibuz +36 -1 -4377625
Interfaces of IMS SIP Application Servers CSE(SCP) Home IMS Network OSA Application Server ISC Sh Sh OSA-SCS IM-SSF ISC Cx HSS Cx Mi Mw Mw Mr P-CSCF BGCF S-CSCF I-CSCF Mg Gi MRF Mw MGW Gi T-SGW MGCF ISUP/BICC GGSN Home Access Network Visited IMS Network P-CSCF PSTN PLMN Internet IP networks Rev A Limited Internal 24 GGSN Visited Access Network ETH/RKC Sarolta Dibuz +36 -1 -4377625 SIP Diameter IP TDM SS 7
End-to-End Qo. S and Policy Enforcement Architecture Control Plane P-CSCF SIP UA Terminal Bearer Plane Rev A The terminal also provides the link between the two planes. Bearer Limited Internal S-CSCF PDF The Go interface provides the link between the control plane and the bearer plane in the network. GGSN 25 ETH/RKC Sarolta Dibuz +36 -1 -4377625
Policy Control (4) Generate Qo. S parameters IMS Control Plane (3) Forward token to terminal (1) Generate Qo. S parameters (2) Generate Authorisation token (0) P-CSCF receives ‘final ‘SDP P-CSCF SIP UA S-CSCF PDF (8) Authorise resources. (5) Request PDP activation with token NOTE: When the service is renegotiated, the approval process as described above is repeated in its entirety with new resource allocations. Terminal UMTS Control Plane (9) Authorise PDP activation Session Manager GGSN (6) Determine PDF. (7) Req authorisation from PDF. Rev A Limited Internal 26 (10) Commence policing of traffic ETH/RKC Sarolta Dibuz +36 -1 -4377625
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