This document provides an overview of the IP Multimedia Subsystem (IMS) standards and architecture. It discusses the evolution from 2G to 3G/4G mobile networks and the integration of IMS. The key components of IMS are described including the Call Session Control Function (CSCF), Home Subscriber Server (HSS), Application Servers (AS), Media Resource Functions (MRF), and Breakout Gateway Control Function (BGCF). Registration and call flow examples are provided to illustrate IMS signaling. Approaches to migrating existing networks to IMS are also summarized.

1. IP Multimedia Subsystem (IMS) standards 2010 Telecom Master Class

2. Agenda 2G - 3G – 4G : UMTS & IMS IMS Overview and components Architecture & Call flows Migration to IMS Summary

3. Simple 2G Mobile Network

4. 3GPP Standard evolution

9. Typical 2G Architecture Fixe + Mobile layer BTS — Base Transceiver Station BSC — Base Station Controller MSC — Mobile Switching Center VLR — Visitor Location Register HLR — Home Location Register BTS BSC MSC/VLR HLR BSC GMSC CO BSC BSC MSC/VLR CO PSTN PLMN CO Tandem Tandem SMS-SC PSDN

10. 2.5G Architectural Detail BSS — Base Station System BTS — Base Transceiver Station BSC — Base Station Controller NSS — Network Sub-System MSC — Mobile-service Switching Controller VLR — Visitor Location Register HLR — Home Location Register AuC — Authentication Server GMSC — Gateway MSC SGSN — Serving GPRS Support Node GGSN — Gateway GPRS Support Node GPRS — General Packet Radio Service 2G MS (voice only) + DATA - IP SS7 BTS BSC MSC VLR HLR AuC GMSC BSS PSTN NSS A E C D PSTN Abis B H MS IP 2G+ MS (voice & data) PSDN Gi SGSN Gr Gb Gs GGSN Gc Gn

11. 3G rel99 Architecture (UMTS) SS7 IP BTS BSC MSC VLR HLR AuC GMSC BSS SGSN GGSN PSTN PSDN CN Gs BSS — Base Station System BTS — Base Transceiver Station BSC — Base Station Controller RNS — Radio Network System RNC — Radio Network Controller CN — Core Network MSC — Mobile-service Switching Controller VLR — Visitor Location Register HLR — Home Location Register AuC — Authentication Server GMSC — Gateway MSC SGSN — Serving GPRS Support Node GGSN — Gateway GPRS Support Node A E PSTN 2G MS (voice only) 2G+ MS (voice & data) UMTS — Universal Mobile Telecommunication System Gb 3G UE (voice & data) Node B RNC RNS IuCS ATM + 3G Radio C D Gc Gr Gn Gi Abis B H Iub IuPS

12. 3G rel4 Architecture (UMTS) + Soft-switching SS7 IP/ATM BTS BSC MSC Server VLR HLR AuC GMSC server BSS SGSN GGSN PSTN PSDN CN C D Gc Gr Gn Gi Gb Abis Gs B H BSS — Base Station System BTS — Base Transceiver Station BSC — Base Station Controller RNS — Radio Network System RNC — Radio Network Controller CN — Core Network MSC — Mobile-service Switching Controller VLR — Visitor Location Register HLR — Home Location Register AuC — Authentication Server GMSC — Gateway MSC SGSN — Serving GPRS Support Node GGSN — Gateway GPRS Support Node A Nc 2G MS (voice only) 2G+ MS (voice & data) Node B RNC RNS Iub IuCS IuPS 3G UE (voice & data) Mc CS-MGW CS-MGW Nb PSTN Mc ATM

13. 3G rel5 Architecture (UMTS) SS7 IP/ATM BTS BSC MSC Server VLR HSS AuC GMSC server BSS SGSN GGSN PSTN CN Gs IMS — IP Multimedia sub-system MRF — Media Resource Function CSCF — Call State Control Function MGCF — Media Gateway Control Function (Mc=H248,Mg=SIP) IM-MGW — IP Multimedia-MGW Nc 2G MS (voice only) 2G+ MS (voice & data) Node B RNC RNS 3G UE (voice & data) CS-MGW CS-MGW Nb PSTN IuCS IuPS ATM IMS IP PSTN MGCF IM-MGW IP Network +IMS Gb/IuPS A/IuCS C D Gc Gr Gn Gi Abis B H Iub Mc Mc Mc MRF CSCF Mg Gs

14. 3GPP view of IMS

15. IMS : IP and PSTN convergence

16. IMS and EV-DO (evolution data only)

17. LTE architecture MME : Mobility Management Entity

18. LTE and Voice MSC SMSC MAP Gs SG Lu-cs A For SMS – light MSC enough For Voice – need MSC upgrade to support SRVCC (SV protocol support) Note : if VoIP is used on 3G, no need for SRVCC – using PS HO (HO = hand over = address mapping ) SV S-Gw P-Gw F

19. VoLTE : LTE and IMS

20. LTE and Policies (QoS) PCRF: Policy Charging and Rules Functions (policy decisions based on HSS/sp, applications/Rx ) P-GW : Policy Gwy = policy enforcer Packet filtering P-GW Gx S-GW S1 S5/S8 Sp eNB

21. IMS overview

22. What is IMS all about? Full IP network and service infrastructure for converged services Providing a new wave of sticky services that Seamlessly integrate multimedia, data and voice within a single user session Are instant, real time in nature Focus on customer environments and their lifestyles Are complex in nature, but simplistic to use Are device and network agnostic Can be easily enhanced and expanded as the IMS network and standards evolve

23. IMS Drivers and Caveats March 23, 2010 Data obtained from Frost &Sullivan Report “ IMS Ready for Primetime” – Feb. 07

24. Viable IMS Applications by Segment Data obtained from Frost &Sullivan Report “ IMS Ready for Primetime” – Feb. 07 X X X 32% Rich Voice (enhanced QoS) X X X 29% Audio Streaming X X X 48% Video Streaming (Push to see,mobile video,etc.) X 55% IP - Centrex X X 75% FMC – Seamless Roaming Application %** Wireless Wireline Cable Instant Multimedia Messaging 73% X X X Video Telephony (mobile video/TV) 68% X X X Interactive Gaming 38% X X X Push to Talk (POC) 33% X Location Services 28% X Push to talk enhanced (QoS) for Enterprise ------ X Cable Applications – Caller ID, Presence change, etc. ------ X

25. Why IMS? Overall Value Proposition Convergence (fixe, mobile, BB) Faster time to revenue Investment protection (standard) Cost containment (standard IT, IP) Provides a flexible, scalable architecture Service innovation enablement (multimedia) Unprecedented flexibility (IP, enablers) New services can be developed rapidly and trialed economically Large developer community (standard API, open)

26. IMS Components CSCF

27. Proxy-CSCF A first contact point inside a local (or visited) IMS Acts as a SIP Proxy Server accepts SIP requests from User Equipment (UE) and then either serves these requests or forwards them to other servers Functions include: Forward SIP REGISTER request from UE to the home network Forward other SIP messages from a UE to a SIP server (e.g.,the mobile’s S-CSCF in the mobile’s home network). Forward SIP messages from the network to a device Perform necessary modifications to the SIP requests before forwarding them to other network entities Maintain a security association with the mobile Detect emergency session Create CDRs

28. Interrogating-CSCF (I-CSCF) Contact point within an operator’s network for all connections destined to a user of that network operator For a roaming user currently located within that network operator’s service area. Multiple I-CSCFs may exist within any given network Functions Registration Assigning a S-CSCF to a user performing SIP registration Session-related and session-unrelated flows Route a SIP request received from another network to the S-CSCF Obtain from HSS the address of S-CSCF Forward the SIP request or response to the S-CSCF Generation of CDRs Topology Hiding Inter-network Gateway Acts has a firewall

29. Serving - CSCF Maintains session states for a registered user ’s on-going sessions and performs the following main tasks Registration Can act as a SIP Registrar to accept users’ SIP registration requests & make users registration & location information available to location servers such as Home Subscriber Server Session Control Can perform SIP session control functions for a registered user Relay SIP requests and responses between calling & called parties Proxy Server May act as a SIP Proxy Server that relays SIP messages between users & other CSCFs or SIP servers Interactions with Application Servers Acts as the interface to application servers & other IP or legacy service platforms Other functions Performs a range of other functions not mentioned above For example, it provides service-related event notifications to users & generates Call Detail Records (CDR)

30. CSCF : orchestration flows

31. IMS Component HSS

32. Home Subscriber Server Provides customer Authentication Accounting and Authorization (AAA) Provides subscriber master database Calls, sessions Info for roaming Responsible for holding user related info Id, Security,Location, Profile One IMS network may include multiple HSS’s SGSN GGSN CSCF D C Gr Gc Cx HSS Subscription Information Location Information GMSC Server MSC Server

33. Logical Functions of an HSS CS Domain PS Domain IM CN Subsystem C Gr D Gc Sh Si Cx GGSN SGSN CSCF IM-SSF SIP AS OSA -SCS GMSC MSC/VLR GSM SCF Mobility Management Home Subscriber Server Identification Handling Access Authorization User Security Info. Generation Service Authorization Support Application Service Support Service Provisioning Support Call/Session Establishment Support Camel Services Support User Security Support

34. IMS Components SIP AS

35. What is an Application Server (AS)? An Application Server offers value added IMS services. It may be SIP Application Server Open Service Access (OSA) Service Capability Server (OSA Gateway) CAMEL IM-SSF An AS can communication with the HSS The Serving-CSCF to AS interface is used to provide services residing in an AS. Two cases are possible Serving-CSCF to an AS in Home Network Serving-CSCF to an AS in a trusted External Network Some vendors already integrate in their IMS solution some SIP AS among which OSA SCS SIP AS for presence SIP AS for instant messaging SIP AS for Push To Talk Etc.

36. IMS Application Server (AS) Architecture OSA AS OSA AS AS : SCIM (broker) ISC Cx OSA SCS Legacy Network Element OSA API S-CSCF (Service Capability Interaction Manager) IM-SSF SS7 Mr MRF ISC Sh Si HSS Sh SIP App. Server SIP App. Server SIP App. Server

37. Legacy integration : * Parlay Application Server * IM-SSF to Camel

38. Parlay Service Capability Server(SCS) Parlay is an OMA standard Focus on legacy services integration : SMS MMS Location Call control with legacy Can sit within or outside network domain Is the controlling mechanism to the network (security, etc.) Has interfaces to network – can connect to wireline, wireless or Voip, IMS Normally uses off the shelf hardware and software OMA : Open Mobile Alliance legacy OSA SCS MRF S-CSCF HSS Diameter Sh IMS Network Cx ISC

39. Open Service Access (OSA) Parlay AS Part of the “Virtual Home Environment” Open, standardized API for 3 rd party application developers Developed in the Parlay group “ Exports” typical network functionality Call Control QOS User Location Terminal Capabilities Content based charging Open Service Access Interface Class OSA API Application Application Server Framework Discovery Service Capability Server(s) Call Control User Location HLR CSE WGW WPP Servers

40. IP Multimedia – Services Switching Function (IM-SSF) Provides the interworking of a SIP message to the corresponding customized applications for Mobile Networks Enhanced Logic (CAMEL) ANSI-41, Intelligent Network Application Protocol (INAP) Transaction Capabilities Application Part (TCAP) messages Enables UE access to legacy services such as Calling name service Freephone services Number Portability One number services Etc. App. Server ISC Legacy Network Element OSA AS OSA AS OSA SCS OSA API S-CSCF (Service Capability Interaction Manager) IM-SSF ISC SS7 IMS Network Elements Non IMS Network Elements MRF Mr SIP App. Server SIP App. Server SIP App. Server

41. Media Resource Function MRF media server (serveur vocal) conference server

42. Standard Media Server functionality Announcements (audio and video) Automated Speech Recognition (ASR) Billing Record Creation (CDR, IPDR) Fax Detection Interactive Voice Response (IVR) Recording Text-To-Speech conversion (TTS) Transcoding between different codecs or rates Multi-unicasting (replicating the audio and video payload of RTP) Open Standard interfaces (SIP, VXML)

43. IMS - Media Resource Function Two components per standards MRF Controller (MRFC) Controls the media stream resources in the MRFP Interprets information coming from an AS and S-CSCF (e.g. session identifier) and control MRFP accordingly Generates CDRs MRF Processor (MRFP) Controls RTP bearers Provides resources to be controlled by the MRFC Mixes incoming media streams (e.g., for multiple parties) Sources media streams (for multimedia announcements) Processes media streams (e.g., audio transcoding, media analysis) Supports multiple audio and video codecs AS MRFP ISC Mr S-CSCF MRFC Mb Mp MRF GGSN

44. IMS Components BGCF

45. Breakout Gateway Control Function (BGCF) C,D, Gc, Gr UE Mm Mk Mk Pstn Pstn Mj Mg Mr Mp Mw Gm Dx Cx Legacy mobile signaling networks Mn Mb Mb IMS Mw PTSN HSS SLF P-CSCF MRFC MGCF BGCF BGCF IMS-MGW MRFP CSCF CSCF Gq Mi Mb Mb Mb Mb Other IMS Networks

46. Breakout Gateway Control Function (BGCF) Process request from S-CSCF to select appropriate PSTN/CS domain breakout point Select 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 signaling to the BGCF of that network If the interworking is in another network & network hiding is required, the BGCF will forward the SIP signaling via an I-CSCF toward BGCF of the other network Select MGCF in the network in interworking with PSTN/CS domain is to occur & forward the SIP signaling to that MGCF CDR generation

47. IMS architecture & Call Flows

48. IMS full picture

49. IMS call flow

50. Registration process turn on phone : I am Here !

51. Incoming Call

52. IMS simplified architecture Media

53. Registration

54. Registration : SIP register ?? ?? ?? ?? ??

55. Session set up : SIP invite UE-1 UE-2

56. Session set up ?? ?? ?? ??

57. Presence : SIP simple Subscribe, Publish, Notify

58. AS to HSS : Diameter

59. Other examples

60. Push to talk session

61. From IMS user to CS user

62. Off-line charging

63. On-line charging

64. GSM to IMS network roaming

65. CS user calling IMS user

66. Toll-free thru TCAP Gwy

67. Off-line charging to CAP Gwy

68. SMS to IMS user

69. Summary : Key call flows 1- Registration : SIP-REGISTER UE - P-CSCF - I-CSCF – S-CSCF - HSS SIP 200 OK 2- Session Set up : SIP INVITE UE1 – S-CSCF – ( I-CSCF - HSS – S-CSCF ) – UE2 SIP 200 OK – SIP ACK 3- Presence : SIP Simple Subscribe, publish, notify 4- AS-HSS : DIAMETER Protocol

70. Migration towards IMS

71. Different approaches to implementing IMS No IMS Keep it simple Proprietary path Convergence is not important Full IMS Technology follower Must wait for IMS to mature Closed IMS Wild card Proprietary path Only IMS Market follower Must wait for IMS to mature Early IMS Market leader Use pre-IMS services Evolution path to full IMS

72. IMS for Global Network as “Overlay” All IP processing is in the new centre A single central HSS Packet Network Local Zone SGSN Central IMS Centre App. Servers MGW GGSN Circuit Network CSCF Mobility Server HSS HLR CRM & Billing MGCF MGW Local Zone Note : Local zone remain unchanged

73. IMS partial local implementation Local HSS, possibly evolved from HLR SLF to select HSS Still central applications Packet Network Local Zone SGSN Central IMS Centre App. Servers MGW GGSN Circuit Network CSCF HLR CRM & Billing MGCF MGW SLF Local HSS Note : - some local zone will have IMS service, and local HSS - others may not Local Zone

74. IMS full local implementation Central SLF to select HSS Local session control (cscf) Some local applications Circuit Network MGW Local Zone GGSN HLR CRM & Billing Local HSS CSCF Local AS Central IMS Centre App. Servers SLF Local Zone GGSN HLR CRM & Billing Local HSS CSCF Local AS MGW Packet Network MGW SGSN MGCF CSCF Note : IMS deployed everywhere