1. IP Multimedia Subsystem
Presenter : InamUllah Khosa
Head of Product Development, Turnotech Pakistan
Cornet Research Lab , Muhammad Ali Jinnah University

2. Presentation Plan
 Background - Evolution of 2G, 2.5G and 3G
 What is IMS
 Standardization Bodies
 Functions of IMS
 IMS Architecture – The Big Picture
 IMS Components and Interfaces
 IMS Services Control Model
 IMS Protocols
 Conclusion

3. Setting the Stage.
Revisiting the Past !
(Network Evolution)

4. 2G
 Digital Network
 Initially was merely designed for voice communication
 Logically divided into Access Network and Core Network
 Access Network is composed number of BTS and BSCs
 Core Network composed of MSC , GMSC , EIR, HLR, VLR,AUC
 Latter 2.5 Enhancements added PS Domain for Packet Data Support
 The PS Domain was composed of SGSN and GGSN
 GPRS Services support data rate of 56Kbps to 114Kbs

5. Background ( 2G)

6. 2.5 G

7. 3rd Generation Networks
 W-CDMA (UMTS)
 HSPA
 HSDPA
 HSUPA
 HSPA+
 UMTS-TDD
 TD-CDMA
 TD-SCDMA
 FOMA
 Super-Charged
 Offer users a wider range of more advanced services
 WAN voice telephony, video calls, and broadband wireless data

8. 3 & 3.5 G

9. 4G
 3GPP LTE
 improving spectral efficiency
 lowering costs
 improving services
 LTE air interface is a completely new system based on
 OFDMA in the downlink
 SC-FDMA (DFTS-FDMA) in the uplink
 Flash-OFDM
 adaptation to severe channel conditions
 Robust against narrow-band co-channel interference
 High spectral efficiency
 Low sensitivity to time synchronization errors

10. The Birth of IMS (the New Kid)

11. New Kid –IMS Block Perspective

12. What is IMS ?
 IP Multimedia Subsystem
 Architectural Framework
 Overlay Network (PS and CS Networks)
 Support for IP-Based Interactive Multimedia (QoS)
 Mandatory Support for IPV6
 Signaling based on IETF Protocol SIP , DIAMETER and COPS
 Core and Access
 Integration with PSTN
 Access Independent
 Wireless ( UMTS , WLAN, WiMAX)
 Wired ( DSL)

13. Overlay Network to PS and CS

14. IMS Standardization
 Worldwide Interoperability
 3rd Generation Party Project (3GPP)
 Groups of Telecommunications Associations
 ITU , ETSI, ARIB/TTC, China Communications Standards Association,
Alliance for Telecommunications Industry Solutions(North-America),
Telecommunications Technology Association (South Korea)
 Internet Engineering Task Force (IETF)
 Technical Specifications TSpecs.
 3GPP Releases

15. 3GPP and 3GPP2
 3GPP standardization is based on IMT-2000 which uses
W-CDMA as air interface
 3GPP2 standardization is based on IS-95 which uses
CDMA2000 as air interface

16. High Level Requirements
 Provisioning for the QoS Negotiation at the start of
session and during
 End to End Quality of Service for Voice Sessions
 Roaming
 Inter-operator QoS negotiations
 Services provided by Home Network and Visiting Network
 Mandatory default set of media types to ensure interop (
audio:AMR, video: H.263)
 Access independence (GPRS, fixed, LAN)
 Support for session-oriented non-3GPP Internet apps

17. Can’t we Live without it ?
 Surely We Can But what about the Operators and Service
Providers?
 Involved parties
 Operators, Users, Content Providers, Legal Authorities, …
 All-IP network
 Interactive Multimedia
 QoS guarantee
 Access transparency, seamless handover
 AAA
 Billing, Charging

18. Continued…
 Services and Service Aggregation
 3rd party Application Servers
 Services: No preferential treatment of voice
 Voice (VoIP) is just one service, positioned at
same level like
 any other services
 Communication security in IP networks
 Signaling and Media
 Access and Core
 Regulatory requirements (lawful interception)

19. Key Functions of IMS network
 Session Control/Management
 Subscription/Registrations Management
 Service Control
 Charging and Billing
 Operations, Administration, Maintenance and
Provisioning (OAM&P/OSS)
 Interworking with PSTN

20. IMS Components
 Call State Control Functions
 P-CSCF, I-CSCF and S-CSCF
 Home Subscriber Server(HSS)
 Media Resource Functions
 MRFC, MRFP
 Interworking Functions
 BGCF, MGCF, IMS-MGW, WAG/PDG, IMS-IWF, IETF-3GPP
IWG
 Charging Functions
 Online Charging System ( OCS)
 Offline Charging System ( CCF/CDF)
 OAM&P Entities

21. The Big Picture !

22. IMS Protocols Interfaces

23. IMS Service Control
 Value Added Services are Provided by AS in IMS
 Application Servers are defined as a part of Service
Profile
 Service Profiles are defined as a Part of User Profile
 Each Service Profile contains Initial Filter Criteria
 Initial Filter Criterion defines a user’s subscribed service

24. Sample Initial Filter Criteria
Method =”INVITE” Session Case =”2”
<? Xml version=”1.0” encoding=”UTF-8”?>
<IMSSubscription>
<PrivateID>sip:inam@mediaroutes.com </PrivateID>
<ServiceProfile>
<PublicIdentity> <Identity>sip:inam@advcomm.net</Identity> </PublicIdentity>
<PublicIdentity> <Identity>tel: +923335251992</Identity></PublicIdentity>
<InitialFilterCriteria>
<TriggerPoint>
<SPT>
<ConditionNegated>0</ConditionNegated>
<Method>INVITE</Method>
<Group>0</Group>
</SPT>
<SPT>
<ConditionNegated>0</ConditionNegated>
<SessionCase>2</SessionCase>
<Group>0</Group>
</SPT>
</TriggerPoint>
</InitialFilterCriteria>
<ApplicationServer>
<ServerName>sip:server@mediaroutes.com </ServerName>
<DefaultHandling>1</DefaultHandling>
</ApplicationServer>
</ServiceProfile>
</IMSSubscription>

25. Initial Filter Criteria Continued….
 Each iFC contains Priority, Trigger Point and Application Server, Default Handling and
 These iFCs are evaluated on the initial requests
 INVITE ,MESSAGE , OPTIONS, SUBSCRIBE
 S-CSCF checks filter criteria
 Once the AS has been identified
 S-CSCF creates Route header to forward message to AS
 Additionally, the S-CSCF places itself to the Route header to get back the message afterwards
 In the user part of the SIP URI of this own Route entry
 the S-CSCF may enter some state information to understand, that it already received and
processed this message (other ways of providing state are possible)

26. Continued..
 On registration the S-CSCF receives user profile from HSS
 Filter criteria determine the services that are applicable to the
collection of Public User Identities of the profile
 S-CSCF assesses the criteria in the order of their priority
 Filter criteria contain trigger points, which are Boolean
conditions
 If the trigger point fires the request goes to the corresponding
AS
 After receiving back the request the next criteria is checked

27. Protocols Used in IMS Networks
 Session Initiation Protocol (SIP)
 Registration , Authentication
 Call Control/Session Establishment
 Interworking Functions
 DIAMETER
 Next Generation AAA Model
 Pull/Push Registrations Data
 User Profiles
 Service Provisioning/Service Control
 IMS Charging
 Common Open Policy Service ( COPS)
 QoS Parameters Negotiations

28. User Identification in IMS
 Public User Identities ( IMPU)
 IMS user has one or more Public User Identity
 Either a SIP URI or a TEL URI
 sip:+92-1111111@ufone.net;user=phone
 tel:+92-42-664-832356
 TEL URIs are required to make calls between IMS/PSTN
- Envision: at least one TEL URI and one SIP URI Per
Subscriber

29. Private User Identity
 Private User Identities(IMPI)
 IMS user has one Private User Identity
 Have the format of a Network Access Identifier (NAI, RFC
2486)
 inam@mobilink.com
 Not used for routing SIP messages
 Used only for subscription identification and authentication
 Similar function for IMS as the IMSI
 (International Mobile Subscriber Identification) for GSM
 Stored on UICC

30. Home Network Domain
 Home Network Domain
 SIP URI that contains the home network domain name
 Used to find the address of the home network during
 registration procedure
 Only one home network domain

31. Playgrounds for IMS
 IMSZONE ( http:imszone.org)
 Diameter Stack
 Home Subscriber Server (Cx,Sh)
 Online Charging System
 Offline Charging System
 Media Server ( MRFC & MRFP)
 OAM&P Manager and OAM&P Agent
 OpenIMSCore – http://openimscore.org
 FHoSS: Home Subscriber Server
 SERIMS: P-CSCF,I-CSCF, and S-CSCF
 OpenIMS Lite: IMS Client

32. End of this Episode
Thank You !