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Presentation at UEA, 2006.
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IMS – IP Multimedia Subsystem
Architecture, Protocols and ServicesWaldir R Pires JrSiemens Manaus
2005.06.21
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Contents
IntroductionIMS OverviewIMS Applications/ServicesConclusionReferences
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Introduction
Shift towards an all IP system Reasons
Reduction of costs, creation of new revenue Increased competition and innovation demands Internet coverage Merge of fixed and mobile networks Services today are obsolete
Multimedia services not yet available to the mobile networks – a natural evolution
Common Infrastructure for services
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Stove pipearchitecture horizontal
architecture
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Why IMS?
Involved parties Operators, Users, Content
Providers, Legal Authorities, …
All-IP network Interactive Multimedia QoS guarantee Access transparency,
seamless handover AAA, Billing, Charging
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, …)
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Contents
IntroductionIMS OverviewIMS Applications/ServicesConclusionReferences
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IMS Definition
The IMS is a standards-based architecture that provides: integrated Internet-based, multimedia, multi-session applications
to mobile users at the same time guaranteeing QoS across different access
network technologies and allowing operators to charge transparently through any medium
used. Defined by 3GPP, 3GPP2 and TISPAN
OMA (service interoperability), IETF (Internet standards)
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IMS Consequences
For users Person2person and
person2content communications in voice, text, pictures and video
Availability anywhere anytime through wireless and fixed networks
Access from different technologies (GSM, cdma2000, WLAN, etc)
For operators Definition of a
horizontal architecture reusability of common
functions in multiple applications (From stovepipe to horizontal services)
Interoperability and roaming
Bearer control, charging and security
Key enabler for fixed-mobile convergence
Secure migration to an all IP architecture
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IMS ArchitectureLegacy Service Control Points
Caller ID, Local number portability and 800 services.
Application ServersIMS ApplicationsOSA – GW (Open Service Access Gateway)
inter-working between SIP and APIs for communication services
It allows applications to access presence and call state information, application registration and resource management
in the network
Non-Telephony Servicesoutside the telephony call model, such as
Instant Messaging, Push To Talk and presence enabled
TAS (Telephony Application Server)back-to-back SIP user agent that maintains
the call stateprovides the basic call processing services including digit analysis, routing, call setup, call waiting, call forwarding, conferencing,
etc.
IM-SSF (IP Multimedia Services Switching Function)
Provides the interworking of the SIP message to the corresponding CAMEL, ANSI-41, INAP
or (TCAP) messages, services such as calling name, 800 services, etc.
HSS (Home Subscriber Services)A database that maintains the unique service profile
for each end user. This includes an end user’s current registration information (i.e., IP address), roaming information, telephony services (i.e., call
forwarding information), instant messaging service information (i.e., buddies list), voice mail box options
(i.e., greetings), etc. CSCF (Call Session Control Function)
It provides the registration of the endpoints and routing of the SIP signaling messages to the
appropriate application server. The CSCF interworks with the transport and endpoint layer to guarantee
QoS across all services. In some IMS proposals, the CSCF is divided into Serving, Proxy and Interrogating
CSCFs.
MRCF – Media Resource Control FunctionIt interworks the SIP signaling with the signaling used by the media servers. It also manages the distribution of sessions
across multiple media servers. It is considered to be the central unit for media processing (transcoding, conferencing, TTS,
etc.),
MGCF – Media Gateway Control FunctionIt interworks the SIP signaling with the signaling used by the
media gateway (i.e., H.248).
Media ServerResponsible for the processing and generation of multimedia
data, such as playing of announcements (audio/video), multimedia conferencing (e.g. mixing of audio), text to speech
conversation (TTS) and speech recognition and realtime transcoding of multimedia data (i.e. conversion between
different formats). Media Gateway
It terminates voice data from a switched network (PSTN) and media (RTP) streams from packet switched network (Internet).
It also acts as relays for multimedia streams i.o. end-2-end connections. Other functions include transcoding, echo
cancellation and packet loss handling
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IMS Architecture
CSCF - Call Session Control Function
Serving CSCFSIP server that maintains
session state for IMS services
Proxy CSCFthe first point of contact for the user entity and forward SIP messages to
the user’s home S-CSCF
Interrogating CSCFthe contact point for a network
when other networks need to be contacted
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IMS Protocols
Session Control SIP
Media RTP and RTCP
Security Diameter (AAA) GSM, GPRS and 3G
standards
IP
UDP TCP
SIP
RSVP RTP RTCP SAP SDP
Multimedia Applications
Audio Video Dados
Used for establishing, modifying and terminating
multimedia sessions. It relies on other protocols for
transport and QoS reservation.
Real Time Protocol: transport of real time media
using UDP
Real Time Control Protocol: control of the real
time media being transported, QoS statistics,
synchronization (audio/video) of packets.
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Contents
IntroductionIMS OverviewIMS Applications/ServicesConclusionReferences
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IMS Services/Application Architecture
Architecture Proposals On the operator’s network
Horizontal architecture
On the mobile device
Client-server Three-layer
From the mobile terminal down to the content providers/application developers
Mobile Terminal
Radio Access Network
IMS
SIP Applications
3rd Party Content Providers
Application Developers
Packet Switch Domain Circuit Switch Domain
Internet PSTN
Mobile Terminal
Radio Access Network
IMS
SIP Applications
3rd Party Content Providers
Application Developers
Packet Switch Domain Circuit Switch Domain
Internet PSTN
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IMS Services/Application Architecture
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IMS Horizontal Architecture
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IMS Services/Application Architecture
On the mobile device Client Server Architecture
Mobile terminal and the A/S Three-layer application architecture
User interface, application logic and the protocol layer
Provide maximum portability and flexibility between different vendors = Componentry
Performance problems for multimedia applications in Java
Efficient Java/Native connectivity for multimedia applications
Various application domains
Access IndependencePush-to-talk Over CellularPresenceUnified MessagingInteractive Voice ResponseEnhanced Voice MailInstant MessagingWeb/Audio/Video ConferencingVideo TelephonyMulti-user Gaming
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Contents
IntroductionIMS OverviewIMS Applications/ServicesConclusionReferences
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IMS Summary
IMS provides AAA (authentication, authorization and accounting) of both
mobile and fixed SIP clients Control over sessions
person-to-person, person-to-group and content-to-person multimedia communication
Charging functionality flexibility for the operator apply time-based, event-based or volume-based charging to
subscribers QoS for the IP services being used in the communications
session Functionality to connect roaming users to the home domain for
IP multimedia services Access network domain security functions
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IMS Summary
Enabler to a true 3G IP convergence
Horizontalarchitecture to servicesand applications
Common services and roaming discovery
Interoperability, charging, roaming control for the operator
Combination of voice, video and data
Access convergence GPRS, cdma2000, WLAN, fixed network, etc.
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Conclusion
Issues/Challenges Costs of conversion to IMS Competition and market divergence Performance Security
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Contents
IntroductionIMS OverviewIMS Applications/ServicesConclusionReferences
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References
[1] V. Koukoulidis and M. Shah, The IP Multimedia Domain in Wireless Networks: Concepts, Architecture, Protocols and Applications, Siemens Information and Communication Mobile, Boca Raton, Fl, Proceedings of the IEEE Sixth International Symposium on Multimedia Software Engineering (ISMSE’04), IEEE, 2004.
[2] P. Polvora, C. Öström, Plan Your IP-Competence Strategically, Ericsson Seminar, http://www.ericsson.com/learning, April 2005, Ericsson AB 2005.
[3] 3GPP Homepage, http://www.3gpp.org/specs/specs.htm
[4] Open Mobile Alliance (OMA) Homepage, http://www.openmobilealliance.org
[5] Session Initiation Protocol Charter Homepage, http://www.ietf.org/html.charters/sip-charter.html
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References
[6] IP Multimedia Subsystem (IMS): Service Architecture, Lucent Technologies, February, 2005,
[7] IMS – IP Multimedia Subsystem: The value of using the IMS architecture, White Paper, Ericsson, October 2004,
[8] Motorola IP Multimedia System White Paper, February, 2004,
[9] IP Multimedia: a New Era in Communications, Nokia White Paper,
[10] The Protocol Dictionary Homepage, http://www.javvin.com/protocolH245.html
[11] P. Howard, 3GPP Security and Authentication, September 13, 2001, http://www.ietf.org/proceedings/01aug/slides/sipping-7/index.htm
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References
[12] Open IMS Homepage, http://www.fokus.gmd.de/bereichsseiten/testbeds/ims_playground/playground/hss.php?lang=de
[13] 3GPP TS 23.228: "IP Multimedia Subsystem (IMS)"
[14] IETF RFC 3261: "SIP: Session Initiation Protocol"
[15] 3GPP TS 23.218: "IP Multimedia (IM) session handling, IM call model"
[16] 3GPP TS 29.228:" IP Multimedia (IM) Subsystem Cx Interface; Signalling flows and message contents"
[17] The Parlay Group homepage, http://www.parlay.org/
[18] H. Montes, G Gomez, H Cuny, Nokia Networks, J. Paris, Deployment of IP Multimedia Streaming Services in Third Generation Mobile Networks, IEEE Wireless Communications, October 2002
[19] Siemens IP Multimedia Subsystem (IMS): The Domain for Services, Whitepaper