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IP Multimedia Subsystem (IMS): Concepts and Architecture
Hamid R. RabieeMostafaSalehi, FatemehDabiran, HodaAyatollahi
Spring 2011
Outlines
² Introduction
² IMS Concepts
² Introductory concepts and IMS general terminology
² Functional Entities and their Roles
² Major nodes/entities
² Roles and functions provided
² Architecture associated with major functional entities
² Overall Architecture
² Summary
Introduction-1² Service providers are looking
² to migrate voice services to VoIP for cost and revenue generating advantages.
² to provide more revenue generating new services to have competitive advantage.
² These new services include
² Instant Messaging
² Push to Talk
² NetMeeting
² Presence Services
² Real Time Multimedia Services
² To implement these converged and new classes of services, the network must have a
consistent and robust architecture to ensure QoS.
Introduction-2
² The solution must include next-generation Voice & data systems, software and professional
services to meet of both wire line and wireless operators.
² The requirement to have that kind of solution includes:
² Separation of Access and Transport Layer from Service layer.
² Session Management across multiple real time communication services.
² Transparent interworking with legacy TDM networks.
² Consistent mechanism for sharing user profile across network.
² Consistent mechanism for authenticating and billing end users.
² Open standard interfaces and APIs for new service providers and 3rd parties.
The answer is IP Multimedia Subsystem (IMS) to get above features and services.
Introduction-3
² IMS is a technology that defines how to set up advanced services for 3G
cellular networks.
² IMS provides a service control platform that allows creation of new
multimedia and multi-session applications utilizing wireless and wireline
transport capabilities.
² IMS-based services enable communications in variety of modes including
voice, text, location, pictures, video or any combination of these
What is IMS?
² IP Multimedia Subsystem (IMS) is a Service Delivery Architecture
²Standardized architecture to provide Internet Protocol
(IP)-based mobile and fixed multimedia services
² IMS architecture has evolved over the past few years
² Today, IMS could allow operators who own different types of networks
with varying architectures to offer the same services to all of their
customers
How did we arrive at IMS?Technology Evolution
PSTN
§ Circuit switched § Analog§ Digital§ SS7§ ISDN
§Circuit switched
§Analog
§Digital
§ 2G (GSM & CDMAANSI-41)
3G WirelessWireless
§ 3G wireless + IP ++
– Standard Services Platform
– Converged Applications & Content
– Access Independence
IPIMS
§ Internet
– VoIP
– Instant Messaging
– Web Applications
§W-CDMA
§GPRS/UMTS
IMS Benefits
Benefits for the Operator
§Fast and flexible service creation (1 SIP client)
§ Innovative realtime multimedia service offers
§Full control of services by operator
§Service differentiation by flexible bandwidth allocation and guaranteed QoS
§Fixed / mobile convergence
§Common service control infrastructure for PS domain for cost optimization and easy service introduction
§Longterm CS migration by shifting voice traffic towards PS domain
§Single sign on
§Application bundling in realtime (e.g. simultaneous usage of voice and data applications)
§Realtime messaging without store & foreward
§Multiparty communication services (e.g. chatting, conferencing)
§Enrichment and personalization (e.g. realtime multimedia, buddy lists, presence, push services, subscriber self administration)
§Anywhere service access from various access networks
Benefits for the User
IMS Concepts
² How Did We Arrive At IMS?
² Definition of IMS
² UE (User Equipment)
² User Identities
² IP Connectivity Access Network (IP-CAN)
² IP Multimedia Sessions
² Transition to IMS Architecture
IMS Architecture
² Today, IMS could allow operators who own different types of networks
with varying architectures to offer the same services to all of their
customers
IMS Concepts User Equipment (UE)
² UE: A device that has IP connectivity and is able to request an
IP address from the network
² Examples: SIP phone, PC, PDA
² UE negotiates its QoS requirements and other capabilities
during a session setup
² UE negotiates items, such as:
² Media Type
² Direction of traffic
² Bit rate, packet size, bandwidth adaptation
IMS Concepts - IMS User Identification
² An IMS user is allocated one or more Public User Identities by the home operator
² A Public User Identity is either a SIP URI or a TEL URL
² When the Public User Identity contains a SIP URI, it typically takes the form
of sip:[email protected]
² When the Public User Identity contains a TEL URL representing a phone
number in international format it typically takes the form of tel:+1-212-555-
0293² It is possible to include a telephone number in a SIP URI using the following
format: sip:[email protected];user=phone
² TEL URLs are needed for inter-working with PSTN phones
² In IMS, Public User Identities are used to route SIP signaling
IMS Concepts - IMS User Identification (contd.)
² Each IMS subscriber is assigned a Private User Identity by the home operator² Unlike Public User Identities, Private User Identities are not SIP URIs or TEL URLs
² They take the format of a NAI (Network Access Identifier)² The format of a NAI is [email protected]
² Private User Identities are exclusively used for subscription identification and authentication purposes
² This identity shall use for NAI (Network Access Identity)² Private User Identities are not used for routing SIP requests ² Characteristics of Private user identities:
² It will not use for routing SIP messages.
² It will be used for all registrations (including de-registration and re-registration)
² It will be a unique Global identity
² It will be used to identify the user’s information (for example user authentication) stores in
HSS
Relationship between Public & Private User Identity
² The home network operator is responsible for defining private and public user identities. (other user identities which are not defined by operator may also exist)
² The IMS Service profile is a collection of services and user data. ² The IMS service profile is defined and maintained by HSS. ² The service profile is downloaded from HSS to S-CSCF (like HLR
to VLR).² S-CSCF can have only one public user identity at a time. One
public user identity can use only one service profile while one service profile can be given to many public user identities.
Relationship Between User Identities
tel:+17324567888
tel:+88028112347
Public User Identities
Private User IdentityIMS Subscriber
IMS Concepts 3GPP IP-CAN
UE
IP-CAN(GPRS-based)
IMS Nodes
SGSNGGSN
RAN
•IMS network utilizes IP-CAN to transport multimedia signaling and bearer traffic•It is the network that connects the UE to the IMS network
IMS Concepts IP Multimedia Session (contd.)
UE1IP-CAN
IMS
Media (data) Flow
Session control signaling
UE2
IP-CAN
•An IP Multimedia Session is comprised of session management control connections and media flow connections between two or more users•IMS users are able to mix and match a variety of IP-based services in a way they choose during a single communication session
IMS Concepts- Transition Public Land Mobile Network (PLMN)
SS7/ISUP
MSC
SCPHLR
Carrier A GSM / ANSI Network
MSC
HLR
Carrier B GSM / ANSI Network
SCP
IMS Concepts-Transition IMS Architecture: High Level View
UE1
SIP
IMS NetworkCarrier A
IMS NetworkCarrier B
ASsHSS
HSS
ASs
CSCFs CSCFsUE2
IMS Concepts-Transition Interoperability: High Level View
UE
SIP
IMS NetworkCarrier A
IMS NetworkCarrier B
ASsHSS
InterworkingFunctions
SSPSCP
PSTN
ISUP
HSS
ASs
CSCFs CSCFs
ISPs
UE
Functional Entities
² IMS Architecture Planes or Layers
² Various Functional Entities and their Roles
Functional Entities IMS Architecture Planes
Application Server
Application Server
Application Server
Session ControlDBDB
Centralized Databases
Media Control & Gateways
PSTN2G/3G Mobile
Wireless Broadband
WirelineBroadband
Res./ Enterprize
Services plane(Application Layer)
Session Control Plane (Session and DB Layer)
Media Control Plane(Media Control & Gateway Layer)
Network Plane(Access and Transport)
Functional Entities Network Plane: Access and Transport
PSTN2G
Mobile/PLMN
Wireless Broadband/
3G
WirelineBroadband
Res./ Enterprize
Network PlaneAccess and Transport
IP
IPMSC
EO/SSP
Circuit Switched Gateways
Session Controllers
SS7
Functional EntitiesNetwork Plane: Access and Transport² This layer initiates and terminates SIP signalling to setup sessions and
provide bearer services such as Voice/Media Streaming over IP packets using RTP (Real Time Protocol).
² This also provides Media Gateways for converting VoIP bearer streams to PSTN TDM format.
² These Media Servers provides many media related services including conferencing, playing announcements, collection of in-band signalling tones, speech recognition, etc.
² The Media Server resources are shared with all applications. Consequently, each application that requires playing announcements, collecting digits, etc can use a common server. These applications may be voicemail, advance 800, interactive VXML services, etc.
² The Media Server can also support non-telephony function like Push-to-talk. So, using common pool of media servers across multiple services, service operators do not have to forecast or engineer media resource for each application.
Functional Entities Session Control Plane
CSCFDBDB
HSSCX
Functional EntitiesSession Control Plane² It is also called CSCF (Call Session Control Function) layer.² The function of this layer to provide registration of the end points and routing
of the SIP signalling messages to appropriate application server. ² The CSCF interworks with transport layer to guarantee QoS across all
services. ² The call session layer also includes HSS (Home Subscriber Server) database,
which maintains unique service profile for each end user. ² HSS includes end users registration information (i.e. IP address), roaming
information, telephone services (i.e. call forwarding), voice mailbox options, etc.
² To have this central database of subscribers, applications can share information to create unified personal directories, multi client type presence information and many more other services.
² The Call Session Control Layer also includes Media Gateway Control Function (MGCF). MGCF interworks the SIP signalling with the signalling used by Media Gateway (i.e. H.248/Megaco). The MGCF manages the distribution of sessions across multiple media gateways.
Functional Entities Session Control Plane: CSCF
Call Session Control Function
DBDBHSS
P-CSCF I-CSCF S-CSCF
UE’s first point of contact
Interrogating to load balance
UE session management
ISC ISC
Cx
Functional Entities Session Control Plane: P-CSCF Roles
Proxy- CSCF
vUE’s first point of contact
vAuthenticates and asserts an identity to the UE
vManages QoS, resource allocation, and controls charging function
vMay contain a PDF which
vManages resource allocation and QoS
vMay reside in the visited or home networkPDF
Functional Entities Session Control Plane: I-CSCF Roles
Interrogating- CSCF
vDetermines UE location by communicating with the HSS
vFinds the appropriate S-CSCF
vPerforms load balancing
vTypically resides in the home network
DBDB
HSS
Functional Entities Session Control Plane: S-CSCF Roles
Serving- CSCF
vResponsible for all session management activities
vRetrieves user profile and authentication information from the HSS
vEnforces the policy of the network operator
vFinds the appropriate AS
vProvides SIP routing
vAlways resides in the home network
DBDB
HSS
Functional Entities Session Control Plane: HSS
² Home Subscriber Server (HSS) is the main data storage for all subscriber
and service-related data of the IMS subscriber
² The HSS contains all the user-related subscription data required to handle
multimedia sessions
o All the data related to a particular user are stored in a
single HSS
² The HSS is always located in the home network
² Although the functionalities are the same, 3GPP and 3GPP2 HSSs are
described differently
Functional Entities Session Control Plane: HSS (3GPP)
CSCF
Home Subscriber Server
•IMS Functionality•HLR/AUC Function for PS•HLR/AUC Function for CS
Contains a user profile - bound to a Private User Identity and to the collection of Public User Identities
The user profile contains a number of service profiles
The service profile is divided into three parts:
•a collection of one or more public identifications
•an optional service authorization
•zero or more filter criteria
Relationship Between User Identities and Service Profiles
tel:+17324567888
tel:+88028112347
ServiceProfile1
ServiceProfile2
Public User Identities
Private User IdentityIMS Subscriber
a user profile is bound to a Private User Identity and to the collection of Public User Identities
user profile
Functional Entities Media Control Plane: MRF
MRFC vThe MRF (Media Resource Function) deals with the media in the IMS networkv MRFC: The MRFC handles communication with the S-CSCF and controls the resources in the MRFPv MRFP: The MRFP in the media plane implements all the media-related functions, such as playing media, providing announcements and mix mediav MRF resides in the home network.
MRF
MRFP
Media Plane
Signaling Plane
Inter-working FunctionsBGCF, SGW, MGCF, & MGW
BGCF
v The MGCF receives SIP call control signal from the IMS network and performs conversion to ISUP/IP and sends to SGW. MGCF also controls MGW.
v The SGW performs signaling conversion in the transport layer and interfaces with PSTN in the control plane
v The MGW performs media conversion and interfaces with PSTN.
v The BGCF selects another BGCF OR an appropriate PSTN/CS gateway
MGW
MGCF
SGW
Inter-working FunctionsBGCF, SGW, MGCF, & MGW (ctd.)
BGCF MGCF
SGW
MGW
Signaling (e.g., ISUP/MTP)
Media (e.g., Voice bit stream)
Switch
SIP
IMS NetworkPSTN Network
Functional Entities Services Plane: Applications Servers
SIP AS OSA-SCS IM-SSF
S-CSCFHSS
ISCSh
CxMRFC
Mr
Functional Entities Services Plane: Applications
² The application server layer contains the application servers, which provide the end-user service logic. The IMS architecture and SIP signaling is flexible enough to support a variety of telephony and non-telephony applications servers.
² Telephony Application Server (TAS): The IMS architecture supports multiple application servers for telephony services. The TAS is back-to-back SIP user agent that maintains the call state. The TAS contains the service logic which
provides the basic call processing services including digit analysis, routing, call setup, call waiting / forwarding / conferencing, etc.
² TAS provides ² IP Multimedia – Service Switching Function (IM-SSF)² Supplemental Telephony Application Servers² Non Telephony Application Servers² Open Service Access – gateway (OSA-GW)
IMS Architecture (3GPP View)
UE
IP-CAN(GPRS-based)
SGSN
GGSN
RAN
IM-MGW
ASUt
P-CSCFGm
I-CSCFMw
Sh, Si HSS SLF
Dh
S-CSCF MRFC
MRFP
MGCF
Cx Dx
Other IP/IMS
Mw
BGCFMj
Mk
Mp
Mb
Mi
SGW CSPDF
Gq
Go
Mr
ISC
Example: CNAM Call Flow
Control
Bearer
Called PartyVisited Network
Calling PartyHome Network
Calling Party Visited Network
UE1
P-CSCF
HSS
S-CSCFSIP
SIP
Diameter
UE2
P-CSCF
AS
HSS
S-CSCF SIP IM-SSF
SIP
I-CSCF
Diameter
ENUM
BackbonePacket
NetworkRANBackbone
PacketNetwork RAN
Initiate SIP Invite1
1
Retrieve Subscriber Profile (if needed) 2
2
3
3 Apply Service Logic
Retrieve Address of CLD Party Home Network4
4
Identify Registrar of CLD Party and Forward INVITE5
6
Retrieve Subscriber Profile6
7 Apply Service Logic to access IM-SSF AS
Forward INVITE to CLD Party9
9
SDP Negotiation / Resource Reservation Control10
12
RTP Stream
Ringing / Alerting11
10
Answer / Connect12
11
RTP Stream
13
13 Session Active
7
8 IM-SSF queries a GSM-SCF if inter-working with PLMN needed
Called PartyHome Network
8SCF
5
LIDB/CNAM
Summary IMS Architecture: High Level View
UE
SIP
IMS NetworkCarrier A
IMS NetworkCarrier B
ASsHSS
InterworkingFunctions
SSPSCP
PSTN
ISUP
HSS
ASs
CSCFs CSCFs
Quality of Services
² Although the functionalities are the same, 3GPP and 3GPP2 HSSs are
described differently
Policy-based control
PEP : Policy Execution Point
PDP : Policy Decision Point
COPS : Common Open Policy Service used for policy data transportUE
P-CSCF
GGSN
SIP/SDP
Gq
Go
Interface Perpose Protocol
Go Media authorization/charging coreletion COPS
Gq Transports policy set up information between the application function (P-CSCF) and the PDF
Diameter
Guaranteed QoS
P-CSCFPDFEdge routerUE
Conclusion
² The 3GPP has specified the IP multimedia subsystem (IMS) for the
provisioning of multimedia services in UMTS Release 5 and later.
² The IMS must be complemented with a guaranteed QoS control
architecture that implements resource admission control, policy control
and makes sure that proper policy enforcement is available in the
network.
² Interconnection at the service layer between 3GPP and LAN networks
requires interworking between IMS and WLAN functionalities.
IMS White PaperAcronyms² 3G Third Generation² 3GPP 3rd Generation Partnership Project² 3GPP2 3rd Generation Partnership Project 2² AAA Authentication, Authorization and Accounting² AMF Account Management Function² ANI Application-to-Network Interface² ANSI American National Standards Institute² API Application Programming Interface² AS Application Server² ASN Abstract Syntax Notation² ATIS Alliance for Telecommunications Industry Solutions² ATM Asynchronous Transfer Mode² ATP Acceptance Test Plan² AUC Authentication Center² BGCF Breakout Gateway Control Function² BT British Telecom² CAMEL Customized Applications for Mobile Network
Enhanced Logic² CAP CAMEL Application Part² CBF Charging and Billing Function² CCF Charging Collection Function² CDF Charging Data Function² CDMA Code Division Multiple Access
IMS White PaperAcronyms² CDR Charging Data Records² CGF Charging Gateway Function² CLEC Competitive LEC² CN Core Network² COPS Common Open Policy Service² CPE Customer Premises Equipment² CS Circuit-switched² CSCF Call Session Control Function² CTIA Cellular Telecommunications and Internet Association² DB Database² DHLR Distributed Home Location Register² DIAMETER AAA or HSS protocol; successor/upgrade of RADIUS² DMS Dual Mode Services² DNS Domain Name System² DSL Digital Subscriber Line² E9-1-1 Emergency Services² ECF Event Charging Function² EDGE Enhanced Data Rates for GSM Evolution² EIA Electronics Industry Association² ENUM Telephone Number Mapping² GGSN Gateway GPRS Support Node² GPRS General Packet Radio Service² GSA Global Mobile Suppliers Association² GSM Global System for Mobile Communication² HLR Home Location Register² HSS Home Subscriber Server
IMS White PaperAcronyms² HTTP HyperText Transfer Protocol² I-CSCF Interrogating Call Session Control Function² IETF Internet Engineering Task Force² IM Instant Messaging² IM-SSF IP Multimedia Services Switching Function² IMS IP Multimedia Subsystem² IMS-MGW IMS Media Gateway Function² IMT-2000 International Mobile Telecommunications 2000² IN Intelligent Networks² IP Internet Protocol² IP-CAN IP Connectivity Access Network² IPDR Internet Protocol Detail Record² IPsec IP Security² IPv4 IP Version 4² IPv6 IP Version 6² ISC IMS Service Control² ISDN Integrated Services Digital Network² ISG Intelligent Services Gateway² ISO International Organization for Standards² ISUP ISDN User Part² IT Information Technology² LAN Local Area Network² LEC Local Exchange Carrier² LNP Local Number Portability² MAP Mobile Application Part² MCS Multimedia Communications Server
IMS White PaperAcronyms² MEGACO Media Gateway Control (protocol)² MGCF Media Gateway Control Function² MGF Media Gateway Function² MGIF Mobile Gaming Interoperability Forum² MGW Media gateway² MPLS Multi-Protocol Label Switching² MRF Media Resource Function² MRFC Media Resource Function Controller² MRFP Media Resource Function Processor² MSF Multiservice Switching Forum² MSO Multi-Service Operator² MTP Message Transfer Part² NAI Network Access Identifier² NANP North American Numbering Plan² NE Network Element² NGN Next Generation Network² NNI Network Node Interface² OAM&P Operations, Administration, Maintenance and Provisioning² OCF Online Charging Function² OCS Online Charging System² OMA Open Mobile Alliance² OSA Open Service Access² OSI Open Systems Interconnection² OSS Operations Support System² PC Policy Controller² P-CSCF Proxy Call Session Control Function
IMS White PaperAcronyms² PDA Personal Digital Assistant² PDF Policy Decision Function² PDS Packet Data Subsystem² PDSN Packet Data Service Node² POTS Plain Old Telephone Service² PSTN Public Switched Telephone Network² PLMN Public land Mobile Network² QoS Quality of Service² RAN Radio Access Network² RADIUS Remote Authentication Dial In User Service² RF Rating Function² RTP Real-Time Transport Protocol² RTCP RTP Control Protocol² SBC Session Border Controller² SCCP Signaling Connection Control Part² SCF Session Charging Function ² SCIM Service Capability Interaction Manager² SCP Service Control Point² S-CSCF Serving Call Session Control Function² S-CSCF Serving CSCF² SCTP Stream Control Transmission Protocol² SCF Service Control Function² SCP Service Control Point² SCS Service Capability Server² SDO Standards Development Organization² SDP Session Description Protocol
IMS White PaperAcronyms² SGF Signaling Gateway Function² SGSN Serving GPRS Support Node² SGW Signaling Gateway² SIGTRAN Signaling Transport² SIP Session Initiation Protocol² SLA Service Level Agreement² SLF Subscriber Locator Function² SMS Short Message Service² SNMP Simple Network Management Protocol² SOA Service Oriented Architecture² SS7 Signaling System 7² SSL Secure Sockets Layer² SSF Service Switching Function² SSP Service Switching Point² TAS Telephony Application Serer² TBCP Talk Burst Control Protocol ² TCAP Transaction Capabilities Application Part² TCP Transmission Control Protocol² TDM Time Division Multiplexing² TIA Telecommunications Industry Association² TSG-CT TSG Core Network and Terminals (3GPP)² TSG-GERAN TSG GSM EDGE Radio Access Network (3GPP)² TSG-RAN TSG Radio Access Network (3GPP)² TSG-SA TSG Service and System Aspects (3GPP)² UDP User Datagram Protocol
IMS White PaperAcronyms² UE User Equipment² UMTS Universal Mobile Telecommunications System² UNI User-to-Network Interface² URI Universal Resource Identifier² URL Uniform Resource Locator² UTRA Universal Terrestrial Radio Access² UWB Ultra-Wideband² VCC Voice Call Continuity² VoIP Voice over IP² VPN Virtual Private Network² VSP Virtual Service Provider² WCIT World Conference on International Telecommunications² WIN Wireless Intelligent Network² WG Working Group² WiFi 802.11x wireless technology² WiMAX 802.16x wireless technology² WIN Wireless Intelligent Network² WLAN Wireless LAN² WTSC Wireless Technologies and Systems Committee (ATIS)² xDSL Variations of DSL
IMS Architecture References
1. The 3G IP Multimedia Subsystem (IMS), Merging the Internet and the Cellular Worlds, by Gonzalo Camarillo and Miguel A. Garc´ıa-Mart´ın, 2006
2. IP Multimedia Concepts and Services by Mikka Poikselka, Georg Mayer, Hisham Khartabill, Aki Niemi, 2006
3. 3GPP TS 23.228: Technical Specifications Group Services and System Aspects; IP Multimedia Subsystems (IMS), Stage 2, 12/2005
4. 3GPP2 X.S0013-000-A: All-IP Core Network Multimedia Domain, Overview , 11/2005
5. 3GPP2 X.S0013-002-A: All-IP Core Network Multimedia Domain, IMS, Stage 2 , 11/2005
