IMS: An Architecture for Convergent Next
Generation Multimedia Services. Research and
Standardisation Challenges
Dr. Sorin Georgescu
sorin.georgescu@ericsson.com
Agenda





IMS Architecture Overview
Standardisation Status
The Service Layer View
IMS and SOA
Research and
Standardisation Challenges
IMS Convergent Multimedia Services
2
Sorin Georgescu
Next Generation Networks Evolution Drivers
Convergence
Societal and Business trends
• Converged devices (Mobile, WLAN,
• Internet is becoming a major enabler
Internet etc.)  Connectivity
of communications
• Converged services  Ease of
use
• Consumers are embracing
computing, mobile and digital
technology in their everyday life
• Converged networks  Reliability,
Security, Reduced OPEX/CAPEX
• Evolution of Business models require
increased levels of personal mobility
• Converged business models 
Increased margins, Avoidance of
twin pitfalls risk
Access Technology Enhancements
• HSPA (High Speed Packet Access) – evolved
WCDMA
• OFDMA (Orthogonal Frequency Division
Multiple Access) – 3GPP LTE, WiMAX, MBWA,
ADSL/VDSL, DVB-T/H etc.
• Spatial Processing – multi-antennas Base
Stations supporting advanced spatial processing
IMS Convergent Multimedia Services
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Sorin Georgescu
The Evolution to IMS Multimedia Applications
Person-to-Content
known usability patterns
Photos
Video Movies
Music
Ring tone
Internet
Streaming
Text/Pictures
Download
HTTP
Video
SMS/MMS
Person-to-Person
dominates traffic growth
Active
phonebook
Image
Sharing
Text
Presence
Push-To-Talk
Voice
MMS
SMS
Voice
IMS Convergent Multimedia Services
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Sorin Georgescu
Watch and Communicate service
• While out in town, Bob stopped by at the Jazz festival. He
made a short clip and would like to ask his friends if they are
interested to go to the evening performance.
• He checks the presence information of Alice and Dave.
• Bob opens a Chat session and sends the clip to his friends. He
asks if they are interested to go to the evening performance.
• Dave is watching TV, therefore the chat session is diverted to
his IMS enabled STB.
Communication services
Personalised content services
Group and context support
IMS Convergent Multimedia Services
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Sorin Georgescu
IMS – a Standard-based Architecture for NG Services
• IMS defines an open IP-based
service infrastructure where service
intelligence is located in the servers
and mobile devices.
• IMS as originally specified by 3GPP,
was aiming to enable real-time
multimedia services over the IP
bearer in GSM and W-CDMA
networks.
• 3GPP2 defined later the MMD for
CDMA2000 networks which is now
aligned with IMS.
• TISPAN provided the specifications
for DSL access.
• CableLabs provided the
specifications for the cable access
and now their work together with
3GPP to incorporate PC 2.0
specifications into IMS release 8.
• Since release 6, interworking with
WLAN is supported.
If IMS is not used:
 Multimedia communication at best effort
 Service orchestration can be complex
 Service roaming can be difficult to implement
 Provisioning and charging are service specific
 Compliance with LI requirements can be an issue
IMS Convergent Multimedia Services
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Sorin Georgescu
IMS/TISPAN Architecture
AS
HSS
Application
‘IMS Data’
IM SSF
SIP AS
SLF
OSA SCS
(SIP AS,
OSA AS,
CAMEL SE)
HLR/AuC (‘CS/PS’)
CSCF
BGCF
S-CSCF
IMS Session Signalling
IMS User Plane Data
I-CSCF
MGCF
P-CSCF
NASS
SPDF/ A-RACF
MRF
DSLAM
UE
BAS
PDF
IMS GW
MRFC
ALG
MRFP
TrGW
SGW
CS Networks
(PSTN, CS PLMN)
3GPP R7 / TISPAN R1
WLAN WAG
UE
3GPP R6
UE
RAN
WLAN
PDG
GGSN
IMS-MGW
IPv4 PDN
(IPv4 Network)
BB
(IPv4/
IPv6)
PEF
BG
IPv6 PDN
(IPv6 Network)
SGSN
3GPP R5
IMS Convergent Multimedia Services
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Sorin Georgescu
Functional Overview (1)
• CSCF (Call Session Control Function) consists of
3 separate functions: P-CSCF, I-CSCF, S-CSCF
• P-CSCF (Proxy-CSCF):
- Entry point to IMS from any access network
- Performs integrity protection
- Local outbound stateful proxy for all SIP
requests/responses, ensuring all signalling is
sent via the home network
- Includes a Policy Decision Function (PDF)
that authorizes bearer resources
• HSS (Home Subscriber Server):
- IMS subscriber records and service profile
- IMS authentication data
• I-CSCF (Interrogating-CSCF):
- First contact point in home network
- Selects assigned S-CSCF
- Performs network hiding (THIG)
• MRF (Media Resource Function) consists of 2
separate functions: MRFC, MRFP
• S-CSCF (Serving-CSCF):
- Stateful proxy that provides session control
- Performs subscriber authentication
- Acts as SIP registrar
- Invokes the AS’ (Application Servers) based
on IFC (Initial Filter Criteria)
• MRFC (Media Resource Function Controller):
- Controls media resources in MRFP
- Acts as SIP B2BUA
• MRFP (Media Resource Function Processor):
- Media stream processing (transcoding etc.)
- Multimedia announcements
- Incoming streams mixing
• SLF (Subscriber Location Function):
- Look-up function used in networks where
multiples HSS’ exist
IMS Convergent Multimedia Services
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Sorin Georgescu
Functional Overview (2)
• SIP AS (Application Server):
- Hosts IMS native applications
• IM SSF (IP Multimedia Switching Service
Function):
- Provides interworking with CAMEL, ANSI-41,
INAP or TCAP services
• OSA SCS (Open Service Architecture Service
Capability Server):
- Provides interworking with OSA services
• BGCF (Breakout Gateway Control Function):
- Selects the network in which PSTN breakout
is to occur and within that network selects the
MGCF
• SGW (Signaling Gateway):
- Performs conversion at transport level
(SCCP, SCTP)
• SBC (Session Border Controller):
• MGCF (Media Gateway Control Function):
- Controls media channels in IMS MGW
- Performs conversion between ISUP/TCAP
and IMS call control protocols
• PDF/SPDF (Policy Decision Function / Serving
Policy Decision Function):
• A-RACF (Access - Resource and Admission
Control Function):
• IMS MGW (IMS Media Gateway):
- Terminates bearer channels from CS
networks and PS media streams
- Owns/handles resources (echo cancellers,
codes, etc.)
IMS Convergent Multimedia Services
• NASS (Network Attachment Subsystem):
• DSLAM (Digital Subscriber Line Access
Multiplexer):
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Sorin Georgescu
IMS Service Routing – the IFCs
Visited A
4
8
Home B
I-CSCF
9
S-CSCF
10
P-CSCF
3
P-CSCF
Visited B
Home A
6
S-CSCF
2
7
5
1
IMS AS
HSS
IMS AS
HSS
• SIP requests in IMS architecture are
always routed to the Home S-CSCF, in
both the originating and terminating
network.
• The S-CSCF uses subscriber’s
Service Profile (downloaded during
registration), to link-in the SIP AS’
which will process the SIP request.
11
IMS Service Routing =
Service Profile based Routing
IMS Convergent Multimedia Services
• In comparison to IETF SIP Routing
where the originator of SIP request may
specify a preferred path in the Route
header, in IMS the P-CSCF removes
this path and ensures that IMS SIP
Routing is followed.
10
• The Initial Filter Criteria (IFC) within
the Subscriber Profile provide a simple
service logic to decide which AS shall
be linked-in. These rules are of static
nature i.e. they do not change on a
frequent basis.
Sorin Georgescu
Service/application identification – ICSI/IARI
A Communication Service is an aggregation of one or several media components and the service
logic managing the aggregation, represented in the protocols used.
An IMS application is an application that uses an IMS Communication Service(s) in order to provide a
specific service to the end-user. Only IMS applications other than the default application associated to
the Communication Service are identified through IARIs.
• 3GPP TS 23.228 R7
introduced the ICSI/IARI
identifiers as a mechanism for
UEs to provide a hint to the
network on the AS’ they wish
to be linked-in the signalling
path.
• The introduction of ICSI/IARI
in 3GPP aims to address to a
certain extent the limitations
due to the use of the Service
Profile routing paradigm. The
ICSI/IARI are used as
parameters in the IFC,
therefore the AS selection
process becomes more
dynamic.
IMS Convergent Multimedia Services
Appl 1
IARI1
Appl 2
IARI2
IARI2
CS 1
CS2
ICSI1
ICSI2
SIP Stack
• The ICSI/IARI provides a
mechanism to control rating
based on selected pricing
model. For example, it is
possible to rate differently a
Messaging Communication
Service when invoked from
a Multimedia application
then when invoked from a
Gaming application.
ICSI = IMS Communication Service ID
IARI = IMS Application Reference ID
CS = Communication Service
11
Sorin Georgescu
Service Convergence in Quadruple Play
End User
experience
=
Access to subscribed
services from any
device in the bundle
Industry
consolidation and
alliances
Service continuity
=
Convergence at Service
Provider level.
Common provisioning,
mgmt and billing
Common service
and subscriber
management
Fixed Mobile
Convergence
=
Converged Service
Architecture
Setup of the
appropriate QoS
and resources
IMS Convergent Multimedia Services
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Sorin Georgescu
Agenda





IMS Architecture Overview
Standardisation Status
The Service Layer View
IMS and SOA
Research and
Standardisation Challenges
IMS Convergent Multimedia Services
13
Sorin Georgescu
Standardisation fora
Multimedia
Telephony
Presence
GLMS
PoC
Messaging
IP
Broadband Access to IMS
CSI
GSM/WCDMA Access to IMS
WLAN Access to IMS
PacketCable™ WiMAX
DSL DOCSIS
Forum
Residential
IMS Convergent Multimedia Services
Forum
Enterprise
14
VCC
Mobile
Sorin Georgescu
3GPP R7 Reference Model
TE
R
MSC
GERAN
MT
C
HLR/AuC*
HSS*
EIR
SMS-GMSC
SMS-IWMSC
SMS-SC
Um
Gb, Iu
Gr
Gf
Gs
PCRF
Gd
Iu
TE
MT
R
Uu
Gn
Ga
Billing
System*
BM-SC
Gi
GGSN
Ga
Gi
PDN
Mb
Gy
SGSN
UE
Gx+ (Go/Gx)
Gmb
Gc
Gn/Gp
SGSN
UTRAN
Rx+ (Rx/Gq)
AF
IMSMGW
Mb
MRFP
OCS*
Wi
CGF*
Gm
IMS
P-CSCF
CSCF
Mw
CDF
Intranet/
Internet
WLAN
UE
Ww
Wa
Wa
WLAN Access
Network
Wf Wf
Wd
3GPP AAA
Proxy
WAG
D/Gr
HSS*
SLF
Wx
Dw
3GPP AAA
Server
Wm
Wg
Wo Wy
Wz
Wu
CGF*
Traffic and signalling
Signalling
IMS Convergent Multimedia Services
**
OCS*
PDG
Wp
Wn
Dx
Cx
HLR/A
uC*
Billing
System*
Note: * Elements duplicated for picture
layout purposes only, they belong to the
same logical entity in the architecture
baseline.
** is a reference point currently missing
15
Sorin Georgescu
TISPAN R1 Reference Model
Application Servers
Ut
P1
PSTN/ISDN Emulation logic
Sh
UPSF
PES
e2
e2
ISC
Cx
Mj
Mg
MRFC
MGCF
SGF
Ie
PSTN/ISDN
Z
Gq '
Gq '
Mp
S/T
Mn
Resource and Admission Control Subsystem
GW
MRFP
S/T
Z
MG
T-MGF
IP Transport (Access and Core)
IMS Convergent Multimedia Services
Ic
16
Sorin Georgescu
I-BGF
Other IP Networks
Mr
P-CSCF
IBCF
Mk
BGCF
Gm
IWF
Mk
Mi
Mw
Ib
P3
Mw/Mk/Mm
I/S-CSCF
P2
Iw
SLF
Dx
Charging
Functions
Rf /Ro
Dh
Mw
AGCF
Gq '
Rf /Ro
Other types of service logic
Ut
Network
Attachment
Subsystem
Rf/Ro
WIs in 3GPP release 7 (02/2008)
• Coexistence between TISPAN and
3GPP authentication schemes study
• Service Identification using ICSI/IARI
• Liberty Alliance and 3GPP security
interworking
• SAE (System Architecture Evolution)
• RAN LTE (Long Term Evolution)
• Location Services for WLAN
interworking
• MMTel (Multimedia Telephony)
• MRFP-MRFC (Mp) Interface
• VCC (Voice Call Continuity) between
IMS VoIP and CS speech
• Parlay X WS:
• Message broadcast
• Geocoding
• Application driven QoS
• Device Management
• Multimedia Streaming/Multicast
Control
• CSiCS (Circuit Switched IMS
Combinational Service)
• SMS/MMS over IP
• FBI (Fixed Broadband access to IMS)
• IMS Emergency Calls
• ISIM API for Java Card
• PCC (Policy Control and Charging
Evolution)
• E2E QoS
• AIPN (All IP Network) Feasibility Study
IMS Convergent Multimedia Services
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Sorin Georgescu
WIs in 3GPP release 8 (tentative 03/2009)
• Architecture impacts of Service Brokering
• Enhancements for support of PacketCable 2.0 requirements
• Multimedia Priority Service
• Personal Network Management
• Enhancements for support of machine to machine communication
• Enhanced Generic Access Networks
• HSPA FDD (Frequency Division Duplex)
• Enhancements to SAE/LTE Architecture
• OAM&P Studies
IMS Convergent Multimedia Services
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Sorin Georgescu
Agenda





IMS Architecture Overview
Standardisation Status
The Service Layer View
IMS and SOA
Research and
Standardisation Challenges
IMS Convergent Multimedia Services
19
Sorin Georgescu
IMS in OMA Service Environment context
Applications
OSE Context
I0+P
SP Domain
Policy Enforcer
Execution
Environment
Execution
Environment
I0
(Software Life
Cycle Mgmt,
Load balancing,
Caching, O&M,
etc.)
Service Binding
Service Binding
Service Binding
Service Binding
Service Enabler
Service Enabler
Service Enabler
Service Enabler
I1
I2
ISC
Sh
Ut
IMS Convergent Multimedia Services
Ro
Rf
Gm
20
Mb
NonIMS
Sorin Georgescu
(Software Life
Cycle Mgmt,
Load balancing,
Caching, O&M,
etc.)
OMA SIMPLE IM Reference Model
XDM Client
XDM -5
Aggregation Proxy
XDM -3
PRS-7
XDM-4
IM-12
IM
XDMS
PRS-6
Presence XDMS
XDM-7
XDM-2
IM Client
IM-1
Shared
Profile
XDMS
Shared
Group
XDMS
Shared XDMSs
CH-1
IM -3
IM -2
PRS-8
Shared List XDMS
PRS-2
Charging
IM-6
IM-5
SIP / IP Core
Pres Client: Watcher
Search
Proxy
IM
Server
IM -4
IM-8
IM -11
IM -10
PRS-5
IM -7
Presence
Server
PRS-3
IP-1
IM-9
DMC
DM-1
DMS
IMS Convergent Multimedia Services
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Sorin Georgescu
Remote SIP/IP Core
XDM -1
PRS-1
Pres Client: Source
XDM-6
Remote
IM
Server
Remote
IM
Client
Limitations of ISC Service Orchestration Model
SIP-AS
SIP-AS
SIP-AS
SIP-AS
Req URI = A
S-CSCF
HSS
SIP-AS
Req URI = B
S-CSCF
HSS
I-CSCF
SIP-AS
I-CSCF
• The application server decides whether to remain
linked-in for the whole session by adding its
address to the Record-Route SIP header.
• If during call handling procedure an AS retargets
the SIP request by changing the Request URI,
subsequent filter analysis in the S-CSCF is stopped
and the S-CSCF forwards the request towards the
new target without linking-in the other AS’ specified
by IFC.
• Application Servers are unaware of the existence
of other AS', and whether these will be linked-in.
• No service or session state will be passed
between application servers unless they use
proprietary extensions i.e. are co-designed.
• Response messages are routed to the AS’s in the
reverse order
1
IMS Convergent Multimedia Services
2
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Sorin Georgescu
SCIM vs. Service Broker
AS
AS
Camel
Services
OSA AS
OSA API
SCIM
OSA SCS
ISC
Sh
ISC
ISC
S-CSCF
AS
CAP
AS
IM SSF
Sh
Cx
AS
AS
Si
HSS
S-CSCF
• The Service Broker architecture has been
introduced as WI in IMS Release 8.
• The Service Capability Interaction Manager
(SCIM) orchestrates service delivery among
application servers.
• The objective is to provide a coherent and
consistent IP multimedia service experience
when multiple applications are invoked.
• Underspecified in TS 23.002, the SCIM has
become a sort of “magic box” that would solve
all issues related to service orchestration.
• The work is handled by 3GPP SA2
(Architecture) group in TR 23.810. So far, just
the some high level deployment scenarios
and some uses cases have been defined.
• Possible types of SCIM:
• AS Internal SCIM (figure above)
• SIP Broker SCIM / Service Broker SCIM
• Can be centralised, distributed or hybrid (as
in the figure above).
• Legacy SCIM
IMS Convergent Multimedia Services
Service Broker
Service Broker
MAP
23
Sorin Georgescu
Parlay X Web Services
WS-I Basic Profile: WSDL + SOAP
• Parlay X Web Services is an
abstraction of Parlay WS
WS-I Secure Profile: WSDL + SOAP + WS-Security
AS
AS
Parlay-X, Customized interfaces
Trusted Domain
AS
AS
WS Security,
WS-Addressing
Customized
Compound
WS
Parlay-X WS GW
IMS Service
Enablers
Sh
ISC
H.248
HSS
CSCF
Media
resources
• Parlay X WS GW acts as a
Service Broker SCIM
• Enablers which only support
WS-I Basic Profile are
enhanced with additional WS
functionality such as WSSecurity, WS-Policy, WSAddressing
• Services defined so far (17)
cover: call control, messaging
(SMS, MMS), payment,
location, geocoding and
mapping, presence etc.
• Described in WSDL. Service
discovery is based on UDDI.
IMS Core Network
IMS Convergent Multimedia Services
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Sorin Georgescu
Agenda





IMS Architecture Overview
Standardisation Status
The Service Layer View
IMS and SOA
Research and
Standardisation Challenges
IMS Convergent Multimedia Services
25
Sorin Georgescu
SOA Reference Model
What is SOA:
A paradigm which defines concepts
and general techniques for the
design, encapsulation and
instantiation of reusable business
functions using loosely coupled
service interactions
Visibility
Service
Description
Reachability
Service
Service
Interface
SOA Reference Model:
 Service
Real world
effect
Functionality
 Service description
Interaction
 Interaction
Contract &
Policy
 Contract & Policy
 Visibility
Information
model
Behavior
model
 Execution Context
SOA Service Description Model
 Real world effect
IMS Convergent Multimedia Services
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Sorin Georgescu
SOA Orchestration
Appl 1
Client
Terminal
Application 1
Enabling
Service 1
Enabling
Service 2
Enabling
Service 3
Routing based on service
identity (equivalent to PSI
routing in IMS)
AS1
Application 2
AS2
Enabling
Service 4
AS3
Service bus functions:
SOA Characteristics
• Supports an asynchronous message
based communication protocol that
uses a common format encoding
scheme (SOAP/XML)
 Services have well defined Service Contracts
• Routes, Translates and can Store
and Forward exchanged messages
• Supports a Discovery mechanism
 Services are encapsulated
 Services share a message bus and messages
exchanged are well documented
 Services can be discovered dynamically
 Services are loosely coupled
 Systems of services are assembled at runtime
IMS Convergent Multimedia Services
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Sorin Georgescu
IMS-SOA Architecture
Service Enablers:
Service
Contract
SOA
• Provide functionality which can be used by other
end-user applications (ex. Location Service)
UDDI
SOA AS
• Unaware of the context in which they are used. Only
the consumer service is aware.
Schema
Service Bus
SOAP/XML
• Handles the communication between IMS
Application Servers and the Service Enablers and the
communication with SOA Application Servers.
MLP
SIP
Service Bus
MM7
SB API
SB API
• Optimized for Server-to-Server communication
• Besides providing support for standard open
protocols (ex. SOAP), may provide support for Native
Interface protocols (ex. MLP, MM7, SIP etc.)
GW AS
IMS AS
SB API
Enabler
CSCF
Service Orchestration
Orig. network
JSR 281
• The consumer AS that invokes the Service Enabler
implements the SCIM function. An external Service
Broker may be used as well.
Heterogeneous Service Bus
IMS-SOA Architecture
• IMS Service Enablers are invoked from SOA
domain through the GW AS.
IMS Convergent Multimedia Services
IMS
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Sorin Georgescu
Agenda





IMS Architecture Overview
Standardisation Status
The Service Layer View
IMS and SOA
Research and
Standardisation Challenges
IMS Convergent Multimedia Services
29
Sorin Georgescu
IMS Core Network
 Coexistence of access specific authentication methods
 Media Adaptation using UE capabilities discovery
 Design of efficient algorithms for real-time adaptation of
MBMS content
 Access agnostic vs. access aware P-CSCF
 QoS awareness, access agnostic control of the QoS
 Media security
IMS Convergent Multimedia Services
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Sorin Georgescu
IMS Service Layer
 Service Orchestration paradigms. The integration with
SOA architecture
 Enhancements to presence service to support device
capabilities, subscription state, user preferences,
context awareness, bearer state
 Multimodal interaction
 Payment brokerage
 Personalised/interactive advertisement
 QoS control over the Service Bus.
IMS Convergent Multimedia Services
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Sorin Georgescu
Thank you for your attention!
sorin.georgescu@ericsson.com
IMS Convergent Multimedia Services
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Sorin Georgescu