The document outlines the IP Multimedia Subsystem (IMS), which facilitates the convergence of voice, video, messaging, and data for both wireless and wireline users through specific functional elements and terminals. It details the architecture, requirements for quality of service, and the roles of various components such as the Call Session Control Function (CSCF) and the Home Subscriber Server (HSS). The IMS is designed to ensure interoperability and support for session-oriented applications across diverse access networks.

1. IMS – IP MULTIMEDIA
SUBSYSTEM

2. What is IMS

3. IP Multimedia Subsystem ?
• The IM CN subsystem should enable the convergence of,
and access to,
• voice,
• video,
• messaging,
• data and
• web-based technologies
for the wireless and wireline user.

4. The complete solution for the support of IP
multimedia applications consists of:
terminals,
IP-Connectivity Access Networks (IP-CAN),
and the specific functional elements of the IM CN
subsystem
Examples of IP-Connectivity Access Network are:
• the GPRS core network with GERAN and/or UTRAN radio
access networks; and
• EPC core network and E-UTRAN radio access network;
and
• 5GS access network.
IP Multimedia Subsystem

5. IMS Requirements
• High-level requirements
• Negotiable QoS for IP multimedia applications
• At session establishment and during session
• End-to-end QoS for voice
• A quality equal to or better than that of mobile CS voice call
• Roaming
• Inter-operator QoS negotiation
• Use services provided by home- and by serving network
• Mandatory default set of media types to ensure interoperability
• Codec (audio: AMR, video: H.263), header compression
• Access independence (GPRS, fixed, LAN)
• Support for session-oriented non-3GPP Internet apps

6. IMS Architecture
6
Management
Provisioning
Charging
Number
Mapping
MGW
SG/MGCF
CSCF
MRF
HSS
SIP, IP
Control Layer
AS AS
SIP / OSA / CAMEL
Application Layer
IP/MPLS PSTN/PLMN
GERAN, UTRAN, WLAN, xDSL,...
Connectivity & Access Layer

7. IMS Architecture
HSS: Home Subscriber Server
CSCF: Call Session Control
Function:
S-CSCF: Serving CSCF
I-CSCF: Interrogating CSCF
P-CSCF: Proxy CSCF
BGCF: Breakout Gateway
Control Function
MGCF: Media Gateway Control
Function
AS: Application Server
SCP: Service Control Point
MGW: Media Gateway
MRFC: Multimedia Resource
Function Controller
MRFP: Multimedia Resource
Function Processor
Applications
and Services
AS
SCP
Mobile
UE
GERAN
UTRAN
SGSN
IM-SSF
OSA-SCS
CSCF
HSS
SGW
Operator 1
CSCF BGCF
Operator 2
BGCF
MGCF
MRFC MRFP
GGSN
Multimedia
IP
Networks
CS Domain
- or -
PSTN
- or -
Legacy
- or -
External
MGW
SGW
Alternative
Access
Network
E-UTRAN

8. IMS Architecture
S-CSCF
MGCF HSSCx
IM
MGW Mn
Mb
Mg
MRFP
Mb
I-CSCF
Mw
Mw
Gm
Mj
Mi
BGCF
Mk
UE
Mb
Mb
Mb
SLFDx
CS
CS
Cx
AS
ISC
Sh
Ut
BGCF
Mg
Dh
Ma
P-CSCF
Mx
Mx
Mx
CS Network MmMm Mm
TrGW
IP Multimedia Networks
IBCF
Ix
Ici, MmIzi
MRB
Rc
ISC
Mr
MRFC
Cr, Mr’
Mb
IMS
AGW
Mp
Mw
Iq

9. IP Connectivity Access Network (IP CAN)
• The IP multimedia subsystem utilizes the IP-CAN to transport:
• multimedia signalling and
• bearer traffic.
• IP-CANs that maintain the service while the terminal moves, hide these moves
from the IP multimedia subsystem.
• The IP multimedia subsystem is independent of the CS domain

10. Call Session Control Function (CSCF)
The roles that the CSCF plays are described below.
• The Proxy-CSCF shall enable the session control to be passed to the Serving-CSCF.
• The Serving-CSCF is located in the home network. The Serving-CSCF shall invoke service logic.
• A Proxy-CSCF shall be supported in both roaming and non-roaming case, even when the
Serving-CSCF is located in the same IM CN Subsystem