A simple yet explainative PPT on IMS architectural nodes, structure & session establishment flow

1. IMS – IP MULTIMEDIA
SUBSYSTEM
Structure, Architectural nodes & Session Establishment
flow
By

2. WHAT IS IMS?
• IP Multimedia Subsystem
• An architectural framework for delivering IP
Multimedia to multiple mobile users.
• Uses IETF (internet) protocol i.e. SIP (Session
Initiation Protocol)

3. STRUCTURE OF IMS

4. IMS STRUCTURE Continued…..
• Consists of common core, enablers, support
systems, internetworking functions enabling
operators & service providers.
• Layered architecture: Application layer,
control layer, connectivity layer.
• Layered architecture allows each layer to
evolve independently as market & technology
demands changes.

5. IMS ARCHITECTURE

6. IMS ARCHITECTURE Continued….
• Definition: IMS is an architecture designed to
support the control layer for packet based
services.
• Types of IMS nodes:
– DATABASE ELEMENTS (HSS, SLF)
– IMS CONTROL ELEMENTS (P-CSCF, I-CSCF, S-CSCF)
– CONTROL PLANE INTERWORKING ELEMENTS
(MGCF, BGCF, S-GW)

7. IMS ARCHITECTURE Continued….
• DATABASE ELEMENTS:
HSS:
 subscriber data & authentication data
 location register
 IMS service profile processing
 accessed by S-CSCF & I-CSCF
 Uses diameter protocol
 SLF:
 accessed by S-CSCF & I-CSCF
 Which HSS stores the user data when 1 or more HSS is present
in the network
 Query contains identification of user
 Response contains the required specific HSS

8. IMS ARCHITECTURE Continued….
• IMS CONTROL ELEMENTS: call session control
functions, acts on control (SIP) signalling
flows.
S-CSCF:
 performs session management
 authenticates the user
 main control point for services
 decides on handling of service requests
 always located in home network

9. IMS CONTROL LAYER Continued….
 P-CSCF:
 main network point towards IMS network
 It is a stateful SIP proxy
 Signalling b/w user & IMS routed through I-CSCF
 Responsible for SIP registration with S-CSCF through I-CSCF
 Responsible for maintaining security with user throughout the
connection.
 Includes PDFs which authorizes use of bearer & QoS resources
 I-CSCF:
 1st point of contact from home to an external network
 main job is to query HSS & find location of S-CSCF.

10. IMS ARCHITECTURE Continued….
• CONTROL PLANE INTERWORKING ELEMENTS:
 MGCF:
Enables communication b/w IMS & CS users
 controls media channels
BGCF: responsible for choosing where a breakout to
the CS domain occurs.
 S-GW:
used to connect signaling networks such as SCTP/IP based &
SS7 networks
 performs signaling conversion

11. IMS SESSION ESTABLISHMENT FLOW