pdfslide.net_architectural-overview-of-ip-multimedia-subsystem-3-3gpp-ims-architectural-overview.pdf

1. 1
Architectural Overview of
IP Multimedia Subsystem -IMS
Presented by:
Masood Khosroshahy
June 2006
Project supervisor:
Prof. Elie Najm
B
E
G
I
N
N
I
N
G

2. 2
Simplified view of the layered
architecture in IMS
From [4]

3. 3
3GPP IMS Architectural Overview
IMS-MGW
IPv6 PDN
(IPv6 Network)
MGCF
PDF
I-CSCF
S-CSCF
BGCF
Application
(Ext. SIP AS, OSA AS,
CAMEL SE)
MRFC
MRFP
MRF
IPv4/IPv6
BB
CS Networks
(PSTN, CS PLMN)
CSCF
P-CSCF
SGW
OSA SCS
IM SSF
SIP AS
AS
BG
SLF
ALG
TrGW
‘IMS IPGW
IPv4 PDN
(IPv4 Network)
IP CAN ABG
TE AN
IMS
Terminal
PEF
/TP
F
HLR/AuC (‘CS/PS’)
HSS
IMS Data Handling
From [2]

4. 4
3GPP IMS Architectural Overview:
Serving CSCF (S-CSCF)
IMS-MGW
IPv6 PDN
(IPv6 Network)
MGCF
PDF
I-CSCF
S-CSCF
BGCF
Application
(Ext. SIP AS, OSA AS,
CAMEL SE)
MRFC
MRFP
MRF
IPv4/IPv6
BB
CS Networks
(PSTN, CS PLMN)
CSCF
P-CSCF
SGW
OSA SCS
IM SSF
SIP AS
AS
BG
SLF
ALG
TrGW
‘IMS IPGW
IPv4 PDN
(IPv4 Network)
IP CAN ABG
TE AN
IMS
Terminal
PEF
/TP
F
HLR/AuC (‘CS/PS’)
HSS
IMS Data Handling

5. 5
Serving CSCF (S-CSCF) Functions
• Acts like a SIP Registrar, it binds the public user ID to a location.
• The S-CSCF retrieves the subscriber profile from the HSS.
• Provides session control for the endpoint's sessions
(service logic is performed by an Application Server, not the S-
CSCF).
• Handles SIP routing for originating and terminating endpoints.
• Ensures that the media for a session, as indicated by SDP, are
within boundaries of subscriber's profile.
• Interacts with Application Server platforms for the support of
services.

6. 6
3GPP IMS Architectural Overview:
Interrogating CSCF (I-CSCF)
IMS-MGW
IPv6 PDN
(IPv6 Network)
MGCF
PDF
I-CSCF
S-CSCF
BGCF
Application
(Ext. SIP AS, OSA AS,
CAMEL SE)
MRFC
MRFP
MRF
IPv4/IPv6
BB
CS Networks
(PSTN, CS PLMN)
CSCF
P-CSCF
SGW
OSA SCS
IM SSF
SIP AS
AS
BG
SLF
ALG
TrGW
‘IMS IPGW
IPv4 PDN
(IPv4 Network)
IP CAN ABG
TE AN
IMS
Terminal
PEF
/TP
F
HLR/AuC (‘CS/PS’)
HSS
IMS Data Handling

7. 7
Interrogating CSCF (I-CSCF) Functions
• Serves as the initial point of contact from other networks.
• Performs a stateless SIP proxy function.
• Selects a S-CSCF for a user during SIP registration.
• Routes SIP requests received from another network to the
S-CSCF.
• Queries the HSS for the address of the S-CSCF.
• If no S-CSCF is currently assigned (e.g., unregistered
subscriber), then assigns an S-CSCF to handle the SIP request.
• Provide Topology Hiding Interworking Gateway (THIG) function.

8. 8
3GPP IMS Architectural Overview:
Proxy CSCF (P-CSCF)
IMS-MGW
IPv6 PDN
(IPv6 Network)
MGCF
PDF
I-CSCF
S-CSCF
BGCF
Application
(Ext. SIP AS, OSA AS,
CAMEL SE)
MRFC
MRFP
MRF
IPv4/IPv6
BB
CS Networks
(PSTN, CS PLMN)
CSCF
P-CSCF
SGW
OSA SCS
IM SSF
SIP AS
AS
BG
SLF
ALG
TrGW
‘IMS IPGW
IPv4 PDN
(IPv4 Network)
IP CAN ABG
TE AN
IMS
Terminal
PEF
/TP
F
HLR/AuC (‘CS/PS’)
HSS
IMS Data Handling

9. 9
Proxy CSCF (P-CSCF) Functions
• Serves as the initial point of contact for the user terminal to
network.
• Performs a stateful SIP proxy function.
• Sends the SIP REGISTER request received from the UE to an
I-CSCF determined using the home domain name, as provided
by the UE.
• Sends all subsequent SIP messages from the UE to the S-
CSCF, whose name the P-CSCF has received as part of
registration.
• Inserts a valid public user identity for UE initiated requests.
• Performs SIP message compression to reduce the amount of
data sent over the radio interface.

10. 10
3GPP IMS Architectural Overview:
Policy Decision Function
IMS-MGW
IPv6 PDN
(IPv6 Network)
MGCF
PDF
I-CSCF
S-CSCF
BGCF
Application
(Ext. SIP AS, OSA AS,
CAMEL SE)
MRFC
MRFP
MRF
IPv4/IPv6
BB
CS Networks
(PSTN, CS PLMN)
CSCF
P-CSCF
SGW
OSA SCS
IM SSF
SIP AS
AS
BG
SLF
ALG
TrGW
‘IMS IPGW
IPv4 PDN
(IPv4 Network)
IP CAN ABG
TE AN
IMS
Terminal
PEF
/TP
F
HLR/AuC (‘CS/PS’)
HSS
IMS Data Handling

11. 11
Policy Decision Function (PDF) Functions
• Responsible for making policy decisions based on session and
media-related information obtained from the P-CSCF
• Acts as policy decision point for Service-based Local Policy
(SBLP) control.
• Some of policy decision point functionalities:
- To store session and media-related information
- The capability to enable the usage of an authorized bearer
(e.g. PDP context)
- To inform P-CSCF when the bearer is lost or modified.
- To pass an IMS-charging identifier to the GGSN and to Pass a
GPRS-charging identifier to the P-CSCF

12. 12
3GPP IMS Architectural Overview:
Home Subscriber Server/
Subscription Locator Function
IMS-MGW
IPv6 PDN
(IPv6 Network)
MGCF
PDF
I-CSCF
S-CSCF
BGCF
Application
(Ext. SIP AS, OSA AS,
CAMEL SE)
MRFC
MRFP
MRF
IPv4/IPv6
BB
CS Networks
(PSTN, CS PLMN)
CSCF
P-CSCF
SGW
OSA SCS
IM SSF
SIP AS
AS
BG
SLF
ALG
TrGW
‘IMS IPGW
IPv4 PDN
(IPv4 Network)
IP CAN ABG
TE AN
IMS
Terminal
PEF
/TP
F
HLR/AuC (‘CS/PS’)
HSS
IMS Data Handling

13. 13
Home Subscriber Server/
Subscription Locator Function
• SLF is used as resolution mechanism to find the
address of the HSS that holds the subscriber data
• The HSS supports IMS level Authentication, and
Authorization.
• Holds IMS subscriber profile.
• Keeps track of currently assigned S-CSCF.
• Supports interactions with CSCFs and ASs.

14. 14
3GPP IMS Architectural Overview:
Application Server (AS)
IMS-MGW
IPv6 PDN
(IPv6 Network)
MGCF
PDF
I-CSCF
S-CSCF
BGCF
Application
(Ext. SIP AS, OSA AS,
CAMEL SE)
MRFC
MRFP
MRF
IPv4/IPv6
BB
CS Networks
(PSTN, CS PLMN)
CSCF
P-CSCF
SGW
OSA SCS
IM SSF
SIP AS
AS
BG
SLF
ALG
TrGW
‘IMS IPGW
IPv4 PDN
(IPv4 Network)
IP CAN ABG
TE AN
IMS
Terminal
PEF
/TP
F
HLR/AuC (‘CS/PS’)
HSS
IMS Data Handling

15. 15
Application Server (AS)
• The AS provides service control for IMS.
• May be directly connected to S-CSCF or via an OSA
Gateway for 3rd party application support with
security.
• Interacts with the HSS to obtain subscriber profile
information.
• Supports applications such as telephony services,
presence, conference control, PoC, etc.

16. 16
Application Server Types
• Not pure IMS entities, rather, functions on top of IMS
• Application Servers:
- SIP Application Server
- Open Service Architecture (OSA) Service Capability
Server
(SCS)
- CAMEL IP Multimedia Service Switching Function
(IM-SSF)
• From the perspective of the S-CSCF, all application
servers exhibit the same reference point behavior

17. 17
3GPP IMS Architectural Overview:
Breakout Gateway Control Function (BGCF)
IMS-MGW
IPv6 PDN
(IPv6 Network)
MGCF
PDF
I-CSCF
S-CSCF
BGCF
Application
(Ext. SIP AS, OSA AS,
CAMEL SE)
MRFC
MRFP
MRF
IPv4/IPv6
BB
CS Networks
(PSTN, CS PLMN)
CSCF
P-CSCF
SGW
OSA SCS
IM SSF
SIP AS
AS
BG
SLF
ALG
TrGW
‘IMS IPGW
IPv4 PDN
(IPv4 Network)
IP CAN ABG
TE AN
IMS
Terminal
PEF
/TP
F
HLR/AuC (‘CS/PS’)
HSS
IMS Data Handling

18. 18
Breakout Gateway Control Function
(BGCF) Functions
• Selects the network in which PSTN breakout is to
occur.
• Selects a local MGCF or a peer BGCF.

19. 19
3GPP IMS Architectural Overview:
Media Gateway Control Function (MGCF)
IMS-MGW
IPv6 PDN
(IPv6 Network)
MGCF
PDF
I-CSCF
S-CSCF
BGCF
Application
(Ext. SIP AS, OSA AS,
CAMEL SE)
MRFC
MRFP
MRF
IPv4/IPv6
BB
CS Networks
(PSTN, CS PLMN)
CSCF
P-CSCF
SGW
OSA SCS
IM SSF
SIP AS
AS
BG
SLF
ALG
TrGW
‘IMS IPGW
IPv4 PDN
(IPv4 Network)
IP CAN ABG
TE AN
IMS
Terminal
PEF
/TP
F
HLR/AuC (‘CS/PS’)
HSS
IMS Data Handling

20. 20
Media Gateway Control Function (MGCF)
• Controls the MGW to provide IMS connections to
PSTN trunks.
• Performs protocol conversion between ISUP and SIP.
• May process out of band information such as DTMF
signaling received in MGCF which it may forward to
the CSCF or MGW.

21. 21
3GPP IMS Architectural Overview:
Media Gateway (MGW)
IMS-MGW
IPv6 PDN
(IPv6 Network)
MGCF
PDF
I-CSCF
S-CSCF
BGCF
Application
(Ext. SIP AS, OSA AS,
CAMEL SE)
MRFC
MRFP
MRF
IPv4/IPv6
BB
CS Networks
(PSTN, CS PLMN)
CSCF
P-CSCF
SGW
OSA SCS
IM SSF
SIP AS
AS
BG
SLF
ALG
TrGW
‘IMS IPGW
IPv4 PDN
(IPv4 Network)
IP CAN ABG
TE AN
IMS
Terminal
PEF
/TP
F
HLR/AuC (‘CS/PS’)
HSS
IMS Data Handling

22. 22
Media Gateway (MGW) Functions
• Interacts with the MGCF for resource control.
• Terminates trunks from the circuit switched network and media
streams from the packet network (e.g. RTP streams).
• Supports media conversion, bearer control, and payload
processing
• May detect events (i.e. bearer loss, DTMF digits, etc.) and
notifies the MGCF.
• May perform DiffServ Code Point (DSCP) markings on the IP
packets sent towards the UE.

23. 23
3GPP IMS Architectural Overview:
Media Resource Function Controller (MRFC)
IMS-MGW
IPv6 PDN
(IPv6 Network)
MGCF
PDF
I-CSCF
S-CSCF
BGCF
Application
(Ext. SIP AS, OSA AS,
CAMEL SE)
MRFC
MRFP
MRF
IPv4/IPv6
BB
CS Networks
(PSTN, CS PLMN)
CSCF
P-CSCF
SGW
OSA SCS
IM SSF
SIP AS
AS
BG
SLF
ALG
TrGW
‘IMS IPGW
IPv4 PDN
(IPv4 Network)
IP CAN ABG
TE AN
IMS
Terminal
PEF
/TP
F
HLR/AuC (‘CS/PS’)
HSS
IMS Data Handling

24. 24
Media Resource Function Controller
(MRFC) Functions
• Controls the media stream resources in the MRFP.
• Interprets information from an AS via the S-CSCF
(using SIP) and controls the MRFP accordingly.
• May be co-located with an AS to provide capabilities
such as conference services.

25. 25
3GPP IMS Architectural Overview:
Media Resource Function Processor (MRFP)
IMS-MGW
IPv6 PDN
(IPv6 Network)
MGCF
PDF
I-CSCF
S-CSCF
BGCF
Application
(Ext. SIP AS, OSA AS,
CAMEL SE)
MRFC
MRFP
MRF
IPv4/IPv6
BB
CS Networks
(PSTN, CS PLMN)
CSCF
P-CSCF
SGW
OSA SCS
IM SSF
SIP AS
AS
BG
SLF
ALG
TrGW
‘IMS IPGW
IPv4 PDN
(IPv4 Network)
IP CAN ABG
TE AN
IMS
Terminal
PEF
/TP
F
HLR/AuC (‘CS/PS’)
HSS
IMS Data Handling

26. 26
Media Resource Function Processor
(MRFP) Functions
• Under the control of MRFC
• Mixes incoming media streams (e.g. for multiple
parties).
• Sources media streams (for multimedia
announcements).
• Processes media streams (e.g. audio transcoding).
• Provide tones and supports DTMF within the bearer
path.
• Notifies the MRFC when an event has occurred such
as DTMF digit collection.

27. 27
3GPP IMS Architectural Overview:
Signaling Gateway
IMS-MGW
IPv6 PDN
(IPv6 Network)
MGCF
PDF
I-CSCF
S-CSCF
BGCF
Application
(Ext. SIP AS, OSA AS,
CAMEL SE)
MRFC
MRFP
MRF
IPv4/IPv6
BB
CS Networks
(PSTN, CS PLMN)
CSCF
P-CSCF
SGW
OSA SCS
IM SSF
SIP AS
AS
BG
SLF
ALG
TrGW
‘IMS IPGW
IPv4 PDN
(IPv4 Network)
IP CAN ABG
TE AN
IMS
Terminal
PEF
/TP
F
HLR/AuC (‘CS/PS’)
HSS
IMS Data Handling

28. 28
Signaling Gateway
• Used to interconnect different signaling networks,
such as SCTP-IP-based signaling networks and SS7
signaling networks.
• Performs signaling conversion at the transport level.
• Does not interpret application layer messages.

29. 29
Two Procedures
• Registration
• Simple Call

30. 30
2-phase registration
UE IMS
GPRS
1. Bearer Level Registration: e.g.GPRS Attach
(2. Establishing signaling link e.g. PDP Context Activation)
3. CSCF Discovery
4. Application (IMS) Level Registration
From [2]

31. 31
SIP Registration of a Mobile Node
From [3]

32. 32
Simple SIP Call: Caller Side (1)
From [3]

33. 33
Simple SIP Call: Caller Side (2)
From [3]

34. 34
References
• [1] “The IMS”
M Poikselka et al. , 2004, John Wiley, ISBN 0-470-87113-X
• [2] “Policy and Regulatory Requirements for Future Mobile
Networks”
F. Courau & M. Olsson, June 22nd 2005,
Alcatel-Ericsson Presentation
• [3] “SIP and Mobility: IP Multimedia Subsystem in 3G Release 5”
Jorg Ott, 11 November 2002, Presentation at Bremen
• [4] “IMS –IP Multimedia Subsystem”
Oct 2004, Ericsson Whitepaper
• [5] “The IP Multimedia Subsystem”
2006, Twister Consulting whitepaper

35. 35
E
N
D
Thank you for your attention …