1. 3GPP2 IMS Charging Infrastructure
Presented for 3GPP2 TSG-X
by Nick Mazzarella
of Lucent Technologies
September 25, 2004

2. 3GPP2 IMS Charging Infrastructure
Contents
Scope
3GPP2 Organization
3GPP2 IP Networking Model
Current Rev 0 Charging Structure
Architecture
Charging Functions and Correlations
Basic Flows
Evolution from Rev 0 to Rev A Charging
Adding On-Line Charging
New Charging Functions
Possible Additional Enhancements
Harmonization between 3GPP and 3GPP2
Abbreviations and References

3. 3GPP2 IMS Charging Infrastructure
Charging functions exist in several areas within TSG-X
CSN Work Group – Circuit Domain Charging
PDS Subworking Group – Packet Data Subsystem Charging
MMD Subworking Group - IMS Charging
This Presentation will focus on Charging in IMS

4. 3GPP2 IMS Charging Infrastructure
Scope
Provide architecture and flows for charging for IMS services.
Objectives
Define principles of charging in an IMS network
Provide a description of the charging architecture
Provide the descriptions of events and triggers for the next generation of charging data.
Provide charging message flows along with charging data triggers, message content and format along with the transport of these messages using the Diameter protocol.

5. 3GPP2 IMS Charging Infrastructure
3GPP2 Organizational Context OP SC
TSG-X
TSG-S
TSG-C
TSG-A
CSN
PSN
CHARGING
PDS
IMS
BAN
MMS
MMD
MMD Work Activities
Others

6. 3GPP2 IP Networking Model
All IP Network Architecture Model (NAM)
Data Bases
OSA-AS
SIP-AS
OSA-SCS
Location
Services
AAA
Charging
PSTN
CSCF
MGCF
PDF
PDS
MGW
Radio
Access
IP Network
Access
Gateway
MRCF
IMS
MRFP

7. Current Rev 0 Charging Structure
Basic Architecture
Home(A)
Home(B) BS BS AS AS AS AS
MRFC
MRFC
MRFC
MRFC Rf Rf
AAA S S - -
CSCF
CSCF S S - -
CSCF
CSCF
AAA I - I -
CSCF
CSCF I I - -
CSCF
CSCF P P - -
CSCF
CSCF P P - -
CSCF
CSCF
BGCF
BGCF
BGCF
BGCF
PDSN
MGCF
MGCF
PDSN
BGCF
1. Off-line IMS Charging architecture for non-roaming scenario

8. Current Rev 0 Charging Structure
Basic Architecture
Home(A)
Home(B) BS AS BS AS AS AS
MRFC
MRFC
MRFC
MRFC Rf
AAA Rf S S - -
CSCF
CSCF S S - -
CSCF
CSCF
AAA I I - -
CSCF
CSCF I I - -
CSCF C
SCF P P - -
CSCF
CSCF P P - -
CSCF
CSCF
BGCF
BGCF
BGCF
BGCF
MGCF
MGCF
Visited(A)
Visited(B) Rf
AAA P P - Rf -
CSCF
CSCF P P - -
CSCF
CSCF
AAA BS BS
PDSN
PDSN
2. Off-line IMS Charging architecture for roaming scenario

9. Current Rev 0 Charging Structure
Charging Functions-
AAA
AAA provides the mechanism to transfer charging (i.e. Accounting) information from the IMS nodes to the network operator's chosen Billing System(s) *Does not define actual end user billing records.
Main functions:
The collection of Session charging information from the IMS node
Intermediate data storage buffering
The transfer of the charging data to the off-line billing systems

10. Current Rev 0 Charging Structure
Correlation between network elements
For a session comprising several media components (such as audio and video), charging data is generated for each media component and needs to be correlated between network elements.
Correlation within a session
The IMS Charging ID may be used to correlate the charging data between network elements.

11. Current Rev 0 Charging Structure
Charging Correlation Capabilities To support the correlation of charging information, the following capabilities apply:
The correlation of charging information for an IMS session is based on the use of IMS Charging Identifiers (ICIDs).
The first IMS network entity within the SIP signalling path is responsible for assigning an ICID.
The ICID is passed to all IMS core network entities in the SIP signalling path. This is performed using SIP signalling.

12. Current Rev 0 Charging Structure
Supported Off-line Interface Types
Rf Offline (Post Paid) Charging Reference Point between an IMS Network Entity and a AAA Rf
IMS nodes (S-CSCF, P-CSCF, I-CSCF, BGCF and MGCF) apply offline charging via the Rf interface using the AAA address as received via SIP signaling or the locally configured AAA address.

13. Current Rev 0 Charging Structure
Basic Off-Line Charging Message Flows
Visited Network
Home Network UE P -
CSCF
AAA S -
CSCF
AAA
(visited)
(home)
1. INVITE
1. INVITE
Service Control
1. INVITE
More SIP signalling
OK (Invite)
Service Control
OK (Invite) OK
3. Accounting Request [Start]
(Invite)
5. Accounting Request [Start]
Open a P -
CSCF AIR
Open a S -
CSCF AIR
6. Accounting Answer
4. Accounting Answer
More SIP signalling
SIP Session established
1. Message Sequence Chart for Session Establishment (Mobile Origination)

14. Current Rev 0 Charging Structure
Basic Off-Line Charging Message Flows-
Visited Network
Home Network UE P -
CSCF
AAA S - C
SCF
AAA I -
CSCF
(visited)
(home)
1. INVITE
Cx Query
with the HSS
1. INVITE
2. Accounting Request [Event]
Open I -
CSCF AIR
3. Accounting Answer
Service Control
1. INVITE
1. INVITE
More SIP signalling OK OK
5. Accounting Request [Start] OK
7. Accounting Request [Start] OK
Open P -
CSCF AIR
Open S -
CSCF AIR
6. Accounting Answer
8. Accounting Answer
More SIP signalling
SIP Session established
2. Message Sequence Chart for Session Establishment (Mobile Termination)

15. Current Rev 0 Charging Structure
Basic Off-Line Charging Message Flows-
Visited Network
Home Network UE P -
CSCF
AAA
(visited) S -
CSCF
AAA
(home)
1. BYE
1. BYE
Service Control
2. Accounting Request [Stop]
1. BYE
Close the P -
CSC
F AIR
4. Accounting Request [Stop]
3. Accounting Answer
Close the S -
CSCF AIR
5. Accounting Answer OK OK OK
3. Message Sequence Chart for Session Release – Mobile Initiated

16. Evolution to Rev A Charging
Revision A Charging will provide standardized functionality for On-line Charging.
On-line Charging Architecture has already been defined in 3GPP2 documentation
New on-line charging stage 3 flows will have to be developed
3GPP2 intends to maintain harmonization with 3GPP Release 6 Charging functionality.
Where applicable, 3GPP2 will adapt some IMS charging functionality from 3GPP

17. Evolution to Rev A Charging
* In 3GPP Rel 5 and 6, a Gateway has been added with an Ro interface. 3GPP2 may consider this as a revision to Rev 0 Architecture.
On-line IMS Charging architecture

18. Evolution to Rev A Charging
Added Functions for On-line Charging
Session Charging Function (SCF)
Responsible for Session Charging including the session control such as e.g. session termination.
Bearer Charging Function (BCF)
The Bearer Charging Function performs the Bearer Charging
Event Charging Function (ECF)
The Event Charging Function (ECF) performs event-based charging (content charging). It makes use of the rating function in order to determine the value of the services rendered. The ECF may correlate several event-based charging requests.

19. Evolution to Rev A Charging
Added Functions for On-line Charging
Subscriber Content Charging Function (SCCF)
The SCCF is always located in the same operator network as the account of the subscriber, and handles content charging requests that are made when the subscriber accesses the content.
Content Provider Charging Function (CPCF)
The CPCF manages the account that is maintained for the content provider. Upon receipt of a charging request from the AS/MRFC, the CPCF processes the request and relays it to the SCCF.

20. Evolution to Rev A Charging
Additional Enhancements
3GPP2 TSG-X MMD will evaluate additional charging functions and decide which to include.
Adoption of consistent terminology between PP/PP2. e.g. CDRs
Discussion Point: In 3GPP the term CDR stands for Charging Data Record. In U.S. legacy systems the acronym stands for Call Detail Records. To eliminate confusion, 3GPP2 chose the term Accounting Information Record-AIR in place of CDR for charging use.

21. Evolution to Rev A Charging
Harmonization
3GPP TS V5.5.0
Current 3GPP Rel. 5 to 3GPP2 Rev. 0 Correlation
3GPP2 X.P
3GPP Ts V5.5.0
3GPP2 X.P
Harmonization
3GPP TS V6.0
3GPP2 X.P A
Possible Correlation for
3GPP Rel. 6 to 3GPP2 Rev. A *
3GPP TS V6.0
3GPP2 X.P A
3GPP TS V6.0
3GPP2 X.P A
*Currently under study in TSG-X MMD Group
Harmonization between 3GPP and 3GPP2

22. Symbols and Abbreviations
AAA Authentication, Authorization, and Accounting
ACA Accounting-Answer
ACR Accounting-Request
AIR Accounting Information Record
AS Application Server
AVP Attribute Value Pair
BCF Billing Control Function
BS Billing System
CDR Charging Data Record
CPCF Content Provider Charging Function
CSCF Call Session Control Function
(I-Interrogating; P-Proxy; and S-Serving)
ECF Event Charging Function
IAM Initial Address Message
ICN IP Connectivity Network
IEC Immediate Event Charging
IMS IP Multimedia Subsystem
ISC IMS Service Control
MGCF Media Gateway Control Function
MMD Multimedia Domain
MRFC Media Resource Function Controller
MRFP Multimedia Resource Function Processor
OCS Online Charging System
PDSN Packet Data Serving Node
REL Release Message
SCCF Subscriber Content Charging Function
SDP Session Description Protocol
SIP Session Initiation Protocol
UE User Equipment

23. References
3GPP2 X.S v1.0 IP Multimedia Subsystem - Charging Architecture
3GPP2 X.S v1.0 IP Multimedia Subsystem - Accounting Information Flows and Protocol