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IP Multimedia Sub-system (IMS) Service Architecture

The Dynamics of IMS Mediation, Charging and Billing

This white paper presents an overview of the IP Multimedia Sub-system (IMS) billing,

mediation and charging architecture, describes billing standards affecting an IMS

architecture, and explains how mediation, charging and billing work in IMS.

S T R A T E G I C W H I T E P A P E R

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Table of Contents

1 Are You Ready for IMS Billing?

2 Whats Different about IMS Mediation?

2 The New 3GPP CDR Standard

3 Correlation and Aggregation

3 IMS Mediation Occurs at Several Levels

3 IMS Core Level Mediation

3 IMS Charging Level Mediation

3 Pre-Billing IMS Mediation:

4 Legacy Billing Mediation

4 What Is Charging in IMS?

4 Multimedia Content Clearing and Reconciliation

4 On-Line Charging vs. Off-Line Charging

5 Conclusion

6 Acronyms

6 About the Author

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1Alcatel-Lucent | IP Multimedia Sub-system (IMS) Service Architecture

Are You Ready for IMS Billing?

With the IP Multimedia Sub-system (IMS) revolution well underway, carriers are racing to gainthe competitive advantage and operational optimization promised from the convergence archi-tecture of an IMS business support systems (BSS). This IMS-enabled strategic advantage is theability to quickly deliver bundled and blended services which will attract and retain moresubscribers looking for service personalization, quality, and value seamlessly and independently

across networks.

Believed to be the telecommunications industrys most far-reaching BSS impacting technology, IMSradically changes the paradigm of how subscriber usage is collected, managed, rated and billed.By bringing services and functions together from disparate network technologies and elements,IMS facilitates the optimization of real-time seamless interactions between services and functions.

In order to prepare for a migration to IMS, carriers with wireline and wireless networks willneed to assess and understand the distinct and significant differences in mediation and billingfor IMS from their legacy BSS infrastructure as well as the critical role played by online real-time charging and rating in this new IMS convergence paradigm.

The simple fact is that IMS exponentially complicates the challenges of mediation and billing,however if approached correctly promises optimal convergence of service delivery, billing andcontrol over subscriber content and network access and usage. This increased complexity extendsto the inherent authorizing; provisioning, charging and billing that must be managed accuratelyin real-time, in addition to the brokering, settlement and reconciliation of services and third-party multimedia content.

Carriers are anticipated to need to ensure that the new mix of blended services are processedproperly and result in the generation of accurate, timely, and verifiable billing transactions.

Figure 1. IMS architecture

Non-SIP IM, PTT, VoIP

CAMEL, ANSI-41INAP, TCAP Parlay API

SIP

SIP-ISC

IM, PTT, VoIP

Transport andEndpoint Layer

VoIP

APX

MAX TNT

PSTN

LMRS

LSS

SDHLR PacketIN SGLSS

SessionControlLayer

ApplicationServerLayer

CSCF

SignalingGateway

Products

Non-TelephonyServices

OSA-GW

ApplicationServers

TelephonyServices (TAS)

IM-SSFSupplemental

TelephonyServices

DSL,802.11,GPRS

HSS

Legacy SCPs

MediaServer

MRFC

MediaGateway

MGCF

Partners

Partners

PacketIN AHEAnypath

EBSSurePay

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2 Alcatel-Lucent | IP Multimedia Sub-system (IMS) Service Architecture

Whats Different about IMS Mediation?

IMS is all about the ultimate convergence of OSS & BSS and from the mediation perspectiveis a major shift from the current mediation model which is based on the sequential collectionof usage representing minutes of use, source, destination, jurisdiction, and sometimes mileageconsiderations. These rigid legacy descriptions of billing parameters are sufficient for traditionalvoice-centric services but do not adequately address the more advanced data and blended

services and may actually inhibit effective convergent billing.

With new blended services delivered across multiple networks using different protocols, carriersare being driven to move to convergent BSS and billing, which ensures that all usage chargesrelated to different types of services or events offered as blended or stand alone services aregathered, correlated and processed into one bill. IMS mediation and billing will require combiningwireline and wireless local and long distance services together with advanced next generationdata-centric services and applications based on SMS, or IM messaging, music downloads, videoclips, streaming or live peer to peer video, digital pictures, stock quotes, traffic alerts, ring tones, andlocation-based services. This convergence of any telecom service from any network or deviceat the billing level is only possible through an effective and accurate mediation architecture.

The New 3GPP CDR Standard

In the IMS architecture the mediation function has taken on a more dynamic and businesscritical role than the legacy collect, store and forward model. The IMS mediation function ismore decentralized with customized collection elements pulling usage directly from multiplenetwork elements concurrently and in real-time, as well as bi-directional to facilitate instantcontrol of subscriber session access and usage. A converged network environment can requirebilling information to be collected from many different network elements and devices thendelivered via several diverse methods, such as CSV, FTP, XMS, flat text files, JMS, Diameter,and RADIUS. Delivering services across these converged next generation networks hasincreased the necessity to track call events & sessions as data is exchanged not only between

users but also between various service providers.

This new paradigm has vastly increased the complexity in ensuring that all billable transactionsare captured and processed accurately and that all earned revenues are billed and collected.Traditionally, voice and data services have been designed to measure usage generated by aspecific network system that would create a single CDR record representing a complete andbillable call transaction. With the IMS architecture, services can be concurrent and multidimen-sional, with service logic distributed across disparate network elements.

The 3GPP Standards organization has developed a complete set of standards specifications witha major focus on mediation, charging and billing of IMS usage and events. These new standardsenable common interfaces between applications, network layers and back office systems. TheIMS CDR format standardized by the 3GPP organization is known as the ASN.1 format.

Thanks to the IMS CDR standard, billing and OSS vendors can simplify the required interactionbetween network elements on any mobile, fixed or WLAN network. The IMS ASN.1 BERformatted CDR may be intermixed with BAF AMA records generated from legacy PSTN networkelements creating an additional potential requirement to aggregate or correlate this usage datawith the ASN.1 BER CDR data representing usage from the IP side of the network. So thereare two basic types of CDRs the legacy BAF AMA CDR record and the new 3GPP IMS standardASN.1 BER format CDR records.

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The 3GPP ASN.1 BER encoded CDR is designed to provide maximum flexibility to accommodatethe wide range and variety of billing data while at the same time providing optimal utilizationof the CDR payload. ASN.1 BER CDR records and the fields they contain are variable in type,make up, and size. Furthermore, the ASN.1 BER CDRs are loaded into a CDR file for transportto the Billing mediation system, and this file is also variable in size.

Correlation and AggregationThe major challenge in mediating usage accounting data from IMS is the requirement to cor-relate and aggregate the usage data into complete billable CDRs, which accurately reflect theactual subscriber transaction. The IMS mediation function will receive or collect usage accountingrecords such as the calling party, terminating party, interconnecting carrier, call connect, callon hold, or call transfer, and call disconnect known as event messages generated by disparatenetwork elements. Call information that previously was presented to a mediation function in asingle CDR is now being delivered in a series of multiple sequential and concurrent event messages.

This major deviation from the traditional subscriber network access and usage where the subscribercan now access and generate usage across multiple networks independent of access method, or

device has resulted in a critical need to accurately correlate data from various sources for each callor data session. This correlation is made possible through the 3GPP standard providing correlationidentifier tags which uniquely identify the event message, its network element source andoriginator which enable the association of multiple events from many network nodes to formthe CDR of a single billable call or session.

With the IMS architecture, the new IMS mediation function must aggregate and correlate billingdata from different sources for each call or session. To facilitate this complex structure theaccounting messaging from each network element includes correlation identifiers to link theseparate parts of a single call. These correlation IDs, as they are called, ensure network andsession uniqueness, so that other elements are not able to use or generate the same correlationID for distinct sessions or calls.

IMS Mediation Occurs at Several Levels

IMS Core Level MediationThe first level or point of mediation in IMS is in the core IMS where subscriber usage is collectedfrom the switching and server elements by various IMS functions such as the P-CSCF, the I-CSCFor the S-CSCF which generate radius diameter accounting messages triggered by subscribercall or session activity.

IMS Charging Level MediationThe second level of mediation in the IMS architecture is at the charging layer which aggregates

usage from the IMS core level element. This charging level consists of IMS elements known asthe Charging Gateway Function (CGF) and or at the Charging and Collection Function (CCF)level which collect, and consolidate billing accounting message records sent from the P-CSCF,the I-CSCF or the S-CSCF. The CDF or CCF functions perform an important mediation conver-sion process, generating ASN.1 BER formatted CDRs from the diameter accounting records.

Pre-Billing IMS Mediation:As most commercial telecom billing mediation systems today are designed to process BAF AMAformatted CDRs there is a third level of mediation required for the implementation of an IMSsystem. This third level of IMS Mediation sits between the CGF and CCF level of IMS andthe service providers Billing Mediation system. This third level of mediation provides a CDR

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conversion function taking the 3GPP ASN.1 BER format CDRs from IMS and converting theminto BAF AMA formatted CDR records. It is at this level of mediation that additional aggrega-tion or correlation may be performed to associate ASN.1 BER CDRs with AMA CDRs collectedfrom PSTN network devices to represent a total call session CDR for billing to the subscriber.

Legacy Billing MediationThe final level of mediation is the service providers legacy billing system mediation function.

The billing systems mediation software typically either pulls or receives pushed BAF AMAformat (or some other standard CDR format) CDR files containing CDRs which represent uniqueand separate billable events, calls, sessions or content. This billing mediation provides basicvalidation and error checking services, as well as reformatting of the CDR record into a formatrequired by the specific billing system software for subsequent off-line rating and billing.

What Is Charging in IMS?

With the advent of the IMS architecture, real-time charging has evolved well beyond its originalfunction in the prepaid world into a mission critical revenue assurance, usage rating charging andcredit control tool. Real-time charging is the core function supporting the IMS SDP (Service

Delivery Platform) enabling carriers to have total control over subscriber calls, sessions, andevents by providing the IN (Intelligent Network) SCP (Service Control Point) function withreal-time status of a subscribers available account balance in session to mitigate revenue leakageor from the credit control perspective to minimize uncollectible receivables leading to revenueleakage and subscriber churn.

Multimedia Content Clearing and ReconciliationThe competitive pressure to deliver ever more complex and resource intensive multimediamessaging content and services has driven the necessity for this ability for service providers tohave more real-time control over subscribers access to services and content based on their accountbalance or ability to pay. To further add to the increased complexity of this multidimensionalservice delivery system is the need to keep accurate and timely tabs on the consumption of

multimedia content provided by third parties.

IMS charging will give the service provider the tools to monitor and manage, in real-time, thesethird-party content transactions to either collect and book revenue as they are purchased by thesubscriber or to limit or restrict access to purchases of content or services from credit challengedsubscribers. Additional reconciliation and settlement for services and content used by yoursubscriber will follow mediation and charging and be necessary in a real-time model enablingcarriers to settle and clear charges not only to subscribers but from third-party content providers.

On-Line Charging vs. Off-Line ChargingOnline charging, also known as credit-based charging, is the function with the charging layer

found in the CCF (charging and collection function) which provides the mechanism calls,sessions or content can be rated and charged against a subscribers account balance in real-time.Online charging is the result of the evolution of the prepaid billing model which has recentlymoved into the network edge as a function of the IN Service Control Point. This real-timemonitoring and metering of usage gives the service provider the control over the session inreal-time due to the direct interaction between the charging mechanism and the session/servicecontrol which can either shut down a session, restrict or limit access, de-provision a feature orservice or trigger the suspension or a subscribers account and or service.

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Off-line charging can be thought of as legacy traditional batch rating and billing of networkbillable events presented to the billing system through mediation as unrated CDRs. A typicalIMS deployment will have a mixed charging architecture depending on the services and contentsupported as well as the bundling or blending of these services which drives the charging model.This ability to offer hybrid post -paid/prepaid plans offering maximum charging flexibilityprovides the carrier as well as the subscriber more control over their telecom revenue andexpenses respectively.

With IMS a subscriber may have both on-line and off-line charging apply to the same sessionwhere the access and usage is off-line or post-paid, and the downloads of music or ring tones ischarged in real time online.

Another important feature of this new billing capability is the convergence of rating for bothpre and post-paid services. Many carriers choose to optimize or centralize their rating by havingthe CCF function perform rating for not only on-line charging but for all off-line charging aswell. With this approach, the rated CDRs mediated to the carriers billing system enable afaster billing cycle process, as the rating of individual calls or event has already been applied.

ConclusionUntil recently, mediating and billing for voice and data services has been a relatively straightforwardprocess but recently has evolved from a store and forward batch process to a dynamic convergenceof real-time charging and control of subscriber access and usage. IMS, being at the heart of thewireless wire-line convergence, has presented service providers with new complex challengesto retrofit and implement IMS into existing BSS infrastructures with minimal cost and impact.

Service providers are now in a position to roll out faster than ever more customized, personalized,bundled and blended services based on the IMS architecture. IMS inherently provides theblending and convergence not only of services and billing, but also of the control mechanismswhich are critical to achieving revenue targets, margins, and market share while reducing churn,

revenue leakage and operational expenditures. In the new IMS, mediation is blended withprovisioning, AAA, service control, and rating in the form of real-time charging.

Service providers will not only need to understand how to effectively leverage an IMS infra-structure, but will need to carefully approach the implementation approach to leverage andextend the lifecycle of their current BSS infrastructure. IMS is the ultimate service creation,delivery and control platform which carriers and service providers will rely on to gain andmaintain a competitive advantage in an ever convoluted market of multi-network competitors.The ultimate measure of success will be their ability to mediate, charge and bill for theseexciting new offerings.

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Acronyms

AAA Authentication, Authorization and Accounting

AMA Automatic Message Accounting

ASN.1 Abstract Syntax Notation One

BAF Bellcore AMA Format

BER Basic Encoding Rules

BSS Business Support Systems

CDR Call Detail Record

CCF Charge and Control Function

FTP File Transfer Protocol

IM Instant Messaging

IMS IP Multimedia Subsystem

IN Intelligent Network

I-CSCF Interrogating- Call Session Control Function

JMS Java Messaging Service

P-CSCF Proxy-Call Session Control Function

S-CSCF Serving-Call Session Control Function

SDP Service Delivery PlatformSCP Service Control Point

SMS Short Messaging System

WLAN Wireless Local Area Network

XML Extended Markup Language

3GPP Third Generation Partnership Project

About the Author

Bob HallahanS E N I O R C O N S U L TA N T

A L C A T E L - L U C E N T S E R V I C E S

B S S S Y S T E M S I N T E G R A T I O N A N D P R O F E S S I O N A L S E R V I C E S

Bob Hallahan has over 25 years experience in the telecommunications industry architecting,developing, and deploying billing and BSS solutions for service providers and solution vendorson a global basis. As Alcatel-Lucents IMS billing SME, he has contributed to several industryconferences and research studies. Mr. Hallahan holds a Bachelors degree in ManagementInformation Systems, as well as an MBA degree.

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www.alcatel-lucent.comAlcatel, Lucent, Alcatel-Lucent and Alcatel-Lucent logo are trademarks of Alcatel-Lucent. All othertrademarks are the property of their respective owners. The information presented is subject tochange without notice. Alcatel-Lucent assumes no responsibility for inaccuracies contained herein. 2007 Alcatel-Lucent. All rights reserved. 23142 (07)

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