Huawei Technologies

2005.10 8

LEADING EDGE

APR 2008 . ISSUE 40

faces fresh challenges

he next-generation broadband mobile network has greatly enriched mobile data services and accelerated its integration with the Internet. While mobile operators are providing richer and more diversified

services, mobile charging support system has been confronted with a range of new challenges.

By Gao Lei & Li Chun

47

LEADING EDGEMobile charging support system faces fresh challenges

T

Mobile charging support system

APR 2008 . ISSUE 40

Huawei Technologies

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Charging & billing for LTE/SAE network architecture

Mobile networks have adopted many technologies during their development inc luding GSM, GPRS/EDGE and WCDMA/HSDPA. Moreover, long-term evolution (LTE) will make its debut before long on the global technical stage. The inception of LTE/SAE (system architecture evolution) network architecture will transform the charging architecture as follows:

Firstly, the LTE network environment illustrated in Fig. 1 requires that operators deploy a network entity to detect and acquire service traffic information, and implement charging control by interacting with the online/offline charging system.

Secondly, LTE/SAE architecture supports access for LTE and 2.5G/3G networks, and also for non 3GPP access mode radio systems such as WLAN and WiMAX. LTE/SAE architecture should enable user terminals’ network handover processes that are supported by the charging system.

The 3GPP SAE adopts packet data network gateway (PDN-GW) between the SAE core network and the PDN, which acts as a data control gateway under different access modes. As a core network central control node, the PDN-GW is similar to the GPRS network’s GGSN in that it can detect service data flows and implement traffic collection. The mechanism is connected with the online/offline charging system through the Ro/Rf interface.

The PDN-GW forms the anchor for various access modes. It controls connections, disconnections and all access mode switching. Unified service flow detection and traffic collection through PDN-GW form the optimum charging solution when LTE/SAE architecture is adopted. Online charging should prompt its corresponding system to manage charging session handover and the tariff changes that are triggered by mobile access mode switching.

FBC and QoS differentiated charging

Next-generation broadband network development towards ALL IP brings quality of service (QoS) challenges as all services, including voice, run on the IP network. Users’ requirements differ significantly to the extent that QoS demands can vary greatly for one service. Thus different service level agreements (SLAs) and charging modes can respond to individual requirements, rendering QoS a necessary element for each charging layer.

Every QoS change demands that the charging and billing system selects a corresponding charging mode that ensures a timely, dynamic and precise charging process. Operators are eager to gain the ability to perceive various services, in order to maintain value chain dominance. Content perception and deep packet detection technologies stimulate service flow and content identification, and sufficient flexibility in all charging modes should fulfill each service provider’s varied requirements.

The 3GPP R6 flow-based charging (FBC) system underpins 3GPP R7 policy and charging control (PCC) specifications relating to PCC system architecture. Its purpose is to implement controls under service data flow levels for access, QoS and charging. 3GPP R7 integrates 3GPP R6 service-based local policy (SBLP), FBC and related interface functions. These are positioned within the newly established and unified PCC architecture, the logical structure of which is exhibited in Fig. 2.

Fig. 1 The charging architecture after LTE/SAE network architecture inception

RNCUTRAN

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3G Access

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LTE Access Network

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None-3GPP Systems

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Application function (AF) describes a f u n c t i o n a l e n t i t y t h a t p rov i d e s applications. These implement appropriate policy and/or charging controls on the user plane in order to provide dynamic application session information to the policy and charging rules function (PCRF).

PCRF includes the policy control decision and FBC functions. It implements service f low-based detection, access control, QoS authorization, and flow-based charging on the policy and charging execution function (PCEF). The PCRF checks whether AF service information is consistent with an operator’s pre-defined policy and with the user subscription information derived from the subscription profile repository (SPR). The PCRF then generates rules according to this information and sends them to the PCEF. The PCRF should also offer QoS authorization for AF service information.

PCEF enables policy execution and FBC functions, and is located in PDN-GW. It is located in a GPRS network’s GGSN and in a WLAN’s package data gateway (PDG). The PCEF controls user plane traffic and QoS, detects and measures service data flows, and interacts with the online/offline charging system. It executes QoS and access control for service data flows according to PCC rules, and reports related service data flow changes to the PCRF.

There are two types of PCC rules: dynamic and pre-defined. Dynamic

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Fig. 2 The logical structure of the PCC

rules are provided by the PCRF to the PCEF through the Gx reference point. Pre-defined rules are directly configured by the operator in the PCEF, and can only be reached by the PCRF. During dynamic configuration, the AF establishes an application session with the PCRF to facilitate a dynamic charging policy. This is issued to the PCEF by the PCRF for execution through DIAMETER.

In 3GPP R6, SBLP and FBC are implemented under different processes that obviate control information interaction. PCC architecture enables both policy and charging during the same process, and enhances its real-time capability.

By coup l ing po l i c y con t ro l and charging operation in the same process, both the number of signals transmitted and time delay within the system are greatly reduced. The interaction of PCC information provides operators with powerful charging measures according to QoS and policy controls.

Multi-service charging correlation

The next-generation broadband mobile network has greatly enriched mobile data services and accelerated its integration with the Internet. This trend requires the charging system to correlate charging information of content layer, service layer

and bearer layer when one service is in use. The charging system can thus flexibly configure charging policies and guarantee precise charges.

Charging correlation comprises two parts. Firstly, when a subscriber uses data services, the charging system receives charging information through the charging interfaces of multiple entities that exist within a hierarchical network. Secondly, the charging system correlates bottom layer data flows with content charging identifiers and service data features of the application and subsystem layer. Consequently, it determines how bottom layer data flows and upper layer services or content applications correspond with each other. Charging correlation shows resource consumption characteristics for one service in different network layers. It allows the accounting system to generate “one-stop” records and helps users to fully understand service usage expenses.

The 3GPP de f ine s the cha rg ing correlation method between the bearer and subsystem layers. This is achieved by exchanging the IMS network’s IMS charging identifier (ICID), the bearer network’s GPRS charging identif ier (GCID), or the charging ident i f ier FlowNumber (when FBC is enabled). The FlowNumber identifies service data flows in the resource reservation and negotiation process. Subsystem and bearer layer NEs write ICID and GCID (or FlowNumber) onto charging data record (CDR) before

sending them to the charging system. The charging system then processes the charging information correlation in line with ICID and GCID (or FlowNumber) correlation.

As data services increase, some prepaid subscribers, or the subscribers who need real-time charging control, require real-time charging correlation. These subscribers are no longer satisfied with the offline charging correlation through which post-service charging is implemented, and instead expect online charging correlation. As such, consideration must be given to online charging interfaces and the charging session process. Compared with offline charging, the online charging system (OCS) generates, allocates and transfers charging correlation identifiers in different ways.

Online charging correlation is not yet mature and further development and standardization are required. In the future, online charging correlation will inevitably form one of the most important OCS functions.

Standardization prospectAs a key standardization organization,

3GPP ha s deve loped and re l e a s ed numerous cha rg ing spec i f i c a t i on s including the OCS, IMS-charging, and push-to-talk over cellular (PoC) charging. In 2007, 3GPP established SAE charging and online charging correlation research programs. Moreover, PCC specifications are under development, and expected to be mature in 2 - 3 years.

Huawei is an important member of and major contributor to 3GPP and the Open Mobile Alliance (OMA). It has submitted a multitude of proposals during standardization of charging solutions, and chairs or vice chairs a number of related focus groups such as 3GPP SA2, SA5, and the OMA MCC. Huawei has gladly assumed the responsibility of leading the 3GPP standardization process. With its rich array of experience in the mobile charging field and an extensive understanding of operators’ charging requirements, Huawei will continue dedicating itself to the development and maturity of charging systems’ standardization.Editor: Liu Zhonglin liuzhonglin@huawei.com

Mobile charging support system faces fresh challenges

Online Charging System (OCS)

Subscription ProfileRepository (SPR)

Policy and ChargingRules Function (PCRF)

Offline ChargingSystem (OFCS)

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Service Data FlowBased Credit Control

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