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EXPERT S FORUM EXPERT S FORUM Shan Mingjun, a senior expert in the charging field. Currently he is the Vice Chairman of 3GPP SA5-Charging Group and leads major charging activities related to OCS, IMS and EPC. In addition, he has been serving as Vice Chairman of OMA MCC for two terms since August 2005. Enabling convergent billing via OCS As a development trend for the operation support system, convergent billing has a broad scope that is not limited by a single standard. Its development may follow different directions. However, which is the best direction? By Shan Mingjun The telecom industry is witnessing the migration of both networks and voice services to comprehensive information service provision. Network technologies are integrating. Both service models and the industry chain are transforming due to the ongoing fixed mobile convergence (FMC) and the combination of IPTV, telephony and Internet networks. With its roots in a convergence environment, convergent billing is not a nascent concept. It existed before the online charging system (OCS) came into being, although the two are now growing together and supplementing each other. Based on the IP multimedia subsystem (IMS) and defined by 3GPP TS32.296, the OCS has gradually emerged as the basic charging infrastructure for the bearer, subsystem, and application layers. As a development trend for the operation support system, convergent billing has a broad scope that is not limited by a single standard. Its development may follow different directions. However, which is the best direction? The answer lies in the analysis of OCS development within the 3GPP framework, coupled with an evaluation of the driving factors and key capabilities required by convergent billing. The evolution of OCS 3GPP Release 5 saw OCS in its infancy stage. It was framed to perform credit control and charging for IMS and packet transport networks. The OCS supported entities such as the serving-call session control function (S-CSCF), application server, media resource function controller (MRFC), and GPRS support node (SGSN) accessed through the CAP interface. OCS was released and more fully defined in 3GPP Release 6. Based on core network development, its functional entities were extended to support bearer layer charging, event-based charging, rating function, and account balance management. As a result of network evolution, network elements (NEs) accessed the OCS for charging included the traffic plane function (TPF) and wireless local area network (WLAN), as well as S-CSCF, IMS gateway function, and media resource function controller (MRFC). Based on IETF DIAMETER, Release 6 also supported the accesses of the multimedia messaging service server, gateway mobile location center (GMLC), and multimedia 5 APR 2008. ISSUE 40
broadcast and multicast service (MBMS). Charging for prepaid voice services was integrated into the online charging system in Release 6. The OCS supported CAP access to realize the charging for prepaid voice services. In other words, the intelligent network (IN) can be regarded as the OCS s voice processing component. Release 7 optimized the OCS by supporting online charging control for open mobile alliance (OMA) enablers, under which OMA applications were facilitated by 3GPP infrastructures to implement both online and offline charging. The major change in Release 8 is to enable correlated online charging among the bearer, subsystem and service application layers during the service processing. It ensures the integrity of charging data to facilitate reasonable charging modes. In addition, 3GPP and 3GPP2 will adopt a common set of IMS architecture, enabling organizations such as 3GPP2 and TISPAN to use OCS more conveniently. The OCS will also support wider access to richer network scenarios. As one of the major protocols to access IN, CAMEL has been playing a crucial role in terms of prepaid voice services. OCS was specified to support CAP access since Release 6. Differing from the DIAMETER-based Ro protocol, CAMEL is implemented independently from the OCS as a charging access protocol. CAMEL s development in 3GPP began in 1997 and its original version was embodied in Release 99. CAMEL 4 was defined in Release 5 and maintained in Releases 6 and 7. Convergent billing s drivers and capabilities Driving factors The development of convergent billing goes along with the changes in both telecom network architecture and new service development. As a focus in the telecom charging field, convergent billing is driven by the following core factors: ALL IP network development: As circuit switched (CS) based or IN based services are shifting to ALL IP based, charging systems should offer support accordingly. Service based on the session initiation protocol (SIP) cannot be effectively implemented without a convergent billing system. SIP-based IMS forms the direct technical driver. Expanding new services: A robust charging system is necessary for the quick deployment of new applications and combination of new services. Prepaid and postpaid charging convergence coupled with flexible charging modes can benefit operators by providing a range of combined services for customers, which accelerates the service provision and effectively tailors services to suit individual needs. Unified service provision: In the early stage of service development only postpaid customers can access some services due to a high credit rating requirement. GPRS provides an example of such a service for which prepaid customers had to wait a considerable length of time. Convergent billing will mitigate this problem by facilitating unified services for both prepaid and postpaid customers. In addition, convergent billing APR 2008. ISSUE 40 6
EXPERT S FORUM Enabling convergent billing via OCS architecture enables the charging of services provided by third parties, such as SPs, while customer loyalty can be enhanced through flexible tariff packages. Four fundamental capabilities As detailed above, the catalysts for convergent billing mainly derive from changes in network architecture, new services, and customer needs. Four fundamental capabilities are required for the successful operation of a convergent billing system: Real-time charging. This applies to charging for convergent networks and services. Charging lays the foundation for telecom operations. The essence of the charging is to meter network usage and statistics of service requests. Billing is over charging. One of the essential parts of charging is to redefine charging elements, and then redefine the structure for network and service control. This simplifies charging methods. Charging now observes service use logic instead of service use quantities. This also presents a challenge in attempting to define the interoperation between the charging system and the network. Bundled service charging. This seeks to satisfy the mixed subscription of voice, message, and data services. A new difficulty has emerged concerning charging based on ad-hoc scenarios, which has arisen due to greater freedom requested by customers. While this increases the challenges face by operators and equipment suppliers, it potentially yields higher customer returns. Postpaid based on offline charging Postpaid based on online charging As 3G packet networks increase demands on online charging systems, OCS will be gradually deployed worldwide following the conclusion of its current and ongoing optimization under the 3GPP framework. Analyses attest that OCS indeed forms the best framework for convergent billing implementation. In C h i n a, t h e n u m b e r o f f i xed broadband customers has grown explosively since 2002, having increased on average by over 50% each year. On the other hand, Chinese fixed network operators have witnessed decreased monthly tariff and reduced revenues, although the quantity of broadband access has increased. This illustrates that simple tariff models cannot help increase ARPU or implement flexible pricing for niche markets. Moreover, improvements will not be derived from increased bandwidth or Internet services. Converged rating engine. Service variety embodies a major development Fig. 1 Charging logic of prepaid and postpaid services Prepaid based on online charging driver for operators and SPs under which a flexible and open rating engine greatly assists new business mode development. A rating engine should be able to charge any event and combined services. Some believe that the rating engine can exist independently from the charging system and provide open interfaces. Whether the rating engine is independent or internally integrated, the key capabilities of the convergent billing should include open and unified interfaces, as well as a holistic service charging mechanism. Customer-centric data organization. Great variations occur in prepaid and postpaid user experience during different charging stages, and this is largely related to deployed technologies. With customer service upgrades, the distinction between prepaid and postpaid services is increasingly blurred. From a technological standpoint, convergent billing should facilitate the switching between customer groups, allowing a customer to select prepaid charging for some services, while postpaid charging for other services to enhance usage flexibility. OCS is the best direction As demonstrated in its development, OCS can deliver a flexible, swift and real-time charging function. It solves the problem of prepaid and postpaid service shifts, and enables operators to quickly assess customer needs in order to more accurately plan the launch of new services and convergent schemes. As 3G packet networks increase demands on online charging systems, OCS will be gradually deployed worldwide following the conclusion of its current and ongoing optimization under the 3GPP framework. Analyses attest that OCS indeed forms the best framework for convergent billing implementation. Ensuring compatibility The 3GPP OCS is heading toward multiple charging access provision for networks bearing different services. To meet network evolution demands, the OCS s internal components are further 7 APR 2008. ISSUE 40
abstracted and modularized, and the Rc and Re reference points are optimized. In Release 7, charging data elements are designed to support charging based on data over cable service interface specifications (DOCSIS) in order to enable seamless access to DOCSIS networks. Charging elements for OMA enablers have been redesigned in line with the original 3GPP charging architecture. Currently Release 8 is enhanced to support further convergence of fixed and mobile networks. Organizations such as TISPAN and 3GPP2 regard 3GPP as the best basis for integration, and this further ratifies the compatibility of 3GPP OCS during network convergence. Fulfilling convergent billing needs A logical foundation is laid for service convergence since the OCS embraces eventbased charging and session-based charging. This meets the charging criteria for both voice and data services, and for the bearing, subsystem, and application layers. The charging network is evolving from postpaid BOSS or prepaid IN to convergent billing. The OCS rating engine comprises the cornerstone of this process, while Re reference points facilitate rating engine deployment and fulfill new service development requirements. The convergent billing system plays a key role in data organization and coordination, and forms the largest customer database. The OCS yields best practice with respect to organizing billing data of all customers and services, which is essential given that the online charging data describes one of the most complex data streams. Fig. 1 illustrates charging logic for various scenarios: online and offline, post and prepaid. Several charging modes and their combinations are possible, including near real-time charging for postpaid or prepaid services, and charging for prepaid service. Online charging (based on Ro and CAP interfaces) and offline charging (based on the Rf interface) describe the interaction between NEs and charging systems. Postpaid and prepaid indicate the interaction between account balance and user payment. As a result, user experiencebased concepts prepaid, postpaid, near The charging system s architecture must be designed according to network and service development, and network architecture should in turn adapt to the charging system. This is one of numerous concepts underpinning core network layout, although conjoining the charging system and the network is not an absolute must. real time and real time can be seamlessly mirrored to network-based concepts such as online and offline charging. The bill-based, postpaid BOSS and the independent prepaid IN charging system are evolving into a convergent billing system. The OCS can develop by expanding itself in the context of account balance management. The OCS can also develop by integrating BOSS and IN, under which OCS serves as a core for them both. These define shortcuts for the development of a convergent billing system. Data organized in this mode in the convergent billing system provides enhanced support for various customer types and user-oriented services. From charging system to charging network In the convergent billing, charging technologies are going to resemble a charging network as opposed to a charging system. The charging network recognizes that charging is neither a separated nor afterward event. The charging system originally forms part of the support network and can be regarded as a supporting platform for networks or services. In a converged environment, the charging system is unable to complete the entire charging process. Many network evolutions, however, are stimulated by changes in charging requirements. The charging system s architecture must be designed according to network and service development, and network architecture should in turn adapt to the charging system. This is one of numerous concepts underpinning core network layout, although conjoining the charging system and the network is not an absolute must. In fact, independent networking of the charging system is more desirable for network architecture. 3GPP delivers an apposite example of charging network application. Encouraging results include TPF introduced in Release 6, and, in Release 7, implementing the policy and charging enforcement function (PCEF), and achieving deep IP packet detection and parsing of content-based charging. Furthermore, IMS supports the generation and delivery of charging IDs, which can identify the relation of charging information generated at each node, facilitate the correlation of charging information, and ensure the integrity of charging data. C o m m e r c i a l r e q u i r e m e n t s a r e constantly emerging and new charging technologies are arising to keep pace with market needs. It has been a challenge for operators to implement content and policy charging, as well as flexible volume based charging. International organizations such as 3GPP and TMF have been working continually to reach solutions based on commercial requirements and suppliers proposals. Operators as the users of the technology, however, broadly shed doubt on suppliers solutions. Nowadays, technologies no longer form an obstacle in terms of service promotion. Deep IP packet detection technology has satisfied the requirements for content or volume based charging, and as such has achieved a goal that was once regarded as impossible. Furthermore, other leading technologies, such as online correlated billing, are heading confidently into the arena of maturity. Editor: Huang Zhuojian huangzhuojian@huawei.com APR 2008. ISSUE 40 8