ACCOUNTING MANAGEMENT IN HETEROGENOUS MOBILE ACCESS NETWORKS: THE MIND APPROACH

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1 ACCOUNTING MANAGEMENT IN HETEROGENOUS MOBILE ACCESS NETWORKS: THE MIND APPROACH Octavian Tirla*, Alejandro Bascuñana Muñoz ±, Peter Schoo #, Serge Tessier* * T-Systems Nova Berkom Innovationsgesellschaft mbh, Goslarer Ufer Berlin, Germany ± Ericsson España S.A. Retama 1, Madrid, Spain [octavian.trila serge.tessier]@tsystems.com Alejandro.Bascunana- Munoz@ece.ericsson.se # DoCoMo Communications Laboratories Europe GmbH, Landsberger Strasse , Munich, Germany schoo@docomolab-euro.com ABSTRACT This paper presents a snapshot of the ongoing work in the IST Project MIND regarding required accounting management in heterogeneous network environments for systems beyond 3G. MIND considers the billing issues in the context of vertical handover and more specifically in the context of handover between UMTS and WLAN networks through scenario-based examples. An idea is given how to approach accounting in heterogeneous permissive networking environment and what are the loose strands that still remain to be recognized and answered in research as well as in standardization. I. INTRODUCTION Accounting is one of the essential functionality in telecommunication networks. Without it network operators could not run their network infrastructure. In this paper and in the project context of MIND we look at vertical handover in heterogeneous mobile access network in conjunction with accounting functionality. The context of MIND, however, is wider. The introduction of QoS within IP networks, and especially within radio access IP networks, is one of the key factors that will push packet-switched technology as the base of all multimedia services (i.e. videoconference, video on demand, etc) in wireless networking. This communication environment is the problem domain addressed by the IST project MIND [1], which is the successor project to the BRAIN [2] one. BRAIN carried out conceptual work concerning a QoS Framework and a terminal architecture called BRENTA (the Brain ENd Terminal Architecture. The design of selected parts of BRENTA is currently under study within MIND. There is a need for an architecture, where system level properties, resources, application level semantics and user preferences can be observed and managed so as to best decide when and how adaptation has to be performed. BRAIN extended the current telecommunication network and the Internet to address micro-mobility and QoS [2]. MIND provides a further evolution to allow mobile networks and Personal Area Networks leveraging the public infrastructure to gain access to the Internet, to long distance calls facilities, and to services assisted by accounting management. Of particular interest are the requirements on technologies that support at the same time, handovers between different network technologies and operator domains, as they are classified in Section II and that also support mechanisms enabling accounting of resource usage. What is understood by accounting is explained more in detail in Section III. Findings regarding accounting management is presented in Section IV. Related work about accounting performed by other related projects is explained in Section V. The particular approach taken in MIND is based on scenarios describing the usage of wireless access technologies and mobile routers; scenarios that help to formulate requirements on the future network architecture as well as on the BRENTA; scenarios that encompass challenges for End-to- End QoS support, security and accounting management. One example extracted from the scenarios is presented in Section VI. II. HANDOVERS CLASSIFICATION This section presents definitions of and rational for different types of Handovers (aka handoff or HO), a concept that is well known in Telecoms supporting terminal mobility. The concept of Roaming, which is the formal agreement between operators that allows a mobile to get connectivity in a foreign network, is not discussed here. Handover is the process that utilized the mobility of sessions within a wireless network. With packet switched technology appeared the need to determine the different types of handovers. The concept is classically defined as: The process of transferring a phone call in progress from one cell transmitter and receiver and frequency pair to another cell /02/$ IEEE PIMRC 2002

2 transmitter and receiver using a different frequency pair without interruption of the call [3]. Some innovative projects like BRAIN, MIND and an IETF Internet draft [4] have tried a redefinition taking in account the IP layers. This class of handover can be called Layer 2 Handover (L2HO). Basically, two types of handovers can be distinguished: horizontal (HHO), and vertical (VHO). We defined these concepts both from the circuit switching (CS) and packet switching (PS) point of view. Later we will introduce new handovers definitions corresponding to PS side. In the classical CS definition if the network is homogenous and the handover is done between equipment of the same type, the HO is called horizontal. If the network is heterogeneous (e.g. between radio based LAN and satellite stations), the handover is more demanding and is called vertical [5]. A Classical definition of HHO in the CS domain is: The process that occurs when a mobile device transfer an end-to-end communication from one base station to another within the same radio technology., Keeping the same technology is essential for HHO. The VHO definition within the CS domain is: The process of handover between different types of [radio] networks. The concepts explained above for the CS domain correspond to new HO definitions in the PS domain: the intra-technology handover (HHO) and inter-technology handover (VHO). In the PS domain the definition of horizontal and vertical handover is more related to changes in the IP network interface. A definition of HHO in the PS domain can thus be: The process that occurs when a mobile device transfer an end-to-end communication from one base station to another within the same radio technology. Obviously, in this definition it is important to keep the same technology for a HHO. From the point of view of PS, another definition for the concept of HHO can be given: A handover in which the mobile node's network interface does not change from the IP point of view; the mobile node (MN) communicates with the access network via the same network interface before and after the HO. Typically, a HHO is an intra-technology handover. However, it can also be an inter-technology handover in case the MN can do a L2HO between two different technologies with-out changing the network interface seen by the IP layer. We can introduce now the Vertical Handover concept in the PS domain as: The process of handover between different types of [radio] networks. Consequently and just referring to the VHO for the IP world we define: In a VHO the mobile node's network interface to the access network changes. A VHO is typically an inter-technology handover. However, it may also be an intra- technology handover, if the MN has several network interfaces of the same type. That is, after the handover, the IP layer communicates with the access network through a different network interface. It can thus be concluded: the definitions depend upon the usage of CS or PS technology. The latter is relevant for this paper, as the MIND project oriented towards the IP domain. With the advent of Wireless Local Area Networks (WLAN) the advantage coincides to have a bandwidth very similar to the wire-line networks. Usually operated by private companies such WLANs (802.11, Bluetooth, etc) became popular to give service on their premises. They run usually indoors and use unlicensed spectra (2,5Gh, 5Gh). Their management model is very similar to the management of the wire-line LANs, having shortcoming in authentication support, charging and billing, whereas, public mobile operators provide mobile telephony service usually in outdoor environments (GSM, GPRS, UMTS, etc). Their networks are operated in a licensed spectrum and issues related to security and accounting are of vital importance. We deliberately do ignore here wireless networks like the Satellite one. In overlay situations, such licensed and nonlicensed networks offer a choice to users for being Always Best Connected. This means for a capable mobile terminal to use any network offering the best access technology and capable of changing the access technology whilst maintaining the user s active sessions. Having this in mind, there is obviously a need for inter-domain or inter-technology HO between different access networks or combinations of them. For a vertical handover, or example, it is not necessary to have a HO between WLAN and a PLMN network. Such a HO appears if the terminal changes access connection, whilst maintain the session from one mobile operator to another, or between two different network providers, etc. Vertical handover needs extra support both in the terminal side and in the network side. Terminals should allow multiaccess technologies to allow connecting to several types of access network (i.e. WLAN b, CDMA, WCDMA, etc). Such types of terminals should be capable to select the best connection each time, and without loss the current data transfer. From the network operator s point of view the network should allow to the user to maintain sessions, using existing authorization and within the same trust relation. Such types of services require standards applicable for companies and operators to provide services that respect user profiles, existing SLAs and accounting agreements. III. ACCOUNTING MANAGEMENT CONCEPTS Billing and charging are important features of a telecommunication network. Without them network operators could not operate their network infrastructure - if you can not bill it, kill it. In the context of MIND accounting is in the context of vertical handover. Because different technologies are used, accounting should be done in a manner independent from technology and therefore the metering, charging and billing concerns IP traffic. One of the main differences between the business in the Internet world (e.g. ISP) and the traditional

3 telecommunications world is the distinction of contractual partners and users making use of such contractual agreement in the name of the party having a contractual agreement. Distinguishable is mainly on -line and off-line billing; in addition we can split the problem into two more classes namely circuit switching and packet switching. These billing systems address different issues. The concept of accounting management is based on the TMN standards. It refers to the quantitative measurement of resource usage of connectivity services. Here, it does not address the accounting and billing of service at the application level. This concept has also been found helpful in the IP networking community. service 1..n resource produces user produces cost settlement subscriber authorizes service usage sent to uses requires 1..n Usage metering describes usage of describes usage of UMR 1..n 1 service usage info expresses combined UMRs Charging Billing responsible Figure 1 Accounting Management Accounting system is one of the important and complicated systems maintained by telecommunications operators. The accounting process in telephone networks today is increasingly based Telecommunications Management Network (TMN), which is specified by ITU-T and provides an organized architecture to achieve the interconnection between various types of Operations Systems (OSs) and telecommunications equipment in order to exchange management information. Generally the accounting process comprises four sub processes, which conceptual relationship is described by Figure 1: Usage metering is the task to recognize and record information relevant to the usage of a resource in a meaningful way [6]. This could be the information about the access to a resource, time and duration of usage, and others. In relation to an identifier of an responsible entity usage metering records (UMR) are created by this process as a consequence of the occurrence of accountable events in systems. Charging is the process of collecting UMRs pertaining to a particular service transaction and combining them into service transaction records, which contain pricing information, e.g. the amount of charge units to be assigned to the service utilization [6]. Charges are established for the use of the resources from the metered information allowing accurate charging. To calculate the charges, tariff schemes are applied and service usage is rated. tariff rate UMR: STR: bill account accumulated 1 0..n STR 1..n contract network operator manages Accounting Usage Metering Record Service Transaction Record Accounting is the subtask to assign charges in term of service transaction records to customers accounts. The charges for service usage may be distributed to service providers that cooperate together to provide the services to the users. Billing is to collect service transaction records and selects from the account that pertains to a particular service subscriber, accumulates the charges and finally send a bill (invoice) to the subscriber. IV. TECHNOLOGY SPECIFIC METERING The two telecommunications technologies GSM & UMTS determine the base classes for metering and vertical handover: circuit switching (CS) and packet switching (PS). In addition, WLAN is a third and relatively new wireless technology, supporting on L2 access to IP network. When handovers occur, appropriate support is required to cope with the metered resources that are specific to any of these technologies. Relevant parameters in CS networks are: time of call set-up, time when call is initiated, end time, time when call is terminated, given support for specific (e.g. location-based) services, distances or quality of service usage, etc. Furthermore, in PS networks parameters that identify measurement point (IP Addr.), flow description (Src/Dest IP and port numbers), reserved resources (flowspec parameters), used resources (amount of packets, amount of Bytes), are appropriate. The metering of used or reserved resources is typically described in term of Usage Metering Records (UMR). Such UMRs are in subsequent procedures factored by the tariff in order to calculate charges. If accounting is not simplified (flat rates) or based on characteristics that are common to any of the network technology (e.g. time), then the accounting procedures will become more complex. The predominant questions are therefore: on which level and in which domain can UMRs be collected and combined, so that the responsible operator has a fair change to apply the tariff he has agreed with the customer? Also, on which level should the necessary balance amongst operators be performed? Currently, leading vendors of accounting and billing solutions for IP based services, management consulting companies who integrate different systems from different vendors and Internet service providers have formed the IP- Detail Record (IPDR) Initiative [7]. Applying XML, as the IPDR Organization has decided for, is certainly an advantage, especially since IPDR aims for interchangeable and interoperable solutions. For systems beyond 3G supporting seamless services amongst heterogeneous network technologies, accounting management systems need to be in place that can cope with technology specific metering characteristics and that are open so that information can be exchanged amongst operators.

4 V. RELATED WORK Because in MIND different technologies are in use, we assume billing and charging should be done in a manner independent from technology and therefore we will consider the metering, charging and billing of IP traffic. The issues of billing and accounting in IP networks and multi domain billing possibilities are not new, and some ideas which have an important relevance for the approach we are considering, raised from remarkable organizations and IST projects: IETF worked on Internet accounting and tried to approach the billing and accounting in a multi ISP environment. Focusing on standardizing the accounting for the transfer of packets trough the Internet, the IETF made a proposal for a provider-based accounting architecture and the AAA Work Group of the IETF selected Diameter [8] as preferred protocol for transport accounting. Object Management Group (OMG) created a standardized object-oriented architectural framework for distributed applications based on specifications that enable and support distributed objects. Objectives of the project included the reusability, portability, and interoperability of object-oriented software components in heterogeneous environments. The resulting Distributed Accounting Facility is a specification of interfaces to other needed systems to fulfill the task of collecting and processing charging information from various sources. The model was based on information interchanging between distributed accounting entities belonging to different operators and required inter-operator services agreement enabling only one operator to bill the end user [9][10]. The IST project SUSIE provided an in-depth analysis of issues in metering, accounting and billing of IP traffic [11]. A General Case architecture was developed in SUSIE, where the metering for IP traffic was done at the edge devices of a provider domain. Then the meter data were collected by the Accounting Layer and regrouped in accounting records (PIP NAR). These accounting records were then forwarded for charging and billing. The Parlay Group is an open multi-vendor consortium [12] formed to develop technology-independent Application Programming Interfaces (APIs). These open applications enable the development of solutions to operate across multiple networking platform environments from technology, Internet and ebusiness Companies, ISVs, Software Developers, Network Device Vendors and Providers, Service Bureaus, large and small Enterprises, Application Suppliers and ASPs. As a summary, it seems clear that a solution covering the trusted and accountable access to wireless networks is required on two levels. First it has to be addressed within the IETF for IP based network environments. Then, for the sake of achieving the integration of existing networks like for example GSM or UMTS, most probably the 3GPP will have to address this standardization task too. However, to sum up, since none of these examples considers wireless environments as of concern for MIND, it will not be possible to use any of these models directly. What appears feasible is to investigate how to apply these solutions to the MIND platform. VI. EXAMPLE FROM THE MIND SCENARIOS The MIND scenarios paid special attention to mobility problems and to the inclusion of ad-hoc sub-networks in the general MIND network. The scenarios have been selected to cover the future activities of MIND users, with special attention to the most innovative elements of MIND proposal. They do not exhaustively covering all services MIND might be capable of delivering, but are providing some carefully chosen snapshots with regard to value added services (e.g. security, billing, location-based services, web-portals, etc). In this section we consider the Nomadic Worker scenario, which describes a workday of the Stephanie Jones, a member of a large multinational corporation based in Frankfurt. Stephanie is constantly on the move from one place to the next, often having to cross international borders. She possess a PWA which allows her to remain connected to the Internet, no matter where in the world she decides to go next. At some point in the day Stephanie arrives at Siemens offices in Munich where she is involved in a meeting. The workgroup needs some advice and invite their reviewer, who is heading from his office toward Brussels airport, to join the meeting. When the reviewer, located in Brussels, goes from the office to the airport he crosses the networks of three different operators and uses each time a different technology. The three operators are the Home Operator, which is charged to administrate the network of the corporation where the reviewer has his office, the Public Operator administrating the UMTS network, and the Airport Operator. Technologies used by these operators will be, Hyperlan2 in the office, UMTS in the public environment, and a Bluetooth network in the airport. During the meeting, the participants can recognize that the video and voice quality of their videoconference changes several times. As the quality or the coverage of the network is no longer sufficient, the reviewer has without taking notice to perform a VHO. The billing issues that are inherent to this example are: Where to meter the different traffic measures? How to accumulate them in a technology independent way? How to combine the costs caused in the networks of the different network technologies? How to achieve one bill when different network operators contribute? In which of the domains shall this combination be achieved? Different approaches can be done to these questions. We consider that all the traffic, which should be metered, billed and charged, is IP traffic. Therefore we consider that it is

5 ((( ))) Hyperlan 2 Home Operator Office UMTS GPRS Public Operator Taxi ((( ))) Bluetooth Airport Operator Airport While the reviewer is in his office, the IP ingress router located in the building meters all his IP traffic. This metering information is recorded and delivered to the central point of billing in form of UMRs. When the reviewer changes from his office network to the UMTS one, the packets go through the UMTS network. The UMR data collector receives the billing information and sent it to the billing central point located at the user s Home Operator. Figure 2 - Involved Network Domains reasonable to meter the traffic at the network edge. In the multioperator-multitechnology environment, each operator meter and account the traffic passing to its own network and delivers this information to a central entity. The accounting performed by the operators is technology dependant. At the end the home operator delivers only one bill to the user, and different percents from the final facture will be charged to the several operators whom networks are used. To do this, operators have an agreement specifying how should be the traffic billed, the percentages of charging between the operators, the SLA, which operators are trusted to use the infrastructure and so on. In our example, we suppose that the corporation s Hyperlan 2 operator has a contract with one of the largest public telecommunications providers in the country. This public operator deploys basically UMTS networks, and has agreements with other smallest local Hyperlan2 and Bluetooth providers. The airport has a contractual agreement with the UMTS operator the reviewer is using in the taxi. A common trust relation that allows the reviewer to make an inter-domain VHO and use the Bluetooth WLAN while being billed by the UMTS operator manifests this agreement When the reviewer leaves the coverage area of the Hyperlan 2 network located at his office, and takes the taxi, his terminal automatically commute to the UMTS technology. His data session is not interrupted and his terminal applications adapt its data rates to the new technical support. This is due because the UMTS data rate is lower than the Hyperlan 2 one. The reviewer continues working in the taxi. Due to the special characteristics of the UMTS network, the capacity provided has continuous variations depending on the number of users, the distance to the base station, the weather, etc. Near the airport area the UMTS is replaced by GSM/GPRS coverage, and the multi-technology access terminal has to commute to the GPRS mode. The data rates are strong decreasing after this handover, and therefore the videoconference between the reviewer and the Munich meeting is changed into audio conference. When the reviewer arrives at the airport, a new vertical handover occurs between the GSM/GPRS technology and the Bluetooth, which is operated by the airport operator. From the billing point of view, four sub-cases (Figure 3) can be identified: Central billing servers Public and private (Airport lounge) operated network Peripheral billing server Public GSM/GPRS network (Close to the Airport) IP Backbone Billing information Peripheral GPRS billing server Private (Reviewer office) WLAN network Public UMTS network (Town) Figure 3 Accounting Technical Approach When the user changes from the UMTS to the GPRS network no changes occurs, because it is different access technology but the operator it is the same. When the reviewer uses other local operator networks (Bluetooth, Hyperlan 2, etc) metering is done by the local operators and data relevant for accounting is collected in UMRs delivered to the UMTS operator who forward this to user s Home Operator for billing. At the end the user will pay the Home Operator, and the others operators will receive a percent from the revenues of the final bill. VII. CONCLUSION One of the main works performed within MIND project is the development of futuristic scenarios where inter-technology and inter-domain handovers appear. In this paper some results as well as an overview of future work still to be achieved and already started within well-known standardizing organizations have been reviewed. These ideas give an approach about how billing could be addressed regarding heterogeneous permissive networking environment

6 and what are the loose strands that still remain to be recognized and answered. MIND considers the billing issues in the context of vertical handover and more specifically in the context of handover between UMTS and WLAN networks through scenario-based examples. The part of a scenario related to a nomadic reviewer has been described in the present paper. This description introduced interesting challenges raised by the charging and billing in the case of the several inter-technology and inter-operators handovers that occurs. A review of the metering within different cellular telecom technologies is resumed and possible applications of these technologies in the context of mobile networking are studied. The MIND consortium will take advantage of the newly solutions proposed by various fora and tune them according to own identified user scenarios. From the network connectivity provider s point of view, things are not so simple. No one will let nodes to connect to the Internet using their infrastructure without some means of authenticating and then charging the nodes for the services they were offered. That is why besides pure mobility management entities the network has to be enriched with another kind of capability that allows for authentication and charging mobile nodes. Please refer to [13][14] and also to our previous Section IV to figure out how the traditional telcos world try to work in a two step approach with the IETF for solving this issue. This paper describes what should motivate our further output work till the end of the project. ACKNOWLEDGEMENTS This work has been performed in the framework of the IST project IST MIND, which is partly funded by the European Union. The authors would like to acknowledge the contributions of their colleagues from Siemens AG, British Telecommunications PLC, Agora Systems S.A., Ericsson Radio Systems AB, France Télécom S.A., King's College London, Nokia Corporation, NTT DoCoMo Inc, Sony International (Europe) GmbH, T-Systems Nova GmbH, University of Madrid, and Infineon Technologies AG. REFERENCES [1] [2] [3] Institute for Telecommunication Science. [4] IMIS Project: [5] BRAIN project, Internet Draft work in progress, Mobility Related Terminology. draft-manner-seamoby-terms- 03.txt [6] Teemu Mäkelä, Accounting in the PSTNlo, Helsinki University of Technology, [7] IPDR Organization [8] Aiko Pras, Bert-Jan van Beijnum, Ron Sprenkels, Robert Parhony: Internet Accounting, IEEE Communications Magazine, May 2001 [9] Object Management Group Telecom Distributed Accounting Facility, May 2001 [10] Fraunhofer FOKUS - Telecom Distributed Accounting Facility, October 2001 [11] Tony Price, Martin Potts, Kevin O Leary (Editors): Charging for Premium IP Services in the European Information Infrastructures & Services Pilot, February 2000 [12] [13] 3GPP TSG SA [14] K. Rosenbrock, S. Bradner et al., 3GPP-IETF Standardization Collaboration, IETF RFC 3113, June 2000