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An Integrated Accounting and Charging Architecture for Mobile Grids

Cristian Morariul, Martin Waldburgerl, Burkhard Stillerl,2

'University of Zurich, Department of Informatics IFI, Communication Systems Group CSG Binzmuihlestrasse 14, CH 8050 Zurich, Switzerland 2 Swiss Federal Institute of Technology ETH Zurich, TIK, Gloriastrasse 35, CH 8092 Zurich, Switzerland [morariulwaldburgerl stiller]@ifi.unizh.ch
The adoption of the Internet Protocol (IP) by a number of non-IP network operators, such as telecom or cable TV operators, opens the path toward new business models. IP will allow operators to provide a unified wired as well as wireless access to a wide range of services to their users. Additionally, using the same communication protocols and standard interfaces, enables different providers to coordinate any type of resources in Virtual Organizations (VO) and supports the composition of services aggregated across multiple domains. On one hand, such an open environment requires new business models to be adopted by the involved parties. On the other hand, Grid middleware infrastructure supporting integrated accounting, charging, pricing, and billing across multiple domains has to be in place to facilitate service provisioning in multiple VOs. Based on the relevant set of requirements derived, a new and extended A4C Architecture (Authentication, Authorization, Accounting, Auditing, Charging) has been developed, implemented, and evaluated for mobile Grids providing pervasive access to knowledge.

qualify here as a well-suited solution. In the same way as IP serves as an integration enabler for underlying protocols and access technologies, grids allow for an integration of various stand-alone services, offered by different providers, to be composed in applications. This demands for accounting and charging mechanisms, since various service providers need to charge service consumption if services are offered in a competitive environment. Several grid-related projects have designed and implemented accounting mechanisms for grid-services, such as APEL [8], DGAS [20], GASA [3], [12], GRASP [13], GSAX [4], Nimrod/G [2], and SGAS [22]. However, the key drawback with those approaches is that these solutions did propose and implement proprietary accounting and charging mechanisms only. Additionally, any interconnection of such accounting tasks with charging functions is not part of those solutions either. Thus, the accounting and charging architecture proposed within this paper extends existing work by far. The term Grid was traditionally used for defining a distributed high-performance computing (HPC) architecture. Computational and storage grids are the two examples everyone thinks Keywords: Mobile Grid, Accounting, Charging, A4C, about when dealing with this domain. However, more recently, Business Grid, IP-based Grid Services, Virtual Organization grid principles are not only applied to HPC, but are used for service virtualization [10] so that Virtual Organizations (VO) I. INTRODUCTION AND PROBLEM STATEMENT can be created by aggregating resources and services from difThe rapid growth of Internet penetration in the mobile com- ferent domains and different providers, irrespective of the munication market as well as the capabilities improvement of underlying infrastructure and protocols used in those different today's mobile devices offer new opportunities for existing domains. Taking the VO concept a step further, by granting technologies designed for traditional wired networks to be mobile or nomadic users pervasive access to knowledge, sets deployed on modern mobile communications platforms. Most the key focus for the work performed here and mobile grids in of the current research efforts on future mobile communication general. Such mobile grids need to integrate and harmonize various technologies adopt the Internet Protocol (IP) as the underlying communication protocol for video, voice, and data. The usage views of all actors involved in an operational VO. These views of IP will ease the process of integration of different communi- are expressed typically by business roles determining a cation infrastructures and will trigger the development of mid- player's specific behavior and requirements. In order to outline dleware services, such as AAA (Authentication, Authorization, the full range of organizational arrangements in providing Accounting), which offer their functionality to a broad range of mobile grid services in VOs, a comprehensive understanding of the underlying role model marks a prerequisite for the develapplications to be deployed. Integration of different access technologies as well as video, opment of the according accounting and charging architecture voice, and data services in an all-IP environment also paves the for mobile grids. Thus, the respective role model for mobile way towards offering of more complex services being com- grids has been developed in a first step, being described in this posed by basic services. This, however, requires an appropriate paper, to provide the basis for the charging and accounting service delivery platform to be in place, providing mechanisms technology developed in a second step, being described afterfor service delivery and service composition. Driven by the wards. Over the last few years multiple research efforts have been main concept of resource coordination across administrative domains and a strong service-orientation [11], grid systems performed on accounting, charging, and billing models for

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general-pur. while B. and sesFrom an organizational point of view. In accordance with the provisioning. a layered model and definition is used. workflows and an accounting system that envisages adaptive tion II extracts as new work the relevant set of requirements context-based charging. The solution proposed here. followed by an extensive Organizations "MDVOs are virtual organizations whose members are able functional evaluation of the architecture against a mobile to change locations while provided or consumed services grid scenario. and bill. one of the two only projects in the world so far address. those terms are also applied to the definition given by Foster for grid systems [11]. A.as it is used in the context of commercial electronic service ing mobile grid support explicitly. This provides the basis for cover all composing elements for commercially offered elecan investigation of the specific organizational characteristics tronic services. conclusions are drawn and ideas for remain available even after temporary loss of reachability. Based on [24] and ing of virtual operators. By following the determining and implementing accounting and charging definition of [27]. Mobile Dynamic Virtual developed and presented in Section III. and while running or yet to be initiated workflows adapt to changed conditions. as Table 1 describes in detail. [15]. Accordingly. user. not only for service provisioning. where charging Thus.main idea namely resource sharing and resource coordipose protocols and interfaces in order to deliver non-trivial nation across administrative borders [11] is reflected by and optimized Quality-of-Service (QoS) depending on the Virtual Organizations (VO). each focusing on differingly. and presents well as with respect to dynamics. Finally. the role model for integrate the specific characteristics of grid systems and mobile grid service provision in a VO is developed. Thus. include as well the evaluation of the architecture against the and service mobility requires a grid system to dynamically scenario drawn for detailed motivation purposes. the extended architecture design is new. a role model is needed that is on one hand goal.sample mobile grid scenario is depicted. Akogrimo domain of mobile grids. incorporating mechanisms evant key requirements on an accounting and charging archifor parameterizable secure authentication and authorization". the grid systems' sion) and communicates using standard. key requirements on the integrated A4C architecing mechanisms used by ISPs and mobile network operators. and to ogy in use has to be determined. AccordSeveral definitions for VOs exist. while key challenges are shown. ture (Authentication. a systems into account suggests an inspection of the VO conMobile Grid is communicating with the underlying network cept with respect to potential extensions or even fundamental in both directions enabling cross-layer cooperation between changes required. Towards this ing in MDVOs. This assures seamless interoperability between dif. the role model has to consider in the . to which has to be supported by The remainder of this paper is structured as follows. defines mobile grids as follows: "A Mobile Grid consists out of resources that are not subject to centralized control. while this model on the other hand has to prevailing in mobile grids. and a VOs. Sec. On the other grid systems in the area of mobile grid resources and users as hand. tecture for mobile grid services by means of a businessMobile grid systems show important extensions over fixed driven role model and a mobile grid scenario. future extensions are discussed in Section V. Since mobility and dynamics tradifor the accounting and charging architecture. This termisupport of mobile users has been undertaken in Akogrimo nology defines the understanding of accounting and charging [1]. Role Modelfor Mobile Dynamic VOs it supports all kind of mobility (such as device. the main problem in a mobile business grid is found in ent." [26] The architecture developed provides relevant mechanisms 1) Mobile Dynamic VO Nature to deploy grid applications in a mobile environment. ACCOUNTING AND CHARGING IN MOBILE GRIDS strong dynamic element with respect to their organizational Accounting and charging mechanisms have to be able to composition and their business processes" [27]. Accounting. capture the specifics of each of the different entities involved. an approach to design and implement a commercial is positioned logically on top of metering and accounting. which will be faced as the and Charging) are derived. device. [16] compares existing accounting. coming to the conclusion that there are still based networks use different terminologies with regard to multiple aspects to be addressed. whereas the latter is proin a detailed manner selected implementation aspects. which is newly tionally are not reflected by VOs.2) VO Role Modelfor Electronic Service Provisioning In order to determine the full picture of service provisionferent business partners. Furthermore. [6]. Grid middleware and the network.telecommunication operators and ISPs (Internet Service Pro. so that MDVOs are characterized by a II. open.charging and its associated processes. Mobility in terms of user. the vider). Taking mobility aspects in grid current context of the resource or the user. VOs for grid systems are perceived as to mechanisms of mobile grid services in a multi-provider set"allow for information and communications technology-supting.and charging-related terminol. of the art and embraces on one hand the identification of relacross administrative domains. two worlds converge. An overview of existing pricing schemes used in broadband IP networks is given in [9]. Authorization. Accounting and Charging Terminology Those schemes are evaluated in terms of technical and ecoThe two worlds of mobile telecommunication and IPnomic efficiency.adapt changing context. charging. Section IV delivers (MDVO) are seen as extensions of VOs: major implementation details. grid solution for service providers and telecom operators in but below billing. which voked by mobility support. the relevant accounting.generic enough to reflect all stake holders incentives. but also for generating and sharing revenue. Based on both. partly overlapping aspects [23].scenario. such as multicast or exist. goes beyond current state accountable and chargeable resource coordination ported. In other words. Auditing.

are assumed to satisfy the characteristics of a full-fledged electronic product. Incorporating those requirements results in the basic role model for electronic service provision within VOs as it is shown in the form of an Entity Relationship diagram in Figure 1. charge calculation) has to be performed in realtime.g. the respective role set dealing with financial flows has to be included in the role model.g. e. With the postpaid charging option. billing provider. The understanding of this role remains unchanged. Charging mechanisms are used to implement and realize charging options. This orthogonal separation helps to emphasize either on the more technical or economic aspects of charging.e. It is expressed in metered resource consumption. most general form an as wide as possible range of grid services that in turn aim at high-level resource (i. Mediation is intended to filter.. management. and economical ones. Online/offline Charging Mechanism |Service Customer| k-L i (. This is caused by its generic nature: While mobility and dynamics show implications on MDVO business flows. while mapping technical values into monetary units. a service user.g. whereof A4C is one important part with regard to commercial service provision. LU-. the charging (i. no strict time constraints concerning the processing time of charging (i. calls.e. service usage may be denied.Table 1: Accounting and Charging Terminology [24]. Services are rather perceived as non-tangible goods with an assigned utility level (macroeconomic and accounting view) or as electronic products (marketing view). applying tariffing theory or marketing methods. which has implications on the understanding of the terminology in use.. or any type of connections. Mediation transforms these data into a form which can be used for storing and further processing. service charges are aggregated on the user's account after service usage and the user is invoiced after a predefined period. consisting of entities that * initiate service provisioning by explicitly expressing a demand for it (service requestor). they do not alter the role of. the customer has to have a certain amount of credits prior to the service usage. including Quality-ofService (QoS). charge calculation) are defined. e. Therefore. \ 7UV Billing Figure 1: Basic Role Model for Electronic Service Provision in Virtual Organizations The proposed role model has been drawn from an organizational viewpoint. periodical credit checks during service usage are performed. This process may combine technical considerations.. Charging acts as an umbrella term for charging options and charging mechanisms. * consume the service results in terms of an electronic product (service user). * are charged for service consumption (service customers). or content and application service provider. takes a set of accounting parameters as its input and outputs the charge to be paid for the particular value of those input parameters. Nevertheless. and networking parameters. The role model does not explicitly reflect mobility or dynamics aspects. independent of whether a service user is mobile or not. Even though those aspects are specific extensions of MDVOs over VOs.. Depending on the type service. Prepaid/postpaid Charging Option ered to be commercial in terms of that they have to be charged to an entity.e. Billing is the process of consolidating charging information on a per customer basis and delivering a certain aggregate of it to a customer. aggregate. and correlate raw technical data which in most cases has been collected by metering. e. for applications. With the prepaid charging option. bundled in an application (potentially including additional benefits like warranty). A real-word entity in terms of an actor can embody one or Accounting Charge Calculation Mediation Metering Pricing Pricing covers the specification and setting of prices for goods. the present gap between the respective service notions from a technical and businessdriven view has to be bridged in order to integrate both understandings what is implemented by means of the grid middleware. and finally * offer and potentially also aggregate services (service provider).g. Accounting defines summarized information (accounting records) in relation to a customer's service utilization. grid service provider. such as communications provider. Prepaid charging influences the delivery of services to the customer. For the offline charging mechanism. e. e.. Coordinating and sharing knowledge requires the aggregation of basic services into more complex. while in fact only aggregated electronic services. knowledge) coordination.g.. specifically networking resources and services in an open market situation. composed services to be in place. resource consumption. Prices may be calculated on a cost/profit base or on the current market situation. [15] Termimnuts Charging Unde*rstandig Charging calculates the charge for a given service consumption based on accounting records and the tariffs defined in the SLA. only an at most generalized minimal role set has been expressed in Figure 1. the same basic role model is valid in both cases. With the online charging mechanism. The role of a service provider will find in specific scenarios more concrete realizations. Note that online charging implies that accounting and metering have to be done in real-time as well. Metering determines the particular usage of resources within end-systems (hosts) or intermediate systems (routers) on a technical level. Since these services are consid- . The term Service accordingly is not understood in a technical sense as a wellin a layered approach defined functionality that is offered through a service access point to a higher layer [7]. Tariff or tariff function. Charge Calculation covers the complete calculation of a price for a given accounting record and its consolidation into a charging record. charge calculation applies a given tariff to the data accounted for.. Since the role model needs to support a wide range of commercial services and organizational arrangements.

user. service usage records and charging records. Single Sign-On (SSO) Functionality A single action of authentication and authorization from the user should give access to all the services she or he is allowed to use. It also allows for the mapping of all service sessions to an initial authentication event. B2C B2B * Robustness of the architecture The A4C architecture should provide mechanisms to overcome faulty behavior of its components. full anonymity a new virtual identity is generated whenever a user requests a service from a foreign domain. A SSO approach allows users to authenticate once and then use services across different domains. a company that subscribed to this service with the service provider so that the company's employees would be informed on important changes and news. a wearable heart monitoring device. The service itself is requested by none (push service type) or one or multiple (pull service type) requestors.multiple roles. for a pull-type service. but specified number of users. The A4C Server in the home domain of the user should be the only network component capable to map between virtual and real user identities. taking the roles of a service requestor. while for broadcast services the full range of potential users in reach are supplied. For the necessary resources to perform health monitoring services.. and customer to have access to multiple services and still receiving a single aggregated bill for all the services used during a given period of time. packets or flows. the user. In commercial as well as in non-free service provision. and more than one in case a cost splitting scheme is applied.in this scenario an individual. From a services viewpoint. For instance. Unavailability of any component should have minimal impact on the user's possibility to access services or provider's ability to charge for service consumption. Mobile Grid Scenario At this stage a realistic mobile-grid scenario has been developed to enable the reader an easy to understanding of interactions among different players as depicted in Figure 2 and of players involved in service provisioning and in revenue distribution. Requirements Driven by the investigated specific scenario and the underlying general role model. Security Confidentiality: As the A4C components transfer sensitive data. at least one service customer must be present. user and customer in basic organizational alignments probably are taken by one organizational entity. InsurerComp (IC) company just released its new service. whereas either one or multiple service users exist. whereas IC acts as a content and application service provider. (Business-to-Business) relationship with IC. communication between these components needs to be secured. Based on a B2B ts to have meaningful accountable units and QoS parameters * .g. a user's real identity should be protected. an inteMobile Grid Scenario grated accounting infrastructure for a mobile grid is In the presented scenario. This device continuously monitors human heart activity and periodically sends data to a monitoring facility that based on a patient's historic records and other patterns in its database can detect when a heart condition is imminent. For delivering this service. thus applying the proposed role model (cf. One user only represents a unicast service. the set of key requirements has been identified. pseudo anonymity a separate identity Inrrrf (virtual identity) for each domain needs to be created and used whenever a service is requested from that domain. Anonymity: When using services in domains other than the home domain. IC concluded a contract with a Mobile Network Operator (MNO) to get access to a large number of potential customers. e. the case of multiple users can be sub-divided in multicast services with more than one. They address the middleware infrastructure related to A4C architecture an protocols as the main links between business and technology view on commercial service provisioning as follows: * C. one service thus has exactly one service provider assigned. With respect to compensation for service consumption. SPI that provides database storage for patient records. and SP2 that provides the necessary computation power for analyzing the real-time data received from different patients. - D. For instance.B). such as user credentials. IC collaborates with two service providers. This requires services and IC for the e-health application. the user is assumed to maintain required to understand and manage a larger set of paramecontractual relationships both with MNO for communication ters and multiple accounting record formats. while this service in the end will be charged to a third entity. * Multi-service and multi-domain accounting and charging Whereas in traditional networks accounting consists Figure 2: Actors and Contractual Relationships in the in counting the number of octets. while IC is concerned with direct customer relations and marketing activities of the e-health application. an authorized agent might trigger upon a certain threshold or event reached that updated stock market analyses are prepared by the service provider and sent to a second entity. exactly one in case a full charging. MNO takes the roles of a communications provider (for voice and data services) and of a billing provider. It should be the user who decides which level of anonymity she or he prefers: No the real identity of the user can be used in anonymity foreign domains. Section II. the roles of a service requestor. This division of tasks allows a user . NINO handles systems integration and runs the technical infrastructure. SPI and SP2 accordingly focus on their specific competencies in the role of grid service providers. while in more complex arrangements different actors play these roles. No service provider should have access to a users's real identity without the user's authorization.

SAML is a secure interoperable language used to share users' information from the A4C Server to other components in order to provide SSO capability to the user and to offer attribute sharing of the user to other components. and the section ends with an overview on how different QoS parameters can influence accounting mechanisms and charging policies. and protocols used for communication. this section describes the main components of the A4C architecture. Thus. A4C Architecture Design The A4C architecture presented in this paper is based on the generic AAA architecture [17] as defined by the IETF. Besides these. The two most important components are the A4C Server and the A4C Client. All communication between A4C Server and A4C Client is based on the Diameter protocol [5]. transported over HTTP. SAML provides an additional security block concerning high confidential information (such as authentication and attribute information of a user) in the A4C architecture. an A4C architecture for mobile grids was designed and prototypically implemented. A. the SSO functionality is supported by the integration of a SAML (Security Assertion Markup Language) Authority component. using any type of access network. Its main tasks cover authentication of users. The A4C Server contacts the SAML Authority when it requires to generate IDTokens and to verify such tokens presented by different components. SAML [21] is used to send security information in the form of authentication and attribute assertions to the mobile grid components. The physical deployment of the A4C Server might include several physical nodes acting as A4C Servers. i. Starting from the the identified requirements. for load-balancing purposes or for distributing A4C tasks to specialized nodes. Furthermore. that hold for all relevant levels. a SAML Authority is needed. The central approach has to be seen only in the context of the architecture design. The solution presented in this paper will be later evaluated in Section IV. grid service as well as content level. In order to provide support for SAML messaging.at hand. Additional tasks are the auditing of service consumption for QoS compliance and storing of user and service specific profiles. A4C Servers also have to manage interdomain related tasks such as authentication and authorization of roaming users. Diameter provides support for delivery of AVPs (Attribute Value Pairs). . For having success a mobile grid should allow its services to be accessible from anywhere.C against these requirements. The accounting and charging components and protocols need to provide the mechanisms to aggregate accounting sessions from different administration domains and allow the aggregation of different service charges into a single bill. the architecture uses a logically centralized A4C Server in every domain. For the communication between the SAML Authority and the A4C Server the SOAP protocol is used. capabilities negotiation. access control to services. A discussion about how inter-domain service composition is supported follows. extensibility through addition of new commands and AVPs and services necessary for applications. Its main task is to give network or grid components access to A4C services. * Deployment For integrating an accounting and charging architecture for mobile grids in an existing infrastructure of a mobile operator compatible technologies need to be used. The A4C Server is the central component of the architecture. Based on IETF (Internet Engineering Task Force) AAA standards. access control to services. All components of the A4C architecture are outlined in Figure 3. or accounting and charging for service sessions spanning across multiple domains. * Roaming and Mobility Typical users of a mobile grid are customers of mobile network operators. an A4C architecture for mobile grids was designed and prototypically implemented on foundation of existing AAA standards. Besides those specific requirements derived. service usage accounting and charging. key requirements and behaviors of AAA architectures as well as protocols are already standardized by the IETF and applied by network operators. Figure 3: A4C Architecture Components III. Besides these. error notification. All nominated tasks are services offered to components located in the same domain as the A4C Server in question. Each service component that requires one of the functionality the A4C Server provides requires to integrate an A4C Client. For achieving this. the A4C Server keeps all internal data integer and consistent. particularly network. The SAML Authority has been designed as an internal subcomponent of the A4C Server. This process was performed partially in the context of the Akogrimo [1] project Therefore. Its task is to generate XML messages based on the SAML standard for sending authentication and attribute information in a secure manner. A4C ARCHITECTURE In response to those requirements listed above. a mobile grid accounting and charging architecture has to be flexible enough to support the full role model set. such as session handling or accounting. its functionality. It aims at supplying IDTokens and SAML assertions to the A4C Server. and collection of data required for service charging. A more detailed view on the interactions between different components can be seen inFigure 4.e. As a clear must. The A4C Client is the counterpart of the A4C Server on the client side. Applications offered in a MDVO will most of the time aggregate services from multiple service providers. and it should be based on existing adopted or upcoming standards in order to be accepted widely by MNOs. the A4C Server is one of the key components in a service provider's domain as it provides those mechanisms for user identification.

QoS (Quality-of-Service) parameters for mobile grids will influence the accounting and charging mechanism with respect to context-based charging. Whenever services are automatically instantiated and aggregated by service composition entities. Besides these individual expectations. the set of QoS parameters for context-based charging needs to include the network. having a broader understanding of QoS than traditional throughput. The A4C Client sends an Accounting-Start-Request to the A4C Server of its own domain sing the Diameter protocol. the Charging component of the A4C Server in domain A can make a request to the A4C Server in the home domain of the user in order to check whether the user is authorized/able to pay for the service. are not standardized or commonly used so far. The use of parent sessions requires a close coupling of the service component to the A4C Client in the sense that services are required to be aware of the session ID of the attached A4C accounting session ID. Section lI.D). propose the complete set of parameters for the purpose of this work. and content view. and then charged accordingly. Thus. This request is also encapsulated in a Diameter message. The SAML Authority is implemented in Java. The IDToken does not reveal a user's real identity. the OpenDiameter library was chosen for the core of the A4C architecture. C. For instance. The IDToken is always generated in the home domain of the user. Figure 4 shows in more detail how the accounting process is realized for a service started in a foreign domain in our proposed architecture. thus. or accounting session for a running service session. Whenever a service component receives an IDToken from a user. an IDToken is generated and handed to the user who requested an authentication. units. the A4C Server is informed and a session record containing a summary of consumed resources and corresponding charges is created and sent to the A4C Server in the home domain of the user. The unique identifier is based on ongoing work performed in [25] and it is globally unique for each session. but only who can prove that the user is authenticated. In mobile grids. as C++ and as Java interfaces. If it proves to be valid. as well as for auditing the SLA compliance. Once the session is terminated. During the service provisioning phase. requirements for multi-service accounting and flexible charging mechanisms. while Domain A has the information required to charge Domain B B for the service session. it needs to contact an A4C Server for checking the validity of this IDToken. since guarantees given on one of these three levels influence the cost drivers of assigned accountable IV. based on previously defined policies. IMPLEMENTATION AND EVALUATION For the prototypical implementation performed. Multi-layer QoS Definition Both. so that service hierarchies across multiple domains can be formed. jitter and loss will determine the basis for mobile grid architectures. grid services. Session hierarchies have the purpose of keeping track of how multiple services interacted in order to assure the delivery of a more complex application. An IDToken is information that can be linked to a previous authentication event. thus preventing other larger jobs from being accepted. the metering component periodically sends accounting records for user's session using the C++/Java interface provided by the A4C Client. authorization. session hierarchies are created. delay. If required. A4C Session Model For accounting and charging purposes. since different customers will probably have different expectations on the service quality and they are ready to pay accordingly. Tracking of parent sessions assure that every service that was executed by a service provider can be linked to a session requested by a user. Domain B has enough information to charge the user for the consumed service in the foreign domain. The creation and transmission of this session record is the task of the charging component. the A4C Server can return the real identity of the user or a virtual identity. At this point. service sessions between service delivery components and users need corresponding A4C sessions between service management and monitoring components and the A4C Server. measure. If the user connects to the access network from a foreign domain the authentication request is forwarded to the home domain of the user. integrated architecture. if on grid level a considerable amount of main memory is reserved for one job request. To enable the integration of the A4C Client in grid components mainly developed in C++ and Java A4C Client interfaces are provided both. These accounting records are encapsulated in Diameter messages and sent to the A4C Server in domain A. B. which will generate an IDToken after authentication and send it via the A4C Server in the visited domain. For exemplification the network access service in a foreign domain has been chosen. Only on the networking level QoS parameters are widely understood to consist of the named parameters as they are presented in detail in the first section of Table 2 For the grid and the content level. . shows impacts on the costliness of service provision. but argues that flexible SLAs and QoS parameters are required for an inter-layer. The respective sections in Table 2. the metering service starts uses the C++/Java interface provided by the A4C Client to start an accounting session for that user. This paper does not address the mechanisms needed to signal. which embraces device and user context elements to be considered. For better understanding. have to be addressed by the A4C architecture in a multi-domain service provisioning environment (cf. The A4C components keep track of the session hierarchies by using two techniques: uniquely identification of each A4C session and tracking the parent session of each session. those parameters. The operating system used for development and testing of the A4C implementation is Linux. The session record is sent using Diameter protocol. An A4C session can be an authentication. Each time an authentication is successful. The remainder of the sec- tion will emphasize major implementation decisions and . The A4C Server and A4C Client are implemented in C++. and enforce the QoS at different layers. If everything is OK an accounting session ID is sent back to the metering component. As soon as a user accessed the network (in the foreign domain) and was authenticated. The IDToken can be used further by the user when requesting for services as a proof of authentication.Support for an SSO and anonymity is achieved by using IDTokens.

g. encoding) CPU Topol- ogy Reserved Throughput Memory Storage Confidentiality Integrity Anonymity Figure 4: Accounting Implementation Architecture in this paper a new authentication/authorization Diameter application was created as well as a new accounting application. and service sessions (such as user profiles. such as authentication in a foreign domain. The A4C Server controller defines a set of interfaces between different A4C Server modules for internal communication. or control of the inter-domain charging messages exchange.. available exclusively for grid-related communication The available amount of main memory available for a process on a given grid resource for a given time period The available amount of background storage available for a process on a given grid resource for a given time period or for permanent storage The guarantee that only authorized entities are provided access to a given piece of infornation The guarantee that data or messages are not altered in any way The guarantee that data or messages are not linkable with an identifying element of an entity The proof of the data or message origin The possibility to restrict personal information about an individual or group of individuals from being distributed to unauthorized entities Availability of an entity that assumes legal responsibility for the delivered content The guarantee that content can be inspected only in the presence of the corresponding decrypting key Parameters that modify the quality degree of a service based on specific context information (e. e. A. Diameter messages are pre-processed by the Diameter protocol handler as depicted in Figure 5 and delivered to the A4C Server module required to process the request. accounting. The A4C Server is implemented in C++ and acts as a stand-alone application. The internal architecture of the A4C Client (cf. the instruction set architecture in use The characteristic pattern of interconnections between single CPUs Guaranteed throughput. resolution.g. It also handles inter-domain-related tasks. SOAP was used simply because of the current OASIS specifications for SAML. but any other database can be used as long as it implements the interface defined. The database is used by the A4C Server. presence. B. or charging) on top of the Diameter protocol.Table 2: Multi-layer Quality-of-Service Parameters Domain A (foreign domain) Access Router Domain B (home domain) Jitter Delay/ Latency Connection Availability lne variance or the expected dutrerence minimal and maximal datagram delay between the The time between an event and the expected effect The ratio of the time a system is functional and the summarized time intervals a system is functional and not functional Packet Loss The ratio of packets that arrived at the destination and the total amount of sent packets Throughput/ The amount of information units transmitted per Data Rate given time interval Response Time CPU Type The time between a grid service request and the arrival time of the expected response The relevant set of CPU architecture architecture characteristics. Figure 6) is quite similar to the inter- . The implementation performed uses a MySQL database [18]. Based on the command code included in the Diameter packet the message is forwarded to the proper module. The A4C Client is responsible to set the right command code in the Diameter request sent to the A4C Server. accounting and auditing records. connection type. and authentication and authorization logs) and a SAML Authority. The A4C Server includes two external components: a database which stores all information related to users. A4C Client The A4C Client implements the client end of the respective applications in the A4C Server.g. service profiles. authentication. services. frames per second. tariff schemes. color depth. (e. location. device type. For the mobile-grid A4C implementation proposed Figure 5: Internal A4C Server Architecture The SAML Authority is implemented in Java [14] and the SOAP protocol is used for communication to the A4C Server.. mood) Guarantees that are specific for an application or a group of applications. but the possibility of using the Diameter protocol for the communication between the A4C Server and the SAML Authority is investigated. A4C Server Implementation The A4C Server implements a set of applications (e. Charging Module Authenticity Privacy A4C Databases Manager Policy Liability Encryption Contextspecific Guarantees Server Controller BASE SIP EAP SAML Auditing Non Rep Charging Acct Applicationspecific Guarantees DIAMETER Protocol Handler details of the A4C Server and the A4C Client.g.

C and all major identified requirements of the A4C. When the service session ends. accounting and charging for service sessions that are executed inside the domain. the EH Service component using its A4C Client starts an accounting session and requests a new database access service instance from SPI and a new computation service instance from SP2. The use of the Diameter protocol is fully in-line with those measures. This way a single point of failure is avoided and the basic robustness of the A4C server infrastructure is achieved. but it is outsourced to external applications through C++ and Java interfaces. Each domain operates an A4C Server that performs access control. Thus. Interdomain A4C Session 1 Service Session . on the other hand. * tion process. the IC can. * Accounting module It creates accounting sessions and handles the accounting messages related to service sessions.nal architecture of the A4C Server. IDToken validation. price) and are required for later billing. the IC can obtain from the MNO the session ID generated for the authentica- 3) Security Security determines the important topic for all tasks performed by the A4C infrastructure. Based on the IDToken. the next messages will be forwarded to one of the other servers from the same domain. even the latest is executed in a different administrative domain. all communication between the A4C Client and the A4C Server is handled by the OpenDiameter library. C++ and Java. service session duration.g. Authentication and Authorization (AA) module It is involved in the processes of initial authentication. Moreover multiple parallel sessions to different A4C Servers allows to load-balance the tasks of A4C infrastructure. Based on this information. summary of accounting data. and. the IC can distribute to SPI and SP2 revenue received for the EH Service. any service request in the IC domain can be related to an authentication process. C. In case the server who is serving a current client becomes unavailable..*- i Money Flow MNO Figure 7: Heart Monitoring Scenario Network Architecture Figure 6: Internal A4C Client Architecture As seen in Figure 6. As A4C session IDs are globally unique. Once charging records have been generated. this A4C Client implementation uses the Java Native Interface (JNI) concept and offers interfaces to the A4C Client library in both. Every service component integrates an A4C Client that connects to the A4C Server of the respective service provider domain. 1) Scenario Mapping Figure 7 depicts the network architecture used in the presented scenario. they are sent to IC. SPI and SP2 apply their own charging schemes on the accounted for data and generate charging records for each of the two services separately. include the costs of the two subservices in the price of the EH Service. Evaluation 2) Robustness of the Architecture Each service component maintains through its A4C Client permanent connectivity with several A4C Servers at the same time. the two services from SPI and SP2 can be related to the EH service. and service access authorization.. Intradomain A4C Session . On top of this. As grid services are typically implemented in Java. on one hand. SPI and SP2 account separately for their services based on their own policies and relate their accounting sessions to the session ID received from IC. All requests for the two subservices contain the accounting session ID of the EH Service. three major modules for handling messages are implemented: * Auditing module It handles auditing related tasks as non-repudiation of messages or event notifications. Any change in the internal A4C mechanisms can be handled locally in the module they belong to. Charging records are generated by the A4C Server of SPI and SP2. After the service request is received. The charging records contain information related to a service session (e.> ~'" . The EH (E-Health) monitoring service is started by connecting to the EH Service component in the IC domain and presenting the IDToken for proofing the authenticity of the user. Whenever a user connects to an access network of an MNO he is first authenticated and a network accounting session is started. The functionality of internal modules is made available to external applications through a set of interfaces.i i M o ble . This section runs a qualitative evaluation of the architecture proposed against the scenario described in Section II. without any impact on external applications or other modules. It shows the major difference that the control of different modules is not internally centralized. respectively. communication between A4C Servers and Clients can be secured by using dedicated IPSec and Transport Layer Security (TLS) channels between these components. The use of TLS and IPSec assures the confidentiality and integrity of the control data transmitted. . Based on those charging records received. The A4C Client is implemented in C++ and deployed as a Linux shared library.

on the integration with the architecture proposed into existing grid metering systems. and on the investigation of detailed grid accounting and charging policies. Guttman. Parallel and Distributed Processing Symposium 2003 (IPDPS 2003). Acknowledgements This work has been performed partially in the framework of the EU IST project Akogrimo "Access to Knowledge through the Grid in a Mobile World" (FP6-2003-IST-2-004293). Devetsikiotis. Calhoun. The solution proposed. Day. J. [8] technology-wise by an integrative effort of the various mechanisms discussed both for the A4C Server and Client compo- V. pp 1334-1340. the solution developed shows the first integrated approach on these subjects in a homogeneous architecture. T. Vol. Nice. Magowan. K.pdf.ac. http://www. GridToday. J. and Ruth del Campo (University of Stuttgart) in particular with respect to multidomain service provisioning and SAML issues are acknowledged kindly.hig. for security purposes SAML Authorities are required in each administrative domain. Finally. http://hovedprosjekter. 2000. Discussions with Peter Racz. [10] I. 1st IEEE/ACM International Symposium on Cluster Computing and the Grid. Hartley. Twigg: GSAX Grid Service Accounting Extensions. May . Loughney. nents. G. David Hausheer (University of Zuirich). Brisbane. which will enable grid service providers to bill for their service in an integrated manner. May 2005.pdf. this paper presented a new and extended A4C architecture for accounting and charging of such mobile grid services. R. Falkner. S. 6. Workshop Presentation. This is achieved by using IDTokens for authentication and having trust between different administrative domains. Gordon: Accounting. Arkko: Diameter Base Protocol. [9] M.e-irg.Additionally. IETF.no/v2004/data/gruppeO5/files/ cgc2004_report. pp 1-18. September 2003 J.D. April 2003. M. The Diameter protocol provides support for creating roaming-aware A4C applications. On the other hand. anonymity. Hawkins.uk/-sjn5/GGF/ggf-rus-gsax-01. 2. and flexible charging 2001. August 2005.org/meetings/2005-NL/johngordon-accounting. Vol. 5) Multi-Service and Multi-Domain Support The support of accounting and charging across multiple domains is provided by the use of globally unique session IDs for all accounting sessions and by mapping them to service hierarchies. addresses on one hand those requirements of single sing-on. only A4C Servers need to be deployed in every service provider domain and each service is required to integrate an A4C Client. [11] I. France. Barmouta: Authorization andAccounting Services for the World Wide Grid. J. while being in a foreign access network. E.mobilegrids. Australia. RFC 3588. Further work will be focused on the integration of a charging settlemtent entity. EU Research Project FP6-2003-IST-2-004293. M. [3] A.doc. while being charged by their home operator. the A4C servers may inter operate between two different domains by applying standard Diameter protocol messages and exchanges. December 1983. Camarinha-Matos: Infrastructures for Virtual Organizations . No. targeted at multi-service service provisioning platforms and spanning across several administrative domains. the use the SAML approach and its respective IDTokens for authentication of users enables a certain degree of anonymity by the hiding of user's real identity from the provider. 3. Vol. the A4C architecture proposed was implemented in key parts and successfully evaluated against a mobile grid scenario as well as major functional requirements. Beardsmore. or accessing services provided by third parties. which operates a customer database and which need to perform authentication. Study Project Report. P. Zorn. [5] [6] [7] http://www. IEEE Communications Review. Foster: What is the Grid? A Three Point Checklist. Lambadaris: An overview of pricing concepts for broadband ip networks. 1. In addition.ic. Wethal: Cluster and Grid Computing: Accounting and Banking Systems. Furthermore. Barmouta. Mandt. S. Frogner. multi-service accounting. A. 12. Extensions of the base protocol are specified and can be added on top of existing implementations. H. March 2006. September 2002. University of Western Australia. 'the last A'. 7) Deployment The A4C architecture described is fully based on the Diameter protocol. J.org. such as HPC clusters and computers. L. For each service an accounting record format is defined in the A4C Server database. every domain may offer independent services or mobility support functions on their own. Foster: The Anatomy of the Grid: Enabling Scalable Virtual Organizations.pdf. June 2004. thus making the integration in existing network infrastructures easier. I. Proceedings of the IEEE. Master thesis. IDTokens also provide support for anonymity. September 2003.Where We Are. [4] A. Zimmermann: The OSI Reference Model. No. pp 1-154. Thus. May 2004. pp 1-59. No. [2] A. Thus. [12] C. The A4C Server retrieves from this database the format of the accounting record expected whenever an accounting session is started. http:H www. pp 1-30. which is widely accepted by mobile operators. 71. Buyya: GridBank: A Grid Accounting Services Architecture (GASA) for Distributed Systems Sharing and Integration. Laws. 6) Roaming and Mobility The use of IDTokens and the trust relationship between different service providers allow users to authenticate. June 2002. pp 6-7. S. which will be based in user as well as customer preferences and provider application markets. 4) Single Sign-on Functionality The A4C architecture developed provides a key functionality for commercial applications: Single Sign-on. CONCLUSIONS AND FUTURE WORK Driven by the key set of newly developed requirements on accounting and charging of electronic service provisioning in Mobile Dynamic Virtual Organizations forming the concrete instantiation of a mobile grid . References [1] Akogrimo: Access to Knowledge through Grids in a Mobile World. Int. IEEE Conference Emerging Technologies and Factory Automation 2003.

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