Christos Chrysoulas #, Nicolas Sklavos #, Athanasios P. Kakarountas *

Transcription

1 Enhancing Service Portability in Upcoming 3G UMTS Networks & Security Aspects Christos Chrysoulas #, Nicolas Sklavos #, Athanasios P. Kakarountas * # Informatics & MM Dept, Branch of Pyrgos, Technological Educational Institute of Patras, Rhga Feraiou Street, Pyrgos, ZIP 27100, Greece cchrys@ece.upatras.gr, nsklavos@teipat.gr * Dpt. of Informatics on Management and Economics Technological & Educational Institute of Ionian Islands Lefkas, Greece, kakarountas@ieee.org Abstract Compared to other wired networks, complexity in the 3G UMTS is due its interactions with different entities. Within the UMTS, services have to deal with a great number of different QoS, small user display, variant bandwidth and small battery power. Most of the services are generally bind to the particular systems or APIs. In this article, we look at the evolution of different technologies on which such service are build and apply the Web services framework to achieve the portability of the such services We take the example scenario and build the Web services model which can be implemented and deployed in the UMTS network. I. INTRODUCTION Although Long term evolution (LTE) [1] is the next release of 3G UMTS system, in this article we look at the architectural trend which it has taken and will be followed in the next releases also. One of the main trends is to put more and more functionality into the same logical/physical node, like putting more functionality in the node B. The other important trend is to put the functionalities as close as possible, avoiding the cross node functionalities as it was common in the earlier releases of UMTS. Such a system will be build to change and probably have the incremental development cycle as far as the services and end-user application are concerned. Most of the entities will be loosely coupled and the implementation will be hidden through the abstract interfaces. A. Service Oriented Architecture A framework in which different logical entities provides services to each other through some standard manner is called Service Oriented Framework. A system based on such architecture framework is considered as Service Oriented Architecture (SOA) [2]. In SOA, services can interact with each other by passing data. Such an interaction can involve multiple services, providing a fully coordinated activity. An example of such service could be the authentication of user through AAA server. Such an authentication service could involve calling several services of different AAA entities. Any such service is generally self-contained and will not depend upon state or status of any other entity within the system. Services based on SOA has the inheritance characteristic to be portable as they all use the generic interfaces and can be controlled, managed, deployed in the same manner. Web services (WS) [3] is one of the ways to accomplish SOA within the System. In such a system, there are three entities namely the service provider, service consumer and service broker. Simplest form of WS will include the Simple Object Access Protocol (SOAP) for the service request and response, Web Services Description Language (WSDL) for the service description and optionally the Universal Description, Discovery, and Integration (UDDI) for the service discovery. WS further can be enhanced with the functionalities required by the system. For example, for the security and privacy of communication WS-Security, XML- Encryption, XML-Signature can be applied. If the parts of the Web services based system is implemented by different vendors, then the Web services-interoperability (WS-I) Basic Profile Specification can be applied to achieve the interoperability between WS. If the services with in the UMTS will be implemented using SOA, then they will be automatically portable. Rest of the article is organized as follows. Section 2 describes the Evolution of mobile cellular Network and SOA. Service Architecture in LTE and beyond is explained in section 3. Section 4 describes different services and interfaces in LTE. Finally, section 5 draws a conclusion about current research and future work. II. STATE OF THE ART A. Evolution of Mobile Cellular Networks Earlier Public switched telephone network (PSTN) has used the signalling system 7(SS7) for the call management, routing and billing. It was relatively simple architecture due to circuit switching (CS). Public land mobile network (PLMN) like 3G UMTS today has to deal with different resources and QoS hence the system is more complex than the earlier networks based on CS. Initially 3G UMTS has taken the same approach for the signalling and used the SS7. Recently, SIP based signalling evolved, which is based on the ideas of HTTP and other related network protocol like SMTP. HTTP and later on

2 XML were the main protocols for the evolution of Internet/SOA. As the PLMN architecture moved towards the Packet Switched (PS) from the CS, more and more SIP based signalling will be used in the future. Worldwide GSM success was due to proper interfaces but it has more issues in deployment/implementation/testing. Most of the GSM entities interact with each other using standard interfaces. MSC interfaces with HLR using logical C interface on the other side HLR and AUC interact with logical H interface. GSM also kept the different functionalities at the different physical or logical nodes. As an example, mobility management (MM) functionality is controlled by MSC, which includes channel allocations, location registration, paging, and handover. However, during the evolution of UMTS first with HSDPA/HSUPA and now with LTE, functionalities are more and more located in the single node. As example, Functionality like radio resource management, HARQ will be in evolved- Node B. After GSM, UMTS added more flexibilities and considered the QoS and related issues. As a result, high data throughput for the same applications can be achieved. This also allows for the more fine-grained controls of resources and hence providing even better charging capabilities (e.g. service and content level charging). Current architecture of the UMTS has taken the layered approach with the transport and bearer services separated from the signalling network and other controlling services. Infect the IMS architecture in the UMTS release 6 had already took a step forward with the SOA. As an example, interworking elements like MGCF, IM-MGW, SGW and databases like HSS, SLF and other related entities provides the different interfaces for the user and for the signalling traffic. B. Evolution of Internet Even before the success of internet and WWW, FTP and other related protocols were able to handle the files transfer between computer nodes. HTTP has taken almost the same path but introduced the HTML as the output format. Later on, Common Gateway Interface (CGI) added more control for the information provided by the HTTP. Initially, it provided dynamic contents from the web server or used for calling the executables on the web server. CGI evolution dramatically changed as it started providing access to the back-end databases together with the session handling. CGI concept was further revolutionized with the introduction of Servlets, java server pages (JSP) and the Active server pages (ASP). Concept of Cookies in one or other form provided the required session handling between the subsequent web requests. HTTP and HTML are the ASCII format and it was one of the main reasons for their success as the contents were readable and easy to parse. It was also possible to use them without any special changes on the different platforms. Another simple ASCII format XML was yet another success, which is now used in the SOAP protocol. SOAP is used for the request/response through the server and able to handle more complex data and objects. SOAP technology led the concept of SOA, which presents any functionality of the system is terms of services and data within the system flows due the services interaction. SOA can be implemented using different technologies. If WS will be used for the SOA implementation then service are represented using the XML format. SOA at its easiest defines is the software architecture with different entities loosely coupled through software services for the different business requirements. SOA can be implemented using any of the technology available like SOAP but can be very simple like RPC or may be very complex CORBA implementation. Using WS, the different service interfaces are described using WSDL that also describes the protocol bindings and the message format required for the interaction with such services. Another XML database called UDDI allows the seamless discovery of services offered by the WS. Portfolio of today SOA using WS includes different new specification and formats for providing encapsulation, loose coupling, security, reliable messaging, transactions, metadata, inter-operability and more. Most of such functionalities were earlier existed within their own domains only. Using WS these functionalities can be provided easily within the LTE system. Interoperability across platforms, programming languages and operating systems is the main factor for the SOA success. In the telecommunication industry almost the same concept i.e. interoperability drove the architecture and design of GSM and UMTS to worldwide success. Therefore, today s Internet and enterprise application architecture (EAA) is already evolved and utilizing the concept of SOA. We understand that the success of current Internet and EAA is due to the open service based architecture, which allows providing different implementations for the different functionalities and services. In the next section we will see how the same concept can be applied in the future mobile networks. III. SERVICE ARCHITECTURE IN LTE LTE architecture has the concept of a 2-node architecture, based on the draft specifications. Figure 1 shows some of the interfaces within the LTE. Details of other entities and interfaces can be found in [1]. It has one logical node for the radio access network (RAN) called evolved-ran and other logical node as core network (CN) called evolved Packet Core Network (evolved-pcn). As there will be only 2 nodes in the LTE, some of the external or existing services like AAA can be accessed through the SOA type interfaces. Layered approach will also allow the addition of new services within the LTE architecture. For example, the interworking architecture with WLAN, DVB-H, and WiMAX, which utilizes the S2a/b interface or the SGi interface for AAA, can be wrapped with WS from the connecting operator. This will allow the fine grain control of the given interface, which can be integrated into their existing system. Without this approach, management of such interfaces could be relatively complex. Once the interface is accessed through WS, a generic approach can be taken for its control and management [4].

3 Fig. 1. LTE Architecture Proceedings of IEEE Mediterranean Electrotechnical Conference (IEEE MELECON'10), specification and implement it using SCA and look at the LTE implications. A. Configuration and Control of the LTE Entities Generally 3G network entities are deployed and maintained throws the fixed interface system, using monitoring tools and using remote terminal. This kind of management of entities, leads to the upgrade and deployment delays, as entities are tightly coupled with each other s. Generally entities depend upon the configuration parameters for the change management. Taking an example of AAA entity, which interacts with LTE s Evolved Packet Core Network (PCN), through S6 Interface. Any parameter change in the AAA entity leads to the change in the configuration parameter of GSN nodes. There is no automatic way to request for the update/change in configuration. Situation can be different, if AAA functionalities are provides as one of the several service, which can be dynamically changed/configured using the SOA framework. In the SOA terminology, update/change of configuration parameter is yet another service, which is provided by the AAA entity. B. SOA in Interworking One of the main issues in interworking and convergence is the interoperability. Different components come from the different sources/companies. Even, they interact with standard interface; still they have to pass the Full conformance and interoperability testing which is a very complex process. There is an easy way to handle interoperability within the interworking architecture by using WS-I [5]. WS-I Basic Profile Specification is the first step to make interoperability at the WS level easy. Those interfaces, which are critical for the functioning of the given interworking architecture, can be managed with WS. Based on the current LTE draft, interface S6, which enables transfer of subscription and authentication data for authenticating/authorizing user access to the LTE system, can be provided by two different providers. Assuming each provides implements a part of the functionality then whole system can be made using the WS and further WS-I can be applied to guaranty the interoperability between both providers. A. Open Service Access Open Service Access (OSA) is a service framework for the 3G UMTS application and end user services. It allows applications to use network services easily by hiding the network complexity. These network services are provided as a set of services capability features (SCF) within the OSA framework. Although OSA tends to hide the network complexity, implementation of OSA APIs or in other terms service provider interface (SPI) is a very complex as far as the design and implementation are concerned. This is obvious after looking at the requirements of OSA [6], which includes: Independent of programming languages, operating system; underlying communication technologies Secure, scalable and extensible Independent of location and transport mechanism On top of such requirements it is recommended that the state of art access technologies like WS might be considered. B. Service Component Architecture SCA is a collection of specifications and methods, which extensively uses existing WS protocols related specifications, for the design and implementation of services. Fig. 2. SCA Component: service and references SCA supports many programming languages for the implementations as it only describes the service as a model. In the SCA terminology, an entity that provides some services is a component. These components provides services through the interface called service and can use other services through the interface called service references as shown in Figure 2. In a SCA based system whole functionality of the given system can be a collection of different components interacting using the service and references pairs. An implementation of particular component is underlying call, which can be changed or updated during the assembly of particular SCA component as shown in Figure 3. IV. SERVICES AND INTERFACES In this section we look at the framework for accessing services from the application perspective. We introduce the Open Service Access (OSA) [6] and look how it can be implemented using the state of art WS technologies like SCA. We take an existing example application from the Fig. 3. Processes using SCA components

4 V. SECURITY ASPECTS & GRID COMPUTING Security issues for wireless communications [6] could be applied, by adopting architectural and implementation aspects from other technologies [6-11] like Grid computing [9-10]. Grid architecture is structured in four layers (Figure 4), where each layer has a specific function. Application & Serviceware Layer Middleware Layer Resources Layer Supercomputers, Storage, Servers, Sensors Uniform Computing Access Authentication, Authorization Communica tion Services Uniform Data Access Unix & OGSA Hosting Grid Information Service Security uniform access to the resources, schedules the applications and organizes the data distributions. It also provides security framework, authentication and authorization protocols for the Grid enabled applications to secure the data transmission. The recent grid toolkits enable the Web Services for data distribution through open standards such as OGSA (Open Grid Service Architecture) or WSRF (Web Services Resource Framework) or OGSI (Open Grid Service Infrastructure). This layer must be completely transparent for the user. D. Application / Serviceware Layer This is the highest layer of the structure, which includes applications in science, engineering, business. This enables the use of resources in a grid environment through various collaboration and resource access protocols. Finance and more, as well as portals and development toolkits to support the applications. This is the layer that grid users see and interact with them. The application layer often includes the so-called serviceware, which performs general management like tracking who is providing grid resources and who is using them. Grid portals offer Web-enabled application services, where the users can submit and collect results for their jobs on remote resources through the Web. Network Layer Switches, Cables, Routers Fig. 4. Grid Layers A. Network Layer The lowest layer is the network that connects network equipments, such as routers and switches. That carries the communication protocols for resources and data sharing in a grid environment. B. Resource Layer Above the network layer lies the resource layer which corresponds to the whole resources that may be shared at the grid environment. This includes computational resources (memory and cpu), computers (such as PCs, clusters) with variety of operating systems (such as UNIX or Windows), storage systems devices, databases, electronic data catalogues, and scientific instruments such as sensors and telescopes that are connected to the network. This layer uses the communication and security protocols (defined by the network layer) to control secure negotiation, initiation, monitoring, accounting and payment for the sharing of functions of individual resources. The resource layer calls the resource layer functions to access and control local resources. C. Middleware Layer This is the brains of a grid environment. Provides the tools that enable the various components (servers, storage, networks, etc.) to participate in a grid. The middleware layer provides E. Grid Components & Transactions The Grid environment consists of various components. The most important of that are: - Resource Broker (RB): This acts as the middle man in the grid.it finds the best site to execute your job anywhere on the grid. - Information Services (IS): It delivers up to date information on the status of the sites and services. - Replica Catalog (RC): This is the yellow pages for the grid environment. It stores information about the location of all data files. - User Interface (UI): UI is the user own computer. It hosts all the programs to interact with the grid. - Logging and Book-Keeping (LB): Service stores information about the status and history of submitted job. - Computing Elements (CE): Provide CPU power. They are typically-duster of worker nodes (i.e. a farm of PCs). - Storage Elements (SE): Provide storage resources and access to mass storage systems. In Figure 5 the common transactions between Grid entities are represented. A user will enter the grid using a software interface (either a grid web portal either an ssh/telnet protocol) that runs on the user computer. After clearing security validation the user computer will be able to talk to the core of the grid environment, the Resource Broker (RB). The RB will find the best resources to execute your job anywhere on the grid. It will query the Information Service (IS) to know which hardware and software are available at the moment and the Replica Catalog (RC) to know the locations of all existing data. Once the appropriate resources have been located, the job is executed and the RB send the result back to the user. To

5 the eyes of the user, the grid acts as a single, huge and powerful computer. Available Grids specific implementation of an OGSA-based Grid security architecture that include as part of the Globus Toolkit Version 4 (GT4). Given the prominent use of Globus within the Grid community, let us briefly revise such implementation. Grid Client reguest response Information Service (knows the Available HW and SW) Fig. 5. Grid Transactions Resource Broker Replica Catalogue (knows the exact location of data) F. Virtual organizations The users of the grid (either are individuals or computing resources) can be organized dynamically into a number of Virtual Organizations (VOs), consisting of resources, services, and people collaborating across institutional, geographical, and political boundaries, each with different Policy Requirements. The collaborations involved in Grid computing lead to the emergence of multiple users/groups that function as one unit through the use of their shared competencies and resources for the purpose of one or more identified goals. Users can join into several VOs, while resource providers also partition their resources to several VOs. G. Grid Security Infrastructure In grid computing environments, the mutual authentication and information service are serious issues [9, 11]. Before their applications are running, the users need choose hosts based on security, availability and many other aspects. The GSI (Grid Security Infrastructure) is designed as one very important part of the Globus grid toolkit. The GSI uses public key cryptography (also known as asymetric cryptography) as the basis for its functionality. The primary motivations behind the GSI are the need for secure communication (authenticated and perhaps confidential) between elements of a computational Grid and the need to support security across organizational boundaries, thus prohibiting a centrally-managed security system. Finally, a fundamental issue is to support single signon for users of the Grid, including delegation of credentials for computations that involve multiple resources and/or sites. GSI, which is designed to solve the security in Globus system, is based on RSA encystations algorithm and employs a standard (X.509v3) for encoding credentials for security principals. Thus, enables secure authentication and communication over open network. At the same time GSI enables Interoperable with local security solutions without changing anything. The Grid Security Infrastructure (GSI) is a VI. CONCLUSIONS In this paper, we applied the concept of SOA in the telecommunication industry. We looks at the architecture of future 3G network like LTE and worked on the example scenario. We modelled this scenario and explained how the system can be modelled for Web services and SCA. We explained the design approach for the example application and modelled its service objects and messages. The OSA based approach takes away the complexity from the application developers or the users of OSA APIs by hiding them using standard APIs. In the current article we had shown how the complexity could be reduced for the system developers or the providers of those APIs. This is done using the WS and its related technology like SCA. Future work in this area will include looking into the LTE and SOA concept using the simulation analysis to understand and analyze the protocol overhead using this approach. Currently we are working on the simulation scenario, with and without the SOA based architecture. 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