2009 International Conference on Network-Based Information Systems
Applying the Service-Oriented Architecture for Network Discovery and Selection in the Next Generation Wireless Mobile Networks Qiang Duan Information Science & Technology Department The Pennsylvania State University - Abington 1600 Woodland Road, Abington, PA U.S.A. email:
[email protected]
network for each user to meet the application requirements becomes a significant research problem. The related network control function is referred to as Access Network Discovery and Selection Function (ANDSF) by the 3rd Generation Partnership Project (3GPP) [14]. Although the networking research community has made progresses in this area, the currently available technologies for ANDSF are still on an early stage. Many important opening issues need further investigations. These issues include how to collect network information from heterogeneous access networks, how to make the information available for network discovery and selection, how to update the network state information in a real-time manner, and how to select the appropriate network that meets application performance requirements. The main challenge lies in the heterogeneity of the coexisting access networks and the wide variety of networking applications. Therefore a key to solving this problem is an network independent architecture that enables flexible and effective interactions among various heterogeneous access networks, the network control plane, and various user equipments. The research presented in this paper explores the application of the Service-Oriented Architecture (SOA) to tackle the network discovery and selection problem in wireless mobile networks. The SOA is currently gaining high attention and acceptance in IT industry, especially in the areas of Web Services and Grid/Clouding computing. The key feature of “loose-coupling” interactions in SOA makes it an effective architecture for coordinating heterogeneous systems to support various application requirements, which is essentially the same challenge faced by ANDSF in the next generation wireless mobile networks. Therefore, application of SOA in wireless mobile networks provides a promising approach to enhancing network discovery and selection. However, the current SOA technologies must be evolved to meet the special requirements of wireless mobile networks. Capability description for network services and performance-based network service selection play a crucial role in SOA-based network discovery and selection. The main contributions made in this paper include an service-oriented system architecture for ANDSF and the related technologies that
Abstract—The next generation wireless mobile network will be a heterogeneous networking environment consisting of various networks with heterogeneous implementations. Discovering and selecting the optimal networks for delivering an end-to-end networking service has significant impact on the service quality offered to networking applications. One of the main challenges to network discovery and selection is the heterogeneity of the coexisting networks in such networking environments. A key to solving this problem lies in flexible and effective interactions among the heterogeneous networks, the network control plane, and various user equipments. The Service-Oriented Architecture (SOA) is gaining high attention and acceptance in IT industry due to its power for coordinating heterogeneous systems for supporting various application requirements. The SOA offers a promising approach to facilitating network discovery and selection in wireless mobile networks. In this paper, we investigate applying the SOA principles in wireless networking environments and propose a service-oriented architecture for network discovery and selection. The developed architecture and technologies are network-independent; thus are applicable to various network systems in heterogeneous wireless mobile networking environments. Keywords-Wireless mobile networks; the Service-Oriented Architecture (SOA); network discovery and selection;
I. I NTRODUCTION In the next generation wireless mobile networks, users often own several possibly networked mobile devices. These devices support a number of heterogeneous access technologies with different radio access capabilities ranging from 3G specific accesses to access technologies like WLAN or WiMAX. The desire to increase service availability is driving the use of multimode terminals and the interconnection of different wireless access technologies. The evolving 3G wireless networks aim to provide access and services to all these devices. Quick evolution of wireless networks has led to parallel operations of heterogeneous network infrastructures, and various access networks will coexist for a long period time. On the other hand, the next generation wireless network aims to support user access to most computing applications available in the Internet. These applications have a wide spectrum of performance requirements on underlying networks. Therefore, how to discover the available access networks and select the optimal access 978-0-7695-3767-2/09 $25.00 © 2009 IEEE DOI 10.1109/NBiS.2009.19
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enable real-time dynamic network discovery and selection in heterogeneous wireless mobile networking environments. The rest of this paper is organized as follows. Section II summarizes the related work on access network discovery and selection. Section III introduces the service-oriented architecture and its application in networking. Section IV proposes a service-oriented architecture for network discovery and selection, and develops a general model for describing network service capabilities. The technologies for supporting real-time dynamic network discovery and selection are discussed in Section V. Section VI draws conclusions.
model. In the Push model, the ANSDF module may regularly send information about available access networks to user equipments. In the Pull model, the user equipment sends a request message to the ANDSF module. On receipt of this request message, the ANDSF module sends a response to the user equipment. The response message includes information about available access networks and/or inter-system mobility policy. The information provided by the ANDSF module about access networks include the type of access network (e.g., WLAN, WiMAX), access network identifier (e.g., SSID of WLAN network), and a preference value indicating the serving operator’s preference to access a particular access network. The 3GPP specification is still at an early stage and there are still many opening issues for further study. The current ANDSF procedure mainly focuses on interactions between user equipments and the ANDSF module. How can the ANDSF module interact with various access networks to collect their state information and how can the network information be made available for selecting the optimal networks are still unsolved issues. In this paper, we investigate the application of the ServiceOriented Architecture principles in wireless networking to come up with a service-oriented architecture for access network discovery and selection. Such an architecture allows flexible and effective interactions among various access networks, the ANDSF module, and the user equipments; thus enable real-time dynamic discovery and selection of the optimal access networks that meet application requirements.
II. N ETWORK D ISCOVERY AND S ELECTION IN W IRELESS M OBILE N ETWORKS Due to the drive for converged communication systems, access network discovery and selection recently attracted intensive attentions from both industry and academia. The wireless networking research community has made many progresses in this area. A system for a terminal-based approach that uses network assistance for network selection has been proposed in [2]. A decision making process that can be used in this system to provide candidate networks for service delivery to terminals is described in [3]. The authors of [12] have proposed an algorithm for network selection between UMTS networks and WLANs. A dynamic system to select the network for service delivery based on current market conditions such as cost attributes is presented in [4]. Network selection based on resource allocation strategy for most efficient resource utilization in a heterogeneous network environment has been proposed in [1]. A fuzzylogic based multiple-criteria decision making system to perform access network selection in a heterogeneous network environments is described in [7]. In [10] the authors develop a dual-stage process based on sequential Bayesian estimation for dynamic network selection. The utility theory is applied in [9] for developing a decision mechanism for access network selection. Although significant research progresses have been made in this area, most of the work reported in literature focuses on algorithms for making selection decisions. These decision making processes assume that the information about access network states and characteristics, which forms the basis for decision making, has already been made available. However, there still lacks an effective and flexible architecture that enables the interactions among various access networks, the network control, and the user equipments; which is essential for obtaining the information needed for network discovery and selection. The 3GPP recently developed a framework for ANDSF [14]. The 3GPP specification defines the interaction procedure between user equipments and the ANSDF module in network control plane, and the roles they play in this procedure. The ANSDF module can be in either Push or Pull
III. T HE S ERVICE -O RIENTED A RCHITECTURE AND I TS A PPLICATIONS IN W IRELESS M OBILE N ETWORKS The Service-Oriented Architecture (SOA) is an application architecture within which all functions are defined as independent services with well defined invokable interfaces, which can be called in defined sequences to form business processes [6]. In essence, services within the SOA are selfcontained, modular, interoperable, composite entities that can cooperate with other services in the shape of service level agreements. SOA provides an effective and flexible approach for cross-domain resource sharing through loosely coupling various computing components that are abstracted in form of services [15]. Collaboration within the SOA is illustrated by Fig. 1. A service provider publishes a service description at a service registry. The service description is a machine-readable document that gives descriptive information about the functions and accessing interfaces of the service. A service customer performs dynamic service location by querying the service registry for a service that matches its criteria. If a service exists, the registry provides the customer with the location and interface information for that service. Then the customer invoke the service by following the conventional request/reply mechanism. Typically a service broker maintains 381
the service registry and process service discovery requests for customers.
geneous network systems and applications, thus greatly enhancing the network intelligence. A network service provides an abstraction of the underlying networking resources. Such an abstraction hides the network implementation details while exposes the networking capability to various user equipments and applications for accessing. Therefore such a service-oriented control mechanism is independent with network implementations and applicable to various heterogeneous access networks. Another important feature of the service-oriented network control technology is that network services are composable. This feature enables internetworking across multiple different types of networks, which will greatly enhance user mobility among heterogeneous networking systems. The composability also facilitate integrating various access networks into the network core infrastructure, for example integrating non-3GPP access networks into the 3GPP evolved packet core (EPC) infrastructure.
service description
service registry service discovery
service customer
Figure 1.
service publication
service access
service provider
The service-oriented architecture.
Currently the Service-Oriented Architecture is mainly realized based on Web Services technologies. The key technologies for implementing SOA include service description, service registration, service discovery, and a message-based interaction protocol. Currently the standards for service description and discovery are respectively Web Service Description Language (WSDL) and Universal Description Discovery and Integration (UDDI). The Simple Object Access Protocol (SOAP) is the current standard protocol for message communications in the SOA. All these protocols are based on the Extensible Markup Language (XML) as a standard for sharing data among different computing systems. A special feature of SOA is the “loose-coupling” interactions among heterogeneous systems in the architecture, including service providers, service users, and the service broker and registry. “Loose-coupling” means entities can effectively interact with each other while keep themselves independent. It is this features that makes SOA an attractive solution to the problem of coordinating heterogeneous IT systems to support various computing applications, which is essentially the same challenges faced by the next generation wireless mobile networks. Therefore, the SOA provides a promising approach to enhancing the control intelligence in heterogeneous wireless networking environments. By applying the principles of SOA in the field of networking, the networking resources in various network systems can be encapsulated into “network services.” The capabilities of the network systems and the approach to accessing the networking resources in these systems are described in form of network service descriptions, which are published at a network service registry. When a network service user, which could be a networking application or a user equipment, needs to utilize the underlying network, it sends a request to a network service broker. The service broker discovers and selects the network service that meets the user’s requirements and optimizes networking performance as well. Such a service-oriented network control mechanism supports effective and flexible interactions among hetero-
IV. S ERVICE -O RIENTED N ETWORK D ISCOVERY AND S ELECTION A RCHITECTURE In this section we apply the service-oriented principles to develop an system architecture for access network discovery and selection in heterogeneous wireless networking environments. The service-oriented ANDSF system architecture is shown in Figure 2. In this architecture, each access network publishes a network service description at the network service registry. This network service description is a machine-readable XML document that provides all the necessary information needed for discovering and selecting the access network for a user application, including networking capability and state information, for example the supported radio interfaces and available transmission capacity. Whenever the network states change in an access network, the corresponding network service description will be updated. The network service registry is maintained by the network service broker. When a user equipment needs to utilize an access network, it sends a request message to the service broker. This request messages specifies the user’s demanding for network accessing and the criteria for selecting access networks. On receipt of this request, the service broker will search the service registry for all available access networks in the vicinity of the user and marked them as candidate networks. Then the service broker examines the service descriptions published by each candidate network at the service registry to select the access network that can guarantees the networking performance required by the user application. Comparing Fig. 2 with Fig. 1 we can see that the proposed ANDSF architecture is compatible with the SOA; thus can be realized by leveraging the key SOA technologies. For example the network service description can be implemented based on WSDL, the network service registry can be built based on UDDI, and the interactions between the service 382
user request
network user
broker reply
applicable to various network implementations. Let T in (t) and T out (t) respectively be the accumulated amount of traffic of a flow that arrives at and departs from a server by time t. Given a non-negative, non-decreasing function, S(·), where S(0) = 0, we say that the server guarantees a service curve S(·) for the flow, if for any t ≥ 0 in the busy period of the server,
network service broker
network service registry
network access
T out (t) ≥ T in (t) ⊗ S(t)
where ⊗ denotes convolution in min-plus algebra; i.e., h(t) ⊗ x(t) = inf s:0≤s≤t {h(t − s) + x(s)}. If a networking system guarantees each flow a service curve r(t − θ), such a system can be modeled as a latency-rate (LR) server [13] and the parameters θ and r are respectively called the latency and service rate for the flow. Many widely deployed network schedulers, such as weighted fair queuing (WFQ) and weighted round-robin (WRR), belong to the LR server category. In our service description approach, we adopt the service curve guaranteed by the route Ri,j as the QoS descriptor Qi,j in the matrix C. Since a service curve is a general data structure that is independent with network implementations, it is flexible enough to describe various networking systems. In a network where a route Ri,j can be modeled by a LR server with a service curve ri,j (t − θi,j ), the matrix element ci,j can be represented by a data structure [ri,j , θi,j ]. An end-to-end connection in heterogeneous wireless mobile networking environments typical crosses multiple heterogeneous networking systems, each of which can be virtualized as a network service. The service curve-based description model can be extended to support composing a set of QoS descriptor into one descriptor for an end-toend network route across multiple networks. Known from network calculus, the service curve S(t) guaranteed by a series of tandem servers G1 , G2 , · · · , Gn , which respectively guarantees the service curves S1 (t), S2 (t), · · · , Sn (t) to a flow, can be obtained through the convolution of all the service curves; that is, S(t) = S1 (t) ⊗ S2 (t) · · · ⊗ Sn (t). Therefore, the QoS descriptor of the end-to-end route can be obtained from the convolution of the QoS descriptors of the links provided by all single services. It can be shown that for n network links modeled respectively by the descriptor Qi = [ri , θi ], i = 1, 2, · · · , n, the convolution of this set of service curves for obtaining the end-to-end route QoS descriptor can be simplified as
network service description
access network #1
Figure 2.
access network #2
access network #n
The service-oriented architecture for ANDSF.
broker/registry and the various access networks can be implemented based on the SOAP protocol. However, the currently available technologies for service description and discovery in SOA must be evolved to meet the special requirements of wireless mobile networking. Network service description forms the foundation of service-oriented ANDSF. Current WSDL-based service description in SOA mainly focuses on functional information that describes what function(s) a service provides and how to interact with the function(s). However, a key characteristic that distinguishes one network from the others is the network capability for achieving a certain level of performance. Therefore, network capability information must be included in service descriptions for network discovery and selection. The main challenge of describing network service capabilities lies in the heterogeneity of the access networks coexisting in the next generation wireless mobile networks. Therefore, the service description approach must be independent with the architectures and technologies of the described networks, so as to be applicable to various heterogeneous networks In order to provide a general description model for network service capabilities, we define a Capability Matrix C. Given a network service S with m ingress ports and n egress ports, the capability matrix C is a m × n matrix ⎞ ⎛ c1,1 c1,2 · · · c1,n ⎜ c2,1 c2,2 · · · c2,n ⎟ ⎟ (1) C=⎜ ⎝ . . . . . . . . . . . . . . . . . . . . . .⎠ cm,1 cm,2 · · · cm,n where the matrix element ci,j is defined as 0 if no route exists from i to j ci,j = Qi,j if a route Ri,j exists from i to j
(3)
Qs = [rs , θs ] = [min{r1 , r2 , · · · , rn },
n
θi ].
(4)
i=1
(2)
This implies that the total latency of an end-to-end network route is described by the summation of the latency parameters of all links on the route, and the bandwidth of the endto-end route is limited by the link with the least transmission capacity.
and Qi,j is called the QoS descriptor for the route Ri,j . We adopt the notion of service curve from network calculus theory [5] to design a general QoS descriptor that is 383
Currently there are various mechanisms available for measuring and managing network state information, for example the technologies reported in [8], [11], which could be used to obtain the data for constructing service curve and building the matrix C. The methods of collecting network state information are implementation dependent and may vary in different networks, but the matrix C provides all network services a general and standard approach to describe their service provisioning capabilities. We propose adding a network service capability profile element into the WSDL document of network service description. Such a profile can be embedded into the network service WSDL document by following the Web Service Resource Frame (WSRF) specification [18]. WSRF provides a set of operations for managing state resources so that web services may implement to become stateful. Using WSRF standard, network services can be defined as WSRF-enable services. Within the WSDL description of a network service, a set of WS-resource property items can be added to describe the state information about the networking resources represented by this network service.
communications and management overhead. user equipment
network broker/registry
access network
network registration service description WSDL document, including WSRF property items
network state subscription subscription confirm notification message including network state update network service description update user request with demaining specification broker response ID for the selected network
access network discovery and selection
start accessing the selected network
V. I NFORMATION U PDATE FOR R EAL -T IME DYNAMIC N ETWORK D ISCOVERY AND S ELECTION
Figure 3.
In large scale dynamic wireless networking environments, the network states and capability information of various access networks change frequently. Therefore keeping the latest network information at the network service registry is significant for discovering and selecting the optimal access network. However, republishing the entire service description document whenever a network state changes may cause a large amount of communications and management overhead between access networks and the service registry. In order to solving this problem, in this paper we develop a mechanism for updating network states and service descriptions based on event-driven processing. Event-driven processing and notification introduces a pattern known as the notification pattern for SOA implementations. In the notification pattern (also referred to as the event pattern) of SOA, an information producer sends one-way notification messages to one or more information consumers. The Organization for the Advancement of Structured Information Standards (OASIS) provides a standard approach to notification using a topic-based publsih/subscribe mechanism [17]. By following this standard, the network service registry can subscribe to an access network and specify a set of network states as subscription topics. Then, the service registry will receive a notification message whenever a network state specified as a topic changes. In this way, the network service registry can obtain the latest network information for supporting real-time network discovery and selection. Since the notification message only contains the changed network states instead of the entire service description document, this updating mechanism greatly reduces the
Interactions in the service-oriented ANDSF architecture.
The interaction procedure in the service-oriented ANDSF architecture is shown in Fig. 3. An access network can make itself available by publishing a service description at the network service registry. The description WSDL document includes WSRF resource property items for various network capability information. Whenever an access network registries at the service registry as a network service, the registry will also subscribe itself to the network in order to receive notification for any change in network states. The registry can specify what network states it is interested in as subscription topics. After this registration-subscription procedure completed, the network service registry will be notified whenever the states specified as subscription topics change in the network. Then the service description for this network will be updated at the registry accordingly. In this way, the network service broker can always access the latest network information from the service registration. When the user equipment needs to utilize an access network, it sends a request message to the service broker with a specification of networking demand and performance requirements. The service broker searches the latest network service descriptions published at the service registry and discovers the access networks that are available in the vicinity of the user. The service broker will analyze the achievable performance of each candidate network based on the network capability information described in network service descriptions. Then the broker compares the achievable performance with the performance requirements specified in the user request message to select the network that meets the requirements. After
384
completing the discovery and selection process, the broker sends a response message back to the user equipment. The response message includes the ID for the selected access network with all information needed by the user to accessing the networking resources. Then the user equipment can start accessing the selected network.
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Quick evolution of wireless networks has led to parallel operations of heterogeneous network infrastructures, and various access networks will coexist for a long period time. Therefore how to discover the available access networks and select the optimal access network for each user to meet the application requirements becomes a significant research problem. A key to solving this problem lies in the interactions among various networks, the network control plane, and network users. The Service-Oriented Architecture provides a promising approach to enable such interactions. In this paper, we investigated the application of the serviceoriented principles in heterogeneous wireless mobile networking environments and propose a service-oriented architecture for access network discovery and selection. A general model was developed for describing network service capabilities. We also discussed the technologies that can be used in this architecture for updating network state information in a real-time manner without causing heavy overhead load. The developed model and technologies support dynamic and real-time discovery and selection of networks that meet the performance requirements specified by network users. The architecture and technologies are network-independent, thus are applicable to heterogeneous networking environments in the next generation wireless mobile networks.
[9] Q.T. Nguyen-Vuong, N. Agoulmine, and Y. Ghamri-Doudane, “On Utility Models for Access Network Selection in Wireless Heterogeneous Networks,” Proc. of the 2008 IEEE/IFIP Network Operations and Management Symposium, April 2008. [10] E. H. Ong and J. K. Khan, “Dynamic Access Network Selection with QoS Parameters Estimation: A Step Closer to ABC,” Proc. of the IEEE 2008 Vechicular Technology Conference, May 2008 [11] R. Prasad, M. Murray, C. Dovrolis, and K. Claffy, “Bandwidth estimation: metrics, measurement techniques, and tools,” IEEE Network Magazine, vol. 17, no. 6, pp. 27–35, June 2003. [12] Q. Song and A. Jamalipour, “Quality of Service Provisioning in Wireless LAN/UMTS Integrated Systems Using Analytical Hierarchy Process and Grey Relational Analysis,” Proc. IEEE GLOBECOM 2004, Nov./Dec., 2004 [13] D. Stiliadis and A. Varma, “Latency-rate servers: a general model for analysis of traffic scheduling algorithms,” IEEE/ACM Trans. Networking, vol. 6, no. 5, pp. 611–624, Oct. 1998.
R EFERENCES
[14] The 3rd Generation Partnership Project, “Access to the 3GPP Evolved Packet Core (EPC) via non-3GPP Access Networks,” 3GPP TS 24.302 v1.2.0, Nov. 2008.
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