Smart home architecture based on event-driven DPWS +

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1 J Shanghai Univ (Engl Ed), 2011, 15(5): Digital Object Identifier(DOI): /s Smart home architecture based on event-driven DPWS + CHEN Peng ( +), ZHI Xiao-li ( s) School of Computer Engineering and Science, Shanghai University, Shanghai , P. R. China Shanghai University and Springer-Verlag Berlin Heidelberg 2011 Abstract With the advances of electronic information technology and computer network, especially the embedded technology, smart home is no more just a vision but being practical. The interoperability of heterogeneous devices and flexibility of devices usage are two key problems that challenge the implementation of smart home. To deal with these two issues, this paper proposes an event-driven service oriented architecture using device profile for web services (DPWS). DPWS inherits the advantages of the traditional web services in achieving interoperability without dependence on platform, while improving service discovery and security as well as being optimized for deploying on resource constrained devices. By providing a visual interface for describing a service workflow (SW), the user can easily customize the actions of devices by services composition. Devices automatically cooperate without user s intervention to complete required business logic. This is achieved by fully exploiting the eventing capabilities on DPWS enabled home devices. Finally, a home theater scenario is given to illustrate the event driven mechanism for the SW in the proposed smart home framework. Keywords device profile for web services (DPWS), smart home, event-driven, service workflow (SW) Introduction In recent years, there emerge two major trends in the world of embedded devices. First, according to the Internet of things (IoT) vision [1],themajorityofthedevices will soon have the capabilities of computation and IP communication. second, in the Internet of services (IoS) vision [2], service oriented software technologies are becoming dominant in enterprise integration across different layers from shop floor device to decision-making application. These two visions provide a new approach to implement smart home. For smart home, web services is identified as a potential solution for solving interoperability of disparate systems. It also has many other merits such as platformindependence, scalable service aggressive, uncoupling of logical and physical aspects, seamless integration with enterprise networks and legacy technology, simplified application development, manageability [3], and so on. By applying this technology in embedded device, the function of the device is abstracted as a service, which will help to reduce the complexity of devices integration and provide a unified access interface [4]. Device reusability can be improved and collaboration among devices becomes possible. There are many middleware technology standards for devices connection and integration, such as organization for the advancement of structured information standards (OASIS) standards, UA standards, OPC-UA Received Apr.10, 2011; Revised May 20, 2011 Corresponding author ZHI Xiao-li, Ph D, Prof, xlzhi@mail.shu.edu.cn standards, ISA-95 standards, UPnP [5], Jini, and devices profile for web services (DPWS) [6].DPWSwhichtakes the same way as service-oriented architecture (SOA) [7] to integrate services, has prominent advantages in flexibility, reusability, combination convenience, massive communication and data protocol standards. Furthermore, it could be seamlessly integrated with high-level business software and is considered as a promising middleware technology for smart home [8]. Research work on smart home mainly concentrates on aspects such as heterogeneous devices integration, flexible collaboration among devices, home services automation, etc. For example, Perumal, et al. had applied embedded technology and web services technology in the connection of entertainment equipment, and their work indicated that web services maximized the interoperability and performance of different systems [9]. However the good performance of [9] is based on rich resource devices such as the embedded CPU supporting inputs and outputs of Ethernet connectivity with 4 ports and 1 GB of system memory availability, which can be hardly met actually as most of smart home devices are resource-constrained. Being different from web services technology s higher requirement on memory and processor, DPWS inheriting only the core protocols of web services is more suitable to smart home. Parra, et al. designed a flexible DPWS-based smart home architecture using a peer-to-peer (P2P) approach that each device or

2 J Shanghai Univ (Engl Ed), 2011, 15(5): service represents a peer and acts autonomously based on the application logic [10]. However, the logic should be pre-given and inconvenient to change. In this paper, the flexibility is expanded to the interaction with the user, and a service workflow (SW) agent is designed to flexibly create or destroy an SW. 1 Web services for devices DPWS, which was developed to enable secure web service capabilities on resource-constrained devices, is a subset of web services but adds a function of helping the client easily find a device service (DS) provided by the network. From web services for perspective [11],DPWS plays a lead role in devices finding target web services, moreover, ensures the devices in compliance with DPWS work together normally. Compared with the traditional smart home network based on embedded technology, DPWS realizes the device to plug and play. The device with DPWS deployed will automatically announce its name when entering the network and learn which other DSs are still online. In this way, devices can realize end-to-end communication and interoperability, and leave the network smoothly without any unnecessary information [12]. In contrast to other middleware technology, DPWS has shown a strong advantage in intelligent device support, platform independence, independent of the network transmission medium, scalability, security, etc. DPWS inherits many core protocols of web services, such as SOAP, WSDL, XML Schema, WS-Addressing, WS-Policy, WS-MetadataExchange, WS-Security, etc. Meanwhile, it also adds two other protocols: WS- Discovery and WS-Eventing, to support service-oriented devices dynamic discovery and interoperability [6] (see Fig.1). Fig.1 DPWS protocol stack DPWS defines the following build-in services: Metadata exchange: WS-MetadataExchange is a specification that defines data types and operations to retrieve metadata associated with an endpoint. It supports service-oriented devices and services metadata accessed dynamically. Services discovery: devices connected publish themselves and find other services by services discovery. There are two kinds of services, Hosting Service and Hosted Service, which help to support dynamic devices discovery, flexible distributed application development and devices seamless integration through web services interface. Events publish and subscription: to subscribe to events, subscribers must release subscription request message to express their interests in certain features. After a subscription request is received, the publisher automatically sends event notification about its current state to the subscriber, as its event state subscribed changes. A variety of lightweight DPWS implementation to small devices has been developed, which includes Microservices framework, esoap, ksoap, gsoap [13] and so on. By using XML type subset, optimized XML serialization, XML streaming technologies, message compression, and support for efficient binary data transfer, variant thin soap processors can be implemented. For example, gsoap code can be reduced to 77 kb. There is also other researches about how to implement web services on certain tiny devices, such as implementing web services in the MSP430 sensor node (48 kb ROM 10 kb RAM) [14]. This work indicates that DPWS can be developed on even very tiny devices. Thus, it is flexible for home devices to be DPWS enabled. 2 DPWS-based smart home design From Section 1, it can be observed that DPWS supports different devices integration with zero configuration, independent networking, self-discovery and other desirable functions, especially, in the service discovery and time processing. This section will present a DPWSbased smart home design, which gives full support of service-oriented architecture. In this design, devices interact with the user in form of services, which can be real atomic services provided directly by devices or highlevel abstract services combined by underlying services in order to provide a more comprehensive and reliable service. 2.1 DPWS-based architecture for smart home The DPWS-based architecture for smart home proposed in this paper is divided into three levels from top to bottom: user layer, middleware layer and device layer, as is shown in Fig.2. In user layer, two types of the user interfaces are provided: browser and SW terminal (SWT). The user can directly access target DSs through a browser, or describe an SW to an SW agency (SWA), which composite chosen services automatically to fulfill user s business logic.

3 388 J Shanghai Univ (Engl Ed), 2011, 15(5): In middleware layer, the SWA analyses user s workflow description and puts component services together into a whole to form a self-governing ecosystem. In device layer, devices encapsulate their implementation details in the form of web services. As the basic unit of business logic, a DS could be provided by either an independent device or act as a service proxy for those physical devices not DPWS enabled. 2.2 Two control methods of device services There are two ways to control DSs: direct control by a browser and indirect control by an SW. Direct control is a method that the user chooses target devices and their functions directly through a browser interface. Although this approach is simple and flexible, it is highly dependent on the user s real-time participation sometimes. Indirect control is a method that the user can easily customize the actions of devices by services composition, and the process of indirect control is shown in Fig.3. (i) User chooses an SW through SWT. If the SW is pre-defined, the user can simply select a target mode. Otherwise, the user has to specify a new SW by choosing target services from available services list and describing the logic among them. For example the user chooses two services: S Projector control and S DVD control, and then gives the trigger conditions between them: when Projector opens, the DVD begins to play. (ii) SWA informs all involved services of their logical relationship. Still keeping the above example, the SWA will notify S DVD control after a SW description is received: subscribe to S Projector control, and begin to play when the Projector opens. (iii) Target DSs subscribe to their predecessors. A service s predecessor is the service to which it subscribes for certain events, and a successor is that service which has event subscription to it. For example, S DVD control subscribes S Projector control. Thus the latter is the predecessor of the former. (iv) Devices keep listening to event notification from their predecessors. Once receiving a notification that matches its trigger condition, the device will run the right service operation, or else continue listening. Fig.2 DPWS-based architecture for smart home Fig.3 Process of indirect control 2.3 Structure of the SWA The SWA contains three main components: user interface module, service analysis module, message passing module. The structure of SWA is shown in Fig.4. Fig.4 Structure of SWA

4 J Shanghai Univ (Engl Ed), 2011, 15(5): The user interface module implement the SWT in Fig.2. Through the SWT all available DSs and predefined SW of the network are displayed. User can choose any pre-defined SW or define a new one by selecting the target devices and describing their logic. The service analysis module is used to implement the mapping between a SW and involved services. The main part SWA itself as a DS keeps open and constantly listening. While a hello packet or bye packet from a certain service is received, the SWA adds this service to or removes from the current available services list on its own initiative, keeping the latest records of all available services. To create a new SW, this module analyzes user s description into business logic by setting for each target service predecessors and successors which together reflects the subscription relationship among different DSs. The current service subscribes to its predecessors and will start to run when subscribed events occur. Similarly, the current service is subscribed by its successors. For example, the target DSs chosen are S projector control and S DVD control, with the relationship description between them as: DVD begins to play when the Projector opens. After service parsing, the description is transformed into business logic as following: (i) service = S projector control, open; predecessor=0; successor= S DVD control, play. (ii) service = S DVD control,play; predecessor= S Projector control, open; successor = 0. The message passing module is used for sending logic to DSs and notifies them subscribe to predecessors actively. Once the current state changed, predecessors will send notification to their successor services to run corresponding operations. In this way, device services can collaborate well with each other. 3 Scenario for home theater 3.1 Description of home theater The home theater, as a custom SW, involves the following services: S DVD control, S Projector control, S Speaker control, S Lighting control, S Curtain control. The scenario is described as following: when the Projector is switched on, which means the home theater SW started, DVD and Speaker will be turned on, Lights will get dim and Curtains closed automatically. The business logic is shown in Fig.5. The event subscription information about the home theater SW can be described as following: the services S Lighting control, S DVD control and S Curtain control subscribe to the S Projector control while the S Speaker control subscribes to the S DVD control. Thus when its status turns to open, the Projector will send notification to the S Lighting control, S DVD control and S Curtain control,and then the S Speaker control is notified to open. Similarly, when the Projector is turned off, DVD and Speaker correspondingly get closed, the Light bright while Curtain open. At this time, home theater SW is closed. Fig.5 Logical relationship among DSs in home theater SW 3.2 Event-driven process for home theater The time-sequence of DPWS event messages among DSs in the home theater SW is illustrated in Fig.6. The SWA keeps open to listen whether there are devices to join or leave the network. As is shown in Fig.6, when the devices Projector, DVD, Speaker, and Curtain join the network, they take the initiative to send hello packets. As soon as these packets are received, the SWA adds new devices information into available services list. Through interacting with the user, the SW and target services can be determined. The next step is for the SWA to analyze services description and send logic information to DSs. Then DSs actively send probe packets to subscribe to services they concern. In addition, apart from the indirect approach, the user can also directly control all of the devices without the involvement of the SWA. Fig.6 Time-sequence of DPWS event among DSs 3.3 Implementation There are many methods to deploy DPWS on devices of smart home theater, such as.net Micro Framework [15],kSOAP [16],gSOAP [17 18],etc. Here, the gsoap toolkit (version 2.7.3), based on a SHIP development board with a 33 MHz ARM7TDMI Microcontroller, is adopted to implement the DPWS for the

5 390 J Shanghai Univ (Engl Ed), 2011, 15(5): home thearter. The gsoap toolkit can help to deploy diverse DPWS applications developed by C/C++ and provides support for SOAP interoperability. The SHIP board has a built-in support for the TCP/IP protocol stack with an Ethernet interface, and can be easily plugged into various home devices. The SHIP board has a minimal operation system but that is enough for supporting DPWS, and nearly 448 kb memory for application. A minimal web service application developed by gsoap only takes about 65 kb memory. In order to run gsoap successfully on SHIP, some changes related to MACRO definitions have to be done in gsoap header files such as configure.h, soapdefs.h and stdsoap2.h. In addition, the certain constants concerning GNU libc portability also must be changed. 4 Conclusions There are two main problems in the field of smart home: interoperability of heterogeneous devices and flexibility of devices usage. In this paper, DPWS is adopted as the middleware to ensure interoperability of a verity of resource constrained smart home devices. On one hand, DPWS is independent of platform, programming language and transport protocol, and can provide the flexibility of adding or removing new or existing devices to/from the home network. On the other hand, a mapping mechanism is proposed with the support of DPWS eventing to expand the flexibility from devicelevel to user-level. In addition the event-driven SW is illustrated by a home theater scenario. Theoretically, the architecture proposed in this paper can provide an implementation reference for smart home well with a full consideration on interoperability and flexibility. However, there exists a shortage of this framework. Since DPWS enables all the web services of smart home exposed to the Internet, the architecture may bring about security issue, and our further work will be focused on this problem. 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