Abstract

The applications built on wireless sensor networks are becoming increasingly attractive for monitoring and control applications in various domains such as smart building, home automation, smart transportation.  However due to characteristic of heterogeneous wireless network in terms of wireless network standards and application protocols, actuation in wireless sensor networks are still largely confined in isolated and constrained intranets, increases more complexities as the heterogeneous wireless networks grow bigger.  While standing in contrast to the concentrating the application logic on the sensing level,  solutions based on IP web will provide convergence for heterogeneous wireless networks, and more semantic interoperability in time and location, facilitating monitoring, control and automation. And furthermore authentication with both user and devices’s access to the web becomes even more significant in security concern. I will present the concept and web service architecture of our semantic sensor web by complying with multiple wireless sensor network standard and sensor web standard.

Introduction

Internet of things, which is the vision of a world where all electronic devices are connected together to form a single, coherent network of heterogeneous devices, is rapidly approaching to a reality, reshaping our world by collecting, processing, analysing huge amounts of real-time data produced from the physical world, thereby notifying users or actuating the devices according to application logic and domain contexts.

Over a long time, large volumes of environmental and personal health information created naturally through our surrounding physical world has been lost or confined in small scale constrained network environments. That is how wireless sensor networks comes to play, connecting a large set of wireless low cost, small size,low power nodes to sense all various of environmental factors such as temperature, humidity, imminence in our physical space. However merely putting application logic on the wireless sensor networks leads to many limitations and weakness.

First of all, the mote is generally resource constrained environments in terms of power,computation capacity and memory, putting application logic takes much space of resource. Booting and updating the software in that environment is also becoming a complex issue. Moreover the implementation of commercial WSN involves, in many case, wireless sensor standards,  and moreover proprietary application programming interfaces and protocol. The use of different proprietary data formats and protocols constitutes a bottleneck for the expansion of these networks, especially on the actuation. In general,  the price of converting different protocols gets higher as more heterogeneous networks are getting involved on the sensing level. For example, Zigbee and 6lowpan are both wireless sensor standards both adopting 802.14 standard who defines the Physical layer and Mac layer, but differs on the networking layer and application layer.

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This should give you a idea of how this could look like!

Therefore shifting the control from resource constrained environment to the IP based web gains enormous advantages over the disadvantages. First of all, with the existing robust Internet infrastructure in terms of standards, scalability, security, web can provide a more powerful environment in the storage, computation, and analysing , concurrently executing process, analysis, which in most circumstances are complex application logic, and invoking the notification and actuation simultaneously on the web service level. Various wireless network applications can be built on top of web instead wrapping the logic inside resource-constrained environment,  the radio-specific wireless network like zigbee should be less about processing application logic, but more on transporting the information. Historically, a network is likely to be more successful if the majority of its logic is pushed to the edges.
Moreover, web addresses the limitations of heterogeneous wireless networks by hiding the underlying layers, the network communication details, and heterogeneous sensor hardware.  In that sense, web offers the convergence of heterogeneous wireless networks through IP standards.

And the emerging concept of semantic web allows semantic information such as location, time to be added to  the sensor data, making raw sensor data meaningful to the web applications and naive users.. Semantic sensor web helps naive user to discover, access and search sensor data on the Web, building context – awareness applications.

Lastly, billions of users has been and will continue relying on the web for growing and reliable information. Obviously over years, web has evolved to be a inter-connecting platform that allow billions of users contributing, sharing, socializing, various applications and services are built upon it, serving the purpose of bridging the user and our digital world. Likewise, thought the web ecosystem, users can get access to exploding amounts of device-generated content in the similar experience, And this time, web serves as mediator building the gap between users and wireless network environment, the long term divide between virtual world and physical world is about to set change.

In going forwards from heterogeneous wireless network to semantic sensor web, several critical issues should be further discussed, including wireless sensor network standards, sensor meta data, sensor web ontology, a uniform solution of semantic sensor web is going to combine 3 of them for the further actuation and monitoring applications. While pushing the application logic to the web for monitoring or significantly controlling and automation, security becomes a critical issue that nobody wants his device to be maliciously accessed or controlled by people who have no authentication. Therefore authentication on the web for user getting access to his device is a pressing emphasis particularly.

 

The pros of zigbee is about its application profile agreed on by vendors, therefore the command identifiers and attributes defined in the public application profile work smoothly though the overall zigbee sensor network .

The cons of zigbee is mixing application logic with networking security methnizthm, and works slowly on its compatiability with IP6.

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