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Contents lists available at ScienceDirect
Ad Hoc Networks journal homepage: www.elsevier.com/locate/adhoc
Survey Paper
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Choices for interaction with things on Internet and underlying issues Ibrahim Mashal a, Osama Alsaryrah a, Tein-Yaw Chung a,⇑, Cheng-Zen Yang a, Wen-Hsing Kuo b, Dharma P. Agrawal c a
Innovation Center for Big Data and Digital Convergence, Yuan Ze University, Taoyuan, Taiwan Department of Electrical Engineering, Yuan Ze University, Taoyuan, Taiwan c Center for Distributed and Mobile Computing, EECS, University of Cincinnati, OH 45221-0030, United States b
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Article history: Received 11 June 2014 Received in revised form 22 October 2014 Accepted 15 December 2014 Available online xxxx Keywords: Internet of Things Social Internet of Things Social Web of Things Web of Things Wireless Sensor Networks
a b s t r a c t Currently, a large number of smart objects and different types of devices are interconnected and communicate via Internet Protocol that creates a worldwide ubiquitous and pervasive network called the Internet of Things (IoT). With an increase in the deployment of smart objects, IoT is expected to have a significant impact on human life in the near future. A major breakthrough in bridging the gap between virtual and physical worlds came from the vision of the Web of Things (WoT), which employs open Web standards in achieving information sharing and objects interoperability. Social Web of Things (SWoT) further extends WoT to integrate smart objects with social networks and is observed to not only bridge between physical and virtual worlds but also facilitate continued interaction between physical devices and human. This makes SWoT the most promising approach and has now become an active research area. This survey introduces necessary background and fundamentals to understand current efforts in IoT, WoT and SWoT by reviewing key enabling technologies. These efforts are investigated in detail from several different perspectives such as architecture design, middleware, platform, systems implementation, and application in hand. Moreover, a large number of platforms and applications are analyzed and evaluated from various alternatives have become popular during the past decade. Finally, we address associated challenges and highlight potential research to be perused in future. Ó 2015 Published by Elsevier B.V.
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1. Introduction
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The Internet has become an indispensable global communication network between people. It supports communications between devices ranging from desktop computers to small handsets. Billions of people rely on the Internet in daily live, work, and business operations. In recent years, Internet has been further extended to connect things, such as power meters, heart beat monitors,
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⇑ Corresponding author. E-mail address:
[email protected] (T.-Y. Chung).
temperature meters, and many powerful operations, such as health care units, green energy services, and smart farming utilities, can be made available to people for enhanced quality of life. A long term vision of the Internet is to integrate human, things, data, and various processes as a neural network for the human body. Out of many prospective visions, how to interact with things over the Internet in a convenient and secure way is considered a critical question to address. To interact with things, making them accessible via the Internet is an essential issue. Nowadays, Wireless Sensor Networks (WSNs) [1] are widely used in many different
http://dx.doi.org/10.1016/j.adhoc.2014.12.006 1570-8705/Ó 2015 Published by Elsevier B.V.
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domains. Usually, a WSN consists of a large number of small, inexpensive, and resource-limited devices called sensors, which are used to collect physical world data that is transferred wirelessly to a central location known as a Sink or Base Station. These sensor devices communicate with each other using different proprietary protocols, such as ZigBee [2]. However, if these protocols are not based on the Internet Protocol (IP), establishing a connection between sensors and the Internet becomes a real challenge. Recent effort in IPv6 over Low-power Personal Area Networks (6LoWPAN) [3] is to bring IPv6 into sensors. 6LoWPAN enables sensors to be natively addressed and seamlessly integrated to the Internet without the need for any extra processing. Besides connecting things to the Internet, appropriate reference architecture is needed to unify global interconnectivity among things. To this end, the Internet of Things (IoT) [4] has been introduced to extend Internet connectivity to things. IoT is a world-wide network, interconnecting a large number of heterogeneous physical objects anytime and anywhere through the IP. This means that all objects must have a unique IP address and has become a real challenge as IP becomes a real issue for tiny devices with low power and constrained resource. Another challenge of IoT is providing communication and collaboration among heterogeneous objects and information system to produce useful services. It is expected that the number of interconnected devices will reach 50 billion by 2020. Managing such a huge number of devices and systems requires unparallel scalability and improved performance of IoT. Within IoT, smart objects, or simply things are essential building blocks, which could be computers, mobile phones, tablets, or sensors. Obviously, in order to connect smart objects, they must be uniquely identified and addressed. This can be achieved using technologies such as Radio-frequency identification (RFID) [5] that automatically identifies objects and tracks materials. However, embedding RFID into every object does not add smartness as they must be able to sense, produce and consume services, perform some computation, communicate, interact, and discover services. Thus, IoT need to connect things beyond RFID. We use the terms things, smart things, objects, smart objects, devices, and nodes interchangeably to refer to things beyond RFID in this paper. The success of the IoT has led to the introduction of Web of Things (WoT) paradigm [6]. Indeed, IoT just presents an idea that addresses the mechanisms of interconnecting objects by making each object IP-enabled; it does not specify any network structure or technology. In order to have more sophisticated applications or services, WoT goes one step further by integrating objects into the Web. For example, users can create applications to mix physical objects with the services provided by the Web, which is called physical mashups. To achieve this, the WoT leverages Web technologies, protocols, and standards like Uniform Resource Identifiers (URIs), Hypertext Transfer Protocol (HTTP), among others. Dealing with objects as Web resources makes objects integration easier, flexible, and reusable. However, to become Web-enabled, objects must embed a Web server. Moreover, the WoT is a comprehensive paradigm; an emerging large number of smart
objects on Web results in great difficulties in discovering, finding, and selecting smart objects [7]. Furthermore, it is very complex for the Web users to manage a huge number of objects and associated data. Interoperability between different systems and heterogeneous objects is vital in a WoT. To serve this purpose, Service Oriented Architecture (SOA) has been developed. SOA is based on what is commonly called Web services protocols (WS-⁄) [8], such as Simple Object Access Protocol (SOAP), Web Service Description Language (WSDL), Universal Description Discovery and Integration (UDDI). However, current WS-⁄ protocols require excessive computing resources and power, and thus are not well suited for accessing objects. Moreover, it introduces a large overhead and is relatively complex. As different architectural design has been introduced such as Resource Oriented Architecture (ROA), a structural design supports direct access and internetworking of resources. On the other hand, Representational State Transfer (REST) [9] technology enables creation of ROA. Recently, Constrained Application Protocol (CoAP) has been proposed for resource constrained network applications. However, CoAP can be optimally used only for IP-enabled objects. More recently, a new paradigm called the Social Web of Things (SWoT) [10] has been introduced to take advantage of the pervasive social networks and promote interaction between people and things. Social Networks, such as Facebook and Twitter, are popular Web 2.0 environments that enable individuals to communicate, exchange, and share contents with other individuals based on the social relationships among users. The SWoT paradigm leverages the social network to include smart objects, which enables users to manage, access, and share their Web-enabled objects and services with people they know and trust. Thus, it represents next natural evolution of WoT and makes interaction with things easy for people. In this paper, we aim to provide better understanding and to gain further insights of the I/W/SW-oT paradigms by providing a comprehensive survey of current technologies. Instead of focusing on single paradigm as that in previous survey, our survey gives an in depth and comprehensive insight of the emerging I/W/SW-oT paradigms. To the best of our knowledge, our work is the first to make a comprehensive study and classification of these paradigms from different perspectives and establish relationship among them. Unlike previous surveys, we evaluate a large number of platforms, prototypes, applications and projects of these paradigms. It is important to fully understand differences between these paradigms so that we can select the best paradigm suitable for a specific application domain. We introduce general definitions of IoT and present a detailed discussion and comparison on IoT enabling technologies. Moreover, we review the IoT architectures and present a detailed analysis of popular middleware and highlight its features. Next, we focus on protocols that are proposed for resource constrained environments such as CoAP protocol. The WoT is sprung out of the IoT. WoT is the core of this paper, we provide a detailed tutorial on the WoT. We start with reviewing Web services and then survey mashup techniques and how to apply it in the WoT. We compare and contrast various types of WoT
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platforms and evaluate it based on various features. We also describe and differentiate several popular WoT applications by highlighting their strengths and limitations. After that, SWoT is presented. An extensive overview on integration of objects into social Web sites is provided. Due to the fundamental role of social networks in SWoT, we explore two widely used social networks namely, Facebook and Twitter. Then, we analyze, compare, and classify SWoT platforms emphasizing the design principles and their characteristics. For the sake of completeness, more applications are reviewed. Finally, we point out future challenging issues, highlight further research directions, and discuss how to tackle these open issues and challenges. The rest of this paper is organized as follows. Section 2 presents an overview of related work. The main purpose of Section 3 is to provide a comprehensive survey of the IoT and propose taxonomy of current IoT middleware. Furthermore, CoAP and MQTT protocols are discussed and compared in terms of their detailed operations, and we highlight their distinct features. Section 4 describes the WoT and its architectures. Web services and its deployment in the WoT are described, Web services classified, and a comparison between them is provided. Mashups are introduced at the end and a comprehensive survey of WoT platforms is given. Several simple examples of the WoT and mashups are also illustrated. Section 5 discusses social networks and SWoT. A number of different applications and platforms are examined as well. Section 6 identifies future research directions and challenges. Finally, Section 7 concludes the paper. For ease of reference, Table 1 provides an alphabetized list of all abbreviations used in this survey paper.
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Several surveys have been conducted for WSN, IoT, WoT, and SWoT. Here, we provide a brief overview of these surveys. In the WSN field, a comprehensive survey of WSN design issues, protocols, physical constraints, routing, and applications has been introduced in [11]. However, it does not cover many state-of-the-art routing protocols and does not provide any classification. Similarly, a comprehensive survey can be found in [12] where the authors summarize and compare different designs, platform, algorithms, communication protocols, and services. A survey on Webbased wireless sensor architecture and Web applications is presented in [13], including design challenges for sensor Web. Analogously, the research activities reported in [14] provide an overview of architectures for IP-based sensor networks. The work in [15] gives a detailed discussion on a new IEEE802.15.4e MAC and routing standard. Yet, the paper concretes on IoT protocols definitions rather than Q4 just providing high-level descriptions. More recently, Chen et al. [16] survey and summarize advancements in home communication technologies specifically for Machine-toMachine (M2M) exchange, and discuss state-of-the-art research on recent developments in communication protocols. Different sensor network applications survey has been conducted, with most recent work presented in [17]
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Table 1 List of abbreviations used in this paper. Acronym
Definition
6LoWPAN AAA ADIs BLIP BPEL CoAP COI CPS CRUD CSV DTLS DNS DOI DPWS EIS EPC EPCIS FAT FBML HTTP IETF IISs IoT IoT-A IP ITIPA
IPv6 over Low-power Personal Area Networks Authorization, Authentication, and Accounting Active Digital Identities Berkeley Low-power IP stack Business Process Execution Language Constrained Application Protocol Community Of Interest Cyber-Physical Systems Create, Read, Update and Delete Comma-Separated Values Datagram Transport Layer Security Domain Name System Digital Object Identifier Device Profile for Web Services Enterprise Information Systems Electronic Product Code EPC Information Services Friends And Things Facebook Markup Language Hypertext Transfer Protocol Internet Engineering Task Force Integrated Information Systems Internet of Things Internet of Things-Architecture Internet Protocol Interactively Trained Illumination based Presence Awareness JavaScript Object Notation Keyhole Markup Language Machine-to-Machine communication Message Queuing Telemetry Transport Near Field Communications Object Directory Service Object Naming Service Peer-to-Peer Quality of Service Representational State Transfer Radio-frequency identification Resource Oriented Architecture Remote Procedure Call Software as a Service Social Access Controller Social Internet of Things Service Oriented Architecture Simple Object Access Protocol Service-Oriented Device Architecture Secure Sockets Layer Social Web of Things ubiquitous Code Universal Description Discovery and Integration. User Datagram Protocol Universal Plug and Play Uniform Resource Identifier Uniform Resource Locator Web of Things WoT toolkit Web Service Description Language Web Services Inspection Language Wireless Sensor Networks Web Services protocols Web Services Interoperability Extensible Markup Language
JSON KML M2M MQTT NFC ODS ONS P2P QoS REST RFID ROA RPC SaaS SAC SIoT SOA SOAP SODA SSL SWoT uCode UDDI UDP UPnP URI URL WoT WoTkit WSDL WSIL WSNs WS-⁄ WS-I XML
where the authors cover a large number of applications from different domains. Several surveys on IoT have recently been published. Atzori et al. [18] provide a comprehensive survey the IoT from three different angles: Internet, things, and
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semantics. Another good survey is [19] where IoT key issues, research challenges, and research directions have been identified. In addition, many relevant applications have been presented along with a number of application situations. More recently, an insight on IoT vision, architecture, and services has been presented in [20]. Existing popular IoT middleware designs are surveyed in [21]. Recently, Xu et al. [22] has reviewed advances of IoT for industries. Context-awareness is expected to be a critical functionality in a typical IoT. A comprehensive survey and analysis of context aware systems for the IoT is presented in [23]. A large number of context-aware middleware solutions are analyzed and compared and the authors argue that privacy is largely unattended in most existing solutions. As IoT generates massive amount of useful data, undoubtedly, data mining techniques play a critical role in making IoT applications smart enough to provide adequate services and enable improved environments. Tsai et al. [24] analyze and discuss several studies on applying data mining techniques for the IoT from different perspective. Koreshoff et al. [25] examine and review 93 commercial products of the IoT and provide insights and full details of the types of sensors to be used in these applications by categorizing them and show how people can easily interact with them. To the best of our knowledge, the work in [26] is the only comprehensive WoT survey. The architecture and key enabling technologies are presented in details. The authors also compare most popular open platforms and prototypes of WoT. Further, open challenging issues that ought to be tackled are also presented. Other than our previous work in [27], no other researcher has conducted any survey on SWoT.
second definition proposed by CASAGRAS combines both things-oriented and Internet-oriented paradigms, and defines IoT as ‘‘A global network infrastructure, linking physical and virtual objects through the exploitation of data capture and communication capabilities. This infrastructure includes existing and evolving Internet and network developments. It will offer specific object-identification, sensor and connection capability as the basis for the development of independent cooperative services and applications. These will be characterized by a high degree of autonomous data capture, event transfer, network connectivity and interoperability’’ [29]. A more technical definition can be found in [30]: ‘‘The semantic origin of the expression is composed by two words and concepts: Internet and Thing, where Internet can be defined as the world-wide network of interconnected computer networks, based on a standard communication protocol, the Internet suite (TCP/IP), while Thing is an object not precisely identifiable. Therefore, semantically, Internet of Things means a world-wide network of interconnected objects uniquely addressable, based on standard communication protocols.’’ We introduce a last definition here that covers a broader vision with IoT defined as ‘‘Internet of Things (IoT) is a concept and a paradigm that considers pervasive presence in the environment of a variety of things/objects that through wireless and wired connections and unique addressing schemes are able to interact with each other and cooperate with other things/objects to create new applications/services and reach common goals’’[31]. Nowadays, the IoT applications have been adopted in many different domains. Several researches focus on the field of health care systems [32], rehabilitation systems [33], and systems assisting peoples with disabilities [34]. In order to improve the quality of human life, IoT technology is also being used widely to create smart environments, such as smart homes [35], smart buildings [36], and smart cities [37] which include intelligent transportation and logistics [38], bus systems [39], smart parking management [40], and so on. On the other hand, IoT technologies are also used to improve the efficiency of business operation, such as enterprise information systems (EIS) and integrated information systems (IISs) including enterprise information systems [41], supply chain [42], automated assembly planning systems [43]. Another domain of IoT application is in environmental monitoring and management [44] including agriculture [45] and water resource management [46]. It is expected that numerous applications of IoT will be introduced in many domains so as to enrich quality of life.
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Recently, IoT has attracted tremendous attention all over the world and is considered as the third wave of information industry. IoT aims to expand existing human– human communication to human–things and things– things communication by connecting a variety of objects with the Internet in order to exchange information between the physical world and the virtual world. Objects come in different sizes, capabilities, processing power, and energy capacity. Moreover, objects embed different types of sensors and actuators, and thus can sense and transmit data, perform computation, and make required intelligent decisions.
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3.2. IoT identification schemes
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As mentioned earlier, IoT is an interdisciplinary field which integrates three paradigms: Internet oriented-, things oriented-, and semantic oriented-paradigm. Many alternative definitions for these IoT paradigms have been introduced in the past. Among them, two definitions are widely used. The first definition is based on the things oriented-paradigm, where IoT is defined as ‘‘Things having identities and virtual personalities operating in smart spaces using intelligent interfaces to connect and communicate within social, environmental, and user contexts’’ [28]. The
In an IoT, things must not only be connected together, but also need to be identified, located, and managed. In other words, each IoT object and resource should have at least a name and/or an address [47]. Objects by themselves are not identifiable and thus object identification and addressing mechanisms such as IPV4, IPV6, RFIDs, URI, and Digital Object Identifier (DOI) are required. In the Internet, hierarchical naming schemes such as the Uniform Resource Locator (URL) are widely used. However, they are not network-location-transparent and thus are not suitable
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for a highly mobile environment such as IoT. Naming and addressing schemes for IoT should satisfy the requirements of transparency, mobility, flexibility, scalability, consistency, interoperability, and security. Thus, object identification and addressing are a crucial task and a number of issues need to be taken into account. One issue that needs to be addressed is the conceptual difference between the ID of an object and its network address. Object identification and object addressing serve different purpose. Identification assigns a name to an object while addressing provides a way to access the object. It is required that the identifier of an object be independent from the connected network and thus should not change when an object moves to another network. An object can be addressed using global IP addressing or by using private addressing. However, connecting objects that use private addressing to the Internet requires using a border gateway for address mapping or translation. Currently, many available object identification technologies have been used, such as barcode and RFID. Barcode identification has many drawbacks, such as a barcode cannot be rewritten; data reading is slow; the reading distance between the scanner and the barcode is limited; and direct line-of-sight between the barcode and the barcode reader is required. RFID is small in size, costs low and device that uses RF signals to uniquely identify things has long lifetime. RFID is a key technology to realize IoT for a number of reasons, such as longer reading distance, data can be rewritten, more secure, and fire-resistant. Thus, RFID has become more popular in identifying things. Numerous IoT applications have been built based on RFID technology. RFID has three basic components, namely tag, reader, and antenna. A tag is a microchip that contains a unique electronic code that is attached to items for identification. Tag information, such as the object identity, the object location, and the read-time is read and written through the reader. The RFID reader can act as a gateway to the Internet. Communication between a tag and a reader is done through an antenna which receives reader signals and transmits the tag ID. RFID tags fall into two main categories: passive RFID tags and active RFID tags. Passive RFID tags are not operated by battery but harvest energy from signals transmitted from the RFID reader. On the contrary, an active RFID is operated by a battery. In many aspects, an active RFID is similar to sensors with limited processing and storage capability. Compared with passive tags, an active RFID has larger radio coverage. Electronic Product Code (EPC) global standard [48] allows deployment and interoperability of RFIDs in an IoT by assigning a unique EPC using 64–96 bit identifiers. Another attempt to realize IoT is called ubiquitous Code (uCode) introduced by the uID center in Japan [49] with focuses on middleware solutions. uCode uses 128-bit identifiers and dual band scanning frequencies at 2.45 GHz and 13.56 MHz. uCode has now gained popularity as a more flexible alternative for identification than EPC. An EPC system is mainly designed for RFIDs and does not support other types of things. However, things are not just RFID tagged objects. Another difference is that EPC is intended to operate mainly via the Internet while uCode is intended to operate across multiple network types.
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Similar to RFID technology, Near Field Communication (NFC) [50] is an IoT enabling technology. NFC is a short-ranged wireless technology that is based on the standards of High Frequency RFID. A unique feature of NFC is that a device can act both as a reader and a tag. In the passive mode, communication occurs between NFC devices and NFC tags. When both devices act as NFC devices, they can use peer-to-peer communication to collect and exchange information, which is called the active mode of NFC. However, these NFC devices must be placed close to each other within a few centimeters. These unique features have made NFC popular. It is no surprise that nowadays almost every smartphone is NFC-equipped and in the near future objects may all have a NFC tag. Unlike RFID, which can scan multiple tags simultaneously, NFC can scan a single NFC tag at a time, which is considered as a limitation of NFC. As sensors are key enabling technology of IoT, it is common to integrate RFID and NFC with sensors and other technologies in applications. Table 2 shows a comparison between these three different techniques. On top of object identification techniques, another issue that needs to be taken into account is whether to use unique global identifiers or multiple distinct identifiers to define various classes of objects (sensors, actuators, tags etc.). In the former case, objects have a unique identifier and unique network addresses can be assigned to objects by using protocols such as IPv6 and 6LoWPAN. Despite that unique global identifiers ensure interoperability, security, and quick address resolution, they require an infrastructure to support object mobility. Thus, they are hard to manage and introduce considerable technical costs. Moreover, having one global identification scheme might be impossible given that several heterogeneous identification schemes have been utilized in the world. In the multiple identifiers schemes, one object can have one or more identifiers. However, multiple identifiers schemes must provide a high degree of interoperability and flexibility. Coupled with object identification, it is important to do object discovery and resolution in IoT where objects may dynamically join and leave the network. IoT discovery mechanisms have high impact on identification and addressing scheme because they need to support scalability, interoperability, and mobility. Discovery mechanisms become necessary if an object becomes available on-thefly. Object identifier needs to be resolved to the information corresponding to the object. On the Internet, Domain Name System (DNS) provides name resolution service used to translate host names to their underlying IP addresses. Object identifiers resolution mechanisms such as Object Naming Service (ONS) and Object Directory Service (ODS) are used in IoT. ONS translates an EPC into a URL(s) in order to resolve and retrieve information of things. However, ONS is introduced by EPC global and has not yet been widely adopted in practice.
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Research on IoT is still at its infant stage, and thus there is no commonly agreed unique IoT architecture. When defining IoT architecture, a number of factors need to be considered, such as scalability, interoperability, data
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Table 2 Comparison between an RFID system and a WSN. Attribute
WSNs
RFID systems
NFC
Purpose
Sense parameters of the environment or provide information on the condition of attached objects. Common application: home, industry monitoring and control ISM
Detect presence of tagged objects. Common application: tracking inventory systems 125–145 kHz/13.56 MHz/ 860–960 MHz 4–128 Kbps 1–100
Secure peer-to-peer communication between NFC devices for reliable applications. Common application: mobile and contactless payment, get access, initiate service 13.56 MHz
No Very small Tags, readers, antenna ISO/IEC 18000, ISO/IEC 14443, ISO/IEC 15693 Single-hop Tags move with attached objects Tags are battery-powered or passive Indefinite Usually closed systems Reader — expensive Tag — cheap Fixed, usually requires careful placement Tags are optimized to perform a single operation, such as read
Yes Very small NFC reader and NFC tag ISO/IEC 18092, ISO 14443, ISO/IEC 15693
Frequency band
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Data rate (b/s) Coverage (meter) Processing Size Component Protocols
2–250 Kbps 10–100
Communication Mobility
Multihop Sensor nodes are usually static
Power supply
Battery-powered
Life time Programmability Price Deployment
