13 research outputs found

    IETF standardization in the field of the Internet of Things (IoT): a survey

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    Smart embedded objects will become an important part of what is called the Internet of Things. However, the integration of embedded devices into the Internet introduces several challenges, since many of the existing Internet technologies and protocols were not designed for this class of devices. In the past few years, there have been many efforts to enable the extension of Internet technologies to constrained devices. Initially, this resulted in proprietary protocols and architectures. Later, the integration of constrained devices into the Internet was embraced by IETF, moving towards standardized IP-based protocols. In this paper, we will briefly review the history of integrating constrained devices into the Internet, followed by an extensive overview of IETF standardization work in the 6LoWPAN, ROLL and CoRE working groups. This is complemented with a broad overview of related research results that illustrate how this work can be extended or used to tackle other problems and with a discussion on open issues and challenges. As such the aim of this paper is twofold: apart from giving readers solid insights in IETF standardization work on the Internet of Things, it also aims to encourage readers to further explore the world of Internet-connected objects, pointing to future research opportunities

    IETF standardization in the field of the internet of things (IoT): a survey

    Get PDF
    Smart embedded objects will become an important part of what is called the Internet of Things. However, the integration of embedded devices into the Internet introduces several challenges, since many of the existing Internet technologies and protocols were not designed for this class of devices. In the past few years, there have been many efforts to enable the extension of Internet technologies to constrained devices. Initially, this resulted in proprietary protocols and architectures. Later, the integration of constrained devices into the Internet was embraced by IETF, moving towards standardized IP-based protocols. In this paper, we will briefly review the history of integrating constrained devices into the Internet, followed by an extensive overview of IETF standardization work in the 6LoWPAN, ROLL and CoRE working groups. This is complemented with a broad overview of related research results that illustrate how this work can be extended or used to tackle other problems and with a discussion on open issues and challenges. As such the aim of this paper is twofold: apart from giving readers solid insights in IETF standardization work on the Internet of Things, it also aims to encourage readers to further explore the world of Internet-connected objects, pointing to future research opportunities.The research leading to these results has received funding from the European Unionโ€™s Seventh Framework Programme (FP7/2007-2013) under grant agreement no 258885 (SPITFIRE project), from the iMinds ICON projects GreenWeCan and Oโ€™CareCloudS, a FWO postdoc grant for Eli De Poorter and a VLIR PhD scholarship to Isam Ishaq

    Application-Driven Wireless Sensor Networks

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    The growth of wireless networks has resulted in part from requirements for connecting people and advances in radio technologies. Recently there has been an increasing trend towards enabling the Internet-of-Things (IoT). Thousands of tiny devices interacting with their environments are being inter-networked and made accessible through the Internet. For that purpose, several communications protocols have been defined making use of the IEEE 802.15.4 Physical and MAC layers. The 6LoWPAN Network Layer adaptation protocol is an example which bridges the gap between low power devices and the IP world. Since its release, the design of routing protocols became increasingly important and the IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL) emerged as the IETF proposed standard protocol for IPv6-based multi-hop Wireless Sensor Networks (WSN). This thesis considers that the sensor nodes form a large IPv6 network making use of above technologies and protocols, and that the sensor nodes are enabled to run one or more applications. It is also assumed that the applications and the sensor nodes to which they are associated, are not always active, alternating between active and inactive states. The thesis aims to design a new energy efficient communications solution for WSN by exploring the hypothesis that the network is aware of the traffic generated by the applications running in the sensor nodes. Therefore, the thesis provides two major contributions: 1) a cross-layer mechanism using application layer and network layer information to constrainRPL-defined routing trees (RPL-BMARQ); 2) an Application-Driven WSN node synchronization mechanism for RPL-BMARQ. RPL-BMARQ is designed as an extension to the RPLrouting protocol using information shared by the application and routing layers to construct Directed Acyclic Graphs (DAGs), allowing the nodes to select parents with respect to the applications they run. By jointly considering the neighbors of each node, the applications each node runs, and the forwarding capabilities of a node, we provide a communications solution which enables the data of every application and sensor node to be transferred, while keeping the overall energy consumed low by reducing the time the nodes are active and reducing the total number of multicast packets exchanged. Therefore, RPL-BMARQ helps reducing the network energy consumption since it restricts radio communication activities while maintaining throughput fairness and packet reception ratio high. The mechanism was evaluated using four scenarios with different network topologies and compared against "standard RPL". The results obtained show that the mechanism enables lower energy consumption since the nodes are more often put a sleep, reducing the total number of packets exchanged, while maintaining fairness and query success rates high. The Application-Driven WSN node synchronization mechanism for RPL-BMARQ was designed to maintain the sensor nodes synchronized according to the duty cycle of the applications they run. The mechanism jointly uses cross-layer information and the Exponentially Weighted Moving Average (EWMA) technique for calculating in run-time average network delays which are used to control the time the sensor nodes would sleep in the next cycle in order to wake up just before the next activity period starts. This mechanism enables all the sensor nodes to go asleep and to wake up in synchronism. The mechanism was theoretically evaluated and simulated, and the results obtained show that the synchronization mechanism works as previewed. The results also showed that, when designing WSN applications with this mechanism, the nodes not involved in communications are kept sleeping as much as possible, waking up when necessary and in synchronism. In order to confirm the validity of the mechanisms designed, we also tested them in real environments where the results were confirmed

    Reduced overhead routing in short-range low-power and lossy wireless networks

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    In this paper we present enhanced routing protocol for low-lower and lossy networks (ERPL), a reduced overhead routing protocol for short-range low-power and lossy wireless networks, based on RPL. ERPL enhances peer-to-peer (P2P) route construction and data packet forwarding in RPLโ€™s storing and non-storing modes of operation (MoPs). In order to minimize source routing overhead, it encodes routing paths in Bloom Filters (BF). The salient features of ERPL include the following: (i) optimized P2P routing and data forwarding; (ii) no additional control messages; and (iii) minimized source routing overhead. We extensively evaluated ERPL against RPL using emulation, simulation, and physical test-bed based experiments. Our results demonstrate that ERPL outperforms standard RPL in P2P communication and its optimized P2P route construction and data forwarding algorithms also positively impact the protocolโ€™s performance in multi-point to point (MP2P) and point to multi-point (P2MP) communications. Our results demonstrate that the BF-based approach towards compressed source routing information is feasible for the kinds of networks considered in this paper. The BF-based approach results in 65% lower source routing control overhead compared to RPL. Our results also provide new insights into the performance of MP2P, P2MP, and P2P communications relative to RPLโ€™s destination-oriented directed a-cyclic graph (DODAG) depth, i.e., a deeper DODAG negatively impacts the performance of MP2P and P2MP communications, however it positively impacts P2P communication, while the reverse holds true for a relatively shallow DODAG

    ๋น„๋Œ€์นญ ์ „์†ก์ „๋ ฅ ๊ธฐ๋ฐ˜ ๋ฌด์„  ์„ผ์„œ ์‹œ์Šคํ…œ ์—ฐ๊ตฌ

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    ํ•™์œ„๋…ผ๋ฌธ (๋ฐ•์‚ฌ)-- ์„œ์šธ๋Œ€ํ•™๊ต ๋Œ€ํ•™์› : ์ „๊ธฐยท์ปดํ“จํ„ฐ๊ณตํ•™๋ถ€, 2016. 2. ๋ฐ•์„ธ์›….๋Œ€๊ทœ๋ชจ ๋งˆ์ผ“์˜ ๊ฐ€๊ฒฉํ‘œ ์—…๋ฐ์ดํŠธ๋Š” ๋‹จ์ˆœํ•˜๊ณ  ๋ฐ˜๋ณต์ ์ธ ์ž‘์—…์ด์ง€๋งŒ, ์—ฌ์ „ํžˆ ๋Œ€๋ถ€๋ถ„์˜ ๋งˆ์ผ“์—์„œ ์ˆ˜๋™์œผ๋กœ ์ด๋ฃจ์–ด์ง€๊ณ  ์žˆ๋‹ค. ์ˆ˜๋™ ๊ฐ€๊ฒฉํ‘œ ์—…๋ฐ์ดํŠธ๋Š” ์žฆ์€ ์ง์›๋“ค์˜ ์‹ค์ˆ˜๋กœ ์ธํ•œ ์†Œ๋น„์ž๋“ค์˜ ๋ถˆ๋งŒ๊ณผ ์นด์šดํ„ฐ์˜ ๊ณ„์‚ฐ ์˜ค๋ฅ˜๋ฅผ ์•ผ๊ธฐํ•˜๋ฏ€๋กœ, ์ƒ๊ธฐ ์—…๋ฐ์ดํŠธ ๊ณผ์ •์„ ์ž๋™ํ™”ํ•˜๋ฉด ๋งŽ์€ ์ด์ต์„ ์ฐฝ์ถœํ•  ์ˆ˜ ์žˆ๋‹ค. ํ•œํŽธ, ์ตœ๊ทผ ์ „์ž ์ž‰ํฌ์™€ ๊ฐ™์€ ์ €์ „๋ ฅ ๋””์Šคํ”Œ๋ ˆ์ด ๊ธฐ์ˆ ์ด ๋ฐœ์ „ํ•˜๋ฉด์„œ ์ „์ž ๋ฌด์„  ๊ฐ€๊ฒฉํ‘œ ์—…๋ฐ์ดํŠธ ์„œ๋น„์Šค์˜ ์‹คํ˜„ ๊ฐ€๋Šฅ์„ฑ์ด ๋†’์•„์กŒ๋‹ค. ๋ณธ ๋…ผ๋ฌธ์—์„œ ์šฐ๋ฆฌ๋Š” ์ƒ๊ธฐ ์ „์ž ๋ฌด์„  ๊ฐ€๊ฒฉํ‘œ ์—…๋ฐ์ดํŠธ ์„œ๋น„์Šค๋ฅผ ์œ„ํ•œ ๋„คํŠธ์›Œํฌ ์•„ํ‚คํ…์ณ๋ฅผ ์ œ์•ˆํ•˜๊ณ  ํ…Œ์ŠคํŠธํ•œ๋‹ค. ์šฐ๋ฆฌ๋Š” ๋จผ์ € ์‹ค์ œ ๋งˆ์ผ“์—์„œ์˜ ์˜ˆ๋น„ ์‹คํ—˜๋“ค์„ ํ†ตํ•ด, ํ˜„์กดํ•˜๋Š” ๋„คํŠธ์›Œํฌ ํ”„๋กœํ† ์ฝœ๋“ค์ด ๋ฐ”์œ ๋งˆ์ผ“ ํ™˜๊ฒฝ์—์„œ ๋ฐœ์ƒํ•˜๋Š” ๋…ํŠนํ•œ ๋ฌธ์ œ๋“ค์„ ๊ทน๋ณตํ•˜์ง€ ๋ชปํ•˜๊ณ , ๋‚ฎ์€ ์„ฑ๋Šฅ์„ ๋ณด์ธ๋‹ค๋Š” ๊ฒƒ์„ ๋ฐํžŒ๋‹ค. ์šฐ๋ฆฌ๋Š” ์ƒ๊ธฐ ์‹คํ—˜๋“ค์„ ํ†ตํ•ด ๊ธฐ์ˆ ์ ์ธ ๋„์ „๊ณผ์ œ๋“ค์„ ํ™•์ธํ•˜๊ณ , ์žฅ์• ๋ฌผ๊ณผ ์ธ๊ตฌ๊ฐ€ ๋งŽ์€ ํ™˜๊ฒฝ์—์„œ ํ•˜ํ–ฅ๋งํฌ ์œ„์ฃผ์˜ ํŠธ๋ž˜ํ”ฝ์„ ์ „์†กํ•˜๊ธฐ์— ์ ํ•ฉํ•œ ๋น„๋Œ€์นญ ์ „์†ก ์ „๋ ฅ ๊ธฐ๋ฐ˜ ์‹œ์Šคํ…œ์ธ MarketNet์„ ์ œ์•ˆํ•˜์—ฌ ์ƒ๊ธฐ ๋„์ „๊ณผ์ œ๋“ค์„ ํ•ด๊ฒฐํ•œ๋‹ค. ์šฐ๋ฆฌ๋Š” ํ•˜๋ฃจ์— 5000๋ช… ์ด์ƒ์˜ ์†๋‹˜์ด ๋ฐฉ๋ฌธํ•˜๋Š” ์‹ค๋‚ด ๋งˆ์ผ“ ํ™˜๊ฒฝ์—์„œ MarketNet์˜ ์„ฑ๋Šฅ์„ ํ‰๊ฐ€ํ•œ๋‹ค. ์ƒ๊ธฐ ์„ฑ๋Šฅ ํ‰๊ฐ€์˜ ๊ฒฐ๊ณผ๋“ค์€ MarketNet์ด ํƒ€๊นƒ ํ™˜๊ฒฝ(์žฅ์• ๋ฌผ์ด ๋งŽ๊ณ  ๋ถ๋น„๋Š” ๋งˆ์ผ“)์—์„œ ํƒ€๊นƒ ์‘์šฉ ๋ถ„์•ผ(์ „์ž ๋ฌด์„  ๊ฐ€๊ฒฉํ‘œ ์—…๋ฐ์ดํŠธ)๋ฅผ ์ ์ ˆํžˆ ์ง€์›ํ•  ์ˆ˜ ์žˆ์„ ๋ฟ๋งŒ ์•„๋‹ˆ๋ผ, RPL๊ณผ LPL๊ณผ ๊ฐ™์€ ๊ธฐ์กด ํ”„๋กœํ† ์ฝœ๋“ค๋ณด๋‹ค ํ˜„์ €ํžˆ ๋†’์€ ํŒจํ‚ท ์ „์†ก๋ฅ ๊ณผ ๋‚ฎ์€ ๋“€ํ‹ฐ์‚ฌ์ดํด์„ ์ œ๊ณตํ•œ๋‹ค๋Š” ๊ฒƒ์„ ๋ณด์—ฌ์ค€๋‹ค.Updating price tags in a large-scale market is a recurrent task, still performed manually in most markets. Given that human-errors can easily lead to customer complaints and accounting inaccuracies, the ability to autonomously reconfigure price tags can be of significant benefit. With the introduction of low-power display techniques such as electronic-ink, applications of enabling electronic, wirelessly reconfigurable price tags show potential for future deployment. In this dissertation, we examine networking architectures that can be applied in such scenarios. Through a series of preliminary pilot studies in an actual supermarket, we show that the performance of existing protocols are not ready to overcome the unique challenges of busy market environments. We identify underlying technical challenges and propose MarketNet, an asymmetric transmission power-based system designed for densely populated, obstacle-rich, downwards traffic-oriented environments. We evaluate MarketNet in a large indoor market visited by 5000+ customers per day. Our results show that MarketNet addresses the challenges of the target application and environment, while achieving higher packet delivery performance with noticeably lower radio duty-cycles than existing protocols such as RPL and LPL.1 Introduction 1 1.1 Motivation 1 1.2 Related Work 4 1.2.1 Wireless Price Tag Update System 4 1.2.2 Wireless Systems Community 5 1.2.3 Wireless Network Community 10 1.3 Contributions and Outline 12 2 Target Application: Wireless and Remote Update of e-Price Tags 17 2.1 Price Representation 17 2.2 Application Scenario 19 2.3 System Requirements 22 3 Preliminary Study in Urban Crowded Markets 25 3.1 Introduction 25 3.2 Wireless Channel Characteristics 27 3.3 Performance of Pre-existing Protocols 38 3.3.1 RPL Operation 38 3.3.2 LPL Operation 42 3.3.3 Performance of RPL over LPL 44 3.4 Summary 48 4 MarketNet 1.0: Asymmetric Transmission Power-based Network 50 4.1 Introduction 50 4.2 Applicability of Asymmetric Transmission Power Networks 54 4.3 MarketNet1.0 System Design 58 4.3.1 Design Overview 58 4.3.2 Neighbor Forwarding over LPL 61 4.4 Mathematical Performance Analysis 66 4.4.1 Packet Reception Ratio 67 4.4.2 Latency 69 4.4.3 Power Consumption 70 4.5 Simulation Results 78 4.5.1 Latency 80 4.5.2 Packet Delivery Ratio 81 4.5.3 Power Consumption 82 4.6 Testbed Experiments 84 4.6.1 Implementation and Environment Setting 84 4.6.2 Downward Traffic Scenario 88 4.6.3 Mixed Traffic Scenario 93 4.7 Market Deployment 98 4.8 Summary 102 5 MarketNet 2.0: Network-wide Superframe Architecture 103 5.1 Introduction 103 5.2 MarketNet2.0 System Design 105 5.2.1 Network-wide Superframe Architecture 107 5.2.2 IPv6 and Routing Layers in MarketNet2.0 112 5.3 System Evaluation 115 5.3.1 Testbed Evaluations 115 5.3.2 Market Deployments 120 5.4 Non-technical but Practical Lessons 126 5.5 Summary 127 6 Conclusion 129 6.1 Research Contributions 129 6.2 Further Research Direction 131 Bibliography 135 ์ดˆ ๋ก 150Docto

    A Two-Level Information Modelling Translation Methodology and Framework to Achieve Semantic Interoperability in Constrained GeoObservational Sensor Systems

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    As geographical observational data capture, storage and sharing technologies such as in situ remote monitoring systems and spatial data infrastructures evolve, the vision of a Digital Earth, first articulated by Al Gore in 1998 is getting ever closer. However, there are still many challenges and open research questions. For example, data quality, provenance and heterogeneity remain an issue due to the complexity of geo-spatial data and information representation. Observational data are often inadequately semantically enriched by geo-observational information systems or spatial data infrastructures and so they often do not fully capture the true meaning of the associated datasets. Furthermore, data models underpinning these information systems are typically too rigid in their data representation to allow for the ever-changing and evolving nature of geo-spatial domain concepts. This impoverished approach to observational data representation reduces the ability of multi-disciplinary practitioners to share information in an interoperable and computable way. The health domain experiences similar challenges with representing complex and evolving domain information concepts. Within any complex domain (such as Earth system science or health) two categories or levels of domain concepts exist. Those concepts that remain stable over a long period of time, and those concepts that are prone to change, as the domain knowledge evolves, and new discoveries are made. Health informaticians have developed a sophisticated two-level modelling systems design approach for electronic health documentation over many years, and with the use of archetypes, have shown how data, information, and knowledge interoperability among heterogenous systems can be achieved. This research investigates whether two-level modelling can be translated from the health domain to the geo-spatial domain and applied to observing scenarios to achieve semantic interoperability within and between spatial data infrastructures, beyond what is possible with current state-of-the-art approaches. A detailed review of state-of-the-art SDIs, geo-spatial standards and the two-level modelling methodology was performed. A cross-domain translation methodology was developed, and a proof-of-concept geo-spatial two-level modelling framework was defined and implemented. The Open Geospatial Consortiumโ€™s (OGC) Observations & Measurements (O&M) standard was re-profiled to aid investigation of the two-level information modelling approach. An evaluation of the method was undertaken using II specific use-case scenarios. Information modelling was performed using the two-level modelling method to show how existing historical ocean observing datasets can be expressed semantically and harmonized using two-level modelling. Also, the flexibility of the approach was investigated by applying the method to an air quality monitoring scenario using a technologically constrained monitoring sensor system. This work has demonstrated that two-level modelling can be translated to the geospatial domain and then further developed to be used within a constrained technological sensor system; using traditional wireless sensor networks, semantic web technologies and Internet of Things based technologies. Domain specific evaluation results show that twolevel modelling presents a viable approach to achieve semantic interoperability between constrained geo-observational sensor systems and spatial data infrastructures for ocean observing and city based air quality observing scenarios. This has been demonstrated through the re-purposing of selected, existing geospatial data models and standards. However, it was found that re-using existing standards requires careful ontological analysis per domain concept and so caution is recommended in assuming the wider applicability of the approach. While the benefits of adopting a two-level information modelling approach to geospatial information modelling are potentially great, it was found that translation to a new domain is complex. The complexity of the approach was found to be a barrier to adoption, especially in commercial based projects where standards implementation is low on implementation road maps and the perceived benefits of standards adherence are low. Arising from this work, a novel set of base software components, methods and fundamental geo-archetypes have been developed. However, during this work it was not possible to form the required rich community of supporters to fully validate geoarchetypes. Therefore, the findings of this work are not exhaustive, and the archetype models produced are only indicative. The findings of this work can be used as the basis to encourage further investigation and uptake of two-level modelling within the Earth system science and geo-spatial domain. Ultimately, the outcomes of this work are to recommend further development and evaluation of the approach, building on the positive results thus far, and the base software artefacts developed to support the approach

    Overlay virtualized wireless sensor networks for application in industrial internet of things : a review

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    Abstract: In recent times, Wireless Sensor Networks (WSNs) are broadly applied in the Industrial Internet of Things (IIoT) in order to enhance the productivity and efficiency of existing and prospective manufacturing industries. In particular, an area of interest that concerns the use of WSNs in IIoT is the concept of sensor network virtualization and overlay networks. Both network virtualization and overlay networks are considered contemporary because they provide the capacity to create services and applications at the edge of existing virtual networks without changing the underlying infrastructure. This capability makes both network virtualization and overlay network services highly beneficial, particularly for the dynamic needs of IIoT based applications such as in smart industry applications, smart city, and smart home applications. Consequently, the study of both WSN virtualization and overlay networks has become highly patronized in the literature, leading to the growth and maturity of the research area. In line with this growth, this paper provides a review of the development made thus far concerning virtualized sensor networks, with emphasis on the application of overlay networks in IIoT. Principally, the process of virtualization in WSN is discussed along with its importance in IIoT applications. Different challenges in WSN are also presented along with possible solutions given by the use of virtualized WSNs. Further details are also presented concerning the use of overlay networks as the next step to supporting virtualization in shared sensor networks. Our discussion closes with an exposition of the existing challenges in the use of virtualized WSN for IIoT applications. In general, because overlay networks will be contributory to the future development and advancement of smart industrial and smart city applications, this review may be considered by researchers as a reference point for those particularly interested in the study of this growing field

    Discovery and Group Communication for Constrained Internet of Things Devices using the Constrained Application Protocol

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    The ubiquitous Internet is rapidly spreading to new domains. This expansion of the Internet is comparable in scale to the spread of the Internet in the โ€™90s. The resulting Internet is now commonly referred to as the Internet of Things (IoT) and is expected to connect about 50 billion devices by the year 2020. This means that in just five years from the time of writing this PhD the number of interconnected devices will exceed the number of humans by sevenfold. It is further expected that the majority of these IoT devices will be resource constrained embedded devices such as sensors and actuators. Sensors collect information about the physical world and inject this information into the virtual world. Next processing and reasoning can occur and decisions can be taken to enact upon the physical world by injecting feedback to actuators. The integration of embedded devices into the Internet introduces new challenges, since many of the existing Internet technologies and protocols were not designed for this class of constrained devices. These devices are typically optimized for low cost and power consumption and thus have very limited power, memory, and processing resources and have long sleep periods. The networks formed by these embedded devices are also constrained and have different characteristics than those typical in todays Internet. These constrained networks have high packet loss, low throughput, frequent topology changes and small useful payload sizes. They are referred to as LLN. Therefore, it is in most cases unfeasible to run standard Internet protocols on this class of constrained devices and/or LLNs. New or adapted protocols that take into consideration the capabilities of the constrained devices and the characteristics of LLNs, are required. In the past few years, there were many efforts to enable the extension of the Internet technologies to constrained devices. Initially, most of these efforts were focusing on the networking layer. However, the expansion of the Internet in the 90s was not due to introducing new or better networking protocols. It was a result of introducing the World Wide Web (WWW), which made it easy to integrate services and applications. One of the essential technologies underpinning the WWW was the Hypertext Transfer Protocol (HTTP). Today, HTTP has become a key protocol in the realization of scalable web services building around the Representational State Transfer (REST) paradigm. The REST architectural style enables the realization of scalable and well-performing services using uniform and simple interfaces. The availability of an embedded counterpart of HTTP and the REST architecture could boost the uptake of the IoT. Therefore, more recently, work started to allow the integration of constrained devices in the Internet at the service level. The Internet Engineering Task Force (IETF) Constrained RESTful Environments (CoRE) working group has realized the REST architecture in a suitable form for the most constrained nodes and networks. To that end the Constrained Application Protocol (CoAP) was introduced, a specialized RESTful web transfer protocol for use with constrained networks and nodes. CoAP realizes a subset of the REST mechanisms offered by HTTP, but is optimized for Machine-to-Machine (M2M) applications. This PhD research builds upon CoAP to enable a better integration of constrained devices in the IoT and examines proposed CoAP solutions theoretically and experimentally proposing alternatives when appropriate. The first part of this PhD proposes a mechanism that facilitates the deployment of sensor networks and enables the discovery, end-to-end connectivity and service usage of newly deployed sensor nodes. The proposed approach makes use of CoAP and combines it with Domain Name System (DNS) in order to enable the use of userfriendly Fully Qualified Domain Names (FQDNs) for addressing sensor nodes. It includes the automatic discovery of sensors and sensor gateways and the translation of HTTP to CoAP, thus making the sensor resources globally discoverable and accessible from any Internet-connected client using either IPv6 addresses or DNS names both via HTTP or CoAP. As such, the proposed approach provides a feasible and flexible solution to achieve hierarchical self-organization with a minimum of pre-configuration. By doing so we minimize costly human interventions and eliminate the need for introducing new protocols dedicated for the discovery and organization of resources. This reduces both cost and the implementation footprint on the constrained devices. The second, larger, part of this PhD focuses on using CoAP to realize communication with groups of resources. In many IoT application domains, sensors or actuators need to be addressed as groups rather than individually, since individual resources might not be sufficient or useful. A simple example is that all lights in a room should go on or off as a result of the user toggling the light switch. As not all IoT applications may need group communication, the CoRE working group did not include it in the base CoAP specification. This way the base protocol is kept as efficient and as simple as possible so it would run on even the most constrained devices. Group communication and other features that might not be needed by all devices are standardized in a set of optional separate extensions. We first examined the proposed CoAP extension for group communication, which utilizes Internet Protocol version 6 (IPv6) multicasts. We highlight its strengths and weaknesses and propose our own complementary solution that uses unicast to realize group communication. Our solution offers capabilities beyond simple group communication. For example, we provide a validation mechanism that performs several checks on the group members, to make sure that combining them together is possible. We also allow the client to request that results of the individual members are processed before they are sent to the client. For example, the client can request to obtain only the maximum value of all individual members. Another important optional extension to CoAP allows clients to continuously observe resources by registering their interest in receiving notifications from CoAP servers once there are changes to the values of the observed resources. By using this publish/subscribe mechanism the client does not need to continuously poll the resource to find out whether it has changed its value. This typically leads to more efficient communication patterns that preserve valuable device and LLN resources. Unfortunately CoAP observe does not work together with the CoAP group communication extension, since the observe extension assumes unicast communication while the group communication extension only support multicast communication. In this PhD we propose to extend our own group communication solution to offer group observation capabilities. By combining group observation with group processing features, it becomes possible to notify the client only about certain changes to the observed group (e.g., the maximum value of all group members has changed). Acknowledging that the use of multicast as well as unicast has strengths and weaknesses we propose to extend our unicast based solution with certain multicast features. By doing so we try to combine the strengths of both approaches to obtain a better overall group communication that is flexible and that can be tailored according to the use case needs. Together, the proposed mechanisms represent a powerful and comprehensive solution to the challenging problem of group communication with constrained devices. We have evaluated the solutions proposed in this PhD extensively and in a variety of forms. Where possible, we have derived theoretical models and have conducted numerous simulations to validate them. We have also experimentally evaluated those solutions and compared them with other proposed solutions using a small demo box and later on two large scale wireless sensor testbeds and under different test conditions. The first testbed is located in a large, shielded room, which allows testing under controlled environments. The second testbed is located inside an operational office building and thus allows testing under normal operation conditions. Those tests revealed performance issues and some other problems. We have provided some solutions and suggestions for tackling those problems. Apart from the main contributions, two other relevant outcomes of this PhD are described in the appendices. In the first appendix we review the most important IETF standardization efforts related to the IoT and show that with the introduction of CoAP a complete set of standard protocols has become available to cover the complete networking stack and thus making the step from the IoT into the Web of Things (WoT). Using only standard protocols makes it possible to integrate devices from various vendors into one bigWoT accessible to humans and machines alike. In the second appendix, we provide an alternative solution for grouping constrained devices by using virtualization techniques. Our approach focuses on the objects, both resource-constrained and non-constrained, that need to cooperate by integrating them into a secured virtual network, named an Internet of Things Virtual Network or IoT-VN. Inside this IoT-VN full end-to-end communication can take place through the use of protocols that take the limitations of the most resource-constrained devices into account. We describe how this concept maps to several generic use cases and, as such, can constitute a valid alternative approach for supporting selected applications
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