CoAP congestion control for the Internet of Things

“© © 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.” August Betzler, Javier Isern, Carles Gomez, Ilker Demirkol, Josep Paradells, "Experimental evaluation of congestion control for CoAP communications without end-to-end reliability", Ad Hoc Networks, pp. , 2016, ISSN 15708705. DOI: 10.1109/MCOM.2016.7509394CoAP is a lightweight RESTful application layer protocol devised for the IoT. Operating on top of UDP, CoAP must handle congestion control by itself. The core CoAP specification defines a basic congestion control mechanism, but it is not capable of adapting to network conditions. However, IoT scenarios exhibit significant resource constraints, which pose new challenges on the design of congestion control mechanisms. In this article we present CoCoA, an advanced congestion control mechanism for CoAP being standardized by the Internet Engineering Task Force CoRE working group. CoCoA introduces a novel round-trip time estimation technique, together with a variable backoff factor and aging mechanisms in order to provide dynamic and controlled retransmission timeout adaptation suitable for the peculiarities of IoT communications. We conduct a comparative performance analysis of CoCoA and a variety of alternative algorithms including state-of-the-art mechanisms developed for TCP. The study is based on experiments carried out in real testbeds. Results show that, in contrast to the alternative methods considered, CoCoA consistently outperforms the default CoAP congestion control mechanism in all evaluated scenarios.Peer ReviewedPostprint (author's final draft

TCP in the Internet of Things: from ostracism to prominence

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.TCP has traditionally been neglected as a transport-layer protocol for the Internet of Things (IoT). However, recent trends and industry needs are favoring TCP presence in IoT environments. In this article, we describe the main IoT scenarios where TCP will be used. We then analyze the historically claimed issues of TCP in the IoT context. We argue that, in contrast to generally accepted wisdom, most of those possible issues fall in one of the following categories: i) are also found in well-accepted IoT end-to-end reliability mechanisms, ii) can be solved, or iii) are not actual issues. Considering the future prominent role of TCP in the IoT, we provide recommendations for lightweight TCP implementation and suitable operation in such scenarios, based on our IETF standardization work on the topic.Postprint (author's final draft

Alternate marking-based network telemetry for industrial WSNs

For continuous, persistent and problem-free operation of Industrial Wireless Sensor Networks (IWSN), it is critical to have visibility and awareness into what is happening on the network at any one time. Especially, for the use cases with strong needs for deterministic and real-time network services with latency and reliability guarantees, it is vital to monitor network devices continuously to guarantee their functioning, detect and isolate relevant problems and verify if all system requirements are being met simultaneously. In this context, this article investigates a light-weight telemetry solution for IWSNs, which enables the collection of accurate and continuous flowbased telemetry information, while adding no overhead on the monitored packets. The proposed monitoring solution adopts the recent Alternate Marking Performance Monitoring (AMPM) concept and mainly targets measuring end-to-end and hopby-hop reliability and delay performance in critical application flows. Besides, the technical capabilities and characteristics of the proposed solution are evaluated via a real-life implementation and practical experiments, validating its suitability for IWSNs

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

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 ’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

Discovery and group communication for constrained Internet of Things devices using the Constrained Application Protocol

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 ’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

Contribution to the publish/subscribe communication model for the development of ubiquitous services in wireless sensor networks

Advances in wireless technologies and the rapid development of integrated electronics have made wireless sensor networks (WSN) one of the key technologies of the Internet of Things (IoT). Thanks to the ability of these networks to measure the physical phenomena of their environment, process and communicate this information using wireless technologies, they have excelled in the development of applications that respond or adapt to the context of a user, as is the case of ubiquitous environments such as smart cities, industrial automation, e-health among others. In addition, the IoT has opened the possibility that intelligent objects or devices are also capable of exchanging status information, conditions and capacity in order to interact with each other, in the same way that human beings have done through systems based on presence. These systems require information of an event in real time to react in a timely manner to the conditions or context of the user or device. These applications open new challenges in the management of WSN resources, since these networks operate in environments that are generally prone to packet loss and consist of generally small nodes with limited resources in memory, processing, bandwidth and power. The main objective of this thesis is the development of several mechanisms that allow the adaptation of the Publish/Subscribe protocols to the characteristics and limitations of the WSN for the provision of ubiquitous services in the context of the IoT. In addition, QoS support is supplied through mechanisms that provide reliability and timeliness in the delivery of packets and data aggregation techniques are applied to be efficient in the power consumption and the WSN bandwidth. Our research proposes an architecture to provide a presence service for WSN based on a Publish/ Subscribe model distributed and focused on mechanisms such as the aggregation of data and the publication of messages on demand to achieve energy efficiency and bandwidth. All these mechanisms have been applied in the design of a system called PASH aimed at home control based on the concept of Ambient Assisted Living (AAL). The reliability provided by Publish/Subscribe protocols in WSN is of great importance in the design of applications that require receiving a message to react on time or in real time to an event. Initially, we focused our study on increasing the proportion of packet delivery (PDR) in the destination node through the improvement of reliability mechanisms. We evaluated the reliability mechanism of the MQTT-SN protocol and several proposed mechanisms of the CoAP protocol. From this evaluation, we propose a new and simple adaptive retransmission mechanism to respond to packet loss in the most appropriate way. Finally, we consider that applications such as: e-health, critical infrastructure control and monitoring, among others, must meet different QoS requirements, such as reliability and timeliness for each type of message received. In addition, data aggregation techniques play an important role in WSN to reduce power consumption and bandwidth. In this thesis, we propose a mechanism that provides the application with three different levels of QoS: we provide an improvement of our previous relay mechanism for reliability, we include the data aggregation in our reliability mechanism and we provide a timeliness mechanism in the delivery of packets.Els avenços en les tecnologies sense fils i al ràpid desenvolupament de l'electrònica integrada, ha convertit les xarxes de sensors sense fils (WSN) en una de les tecnologies claus de l'Internet de les Coses (Iot). Gràcies a la capacitat que tenen aquestes xarxes de mesurar els fenòmens físics del seu entorn, processar i comunicar aquesta informació utilitzant tecnologies sense fils, s'han destacat en el desenvolupament d'aplicacions que responguin o s'adaptin al context d'un usuari, com és el cas dels entorns ubics com a ciutats intel·ligents, automatització industrial, salut electrònica entre d'altres. A més, el IOT ha obert la possibilitat que els objectes o dispositius intel·ligents també siguin capaços d'intercanviar informació d'estat, condicions i capacitat per tal d'interactuar entre si, de la mateixa manera que els éssers humans ho han fet a través de sistemes basats en presència. Aquests sistemes requereixen informació d'un esdeveniment en temps real per reaccionar de manera oportuna a les condicions o al context de l'usuari o dispositiu. Aquestes aplicacions obren nous desafiaments en l'administració dels recursos de WSN, ja que aquestes xarxes operen en entorns que generalment són propensos a la pèrdua de paquets i consten de nodes generalment petits amb recursos limitats en memòria, processament, ample de banda i alimentació. El principal objectiu d'aquesta tesi és el desenvolupament de diversos mecanismes que permetin l'adequació dels protocols d'Publish / Subscribe a les característiques i limitacions de la WSN per a la provisió de serveis ubics en el context de la IOT. A més, es brinda suport de QoS a través de mecanismes que proporcionen fiabilitat i puntualitat en el lliurament de paquets i s'apliquen tècniques d'agregació de dades per a ser eficients en el consum d'energia i l'ample de banda de la WSN. La nostra investigació proposa una arquitectura per a proporcionar un servei de presència per WSN basat en un model de Publish / Subscribe distribuït i centrat en mecanismes com ara l'agregació de dades i la publicació de missatges en demanda per aconseguir eficiència en l'energia i l'ample de banda . Tots aquests mecanismes han estat aplicats en el disseny d'un sistema anomenat Pash dirigit al control de la llar basat en el concepte de Vida Assistida (AAL). La fiabilitat proporcionada pels protocols de Publish / Subscribe WSN és de gran importància en el disseny d'aplicacions que requereixen rebre un missatge per reaccionar a temps o en temps real davant un esdeveniment. Inicialment enfoquem el nostre estudi en augmentar la proporció de lliurament de paquets (PDR) en el node de destinació a través de la millora dels mecanismes de fiabilitat. Avaluem el mecanisme de fiabilitat del protocol MQTT-SN i diversos mecanismes proposats del protocol COAP. A partir d'aquesta avaluació, proposem un nou i senzill mecanisme de retransmissió adaptable per respondre a la pèrdua de paquets de la manera més adequada. Finalment, considerem que les aplicacions com: salut electrònica, control d'infraestructura crítica i monitoratge, entre d'altres, han de complir diferents requisits de QoS, com la fiabilitat i la puntualitat per a cada tipus de missatge rebut. A més, les tècniques d'agregació de dades tenen un paper important en WSN per reduir el consum d'energia i l'ample de banda. En aquesta tesi, proposem un mecanisme que proporciona a la aplicació tres nivells de QoS diferents: proporcionem una millora del nostre mecanisme de retransmissió anterior per a la fiabilitat, incloem l'agregació de dades en el nostre mecanisme de fiabilitat i proporcionem un mecanisme de puntualitat en el lliurament de paquets.Postprint (published version

Contribution to the publish/subscribe communication model for the development of ubiquitous services in wireless sensor networks

Advances in wireless technologies and the rapid development of integrated electronics have made wireless sensor networks (WSN) one of the key technologies of the Internet of Things (IoT). Thanks to the ability of these networks to measure the physical phenomena of their environment, process and communicate this information using wireless technologies, they have excelled in the development of applications that respond or adapt to the context of a user, as is the case of ubiquitous environments such as smart cities, industrial automation, e-health among others. In addition, the IoT has opened the possibility that intelligent objects or devices are also capable of exchanging status information, conditions and capacity in order to interact with each other, in the same way that human beings have done through systems based on presence. These systems require information of an event in real time to react in a timely manner to the conditions or context of the user or device. These applications open new challenges in the management of WSN resources, since these networks operate in environments that are generally prone to packet loss and consist of generally small nodes with limited resources in memory, processing, bandwidth and power. The main objective of this thesis is the development of several mechanisms that allow the adaptation of the Publish/Subscribe protocols to the characteristics and limitations of the WSN for the provision of ubiquitous services in the context of the IoT. In addition, QoS support is supplied through mechanisms that provide reliability and timeliness in the delivery of packets and data aggregation techniques are applied to be efficient in the power consumption and the WSN bandwidth. Our research proposes an architecture to provide a presence service for WSN based on a Publish/ Subscribe model distributed and focused on mechanisms such as the aggregation of data and the publication of messages on demand to achieve energy efficiency and bandwidth. All these mechanisms have been applied in the design of a system called PASH aimed at home control based on the concept of Ambient Assisted Living (AAL). The reliability provided by Publish/Subscribe protocols in WSN is of great importance in the design of applications that require receiving a message to react on time or in real time to an event. Initially, we focused our study on increasing the proportion of packet delivery (PDR) in the destination node through the improvement of reliability mechanisms. We evaluated the reliability mechanism of the MQTT-SN protocol and several proposed mechanisms of the CoAP protocol. From this evaluation, we propose a new and simple adaptive retransmission mechanism to respond to packet loss in the most appropriate way. Finally, we consider that applications such as: e-health, critical infrastructure control and monitoring, among others, must meet different QoS requirements, such as reliability and timeliness for each type of message received. In addition, data aggregation techniques play an important role in WSN to reduce power consumption and bandwidth. In this thesis, we propose a mechanism that provides the application with three different levels of QoS: we provide an improvement of our previous relay mechanism for reliability, we include the data aggregation in our reliability mechanism and we provide a timeliness mechanism in the delivery of packets.Els avenços en les tecnologies sense fils i al ràpid desenvolupament de l'electrònica integrada, ha convertit les xarxes de sensors sense fils (WSN) en una de les tecnologies claus de l'Internet de les Coses (Iot). Gràcies a la capacitat que tenen aquestes xarxes de mesurar els fenòmens físics del seu entorn, processar i comunicar aquesta informació utilitzant tecnologies sense fils, s'han destacat en el desenvolupament d'aplicacions que responguin o s'adaptin al context d'un usuari, com és el cas dels entorns ubics com a ciutats intel·ligents, automatització industrial, salut electrònica entre d'altres. A més, el IOT ha obert la possibilitat que els objectes o dispositius intel·ligents també siguin capaços d'intercanviar informació d'estat, condicions i capacitat per tal d'interactuar entre si, de la mateixa manera que els éssers humans ho han fet a través de sistemes basats en presència. Aquests sistemes requereixen informació d'un esdeveniment en temps real per reaccionar de manera oportuna a les condicions o al context de l'usuari o dispositiu. Aquestes aplicacions obren nous desafiaments en l'administració dels recursos de WSN, ja que aquestes xarxes operen en entorns que generalment són propensos a la pèrdua de paquets i consten de nodes generalment petits amb recursos limitats en memòria, processament, ample de banda i alimentació. El principal objectiu d'aquesta tesi és el desenvolupament de diversos mecanismes que permetin l'adequació dels protocols d'Publish / Subscribe a les característiques i limitacions de la WSN per a la provisió de serveis ubics en el context de la IOT. A més, es brinda suport de QoS a través de mecanismes que proporcionen fiabilitat i puntualitat en el lliurament de paquets i s'apliquen tècniques d'agregació de dades per a ser eficients en el consum d'energia i l'ample de banda de la WSN. La nostra investigació proposa una arquitectura per a proporcionar un servei de presència per WSN basat en un model de Publish / Subscribe distribuït i centrat en mecanismes com ara l'agregació de dades i la publicació de missatges en demanda per aconseguir eficiència en l'energia i l'ample de banda . Tots aquests mecanismes han estat aplicats en el disseny d'un sistema anomenat Pash dirigit al control de la llar basat en el concepte de Vida Assistida (AAL). La fiabilitat proporcionada pels protocols de Publish / Subscribe WSN és de gran importància en el disseny d'aplicacions que requereixen rebre un missatge per reaccionar a temps o en temps real davant un esdeveniment. Inicialment enfoquem el nostre estudi en augmentar la proporció de lliurament de paquets (PDR) en el node de destinació a través de la millora dels mecanismes de fiabilitat. Avaluem el mecanisme de fiabilitat del protocol MQTT-SN i diversos mecanismes proposats del protocol COAP. A partir d'aquesta avaluació, proposem un nou i senzill mecanisme de retransmissió adaptable per respondre a la pèrdua de paquets de la manera més adequada. Finalment, considerem que les aplicacions com: salut electrònica, control d'infraestructura crítica i monitoratge, entre d'altres, han de complir diferents requisits de QoS, com la fiabilitat i la puntualitat per a cada tipus de missatge rebut. A més, les tècniques d'agregació de dades tenen un paper important en WSN per reduir el consum d'energia i l'ample de banda. En aquesta tesi, proposem un mecanisme que proporciona a la aplicació tres nivells de QoS diferents: proporcionem una millora del nostre mecanisme de retransmissió anterior per a la fiabilitat, incloem l'agregació de dades en el nostre mecanisme de fiabilitat i proporcionem un mecanisme de puntualitat en el lliurament de paquets.Postprint (published version

Facilitating the creation of IoT applications through conditional observations in CoAP

With the advent of IPv6, the world is getting ready to incorporate smart objects to the current Internet to realize the idea of Internet of Things. The biggest challenge faced is the resource constraint of the smart objects to directly utilize the existing standard protocols and applications. A number of initiatives are currently witnessed to resolve this situation. One of such initiatives is the introduction of Constrained Application Protocol. This protocol is developed to fit in the resource-constrained smart object with the ability to easily translate to the prominent representational state transfer implementation, hypertext transfer protocol (and vice versa). The protocol has several optional extensions, one of them being, resource observation. With resource observation, a client may ask a server to be notified every state change of the resource. However, in many applications, all state changes are not significant enough for the clients. Therefore, the client will have to decide whether to use a value sent by a server or not. This results in wastage of the already constrained resources (bandwidth, processing power,aEuro broken vertical bar). In this paper, we introduced an alternative to the normal resource observation function, named Conditional Observation, where clients tell the servers the criteria for notification. We evaluated the power consumption and number of packets transmitted between clients and servers by using different network sizes and number of servers. In all cases, we found out that the existing observe option results in excessive number of packets (most of them unimportant for the client) and higher power consumption. We also made an extensive theoretical evaluation of the two approaches which give consistent result with the results we got from experimentation

A holistic approach to ZigBee performance enhancement for home automation networks

Wireless home automation networks are gaining importance for smart homes. In this ambit, ZigBee networks play an important role. The ZigBee specification defines a default set of protocol stack parameters and mechanisms that is further refined by the ZigBee Home Automation application profile. In a holistic approach, we analyze how the network performance is affected with the tuning of parameters and mechanisms across multiple layers of the ZigBee protocol stack and investigate possible performance gains by implementing and testing alternative settings. The evaluations are carried out in a testbed of 57 TelosB motes. The results show that considerable performance improvements can be achieved by using alternative protocol stack configurations. From these results, we derive two improved protocol stack configurations for ZigBee wireless home automation networks that are validated in various network scenarios. In our experiments, these improved configurations yield a relative packet delivery ratio increase of up to 33.6%, a delay decrease of up to 66.6% and an improvement of the energy efficiency for battery powered devices of up to 48.7%, obtainable without incurring any overhead to the network.Postprint (published version