Contributions to the performance evaluation and improvement of the IPv6 routing protocol for low-power and lossy networks

Wireless Sensor Networks (WSNs) have become increasingly important. These networks comprise sensor and actuator nodes that enable intelligent monitoring and control applications in a wide spectrum of environments including smart cities, home automation, remote health and precision agriculture to mention a few. In certain IETF circles, networks of these characteristics are called Low Power and Lossy Networks (LLNs). Whereas most LLN protocol architectures were born without native IP support, there exists a tendency in the market towards IP convergence, since IP-based LLNs offer an open and tandardized way of connecting LLNs to the Internet, thus nabling the Internet of Things (IoT). Since most LLN configurations are multihop, and thus a routing protocol is required, the IETF created the Routing Over Low power and Lossy networks (ROLL) working group, which decided to develop a new routing protocol called IPv6 Routing Protocol for LLNs (RPL). RPL was specifically designed to meet the requirements of LLNs and is a central component of the IETF protocol suite for the IoT. Since RPL has already been deployed in millions of nodes, it is fundamental to characterize its properties, evaluate the influence of its main parameters and options on network performance, and analyze performance improvement possibilities. This PhD thesis presents the following original contributions in this field: 1. Evaluation of the influence of the main RPL parameters on the network convergence process over IEEE 802.15.4 multihop networks, in terms of network characteristics such as size and density. In addition, a mechanism that leverages an option available in RPL for accelerating network convergence has been proposed and evaluated. This study provides a guideline for configuring and selecting adequately crucial RPL parameters and mechanisms for achieving high network convergence performance, as well as a characterization of the related performance trade-offs. 2. Development of an analytical model for estimating the network convergence time of RPL in a static chain topology network of IEEE 802.15.4 nodes, in the presence of bit errors. Results show the scenarii in terms of BER and chain topology length that may dramatically degrade performance experienced by a user. The model provides a lower bound on the network convergence time for a random topology network. 3. Development of an analytical tool to estimate the number of control messages transmitted in a random topology static network which uses the Trickle algorithm (a transmission scheduling algorithm used in RPL) under steady state conditions. Results show the accuracy of the model, which can be used for both synchronous and asynchronous networks. The slight difference in performance between these two network configurations is discussed and illustrated. 4. Theoretical evaluation of the route change latency incurred by RPL when 6LoWPAN Neighbor Discovery (ND) is used. On this basis, a study on the impact of the relevant 6LoWPAN ND and RPL parameters on path availability and the trade-off between path availability and message overhead, has been carried out. 5. Development of a RPL simulator for OMNeT++ using the MiXiM framework.La importància de les Wireless Sensor Networks (WSNs) ha estat creixent significativament en els darrers anys. Aquestes xarxes comprenen node sensors i actuadors que possibiliten aplicacions de control i monitorització en un ampli ventall d'entorns, incloent les ciutats intel·ligents, automatització residencial, etc. En alguns cercles de l'IETF, aquestes xarxes són anomenades Low Power and Lossy Networks (LLNs). La majoria d'arquitectures de protocols van néixer sense suport natiu per a IP, per ha existit recentment una tendència en el mercat envers la convergència IP, ja que les LLN basades en IP ofereixen una manera oberta i estandaritzada de connectar LLNs a Internet, tot creant la Internet de les Coses. Atès que moltes configuracions de LLNsn multisalt, i per tant es requereix un protocol d'encaminament, l'IETF va crear el Routing Over Low power and Lossy networks (ROLL) working group, que va decidir dissenyar un nou protocol anomenat IPv6 Routing Protocol for LLNs (RPL). RPL va ser específicament dissenyat per complir amb els requeriments de les LLNs i és un component central de la pila de protocols de l'IETF per a la Internet de les Coses. Atès que RPL ha estat desplegat en milions de nodes, és fonamental caracteritzar les seves propietats, avaluar la influència dels seus paràmetres principals i opcions en el rendiment, i analitzar les possibilitats de millora del protocol. Aquesta tesi presenta les següents contribucions originals en aquest camp: 1. Avaluació de la influència dels principals paràmetres de RPL en el procés de convergència de la xarxa en xarxes IEEE 802.15.4, en termes de característiques com la mida i la densitat de la xarxa. A més a més, s'ha proposat i avaluat un mecanisme que utilitza una opci disponible en el RPL per a accelerar la convergència de xarxa. Aquest estudi proporciona una guia per configurar i escollir adequadament paràmetres crucials del protocol RPL per tal d'assolir una ràpida convergència de xarxa, això com una caracteritzaci dels compromisos relacionats. 2. Desenvolupament d'un model analátic per estimar el temps de convergència de xarxa de RPL en una topologia de xarxaestàtica en cadena de nodes IEEE 802.15.4, en presència d'errors. Els resultats mostren els escenaris en termes de BER i mida de la cadena que poden degradar les prestacions percebudes per l'usuari. El model proporciona una fita inferior del temps de convergència de xarxa per a una topologia aleatòria. 3. Desenvolupament d'una eina analítica per estimar el nombre de missatges de control transmesos en una xarxa de topologia aleat ria i estàtica on s'usa l'algoritme Trickle (algoritme de planificació i control de les transmissions emprat en RPL), en condicions de règim permanent. Els resultats mostren la precisió del model, que pot ser emprat en xarxes síncrones i asíncrones. La lleugera diferència de prestacions entre un escenari i l'altre és discutida i il·lustrada. 4. Avaluació teòrica del temps de canvi de ruta de RPL quan s'usa 6LoWPAN Neighbor Discovery (ND). En base a aixó , es realitza un estudi de l'impacte dels paràmetres rellevants de RPL i 6LoWPAN ND en la disponibilitat de cambi el compromís amb l'overhead de missatges. 5. Desenvolupament d'un simulador de RPL per a OMNeT++ usant el MiXiM framewor

Route change latency in low-power and lossy wireless networks using RPL and 6LoWPAN neighbor discovery

The IETF ROLL WG is currently in the final steps of the specification of RPL, a new routing protocol for low power and lossy networks (e.g. wireless sensor networks). RPL may use layer two- and layer three-based mechanisms for neighbor reachability maintenance. Since layer two mechanisms may not always be available, RPL relies by default on the 6LoWPAN Neighbor Discovery, a version of the IPv6 Neighbor Discovery which is optimized for LLNs. This paper provides an analysis of the impact of various RPL and 6LoWPAN Neighbor Discovery parameter settings on the link availability and end-to-end path availability, and the related message overhead. Results show that careful tuning of the relevant parameters is critical for obtaining good network performance

Modeling the network convergence time in RPL in error-prone, IEEE 802.15.4 chain topology multihop networks

This paper presents an analytical model for estimating the network convergence time of IPv6 Routing Protocol for Low-power and Lossy Networks (RPL) in a static chain topology network of IEEE 802.15.4 nodes, in the presence of bit errors. The model presented is validated by extensive simulation results. We show that performance degradation may be noticed by a user for BER values around or greater than 8·1

Modeling the network convergence time in RPL in error-prone, IEEE 802.15.4 chain topology multihop networks

This paper presents an analytical model for estimating the network convergence time of IPv6 Routing Protocol for Low-power and Lossy Networks (RPL) in a static chain topology network of IEEE 802.15.4 nodes, in the presence of bit errors. The model presented is validated by extensive simulation results. We show that performance degradation may be noticed by a user for BER values around or greater than 8·10Postprint (published version

On the network convergence process in RPL over IEEE 802.15.4 multihop networks: improvement and trade-offs

The IPv6 Routing Protocol for Low-power and Lossy Networks (RPL) has been recently developed by the Internet Engineering Task Force (IETF). Given its crucial role in enabling the Internet of Things, a significant amount of research effort has already been devoted to RPL. However, the RPL network convergence process has not yet been investigated in detail. In this paper we study the influence of the main RPL parameters and mechanisms on the network convergence process of this protocol in IEEE 802.15.4 multihop networks. We also propose and evaluate a mechanism that leverages an option available in RPL for accelerating the network convergence process. We carry out extensive simulations for a wide range of conditions, considering different network scenarios in terms of size and density. Results show that network convergence performance depends dramatically on the use and adequate configuration of key RPL parameters and mechanisms. The findings and contributions of this work provide a RPL configuration guideline for network convergence performance tuning, as well as a characterization of the related performance trade-offs