Iain W. Phillips

Stateless multicast forwarding with RPL in 6LowPAN sensor networks

Recent research efforts have resulted in efficient support for IPv6 in Low power Wireless Personal Area Networks (6LoWPAN), with the “IPv6 Routing Protocol for Low power and Lossy Networks” (RPL) being on the forefront as the state of the art routing approach. However, little attention has been paid to IPv6 multicast for networks of constrained devices. The “Multicast Forwarding Using Trickle” (Trickle Multicast) internet draft is one of the most noteworthy efforts, while RPLs specification also attempts to address the area but leaves many questions unanswered. In this paper we expose our concerns about the Trickle Multicast (TM) algorithm, backed up by thorough performance evaluation. We also introduce SMRF, an alternative multicast forwarding mechanism for RPL networks, which addresses TMs drawbacks. Simulation results demonstrate that SMRF achieves significant delay and energy efficiency improvements at the cost of a small increase in packet loss. We have extended the TCP/IP engine of the Contiki embedded Operating System to support both algorithms. Both implementations have been made available to the community.

Experiences from porting the Contiki operating system to a popular hardware platform

In contrast to original belief, recent work has demonstrated the viability of IPv6-based Wireless Sensor Networks (WSNs). This has led to significant research and standardization efforts with outcomes such as the “IPv6 over Low-Power Wireless Personal Area Networks” (6LoWPAN) specification. The Contiki embedded operating system is an important open source, multi-platform effort to implement 6LoWPAN functionality for constrained devices. Alongside its RFC-compliant TCP/IP stack (uIP), it provides support for 6LoWPAN and many related standards. As part of our work, we have made considerable fixes and enhancements to one of Contikis ports. In the process, we made significant optimizations and a thorough evaluation of Contikis memory and code footprint characteristics, focusing on network-related functionality. In this paper we present our experiences from the porting process, we disclose our optimizations and demonstrate their significance. Lastly, we discuss a method of using Contiki to deploy an embedded Internet-to-6LoWPAN router. Our porting work has been made available to the community under the terms of the Contiki license.

TRENDY: an adaptive and context-aware service discovery protocol for 6LoWPANs

We propose, trendy, a new registry-based Service Discovery protocol with context awareness. It uses CoAP-based RESTful web services to provide a standard interoperable interface which can be easily translated from HTTP. In addition, trendy introduces an adaptive timer and grouping mechanism to minimise control overhead and energy consumption. trendys grouping is based on location tags to localise status maintenance traffic and to compose and offer new group based services. Our simulation results show that trendy techniques reduce the control traffic considerably and also reduce the energy consumption, while offering the optimal service selection.

A comparative study of congestion control algorithms in IPv6 Wireless Sensor Networks

In Wireless Sensor Networks (WSNs), congestion can cause a plethora of malfunctions such as packet loss, lower throughput and energy inefficiency, potentially resulting in reduced deployment lifetime and under-performing applications. This has led to several proposals describing congestion control (CC) mechanisms for sensor networks. Furthermore, the WSN research community has made significant efforts towards power saving MAC protocols with Radio Duty Cycling (RDC). However, careful study of previous work reveals that RDC schemes are often neglected during the design and evaluation of congestion control algorithms. In this paper, we argue that the presence (or lack) of RDC can drastically influence the performance of congestion detection. In addition, most WSN CC mechanisms are evaluated under traditional sensor network topologies and protocols (e.g. trickle data dissemination, tree data collection). The emerging IPv6 over Low power Wireless Personal Area Networks (6LoWPAN) and related standards pose a new requirement: we now need to investigate if previous findings regarding congestion control are still applicable. In this context, this paper contributes a comprehensive evaluation of existing congestion detection mechanisms in a simulated, multi-node 6LoWPAN sensor network. We present results from two sets of experiments, differentiated by the presence or lack of RDC.

Dynamic Node Lifetime Estimation for Wireless Sensor Networks

Wireless sensor networks (WSNs) consist of a large number of nodes each with limited battery power. As networks of these nodes are usually deployed unattended, network lifetime becomes an important concern. This paper proposes a novel, feasible, dynamic approach for node lifetime estimation that works for both static and dynamic loads. It covers several factors that have an impact on node lifetime, including battery type, model, brand, self-discharge, discharge rate, age, and temperature. The feasibility of the proposed scheme is evaluated by using the real testbed experiments with two wireless sensor platforms: Mica2 and N740 NanoSensor, two operating systems: TinyOS and Contiki, and different brands of alkaline and nickel-metal-hydride batteries. The deviation of the proposed estimation is in the range of -3.5%-2.5%. Three major contributions are presented in this paper: 1) the impact factors on node lifetime; 2) lifetime equations for any starting voltage, ageing, charge cycles, and temperatures; and 3) the dynamic node lifetime estimation technique, which is proposed and implemented on real hardware and software platforms in WSNs.

Adaptive and Context-Aware Service Discovery for the Internet of Things

The Internet of Things (IoT) vision foresees a future Internet encompassing the realm of smart physical objects, which offer hosted functionality as services. The role of service discovery is crucial when providing application-level, end-to-end integration. In this paper, we propose trendy: a RESTful web services based Service Discovery protocol to tackle the challenges posed by constrained domains while offering the required interoperability. It provides a service selection technique to offer the appropriate service to the user application depending on the available context information of user and services. Furthermore, it employs a demand-based adaptive timer and caching mechanism to reduce the communication overhead and to decrease the service invocation delay. trendy’s grouping technique creates location-based teams of nodes to offer service composition. Our simulation results show that the employed techniques reduce the control packet overhead, service invocation delay and energy consumption. In addition, the grouping technique provides the foundation for group-based service mash-ups and localises control traffic to improve scalability.

Network visualisation: a review

As communication networks increase in performance and complexity, and more dependence is placed upon them, it becomes ever more important that their behaviour is understood in an efficient and timely manner. Visualisation is an established technique for the presentation of the vast volume of data yielded in monitoring such networks. It is apparent, however, that much of the work in this area has been performed in isolation, and it is timely that a review of this research is conducted. The techniques for the visualisation of communication networks and related measurements are surveyed. The research is classified by the type of visualisation used and is separated into three classes: geographic visualisations, in which the data are presented with respect to the physical location of nodes in the network; abstract topological visualisations, in which the relationships between nodes are presented independently of physical location; and plot-based visualisation, in which the focus is a single point in the network, often presented with respect to time. The research in this area is reviewed and the techniques proposed are discussed in terms of these three classes.

IPv4 address sharing mechanism classification and tradeoff analysis

The growth of the Internet has made IPv4 addresses a scarce resource. Due to slow IPv6 deployment, IANA-level IPv4 address exhaustion was reached before the world could transition to an IPv6-only Internet. The continuing need for IPv4 reachability will only be supported by IPv4 address sharing. This paper reviews ISP-level address sharing mechanisms, which allow Internet service providers to connect multiple customers who share a single IPv4 address. Some mechanisms come with severe and unpredicted consequences, and all of them come with tradeoffs. We propose a novel classification, which we apply to existing mechanisms such as NAT444 and DS-Lite and proposals such as 4rd, MAP, etc. Our tradeoff analysis reveals insights into many problems including: abuse attribution, performance degradation, address and port usage efficiency, direct intercustomer communication, and availability.

DCCC6: Duty Cycle-aware congestion control for 6LoWPAN networks

In Wireless Sensor Networks (WSNs), congestion can cause a number of problems including packet loss, lower throughput and poor energy efficiency. These problems can potentially result in reduced deployment lifetime and under-performing applications. This has led to several proposals for congestion control (CC) mechanisms for sensor networks. Furthermore, the WSN research community has made significant efforts towards power saving MAC protocols with Radio Duty Cycling (RDC). However, careful study of previous work reveals that RDC schemes are often neglected during the design and evaluation of CC algorithms. In this context, this paper contributes a new CC scheme for Duty Cycle and IPv6 over Low power Wireless Personal Area Networks 6LoWPAN sensor Networks - DCCC6. DCCC6 detects the presence of duty cycling and adjust its operation accordingly. We evaluate DCCC6 both with simulations and on a testbed with multi node topologies. The experimental results have shown that DCCC6 achieved higher goodput and lower packet loss than previous works. Moreover, simulations show that DCCC6 maintained low energy consumption, average delay times and achieved a high degree of fairness.

Neighbour Discovery for Transmit Power Adjustment in IEEE 802.15.4 Using RSSI

Neighbour discovery (ND) is an important process for self-configuration as it provides useful information, such as neighbour nodes with some power saving parameters, for other processes. In wireless sensor networks, transmission power adjustment is one of the possible ways to minimise energy consumption and prolong network lifetime. This paper proposes the ND technique which provides the received signal strength indicator (RSSI) value for dynamic transmit power adjustment in IEEE 802.15.4. This work focuses on a single-hop network of wireless devices with different maximum transmission powers, where an asymmetric wireless link is very common. The energy consumption and packet loss rate are investigated through testbed experimentation. The proposed algorithm shows transmission efficiency which does not affect the packet loss rate. Moreover, it supports both environment change and the change of distance between nodes.