Synchronization of multihop wireless sensor networks at the application layer

Time synchronization is a key issue in wireless sensor networks; timestamping collected data, tasks scheduling, and efficient communications are just some applications. From all the existing techniques to achieve synchronization, those based on precisely time-stamping sync messages are the most accurate. However, working with standard protocols such as Bluetooth or ZigBee usually prevents the user from accessing lower layers and consequently reduces accuracy. A receiver-to-receiver schema improves timestamping performance because it eliminates the largest non-deterministic error at the sender’s side: the medium access time. Nevertheless, utilization of existing methods in multihop networks is not feasible since the amount of extra traffic required is excessive. In this article, we present a method that allows accurate synchronization of large multihop networks, working at the application layer while keeping the message exchange to a minimum. Through an extensive experimental study, we evaluate the protocol’s performance and discuss the factors that influence synchronization accuracy the most.Ministerio de Ciencia y Tecnología TIN2006-15617-C0

Enabling limited traffic scheduling in asynchronous ad hoc networks

We present work-in-progress developing a communication framework that addresses the communication challenges of the decentralized multihop wireless environment. The main contribution is the combination of a fully distributed, asynchronous power save mechanism with adaptation of the timing patterns defined by the power save mechanism to improve the energy and bandwidth efficiency of communication in multihop wireless networks. The possibility of leveraging this strategy to provide more complex forms of traffic management is explored

Low Power, Low Delay: Opportunistic Routing meets Duty Cycling

Traditionally, routing in wireless sensor networks consists of two steps: First, the routing protocol selects a next hop, and, second, the MAC protocol waits for the intended destination to wake up and receive the data. This design makes it difficult to adapt to link dynamics and introduces delays while waiting for the next hop to wake up. In this paper we introduce ORW, a practical opportunistic routing scheme for wireless sensor networks. In a dutycycled setting, packets are addressed to sets of potential receivers and forwarded by the neighbor that wakes up first and successfully receives the packet. This reduces delay and energy consumption by utilizing all neighbors as potential forwarders. Furthermore, this increases resilience to wireless link dynamics by exploiting spatial diversity. Our results show that ORW reduces radio duty-cycles on average by 50% (up to 90% on individual nodes) and delays by 30% to 90% when compared to the state of the art

Analysis of Denial-of-Service attacks on Wireless Sensor Networks using simulation

Evaluation of Wireless Sensor Networks (WSN) for performance evaluation is a popular research area and a wealth of literature exists in this area. Denial-of-Service (DoS) attacks are recognized as one of the most serious threats due to the resources constrained property in WSN. The Zigbee model provided in OPNET 16 is suitable for modelling WSNs. This paper presents an evaluation of the impact of DoS attacks on the performances of Wireless Sensor Networks by using the OPNET modeller. Numerical results, discussions and comparisons are provided for various simulation scenarios. The results can be of great help for optimisation studies in WSN environments under DoS attacks as well as understanding the severity and critical nodes within the WSN. The effects of DoS attacks on the performance of WSNs are considered to critically analyse these issues

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

Active Queue Management for Fair Resource Allocation in Wireless Networks

This paper investigates the interaction between end-to-end flow control and MAC-layer scheduling on wireless links. We consider a wireless network with multiple users receiving information from a common access point; each user suffers fading, and a scheduler allocates the channel based on channel quality,but subject to fairness and latency considerations. We show that the fairness property of the scheduler is compromised by the transport layer flow control of TCP New Reno. We provide a receiver-side control algorithm, CLAMP, that remedies this situation. CLAMP works at a receiver to control a TCP sender by setting the TCP receiver's advertised window limit, and this allows the scheduler to allocate bandwidth fairly between the users

Experimental trade-offs between different strategies for multihop communications evaluated over real deployments of wireless sensor network for environmental monitoring

Although much work has been done since wireless sensor networks appeared, there is not a great deal of information available on real deployments that incorporate basic features associated with these networks, in particular multihop routing and long lifetimes features. In this article, an environmental monitoring application (Internet of Things oriented) is described, where temperature and relative humidity samples are taken by each mote at a rate of 2 samples/min and sent to a sink using multihop routing. Our goal is to analyse the different strategies to gather the information from the different motes in this context. The trade-offs between 'sending always' and 'buffering locally' approaches were analysed and validated experimentally, taking into account power consumption, lifetime, efficiency and reliability. When buffering locally, different options were considered such as saving in either local RAM or FLASH memory, as well different alternatives to reduce overhead with different packet sizes. The conclusion is that in terms of energy and durability, the best option is to reduce the overhead. Nevertheless, sending larger packets is not worthy when the probability of retransmission is high. If real-time monitoring is required, then sending always is better than buffering locally