Impact of mobility on the IoT MAC infrastructure: IEEE 802.15.4e TSCH and LLDN platform

Realizing the target of high reliability and availability is a crucial concept in the IoT context. Different types of IoT applications introduce several requirements and obstacles. One of the important aspects degrading network performance is the node mobility inside the network. Without a solid and adaptive mechanism, node mobility can disrupt the network performance due to dissociations from the network. Hence, reliable techniques must be incorporated to tackle the overhead of node movement. In this paper, the overhead of mobility on both IEEE 802.15.4e timeslotted channel hopping (TSCH) and low latency deterministic (LLDN) modes is investigated. These two modes can be considered as the MAC layer of the IoT paradigm because of their importance and resilience to different network obstacles. In addition, the set of metrics and limitations that influence the network survivability will be identified to ensure efficient mobile node handling process. Both TSCH and LLDN have been implemented via the Contiki OS to determine their functionality. TSCH has been demonstrated to have better node connectivity due to the impact of frame collision in LLDN. In addition, by neglecting the overhead of collision, the LLDN has been shown to have better connectivity and low radio duty cycle (RDC)

Mesh-under cluster-based routing protocol for IEEE 802.15.4 sensornetwork

The radio duty cycle (RDC) of wireless sensor nodes can be considered as a crucial factor that determines the wireless sensor network (WSN) lifetime and its service availability. Clustering would be a preferable solution to minimize node radio duty cycle by electing multiple cluster heads (CHs) around the network to schedule node transmissions and collect readings. This paper presents a mesh-under cluster-based routing (MUCBR) protocol that will divide the sensor network into multiple clusters and perform the routing function within the IEEE 802.15.4 platform. MUCBR is implemented via the Contiki operating system (OS). It reschedules the structure of the 802.15.4 standard in order to reduce the RDC of the sensor nodes and minimize the number of collisions. The election of the CHs is density-aware and determined by the routing direction inside the network which in turn reduces the number of hops and minimizes the number of collisions caused by the existence of multiple CHs in a single area. The proposed MUCBR manages to achieve a RDC of 0.08% for non-CH nodes and 1.3% for CH nodes while reducing the impact of collision by 40% as compared to the 802.15.4 standard

Dynamic cluster head election protocol for mobile wireless sensor networks

A dynamic cluster head election protocol (DCHEP) is proposed in this work to improve network availability and energy efficiency for mobile wireless sensor networks (WSNs) under the beacon-enabled IEEE 802.15.4 standard. The proposed protocol (DCHEP) is developed and simulated using CASTALIA/OMNET++ with a realistic radio model and node behaviour. DCHEP improves the network availability and lifetime and maintains clusters hierarchy in a proactive manner even in a mobile WSN where all the nodes including cluster heads (CHs) are mobile, this is done by dynamically switching CHs allowing nodes to act as multiple backup cluster heads (BCHs) with different priorities based on their residual energy and connectivity to other clusters. DCHEP is a flexible and scalable solution targeted for dense WSNs with random mobility. The proposed protocol achieves an average of 33% and 26% improvement to the availability and energy efficiency respectively compared with the original standard

Tackling Mobility in Low Latency Deterministic Multihop IEEE 802.15.4e Sensor Network

Providing reliable services for low latency (LL) applications within the IoT context is a challenging issue. Several wireless sensor network (WSN) applications require deterministic systems that ensure a reliable and low latency aggregation service. The IEEE 802.15.4e standard, which is considered as the backbone of the IoT regarding WSN, has presented the low-latency deterministic network mode (LLDN) that can fulfil the major requirements of low latency applications. Meanwhile, several LL applications, for example in the automotive industry, demand the support of sensor node mobility which in turn affects network performance. Node mobility triggers several dissociations from the network that will increase latency and degrade node throughput. In this paper, we investigate the impact of node mobility over the LLDN mode while defining key factors that maximize latency and degrade throughput. In addition, an enhanced version of the LLDN mode is presented and evaluated that supports node mobility while maintaining the targeted limits of LL application requirements. The proposed mobility aware (MA-LLDN) technique manages to reduce the dissociation overhead by a factor of 75% while the packet delivery ratio (PDR) has been enhanced by 30%. Furthermore, this paper presents an analytical model that provides a snapshot of the tradeoff process between different metrics in the IEEE 802.15.4e LLDN design, which must be considered prior network deployment in mobile LL applications

Dynamic RPL for Multi-hop Routing in IoT Applications

The Routing Protocol for Low Power and Lossy Networks (RPL) has become the standard routing protocol for the Internet of Things (IoT). This paper investigates the use of RPL in dynamic networks and presents an enhanced RPL for different applications with dynamic mobility and diverse network requirements. This implementation of RPL is designed with a new dynamic Objective-Function (D-OF) to improve the Packet Delivery Ratio (PDR), end-to-end delay and energy consumption while maintaining low packet overhead and loop-avoidance. We propose a controlled reverse-trickle timer based on received signal strength identification (RSSI) readings to maintain high responsiveness with minimum overhead and consult the objective function when a movement or an inconsistency is detected to help nodes make an informed decision. Simulations are done using Cooja with random waypoint mobility scenario for healthcare applications considering multi-hop routing. The results show that the proposed dynamic RPL (D-RPL) adapts to the nodes mobility and has a higher PDR, slightly lower end-to-end delay and reasonable energy consumption compared to related existing protocols

Mobility Aware Framework for Timeslotted Channel Hopping IEEE 802.15.4e Sensor Networks

Ubiquitous object networking has sparked the concept of the Internet of Things (IoT), which defines a new era in the world of networking. Realization of this concept needs to be addressed by standardization efforts that will shape the infrastructure of the networks. This has been achieved through the IEEE 802.15.4e, 6LoWPAN, and IPv6 standards. In addition, the IEEE 802.15.4e standard, which can be considered as the backbone of the IoT structure, has presented timeslotted channel hopping (TSCH). Although these standards provide a coherent and diffused system, several implications challenge these standards to achieve optimal performance and reliability. Node mobility can be considered as the delimited factor for realizing a fully connected network, especially with the inclusion of TSCH mode that will complicate the association process of the mobile nodes, as a result of the frequency hopping mechanism. In this paper, we investigate the impact of mobility over the TSCH sensor network, and a Markov chain model is presented to determine the parameters that affect mobile node association process. Second, we provide a proposed mobility-aware Mobile Timeslotted Channel Hopping (MTSCH) protocol that will facilitate the mobile nodes association and minimize the latency incurred by leaving the nodes dissociated from the network. TSCH and the proposed MTSCH techniques have been implemented and evaluated through Contiki OS. The proposed MTSCH manages to reduce the radio duty cycle of the mobile nodes by an average of 30% while increasing the connectivity of the nodes by 25%. Moreover, cluster heads managed to save energy by a ratio of 14%

Congestion analysis for low power and lossy networks

Low Power and Lossy Networks (LLNs) represent one of the interesting research areas in recent years. The IETF ROLL and 6LoWPAN working groups have developed new IP based protocols for LLNs such as the RPL routing protocol. In LLNs e.g. 6LoWPANs, heavy data traffic causes congestion which significantly degrades network performance. In this paper, we explore the impact of congestion on 6LoWPAN networks where an extensive analysis is carried out with different scenarios and parameters. Analysis results show that when congestion occurs, the majority of packets are lost due to buffer overflow as compared to channel loss. Also, we found that when the application payload length is increased since IPv6 packets are fragmented, the reassembly timeout parameter value has a significant effect on network performance. Thus, it is important to consider buffer occupancy and the reassembly timeout parameter in protocol design, e.g. RPL, to improve network performance when congestion does occur

Congestion-aware RPL for 6L0WPAN networks

IPv6 over low power wireless personal area network (6L0WPAN) is promising to be used in many different IoT applications. Recently, many protocols have been proposed for 6LoWPAN networks such as RPL routing protocol which is developed by the ROLL working group and expected to be the standard routing protocol for 6LoWPAN. Many problems are facing 6LoWPAN as it connects to the Internet such as congestion. In this paper, we propose a new RPL routing metric called Buffer Occupancy which reduces the number of lost packets due to buffer overflow when congestion does occur. Also, a new RPL objective function called Congestion-Aware Objective Function (CA-OF) is presented. The proposed objective function works efficiently when congestion occurs by selecting less congested paths. Simulation results show that CA-OF improves performance in the presence of congestion by an overall average of 37.4% in term of number of lost packets, throughput, packet delivery ratio and energy consumption