A Survey of Limitations and Enhancements of the IPv6 Routing Protocol for Low-power and Lossy Networks: A Focus on Core Operations <s> b) Additive Based Composition Enhancements <s> The design and implementation of healthcare system using sensor network technology has been one of the most active research topics currently. The research on wireless sensor network mostly focuses on energy saving, such as duty cycle scheduling, and path routing, such as routing protocol for low power and lossy networks (RPL) which however only takes into account a single metric, reliability or energy, as routing decision. If RPL only considers the reliability metric, nodes will suffer from uneven energy. If it only considers the energy metric, nodes will suffer from the rise of packet loss ratio. In this paper, we propose an energy-oriented routing mechanism to improve RPL routing protocol by combining the expected transmission count (ETX) and remaining energy metrics. The simulation will be conducted to analyze the performance of the proposed mechanism. <s> BIB001 </s> A Survey of Limitations and Enhancements of the IPv6 Routing Protocol for Low-power and Lossy Networks: A Focus on Core Operations <s> b) Additive Based Composition Enhancements <s> In the recent past, we witnessed to a dramatic growth of networks with a huge number of interconnected wireless nodes exchanging large amounts of information. This has brought to the need of ad-hoc, energy-aware protocols suitable for low-power and lossy networks. Among these, Routing Protocol for Low Power and Lossy Networks (RPL) is surely one of the most interesting ones. It chooses the optimal routes from a source to a destination node, based on specific metrics. In this work we present a RPL compliant composite metric that considers both reliability and energy. Its aim is twofold. First, it realizes energy consumption balancing, so that each node tends to consume the same amount of energy of all the others, thus prolonging the overall network lifetime. Second, it takes into account data reliability along the paths, expressed by the well known Expected Transmission Count (ETX). The effectiveness of the proposed metric is confirmed by some interesting simulation results, that strongly encourage a deeper investigation on this issue. <s> BIB002
The study in BIB001 addresses the issue of RPL relying only on a single metric: energy or reliability. The authors in this study highlighted the problems of unbalanced traffic and the consequently uneven energy consumption distribution among network nodes in RPL. In particular, the study pointed that using ETX as single metric in RPL network would result in excessive use of some paths, especially those with high delivery rates. This excessive use of good-quality paths will result eventually in network partition and reduce the overall lifetime of the network BIB001 . If energy is selected as the sole routing metric, on the other hand, the reliability of the path might be impacted negatively. To balance energy consumption of nodes while providing highly reliable paths, the study proposes a weighted energy-oriented composite metric that takes into consideration a node's residual energy in addition to ETX. The study results show that energy consumption is balanced to some extent by the proposed technique, which enhances network lifetime by up to 12%. An Energy Efficient and Reliable Composite Metric for RPL Networks is proposed in BIB002 . This composite metric takes into consideration both the reliability, represented by the ETX metric, and energy efficiency to balance energy consumption among nodes and enhance the network lifetime. The proposed metric is called the Lifetime and Latency Aggregateable Metric (L2AM). In particular, a node running L2AM, first combines transmission power of the link and a node's residual energy using an exponential function to produce what is called the primary metric. The ETX metric is then multiplied by the primary metric to get the composite metric overall cost: this is what must be minimized when selecting the preferred parent. For evaluation purposes, the proposed metric is compared to ETX RPL in terms of network lifetime and remaining energy. The results have shown that the L2AM outperforms ETX RPL by up to 56% in terms of network lifetime. Under-specification of metrics composition (Section IV-A-2) The superiority of proposed OF over ETX-based OF in terms of PDR seems unjustifiable. No real testbed experiments. Combining the non-storing and storing modes of operation to carry out the forwarding decisions in the downward direction.