You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: A Survey of Limitations and Enhancements of the IPv6 Routing Protocol for Low-power and Lossy Networks: A Focus on Core Operations 
Chapter Title:  2) Under-specification of Metrics Composition 
1. Abstract of Cited Paper (BIB001):  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. 
2. Abstract of Cited Paper (BIB002):  Low power and lossy networks (LLNs) require efficient routing protocols that should meet the requirements of the critical applications, such as real-time, reliability and high availability. RPL has been recently proposed by the ROLL working group as a tree routing protocol specifically designed for LLNs. It relies on objective functions to construct routes that optimize or constrain a routing metric on the paths. However, the working group did not specify the set of metrics and/or constraints to be used to specify the preferred path, and left it open to implementations. In this paper, we design OF-FL, a novel objective function that combines a set of metrics in order to provide a configurable routing decision based on the fuzzy parameters. OF-FL has the advantage to consider the application requirements in order to select the best paths to the destination. Our evaluation with a large-scale testbed in ContikiOS reveals that OF-FL can achieve remarkable performance of the RPL-based LLNs in comparison with the existing objective functions, and appropriately satisfy the quality of service contract of the different applications.

Literature Review:
RPL supports the use of multiple metrics for routing with the possibility of optimizing the routes based on combining several metrics, however, no guidelines are provided on how such combination should be achieved BIB001 . Hence, relying on a single routing metric in the OF may satisfy one application requirement, yet also violate another BIB002 [92] BIB003 . For example, while the ETX routing metric allows the protocol to select the most reliable path, it may also result in early network partitioning due to the absence of a load-balancing mechanism that might protect vulnerable nodes from exhausting their battery power. The problem of unbalanced traffic is exaggerated by the fact that standard RPL permits forwarding the traffic through the preferred parent only, even in the case when several candidate parents are available to do the job BIB001 . The downward MOPs are not specified to understand each other. A path with better global quality (usually due to its less number of hops) may contains one or more links with critically low-quality links that undermine its apparent quality May impact negatively any performance aspect