A Survey of Limitations and Enhancements of the IPv6 Routing Protocol for Low-power and Lossy Networks: A Focus on Core Operations <s> B. Overview of Related Survey Articles <s> A multicast routing protocol should be scalable, robust, use minimal network overhead, consume minimal memory resources, inter-operate with other multicast routing protocols, and be easy to implement. The mechanism used to manage the multicast group (participants join and leave throughout the multicast session) is an important issue when designing a protocol for multicast routing. Other design choices are influenced by the distribution of the participants over the routing domain (sparse or dense), the role of the participants in the group (source, receiver, or both), the number of groups and participants per group, and the requirements of the participants in terms of transmission delay. In this study a taxonomy of IP multicast routing protocols for dynamic groups will be presented. This taxonomy will be used to classify a surveyed set of intra- and inter-domain multicast routing protocols and to discuss successful protocol design regarding satisfaction of the multicast application's latency requirements as well as the network's resource consumption requirements. <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. Overview of Related Survey Articles <s> With RPL - the “IPv6 Routing Protocol for Low-power Lossy Networks” - emerging as a Proposed Standard “Request For Comment” (RFC) in the Internet Engineering Task Force (IETF) after a ∼2-year development cycle, this paper presents a critical evaluation of the resulting protocol and its applicability and limits. The paper presents a selection of observations of the protocol characteristics, exposes experiences acquired when producing a prototype implementation of RPL, and presents results obtained from testing this protocol - both in a network simulator, and in real-world experiments on a wireless sensor network testbed. The paper aims at providing a better understanding of possible weaknesses and limits of RPL, notably the possible directions that further protocol developments should explore, in order to address these. <s> BIB002 </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. Overview of Related Survey Articles <s> With the recent initiatives to upgrade the existing power grid to the Smart Grid (SG), there has been a significant interest in the design and development of an efficient communications infrastructure for connecting different components of the SG. In addition to the currently used underlying networks and protocols, new wired/wireless approaches are being planned for deployment for different components/applications of the SG. Based on the data requirements of the applications, new challenges have arisen at the network layer of the protocol stack with respect to routing and data forwarding. In this paper, we focus on the routing issues in the SG communications infrastructure which consists of different network components, such as Home Area Networks (HANs), Neighborhood Area Networks (NANs) and Wide Area Networks (WANs). We provide a comprehensive survey of the existing routing research and analyze the advantages and disadvantages of the proposed protocols with respect different applications areas. We also identify the future research issues that are yet to be addressed with respect to the applications and network components. This survey is the first to identify routing design issues for the SG and categorize the proposed routing protocols from the SG applications perspective. We believe that this work will be valuable for the utilities and other energy companies whose target is to develop and deploy a specific SG application that may span different network components. In addition, this work will provide valuable insights for the newcomers who would like to pursue routing related research in the SG domain. <s> BIB003 </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. Overview of Related Survey Articles <s> The great advances made in the wireless technology have enabled the deployment of wireless communication networks in some of the harshest environments such as volcanoes, hurricane-affected regions, and underground mines. In such challenging environments suffering from the lack of infrastructure, traditional routing is not efficient and sometimes not even feasible. Moreover, the exponential growth of the number of wireless connected devices has created the need for a new routing paradigm that could benefit from the potentials offered by these heterogeneous wireless devices. Hence, in order to overcome the traditional routing limitations, and to increase the capacity of current dynamic heterogeneous wireless networks, the opportunistic routing paradigm has been proposed and developed in recent research works. Motivated by the great interest that has been attributed to this new paradigm within the last decade, we provide a comprehensive survey of the existing literature related to opportunistic routing. We first study the main design building blocks of opportunistic routing. Then, we provide a taxonomy for opportunistic routing proposals, based on their routing objectives as well as the optimization tools and approaches used in the routing design. Hence, five opportunistic routing classes are defined and studied in this paper, namely, geographic opportunistic routing, link-state-aware opportunistic routing, probabilistic opportunistic routing, optimization-based opportunistic routing, and cross-layer opportunistic routing. We also review the main protocols proposed in the literature for each class. Finally, we identify and discuss the main future research directions related to the opportunistic routing design, optimization, and deployment. <s> BIB004 </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. Overview of Related Survey Articles <s> Cooperative diversity has gained much interest due to its ability to mitigate multipath fading without using multiple antennas. There has been considerable research on how cooperative transmission can improve the performance of the physical layer. During the past few years, the researchers have started to take into consideration cooperative transmission in routing, and there has been a growing interest in designing and evaluating cooperative routing protocols. Routing algorithms that take into consideration the availability of cooperative transmission at the physical layer are known as cooperative routing algorithms. This paper presents a comprehensive survey of the existing cooperative routing techniques, together with the highlights of the performance of each strategy. This survey also provides a taxonomy of different cooperative routing protocols and outlines the fundamental components and challenges associated with cooperative routing objectives. Existing cooperative routing algorithms are compared and lay the groundwork for further research. <s> BIB005 </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. Overview of Related Survey Articles <s> Utilizing the dormant path diversity through multipath routing in the Internet to reach end users—thereby fulfilling their QoS requirements—is rather logical. While offering better resource utilization, better reliability, and often even much better quality of experience (QoE), multipath routing and provisioning was shown to help network and data center operators achieve traffic engineering in the form of load balancing. In this survey, we first highlight the benefits and basic Internet multipath routing components. We take a top-down approach and review various multipath protocols, from application to link and physical layers, operating at different parts of the Internet. We also describe the mathematical foundations of the multipath operation, as well as highlight the issues and challenges pertaining to reliable data delivery, buffering, and security in deploying multipath provisioning in the Internet. We compare the benefits and drawbacks of these protocols operating at different Internet layers and discuss open issues and challenges. <s> BIB006 </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. Overview of Related Survey Articles <s> RPL is the IPv6 routing protocol for low-power and lossy networks, standardized by IETF in 2012 as RFC6550. Specifically, RPL is designed to be a simple and inter-operable networking protocol for resource-constrained devices in industrial, home, and urban environments, intended to support the vision of the Internet of Things with thousands of devices interconnected through multihop mesh networks. More than four-years have passed since the standardization of RPL, and we believe that it is time to examine and understand its current state. In this paper, we review the history of research efforts in RPL; what aspects have been (and have not been) investigated and evaluated, how they have been studied, what was (and was not) implemented, and what remains for future investigation. We reviewed over 97 RPL-related academic research papers published by major academic publishers and present a topic-oriented survey for these research efforts. Our survey shows that only 40.2% of the papers evaluate RPL through experiments using implementations on real embedded devices, ContikiOS and TinyOS are the two most popular implementations (92.3%), and TelosB was the most frequently used hardware platform (69%) on testbeds that have average and median size of 49.4 and 30.5 nodes, respectively. Furthermore, unfortunately, despite it being approximately four years since its initial standardization, we are yet to see wide adoption of RPL as part of real-world systems and applications. We present our observations on the reasons behind this and suggest directions on which RPL should evolve. <s> BIB007 </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. Overview of Related Survey Articles <s> With growing needs to better understand our environments, the Internet-of-Things (IoT) is gaining importance among information and communication technologies. IoT will enable billions of intelligent devices and networks, such as wireless sensor networks, to be connected and integrated with computer networks. In order to support large scale networks, IETF has defined the routing protocol for low power and lossy networks (RPL) to facilitate the multihop connectivity. In this paper, we provide an in-depth review of current research activities. Specifically, the large scale simulation development and performance evaluation under various objective functions and routing metrics are pioneering works in RPL study. The results are expected to serve as a reference for evaluating the effectiveness of routing solutions in large scale IoT use cases. <s> BIB008 </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. Overview of Related Survey Articles <s> The vision of wireless multimedia sensor networks (WMSNs) is to provide real-time multimedia applications using wireless sensors deployed for long-term usage. Quality of service assurances for both best effort data and real-time multimedia applications introduced new challenges in prioritizing multipath routing protocols in WMSNs. Multipath routing approaches with multiple constraints have received considerable research interest. In this paper, a comprehensive survey of both best effort data and real-time multipath routing protocols for WMSNs is presented. Results of a preliminary investigation into design issues affecting the development of strategic multipath routing protocols that support multimedia data in WMSNs are also presented and discussed from the network application perspective. <s> BIB009 </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. Overview of Related Survey Articles <s> A variety of communication networks, such as industrial communication systems, have to provide strict delay guarantees to the carried flows. Fast and close to optimal quality of service (QoS) routing algorithms, e.g., delay-constrained least-cost (DCLC) routing algorithms, are required for routing flows in such networks with strict delay requirements. The emerging software-defined networking (SDN) paradigm centralizes the network control in SDN controllers that can centrally execute QoS routing algorithms. A wide range of QoS routing algorithms have been proposed in the literature and examined in individual studies. However, a comprehensive evaluation framework and quantitative comparison of QoS routing algorithms that can serve as a basis for selecting and further advancing QoS routing in SDN networks is missing in the literature. This makes it difficult to select the most appropriate QoS routing algorithm for a particular use case, e.g., for SDN controlled industrial communications. We close this gap in the literature by conducting a comprehensive up-to-date survey of centralized QoS routing algorithms. We introduce a novel four-dimensional (4D) evaluation framework for QoS routing algorithms, whereby the 4D correspond to the type of topology, two forms of scalability of a topology, and the tightness of the delay constraint. We implemented 26 selected DCLC algorithms and compared their runtime and cost inefficiency within the 4D evaluation framework. While the main conclusion of this evaluation is that the best algorithm depends on the specific sub-space of the 4D space that is targeted, we identify two algorithms, namely Lagrange relaxation-based aggregated cost (LARAC) and search space reduction delay-cost-constrained routing (SSR+DCCR), that perform very well in most of the 4D evaluation space. <s> BIB010
In the literature, there are a few surveys on RPL within the context of LLNs  - BIB003 . However, the majority of these surveys have focused on analyzing the limitations of the protocol itself rather than assessing various research efforts made towards overcoming such limitations, which is the main objective of this survey. In  , the authors reviewed the relevant research efforts pertaining to the implementation, performance evaluation, and deployment of RPL. Nevertheless, their survey did not discuss the research efforts made toward overcoming RPL limitations. The study in BIB002 described the standard limitations without analyzing any of the recent studies proposed to mitigate them. Although the authors in  reviewed and analyzed some contributions that enhanced protocol operations, these are restricted to mobility extensions and the authors did not consider RPL's core operations aspects. The authors in BIB007 introduced a survey that presents the history of research efforts in RPL from 2012 to 2016. In particular, the authors investigated how RPL has been used and evaluated in the context of LLNs; however, their survey is different in two primary aspects, namely, their primary focus and the scope. The primary focus of their article was to report on the success of RPL itself as a routing protocol. In contrast, our article primary focus is to report on the success of the state-of-the-art solutions that were proposed in the literature to overcome RPL limitations. Yet, we have devoted an ineligible portion of our survey to report on the success of RPL (i.e. elaborating on RPL limitations and weaknesses), the scope and the depth of both surveys articles differ significantly. While our survey tackles the issues related to routing maintenance, routing selection, optimization mechanism, downward routing, under-specification of some RPL aspects, incompatibility between RPL modes, memory limitations among many others, with providing a classification for RPL limitations under those categories, their survey tackled the issues related to upward routing, multi-sink, interoperability, multicast, interference, load-balancing, downward routing, mobility and security. The authors in BIB008 overviewed RPL's key metrics, features and OFs. However, they surveyed only a few number of articles related to RPL's objective functions without providing an in-depth analysis for the feasibility of reported studies. In addition, the authors have never analyzed any of the state-of-art solutions proposed to mitigate RPL weaknesses in terms of routing maintenance, and downward routing, nor they elaborated on the problems themselves. The study in  has analyzed whether RPL has satisfied the original requirements defined by the IETF related to mobility, traffic patterns, resource heterogeneity, scalability, and reliability. In the light of this analysis, they highlighted the current IoT trends and new requirements that may challenge the future adoption of RPL. However, the study did not assess any of RPL's extensions proposed in the literature to overcome its challenges, which is the core goal of our survey. Several other surveys in the wider field of routing protocols are existed BIB001 - BIB010 . One of the previous studies in this regards is the survey presented in BIB001 , which surveyed around 13 inter-domain, and intra-domain multicast routing protocols. The authors also provided a comparative study among the surveyed protocols in terms of multiple features such as memory requirements and latency among several others BIB001 . A taxonomy of geocast routing protocols in ad-hoc networks was introduced in  . The authors classified these protocols (i.e. geocast routing protocols) based on network structure they support and the presence of flooding mechanism. They also conducted a comparison study among the reported protocols in terms of message/memory complexity, robustness and delivery capability in partial networks. However, apart from being devoted for ad-hoc networks, this survey is outdated. The authors in BIB004 provided a comprehensive survey of opportunistic routing protocols in WSNs. In particular, they discussed the limitations, features, variations and the building blocks of opportunistic routing protocols categorizing them into five classes, namely, optimization-based routing, probabilistic routing, geographic routing, link-state routing, and cross-layer routing. The authors also identified the key open research issues related to optimization, deployment and design of such protocols. However, the survey did not discussed the routing protocols targeting specifically the LLNs environments. A comprehensive survey of cooperative routing protocols in WSNs is presented in BIB005 . The authors introduced a taxonomy of such protocols in terms of centralization optimality, and objective function. They also conducted a performance evaluation of a representative set of cooperative routing protocols highlighting their key challenges. However, this survey also did not elaborate on routing protocols developed specifically for LLNs. The authors in BIB006 introduced a survey that reviews the multipath routing and provisioning protocols in wired networks. They presented a layer-based overview of such protocols highlighting their key benefits, challenges, and drawbacks and discussing related open research issues. In BIB009 , the authors presented a new taxonomy for Multipath Routing Protocols in Real-Time Wireless Multimedia Sensor Networks (WMSNs) highlighting their advantages and disadvantages. They pointed out that multi-constraint multi-path routing in WMSNs is still an open issue that needs to be addressed by future research efforts. The authors in BIB010 conducted a comprehensive survey of QoS routing algorithms in SDN networks. A four-dimensional evaluation framework based on topology, scalability and delay was proposed in this survey to evaluate and compare the reviewed QoS routing algorithms. Nevertheless, these last surveys are not targeting the routing issue in the LLNs. Compared with the surveys in literature, we aim at providing a deep understanding and thorough discussions on the core technical bottlenecks encountered in the design of RPL routing protocol and their corresponding solutions. Moreover, this survey will discuss whether the solutions have overcome the reported limitations and drawbacks. Uniquely therefore, this paper surveys key elements of the latest attempts to overcome the standard limitations of RPL pertaining to its downward traffic, objective functions and routing maintenance operations. We seek to answer the following question: have the research attempts to address the limitations of RPL succeeded, or do more need to be done?