A Survey of Limitations and Enhancements of the IPv6 Routing Protocol for Low-power and Lossy Networks: A Focus on Core Operations <s> 1) Single-path Routing <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> 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> 1) Single-path Routing <s> In many-to-one or many-to-few traffic scenarios, It is inevitable that `hot spots? will occur where traffic from a number of sources gets accumulated. While these hot spots can not be avoided, they can be mitigated by means of distributing the traffic across forwarders with load balancing techniques. In this paper, we define a load imbalance metric, which is applicable to any tree/hierarchy based data collection and/or dissemination.We show how current load balancing techniques existing in wireless sensor networks literature can not be applied to large scale Low Power Lossy Networks (LLNs) and the Internet of Things (IoT). We thus propose a greedy algorithm, that requires only partial topology knowledge, and works with the IETF standardized Routing Protocol for LLNs (RPL), without adding extra control overhead. By not requiring full topology information or all link states, this approach can work in highly varying link condition and large scale deployments. We also provide worst case run-time complexity of our heuristic and simulation results on realistic topology and traffic profiles to establish the validity of our approach. <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> 1) Single-path Routing <s> RPL is an IPv6 routing protocol for low-power and lossy networks (LLNs) designed to meet the requirements of a wide range of LLN applications including smart grid AMIs, industrial and environmental monitoring, and wireless sensor networks. RPL allows bi-directional end-to-end IPv6 communication on resource constrained LLN devices, leading to the concept of the Internet of Things (IoT) with thousands and millions of devices interconnected through multihop mesh networks. In this paper, we investigate the load balancing and congestion problem of RPL. Specifically, we show that most of packet losses under heavy traffic are due to congestion, and a serious load balancing problem exists in RPL in terms of routing parent selection. To overcome this problem, this paper proposes a simple yet effective queue utilization based RPL (QU-RPL) that significantly improves end-to-end packet delivery performance compared to the standard RPL. QU-RPL is designed for each node to select its parent node considering the queue utilization of its neighbor nodes as well as their hop distances to an LLN border router (LBR). Owing to its load balancing capability, QU-RPL is very effective in lowering the queue losses and increasing the packet delivery ratio. We verify all our findings through experimental measurements on a real testbed of a multihop LLN over IEEE 802.15.4. <s> BIB003
In RPL, once a preferred parent has been selected, all traffic will be forwarded through this preferred parent, as long as it is reachable, without any attempt to perform load balancing among other available parental candidates  [14] BIB001 . This behavior may drain the power of overloaded parents leading to network disconnections and unreliability problems, as it is likely that overloaded nodes will die earlier BIB002 [103] BIB003 .