978-1-7281-9183-6/20/$31.00 ©2020 IEEE A Comprehensive Study on RPL Challenges Sreelakshmi Tadigotla Department of Electronics and Telecommunication Engineering, Visvesvaraya Technological University Bengaluru,India sreelakshmi_te@sirmvit.edu Jayanthi K Murthy Department of Electronics and Communication Engineering, Visvesvaraya Technological University Bengaluru,India jayanthi.ece@bmsce.ac.in Abstract— Wireless Sensor Networks (WSN) consists of sensor nodes that are limited in terms of energy, size, processing speed and memory. Routing in WSN demands quick and large data transfer uninterruptedly. Due to the dynamic nature of WSN, better bandwidth utilization and routing stability are essential. Depending on the network structure appropriate routing protocol is required. IPv6 Routing Protocol for LLN’s (RPL) is a proactive routing protocol for Low power Lossy Networks (LLN’s). Mobility, topology control and effective resource managements are still hard challenges for researchers. This paper provides an overview of recent advancements in RPL protocol that support mobility. Also, in addition to mobility, the bandwidth utilization and topology control are also highlighted. Finally, a comparative analysis for various protocols is presented. Keywords-RPL, mobile node, topology, link quality, transmission power, routing algorithms. I. INTRODUCTION Low power and Lossy Networks (LLN’s) contain large resource constraint nodes. These nodes are constrained in terms of size, weight, available power, energy, memory and processing resources and they are interconnected by lossy links that provides less data rates [1]. But LLN’s supports wide range of applications like home and building automation, healthcare, connected home, environmental monitoring, assets tracking and industrial monitoring. LLN’s are also part of IoT which connects all the things to the internet. IPv6 packets are carried on top of physical layer of IEEE802.15.4through6LoWPAN. Fig.1. Routing mechanism in LLN’s IPv6 routing protocol for LLN’s is RPL and is developed by ROLL IETF Working Group. RPL supports PTMP (from a central node to a group of nodes inside the network), MPTP (from nodes inside the network to the central node) as well as PTP (between nodes inside the network) traffic. Features of RPL [10] include upward routing, downward routing, Load balancing, Interoperability, Multicast, Multi-sink, Multi- instance, General DAG, Interference, Mobility, LOADng (next generation), Security. There are many objective functions (OF’s) that includes ETX (link), PDR, hop count, latency (link) and throughput. There are several issues to be addressed related to RPL. In this paper an expansive study of performance evaluation is carried out for variants of RPL by listing its pros and cons. Different implementations were developed to identify features to improve the protocol. This Survey paper mainly considers mobility, connectivity and topology control. Lastly, we highlight on the future directions to scheme the optimal and dynamic routing algorithms in LLN’s. II. BACKGROUND AND LITERATURE REVIEW RPL organizes a topology as a DAG [1] which is partitioned into one or more DODAG’s. RPL Instance ID is a unique identifier within a network. DODAG’s with the same identification in terms of Instance ID share the same objective function (OF) used to compute the position of a node in the DODAG graph. Three types of ICMPv6 messages exists DIS, DIO, & DAO. RPL control messages are used to build topology. RPL nodes send DIO messages using a Trickle Timer which will reduce the traffic overhead by either increasing the sending rate of the transmission messages. Increase in sending rate occurs if there is any irregularity detected and decrease in sending rate in normal situations. A. Mobility RPL was designed for static sensor networks. Mobility is not a basic consideration in the standard RPL [11]. But for healthcare, industrial and surveillance applications require the modifications in RPL and adapt it to mobility environments. a. Initial Approaches To begin with, according to the studies standard RPL does not identify the mobile nodes and experiences a significant decline in performance while operating with the nodes under mobility. To lessen the mobility issues, author [11] proposed Mobility Enhanced RPL (ME-RPL), which 2020 Third International Conference on Advances in Electronics, Computers and Communications (ICAECC) | 978-1-7281-9183-6/20/$31.00 ©2020 IEEE | DOI: 10.1109/ICAECC50550.2020.9339505