Multiple Path RPL for Low Power Lossy Networks Abstract—Routing protocol for low-power and lossy networks (RPL) is the standard IPv6 based routing protocol for low power, lossy Networks (LLNs) proposed by IETF. It is proposed for networks with characteristics like small packet size, lossy links, low bandwidth, low data rate and low power resources. RPL is a single path routing protocol and the existing objective functions do not support creation of multiple routing paths between source and destination. Multipath routing can be used to achieve multi- fold objectives, including higher reliability, increased throughput, fault tolerance, congestion mitigation and hole avoidance. In this paper, M-RPL a multi-path extension of RPL is proposed that aims to provide temporary multipath routing during congestion over a path. Congestion is primarily detected by a forwarding node by monitoring packet delivery ratio and is mitigated by providing partially disjoint multipath routing. Detailed simulation analysis of M-RPL against RPL shows that using multi-path RPL reduces congestion and increases the overall throughput. Hence M-RPL is suitable for supporting high data rates as compared to single path RPL. Keywords—Low power and lossy networks, multipath routing, RPL, congestion control, partially disjoint paths. I. INTRODUCTION Wireless sensor network (WSN) is a class of low power networks that are comprised of distributed and self-governing sensor nodes. These sensor nodes are used to sense the physical environment and they supportively forward the data in a multi-hop fashion to the sink node (data collector). Today, WSNs are used in various military applications, health care applications and industrial monitoring. Low power lossy network (LLN) is a terminology that refers to networks that are comprised of miniature sized battery powered devices having lossy wireless connectivity. Examples of LLNs include wireless sensor networks and wireless personal area networks (WPAN). Design of routing protocols that can select reliable and low delay paths for providing high data rates is an uphill task in LLNs because of poor link connectivity and resource constrained nature of devices. Internet engineering task force (IETF) in this regard established a research group termed routing over low power lossy network (ROLL) for the design of a routing protocol suitable for LLNs. The objective of ROLL is to design a sophisticated routing protocol that establishes reliable paths, promptly reacts to link failure, utilize minimum energy and reduces computational costfor routing. The reason for the formation of new routing protocol by ROLL is that the existing routing protocols are not deemed suitable for LLNs [1]. The ROLL working group published RPL protocol for low power lossy network in 2008 [2]. RPL is a gradient-based proactive routing protocol with bidirectional links that builds directed acyclic graphs (DAGs) based on routing metrics and constraints [3]. RPL can create one or more destination oriented DAG (DODAG) for every root (sink) node within the network. DODAG root is the main root node which constructs the complete DODAG. To build DODAG, root node first multicast DODAG information object (DIO) with initial rank value 1. Rank defines the individual node positions within the respective DODAG [2]. Apart from rank value, the DIO contains information about objective function, IDs, routing cost, related metrics and network information [2]. Different objective functions are proposed in RPL such as objective function zero (OF0) [4] and the minimum rank with hysteresis objective function (MRHOF) [5] for the construction of DODAG.RPL strives to minimize the cost for reaching the root (sink) from any node in the LLN using an object function [1]. Neighbors of root node receive DIO message and use this information to update their rank, join DODAG and choose preferred parent by sending feedback to the root. The best preferred parent is used by a child node for routing based on expected transmission count (ETX) and energy. The DIO messages are periodically multi-casted by nodes for topology maintenance. Periodic feedback is also uni-casted by child nodes to their respective parent node using destination advertisement object (DAO) to maintain point-to-multipoint and point-to-point connectivity [2]. RPL provide single path routing and does not support multi-path routing. Single-path routing is achieved with minimum computational complexity and resource utilization but it reduces the achievable output of the network [6, 7]. In high traffic load when an active path is congested and fails to transmit the data then finding multiple paths for data forwarding can increase throughput. Multipath routing strives to find several paths from a source node to destination. Multipath routing improves reliability, provides fault-tolerant routing and reduces congestion. Existing literature [8, 9] has identified the need for supporting multipath routing in RPL. Despite few research efforts in this domain, providing multipath routing using RPL to support high data rate is still an open research area. In this paper, multi-path RPL (M-RPL) is proposed that aims to provide temporary multiple paths during congestion M Ali Lodhi Department of Computer Science Bahria University Islamabad, Pakistan alilodhi30@gmail.com Abdul Rehman Department of Computer Science Bahria University Islamabad, Pakistan a.rehman321@yahoo.com Meer M Khan Department of Computer Science Bahria University Islamabad, Pakistan meer.khan78@gmail.com Faisal Bashir Hussain Department of Computer Science Bahria University Islamabad, Pakistan faisalbashir@bahria.edu.pk 978-1-4799-8290-5/15/$31.00 ©2015 IEEE 2015 IEEE Asia Pacific Conference on Wireless and Mobile 279