# Reduced Overhead Routing in Short-Range Low-Power and Lossy Wireless Networks +
## 1 Introduction  
Typically, Wireless Sensor Networks (WSNs), Internet of Things (IoT), and Cyber-Physical Systems (CPS) all require low-power and lossy networks (LLNs) for some or all of their operation. These networks are characterized as LLNs because nodes in such networks possess limited resources and often operate in harsh communication environments, resulting in transmission losses over wireless links. Communication and computing devices are increasingly being embedded in objects and structures to enable networked sensing and actuation functions. This is resulting in sophisticated CPS, such as power generation and distribution networks, assisted living, traffic control, home automation, safety systems, autonomous vehicles, and distributed robotics. Unlike the pure sensing focus of traditional WSNs, CPS require distributed decision making, control, and actuation. Hence, low power devices need to communicate not only with a central gateway, but also need to directly communicatewith other sensor or actuator devices. Here, we refer to these types of communication as multi-point to point (MP2P), point to multi-point (P2 MP), and peer-to-peer (P2P) communications. Due to energy and radio communication limitations, devices in a LLN may not connect directly to the gateway or to all other devices in the same network, but collaborate to relay or multi-hop data packets wirelessly to each other and to the gateway. Hence, a routing protocol is required to discover MP2P, P2P, and P2 MP data forwarding paths. Considering the limitations of LLNs, the Internet Engineering Task Force (IETF) ROLL (routing over low-power and lossy networks) working group has standardized the routing protocol for low-lower and lossy networks (RPL) [1]. RPL supports MP2P, P2 MP, and P2P route discovery and data forwarding. Moreover, it is a generic routing framework for LLNs and uses the concept of an objective function (OF) to influence how routes are constructed in a particular LLN. If there is no RPL OF defined in the standard that meets the requirements of a particular LLN and/or to satisfy the requirements of application(s), a new OF can be designed. Hence, the concept of OFs adds flexibility, scalability, and adaptability to RPL. Due to these reasons, RPL has emerged as a standard and widely adopted routing protocol for IPv6/6 LoWPAN-based networks. Considering the popularity of RPL, recent research has also focused on using RPL in low-power wide-area networks, an emerging networking technology for IoT [2]. Existing RPL design handles many of the challenges imposed by LLNs, however in this paper we further enhance RPL to satisfy the requirements of emerging CPS and IoT use cases. Despite RPL's flexibility, here we highlight some of its inefficiencies, such as sub-optimal P2P route discovery and data forwarding, and use of source routing for P2 MP and P2P communications in RPL's non-storing mode of operation (MoP). We present enhancements to improve P2P route construction and data forwarding in RPL's storing and non-storing MoPs, and we also present a bloom filter (BF) based routing and data packet forwarding approach to minimize source routing overhead. We capture these enhancements in an improved protocol, called Enhanced RPL (ERPL). The following are our main contributions:  
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2. Identification of inefficiencies in RPL's route construction and data forwarding algorithms. 3. Improvements to P2P route construction and data forwarding algorithms for RPL's storing and non-storing MoPs. 4. A Bloom Filter based approach for P2 MP data forwarding to minimize source routing overhead in RPL's non-storing MoP. 5. Analyzing the impact of RPL's destination-oriented directed a-cyclic graph (DODAG) depth on MP2P, P2 MP, and P2P communications. 6. An analysis of the protocol using emulation, simulation, and test-bed based experiments. Our results show that ERPL demonstrates overall lower packet loss, delay, requires fewer transmissions to deliver P2P packets, lower control overhead, and is more energy-efficient compared to RPL.