# Routing Protocols for Low Power and Lossy Networks in Internet of Things Applications
## 1 Introduction  
In the near future, it is expected that all things will be able communicate among themselves through the Internet. It is easy to perceive this evolution in a time when things are more and more connected to the global computer network. This reason leads to the emergence of a new paradigm called the Internet of Things (IoT) [1]. According to [2], the core idea of the IoT is the pervasivepresence of a variety of objects and things around us that can exchange information to reach a common objective. According to [3], in 2025, Internet nodes will be present in people's daily routines in the form of furniture, papers, televisions, refrigerators, and food packaging. According to [4], IoT is a multidisciplinary domain that encompasses a vast number of topics, including purely technical challenges and a mix of technical and social tasks, as well as social and enterprise efforts. Ambient and personal care monitoring, industrial planning monitoring, including agriculture, smart environments, and smart cities are examples of IoT applications [5; 6; 7]. Wireless Sensor Networks (WSN) are an essential component of the IoT because they enable the development of applications with a capacity to sense several variables related to the environment in which the devices are inserted [8]. WSN is a specific kind of LoWPAN (Low-power Wireless Personal Area Network) composed by nodes equipped with different types of sensors (e.g., temperature, humidity, and luminosity). To begin with, the interoperability between WSN and the Internet was limited due to the absence of IP communication infrastructure. Thus, seeking to solve this problem, several works were dedicated to proposing a structure that could provide the use of IP over LoWPAN [9]. Aiming to provide a standard solution for this problem, in October 2004, IETF (Internet Engineering Task Force) proposed a Working Group (WG) named 6 LoWPAN (IPv6 over Low-power Wireless Personal Area Networks). The 6 LoWPAN working group's objective was to create ways to enable the use of IPv6 over IEEE 802.15.4 networks. Thus, 6 LoWPAN suggested the inclusion of an adaption layer in the IP stack between the network and data link layer. This new adaption layer permits the fragmentation and defragmentation of IPv6 packets in IEEE 802.15.4 frames, realizing the compression of the IPv6 head [10]. After the publication of six RFC (Request For Comments) documents (RFC 4919 [10], RFC 4944 [11], RFC 6282 [12], RFC 6568 [13], RFC 6606 [14], RFC 6775 [15]), the IETF defined the end of the 6 LoWPAN working group as January 2014. The contributions of 6 LoWPAN WG allowed the use of an IP-based network of tiny devices and, consequently, the existence of IoT applications [16]. Through the work of 6 LoWPAN WG, a new working group was created to study routing solutions for the emerging Low-power and Lossy Networks (LLN) [17]. Created in February 2008, the Routing over Low-power and Lossy networks (RoLL) working group initially defined the routing requirements for urban LLNs [18], industrial LLNs [19], home automation LLNs [20], and building automation LLNs [21]. In parallel to the definition of the routing requirements, the RoLL working group initiated a study to verify whether the IETF standard routing protocols could supply the identified requirements [22]. Through the first conclusions, the RoLL detected that the existent routing solutions could not satisfy the requirements of LLNs. Since then, the working group has studied new routing solutions to provide the specific requirements of several types of LLN applications [17; 23]. In March 2012, the RoLL working group defined the IPv6 Routing Protocol for LLNs (RPL) as the standard routing protocol for LLN. Presented in the RFC 6550 [24], RPL is a proactive tree-based routing protocol that builds a directed acyclic graph between the leaf nodes and the border route (sink node). Although considered as the standard routing protocol for IoT networks [25], since its creation, RPL has presented several drawbacks, and new solutions have been emerging to solve them.