# Multiple Instances QoS Routing in RPL: Application to Smart Grids +
## 1 Introduction  
Current electric grid no longer satisfies the need of energy of the twenty first century. The increased electricity offer per person is limited by the restrained electricity production and the aging and unsuitable infrastructures. This limitation is due to inaccurate management systems, inefficient operations and maintenance processes and a centralized communication system that lacks interoperability. Besides that, the introduction into the electricity grid of multiple sporadic Distributed Energy Resources (DERs) i.e., electric vehicles, photovoltaic cells, wind farms, located in sometimes unexpected places, makes the control of it even more complicated [1]. SG promises to solve these issues by operating with automatic control and operation in response to user needs and power availabilityimproving efficiency, reliability and safety, with smooth integration of renewable and alternative energy sources. Managing the SG with a ubiquitous network to exchange regular and critical control messages all-over the power network becomes then crucial. Based on these observations and in order to shift from the existing electric grid to the SG, it appears necessary to instrument and master the high level and complex energy management on the electric grid. Consequently, one of the potential solutions envisioned is to equip the electrical grid with wireless sensors located at strategic measuring points to achieve remote monitoring, data collection and control of the grid [2]. Such sensors will constitute a parallel wireless data network to the electrical grid. A typical smart grid communication network consists of a Home Area Network (HAN), which is used to gather data from a variety of devices within the household, a Neighborhood Area Network (NAN) to connect smart meters to local access points, and a Wide Area Network (WAN) to connect the grid to the utility system as shown in Figure 1, the proposed WSN will operate mostly on HAN and NAN levels within this architecture. SG applications are heterogeneous in terms of requirements, criticality and delay tolerance [3; 4; 5]. However, since these applications will generate different types of traffic (real-time, critical, regular) [6], they require different levels of QoS. Thus, for a wireless sensor network, different criteria have to be taken into consideration in order to achieve a proper communication with the following requirements: reliability, latency, auto-configuration, auto-adaptation, network scaling and data prioritization [6]. Among all the existing routing protocols used in the SGs, the IETF standard RPL [7] remains the most recognized and widely used [8; 9]. As described in [10] RPL meets the scalability and reliability constraints of SG applications (e.g., Advanced Metering Infrastructure) and is recommended by the SG standards. Alongside with its support for wireless communications, RPL can be used with Power Line Communication (PLC) [11]. Figure 2 shows how smart meters (represented by houses) can send their measurements to the concentrator via wireless or PLC links. The same Media Access Control (MAC) layer can be compatible with a physical layer using wireless or PLC communications. We note that other protocols like LOADng [12] are used for SGs but this latter doesn't support traffic differentiation which is an important aspect for SG applications. As a general protocol, RPL is intended to meet the requirements of a wide range of Low-Power and Lossy Networks (LLNs) application domains including the SGs ones. It provides different QoS classes at the network layer through multiple logical subdivisions of the network called instances (more details in Section 2.1). RFC8036 [11] explains how RPL meets the requirements of SG applications and describes the different applications in SGs that can be done through RPL multiple instances. Following RPL, RFC8036 proposes five different priority classes for the traffic in SG AMI (Advanced Metering  
Figure 1: Smart Grid Communication Network [13]. Infrastructure).