## 1 Introduction  
Internet of things (IoT) is a transformative paradigm that is propelling industries into smart and connected ones. Based on Cisco [1], 500 billion devices are expected to be connected to the Internet by 2030. This is triggered by the evolution of many IoT technologies such as LTE-M, NB-IoT, LoRaWAN, Sigfox and others [2, 3]. IoT can be employed in various sectors that include, but are not limited to, agriculture, environmental monitoring, building and home automation, healthcare, transportation, energy management, asset tracking and smart metering [4, 5]. Advanced metering infrastructure systems are rapidly growing in number and size [6, 7]. They consist of smart meters that support bidirectional communication with a service provider. To provide interoperability among meter vendors, several protocols are proposed for the application layer such as Device Language Message Specification/Companion Specification for Energy Metering (DLMS/COSEM), Smart Message Language (SML), Manufacturing Message Specification (MMS) and Simple Object Access Protocol (SOAP) [8]. However, the smart metering traffic model/pattern changes from one application to another (water, electricity, gas, etc.). Even for the same application, it changes from one utility provider to another. Furthermore, it changes within the same utility depending on the use case (residential, commercial, etc.) [9]. Among the main changes are the reporting interval (frequency) and the size of the exchanged messages. It is worth noting that there might be a difference between the required measurement period and the reporting interval. In other words, several measurements can be sent within one transmission, lowering the communication overhead. Most of the time, metering sensors are battery-powered. For example, it is unusual to find an electricity supply close to a water meter [10]. In order to mitigate the cost of deploying a smart metering infrastructure, it is required that the batteries last at least several years, typically a decade or so. In light of these observations, a number of questions arise that must be addressed:  
* How can energy consumption be reduced to meet the strong lifetime requirements of metering devices? * How to ensure interoperability between different vendors and applications? * How can a high level of security be provided with low-power devices operating over constrained networks? In this paper, we focus on enabling extremely energy-efficient end-to-end secure communications for smart metering IoT applications. Narrowband IoT (NB-IoT), introduced by the 3 GPP and standardized as part of 3 GPP Release 13, is a radio access technology solution designed to connect millions of IoT devices spread over large geographic areas while minimizing their power consumption. Evolved from LTE, this Low-Power Wide-Area (LPWA) technology is particularly well suited to smart metering. One of the aims of this study is to make the most of NB-IoT in terms of energy consumption, while maintaining interoperability. Radio communications account for a very large share of the energy consumption of the metering devices [11]. To limit their energy consumption due to radio communications, we recommend limiting their duration and number to the minimum possible. In order to reduce the time it takes to send a message, it is possible to reduce its size, for example, by using a header compression mechanism such as SCHC. In this study, we intend to evaluate the ability of SCHC and NB-IoT to provide energy-efficient, secure and interoperable communications for smart metering applications. The main contribution aspects of this work are summarized as follows:  
* SCHC and NB-IoT are examined through an extensive review of relevant literature to address then questions that have been raised, specifically their ability to efficiently work together in order to optimize the energy consumption while guaranteeing the security and interoperability of communications. In addition, we provide a detailed technical background on SCHC and NB-IoT.