# Wireless Mesh Networking: An IoT-Oriented Perspective Survey on Relevant Technologies
## 1 Introduction  
In the current era, the fourth industrial revolution and new generation wireless communication technologies are enabling pervasive connectivity between objects. These communication systems, involved in the so called \"network of networks\" Internet of Things (IoT), will eventually allow humans to interact with billions of devices, including sensors, actuators, services, and other connected objects, in an Internet-like way, with a forecast of more than 40 billion connected (with short-range radio communication technologies) \"things\" by 2020 [1] (and more than 125 billion by 2030 [2]), and more than 2.7 billion Low Power Wide Area Network (LPWAN) connections by 2029 [3]. In this context, connected things are generally defined as Smart Objects (SOs) and, thanks to the IoT, dynamically integrated in several scenarios, such as: smart industries applications, smart cities, smart agriculture, smart health, etc. Each application area has specific requirements to be taken into account, thus having implications for the communication technologies to be considered and, possibly, adopted. In particular, IoT-related wireless technologies developed in recent years are extremely heterogeneous in terms of protocols, performance, reliability, latency, cost effectiveness, and coverage. For instance, some of them are designed for short-range radio communications (e.g., Bluetooth and ZigBee), others are more suitable to cover wide areas with very small bandwidth (e.g., Sub-GHz), while others are designed for middle-range communications and high transmission rate (e.g., IEEE 802.11). Moreover, IoT network topologies are generally star- or tree-based, with data collected by groups of sensors and sent to a central collector or border router, in order to guarantee centralized processing. The emerging and constantly evolving IoT applications require more complex networktopologies, without a predefined hierarchy but able to dynamically adapt themselves to changing conditions. For this reason, there is a strong academic and industrial interest on the development of hardware and protocols able to support Wireless Mesh Networks (WMNs). In mesh topologies, network nodes are directly and dynamically connected in a non-hierarchical way, thus allowing many-to-many communications (among nodes cooperating with each other) to efficiently route data from a generic source to a generic destination. In fact, in a WMN each node composing the network can operate both as a host and as a router, relaying packets sent by other nodes when the destination is not in the visibility range of the source. Moreover, mesh networks do not require an infrastructure, since they dynamically self-organize and configure themselves, with consequent relevant advantages, in terms of: (i) deployment, installation and maintenance's overhead and cost reduction; (ii) dynamic workload distribution; (iii) better reaction to node failures; and (iv) easy network topology modification. The organization of a WMN is generally handled through the definition of a routing policy shared among all nodes, aiming at discovering and determining the best routes, on the base of different metrics (e.g., throughput, link quality, hops number, etc.) measured on data streams. Therefore, streams of data in WMNs cross all nodes connecting the source and the destination. Mesh topologies are thus the most attractive alternative to traditional centralized or tree-based network topologies, where nodes are directly linked to small subset of other nodes and the links between these infrastructure neighbors are hierarchically organized. While star- and tree-oriented topologies are very well established, highly standardized and vendor-neutral, in the case of mesh networks the research community and vendors have not yet all agreed on common standards, with the interoperability among devices from different vendors seldom assured. Moreover, comprehensive surveys on available options in the field of mesh networks for IoT are lacking in the literature.