**1. Introduction**

The number of sensors/actuators implemented in the real world today in various kinds of applications (agriculture, weather observation, marine observation, monitoring of seismic movements, medicine, or industrial applications, for example) is immense. In the world of Internet of Things, almost all of these sensor's nodes have the same requirements in terms of the need for low power, self-configurability, low cost, moderate data rate, and wireless communication capability. Traditionally, the wireless networks used for communication between the nodes and the gateway that connects the things networks with the IP network was of the star type. However, at present, the rapid mass introduction of new elements in networks of this type (Massive Machine to Machine Networks) demands greater flexibility in the topologies and architectures used, as well as the ability to interoperability between the various existing technologies in a transparent way to the end users of the system. In addition, this interoperability allows to extend the coverage of the network if the appropriate

protocols and architectures are used that allow, in turn, the adaptation to the conditions of each medium.

In urban and suburban areas, it is easier to resort to cloud connection techniques such as NB-IoT or LTE-M, where 4G or 5G coverage is required to reach the final network, meeting the requirements of data rate, consumption, and low cost. However, many of the possible applications mentioned above are developed in environments, where internet connectivity is very limited or nonexistent, but it is necessary to cover large areas where the sensors are located. These can be large agricultural, livestock farms, or marine or river environments. It is in these cases where hybrid strategies and architectures that combine different technologies and require adequate interoperability between different technologies acquire their importance. In short, to achieve greater coverage there are two main strategies: Development of multi-hop topologies using the appropriate routing protocols of mobile nodes in each case, and on the other hand, the combination of different wireless communication technologies depending on the characteristics of the environment. In the case of remote areas, where there is no cellular network coverage, the immediate thing is to think about LPWAN technologies that use unlicensed bands (LoRa, LoRaWAN, Sixfox, and Weightless). Typically, these techniques employ star technology with a high range. In the case of LoRaWAN, it uses the physical layer of LoRa, based on Chirp spread spectrum, integrating, in addition, the network layer. Where it is necessary to increase coverage, this technology could be implemented by developing clusters of clusters around a gateway that intercommunicates with another until reaching the final destination [1, 2]. This chapter will emphasize networks that allow the rapid incorporation of new mobile nodes, so this structure does not seem the most appropriate in principle. The following are the two strategies mentioned above (Multi-hop and Combination of technologies).
