## 1 Introduction  
A major challenge to implement distributed sensing applications lays in the selection of the appropriate wireless technology, as the communication requirements are not the same for each application [1; 2; 3]. In general, the collection of sensor data from nodes can be classified into two categories according to the periodicity of the samples being collected. First, are periodic sensing applications in which sensors are sampled continuously at a given rate. This is the case of control loops that require having continuous information about the status of each sensor to decide which action to take. Second, are on-demand sensing applications in which all sensor data need to be collected when required. This is the case of the scenarios that require obtaining information from all sensors at a given instant of time. In addition to the communication requirements, there are other aspects that need to be considered when selecting an appropriate wireless technology for a distributed sensing application. As nodes typically operate using batteries, this mandates the use of low-power wireless technologies to enable operation for several years. Low-power wireless technologies are achieved through strict duty cycling of the radio transceiver, as these are the elements that consume most of the node's energy. Such control is conducted at the medium access control (MAC) layer, as it is ultimately responsible for managing the operation of the transceiver. Over the last few decade, standards for low-power wireless communications have been developed to cope with the requirements of different sensing applications [4]. For example, the IEEE (institute of electric and electronic engineers) 802.15.4 standard [5] was published in 2003 for WPAN (wireless personal area networks), whereas the ISO (international organization for standardization) 18000-7 standard [6] was developed around 2004 for active RFID (radio frequency identification). Both protocols define the lowest layers of the communications protocol stack, _i.e._, the physical and data-link layers, and depend on other protocols, e.g., ZigBee or RPL (IPv6 routing protocol for low-power and lossy networks) [7] and CoAP (constrained application protocol) [8], to provide a complete stack. IEEE 802.15.4 is more suitable for periodic data collection scenarios, where a node monitors the physical quantities at a given rate and reports the data periodically to a coordinator. This is due to the fact that, despite that the GTS (guaranteed time slot) can be adapted dynamically, changing the number of dedicated slots is challenging, because traffic bursts cannot be predicted. Contrarily, ISO 18000-7 is more suited for on-demand data collection scenarios, where the sensors need to be collected at once. These protocols have demonstrated the applicability of sensing distributed technologies, but suffer from different problems that limit their applicability, such as low network reliability, due to interferences, and high energy consumption under traffic load, due to channel access inefficiency. To overcome these limitations, new wireless communication technologies specifically targeted at low-power scenarios have been already or are in the process of being standardized. This is the case of TSCH (time-slotted channel hopping) in IEEE 802.15.4e [9] and D7 AM (DASH7 alliance mode) [10]in the DASH7 Alliance. TSCH is a protocol targeted at periodic sensing applications, whereas D7 AM is more suitable for on-demand sensing applications. However, despite the current efforts to develop and standardize such low-power wireless technologies, few vendors are already implementing and selling these latest standards. In fact, most vendors are still sticking to earlier wireless technologies, such as ZigBee, due to the the inertia of introducing new protocols to slowly adopting markets, low volumes for hardware manufacturers and the costs of implementing quickly evolving protocols.