## 9 Discussion and Conclusions
In order to overcome the egocentrism of the existing expandable OSH architectures, SensoTube architecture introduces the concept of the inter-layer services. In particular, there are four inter-layer services, according to the SensoTube: the inter-layer signals management service, the inter-layer communication service, the inter-layer programming and debugging service, and the energy management service. These services are easily implemented by the use of BECs and with some enhancements at the PCB design level (see Section 4). With these four straightforward and comprehensive supportive mechanisms, it can be guaranteed that a WSAN system can be built not by using partly suitable expansion shields with superfluous circuitry, but with functional dedicated shields. SensoTube, with its seven functional layers shields, together with the four inter-layer services, can really be used to decompose a WSAN system into its vital functions and ensure the desirable separation of concerns. Furthermore, the introduction of polymorphism in the signal connections together with the anticipation of shields' local intelligence, by supporting the multi-processor collaboration development, allows for the facilitation of the embedding of any challenging technology into the WSAN system. For instance, it was explained how to exploit the SensoTube architecture in order to host, on an occasional basis, challenging features such as energy monitoring and control, over-the-air programming, and so on. Fortunately, the recent progress in MCU technology allows for several ultra-low energy solutions, and there is practically no change either in the system's energy balance or in the manufacturing budget. On the contrary, through the use of software and hardware techniques for, e.g., idleness, the multi-processor approach can contribute towards energy consumption reduction. Moreover, the SensoTube architecture can essentially support the modeling of the component functions of a WSAN system not relying on simulation and arbitrary approaches but on the basis of the real behavior of the operational entities under the post-deployment real-world conditions. The ability for a realistic modeling together with the energy management insights of the SensoTube-based systems can lead to the design of really energy- and function-optimized WSAN solutions that will meet the demands of applications not only in the agricultural domain, but also in applications such as the forestry domain, the environmental monitoring domain, the wildlife monitoring domain, and others. To further support the real-world deployments in agriculture, particular emphasis was given in the encapsulation of the systems, so plastic irrigation tubes were chosen to be the system encapsulation, because they constitute a novel, low-cost, and extra durable medium that not only can withstand the harsh agricultural environment, but can also allow for better facilitation of antennae, energy storage media, etc. (see Section 6). In conclusion, the SensoTube is an open architecture that allows the design of scalable, flexible, reliable, and optimized WSAN systems, while, at the same time, it ensures enhanced versatility by facilitating novel and challenging technologies by multi-skilled designers. As presented through certain use case examples (see Section 7), the migration of existing open-source designs to the SensoTube system entails several advantages for energy efficiency, explicit circuitries' design, multi-MCU concurrent development support, and low cost. The cost of implementation has been kept to the minimum, because the proposed novelties have been limited just to the system's physical layer, i.e., to the PCB design. With the SensoTube architecture, the WSAN stakeholders (see Section 2) can have the maximum expandability, scalability, reconfigurability, reusability, and standardization needed in order to fulfill their particular requirements.