Message oriented middleware (MOM) refers to the software infrastructure supporting sending and receiving messages between distributed systems. AMQP and MQTT are the two most relevant protocols in this context. They are extensively used for exchanging messages since they provide an abstraction of the different participating system entities, alleviating their coordination and simplifying the communication programming details. These protocols, however, have not been thoroughly tested in the context of mobile or dynamic networks like vehicular networks. In this paper we present an experimental evaluation of both protocols in such scenarios, characterizing their behavior in terms of message loss, latency, jitter and saturation boundary values. Based on the results obtained, we provide criteria of applicability of these protocols, and we assess their performance and viability. This evaluation is of interest for the upcoming applications of MOM, especially to systems related to the Internet of Things.

Connectivity clearly plays an important role in Internet of Things (IoT) solutions, and the efficient handling of mobility is crucial for the overall performance of IoT applications. Currently, the most widely adopted protocols for IoT and Machine to Machine (M2M) environments, namely MQTT, CoAP or LWM2M, are directly dependent on the TCP/IP protocol suite. This suite is highly reliable when using wired networks, but it is not the best solution in the presence of intermittent connections. In this work we provide a solution to improve MQTT with an emphasis on mobile scenarios. The advantage of the solution we propose is making the system more immune to changes in the point of attachment of mobile devices. This way we avoid IoT service developers having to explicitly consider this issue. Moreover, our solution does not need extra support from the network through protocols like MobileIP or LISP. The obtained results show that our proposal, based on intermediate buffering, guarantees that there is no information loss during hand-off periods due to node mobility; furthermore, based on discrete event simulation results, we determine the maximum number of sources and the required amount of buffers for a mobile node.

In the IoT world, establishing a strong mobile network architecture will be critical for organizations to bring together people, processes, data and things. Among the various available protocols and standards to network IoT entities, the Message Queue Telemetric Transport (MQTT) is already a reference solution. It provides a publish/subscribe messaging transport specifically designed to be used in devices with limited resources over constrained networks. MQTT's main limitation is its low resilience with respect to device mobility, so that the connections could suffer frequent and long lasting disruptions or high bit error rates that severely degrade normal communications. In this work we propose an architecture to increase the robustness of MQTT by integrating a Disruption Tolerant Network (DTN) approach. The architecture has been evaluated through several experiments using real devices to validate its feasibility, and to derive some guidelines for its use.

The temporal evolution of the electrical signal generated by Pinus halepensis was measured in a sample of 15 trees. Weekly experiments were carried out during a long-term campaign lasting over a year, while trials with a high frequency of measurements were also performed during several days. In the latter case, day-night oscillations of the electrical magnitudes were observed. Additionally, punctual meteorological events such as rainfall and electrical storms affect the electrical signal as well. The measured electrical intensity grows exponentially with the voltage. In fact, no electrical intensity that exceeds the threshold of 0.01 μA is gathered when voltage values are lower than 0.6 V. In general, higher electrical signals were gathered during the rainy seasons with moderate temperatures; while very low signals, including few measures of zero intensity, were obtained during the most stressful periods over the year, mainly by mid-summer. There is a strong correlation between the rainfall and the electrical signal. The rain-intensity correlation, together with sustained intensity values during the reproductive period in spring, suggests that this electrical magnitude could be an indicator of the physiological state of the tree and thus used for in situ and minimally invasive forest monitoring.

Electric potential differences in living plants are explained by theories based on sap flow. In order to acquire more advanced knowledge about the spatial distribution of these electric potential measures in trees, this research aims to analyze electrical signals in a population of Aleppo pines (Pinus halepensis Mill.) in a representative Mediterranean forest ecosystem. The specific research objective is to assess some of the most significant factors that influence the distribution pattern of those electric signals: tree age, measurement type and electrode placement. The research has been conducted in representative forest stands, obtaining measurements of different representative trees. After a statistical evaluation of the obtained results, the main conclusions of our research are: