We propose an adaptation of the well-known Time Slotted Channel Hopping (TSCH) Medium Access Control (MAC) protocol, which was initially specified for IEEE 802.15.4 based networks, for operation over the LoRa PHY layer. Thanks to its deterministic nature, multiple concurrent communications can be handled, while reducing channel collision and ensuring reliability in a power-efficient manner. The proposed solution was implemented in the Contiki-NG operating system and tested on real motes.

The Medium Access Control (MAC) protocol proposed by the evolving IEEE 802.15.4 standard for Low-power and Lossy Networks (LLNs) includes a multichannel mode known as Time-Slotted Channel Hopping (TSCH). TSCH, published in 2015, is part of the most recent version of the IEEE 802.15.4 standard. In this paper, we present a performance comparison between TSCH (with Orchestra scheduling algorithm) and EM-MAC, a contention-based multichannel MAC protocol for LLNs, in terms of average packet delivery ratio, power consumption and latency after network start-up phase. Results obtained from experiments on a testbed with Z1 nodes sending traffic to the sink in an environment with negligible external interference, follow the same trend as the ones obtained through a simulation study. TSCH/Orchestra outperforms EM-MAC or performs equally well for all considered loads. A point of attention though for TSCH, is the significant time required by newly joining nodes to associate to the TSCH network and to join the tree created by the IPv6 Routing Protocol for LLNs (RPL).

As part of the recent advances in the IoT world, constrained platforms featuring more than one radio interface have emerged. Typically, they combine the more classical short-range radio and the long or medium range technologies. However, their full potential is not yet exploited. The modifications to the IPv6 routing protocol for Low-Power and Lossy Networks (RPL) and the Medium Access Control (MAC) layer presented in this paper are a first step in this direction. They allow the node to automatically select the most suitable radio link if more than one is available, improving network reliability. This can be especially relevant for monitoring and smart cities applications. The solution is implemented in the ContikiOS, and tested with the Zolertia Re-mote platform, but can be extended to any platform featuring more than one radio interface. The presented testbed experiments indicate that more investigation is needed to optimally tune RPL's metrics for networks featuring nodes with dual-band communication capabilities.

To enable interoperability in the very fragmented IoT market, different integration platforms are emerging. oneM2M is one of such platforms that enables interoperability in two ways: by standardizing the HTTP, CoAP and MQTT message format as transport vehicle for oneM2M primitives, or by including custom-developed Interworking Proxy Entities (IPEs). We present an architecture that enables horizontal integration of long range low power LoRa motes that run CoAP or MQTT on a full TCP/IPv6-stack in a oneM2M framework. OneM2Ms standardized bindings are used for interoperating these disparate application layer protocols as they allow to reduce the development time of an IoT application integrated in the Internet. However, they also cause extra overhead in terms of payload size. Consequently, for LoRa motes, Time-on-Air is impacted, increasing power consumption and limiting the amount of data that can be sent over the Low Power Wide Area Network (LPWAN). Therefore, an alternative solution with reduced payload size, featuring IPEs for oneM2M, is also discussed. This paper shows that although oneM2M is a good interoperability enabler, a tradeoff exists between ease of development/deployment and the amount of useful data that can be sent over LPWANs.

Several recent sensor platforms combine long-range and more classical short-range radio technologies. In this poster we propose some modifications to the RPL routing protocol such that it automatically selects the most suitable radio link when more than one is available. The solution has been implemented in the ContikiOS and tested on the Zolertia Re-mote platform.

New Long-Range radio technologies have recently emerged in the IoT landscape. These technologies work in the Sub-GHz bands, allowing low-power communications over long distances. They are typically based on star-topology networks, where nodes send the data directly to a base station connected to the Internet. One of such technologies is LoRa. Enabled LoRa-based multihop communications would open up new possibilities. In this paper we present a solution allowing to have multihop LoRa communications. This is done by means of a newly designed MAC protocol (RLMAC), used to select the Spreading Factor for each available neighbor. The proposed Objective Function used by RPL will therefore be able to select the routing path that minimizes time on-air. By selecting the path with the lowest time on-air, the power consumption can be decreased, enlarging network lifetime. Preliminary validation tests are also presented in the paper.