Performance evaluation of congestion control for CoAP in 6TiSCH networks

The Internet of Things (IoT) is making changes in everyday life. The same is happening in the world of industry, where sensor networks monitor industrial processes. These networks are composed of devices with limited computational capacity, memory and autonomy. In the Industrial Internet of Things (IIoT) reliability and low latency are required, to meet these requirements the 6TiSCH architecture has been defined by IETF (Internet Engineering Task Force). In this work we evaluate the performance of Constrained Application Protocol (CoAP) over 6TiSCH networks with default congestion control policy, specifically we assess the performance and the challenges that comes from the adoption of CoAP congestion control when employing with IEEE 802.15.4 Time Slotted Channel Hopping (TSCH) MAC Protocol. This protocol guarantees low latency and high reliability. The communication resources in 6TiSCH networks are managed by Scheduling Functions (SFs), the nodes manage the communication schedule in a distributed manner with Distributed SF in the 6TiSCH schedule, that continuously monitor the traffic to allocate resources. The results show that there is a problem with the way distributed SFs are conceived, the tested system had performance limitations due to a lack of slots dedicated to communication between nodes. Changes have been made to the SF, adding dedicated downward slots. The results show that with this modification there is an increase in performance. The changes have been implemented in Contiki-NG, and simulations have been performed on the Cooja network simulator