BDPC: Controlling Application Delay in 6TiSCH networks for the Industrial Internet of Things

One of the essential requirements of the Industrial Internet of Things (IIoT), is to have an extremely high packet delivery rate, generally over 99.9%. However, packets which arrive after a predefined deadline shall be considered lost too. Industrial applications require a predictable delay. To solve this problem, we propose a new mechanism, called BDPC (Bounded Delay Packet Control). BDPC combines the knowledge of a node's delay to its root with the time budget of a data packet traversing the IoT network, to allocate cells in 6TiSCH slotFrames in order to fulfill the application's maximum delay requirements in a controlled manner: the application packets must arrive before the deadline, but not faster. This is achieved by allocating cells from a parent node to a child node, thereby adapting the cell capacity and attaining the bounded delay goal, by the analysis of the new variable $latePaqs$. In other words, the resource allocation is a function of $latePaqs$. Moreover, the number of packets arriving after the predefined deadline can be controlled by two thresholds: sfMax and sfMin. Our results show that using BDPC, the number of packets arriving before the deadline can be improved more than 2.6 times compared to the case when using the default Minimal Scheduling Function from the standard. As a further advantage, BDPC involves minor modifications to the 6TiSCH protocol stack, which makes it compatible with current implementations.