Link-layer security in TSCH networks: Effect on slot duration

The IEEE802.15.4e-2012 standard is widely used in multi-hop wireless industrial Internet of things applications. In the time-slotted channel hopping mode, nodes are synchronised, and time is cut into timeslots. A schedule orchestrates all communications, resulting in high reliability and low power operations. A timeslot must be long enough for a node to send a data frame to its neighbour, and for that neighbour to send back an acknowledgement. Shorter timeslots enable higher bandwidth and lower latency, yet the minimal timeslot duration is limited by how long link-layer security operations take. We evaluate the overhead of link-layer security in time-slotted channel hopping networks in terms of minimal timeslot length, memory footprint and energy consumption. We implement full link-layer security on a range of hardware platforms, exploring different hardware/software implementation strategies. Through an extensive measurement campaign, we quantify the advantage of hardware accelerations for link-layer security and show how the minimal duration of a timeslot varies between 9 and 88ms for the most common configuration, depending on hardware support. Furthermore, we also highlighted the impact that the timeslot duration has on both high-level application design and energy consumption.