LoRaWAN SCHC Fragmentation Demystified

Low Power Wide Area Networks (LPWANs) have emerged as new networks for Internet of Things (IoT). LPWANs are characterized by long-range communications and low energy consumption. Furthermore, LPWAN technologies have a small data unit and do not provide a fragmentation mechanism. To enable these technologies to support IPv6 and, thus, be compliant with the IPv6 Maximum Transmission Unit (MTU) of 1280 bytes, the LPWAN Working Group (WG) of the Internet Engineering Task Force (IETF) has defined a new framework called Static Context Header Compression (SCHC). SCHC includes Fragmentation/Reassembly (F/R) functionality for transmitting larger packet sizes than the layer 2 MTU that the underlying LPWAN technology offers and a header compression mechanism. Moreover, SCHC defines three operational modes to perform the F/R process: No-ACK, ACK-Always and ACK-on-Error. Each mode provides different reliability levels and mechanisms. In this paper, we provide an overview of the SCHC F/R modes and evaluate their trade-offs over LoRaWAN by simulations. The analyzed parameters are the total channel occupancy, goodput and total delay at the SCHC layer. The results of our analysis show that No-ACK mode is the method with lowest total channel occupancy, highest goodput and lower total delay, but lacks a reliability mechanism. ACK-Always and ACK-on-Error modes offer the same total delay, and similar total channel occupancy, whereas ACK-on-Error offers greater goodput.