# SCHC over LoRaWAN Efficiency: Evaluation and Experimental Performance of Packet Fragmentation
## 3 SCHC over LoRaWAN
### Brief Introduction to SCHC  
The SCHC specification proposal [1], henceforth SCHC, establishes the compression and fragmentation functionalities of the low power wide area networks family technologies: Sigfox, LoRaWAN(tm), and NB-IoT. SCHC is considered an adaptation layer between a  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Publication** & **Technology** & **Type of Model** & **Metric** \\ \hline \multirow{4}{*}{[3]} & \multirow{4}{*}{Sigfox} & Theoretical & \({}^{*}\) Transmission duration of a packet \\  & & Experimental & \({}^{*}\) Uplink messages exchanged \\  & & & \({}^{*}\) Downlink messages exchanged \\  & & & \({}^{*}\) Energy performance \\ \hline \multirow{2}{*}{[4]} & \multirow{2}{*}{Sigfox} & Theoretical & \({}^{*}\) Packet transfer times \\  & & Experimental & \({}^{*}\) Number of uplink messages \\  & & & \({}^{*}\) Number of downlink messages \\ \hline \multirow{2}{*}{[5]} & \multirow{2}{*}{LoRaWAN} & \multirow{2}{*}{Experimental} & \({}^{*}\) Latency \\  & & & \({}^{*}\) Delivery ratio \\ \cline{3-4}  & & & \({}^{*}\) Overhead in end node resources \\ \cline{3-4}  & & & \({}^{*}\) Useful payload sent per fragment \\ \hline \multirow{2}{*}{[6]} & Sigfox & \multirow{2}{*}{Theoretical} & \({}^{*}\) ACK traffic \\  & LoRaWAN & & \({}^{*}\) Quality of the radio link \\ \cline{3-4}  & & & \({}^{*}\) SCHC F/R parameters \\ \hline \multirow{2}{*}{[7]} & \multirow{2}{*}{LoRaWAN} & \multirow{2}{*}{Simulation} & \({}^{*}\) Total Channel Occupancy \\  & & & \({}^{*}\) Goodput of SCHC layer \\ \cline{3-4}  & & & \({}^{*}\) Total Delay of SCHC layer \\ \hline \hline \end{tabular}
\end{table}
Table 1: List of related works that consider the modeling of the SCHC standard.  
network layer protocol such as IPv6 and a data link layer such as LPWAN-type technologies. This adaptation layer is made up of two sublayers called compression and fragmentation, as shown in Figure 1.  
The Maximum Transmission Unit (MTU) is the maximum data size that a protocol can transport as useful information. On the other hand, the spreading factor reflects the relationship between the symbol rate and the chirp rate. A lower spreading factor decreases the sensitivity and range, but also shortens the airtime of a packet and decreases the probability of a collision. LoRaWAN uses six different spreading factors numbered 7 to 12. The higher the spreading factor, the lower the MTUs.  
Before an IPv6 packet is transmitted, it is processed by the SCHC compression sublayer. The result of this process is a SCHC Packet. If the SCHC Packet is less than or equal to the MTU of the LPWAN protocol, it is transmitted without fragmentation; otherwise, the SCHC Packet is delivered to the fragmentation sublayer. Figure 2 illustrates the transmission process of an IPv6 packet as it passes through the SCHC sublayers. The fragmentation sublayer and its modes of operation are explained below as a theoretical basis for understanding the study of efficiency in this sublayer.  
Figure 1: Location of the compression and fragmentation sublayers for the SCHC standard.  
Figure 2: Flow that a message follows when entering the SCHC stack both in the transmitter and in the receiver of the message. Note that the message can go through only the compression layer or through both layers (compression/fragmentation).