# SDN Architecture for 6 LoWPAN Wireless Sensor Networks
## 2 Related Work
However, in AMI networks, there is a need for power meters or load controllers to receive commands frequently, and these types of traffic cannot be overlooked. The results showed that RPL provides less latency and that LOAD introduces less control traffic into the network. [PERSON] et al. [PERSON] et al. (2017) compared RPL with the LOADng (lightweight on-demand ad-hoc distance-vector routing protocol), which was developed by the 6 LoWPAN working group. The authors pointed out a very large dependency of RPL on the root node of the network, which can become a critical point in the case of traffic bottlenecks. The results also show a high tendency of loops and packet fragmentation in RPL. [PERSON] et al. [PERSON] et al. (2017) presented a centralized control proposal for scheduling timeslots and channels for 6 TiSCH networks using CoAP messages for the installation of schedule tables using the CoAP management standard interface (CoMI) and with messages encoded by concise binary object representation (CBOR) [PERSON] et al. (2017) to optimize the control messages' length, following the YANG data model. Similar to our research, the observed CoAP notifications are used to monitor changes in topology and link quality with neighboring nodes. The changes in the read parameters cause the nodes's schedules' recalculation, with subsequent sending of these new schedules to the nodes involved in the changes through the 6 TiSCH CoMI interface. Their approach is similar to ours, but the SD6 WSNP also uses CoAP messages for the installation of entries in the flow tables to program data plane forwarding, according to the SDN approach. Other studies propose the implementation of SDWSN in open-source platforms, such as TinySDN [PERSON] et al. (2016); [PERSON] et al. (2017) and CoAP-SDAN [PERSON] et al. (2017). TinySDN [PERSON] et al. (2016) is an SDWSN tool for the TinyOS operating system, where the topology and link quality information collected from the CTPprotocol are informed to the central controller through the ActiveMessageC TinyOS component. From this information, layer 2 paths were computed and installed in the nodes' flow tables using the same messaging component. In a subsequent paper [PERSON] et al. (2017), the authors of TinySDN evaluated the change of the CTP protocol to RPL. The research on CoAP-SDAN [PERSON] et al. (2017) proposed employing CoAP messages to acquire network quality information from the nodes and to install the centrally-computed routes in the nodes. The paper presented a packet delivery ratio comparison between the AODV, DSDVand their proposal, in a simulation environment. No details about the implementations on real constrained devices or protocol descriptions were presented. Unlike these preceding papers, ours provides a detailed specification of the architecture, which includes the control plane protocol, the flow table structure, the forwarding mechanisms in the data plane, the topology discovery and flow control. Moreover, a comprehensive description of the implementation of the SD6 WSN in Contiki OS is provided, plus the description of our functional testbed based on real motes.