# Building SDN-Based Agricultural Vehicular Sensor Networks Based on Extended Open vSwitch
## 6 Conclusions  
Nowadays, SDN-based vehicular sensor networks are becoming more and more popular in the precision agriculture field. The introduction of a centralized controller makes the vehicle sensor network data plane simple and efficient. However, the unstable wireless links in mobile scenarios may lead to connection failures between the controller and switches. Hence the vehicular sensor network has to select a main controller again, and communication will be interrupted because switches do not know how to process and forward new packets because of the loss of control. Meanwhile, the topology of vehicular sensor networks in agriculture can easily change and then the old rules continue to beused incorrectly. According to the idea of stateful matching and a packet-processing service invoked in the data plane, this paper proposes a SDN-based vehicular sensor network architecture based on extended OVS.  
The proposed architecture mainly develops a connection-state processing service and self-learning service. We also attempt to make the design modular and implement it in extended OVS. The connection-state processing service can track the connection state between a controller and switches. Then it can synchronously transmit the state to the kernel datapath and user space and then it performs stateful matching. This mechanism can achieve smooth handoffs as the scenario state changes and maintains throughput stable in vehicle sensor networks. The self-learning service can enhance packet-processing capability in the data plane, such as L2/L3 functions. If so, the switch can decrease the number of Packet-In packets sent up to controller, which avoids some packet-proceeding delays and reduces the controller load. Of course, this architecture can ensure that a packet is processed and forwarded properly after the loss of communication with the SDN controller. Besides, sensor data packets can match against the corresponding stateful rules in different scenarios, which can prevents rules from being used incorrectly when the vehicle sensor network topology changes.  
The experimental results show that, compared with traditional solutions (refer to Section 4), the solution we propose can decrease the effect of controller failure and strengthen the stability and survivability of SDN-based vehicular sensor networks in the precision agricultural field. More importantly, it is worth considering that the ideas of stateful matching and a packet-processing service called in the data plane can be applied in more agricultural scenarios.  
This research was supported by the Science and Technology on Information Transmission and Dissemination in Communication Networks Laboratory and State Key Laboratory of Networking and Switching Technology under Research Project.  
[PERSON], [PERSON] and [PERSON] contributed significantly to the conception of the study and analysis. [PERSON] and [PERSON] designed the architecture of SDN-based agricultural vehicular sensor networks and the experiments. [PERSON] performed the architecture implementation based on OVS and wrote the paper. [PERSON], [PERSON] and [PERSON] helped performing the analysis with constructive discussions.  
The authors declare no conflict of interest.