Research On Routing Protocol In Low Power And Lossy Networks For Industrial Demand

In view of the special demand of low-power and lossy networks and four main directions of the application scenario,the ROLL working group of the Internet Engineering Task Force developed the RPL routing protocol.RPL protocol applies to industrial automation application scenarios.At present,WSN is suitable for the direction of industrial automation,the highest market share for ISA100.11 a,which connect network with 6LoWPAN,6LoWPAN uses RPL as the routing protocol.RPL protocol is based on the IPV6 architecture,which forms a network topology by constructing DODAG.The construction of DODAG relies on the routing metrics and routing constraints which defined by the objective function OF.RPL mainly contains two types of objective functions OF0 and MRHOF.OF0 uses a single routing metric,which is the closest point of the distance to the root node as the criterion for selecting the optimal parent node.This can lead to unbalanced load and energy consumption.In LLN,the uneven energy consumption of nodes will significantly reduce the network coverage and lifetime.The routing loop is also an urgent problem to be solved in RPL protocol.Routing loop will affect the convergence of the network,resulting in a drop in packet delivery ratio,and will occupy a large number of link bandwidth.In RPL protocol,when the link quality level changes or network topology changes,routing loop is very easy to occur.The DODAG loop and the DAO loop are typical loops in RPL.Although RPL uses the max_depth rule and the reject greedy rule to avoid the loop,it is still unable to avoid the routing loop.Based on the industrial application of RPL protocol,This paper focuses on energy consumption and reliability.This paper mainly researches the objective function OF0 optimization and loop avoidance Optimization.The main work is shown as bellow:(1)In order to solve the problem of unbalanced load and energy consumption,which is caused by OF0,this paper selects the energy metric from the MC metric container in the protocol.By setting the node energy format and calculating energy consumption,this paper uses an integrated routing metric Metric(R,E),which contains energy metric and default routing metric of OF0.When the node selects the candidate parent nodes,it is no longer a single comparison of Rank value,but a comprehensive consideration of the Rank value and residual energy.(2)In order to improve the optimization performance,the Metric(R,E)using twooptimization schemes: The first scheme only compare the residual energy of nodes based on the original protocol.When the Rank1 is greater than or equal to Rank2,the second scheme compares the residual energy of nodes.When the residual energy is equal and Rank1 is less than Rank2,the best parent node is determined by Rank value comparison.In the Contiki system,modify the OF0 code.Comparing energy consumption and the number of forwarding packets before and after optimization by the COOJA simulation.It is proved that the optimization scheme partially solves the problem of significant difference of energy consumption among nodes in the network,and the optimal performance of the second scheme is better.It has been proved that the SINK node is located at the center position,the energy consumption is the lowest.On this basis,the energy consumption is lower.This paper compares the differences in energy consumption under the second scheme,single SINK node or double SINK node,with or without the optimization scheme.It shows that the difference of OF0 optimization scheme under single SINK node is the most significant.(3)In order to solve the routing loop problem,this paper uses the candidate parent selection mechanism based on Rank threshold which is based on the reject greedy and max_depth rules.In DODAG,the equal rank nodes may cause the routing loop.When the link changes,the DIO message and the node information update lag,which causes the nodes and the child nodes to select each other as the parent node.This will also result in routing loop.Remove the two classes of nodes that easily cause the loop from the candidate parent node collection.After modifying the protocol code,by comparing the packet delivery ratio and average end to end delay under the 100 nodes and 160 nodes,the optimization scheme partially solves the routing loop problem.