Applicable VersionsNetSim StandardNetSim Pro


Applicable Releasesv12v13


In NetSim's implementation of the Routing Protocol for Low-Power and Lossy Networks (RPL), compliance is maintained with RFC 6550. This standard specifies that "Rank" serves as a scalar indicator of a node's position or extent within a Destination-Oriented Directed Acyclic Graph (DODAG) version. Furthermore, RFC 6550 delegates the determination of Rank to the Objective Function, which is responsible for computing it based on specific criteria.


The Objective Function within NetSim's RPL framework aims to identify paths characterized by superior link quality. The factors influencing link quality and the radio range of a node in NetSim include:

  • Transmitter Power: An increase in transmitter power typically enhances the radio range, allowing signals to be transmitted over greater distances.
  • Path Loss: The path loss exponent directly affects the radio range; a higher exponent means more signal attenuation over distance, thereby reducing the range.
  • Receiver Sensitivity: Receiver sensitivity, expressed in negative decibels (dB), impacts the range as well. A lower (more negative) receiver sensitivity value suggests a device's capability to detect weaker signals, thus potentially increasing the effective range.
  • Spatial separation between nodes:  As the distance between nodes increases, path loss increases, reducing the signal strength accordingly. 
 
In the network sample shown below, the following parameters are configured. These will have a direct impact on the radio range of the devices:


  • Length of the grid environment: 1000 x 1000 meters
  • Wireless Channel Characteristics (Adhoc Link Properties): Path Loss Only (Log Distance with Path loss exponent=2).
  • ZigBee Node's Transmitter Power: 1 mW
  • Receiver Sensitivity: -85 dBm




For the above settings, NetSim computes the ranks; DODAG formation is as per the figure shown below:



The Gateway acts as the root node and has a Rank value of 1.
Node 5 has a higher link quality and has a rank of 15.
Nodes 4 and 7 have a rank value of 16.
Nodes 6 and 8 have a rank value of 30.

Since, nodes 4, 5, and 7 are directly within the range of the root node, they become the root's children. For node 8, both nodes 5 and 7 are within their range, however, it chooses node 5 as its parent, as it has a lower rank value. Node 6 chooses node 4 as its parent node.

Next, we look another example. In the network scenario shown below, the settings are as follows:
  • Length of the grid environment: 1000 x 100 meters
  • Wireless Channel Characteristics (Adhoc Link Properties): No Path Loss
  • ZigBee Node's Transmitter Power: 1 mW
  • Receiver Sensitivity: -85 dBm


NetSim computes the ranks and the DODAG is per the figure shown below:



Node 10 which is the gateway acts as the root and has a rank value of 1.  Since there is no path loss configured, the signal strength does not get attenuated with distance. Hence, all nodes are assigned a similar rank value of 2 and become children of the root node.

For the same network scenario, once channel characteristics are set to Path Loss Only (Log Distance with Path loss exponent=2), we get the following DODAG:


You can see that the ranks calculated are different when compared to the previous case. This is because the link quality varies based on the path loss. However, the nodes are still within the range of the Gateway, 

When the Path Loss exponent is set to a higher value of 4 we get the following DODAG with some of the nodes out of range of the Gateway and hence multiple levels in the DODAG:


 

Similarly, as parameters that affect the radio range of the nodes are varied, you can see its impact on the rank calculation and DODAG formation.

Route formation plots with Rank information as shown for the above cases can be obtained for IoT network simulation, using the RPL DoDAG Visualization project relevant to the version of NetSim used, from TETCOS File Exchange (https://www.tetcos.com/file-exchange.html). 

Please note that the above DODAG plots used MATLAB for plotting. If you wish to obtain DoDAG plots without MATLAB, a python based visualizer can be used as explained in the article: How to visualize the RPL DoDAG formed in NetSim IoT network? : NetSim Support Portal (tetcos.com) 


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