Modes of Operation in IOT RPL

The DODAG nodes process the DAO messages according to the RPL Mode of Operations (MOP), which are presented below. Independent of the MOP used, DAO messages may require reception confirmation, which should be done using DAO-ACK messages.

Although it is designed for the Multipoint-to-Point (MP2P) traffic pattern, RPL also admits the data forwarding using Point-to-Multipoint (P2MP) and Point-to-Point (P2P). In MP2P, the nodes send data messages to the root, creating an upward flow as shown in Figure 4‑17: Multipoint to Point. In P2MP, sometimes termed as multicast, the root sends data messages to the other nodes, producing a downward flow depicted in Figure 4‑18: Point to Multipoint..

In P2P, a node sends messages to the other node (non-root) of DODAG; thus, both upward and downward forwarding may be required as illustrated in Figure 4‑19: Point to Point. RPL defines four MOPs that should be used considering the traffic pattern required by the application and the computational capacity of the nodes. In the first, MOP 0 (Point to multipoint), RPL does not maintain downward routes; thus, consequently, only MP2P traffic is enabled. In non-storing MOP (MOP 1 (Multipoint to point)), downward routes are supported, and the use of P2P and MP2P is allowed. However, all downward routes are maintained in the root node. Thus, the total downward traffic should be initially sent to the DODAG root and subsequently be forwarded to its destination as shown in Figure 4‑20: RPL Non-Storing Mode. In storing without multicast MOP (MOP 2 (Point to point)), downward routes are also supported, but are different from MOP 1; the nodes maintain, individually, a routing table constructed using DAO messages to provide downward traffic. Hence, downward forwarding occurs without the use of the root node, as illustrated in Figure 4‑21: RPL Storing Mode. Storing with multicast MOP (MOP 3 (non-Storing mode)) has a functioning similar to MOP 2 (Point to point) plus the possibility of multicast data sending. This type of transmission permits the non-root node to send messages to a group of nodes formed using multicast DAOs.

Figure 4‑17: Multipoint to Point

Figure 4‑18: Point to Multipoint

Figure 4‑19: Point to Point

Figure 4‑20: RPL Non-Storing Mode

Figure 4‑21: RPL Storing Mode

Open NetSim, Select Examples->IOT-WSN->Internet of Things->Mode of Operations IoT RPL then click on the tile in the middle panel to load the example as shown in Figure 4‑22.

Graphical user interface, application Description automatically generated

Figure 4‑22: List of scenarios for the example of Mode of Operations IoT RPL

The following network diagram illustrates, what the NetSim UI displays when you open the example configuration file.

Figure 4‑23: Network set up for studying the Mode of Operations IoT RPL