Stability Analysis of the Delays of the Routing Protocol over Low Power and Lossy Networks

Abstract: Wireless Sensor Networks (WSNs) are being widely employed in industry, where the traditional wired communication infrastructure for control can be efficiently replaced by wireless sensors. In control applications, a low delay and a reduced jitter to send information from a plant to the controller is usually required so that the control system can act correctly and lead the plant to the desired state. In this thesis, we investigate the RPL routing protocol for WSNs in industrial control applications. RPL is a networking protocol currently being proposed by the working group Routing Protocol over Low Power and Lossy network (ROLL) of the Internet Engineering Task Force (IETF) and is mostly based on the beaconless IEEE 812.15.4 medium access control (MAC) protocol. One of the essential metric used by RPL to build a route is the delay needed to send packets from the node source to the destination. However, in the current standardization draft, such a delay is computed without considering the effects of the medium access control layer. In this thesis, we investigate the stability of the delay to route information. By the software OMNET++, we simulate the RPL protocol, where the MAC layer is implemented according to the IEEE 802.15.4 and the RPL is implemented at the network layer according to the current release of the standard. The simulator allows us to characterize the delay as function of the traffic load and network topology. By simulations, we show that there is a strong connection between the MAC and the routing. The results show that the delay introduced by the CSMA/CA influences significantly the RPL routing algorithm. We note that nodes change often their best parent along the routing path and that RPL is not stable delay-wise. Moreover, we compare the simulation results to an analytical model of the delay induced by the MAC that has been recently proposed in the literature. To improve the routing stability and alleviate the RPL jitter, a method based in this analytical model is then suggested.