In this research, our main focus was on enabling mobility support within commercial and standard low-power wireless network protocols. In this way, we integrated smart-HOP within an existing standard routing algorithm (RPL). smart-HOP is able to keep a low overhead while responding to network changes (~90 ms hand-off delay). Moreover, the QoS requirement in terms of reliability is achieved by forwarding nearly 100% of data packets.
To evaluate the proposed algorithm, we considered three network topologies; (1) with two APs, (2) with four APs
deployed in a row, and (3) with eight APs deployed in two parallel rows. In the first deployment with two APs
(APs were separated by 10 m) and the MN traveled 15 times between the edges with a constant speed (v = 2 m/s) and the transmit power of -25 dBm, while generating data with the rate of 30 pkt/sec.
RPL responsiveness is directly related to the Trickle Timer values. This timer is responsible for the periodicity of DIO transmissions and is limited between 2 values. The following configurations were used in simulations:
Table 1. Description of the RPL scenarios
The following sections depict the results attained with different topologies and RPL scenarios.
RPL responsiveness is directly related to the Trickle Timer values. This timer is responsible for the periodicity of DIO transmissions and is limited between 2 values. The following configurations were used in simulations:
The following sections depict the results attained with different topologies and RPL scenarios.
RPL Topology 1
In the following video, MN (ID=1) is communicating with the root node (ID=4), from which it gets reply packets.
It is clear that at certain points, no packets are received from the root, showing the inability of RPL to
cope with the mobility of nodes in dynamic environments.
To establish downward routes, RPL nodes (child nodes) send unicast DAO message upward. The next hop destination of this DAO message is the preferred parent. After switching the best parent, the child node informs the selected parent its reachability.
RPL Topology 2
The number of APs was increased to evaluate the impact in the amount of control messages. RPL uses ICMPv6 messages to propagate network information through the tree. The higher the number of nodes, the higher the overhead is in the network.
RPL Topology 3
smart-HOP
smart-HOP withing the RPL was evaluated in both simulation and experiment. The following figure depicts the real position of nodes in the real deployment of nodes. We performed a simulation test with this network setting.
The following video is a smart-HOP simulation with the experimental deployment setting. In this test, the mobile node moves randomely in the room.
