Millennial Net has developed and optimized its protocol to address the unique characteristics and challenges associated with wireless sensor networking.

The end result is a networking system and associated protocol that is highly scalable, ultra-efficient, and extremely responsive and resilient in dynamic environments. The Millennial Net protocol for wireless sensor networks provides the industry’s longest battery life at sensor nodes while delivering data over fault-tolerant links with end-to-end redundancy. The Millennial Net protocol is based on set of techniques including Persistent Dynamic Routing for reliable and scalable wireless sensor networks. When forming an ad hoc sensor network, Persistent Dynamic Routing requires minimal overhead for requesting and establishing connectivity without relying on the bandwidth-consuming flooding technique.

How it Works

Persistent Dynamic Routing provides a mechanism for the network to ensure reliable data transmission without dropping data packets. Combined with the technique of dynamic route discovery that discovers the best route for packet delivery on the fly, Persistent Dynamic Routing enables a level of scalability and power efficiency that other networking systems cannot achieve.

Almost every existing ad hoc network protocol assumes some level of static status of the network. For example, the route discovery process of AODV assumes there is at least a short duration during which a “snapshot” of the complete route to the destination is possible. The data packet of DSR carries the full route information in itself, which assumes the existence of a “full” route at that moment.

In the case of relatively static network with low fluctuation and interference, this assumption can hold with reasonable level of success. But in a highly dynamic environment, the assumption of this kind of “quasi-static” status does not hold. In other words, the network may be continuously changing, making it impossible to establish a full route from the source to the destination at a point in time. In this case, traditional routing algorithms such as AODV or DSR can present difficulties. For example, in an AODV system, the source will keep sending the route discovery packet, but will not get a definite route response from the destination, which will result in continuous flooding of the network with route discovery packets. As a result, the data packet will not even be sent into the network, since the route discovery process is incomplete. More route discovery packets translate into more overhead, and since the route discovery process is essentially a flooding process, the impact on the efficiency of the network will drop significantly; especially in large-scale networks.

The gateway establishes a tree structure for dynamic addressing. The route discovery packet broadcasts through the network, establishing mesh routing (AODV), which floods the network. The route response packet broadcasts to validate the route, and the data packet is sent to the gateway.

FIgure 1: Flooding approaches. Gateway establishes tree structure for dynamic addressing. Route discovery packet broadcasts through the network establishing mesh routing (AODV) which floods the network. Route response packet broadcasts to validate the route. Data packet sent to the gateway.

With Persistent Dynamic Routing, the data packet does not need to wait until the route discovery process grabs a “full” route at a moment in time. A data packet is released and navigates through the network with the best knowledge it has collected from its neighbors at that moment. It works in a manner similar to the mechanism of navigating a maze without any prior knowledge of the maze. The data packet does not wait until the full route is confirmed; rather, it starts navigating the network with whatever information it has about the destination.

Figure 2: Persistent Dynamic Routing. With PDR, the end node sends the data packet, which is dynamically propagated through the network and delivered to the gateway.

Persistent Dynamic Routing can significantly decrease the overhead of packet delivery in a highly dynamic network since it does not send excessive numbers of route discovery packets, nor does it use proactive route updates. Also, the route discovery packet in Persistent Dynamic Routing does not go more than one hop in each discovery process, resulting in less flooding of the network. In practice, flooding is used only once at the very beginning of the network formation and, from then on, route discovery is only done in the local area to collect knowledge on the best route to the destination. This “best knowledge” has no guarantee that it is correct, and the data packet does not “ask” for that kind of guarantee. In this sense, Persistent Dynamic Routing is based on the probabilistic rather than deterministic approach. In a relatively static network, the higher probability that the destination matches the actual deterministic route would give Persistent Dynamic Routing the same level of performance as AODV, if not better. In highly dynamic environment, Persistent Dynamic Routing produces significantly less overhead in packet delivery than the AODV flooding approach.