The concept of multihop wireless networks is however still at a nascent stage of development and a number of researchers are working toward addressing the challenges accompanying the technology. One of the key challenges is the vulnerability of these networks to failures due to factors such as nodal mobility, error prone wireless channels, selfishness of nodes that refuse to forward packets of other nodes and denial of service (DoS) attacks.
The selfishness of nodes is the key contributor to the vulnerability of multihop wireless networks. Misbehaving nodes that refuse to forward packets often significantly damage the connectivity of wireless networks. This has made researchers work on improving the overall design of multihop wireless networks so that they are resilient to the problems caused by misbehaving nodes.
To address this, a team of researchers from North Carolina State University has come out with a research study on designing overlay topologies in multihop wireless networks such that the overlays achieve perfect resilience. From their research, the researchers have proposed a new distributed and localised protocol called PROACtive, which generates a resilient overlay for multihop wireless networks.
With this protocol, every node in the network proactively selects only cooperative nodes as its neighbours. This results in exclusion of all misbehaving nodes from the overlay network, thus avoiding failures. The protocol is designed in such a way that it is extremely lightweight with very low message complexity. It has also been incorporated with many unique features that overcome challenges pertaining to multihop wireless networks.
Firstly, the researchers have defined an 'individual' threshold for each node to achieve a trade-off between individual system resilience and individual connectivity when compared to a global threshold. This is because a node with neighbours that does not cooperate completely could be plagued with problems, although a relatively high global threshold could achieve a resilient overlay of only cooperatives nodes. Thus, if an individual threshold is defined for a node surrounded by relatively low cooperatives, the neighbouring cooperative threshold could increase accordingly. Thus, the node would still have neighbours.
Secondly, the PROACtive protocol has been incorporated with the ability to deal with dynamic topology changes due to node mobility. With the protocol, a mobile node automatically detects the loss of a neighbour and updates its set of neighbours accordingly. If the topology is highly dynamic, the mobile nodes, with the help of PROACtive, could retain records of the neighbours so that it need not update its neighbour set frequently. Thus, the protocol works efficiently with both highly dynamic and moderately dynamic topologies.
Lastly, the protocol is completely distributed and localised. In addition, it could be implemented locally in an on-demand manner, thus satisfying the demands of a real-world scenario.
According to Fei Xing, one of the researchers involved in this work: "PROACtive can generate perfect resilient overlays, which contain only cooperative nodes of the original wireless multihop networks. From our analysis, we have proved that the protocol has a light-weighted message complexity and the overlays drastically improve the overall performance of the network."
She also mentioned that a key advantage of applying the PROACtive protocol is that the resilient overlays essentially provide cooperative platforms for multihop routing and data transmission when misbehaving nodes are present.
In the future, the researchers are planning to design new routing strategies and data aggregation schemes based on resilient overlays. They also intend to explore more advanced cooperative measurement schemes and techniques.
For more information contact Patrick Cairns, Frost & Sullivan, +27 (0)21 680 3274, patrick.cairns@frost.com, www.frost.com
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