The Optimum Number of OSPF Areas for MANETs

Mobile ad hoc networks (MANETs) are a critical technology in tilling the gap where the network infrastructure is insufficient or does not exist at all. The dynamic topology of MANET requires relatively large control overhead which impedes the scalability of the network. Recently, adapting a widely-used Internet protocol such as Open Shortest Path First (OSPF) for MANETs has been actively investigated to benefit from its maturity, interoperability, and scalability. To enhance the scalability of OSPF, several extensions have been proposed including flooding backbone, differential hollos, smart peering, and distance effect. However, most of the existing work is based on the assumption of single OSPF area. In this paper, we present promising results from employing multiple OSPF areas as an efficient mean to enhance the scalability of MANETs. A novel analytical model is developed to capture the relationship between the number of areas and the flooding overhead. We perform theoretical analysis to show that there exists an optimum number of areas that minimizes the overhead. By using areas, the overhead can be significantly reduced (in some cases by 95%). The analytical results are verified with detailed simulation experiments. Finally, several candidate dynamic area formation schemes are investigated with different mobility models. The results show that the optimum number of areas has an even greater impact on the scalability of the scenarios with higher degree of realism.